CLAIM OF PRIORITY TO PRIOR APPLICATION

[0001] The present application claims the benefit of previously filed co-pending U.S. Provisional Application, Serial Number 62/367, 105, filed on July 26, 2016. By this reference, the full disclosure, including the claims and drawings, of U.S. Provisional Application, Serial Number 62/367, 105, is incorporated herein as though now set forth in its entirety.

BACKGROUND

[0002] 1 . Field of the Invention. The present invention principally relates to turbocharged, spark-ignited natural gas internal combustion engines (turbocharged NGIC engines) and the control of exhaust gas recirculation (EGR) systems for NGIC engines. More particularly, many aspects of the present invention relate to turbocharged NGIC engines with practical yet effective EGR system control based in part on sensed oxygen concentrations, especially in engines capable of meeting low-emission standards despite varied dynamic power ranges.

[0003] 2. Related Art. Exhaust gas recirculation (EGR) engine configurations are commonly used to enhance engine efficiency, fuel economy, and to reduce undesirable pollutants. Such EGR engine configurations fundamentally involve the recirculation of exhaust gas into the intake air supply for the engine. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold and reintroduced directly into or adjacent to the intake manifold. Examples of EGR systems are illustrated in U.S. Patent Nos. 6,216,458 (1997 priority, owned by Caterpillar, listing Alger as first inventor), 6,880,535 (2003 priority, owned by Chapeau, Inc. , listing Sorter as first inventor), and 7,715,975 (2007 priority, owned by Hitachi, listing Yamaoka as first inventor), each of which are incorporated here in their entirety by this reference.

[0004] As with many types of engines, turbocharged NGIC engines have long used EGR configurations for optimizing performance in engine applications having variable power demands. EGR, configurations are particularly beneficial for stoichiometric control strategies, which generally balance air/fuel ratios to approximate stoichiometric conditions within the combustion chambers of the engine. Engine operation can be more efficient with EGR in part because the recirculated exhaust gas tends to pre-heat the air/fuel mixture before combustion. Furthermore, while exhaust gases typically contain a fractional amount of unburned hydrocarbons, the recirculation of exhaust gas helps more completely burn those residual hydrocarbons when the exhaust gas recirculates through the engine cylinders.

[0005] Most importantly, EGR configurations are highly beneficial for NGIC engines designed to meet aggressive emission standards, especially if those engines need to be suitable for highly varied power demands. When air/fuel mixtures are blended with exhaust gases in EGR systems, the chemical reactions of combustion tend to be slightly slower and tend to peak at lower temperatures, which in turn decreases the formation of nitrogen oxides (NO _x ) and other exhaust pollutants that are undesirable by-products of high temperature combustion. As a result, EGR engine enhancements are especially beneficial when trying to meet the strict emission standards anticipated since at least the 1970's and 1980's. Such strict emission standards are evident in the most recent implementations of the ULEV engine emissions directives as well as the European Community's EURO 5 and EURO 6 standards, which are each incorporated herein by this reference. Corresponding EGR system benefits have proven especially useful for controlling NO _x emissions while also enabling engine operations that very closely approximate stoichiometric combustion and therefore minimize emission of both carbon monoxide and unburned hydrocarbons. Such general benefits are well known objectives for controlling NGIC engine emissions in a wide variety of motor vehicle applications, ranging from passenger cars to buses and on-highway freight haulers, and from light-duty trucks to heavy-duty earthmovers.

[0006] Conventional control strategies for EGR systems typically involve closed-loop feedback EGR flow controls, often hybridized with open-loop modes for accommodating changing power demands or the like. Although the algorithms controlling exhaust gas recirculation can be highly complex, typical strategies fundamentally vary the flow of recirculated exhaust gas relative to the air/fuel mix flow. Such variations typically depend on a combination of (a) actual flowrates for the recirculated exhaust gas, as measured in EGR system, and (b) exhaust gas oxygen (EGO) concentrations, as measured in or in close communication with the exhaust manifold. Knowing the exhaust EGO concentration and the actual EGR flowrate, the engine's control module (ECM or ECU) is able to make conclusions about the resulting-. fuel/air ratio in the combustion cylinders of the engine, based on various assumptions. Such control strategies have long been the trusted norm in the industry.

[0007] While EGO measurement has long been central to conventional EGR and emission control strategies, various types of exhaust gas oxygen (EGO) sensors have been widely available at various times over the years since the 1970s. For purposes of these descriptions, each of such known types of EGO sensors may be referred to as a "conventional" EGO sensor, whether or not they are actually positioned in the exhaust manifold of a particular engine. Most such conventional EGO sensors depend on oxygen permeable elements whose voltage or resistance properties vary based on the partial pressure of oxygen in the gas flowing through the oxygen permeable element, often as compared to the partial pressure of oxygen in a reference sample - such as that of ambient air. Various types of conventional EGOs include universal (a.k.a. "wideband") EGOs (commonly known as "UEGOs"), as well as lambda sensors, and hot-wire EGOs (commonly referred to as "HEGOs").

[0008] Conventional UEGO sensors, and indeed many if not most conventional EGO sensors, use sensor elements made of zirconia, although some conventional EGOs are known to use titania membranes rather than zirconia, and others might be formed of other semiconductor ceramics. Numerous structural, compositional, calibration and other feature variations for such EGOs are or have been available from various manufacturers, including Bosch, NTK, Delphi, and Denso. For purposes of the following descriptions, any general reference to oxygen sensors is meant to broadly encompass any and all types of oxygen sensors - including EGO, UEGO, HEGO and others - unless of course the context is clearly limited otherwise.

[0009] Although the relative cost of conventional EGO sensors has gradually dropped over the years, and dependability has generally increased, EGO sensor technologies function most reliably in exhaust manifold conditions. The performance characteristics of conventional EGO sensors can also have non-linear outputs over some operating ranges, can be susceptible to other environmental variations, and can tend to degrade and provide varied output over time.

[0010] Measuring the flow of recirculated exhaust gas is generally essential for controlling an EGR system to balance NO _x mitigation while minimizing undesirable engine operation effects, such as knock and misfire. As a result, typical configurations for prior art EGR control systems manage engine performance and emissions by controlling the flowrat© of recirculated exhaust gas using flowmeters, temperature sensors and/or differential pressure measurements. However, such prior art EGR configurations can produce aberrant results due to variations in the oxygen concentration or other characteristics of the exhaust gas that is being recirculated. Mixing exhaust gas with fresh air through an exhaust gas recirculation (EGR) system helps achieve the key purpose of reducing nitrogen-oxide (NO _x ) emissions, which is now state of the art. Although the share of exhaust gas in total engine mass flow may be unknown, it can be determined indirectly by controlling air-mass flow, such that the EGR flowrate can effectively control the amount of oxygen in the combustion chamber. Controlling the EGR flowrate, however, still only reveals an indirect correlation with the generation of NO _x .

[001 1] Others have tried to address needs in EGR control systems by deducing the oxygen concentrations in the combustion chamber or in the upstream intake manifold. Some of those attempts involve sophisticated algorithms, and other attempts have involved the use of special oxygen sensors ported in the EGR system or other locations upstream from the intake manifold. Unfortunately, such configurations are not reliable enough for highly accurate control of high-demand NGIC engines. In U.S. Patent Nos. 7,346,446 (Kang) and 8,751 , 136 (Yun), for comparison, General Motors disclosed uses of an oxygen sensor for monitoring intake oxygen concentration as part of their efforts to control operation of homogeneous-charge compression-ignition (HCCI) engines, where the auto-ignition process is controlled by oxidation chemistry rather than by fluid mechanics. In published U.S. Patent Application Publication 2013/0206100, (2012 priority, listing Yacoub as first inventor), Ford Global Technologies disclosed a configuration using upstream sensors that purportedly might be enhanced with an oxygen sensor. As shown in U.S. Patent No. 8,630,787 (2005 priority date, listing Shutty as first inventor), at least one other - BorgWarner Inc. - has considered alternative use of an oxygen sensor located directly in the intake manifold, for controlling exhaust gas recirculation within turbocharged engine systems.

[0012] Various other departures from conventional EGR system control strategies are also reflected in U.S. Patent Nos. 6,948,475 (2002 priority, owned by Clean Air Power, Inc., listing Wong as first inventor) and 7, 107, 143 (2004 priority, owned by General Motors Corporation, listing Kang as first inventor). Each of the patents and patent applications referenced by number in this background discussion is incorporated herein, in its entirety, by this reference. Still other EGR system control configurations-, and control, strategies- are. also ^, well- known, as wiJI- be- vident to -those. of skill in the art, although seemingly all such approaches present various challenges to accuracy, practicality, efficiency and reliability.

SUMMARY OF THE INVENTION

[0013] Given the problems and challenges with the prior art, there is still a longstanding unresolved need for reliable highly accurate EGR control systems and strategies that optimize engine efficiency, durability and performance while minimizing undesirable emissions. This includes the need to simultaneously balance real-world objectives such as the needs for simplicity, practicality, affordability, ease of use, ease of maintenance, and ease of repair. What has long been needed is an elegantly simple yet reliable control system and strategy for accurately controlling the flow of recirculated exhaust gas in low-emission, turbocharged, spark-ignited NGIC engines despite highly variable operating demands. Even more, Applicant has discovered and developed a system and method that reliably enables highly accurate operating control of NGIC engines. The approach achieves such highly accurate control based on simple measurements that are reliably accurate despite the confluence of numerous challenges. The approach achieves as much despite pressure and temperature fluctuations, despite recirculated exhaust gas flow reversals, despite water vapor and impurities in exhaust gas/air mixtures, and despite considerable variations in power demands over the duration of engine operation, all while also overcoming many of the other challenges and obstacles that are presented by the known prior art.

[0014] Even though strict engine emission standards have been grappled with and anticipated for decades, and even though the background technologies have long been known in the field, simple yet reliable NGIC engine controls are still not readily available in forms that reliably meet strict emission standards. It is a fundamental object of the present invention to address such needs despite the confounding challenges of the prior art. It would therefore be desirable to have a system and method that implements and capitalizes on the benefits of EGR system control configurations in a way that can simply and reliably achieve highly accurate EGR system control. It would be particularly desirable if such control could be achieved practically yet reliably over large dynamic power ranges, while also reliably meeting strict emission standards. It would also be desirable to do so while also enjoying the benefits and advantages of turbocharged, spark-ignited NGIC engines, despite all the obstacles and challenges that have prevented the field from doing so effectively for all these many years.

[0015] Meeting such objectives, however, is easier said than done. Laboratory test configurations might be imagined with numerous banks of different sensors in every chamber, for exhaustive knowledge and ideal control of every aspect of engine operation, supposing that highly-accurate optimal performance was the only objective. However, real-world engine designs must balance optimal performance. Simplicity, practicality, affordability, ease of use, ease of maintenance, and ease of repair are also critical objectives in real-world engine design. Indeed, even if cost management were less important, the most advanced of prior art NGIC EGR system controls inherently make assumptions and predictions about various aspects of flow characteristics in various segments of engine operation. Likewise, it remains an important object of the present invention to enable more durable and reliable engines that achieve superb operating efficiencies and fuel economies, while also enabling exhaust emission controls that meet or exceed strict emission standards. The ultimate object is directed to providing as much through elegant and synergistic combinations of conventional sensors in reliably accurate EGR system control configurations and strategies.

[0016] One of the challenges in accurately controlling the flow of recirculated exhaust gas is the occasional reversal of the EGR flow direction, which can be caused by pressure pulsations in the flow paths. Such pressure pulsations and corresponding flow reversals increase with increasing and/or varying loads. Such pulsations and flow reversals can easily lead to erroneous conclusions when using conventional measurement methods. Resulting miscalculations of commanded EGR system controls based on erroneous measurements can lead to reduced drivability, engine durability issues, and even catastrophic failure, especially at high load operating conditions.

[0017] Accordingly, a fundamental object of the disclosed system is to improve over the prior art, including providing more accurate and more reliable monitoring of NGIC engine operation for EGR system control. Under such fundamental objects, it is also an object of the present invention to enable subsystems as well as finished designs that are safer, cleaner, simpler, quieter, and easier to assemble, install, connect, maintain, troubleshoot and repair, as well as being more reliable, accurate, affordable, efficient, durable, versatile, effective, interchangeable and. adaptable. [0018] It is also a fundamental object of the disclosed system to generally improve over the prior art, including to provide a more flexible and adaptable EGR system for NGIC engine control. Fundamental objects of the present invention also include overcoming the obstacles and challenges of the prior art in ways that help optimize accurate EGR system control as well as fuel economy and engine efficiency. Related objects include affordably enhancing NGIC engine and EGR system control strategies while addressing the known needs without dramatically increasing the costs of NGIC engines or their operation, preferably in ways that can be readily commercialized, easily implemented, easily structured, and easily used in the majority of applications. It is also an object of the disclosed system to enable subsystems as well as finished engine designs that are versatile, reliable, safer, cleaner, simpler, quieter, and easier to operate, adapt, connect, maintain, troubleshoot, and repair as well as being more reliably accurate, affordable, efficient, versatile, effective, interchangeable and adaptable.

[0019] Aspects of the disclosed system address these and other objects, in part, by using conventional UEGO sensors for measuring real-time oxygen concentrations in the intake system of an NGIC engine, preferably in direct communication with the engine's intake manifold. The present invention addresses identified needs by enabling an EGR system in an internal combustion engine, preferably a turbocharged gaseous fuel engine, that utilizes a Universal Exhaust Gas Oxygen (UEGO) sensor during boosted operation to indirectly but accurately measure the oxygen concentration of the recirculated exhaust gas/air mixture in the intake charge.

[0020] In equivalent arrangements, a conventional UEGO sensor configuration directly measures the oxygen concentration of fresh intake air, either selectively or when manifold pressure allows, such as during non-boosted operation. Such direct measurement of fresh air oxygen concentration allows effective, real-time re-zeroing during the course of engine operation, allowing the ECM to know the actual concentration of oxygen in the atmosphere rather than relying on assumptions or predictions of normal oxygen concentrations. With each such re-zeroing to actual oxygen concentration in the surrounding atmosphere, the ECM is programmed to adjust itself to use the current fresh air reading as a baseline for comparison to the measurement of the recirculated exhaust gas/air mixture during boosted operation.

[0021] Aspects of the invention may also be characterized as an innovative method- . of measu ng. EGR concentrations* during, non-boosted . operation; Such _* method uses delta pressure feedback (DPFE) across a flow restriction in conjunction with EGR valve position to calculate the mass flow rate of recirculated exhaust gas - and subsequently the EGR and oxygen concentration - in the intake charge. Such DPFE-based concentration measurements may also be used as a redundant measurement during boosted operation, to increase engine reliability.

[0022] UEGO or wide-band oxygen sensors typically include both a pumping cell and a sensing cell. The pumping cell of the UEGO moves oxygen through a porous substrate within the UEGO. When current is applied to the pumping cell, it passes oxygen ions from one side of the porous substrate to the other side of the porous substrate. The sensing cell of the UEGO senses the oxygen content difference between the two sides of the UEGO. The sensing cell has a reference chamber on one side and an exhaust sensing chamber on the other side. Consequently, the sensing cell will generate a voltage proportional to the oxygen content difference between the reference chamber and the exhaust sensing chamber.

[0023] In raw air at sea level, a UEGO sensor would measure approximately 21 % oxygen concentration in air. However, varying pressures and humidity can have a significant effect on the accuracy of the UEGO sensor. The signal from a UEGO sensor changes approximately linearly with changes in pressure. UEGO sensors actually measure the partial pressure of oxygen, so an increase in the pressure in the environment in which the UEGO sensor is operating will result in an inaccurately elevated reading from the UEGO sensor. This has to do with the porosity of the porous substrate between the pumping cell and the sensing cell. If the porous substrate has pores that are too small, then exhaust gases will be restricted, and back pressure will vary the effectiveness of the pumping cell. If the pumping cell effectiveness changes, then the pumping cell current has a varying effect upon the sensing cell. If the porous substrate between the pumping cell and the sensing cell has pores that are too large, then contaminants can get lodged into the pores of the porous substrate and once again reduce the effectiveness of the pumping cell.

[0024] The normal pressure in the intake manifold of a throttled, natural gas engine that also has a turbocharger is anywhere from 3-45 psi absolute. As a consequence of the previously discussed problem relating to how pressure may affect the accuracy of a conventional UEGO sensor, installing a conventional UEGO sensor in the intake manifold subjects the UEGO sensor to potentially great fluctuations in pressure. Sudi fluctuations in pressure are. known in the field to. result in much> different signals from the UEGO sensor across the possible range of pressures that may occur. Having to correct for the effects of pressure fluctuations can produce errors in measurement of the flow of recirculated exhaust gas.

[0025] Many existing systems and methods either mount an oxygen sensor in the exhaust system downstream of the combustion chamber, or some use a venturi in the exhaust system. When an oxygen sensor is mounted only in the exhaust system, the measurements are indirect. When using a venturi in the exhaust system, this typically measures changes in pressure across an orifice in the exhaust system in the EGR loop. Specifically, where the recirculated exhaust gas enters, the system measures the mass flow rate of recirculated exhaust gas. This method is error-prone for a number of reasons. First, there are fluctuations in pressure resulting in pulsations in the EGR loop. Measurements, as a result, can be difficult to determine. Second, using a venturi in the exhaust system only provides a measurement of mass flow rate of exhaust gas and not the concentration of oxygen in the exhaust system.

[0026] Another challenge in accurately controlling the flow of recirculated exhaust gas is presented by water vapor and other impurities that might be present in the recirculated exhaust gases, or potentially even in the fuel or fresh air drawn from ambient. Not only are there generally some impurities in the fuel and fresh air, but additional water vapor is produced as a byproduct of combustion, such that recirculated exhaust gas or exhaust gas/air mixtures inevitably include a significant amount of water vapor. While engine designs have long incorporated EGR systems that function adequately despite water vapor or other impurities, such challenges are likely immaterial if not completely non-existent for the operation of EGR systems controlled based on intake oxygen or conventional exhaust gas sensors. Moreover, there are various filters and dryers that are well known conventional measures to help manage water vapor when necessary.

[0027] However, Applicant has discovered that water vapor can condense out of the exhaust gas/air mixture in the intake manifold, particularly when pressures and temperatures are aggressively managed. One contributor to the increased risk of intake condensation is the conventional wisdom of reducing the elevated temperatures of recirculated exhaust gases through the use of intercoolers or the like. Intake condensation would be unnoticed and likely of no concern in conventional EGR systems, and would likewise be unimportant for UEGO sensors in an exhaust manifold,- But,' Applicant, has, discovered that , exposing even _; high sensors to excess moisture can affect the accuracy of the sensor output and, hence, the key measurements relied upon in systems and methods that are presently disclosed. To overcome such challenges, Applicant's preferred systems and methods incorporate novel innovations for eliminating the risk of intake condensation, which thereby further increases the reliability of data provided by UEGO sensors in the intake manifold, where Applicant has discovered that such condensation is more likely. More particularly, some aspects of Applicant's invention provide localized heating of intake gasses slightly upstream or at the location of a sensor for monitoring the real-time oxygen concentration in the intake manifold, and controlling EGR and other engine operation based on such sensor.

[0028] In addition, Applicant's preferred systems and methods also incorporate novel innovations for systems with which one has to know the airflow fairly accurately because any errors in air flow are compounded by errors in the flow of exhaust gas.

[0029] Without reliably accurate measurements of the flow of recirculated exhaust gas, problems can arise in the operating condition of the engine. In conditions during which an engine is creating the most power, if the flow of recirculated exhaust gas is higher than what is expected or predicted due to a possible error in measurement, the engine may start to misfire. In the other direction, if the flow of recirculated exhaust gas is lower than what is expected or predicted, once again due to the limitations that exist in measuring the flow of recirculated exhaust gas in many existing EGR systems, the engine may start to knock. These and other conditions caused by inaccuracies in the prior art systems can not only reduce engine efficiency and fuel economy, but they can even result in permanent damage to the engine.

[0030] The disclosed system innovatively controls the operation of an NGIC engine with a conventional engine control module. The overall system includes: an intake system for conducting the flow of a mixture of fresh air, recirculated exhaust gas and fuel into the combustion chambers of the NGIC engine; an exhaust gas recirculation system for controlling the flow of exhaust gas from the combustion chambers of the NGIC engine; an oxygen concentration sampling and sensor assembly connected in direct fluid communication with the intake manifold; said oxygen concentration sampling and sensor assembly providing a signal to the engine control module of the oxygen concentration in the fresh air drawn into said intake system when the NGIC engine is in an unboosted operating regime; and said oxygen concentration sampling, and sensor. assembly providing .a- signal to he engine control*. module of the oxygen concentration in the mixture of fresh air and recirculated exhaust gas drawn into said intake system when the NGIC engine is in a boosted operating regime.

[0031] Aspects of the disclosed system also address problems, obstacles, limitations and challenges related to achieving highly accurate control while also achieving stoichiometric combustion with low emissions in an internal combustion engine. More particularly, in fulfillment of the above and further objects, aspects of the disclosed system surprisingly capitalize on use of a conventional EGO sensor, preferably a universal exhaust gas oxygen (UEGO) sensor, in configurations that simply and elegantly allow reliably accurate control of EGR system operation. Aspects of such EGR system control configurations and the resulting strategies enable direct intake manifold monitoring of the intake charge as well as re-zeroing of the UEGO sensor to the fresh air from the air intake. Moreover, approaches of the present invention also simultaneously isolate the UEGO sensor from pressures significantly above ambient as well as from pressure fluctuations, in order to more accurately measure the oxygen concentration of the resulting air/fuel mixture after introduction of the recirculated exhaust gas into the intake system. Other aspects of the disclosed system address condensation of water initially present in vapor form in the exhaust gas/air mixture, wherein the condensation may affect the accuracy of the measurements made by the UEGO sensor.

[0032] These and other aspects of the present inventions will be understood by those of skill in the art from the various descriptions included in this specification, although they are to be generally defined in appended claims, as they may be added, supplemented or amended from time to time. Those of skill in the art will also recognize many other aspects of our inventions based on further consideration of the prior art, particularly after reading this specification and thoughtfully contemplating its implications. It must be understood that many other aspects of our inventions and many other advantages, disadvantages, alternatives, variations, substitutions and modifications will also fall within the scope of the inventions, both those inventions that are now claimed as well as those inventions that are described but not yet claimed. BRI EF DESCRI PTION OF THE DRAWINGS

[0033] FIGURE 1 is a schematic diagram illustrating one of the best presently-contemplated modes of practicing the present invention, which provides a turbocharged NGIC engine 1 00 having an EGR system 140 controlled in part based on readings from an oxygen sensor assembly 150 connected to the intake manifold 135, all to provide an improved EGR system 140 that achieves desirable exhaust emissions despite elevated and varied power demands.

[0034] FIGURE 2A shows a centrally-cross-sectioned pictorial view of an oxygen sensor assembly 150 in a boosted engine operating regime that may be used with or without variations for the oxygen sensor assemblies 150, 350, 450, 550 and 750 of FIGURES 1 , 3, 4, 5 and 7, respectively.

[0035] FIGURE 2B shows a centrally-cross-sectioned pictorial view of an oxygen sensor assembly 150 in a non-boosted engine operating regime that may be incorporated for the oxygen sensor assemblies 150, 350, 450, 550 and 750 of FIGURES 1 , 3, 4, 5 and 7, respectively.

[0036] FIGURES 3 and 4 illustrate two particularly advantageous alternative configurations for oxygen sensor assemblies 350 and 450 as alternate embodiments for any of the configurations for oxygen sensor assemblies 1 50, 550 and 750 of FIGURES 1 , 5 and 7, respectively. FIGURE 4, particularly, illustrates an alternative configuration for an oxygen sensor assembly 450 for enabling multi-mode operation of an oxygen sensor assembly 450 based in part on selective actuation of a three-way valve 480 under command of an ECM 360, as an alternative for any of the configurations for oxygen sensor assemblies 150, 550 and 750 of FIGURES 1 , 5 and 7, respectively.

[0037] FIGURE 5 illustrates an alternative configuration for oxygen sensor assembly 550 as an alternate embodiment for any of the configurations for oxygen sensor assembly 150, 350, 450 and 750 of FIGURES 1 , 3, 4 and 7, respectively. FIGURE 5 particularly illustrates a configuration wherein UEGO sensor 653 is positioned within the main flow of the exhaust gas/air mixture through compressed air fluid passage 633, with UEGO sensor 653 particularly being advantageously positioned within a perforated tube 580. [0038] FIGURES 6A and 6B illustrate a close-up partially-cross-sectional view of the portion of oxygen sensor assembly 550 outlined in dashed line 6-6 of FIGURE 5, wherein two different versions of perforated tube 580 are shown.

[0039] FIGURE 7 is a schematic illustration of a representative turbocharged NGIC engine 700 having an EGR system 740 controlled by an ECM 760 based in part on readings from an oxygen sensor assembly 750.

[0040] FIGURE 8A is a partial cross-sectional perspective view of an alternative configuration of oxygen sensing assembly 850 that may be used with or without variations for oxygen sensor assemblies 1 50, 350, 450, 550, 750, and 950 of FIGURES 1 , 3, 4, 5, 7, and 9A-9C, respectively.

[0041] FIGURE 8B is a centrally cross-section view of the oxygen sensor assembly 850 of Figure 8A.

[0042] FIGURE 8C is a top perspective view of a portion of the oxygen sensor assembly 850 of Figures 8A and 8B.

[0043] FIGURE 9A is a partial cross-sectional perspective view of an alternative configuration of an oxygen sensor assembly 950 that may be used with or without variations for oxygen sensor assemblies 1 50, 350, 450, 550, 750, and 850 of Figures 1 , 3, 4, 5, 7, and 8A-8C, respectively.

[0044] FIGURE 9B is a partial exploded perspective view of a cover 990 and a portion of associated features of oxygen sensor assembly 950.

[0045] FIGURE 9C is a partial cross-sectional perspective view of a portion of the features of oxygen sensor assembly 950.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIM ENTS

[0046] Information Incorporated By Reference. In addition to the various background materials incorporated by reference elsewhere, this description also incorporates by reference the entire disclosure of Published U.S. Patent Publication No. 2013/0333671 A1 dated December 19, 2013, entitled "Highly Accurate Continuous-Flow Vaporized Fuel Supply for Large Dynamic Power Ranges," owned by the assignee of this patent application.

[0047] Descriptive Simplifications. The following descriptions are of the best representative modes presently contemplated for carrying out the present invention. In the course of contemplating these various descriptions of preferred and alternative embodiments, those of skill in the art will be able to gain a greater understanding of not only the disclosed systems but also many of the various ways to make and use those systems. Throughout, these descriptions are not to be read in a limiting sense, but should be understood as describing general principles of the structures and operations of particular embodiments, whereas the scope and breadth of the invention should be determined much more broadly, with primary reference to the claims.

[0048] The reader may notice that reference numbers first introduced or first uniquely varied with reference to a particular drawing typically use the number of that drawing in the hundreds digit. Whereas, to help identify similarities and differences between the various embodiments of FIGURES 1 -7, like numerals in the tens and ones digits are used throughout in referring to identical or analogous parts, components, subassemblies or the like. For instance, the hundreds digit of the ECM 160 of FIGURE 1 is a "1 ", and the hundreds digit of the reference numeral for the ECM 760 of FIGURE 7 is a "7". Plus, even though the embodiments of FIGURES 1 and 7 are different one from another, the reference numbers of their respective ECMs 160, 760 (which are analogous if not identical to each other) both end in "60". Likewise, although many of the components of the embodiment in FIGURE 3 are identical to comparable components of the embodiment in FIGURE 4 and are therefore numbered identically (such as the fuel supply 320 in each), some of the components of FIGURE 4 are analogous but slightly varied from those of FIGURE 3, and the corresponding reference numbers in FIGURE 4 are therefore given a "4" in the hundreds digit but otherwise have the same number in the tens and ones (such as with the heating element 471 of FIGURE 4, which has a structure and function that are analogous or comparable to those of heating element 371 of FIGURE 3). Therefore, whenever the reader notices such similarities in reference numerals, it should be understood as signaling such relationships unless the particular context suggests otherwise.

[0049] Various wording simplifications will also be evident throughout these descriptions. For instance, while the field of the invention relates to spark-ignited NGIC engines, descriptive references to an "engine" of a disclosed embodiment presumably refers most directly to a turbocharged, spark-ignited NGIC engine unless otherwise evident from the context.

[0050] Please understand that the drawings and descriptions in this application depict specific examples to teach EGR engine systems and controls, and those skilled in the art should understand how to make and use such systems and. controls even. though these descriptions are not exhaustive and may occasionally simplify or omit things. To concisely teach inventive principles, some conventional aspects of the invention have been simplified or omitted. Despite such simplifications and omissions, and the possibility of a few misstatements, those of skill in the art should be very familiar with existing ways of accomplishing incidental aspects of the embodiments otherwise generally described herein. Despite the possibility of inadvertent misstatements or the like, those of skill in the art should understand many different configurations, combinations, subcombinations, and variations that are not specifically disclosed but would still fall within the scope of the invention.

[0051] Descriptions. Turning now to the drawings, FIGURE 1 shows a schematic diagram of a preferred embodiment of a turbocharged NGIC engine 100. Engine 100 characteristically has an EGR system 140 controlled by an ECM 160, based in part on readings from an oxygen sensor assembly 1 50 incorporating a conventional UEGO sensor 153. As is illustrated, the engine 100 can be viewed as including several operatively linked subsystems - namely, a turbocharger 1 10, a fuel supply 120, combustion chambers (or cylinders) 130, an EGR system 140, an oxygen sensor assembly 1 50, and an ECM 160, together with various operative inlets, outlets, sensors, and connections therebetween. The turbocharger 1 10 of the engine 100 conventionally incorporates a turbo compressor 1 1 1 and a turbo turbine 1 1 2. As is conventional, the turbo turbine 1 12 is mechanically coupled to operatively cooperate in a conventional manner with the turbo compressor 1 1 1 , such that the pressures in the intake passage 133 and the intake manifold 135 are elevated above ambient during normal operation - typically to within the range of 3 to 45 psi absolute in the preferred embodiment. Alternative embodiments achieve or may occasionally involve pressures below 3 psi and may achieve even greater pressures than 45 psi; however, configurations that achieve pressures above 45 psi preferably involve specially chosen and/or blended gaseous fuels in order to manage the increased risk of premature combustion.

[0052] As will be understood by those of skill in the art, the general fluid flow in the engine 100 proceeds from the fresh air intake 101 to the exhaust outlet 199, generally in the directions as indicated by the various flow arrows 102-109 shown in FIGURE 1 . Hence, the fresh air operatively flows under control of the ECM 160 from the inlet 101 and is compressed through a turbocharger 1 1 0 (via compressor 1 1 1 ) and directed into the intake passage 133 of intake manifold.135. Although .not. illustrated in the drawings, those of skill in the art will understand that preferred embodiments would include various components that are not shown. An intercooler and a throttle, for instance, will normally be deployed along intake passage 1 33, upstream of the EGR inlet 145. In addition, the EGR system 140 itself would also preferably have an intercooler along EGR line 141 , generally downstream of EGR valve 142. Moreover, other components like filters and pressure relief valves are also not shown. With respect to any such simplifications and omissions from the drawings, it should be understood that preferred embodiments include them in such character and configuration as would be generally understood within the discretion of those of skill in the art.

[0053] In the intake passage 133, the fresh air is mixed first with any recirculated exhaust gas 107 that is delivered from EGR system 140, preferably using a throat- ported venturi mixer much like the mixer 345 of FIGURE 3. Although the detail of mixer 145 is omitted in FIGURE 1 , it would be situated at the indicated junction 145.

[0054] After the mixing of fluid streams that occurs at mixer 145, the recirculated exhaust gas/air mixture proceeds through intake manifold 135 and is mixed with fuel supplied by a fuel supply 120 along the way, again preferably using a venturi mixer 122 and preferably all under control of the ECM 1 60. Much as with mixer 145, the detail of mixer 122 is omitted in FIGURE 1 , but it would be situated at junction 122, where the nozzle 21 of fuel supply 1 20 introduces its mass-flow-controlled fuel supply to the intake manifold 135 or directly into the individual combustion chambers 1 30 or their corresponding intake ports (symbolically represented by combustion chamber inlet 129) . Although FIGURE 1 is a simplified illustration, the intake ports 1 29 and the like, should be understood as including conventional features such as an intake valve and corresponding controls.

[0055] Although not essential to many aspects of the present invention, the fuel supply 120 is preferably a highly accurate, mass-flow controlled natural gas fuel supply. Most preferably, the fuel supply 120 is in the form of a continuous-flow fuel supply such as one of those described and controlled in accordance with the descriptions of Published U.S. Patent Publication No. 2013/0333671 A1 dated December 19, 2013. Despite the particulars for preferred embodiments, the fuel supply 120 preferably feeds a controlled supply of natural gas fuel to the recirculated exhaust gas/air mixture flowing in the engine intake passage 133, which is in open communication with the intake, manifold, 135 [0056] From the intake manifold 1 35, the air/fuel mixture is directed into the cylinders 1 30 where it is combusted under the timing control of the ECM 160 in a manner as would be generally understood from other descriptions in this specification. Once the resulting burned natural gas mixture is ejected from the cylinders 1 30, the exhaust flow proceeds in one of two general paths - either through the turbine 1 12 of turbocharger 1 10, or recirculated to the intake manifold 1 35 at junction 144 through ECM-controlled operation of the EGR subsystem 140.

[0057] EGR System. Although details may vary according to the particular choice of designers, EGR System 140 generally includes an EGR passage 141 fluidically connecting exhaust manifold 1 31 to intake manifold 135, through which exhaust gases may be recirculated to the combustion chambers 130. Although other forms of flow control may be used as alternatives, the portion of the flow of exhaust gas through the EGR subsystem 140 generally proceeds based largely on operation of an EGR valve 142 as determined and controlled by the ECM 160. Meanwhile, the bulk of the exhaust gas generally proceeds through the turbine 112 and out the exhaust outlet 199 due to pressure gradients.

[0058] The EGR system 140 is controlled by the ECM 160 based in part on readings from the oxygen sensor assembly 150. The logic of the ECM 160 is preferably adapted for controlling the engine 100 and its EGR system 140 to achieve low exhaust emissions despite elevated and varied power demands. The ECM 160 is also programmed to control a turbocharged gaseous-fuel internal combustion engine (e.g., a natural gas engine) 100 that is preferably configured to operate according to a stoichiometric combustion strategy, although alternative embodiments may be implemented following lean burn strategies as described below. As evident in FIGURE 1 , the turbocharged spark-ignited engine 100 includes an intake manifold 1 35, an exhaust manifold 1 31 , a turbocharger 1 10, an EGR system 140, and an oxygen sensor assembly 1 50. The turbocharger 1 10 may be a fixed geometry turbocharger or a variable geometry turbocharger (VGT) and consists of an exhaust gas driven turbine 1 12 mechanically coupled to an intake air compressor 1 1 1 .

[0059] Oxygen Sensor Assemblies. Oxygen sensor assembly 1 50 generally includes an oxygen sensor 153 positioned to sense the oxygen concentration of gases flowing through intake manifold 135 at least during its primary mode of operation. Preferably, the oxygen sensor 153 includes a conventional UEGO sensor 153, although other oxygen sensors may be used while still appreciating benefits of certain aspects of the invention.

[0060] Disposed in the sample conduit 1 55 is an oxygen sensing subsystem 150 that essentially combines a conventional EGO sensor (preferably of the UEGO type) 153 together with a restriction 1 54 for substantially reducing the pressure of sampled gases at the location of the UEGO 153. The oxygen sensing assembly 150, more completely, includes a recirculated exhaust gas sample manifold 155, a UEGO sensor 1 53 and a flow orifice 154. The flow orifice 154 may be a variable orifice in alternate embodiments, but it is preferably a fixed orifice of a size that is determined during design based on desired operating ranges for the engine 100.

[0061] Also shown included in oxygen sensing subsystem 150 are resistive heating elements 170, 171 along with temperature sensor 158. As described above with regard to the illustrated embodiment of FIGURE 1 , resistive heating elements 170, 171 are preferably glow plugs having at least a portion of the body of each extending into sample conduit 155 for heating the exhaust gas/air mixture to preferably remove moisture which may affect the accuracy of UEGO sensor 153. Temperature sensor 158 is configured for measuring the temperature of exhaust gas/air mixture flowing in sample conduit 155. Connections 161 -168 are provided between ECM 160 and each of the elements of engine 100 as shown. Accordingly, connections 165-168 are provided between ECM 160 and each of the elements of oxygen sensing subsystem 150 as shown, namely for sending appropriate output signals to control operation of resistive heating elements 170, 171 , and for receiving input signals from UEGO sensor

153 and temperature sensor 158.

[0062] Although both FIGURES 1 and 7 illustrate that the UEGO sensor 153 and 753, and the flow orifice 154 and 754 are upstream of the respective fuel supplies 120 and 720, alternate embodiments may include configurations wherein the UEGO sensor 153 and 753 and the flow orifice 154 and 754 are operatively mounted downstream of the fuel supply, such as shown in FIGURE 1 . Other configurations may also be evident to those of skill in the art while still ensuring readings that achieve the intended purpose for the oxygen sensing assembly 1 50 and 750. The flow orifices

154 and 754 are preferably fixed to set the flow rate of recirculated exhaust gas into the recirculated sampling conduit 155 and 755 through the recirculated exhaust gas sample conduit 1 55 and 755 and across the UEGO sensor 153 and 753 in a manner such that most, if not all, of the pressure effects previously described are minimized in order to increase the measurement accuracy of the UEGO sensor 153 and 753.

[0063] In the configuration as shown in FIGURE 1 , operation of the EGR system 140 is determined in part based on the temperature and pressure of the flow of recirculated exhaust gas. Such temperatures and pressures are preferably directly measured by the sensor module 143 that is upstream of the EGR valve 142 and includes an integrated pressure transducer and an integrated temperature sensor. Corresponding signals 161 from this sensor module 143 are communicated to the Engine Control Module (ECM) 160 for use in engine control calculations. The ECM 160 also provides an output signal 162 which controls operation of the EGR valve 142. Alternative embodiments may include a recirculated exhaust gas mixer (not shown) which might also serve as a recirculated exhaust gas pump for high-load conditions. Such recirculated exhaust gas mixer preferably would be located downstream of the EGR valve 142 at the junction in the compressed fresh air intake 133 in the intake manifold 135 where recirculated exhaust gases are mixed with intake air from the turbo compressor 111 prior to combustion. To maximize efficiency and fuel economy in turbocharged engines, the recirculated exhaust gas is preferably removed by the EGR system 140 upstream of the turbocharger's exhaust-driven turbine 112 and is then re-introduced downstream of the turbocharger's compressor 111 and its primary intercooler (not shown in FIGURE 1 ). By controlling the EGR system 140 to keep the temperature of combustion in cylinders 130 at levels peaking less than 1300 Kelvin, the ECM 160 effectively keeps NO _x byproducts to a minimum, thereby reducing pollutant levels that would otherwise contribute to smog and acid rain.

[0064] In the simplified illustration of FIGURE 1 , the fresh air inlet 101 is preferably open to the atmosphere surrounding the engine 100, although it should be understood that an air filter and other components and adaptations are preferably included in the fresh air inlet 101 according to particular preference or design. Those of skill in the art will also recognize that the air inlet may itself be a controlled supply of air, such as the air from a first stage turbocharger (not shown) that is further upstream from turbocharger 110, and many other adaptations can be made in alternative embodiments for drawing fresh air or other oxygen source gases from sources other than the ambient atmosphere.

[0065] Various flow direction arrows 102-109 are shown in FIGURE 1 to illustrate the predomjnant .djrection. that fluids will typically, flow in fluid passa§es .10.1v 133, .131 141 and 155 when valves and the like in those passages are open during normal operation of the engine 100. Two opposite arrows 156 and 157 are shown on either side adjacent the fluid passage 155 to illustrate that fluids flow predominantly in one direction 156 in a unboosted operating regime for the engine 100, and predominantly in the opposite direction 157 during a boosted operating regime for the engine 100, as will be evident from further descriptions in this specification. It should be understood that "fluid passages" is a generic reference to various kinds of manifolds, fluid conduits and the like. Nonetheless, reference to a particular one of the fluid passages 101 , 133, 131 , 141 and 155 (or to a particular subpart of such fluid passages, such as subparts 131 a and 131 b of the fluid passage 131 , 133a and 133b of the fluid passage 133 and 141a and 141 b of the fluid passage 144) may use more specific wording to reflect a particular type of fluid passage that is used in one or more of the preferred embodiments. It should also be understood that the particular type of any particular fluid passage is not critical to all aspects of the disclosed system, even if one of those more particular terms is used for describing preferred and alternate embodiments. For reference, this description also occasionally uses those same reference numerals - the reference numerals for the various flow direction arrows 102-109 and 156-157 used to designate the various fluids that are flowing in the corresponding fluid passages 101 , 133, 131 , 141 and 155, respectively.

[0066] Hence, in preferred configurations, fresh air naturally flows from the atmosphere surrounding the engine 100 into an air inlet 101 in the direction 102 toward the turbocharger 110 and the intake manifold 135. Although probably not critical for all embodiments, the fresh air flow 102 is preferably metered by a throttle (not shown in FIGURE 1 ) within the fluid passage of the inlet 101 , for communication to the compressor portion 111 of the turbocharger 110 and, therefore, for also controlling the flow of fresh air to the intake manifold 135 through the compressed air passage 133. Although such a throttle may be located within the fluid passage 133 in alternative embodiments, even in such alternatives, such a throttle is preferably located in the upstream section 133a of the compressed air fluid passage 133, which is the section 133a that is between the compressor 111 and a mixer 145 downstream from the EGR valve 142.

[0067] As mentioned, the fuel supply 120, controlled by a signal 163 from the ECM 160, is also preferably provided in controlled communication with the compressed air. fluid- passage, 133, . preferably through a< fuel-, supply . mixer 122. positioned somewhere in the fluid passage 133 between the compressor 111 and the combustion chambers 130. Although not essential for all embodiments, the fuel supply mixer 122 is preferably a venturi mixing nozzle positioned within the course of the fluid passage 133. Most preferably, the fuel supply mixer 122 is positioned within the section 133b of the fluid passage 133 that is downstream of the exhaust gas mixer 145, such that the fuel from the fuel source 120 is mixed into a flow of pre-mixed air and recirculated exhaust gas 105 when the EGR valve 142 is operatively opened by a signal 162 from the ECM 160. Other alternative configurations for fuel introduction may be beneficial if aspects of the present invention are used for other types of fuel and/or other types of fuel supplies.

[0068] More particularly, the gaseous fuel from the fuel source 120 is inserted into the recirculated exhaust gas/air charge 103 by a fuel insertion manifold 121 located downstream of the EGR valve 142 with the functioning of the EGR valve 142 being controlled, at least in part, by a signal 162 from the ECM 160. Although two or more separate sensors are used in some alternative embodiments, manifold absolute pressure (MAP) and intake air temperature (IAT) are preferably measured using a conventional temperature and manifold absolute pressure (TMAP) sensor 134. As is typical for TMAP sensors, the TMAP sensor 134 incorporates both a MAP sensor and an IAT sensor in a single module. The TMAP sensor 134 is preferably located downstream of the fuel insertion mixer 122 for the fuel supply 120 and upstream of the intake manifold 135. The MAP and IAT signals are communicated from the sensor module 134 via electronic communication line 164 to the ECM 160 for engine control calculations.

[0069] The embodiment shown in FIGURE 1 contains a gaseous fuel insertion manifold 121 , preferably supplied directly from the mass flow-controlled fuel supply 120 utilizing a continuous-flow valve (CFV) that is also controlled by a signal 163 from the ECM 160. Such a mass-flow-controlled fuel supply 120 as described in the co- owned pending U.S. Patent Application entitled "Highly Accurate Continuous-Flow Vaporized Fuel Supply for Large Dynamic Power Ranges," Serial No. 13/918,882, the disclosure of which is hereby incorporated by reference.

[0070] Sampling Conduit. With respect to the oxygen sensor assembly 150, its assembly revolves around a sample conduit 155 primarily for sampling gases from the intake manifold 135 and for measuring the oxygen concentration of gases that are so sampled, preferably through-specialty configured use of a conventional UEGO. sensor 153 whose output signal 165 is sent to the ECM 160. To achieve such sampling, an EGR sample tap 151 in the sample conduit 155 is preferably openly ported directly into the intake manifold 135, thereby ensuring direct measurement of oxygen concentrations of the recirculated exhaust gas/air/fuel mix 103 that is within the intake manifold 135.

[0071] Also shown in proximity to UEGO sensor 153 in the configuration illustrated in FIGURE 1 is temperature sensor 158, which is configured to send an output signal 166 representing temperature readings to ECM 160. Temperature sensor 158 measures the temperature of the exhaust gas/air mixture within sample conduit 155.

[0072] Heated Sensor Flow. Also shown are resistive heating elements 170, 171 that are incorporated into oxygen sensor assembly 150. In preferred embodiments, resistive heating elements 170, 171 are glow plugs having at least a portion of the body of each extending into sample conduit 155 for heating the exhaust gas/air mixture. Resistive heating elements 170, 171 may be diesel glow plugs such as those commercialized by Bosch ^® under the name "Duraterm." Although glow plugs 170, 171 are included in the illustrated embodiments, those of skill in the art may recognize that some facets of the invention might be appreciated through use of many other types of heat sources employed relative to the intake manifold and/or sensor line, for increasing the temperature of the gases flowing therethrough, especially in proximity to UEGO 153.

[0073] By locally heating the exhaust gas/air mixture through the use of heating elements 170 (Qi) or 171 (Cb), whichever is upstream of UEGO 153 in the current flow conditions through sensor assembly 150, condensation on the sensor element of oxygen sensor 153 is prevented. Preferably, depending on the direction 156 or 157 of flow through sensor assembly 150, which is monitored or controlled by ECM 160, the one of elements 170 (Qi) or 171 (Q ₂ ) that is then upstream of sensor 153 is controlled to raise the temperature of the mixture of gases flowing past the sensor element of sensor 153 to a temperature which is above the dew point of that mixture, such that the mixture is free of moisture in proximity to that sensor element as the exhaust gas/air mixture flows through sample conduit 155. Since moisture may affect the operation of sensor 153, more particularly affecting the accuracy of its readings, it is preferable to remove moisture in the exhaust gas/air mixture to reduce or eliminate the source of any inaccuracies in the measurements made by UEGO sensor 153 during its operation. ECM 160 controls operation of resistive heating elements 170, 171 through data signal lines 167, 168, respectively.

[0074] As an alternative approach for locally heating the gasses above their dew point, FIGURE 1 also symbolically illustrates a third heating mechanism "Cb" which is adapted to deliver heat into the flow 156 or 157 of gasses through thermally conductive walls of the passage 153a immediately surrounding the sensor 153, as is represented by a dashed circle in FIGURE 1. Such a third heating mechanism 172 (Ch) may be used either in addition or as an alternative to heating elements 170 (Qi) or

171 (Q2). As a particular example, FIGURES 2A and 2B include a third heating mechanism Q3 by circulating hot engine coolant 272 through conduit 273 (or through jackets or the like) bored through the aluminum block which defines sensor passage 153.

[0075] Regardless of the type of heating elements 170 (Qi), 171 (Q2) and/or

172 (Q3), the heat delivered by such elements is preferably controlled based on feedback signals, at least in part. The feedback signals are provided resulting from temperature measurements received by ECM 160 from temperature sensor 158. It will be understood that a temperature sensor and one or more resistive heating elements, such as those illustrated in FIGURE 1 , may be incorporated in any alternative embodiments of the disclosed system whether or not such features are illustrated or described herein with reference to such alternative embodiments.

[0076] In addition or as an alternative, the engine 100 may also utilize a recirculated exhaust gas sample tap in fluid communication with an alternative location along the fluid passage 133. For instance, in slight contrast to the configuration of FIGURE 1 , alternative configurations for engine 100's use of an alternative location of the sample tap 151 , in a location that can still be used to directly infer the oxygen concentration or oxygen molecules within the intake manifold 135 of the engine 100 but without the presence of fuel molecules.

[0077] Sample Conduit Details. Turning now to FIGURE 2A, there is shown a detailed section view of the oxygen sensor assembly 150 in one of two operating regimes - particularly, in its boosted operation. In the boosted operating regime shown in FIGURE 2A, the turbocharger is engaged and generating manifold absolute pressure (MAP) that is higher than the barometric pressure (BP) existing in the fresh air intake 101. Under these conditions, the recirculated exhaust gas/air mixture passes through the sample conduit 155 from the recirculated exhaust gas sample tap 151 to the fresh air intake 101 in the direction indicated by direction arrow 156. The flow orifice assembly 154 is preferably located in the sample conduit 155 at a location fluidly between the intake manifold port 129 and the UEGO sensor 153, although alternative embodiments may integrate the orifice assembly 154 with port 151 such that the orifice assembly 154 and the port 151 are one and the same. As shown in FIGURE 2A the UEGO 153 is positioned in a mounting manifold 153a which contains an opening 153b into which the UEGO 153 is inserted.

[0078] Oxygen sensor assembly 150 preferably incorporates temperature sensor 158, which is configured to measure the temperature of the exhaust gas/air mixture flowing through sample conduit 155. Temperature sensor 158 is preferably located adjacent or within proximity to UEGO sensor 153. Also shown in FIGURE 2A are resistive heating elements 170, 171. These are preferably glow plugs having a body portion 170a, 171 a, respectively, inserted into sample conduit 155. Under control of ECM 160, and based at least in part on an output signal received by ECM 160 from temperature sensor 158, such output signal representing the temperature of the exhaust gas/air mixture in sample conduit 155, resistive heating elements 170, 171 are actuated to heat the exhaust gas/air mixture in order to remove excess moisture which may affect the accuracy of UEGO sensor 153.

[0079] In some preferred embodiments, as shown in FIGURES 2A and 2B, there is a fluid conduit 273, a portion of which is mounted in the engine block. During operation of the engine, heated engine coolant flows through fluid conduit 273, such that this heat is conducted from fluid conduit 273 through the engine block and into sample conduit 155 to assist the heating of the exhaust gas/air mixture in sample conduit 155. This serves as a complementary heating mechanism to resistive heating elements 170, 171 for heating the exhaust gas/air mixture flowing through sample conduit 155. As shown by the partial phantom line depiction of a portion of fluid conduit 273 in FIGURES 2A and 2B, no part of fluid conduit 273 is intended to enter sample conduit 155 but passes through a portion of the engine block adjacent or in proximity to sample conduit 155. Although fluid conduit 273 is shown as a simple straight tube, it will be understood by those of skill in the art that other configurations and shapes of fluid conduit 273 may be incorporated which can perform in the same or similar manner and achieve the same or similar results as the embodiment illustrated in FIGURES 2A and 2B. [0080] Irrespective of which of these configurations is used, the flow orifice located in plate 154a, mounted between flanges 154b and 154c preferably has a tiny diameter (on the order of one or two millimeters, or smaller, subject to managing the risks of clogging the orifice in plate 154a if it is too small). The tiny size of the orifice in plate 154a serves to dramatically, if not completely, reduce the pressure of sampled gases 156 to be approximately if not exactly the same as the pressure of the fresh inlet air 101 at the opposite end 152 of the sample conduit 155. Hence, with the pressure at the UEGO sensor 153 the same as the flow 101 that is used as a baseline re-zeroing for UEGO 153, any effects that pressure may have on the accuracy of the UEGO 153 are eliminated, to ensure accuracy of the UEGO 153. Accordingly, accurate measurement is achieved by mounting the UEGO sensor 153 at low pressure yet within direct contact with the recirculated exhaust gas/air/fuel mix in the intake manifold.

[0081] Due to such functionality of the flow orifice assembly 154 in reducing the pressure of sampled intake manifold gases, increased measurement accuracy can be expected during pressure pulsations in the intake manifold due to engine operation and/or exhaust flow from the EGR system 140. This operative configuration of the recirculated exhaust gas oxygen concentration measurement subsystem 150 - most notably, by isolating the UEGO sensor 153 in a sample conduit 155 location that is shielded from fluctuating pressures and pressures that are considerably higher than ambient pressures - results in oxygen concentration measurements that are reliably highly accurate despite using a conventional UEGO sensor 153 (or an alternative conventional EGO sensor). The recirculated exhaust gas/air mixture 156 flowing across the UEGO sensor 153 in boosted engine operation can then be measured for oxygen concentration. Additionally, in certain alternate embodiments, one such embodiment illustrated in FIGURE 7, the exhaust gas measurements taken by the DPFE sensor 725 may be used as a comparative measurement value during boosted engine operation.

[0082] In the boosted engine operating regime, the pressure within the intake manifold can be anywhere from 3-45 psi absolute. As is known by those skilled in the art, the UEGO sensor 153 measures the partial pressure of oxygen present in the sample. As MAP increases, possibly during heavy power loads, or as pressure fluctuations occur in the exhaust flow, signals from an oxygen sensor may be used in a more commonly configured. EGR . system wherein-the oxygen .sensor is located ator _* near the exhaust system rather than the configuration described herein. Since the accuracy of the UEGO sensor 153 can be affected by these increased pressure conditions or pressure fluctuations during operation, the operative configuration of the oxygen concentration measurement assembly 150, as discussed above, should counter most effects due to the increased MAP or pressure fluctuations that may occur and which could result in inaccurate measurements by the UEGO sensor 1 53 if there were no corrective measures taken to respond to increased pressure or fluctuations thereof.

[0083] The reduced pressure environment in which the UEGO sensor 153 operates allows for more accurate measurements of oxygen concentration by the UEGO sensor 153, which in turn will produce a much more reliably accurate and efficient EGR system for reducing harmful emissions. As an additional benefit resulting from the preferred configuration of oxygen concentration measurement subsystem 150 as described, much more accurate flow measurements of recirculated exhaust gas will result. As a consequence, the more accurate the flow measurements of the flow of recirculated exhaust gas are, the higher the power density at which the NGIC engine can operate. Discrepancies or errors in the flow measurements of recirculated exhaust gas could lead to a de-rating of the NGIC engine which can lead to a reduction in horsepower. One of the objects of the preferred embodiment of the present invention is to avoid such loss in horsepower while operating a reliably efficient and highly accurate recirculated exhaust gas flow measurement system, which will help reduce the release of harmful emissions such as NO _x into the atmosphere during the operation of the NGIC engine.

[0084] Turning now to FIGURE 2B, there is shown a detailed section view of the recirculated exhaust gas oxygen concentration measurement subsystem 150 in the second of the two operating regimes - non-boosted operation. In the non-boosted operating regime, the turbocharger is not engaged, and the intake strokes of the cylinders of the internal combustion engine are drawing in intake charge gas, which generates a vacuum in the intake manifold 135 as well as in the compressed air conduit near the intake manifold 135. A portion of the compressed air conduit 133 that is subject to the vacuum includes the EGR sample tap 151 .

[0085] In this non-boosted operating regime, MAP is lower in value than BP, which results in a flow of fresh intake air through the sample conduit 155 in a direction 157 counter to the recirculated exhaust gas/air mixture flow in the boosted operating regime, represented in FIGURE 2B by directional arrow 157. This fresh airflow across the UEGO sensor 1 53 in the non-boosted operating regime can then itself be measured for oxygen concentration. This measurement result is then compared with the oxygen concentration of the recirculated exhaust gas/air mixture, and the two measurements can be used by the ECM to calculate the current mass concentration of recirculated exhaust gas in the intake air charge. This counter-flow of fresh air intake 101 , without recirculated exhaust gas, re-zeros the UEGO sensor 153 by measuring the oxygen content of only fresh air intake 101. Signal drifts with the UEGO sensor 153 may occur during operation, and the measurement of oxygen in fresh air intake 101 corrects for these signal drifts. By knowing the amount of oxygen in fresh air intake 101 during the non-boosted operating regime, once recirculated exhaust gas is mixed with fresh intake air 101 in the intake air charge during boosted operation, the UEGO sensor 153 is able to provide a more accurate measurement of oxygen concentration which results in more accurate calculations by the ECM 160 of the mass flow oxygen concentration of the recirculated exhaust gas. As an alternative or supplemental determination for use in other embodiments, for example the embodiment illustrated in FIGURE 7, the DPFE sensor 725 measurement may be used for determining the flow of exhaust gas during non-boosted operation.

[0086] Real-time re-zeroing of the UEGO sensor 153 may preferably reduce sensor errors in addition to reducing the incidence of sensor errors that might occur in systems that are unable to calibrate to environmental conditions. In contrast to the preferred embodiments of the present invention as described, some systems that only measure the flow of recirculated exhaust gas at some location within the EGR loop itself do not likely have the functionality and/or configuration which allows for re- zeroing the associated sensors within the EGR loop during operation. In some EGR systems, there is no mechanism or configuration for passing fresh air without exhaust gases across an associated oxygen sensor(s) to achieve a similar method of calibration such as that described above with regard to the present invention. Such EGR systems likely must compensate for temperature and pressure variations in order to measure the flow of recirculated exhaust gas. Less accurate flow measurements of recirculated exhaust gas, or even estimations of the flow of recirculated exhaust gas, in some other EGR systems require greater margins of error when pushing the limits for low emissions despite high and varied power demands, which in all likelihood leads .-to less efficienc in engine performance, lower fuel economy, and/or may possibly lead to engine damage due to knock or misfires as a result of such less accurate measurements of the flow of recirculated exhaust gas.

[0087] In turbocharged NGIC engines having EGR enhancements, there is a general desire to maximize the percentage of EGR gases in the combustion chamber. Higher EGR percentages generally minimize NO _x emissions while maximizing fuel economy and operation of an NGIC engine. However, with known prior art approaches, relatively inaccurate measurement and/or estimation of recirculated exhaust gas results in greater margins of error, which consequently requires the ECM to maintain a greater margin of error on targeted EGR percentages.

[0088] Maintaining a safe margin of error is especially important because maximizing EGR also increases the risk of misfire, particularly with stoichiometric natural gas combustion. Applicant has found that pushing even slightly past a particular EGR percentage for particular conditions in any particular NGIC engine (for reference, the engine's "misfire breakpoint EGR percentage") will dramatically increase the likelihood of misfire. As a result of such challenges, operating with a comfortable margin of safety has long been standard fare and accepted as a necessary compromise in NGIC EGR systems. Typical NGIC engines therefore compromise optimal fuel economy, emissions control, and engine efficiency in order to avoid misfire and the like.

[0089] Despite the accepted norms in the design of NGIC engines, Applicant has found that reducing the necessary safety margin dramatically increases the amount of EGR that can be achieved without risking misfire, at levels that make a dramatic difference in an engine's ability to reliably meet NO _x emission standards. To address the countervailing needs, Applicant has found that highly accurate control of the intake gases - such as is achievable through the teachings of the present invention - is key to enabling the ECM to maximize EGR without exceeding an NGIC engine's breakpoint EGR percentage above which there is a dramatically higher risk of misfire.

[0090] It is thus all the more important for Applicant that the oxygen content and flow of recirculated exhaust gas be accurately determined. With preferred embodiments of the present invention, such accurate determinations are achieved in part by more directly measuring the oxygen content within the recirculated exhaust gas/air mixture - measuring such content as accurately as possible in order to achieve this objective, while doing so with a cost-efficient approach. Also important to the operation , and. function. of.» the. recirculated exhaust, gas , oxygen concentration., measurement assembly 150, and thus important to the operation of the NGIC engine with EGR enhancements, is that the components of the recirculated exhaust gas oxygen concentration measurement assembly, specifically UEGO sensor 153, perform highly accurately across large power ranges.

[0091] It is known to those of skill in the art that highly accurate determinations of the flow rate of recirculated exhaust gas, as well as control of such a flow rate, is desirable in order to prevent damage to an NGIC engine. Misfire can occur in an NGIC engine when the flow rate of recirculated exhaust gas is higher than expected, and knock can occur in an NGIC engine if the flow rate recirculated exhaust gas is lower than expected, both problems which could result from inaccurate measurement and control of the oxygen concentration measurement assembly 150. Thus, highly accurate measurements of the flow of recirculated exhaust gas, as well as oxygen content by the UEGO sensor 153 are significantly important to help reduce or prevent damage to the NGIC engine.

[0092] Turning now to FIGURES 3 and 4, there are shown alternate embodiments

350 and 450 of the EGR sampling and oxygen sensing assemblies 150 and 750 and related interacting components of FIGURES 1 and 7, respectively. As will be understood by those of skill in the art, many aspects of the embodiment shown in FIGURES 3 and 4 are similar or comparable in configuration and function as those shown in FIGURE 1. As will be evident to those of skill in the art, the oxygen concentration sensing assemblies 350 and 450 (a.k.a. EGR sampling systems 350 and 450) and the other unique details and components of FIGURES 3 and 4 may be used together with any of the other subsystems of the embodiments illustrated in FIGURES 1 , 5 and 7, with corresponding benefits and compromises as will be understood.

[0093] Focusing first principally on FIGURE 3, the oxygen sensor assembly 350 is configured somewhat similarly to the configurations of the oxygen sensor assemblies 150 and 750 of FIGURES 1 and 7, respectively, with differences as will be evident. Rather than a single sampling port, however, the sampling port 351 of FIGURE 3 is embodied as an array of multiple ports, namely ports 351 a-351e, which are preferably spaced in parallel orientations along a strut 359 that is configured and positioned to span across the interior width of intake conduit 333. Much as with the sampling ports 151 and 751 of engines 100 and 700, the location for sampling port

351 (i.e., a collective reference for the array of ports 351a-351 e) is in compressed air fluid, passage, 333. The, location of strut 359 -which contains the. ports. 351 a-351e : is, preferably downstream from the recirculated exhaust gas mixer 345 that is supplied with recirculated exhaust gas 307 from the EGR system 340. Also, much as with the engines 100 and 700, the location for the sampling port 351 is preferably upstream from the mixer nozzle 322 supplied by the fuel supply 320. Hence, the compressed fresh air 303 flows away from the turbocharger and, at the EGR mixing nozzle 345, the fresh air 303 is blended with the recirculated exhaust gas 307 under control of the ECM 360. The sample port 351 is then next downstream from the EGR mixer 345 in both FIGURES 3 and 4.

[0094] Similar to other described embodiments, FIGURES 3 and 4 show a pressure sensor 358, which as illustrated, can be incorporated into recirculated exhaust gas sample manifold 353a and being adjacent or in proximity to UEGO sensor 353. Also shown in FIGURES 3 and 4 are resistive heating elements 370, 371 which are intended to perform the same functions as the other resistive heating elements described in the context of other embodiments, namely to heat exhaust gas/air mixture flowing through sample conduit 355 in order to control condensation from the exhaust gas and/or air. Such condensation control is intended to improve the accuracy of measurements of oxygen concentrations made by UEGO sensor 353. Similarly to the other described heating elements, resistive heating elements 370, 371 are preferably glow plugs having at least a portion of the body of each extending into sample conduit 355. As illustrated, at least a portion of the body of resistive heating elements 370, 371 may preferably be coaxial with the flow of the exhaust gas/air mixture in a segment of sample conduit 355. 373

[0095] However, rather than the simple open port approach of the sample port 151 (of FIGURE 1 ), the sample tap 351 in both FIGURES 3 and 4 is provided by a series of unrestricted openings 351 a-e that are oriented to face directly into the flow 303 from the turbocharger compressor 310. Preferably, the sampling ports 351 a-e are located in the flow of the recirculated exhaust gas/air mixture 304, at a location positioned downstream of recirculated exhaust gas mixer 345 and upstream of the fuel supply 320. The series of ports 351a-e are preferably aligned along the length of a straight piece 359 of conduit that spans transversely across the interior diameter of the compressed air fluid passage 333, with the ports 351 a-e machined into an upstream sidewall of the conduit piece 359. Each of the upstream facing ports 351 a-e are preferably circular, or alternatively elliptical or elongated ovoid-shaped, bores that are severa millimeters in diameter, in order to ensure free entry of fluid flow 303. therein. <>■ Recirculated exhaust gas 306 is introduced into the compressed air fluid passage 333 (which becomes an open extension of the intake manifold), which is in open fluid communication with the entirety of the intake manifold. The introduction of the recirculated exhaust gas 306 is preferably enhanced by a mixer 345 at which the recirculated exhaust gases 306 are mixed with the fresh air 303 downstream of the turbocharger compressor (not shown in FIGURE 3 or 4). Sample tap 351 , a conduit with ports open to the flow of the recirculated exhaust gas/air mixture, is positioned downstream of the recirculated exhaust gas mixer 345 and upstream of the fuel supply 320. With sufficient pressure due to the flow 304 of the recirculated exhaust gas/air mixture, a portion of this recirculated exhaust gas/air mixture enters the oxygen sensor assembly 350 via sample tap 351.

[0096] Because the strut 359 spans transversely across the fluid flow 304, the flow into each port 351 a-e has a stagnation point (or the like) within the conduit piece 359. The orientation of the conduit piece 359 and its open sampling ports 351 a-e therefore tends to slightly increase the pressure within the conduit piece 359, which in turn helps ensure a pressure gradient to bias flow of the blended gases in the conduit piece 359 through the oxygen sensing assembly 350, in the direction of arrow 356.

[0097] Also in contrast to the configurations of oxygen sensing assemblies 150 and 750 of FIGURES 1 and 7, respectively, although the sampling ports 351 a-e are in much the same location in compressed air fluid line 333, the opposite end 352 of the sampling conduit 355 is in an entirely different location than the reference ports 152 and 752 of FIGURES 1 and 7. Particularly, the opposite end 352 (a.k.a. the "reference end" 352) of the sampling conduit 355 is uniquely downstream sampling ports 351a-e - most preferably oriented to open toward what is predominantly the downstream direction in the normal operation of engine 300. The reference end 352 is also preferably positioned in the center of the fluid passage 333. More particularly, the reference end 352 is also preferably positioned in the center of the throat 322a of the fuel mixing nozzle 322, which tends to be at considerably lower pressure than the sampling ports 351a-e, thereby further ensuring a pressure gradient to bias the flow of the blended gases in the conduit piece 359 through the oxygen sensing assembly 350 and toward the reference end 352, in the direction of arrow 356. This bias is accomplished despite that both the reference end 352 and the sampling ports 351 a-e are in the same fluid passage 333, without any significant restrictions in the length of the fluid passage 333- between the two ends,351. and -352, [0098] Hence, due to a combination of the upstream facing of the sampling ports 351 a-e and the downstream facing reference end 352, and its position in a low- pressure throat 322, the operative flow of sampled fluids 356 is assured through the oxygen sensing assembly 350 whenever flow within the compressed air fluid passage 333 is as shown in FIGURES 3 and 4.

[0099] With sufficient pressure due to the flow of the recirculated exhaust gas/air mixture, a portion of this recirculated exhaust gas/air mixture enters the oxygen sensor assembly 350 via an opening in the sample manifold 353a. The oxygen sensor assembly 350 also includes a UEGO sensor 353, which is preferably mounted in recirculated exhaust gas sample manifold 353a in combination with the flow orifice device 354 which restricts the flow of the recirculated exhaust gas/air mixture 356 to volumes sufficiently controlled to allow for highly accurate measurements by the UEGO sensor 353.

[00100] Due to the nature of conventional UEGO sensors, the pumping cell current of such a UEGO sensor 353 has been found to be susceptible to considerable variability depending on the pressure of its operating conditions. In a vacuum, as may naturally occur during closed-throttle operation of engine 300, the output signal of the UEGO sensor 353 is substantially linear in relation to oxygen concentration flowing past the UEGO sensor 353. As an example, at 14.7 psi (atmospheric pressure), the pumping cell current may be 2.5 mA. For the same sample at a different pressure, for example at 7.0 psi absolute, the pumping cell current might read approximately 1 .25 mA - half the value that would be seen in a vacuum. Since the UEGO sensor 353 is actually measuring the partial pressure of oxygen in the measuring sample, the pressure sensor 358 is preferably located adjacent to or nearby the UEGO sensor 353 to send a signal 366 to ECM 360 to make correction as necessary for any pressure effects that may affect the outputs of the UEGO sensor 353. Pressure sensor 358 preferably has temperature sensing capabilities in addition to measuring the pressure within sample conduit 355.

[00101] Similar to other described embodiments, FIGURE 3 shows the intake manifold oxygen sensor assembly 350 with a sampling port 351 positioned downstream of the EGR mixing nozzle 345 in the turbocharged supply conduit for intake manifold 335. Such a relative location allows the port 351 to sample the mixture of fresh air 303 and recirculated exhaust gas 307, preferably upstream of the fuel introduction , point, 322, However, unlike most of the other described, embodiments,. FIGURE 3 shows the intake manifold oxygen sensor assembly 350 with the sample conduit 355 terminating downstream of the sampling port 351 , While such a downstream location eliminates the benefit of ensuring that the gas pressure in UEGO manifold 353a is at atmospheric pressure, comparable low pressure is assured by locating the outlet 352 in the throat 322a of fuel mixing nozzle 322.

[00102] Similar to other described embodiments, FIGURE 4 shows the intake manifold oxygen sensor assembly 450 with an alternate outlet for sample conduit 355 terminating in the fresh air source 301 , at a location downstream of an air filter (not shown) and upstream of compressor 311.

[00103] In the alternate embodiment illustrated in FIGURE 4, there is included as a component of the oxygen sensor assembly 450 a three-way solenoid or valve 480 at the terminal end of the sample manifold 353a where the mixture of air and recirculated exhaust gas would exit the sample manifold 353a. Actuation of the three- way valve 480 is controlled by the signal 462 from ECM 360. In this configuration, the three-way valve 480 controls the direction of flow of the recirculated exhaust gas/air mixture after the sample mixture is measured by the UEGO sensor 353. Three-way valve 480 has a common port which may be connected to a conduit to route and reintroduce the recirculated exhaust gas/air mixture at a point downstream of an air filter and upstream of compressor 311. However, the common port of three-way valve 480 can connect to a second fluid conduit which then routes the recirculated exhaust/air mixture to be reintroduced where the fuel supply 320 enters the intake.

[00104] In addition to the UEGO sensor 353, pressure sensor 358 may also be mounted in the recirculated exhaust gas sample manifold 353a to measure the pressure within recirculated exhaust gas sample manifold 355. The ECM 360 receives a signal input 365 from the UEGO sensor 353 and a signal input 366 from the pressure sensor 358 and sends a signal output 462 for control and selective actuation of the three-way valve 480.

[00105] When MAP is lower than BP (or atmospheric barometric pressure), for example when MAP is between three and fourteen psi absolute, ECM 360 controls the three-way valve 480 preferably so that it is periodically connected to the fresh air source 101 via the common port of the three-way valve 480. Such connection allows flow of fresh intake air across the UEGO sensor 353 in order to achieve a baseline measurement of oxygen concentration, as indicated in FIGURE 4 by flow arrow 457a. The common port of .the, three-way valve 480 may then,, under tha control, -oktfoe.EC , 360, connect with the EGR sample conduit 355 such that the flow now includes recirculated exhaust gases as well as intake air, with this mixture flowing in the direction indicated by flow arrow 461. This flow regime allows for measurement of oxygen by the UEGO sensor 353 in the recirculated exhaust gas/air mixture. This flow terminates at the reference end 352 of the sample conduit 355 wherein the recirculated exhaust gas/air mixture is mixed with the fuel source 320 prior to combustion.

[00106] As is known by those of skill in the art, it is not uncommon, when operating conditions exist wherein MAP is lower than atmospheric pressure, such as in a non-boosted regime, no exhaust gases are being recirculated due to lower engine flow. In such a regime, the common port of three-way valve 480 may be continuously connected to the fresh air source 101 which, as previously described, will provide a baseline measurement of oxygen concentration which in turn should result in more highly accurate measurements by the UEGO sensor 353. Although pressures within the EGR sample tap 351 or the conduit piece 359 may be higher than the pressure within the fluid conduit 333 or at the location wherein the fresh air 303 mixes with the recirculated exhaust gas, such pressure differential should not adversely affect the ability to garner a baseline measurement of oxygen concentration in the fresh air 303 by the UEGO sensor 353 when the fresh air 303 flows from the fresh air source 101 in the direction of flow arrow 457a.

[00107] In operating conditions, for example in a boosted regime, when MAP is greater than atmospheric pressure (or a positive gage pressure), there is the potential for exposing the UEGO sensor 353 to pressures which could affect the accuracy of its measurements. To reduce or eliminate such pressure effects, the flow of fresh air 357b to the calibrated flow restriction orifice device 354 is designed and configured to regulate the flow of the recirculated exhaust gas/air mixture, which in turn lowers the pressure under which the UEGO sensor 353 operates. Thus, sizing the calibrated flow restriction orifice device 354 is vitally important in order to maintain the efficiency of operation of the engine 300. If the calibrated flow restriction orifice device 354 is sized too small, the result will be a low flow of recirculated exhaust gas/air mixture across the UEGO sensor 353. Consequently, the UEGO sensor 353 will respond more slowly which can affect the overall performance of the engine 300. Preferably, the size of the calibrated flow restriction orifice device 354 is fixed and being as large as possible for fast sample measurement but also as small as possible to alleviate any problems that may occur due to pressure rise _^ or _f ressure iuctuation&«as well -as for. passage of fresh air to produce a baseline measurement by the UEGO sensor 353. By way of example and in no way intended to limit the scope of the present invention, when MAP is low, such as in engine idle conditions, the calibrated flow restriction orifice device 354 may be sized such that, if the common port of the three-way valve 480 is continuously connected to the fresh air source 101 , the air flow across the calibrated flow restriction orifice device 354 would be less than 5% of the total engine flow.

[00108] Also shown in FIGURES 3 and 4 is a motor designated as "M." As described above with respect to other embodiments, a counter-flow of ambient air through sample conduit 355, without exhaust gas, re-zeros UEGO sensor 353 by measuring the oxygen content of only the ambient air. In some embodiments, motor M may be mechanically connected to conduit piece 359. Because a pressure gradient due to the flow 304 of the recirculated exhaust gas/air mixture typically exists at ports 351a-e of sample tap 351 , a counter-flow would likely not be possible during operation of engine 300. In order to achieve such counter-flow of ambient air without exhaust gas, motor M may be configured to turn sample tap 351 and/or conduit piece 359 such that ports 351 a-e are turned away from flow 304. In other words, ports 351 a-e would then be facing in a downstream direction, which would be expected to reduce or eliminate the pressure gradient that exists during operation of engine 300. Reduction or removal of the pressure gradient can then allow a counter-flow of ambient air, as indicated by arrow 357b, which may then pass across UEGO sensor 353 for the purpose of real-time re-zeroing of UEGO sensor 353 by measuring the oxygen content of only ambient air without exhaust gas. In other embodiments, motor M may serve to operate a valve, rather than turning sample tap 351 , for achieving a similar pressure reduction or pressure elimination as described above.

[00109] Turning now to FIGURE 5, there is shown an alternate embodiment 550 of the EGR sampling and oxygen sensing assembly and related interacting components. The oxygen sensor assembly 550 is generally configured similarly to the configurations of the oxygen sensor assemblies 150, 350, 450 and 750 of FIGS. 1 , 3, 4 and 7, respectively, with the differences being evident as detailed in this description. Comparable to the assemblies previously illustrated and described, a mixture of exhaust gas and air is sampled from the main flow passing through compressed air fluid passage 533. However, in contrast to other described embodiments, oxygen sensor . assembly 550 does not use a separate sample conduit, but instead, directly samples the exhaust gas/air mixture in the main flow of compressed air fluid passage 533.

[00110] As is shown in FIGURE 5, UEGO sensor 553 is preferably located downstream of the recirculated exhaust gas mixer 545 and upstream of fuel supply 520. UEGO sensor 553 is shown directly mounted at a point along compressed air fluid passage 533 such that at least of portion of the body of UEGO sensor 553 is positioned in the main flow of the exhaust gas/air mixture. The portion of UEGO sensor 553 that extends into compressed air fluid passage 533 is substantially enclosed or enshrouded by a tube 580. Tube 580 is preferably a perforated cylindrical structure, having one or more ports (shown in more detail in FIGURES 6A AND 6B as ports 651a-651f) penetrating through the leading edge of tube 580, the ports 651 a- 651f being generally positioned on the upstream side of tube 580. This placement of ports 651 a-651f on tube 580 allows a sample of the exhaust gas/air mixture within the main flow stream to flow through tube 580 and to come into contact with the sensing portion of UEGO sensor 553 for the purpose of measuring the oxygen concentration of the exhaust gas/air sample mixture. Tube 580 is also shown having a single port 651 g positioned on the downstream side of tube 580 such that a sample of the exhaust gas/air mixture is able to exit tube 580. In some respects, it may be said that the ports 651a-651f on the upstream side of tube 580 perform a similar function as flow orifice 154, 354, 754 and 354, as described with respect to the other embodiments. More particularly, the flow of the exhaust gas/air mixture is regulated as it passes through the ports 651 a-651f of tube 580 and through tube 580 in the direction indicated by the arrows shown in FIGURES 6A and 6B and across UEGO sensor 553.

[00111] As shown in more detail in FIGURES 6A and 6B, tube 580 preferably has at least two layers of material, outer layer 681 on its outer surface and inner layer 682 on its inner surface. The material making up the outer layer 681 of tube 680 is preferably a thermally insulative material such as ceramic or plastic. The inner layer 682 of tube 580 is preferably a material which has the ability to efficiently conduct heat such as copper, aluminum, or another efficient heat-conductive metal. Lining the inner layer 682 of tube 580 with heat-conductive material is preferred because inside tube 580 is at least one heating element 570 which effectively heats the interior of tube 580 around, and preferably in close proximity to, UEGO sensor 553. Therefore, as the sample of the exhaust gas/air mixture from the main flow stream passes through ports 651a-651f of tube 580, the sample is heated before or simultaneously as it passes along the sensing portion of UEGO sensor 553.

[00112] FIGURE 6B illustrates an alternate embodiment to the embodiment shown in FIGURE 6A. More particularly, there are shown two sleeves/jackets 683a, 683b positioned between inner layer 682 and the interior space of tube 580, and containing fluid jackets 684a, 684b, respectively. During operation of engine 500, heated liquid such as heated coolant is piped to circulate through fluid jackets 684a, 684b. The flow of heated liquid through fluid jackets 684a, 684b is intended to result in heating the inner space of, and thus the exhaust gas/air mixture flowing through, tube 580. This serves as a complementary heating mechanism to resistive heating element 570 for heating the exhaust gas/air mixture flowing through tube 580. Although fluid jackets 684a, 684b are shown as a simple straight tube-shaped structures, it will be understood by those of skill in the art that other configurations and shapes of fluid jackets 684a, 684b may be incorporated which can perform in the same or similar manner and achieve the same or similar results as the embodiment illustrated in FIGURE 6B.

[00113] Turning back to the alternate embodiment illustrated in FIGURE 5, oxygen sensor assembly 550 is also shown to include pressure sensor 534 and temperature sensor 558, both of which are preferably positioned adjacent or in proximity to UEGO sensor 553. UEGO sensor 553, temperature sensor 558, and pressure sensor 534 send output signals to ECM 560 via signal outputs 565, 566, and 564, respectively. Heating element 570 operates, under the control of ECM 560, to heat the interior of tube 580, as determined by feedback received by ECM 560 from the output signal of temperature sensor 558.

[00114] During operation of the EGR subsystem 540, exhaust gas is recirculated into compressed air fluid passage 533 by operation of EGR valve 542 as determined and controlled by ECM 560 through signal 562. In some embodiments, EGR valve 542 is located upstream of EGR mixer 545. Insertion of exhaust gas occurs in compressed air fluid passage 533, wherein the exhaust gas is mixed with ambient air flow 503. This exhaust gas/air mixture 504 then flows through compressed air fluid passage 563 toward fuel introduction point 522 and the intake manifold.

[00115] Fuel supply 520 is controlled by a signal 563 from ECM 560. In preferred embodiments, the mass flow-controlled fuel supply 520 utilizes a continuous-flow valve (CFV) that is also controlled by a signal 563 from ECM 560, as previously described with other embodiments of the disclosed system.

[00116] With reference to the more detailed description of the embodiment shown in FIGURE 7, there is shown a representation of the exhaust gas recirculation (EGR) system 740 for a turbocharged, gaseous-fuel internal combustion engine 700 (e.g., a natural gas engine) configured to operate in a stoichiometric combustion strategy. As seen therein, the turbocharged spark-ignited engine 700 includes an intake manifold 735, an exhaust manifold 731a, a turbocharger 710, and an intercooler 707. The turbocharger 710 is preferably a variable geometry turbocharger (VGT), although it may be a fixed geometry turbocharger in alternative embodiments. Turbocharger 710 consists of an exhaust gas driven turbine 712 coupled to an intake air compressor 711. The exhaust gas driven turbine 712 of turbocharger 710 is connected in sealed fluid communication between exhaust manifold 731 and exhaust pipe 799, such that turbine 712 operatively receives exhaust discharged from the combustion chambers 730, and mechanically converts the energy of exhaust into torque for driving the intake air compressor 711. Once the exhaust gas is operatively expanded by turbine 712, turbine 712 then directs the exhaust gas through exhaust pipe 799.

[00117] Exhaust pipe 799 includes an exhaust gas inlet 799a and an exhaust gas outlet 799b, both in fluid communication with the exhaust gas driven turbine 712.

[00118] The air intake compressor 711 turbocharger 710 is connected in fluid communication between a filtered segment 701 b of fresh intake air conduit 701 and a first segment 733a of a compressed air conduit 733. Fresh intake air conduit 701 is a continuous air conduit having an atmospheric end 701 a and a filtered end 701 b, with an air filter 701 c therebetween. Atmospheric end 701 a is preferably adapted and positioned to freely receive fresh atmospheric air 702. Intake air filter 701 c is a conventional air filter integrated upstream of the filtered air segment 701 b, such that the same filtered fresh air is in open communication with both the air intake compressor 711 as well as with the ambient pressure end 752 of sample conduit 755.

[00119] In this preferred embodiment, the EGR system includes a liquid-to-gas exhaust gas cooler 723 which is supplied with exhaust gas from the exhaust manifold 731a through an exhaust gas pre-cooler conduit 741 a. The cooled exhaust gas is communicated to the compressed fresh air conduit 733 through a cooled exhaust gas conduit 741 at a rate that is controlled with an EGR valve, 742 by, the ECM 760. From, EGR valve 742, a controlled amount of recirculated exhaust gas is introduced into the fresh air conduit 733 by means of a gas flow mixer 745. Although mixer 745 is illustrated at the same location as EGR valve 742, it should be understood that EGR valve 742 controls the amount of recirculated exhaust gas flowing from EGR line 741 , before that EGR flow 707 is mixed with fresh intake air 703 in turbocharger- compressed air conduit 733.

[00120] Temperature and pressure signals 733a and 733b, representative of the temperature and pressure of the flow of recirculated exhaust gas are measured upstream of the EGR valve 742 are communicated to the Engine Control Module (ECM) 760 for use in engine control calculations. The ECM 760 also controls operation of the EGR valve 742. Alternative embodiments may include a recirculated exhaust gas mixer (not shown), which might also serve as a recirculated exhaust gas pump for high-load conditions. Such recirculated exhaust gas mixer preferably would be located downstream of the EGR valve 742 where recirculated exhaust gases are mixed with intake air 702 prior to combustion. To maximize efficiency and fuel economy in turbocharged engines, the recirculated exhaust gas is preferably removed upstream of the turbocharger's exhaust-driven turbine and is then re-introduced downstream of the turbocharger's compressor and the primary intercooler. By keeping the temperature of combustion less than 1300 Kelvin, NO _x byproducts are kept to a minimum, thereby reducing pollutant levels that would otherwise contribute to smog and acid rain.

[00121] The oxygen sensor assembly 750 preferably includes a conventional UEGO sensor 753 for controlling an NGIC engine 700 and its EGR system 740 to achieve low exhaust emissions despite elevated and varied power demands, which illustration provides a more detailed understanding of an embodiment in comparison to the more general schematic diagrams of FIGURES 1 , 3, 4 and 5.

[00122] The embodiment shown in FIGURE 7 also includes a Differential Pressure Feedback (DPFE) sensor 725 which measures the pressure differential across a flow restriction device 726. The DPFE signal is communicated via communication line 736 to the ECM 760, which uses the information in the signal from line 736 in calculating the mass flow rate of recirculated exhaust gas. Alternative embodiments may include configurations without the DPFE sensor 725 or the flow restriction 726.

[00123] In FIGURE 7, the intake air flow is communicated from the compressor 711 to. the. intake manifold 735 through the compressed, air conduit 733. The intake air 702 is cooled via an intercooler 707, which may be either gas- or liquid-cooled. Airflow is metered for stoichiometric combustion using a throttle 713 which is located upstream of the EGR valve 742. Alternative embodiments may eliminate throttle 713, such as in lean burn natural gas or lean burn diesel applications. Gaseous fuel 720 is inserted into the recirculated exhaust gas/air charge by a fuel insertion manifold 722 located downstream of the EGR valve 742 with the functioning of the EGR valve 742 being controlled, at least in part, by a signal(s) from the ECM 760. Throttle inlet pressure (TIP) is measured via a pressure sensor 746 located at the inlet to the throttle 713, while manifold absolute pressure (MAP) and intake air temperature (I AT) are measured using the signal from a MAP sensor 734a and the signal from an IAT sensor 734b, respectively, both of which are located downstream of the fuel insertion manifold 722 and upstream of intake manifold 735. TIP, MAP and IAT signals are communicated to the ECM 760 for engine control calculations.

[00124] The preferred embodiment shown in FIGURE 7 contains a recirculated exhaust gas sample tap 751 disposed in the compressed air conduit 733 between the EGR valve 742 and the gaseous fuel insertion manifold 722. A mass-flow-controlled fuel supply 720 preferably supplies a gaseous fuel supply to the gaseous fuel insertion manifold 722. Most preferably, such a fuel supply 720 is of a type utilizing a continuous-flow valve (CFV), such as described in the co-owned pending U.S. Patent Application entitled "Highly Accurate Continuous-Flow Vaporized Fuel Supply for Large Dynamic Power Ranges," Serial No. 13/918,882, the disclosure of which is incorporated herein by this reference.

[00125] The recirculated exhaust gas sample tap 751 is in fluid communication with the fresh intake air conduit 701 via the sample conduit 755. Disposed in the sample conduit 755 is the recirculated exhaust gas oxygen concentration measurement assembly 750, which consists of a recirculated exhaust gas sample manifold 753a, a UEGO sensor 753 and a flow orifice 754. Although FIGURE 7 illustrates that the UEGO sensor 753 and the flow orifice 754 are upstream of the fuel supply 720, alternate embodiments may include configurations wherein the UEGO sensor 753 and the flow orifice 754 are operatively mounted downstream of the fuel supply 720 as shown in FIGURE 1. The flow orifice 754 is preferably fixed to set the flow rate of recirculated exhaust gas into the recirculated exhaust gas sample manifold 753a such that any pressure effects are minimized in order to increase the measurement accuracy of- the UEGO. sensor 753. [00126] Additional features of the illustrated embodiment of the EGR system in FIGURE 7 include an intake air filter/cleaner 701 c and an exhaust after-treatment subsystem 799c. As is conventional, ECM 760 also preferably receives and uses data from a barometric pressure (BP) sensor and an ambient air temperature (AAT) sensor that are included in a conventional configuration associated with engine 700. For illustration, the BP sensor signal is received by ECM 760 via electronic communication line 732 and the (AAT) sensor signal is received by ECM 760 via electronic communication line 729. It should be understood that ECM 760 also preferably receives data from speedometers, RPM gauges and other performance sensors, depending on the engine application. In addition, it should be understood that ECM 760 preferably receives data and sends command signals to and from mass flow controlled fuel supply 720 as well as to and from user interfaces and operator input devices (not shown).

[00127] Another embodiment is shown in FIGURES 8A-8C which includes some similar features to those of the embodiment illustrated in FIGURE 5. As will be evident to those of skill in the art, the oxygen concentration sensing assembly 850 and other unique details and components of FIGURES 8A-8C may be used together with any of the other subsystems of the embodiments illustrated in FIGURES 1 , 3, 4, 5, 7, and 9A- 9D with corresponding benefits and compromises as will be understood.

[00128] Turning first to FIGURE 8A, a configuration is illustrated wherein UEGO sensor 853 is positioned within the main flow 804 of the exhaust gas/air mixture passing through compressed air fluid passage 833, with UEGO sensor 853 particularly being advantageously positioned within a perforated sample tube 880. Although not shown in FIGURES 8A-8C, UEGO sensor 853 is preferably located downstream of a recirculated exhaust gas mixer and upstream of a fuel supply similarly to those embodiments shown in FIGURES 1 , 3, 4, 5, and 7.

[00129] UEGO sensor 853 is particularly shown to be mounted at a point along compressed air fluid passage 833 such that at least a portion of the body of UEGO sensor 853 is positioned in the main flow 804 of the exhaust gas/air mixture. The portion of UEGO sensor 853 that extends into compressed air fluid passage 833 is substantially enclosed or enshrouded by a sample tube 880. Sample tube 880 is preferably a perforated cylindrical structure, having one or more ports 851 a-851f positioned on the upstream side of sample tube 880 as shown. Sample tube 880 further is shown to have a single port 851 g positioned on the downstream side such that a sample of exhaust gas/air mixture is able to exit sample tube 880. Main flow 804 of the exhaust gas/air mixture flows into sample tube 880 through one or more ports 851a-851f, the flow being directed toward UEGO sensor 853 as shown by the flow arrow in the interior of sample tube 880 in FIGURE 8A. The exhaust gas/air mixture may also exit sample tube 880 through downstream port 851g, also as shown by the flow arrow in FIGURE 8A. Although FIGURE 8A illustrates only a single downstream port 851 g, other embodiments may incorporate more than one downstream port in sample tube 880.

[00130] It should be understood that, in most respects, sample tube 880 performs similarly to tube 580 shown in FIGURE 5. However, unlike tube 580 shown in FIGURE 5, sample tube 880 does not extend across the entire width of compressed air fluid passage 833 but stops just short of reaching the portion of the wall opposite from the position which UEGO sensor 853 enters compressed air fluid passage 833. It should be understood that other embodiments may include a sample tube 880 that does extend across the entire width of compressed air fluid passage 833.

[00131] UEGO sensor 853 is positioned in a housing 891 which in turn passes through a cover 890 that is mounted to compressed air fluid passage 833. Cover 890 is preferably constructed of material which readily conducts heat such as a metal. In preferred embodiments, cover 890 is constructed of aluminum.

[00132] Preferably, there is a condition sensor (not shown) positioned in proximity to UEGO sensor 853. The condition sensor may be disposed in sample tube 880, and is preferably a pressure sensor having temperature sensing capabilities as well. When incorporated as a feature in the disclosed embodiment, the condition sensor may be configured to measure the pressure within sample tube 880, as well as the temperature of the sample portion of the main flow 804 of the exhaust gas/air mixture which enters the interior of sample tube 880. Furthermore, the condition sensor may further be configured to send output signals relating to the pressure and temperature within sample tube 880 to the ECM.

[00133] Notably, the embodiment illustrated in FIGURES 8A-8C does not include a resistive heating element, in contrast to other disclosed embodiments. Rather, to perform the function of heating the exhaust gas/air mixture sample which enters sample tube 880, there is a fluid conduit 873 for carrying heated liquid such as heated engine coolant. For example, during operation of the engine, a portion of heated engine coolan is diverted from ^, the .engine -coolant ..system.- and flows through fluid » conduit 873. The heated engine coolant may be diverted from any convenient location within the engine coolant system. Fluid conduit 873 is preferably located adjacent to and within sufficient proximity to the position which UEGO sensor 853 enters compressed air fluid passage 833 such that the heat is conducted from fluid conduit 873 to sample tube 880 to effectively heat the interior space of sample tube 880 to above the dew point of at least a constituent of the sample of exhaust gas/air mixture which enters sample tube 880.

[00134] With respect to the temperature of the heated engine coolant that is diverted into fluid conduit 873, it is anticipated that the heated engine coolant would have a temperature within the range of typical engine coolant during operation of the engine. Such temperatures may range from about 180°F to about 235°F.

[00135] No part of fluid conduit 873 is intended to enter sample tube 880. Although fluid conduit 873 is shown as a substantially U-shaped passage having an inlet 874, an outlet 875, and a middle section 876 positioned between inlet 874 and outlet 875 that is somewhat curved, it should be understood that other configurations and shapes of fluid conduit 873 may be incorporated which can perform in the same or similar manner and achieve the same or similar results. As illustrated in FIGURE 8C, heated engine coolant, which is diverted from a point along the engine coolant system, enters fluid conduit 873 through inlet 874 as indicated by flow arrow 874a. The heated engine coolant travels through middle section 876 of fluid conduit 873, and exits fluid conduit 873 through outlet 875 as indicated by flow arrow 875a.

[00136] FIGURES 9A-9C illustrate still another variation of the system herein described, this embodiment having similarities in structure and function to those embodiments shown in FIGURES 3 and 4. As will be evident to those of skill in the art, the oxygen concentration sensing assembly 950 and other unique details and components of FIGURES 9A-9C may be used together with any of the other subsystems of the embodiments illustrated in FIGURES 1 , 3, 4, 5, and 7, with corresponding benefits and compromises as will be understood.

[00137] UEGO sensor 953 is positioned in a housing 991 which in turn passes through a cover 990 which is mounted to compressed air fluid passage 933. Cover 990 is preferably constructed of material which readily conducts heat such as a metal. In preferred embodiments, cover 990 is constructed of aluminum.

[00138] Beginning with FIGURE 9A, there is shown an oxygen concentration sensing assembly 950» Although. not shown: in-any of FIGURES 9A-9C _? itis anticipated. that oxygen concentration sensing assembly 950 and the related components shown would be located downstream from an EGR mixer and upstream of a fuel supply. Located within compressed air fluid passage 933 is a sample tap 951. Sample tap 951 is configured and positioned to span across the entire width of compressed air fluid passage 933. Sample tap 951 is shown to contain a number of ports 951a-951 d preferably spaced in parallel orientations on the upstream side of sample tap 951. An exhaust gas/air mixture within flow 904 enters sample tap 951 through one or more ports 951a-951d. Sample tap 951 further is shown to have a single port 951g positioned on the downstream side such that a sample of exhaust gas/air mixture is able to exit sample tap 951. Although not shown in FIGURES 9A-9C, similar to the earlier described embodiments illustrated in FIGURES 1 , 3, 4, 5, and 7, sample tap 951 is preferably located downstream of an EGR mixer such that sample tap 951 is supplied with recirculated exhaust gas from the EGR system. Furthermore, sample tap 951 is preferably located upstream of a mixer supplying fuel from a fuel supply.

[00139] Shown at the top of sample tap 951 is flow orifice 954 which is designed to restrict and thereby regulate the flow of the recirculated exhaust gas/air mixture to volumes sufficiently controlled to allow for highly accurate measurements by UEGO sensor 953. It is anticipated that flow orifice 954 will be of a fixed size and be as large as possible for fast sample measurement but also as small as possible to alleviate any problems that may occur due to pressure rise or pressure fluctuations. However, alternative embodiments may employ a variable flow orifice 954, the size of which may be modulated to suit particular operating conditions.

[00140] As can be seen, particularly in FIGURE 9A, after passing through flow orifice 954, a sample of recirculated exhaust gas/air mixture passes into sample conduit 955 which leads to UEGO sensor 953. UEGO sensor 953 is located in an offset position from the flow orifice 954. Such off-set position would necessarily avoid any spray of condensate onto UEGO sensor 953 that may be within the recirculated exhaust gas/air mixture as it passes through flow orifice 954.

[00141] As shown in FIGURES 9A and 9B, it can be seen that oxygen sensing assembly 950 includes sensor 958. Sensor 958 is disposed in sample conduit 955 through cover 990, preferably in proximity to UEGO sensor 953. Sensor 958 is preferably a pressure sensor having temperature sensing capabilities as well. Accordingly, sensor 958 is configured to measure the pressure within sample conduit 955, as well as the temperature of the. sample portion, of, the . main flow 804. of the _* exhaust gas/air mixture which enters the interior of sample conduit 955. Sensor 958 is further configured to send output signals relating to pressure and temperature within sample conduit 955 to the ECM.

[00142] Notably, the embodiment illustrated in FIGURES 9A-9C does not include a resistive heating element. Rather, to perform the function of heating the exhaust gas/air mixture sample which enters sample tap 951 , there is a fluid conduit 973 (particularly shown in FIGURE 9D) for carrying heated liquid such as heated engine coolant. For example, during operation of the engine, a portion of heated engine coolant is diverted from the engine coolant system and flows through fluid conduit 973. The heated engine coolant may be diverted from any convenient location within the engine coolant system. Fluid conduit 973 is preferably located adjacent to and within sufficient proximity to sample conduit 955 as well as to the position of UEGO sensor 953 within sample conduit 955 such that the heat is conducted from fluid conduit 973 to sample conduit 955 to effectively heat the interior space of sample conduit 955 to above the dew point of at least a constituent of the sample of exhaust gas/air mixture which enters sample conduit 955.

[00143] As shown in FIGURE 9C, fluid conduit 973 is disposed within cover 990, and is positioned in proximity to sample conduit 955, particularly near the position at which UEGO sensor 953 is disposed within sample conduit 955. No part of fluid conduit 873 is intended to enter sample tube 980. Although fluid conduit 973 is shown as a substantially U-shaped passage having an inlet 974, an outlet 975, and a substantially straight middle section 976 positioned between inlet 974 and outlet 975, it should be understood that other configurations and shapes of fluid conduit 873 may be incorporated which can perform in the same or similar manner and achieve the same or similar results. As illustrated in FIGURES 9A and 9C, the heated engine coolant enters fluid conduit 973 through inlet 974 in a direction indicated by flow arrow 974a. Once in fluid conduit 973, the heated engine coolant passes through the middle section 976 in a direction indicted by flow arrow 976a. The heated engine coolant then exits fluid conduit 973 through outlet 975 in a direction indicated by flow arrow 975a.

[00144] Although the embodiments of FIGURES 8A-9C show the fluid conduit 873, 973 in the cover 890, 990, respectively, it should be recognized by those of ordinary skill in the art that the fluid conduit 873, 973 could be plumbed through the walls of the sample tube 880 and the sample tap 951 , respectively, much like the fluid jackets 684a, :684b,- which are, illustrated ,in. FIGURE 6B. Preferably, with. specific reference .,to< FIGURE 9A, this would be accomplished by a sample tube 951 that extends completely across the intake manifold such that the coolant is directed to flow through the walls of the sample tap 951 from one side of the intake manifold to the other. With such a configuration, the fluid conduit 973 through the walls of the sample tap 951 would be connected to a liquid passage as part of a liquid circuit from the other side of the intake manifold to the near side of the intake manifold (i. e. , near the UEGO sensor 953, or vice versa). It should be understood that such liquid circuit would involve o-ring seals on each side of the length of the sample tap 951 . A similar configuration could be utilized with respect to the embodiments illustrated in FIGURES 8A-8C in a like manner as herein described with reference to FIGURE 9A, although some modifications may be made for those embodiments in which sample tube 880 does not extend across the entire width of the compressed air fluid passage 833.

[00145] Other Alternatives. Having described several separate embodiments, one skilled in the art can appreciate that the various features disclosed in one or more of the embodiments might be used in other embodiments and other EGR systems. Although the foregoing disclosure describes the present invention in the context of use with a stoichiometric turbocharged, spark-ignited natural gas engine, it is anticipated that the highly accurate recirculated exhaust gas oxygen concentration measurement s assembly could be employed in a variety of other applications. One such alternative embodiment could be used in a lean burn natural gas system. A lean burn regime, as is known and understood by those of skill in the art, refers to a system in which fuel is burned with an excess of air in the air/fuel mixture resulting in a higher air-to-fuel ratio during operating conditions, possibly as high as 65-to-1 in contrast to a stoichiometric ratio of approximately 14.7-to-1 . Such a regime would include many of the same components as the system previously described in a similar operative configuration. The recirculated exhaust gas oxygen concentration measurement assembly would include, as previously described, a recirculated exhaust gas sample tap being in fluid communication with the fresh intake air conduit via a sample conduit. Along the sample conduit would be a recirculated exhaust gas sample manifold to which a UEGO sensor is plumbed. A flow orifice located along the sample conduit serves to regulate the flow of recirculated exhaust gas through the sample conduit and into the recirculated exhaust gas sample manifold. However, within the lean burn natural gas regime, in contrast to the previously described operating conditions including a stoichiometric natural gas regime, it .-may - e - that -the .- throttle, would- -be >eliminatedv The- recirculated exhaust gas oxygen concentration measurement assembly would still perform the same function in the lean burn natural gas context, providing a highly accurate measurement system for measuring oxygen content in the recirculated exhaust gas /air mixture for significantly more accurate control of the EGR system.

[00146] Another alternative embodiment that would capitalize on some aspects of the present invention is anticipated for use in a lean burn diesel engine application. Similarly to the previously described lean burn natural gas application, a lean burn diesel application would likely have the same or similar components of the described recirculated exhaust gas measurement system with some modifications possibly required for operation within a diesel engine system, as would be recognized and understood by those skilled in the art. Such modifications would likely include elimination of the throttle. Also in a lean burn diesel application, there would not likely be a need for a CFV fuel flow rate control, as described in the pending patent application previously mentioned.

[00147] From the foregoing, it should be appreciated that the present inventions provide for the controlled recirculation of exhaust gas in a turbocharged engine, effectively based on direct or substantially direct measurement of the exhaust gas concentration of the intake air charge, all while innovatively circumventing problems threatened by practical oxygen sensors and related technologies. While the subject inventions have been described by means of various specific embodiments and methods associated therewith, numerous modifications and variations can be made by those skilled in the art without departing from the scope of those inventions as may be set forth in the claims, ideally while still preserving some if not many of the advantages of those inventions.