Engine Arrangement with Charge Air Cooler and EGR system

TECHNICAL FIELD

The present invention relates to an engine arrangement having an engine comprising an EGR system and a charge air cooler.

BACKGROUND OF THE INVENTION

It is known from the state of the art that an engine arrangement having an engine, preferably for a vehicle such as a truck, bus, lorry, car, boat or the like, comprises an EGR system. In internal combustion engines, exhaust gas recirculation (EGR) represents a nitrogen oxide (NOx) emission reduction technique used in petrol/gasoline and diesel engines. NOx primarily forms when a mixture of nitrogen and oxygen is subjected to high temperatures. EGR works by recirculating an engine exhaust gas portion back to the engine cylinders. In a gasoline engine, this inert exhaust gas displaces the amount of combustible matter in the cylinder. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre- combustion mixture. Since NOx formation progresses much faster at high temperatures, EGR reduces the amount of NOx generated as a result of combustion. Replacing air with EGR lowers the lambda value whereby EGR lowers the combustion temperature and reduces the concentration of O ₂ .

An EGR cooler is a heat exchanger installed in the EGR circuit. The EGR system recirculates exhaust gas back to the engine in order to reduce NOx emissions. The cooler simply cools the exhaust gas prior to reintroduction of the gas into the engine. By cooling the gas, the combustion temperature is decreased, whereby NOx is formed at higher temperatures. During this cooling process, EGR gas may become excessive, for example during engine start or during a cold start period, deteriorating the combustion efficiency in each cylinder and in the exhaust gas components. Hence, the EGR system having the EGR cooler is arranged in this instance so as to cause the EGR gas to flow in an EGR bypass provided by bypassing a passage of the EGR cooler. For switching this EGR cooler during use and during non-use, a passage switching valve is frequently used to change a flow of exhaust gas from one direction to another direction or to two directions or a flow of exhaust gas from two directions to one direction, or from one direction to another direction.

It is also known in the state of the art to use a turbocharger or turbo compressor in an internal combustion engine, which is a gas compressor to enhance induction of air in an engine cylinder or which is a form of a supercharger. The turbocharger increases the density of air entering the engine to produce more power. A turbocharger has the compressor being powered by a turbine which is driven by the engine's own exhaust gas. Compressing air in the turbocharger increases the air temperature, which may cause a number of problems. Excessive charge air temperatures can lead to detonation, which is highly detrimental to engines. When a turbocharger is installed on an engine, it is common practice to fit the engine with an intercooler system (also known as a charge air cooler system, or CAC system), being a type of heat exchanger which releases heat energy in the charger to ambient air. For a compression ignition engine having at least one turbocharger and an intake air cooler, operation of the engine at or around idle is difficult to optimize for various reasons. Firstly, due to the aspect that low ambient temperature air flows into the engine through the intake charge air cooler under low ambient temperatures, the air entering the intake manifold may be over-cooled and, when an exhaust gas recirculation (EGR) system is utilized, may cause excessive carbon deposits on the EGR valve and intake sensors. Secondly, low intake air temperatures at idle engine conditions may result in undesirable white smoke and odors in the exhaust gas of compression ignition engines due to incomplete combustion of the fuel. Therefore, CAC bypass valves are known in spark ignition engines e.g. in aeroplane motors for preventing motor failure due to ice formation in the CAC at high altitudes and in gasoline internal combustion engines e.g. for reducing white smoke during cold start.

In order to reduce emissions, a selective catalytic reduction catalyst (SCR catalyst) is widely used, converting NOx with the aid of a catalyst into diatomic nitrogen, N2, water, H20. A gaseous reductant, typically anhydrous ammonia, aqueous ammonia or urea, is added to a flue or exhaust gas flow and is absorbed onto a catalyst. A SCR catalyst works more efficiently with warmer exhaust gas. Starting with diesel engines manufactured on or after January 1 , 2010, engines are required to meet lower NOx standards. A majority of heavy-duty engine (Class 7-8 trucks) manufactures utilize such SCR catalysts to efficiently reduce NOx emissions to meet upcoming EPA standards, which are the emission standards of the United States. The EU has introduced Euro 4 being effective since January 1 , 2008, Euro 5 being effective since January 1 , 2010 and will introduce Euro 6 taking effect on January 1 , 2014. Asian countries, such as China, India and Japan, pursue similar regulations.

From US 7257950 B2 an engine arrangement is known comprising a CAC system and an EGR system, wherein the CAC system comprises a CAC bypass. The CAC bypass enters the EGR system at a cold side of the engine.

SUMMARY OF THE INVENTION

In order to meet the above-mentioned emission standards, it is an object of the invention to provide an engine arrangement, wherein the exhaust gas temperature can be controlled in an optimal way under various engine and environmental conditions, especially at low engine load and/or low engine or low external air temperature, such that a SCR catalyst is enabled to work efficiently. Another object is to provide an engine arrangement with improved emission values based on various existing engine arrangements with a high packing density, such that a voluminous modification, additional installations and reconstruction can be avoided. In this way, existing engine arrangements can be modified to meet improved emission standards with little effort.

These objects are achieved by the features of the independent claims. The dependent claims, drawings and the description disclose advantageous

embodiments of the invention. An engine arrangement is proposed, comprising an engine, a charge air cooler connected to an engine inlet side of the engine, an air bypass for bypassing the charge air cooler, and comprising an EGR system connected between an engine outlet side and an engine inlet side of the engine via one or more EGR lines. The air bypass enters the EGR system at an air-bypass port of an EGR line for mixing air with exhaust gas at the engine outlet side of the EGR system and/or upstream of an EGR cooler. In order to arrange the CAC air bypass on the engine outlet side of the EGR system, which is the high temperature side of the engine, charged air mixes with exhaust gas at the hot side of the EGR system, e.g. between a downstream side of a high temperature EGR cooler (HT EGR cooler) and an upstream side of a low temperature EGR cooler (LT EGR cooler). In order to transform an existing engine arrangement into an inventive arrangement, an additional CAC air bypass line and an air-bypass port can be installed connecting the CAC system and the EGR system at a high temperature side of the engine, which is a slight modification of an existing engine arrangement. A predetermined thickness of the air bypass line, a flow orifice or a binary or proportional throttle can control the amount of charged air flowing through the air bypass into the EGR system. Thus, an optimized air/exhaust gas mixture is provided at low ambient temperature and/or low engine load such that an increased exhaust gas

temperature can be provided for enabling a SCR catalyst to work more efficiently. Existing components of an engine arrangement can be used such that

modification effort is minimal. Early mixing of charged air and exhaust gas decreases the temperature in the EGR system so that certain components of the EGR system, such as thermal insulation and cooler dimensions, can be reduced providing additional constructional space. In an engine arrangement having a dual- stage turbo compressor, the air bypass should be arranged downstream of the second compressor.

According to an advantageous embodiment of the invention, a control device may be provided for controlling an engine inlet temperature T in of an air/exhaust gas mixture by controlling a ratio of cooled/uncooled air and/or cooled/uncooled exhaust gas in the air/exhaust gas mixture. The ratio between air and EGR can remain the same and can depend on engine parameters like combustion condition, speed, load etc.. The inlet temperature T_in can be controlled by cooling or not cooling the charge air using a CAC bypass valve or throttle. Furthermore the inlet temperature T_in can be controlled by cooling or not cooling the EGR using an EGR cooler bypass valve or throttle. Both types of controlling amount of cooled/uncooled charged air and cooled/uncooled exhaust gas can be used in a combined way and can also be used independently from another. The control device can control the above mentioned ratio such that an optimized exhaust gas temperature can be provided for the SCR catalyst. Typically, hot exhaust gas has a hot temperature of 650°C to 700°C, and cold exhaust gas (low load or cold engine) has a temperature of 00°C to 350°C. Turbocharged air has a typical temperature of 50°C to 280°C. The engine inlet temperature is crucial for exhaust gas emission and for the lubricating system of the engine. If T_in is too high, an engine oil film may deteriorate. The control device can control the ratio such that a mixture of cooled/uncooled exhaust gas and cooled/uncooled charged air enters the engine inlet side at a predefined temperature and ratio independent of engine load and temperature, for instance with T_in>60° and T_in<125°C, optimally T in in a range between 100°C to 120°C, such that an SCR catalyst is enabled to work efficiently. The control device can be a controller system or the like comprising means for measuring or evaluating an actual engine inlet temperature in a direct manner (temperature sensor) or indirect manner (based on driving conditions using a map considering accelerator pedal angle, clutch status or the like). The control device can be connected to one or more binary or proportional throttles or valves located in the EGR system line, CAC system line and/or air bypass line in order to control an amount of air or gas flowing through the air or gas line. The control device can be connected to an EGR cooler and/or CAC system to control cooling temperature and can control a gas flow through an EGR cooler bypass and/or air flow through a CAC air bypass such that an air/exhaust gas mixture can enter the engine at a predefined temperature T in.

According to a second aspect of the invention, an engine arrangement, particularly as mentioned above, comprises an engine, a charge air cooler connected via an airline to an engine inlet side of the engine, an air bypass for bypassing the charge air cooler, and an EGR system connected between an engine outlet side and an engine inlet side of the engine via one or more EGR lines. The control device is provided for controlling an engine inlet temperature TJn of an air/exhaust gas mixture by controlling a ratio of cooled/uncooled air and/or cooled/uncooled exhaust gas. The control device can control the flow of cooled air through the CAC system, the flow of cooled exhaust gas through the EGR system and/or the flow of uncooled air through the air bypass and optionally the flow of cooled EGR thorugh an EGR cooler and/or uncooled EGR through an EGR cooler bypass such that the exhaust gas temperature can be provided high enough for the SCR catalyst but low enough under a critical temperature, thus avoiding damage to the engine. The control device can be arranged as described above. According to an advantageous embodiment of the aforementioned engine arrangement, the control device can control the engine inlet temperature T_in of the air/exhaust gas mixture by mixing uncooled air from the air bypass or cooled air from a charge air cooler with exhaust gas from the EGR system at the engine outlet side of the EGR system. The control device can control at least a throttle or valve opening or closing the air bypass passage such that a ratio of uncooled air flowing through the air bypass and cooled air flowing through the charge air cooler can be adjusted. A first throttle disposed in the airline and a second throttle disposed in the air bypass line can control the amount of air and the ratio of cooled/uncooled air for mixing with the EGR. The air bypass line can enter the EGR system at an EGR line with an EGR cooler or can enter the EGR system at an EGR cooler bypass line.

According to an advantageous embodiment, the control device can control the engine inlet temperature T in of the air/exhaust gas mixture by mixing charged air with uncooled exhaust gas from an EGR bypass or with cooled exhaust gas from an EGR cooler. The control device can control at least a throttle or valve opening or closing an EGR cooler bypass passage such that a ratio of uncooled exhaust gas flowing through the EGR bypass and cooled exhaust gas flowing through the EGR cooler can be adjusted. A first throttle disposed in the EGR bypass and a second throttle disposed in the EGR cooler line can control the amount of EGR and the ratio of cooled/uncooled EGR for mixing with the charged air.

The controlling device can control the passage throught the air bypass line and the EGR bypass line for controling the ratio of cooled/uncooled EGR mixed with cooled/uncooled air independently and can also combine the control of both ratios for optimizing the exhaust gas temperature such that an SCR catalyst can work efficiently at all load and temperature conditions. According to an advantageous embodiment, a throttle can be arranged in the airline. The throttle can be a binary throttle or valve for opening or closing the airline or can be a proportional throttle or valve such that an amount of air flowing through the airline can be controlled. Closing the throttle separates the CAC system from the EGR system on the hot side of the engine. Opening the throttle enables mixing of air and exhaust gas within the EGR line between hot side and cold side of the engine. If an EGR cooler bypass line exists it can also be favourable to arrange a throttle in the EGR bypass.

According to an advantageous embodiment, a throttle can be arranged in the airline and the air bypass. The airline connects a turbocharger with the CAC system. Opening or closing the airline throttle actives/deactivates cooling of the charged air. Preferably at low load of the engine, the airline throttle should be closed and the air bypass throttle should be opened. At high load, the air bypass throttle should be closed. If an EGR cooler bypass line exists it can also be favourable to arrange a throttle in the EGR bypass and in the EGR line.

According to an advantageous embodiment, the engine inlet temperature Tjn of the air/exhaust gas mixture can be determined between a minimum temperature T_scr and a maximum temperature T max. The maximum temperature T max can be chosen so as to prevent damage to the engine, especially at low load or at low ambient temperatures, and can be chosen to be preferably T_max<=125°C. The minimum temperature T_scr can be chosen to guarantee low emissions of the engine, preferably such that a SCR catalyst is enabled to work efficiently and can be set T_scr>=60°C. Values of T scr and T max may vary depending on the current engine status and environmental and driving conditions. The minimum and maximum temperature T scr, T max can be taken from a map. According to an advantageous embodiment, the engine outlet side and the engine inlet side can be connected via a direct EGR line free of an EGR cooler, and the air bypass can enter the EGR system via the direct EGR line. Additionally, the direct EGR line can be an EGR bypass for bypassing one or more EGR coolers, e.g. a HT and/or a LT EGR cooler. As a consequence, the direct EGR line can be an EGR cooler bypass line for bypassing one or more EGR coolers in a low temperature state of the exhaust gas. Exhaust gas can flow either partly or selectively through the direct EGR line or through an EGR line comprising at least one EGR cooler. Charged air can flow through the direct EGR line independent of the flowing direction of the exhaust gas.

According to an advantageous embodiment, the air bypass can enter the EGR system between a first EGR cooler and a second EGR cooler. The first EGR cooler can be a HT EGR cooler and the second EGR cooler can be a LT EGR cooler. The air bypass enters the EGR system downstream of the HT EGR cooler and upstream of the LT EGR cooler and the air is mixed with pre-cooled exhaust gas. As a consequence, the dimensions of the LT EGR cooler and the insulation thickness of the EGR line downstream of the HT EGR cooler can be reduced, since temperature of the mixed air/exhaust gas can be further decreased.

According to an advantageous embodiment, an EGR line segment can be arranged downstream of the air bypass port in the EGR line and can be adapted as a mixing chamber. The air bypass enters the EGR system either upstream of an EGR cooler or can be connected to a direct EGR line. The EGR line

downstream of the air bypass port leads to the cold side of the engine and can be adapted for adequately mixing charged air and exhaust gas. Thus, the EGR line segment functionally acts as a mixing chamber and can be adapted in form, width and internal configuration to provide thorough mixing of air and exhaust gas during the flow between air bypass entry point and inlet into the engine's cylinder.

According to an advantageous embodiment, the charge air cooler can be an air- cooled device or can be a coolant-cooled device. Furthermore, it may be possible to use a hybrid-cooled device having an air-cooled and a coolant-cooled part. Cooling performance of a coolant-cooled device can be controlled in limited ranges such that efficient control of the inlet temperature of the exhaust gas/air mixture by controlling the cooling behaviour of the CAC system is possible. A hybrid-cooled device can be used for scaling the cooling performance dependant on the engine's temperature status.

According to another aspect of the invention, a vehicle is proposed comprising an engine arrangement according to any of the above-mentioned embodiments. The vehicle's engine comprises a CAC system and an EGR system, wherein the temperature of an exhaust gas/charged air mixture at an engine's inlet on the cold side of the engine can be controlled such that the vehicle emissions can be reduced preferably in a low load situation or at a low ambient temperature. A conventional vehicle can be converted into an embodiment of the invention by installation of an air bypass between an airline upstream of the CAC system and an EGR line at the hot side of the engine. Additionally, a control device comprising means for sensing an exhaust gas/air mixture inlet temperature and one or more throttles for controlling gas/air flow in the air bypass, EGR system and/or CAC system, can be provided to meet upcoming emission standards.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above-mentioned and other objects and advantages may best be understood from the following detailed description of the embodiment(s), but is not restricted to these embodiments, wherein: Fig. 1 is a schematic view of an engine arrangement of the state of the art;

Fig. 2 is a schematic view of a first embodiment of an engine arrangement according to the invention; Fig. 3 is a schematic view of a second embodiment of an engine

arrangement according to the invention; is a schematic view of a third embodiment of an engine arrangement according to the invention; is a schematic view of a fourth embodiment of an engine

arrangement according to the invention; is a zoomed view of the CAC air bypass section according to the fourth embodiment; is a schematic view of a fifth embodiment of an engine arrangement according to the invention; shows a vehicle comprising an embodiment of an engine arrangement according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the drawings, equal or similar elements are referred to by equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention.

Fig. 1 schematically depicts a state-of-the-art engine arrangement comprising an engine 12, an EGR system 22 and a charge air cooling system comprising a turbocharger 60 and a charge air cooler arrangement 70. The EGR system 22 recirculates exhaust gas produced by the engine 12 from a engine outlet side 18, which is a hot engine side to an engine inlet side 16 which is a cold engine side. Exhaust gas being released by the engine outlet side 18 usually has a

temperature of between 100°C (low load) and 700°C (full load). Typically, the gas pressure of the exhaust gas may vary between 1 .5 to 500 kPa. At least part of the exhaust gas will be recirculated by the EGR system to the engine inlet side 16 and will be mixed with charged air from the turbocharger 60 to reduce emission of the engine 12. The exhaust gas is cooled down by a two-step cooling EGR cooler 38 comprising a high temperature EGR cooler 38a being attached close to the exhaust gas output port 68 of the engine 12 and a low temperature EGR cooler 38b being arranged downstream of the EGR line 24. The turbocharger 60 is driven by exhaust gas flowing towards an exhaust pipe 62 and compresses ambient air entering an air intake 64 of the turbocharger such that charged air can flow through an airline 30 to the engine inlet side 16 of the engine 12. In the course of the air compression, the temperature of the charged air can rise up to 60°C (low load) and 260°C (full load). For efficiently increasing and improving exhaust properties of the engine 12, charged air is cooled down by a charge air cooler 14 which is comprised in a cooling device 70. The cooling device 70 further

comprises a low temperature cooling device 72 and a high temperature cooling device 74 for cooling a vehicles cabin or the engine block. From the output side of the cooling device 70, the cooled charged air mixes with recirculated EGR exhaust gas at an EGR-cooled air mixing port 58 and enters the cylinder of the engine 12 at the EGR air input port 56.

Under certain conditions, such as low load or low engine temperature, an excessive cooling of charged air can be detrimental to the engine 12. Therefore, it is well known to bypass the charge air cooler 14 via a conventional air bypass line 66. Switching between charged air being cooled by a charge air cooler 14 and charged air being bypassed through the air bypass 66 can be controlled by a single or a double throttle (not shown). Conventionally, the EGR-cooled air mixing port 58 comprises a mixing chamber for thoroughly mixing exhaust gas and charged air. Also it is common that an EGR system 22 comprises thick isolated EGR lines 24 and high performance EGR coolers 38a and 38b, since EGR exhaust gas can reach temperatures of more than 700°C, so that other parts of the engine must be protected from overheating. Furthermore, a large number of EGR lines 24 and charge airlines 30 have to be installed in an engine arrangement 10, whereby constructional space is strongly limited. Controlling an optimal

temperature of the air/exhaust gas mixture entering the engine 12 at the EGR/air input port 56 is difficult due to the high volume of air and gas being stored in the air and EGR system leading to slow reaction times and difficult control of the air/exhaust gas temperature and amount. An accurate control of the gas/air mixture's temperature preferably at low load condition or at low engine temperature is advantageous, leading to a more efficient work of a SCR catalyst installed in the exhaust gas pipe 62.

Fig. 2 schematically depicts a first embodiment 10 of an engine arrangement according to the invention, whereby mixing of exhaust gas and charged air is performed on the hot side 18 of the engine 12 such that a common exhaust gas/air mixture flows through the EGR system 22 to the engine inlet side 16. The overall configuration is similar to the configuration of the engine arrangement 10 shown in Fig. 1. The conventional air bypass 66 is not needed any more, thus saving constructional space and reducing structural complexity of the EGR/CAC system. The engine arrangement 10 comprises an EGR system 22, wherein exhaust gas from the engine 12 enters a first high temperature EGR cooler 38a, and flows through an EGR line 24 to a second low temperature EGR cooler 38b. The outputted gas of the second LT EGR cooler 38b flows into an EGR-cooled air mixing port 58, where the exhaust gas can be mixed by the cool charged air from the charge air cooler 14 and enters the engine 12 at the EGR air input port 56. For providing a CAC bypass, an air bypass 20 connects the airline 30 downstream of the turbocharger 60 at a bypass port 76 by an air bypass 20 with the EGR connection line 24 at an air-bypass port 26 between the first HT EGR cooler 38a and the second LT EGR cooler 38b . Charged air enters the EGR system 22 at the air bypass port 26, wherein exhaust gas and charged air can mix during their flow through the EGR line 24 and during cooling down process in the second EGR cooler 38b. A thorough mixing is provided through the long passage of the exhaust gas and the air in the same EGR line 24, and efficient control of the air/exhaust gas temperature with a fast response time can be achieved. The efficient temperature of the exhaust gas/air mixture in the EGR system 22 is lowered such that thermal insulation and cooling capacity of the second EGR cooler 38b can be reduced. The engine arrangement is more compact and exhaust emission values can be decreased at low load. The charge air cooler 14 is bypassed through the low temperature EGR cooler 38b. Already existing components in conventional engine arrangements can be used, thus constructional modifications and costs are low. A mixing chamber at the EGR cooled air mixing port 58 is redundant.

Conventionally in a normal operation situation, the LT EGR cooler 38b can be cooled by a coolant from the low temperature radiator 72. In this configuration, when the engine 12 is running at low load or in a cold start phase, either the coolant supply can be shut off to avoid cooling of the air/exhaust gas mixture or the LT EGR cooler 38b can be connected to a high temperature cooling device 74 and the exhaust gas air mixture can be heated by a hot coolant. An additional bypass of the LT EGR cooler 38b is no longer needed. In consequence a single bypass of the charge air cooler 14 as well as a bypass of the EGR cooler 38a or 38b can be omitted by actively cooling the exhaust gas by charged air. If the turbocharger 60 is a dual-stage turbo engine, the air bypass 20 can preferably be arranged downstream of the second turbo compressor stage. A controlling device (not shown in Fig. 2) can control one or several throttles, e.g. a double throttle arranged in the air bypass 20 and in the airline 30 to control the amount of charged air flowing in the EGR system 22 and in the charge air cooler 14. The control device can control the mixing such that the exhaust gas/air mixture entering the engine 12 at the EGR/air input port 56 has a temperature below 125°C. The one or the several throttles can be a binary switch or a proportional throttle and the control device can comprise a PD-, PI- or PID- controlling unit. The velocity of air flowing in the airline 30 can be up to 20 to 25 m/s at full load such that a low reaction time can be reached. A continues throttling at a high rate can reduce the response time.

Fig. 3 shows another embodiment of an engine arrangement 10 which basic configuration is essentially based on the embodiment of Fig. 2 and which additionally comprises a direct EGR line 28 connecting the exhaust gas output port 68 on the engine outlet side 18 with the input port 56 at the engine inlet side 16 to bypass the EGR cooler 38. Here, throttles (not shown) can control direction and amount of exhaust gas flowing through the cooled EGR line 24 or the direct EGR line 28. As depicted in Fig. 3 and in Fig. 4, the air-bypass line 20 can enter the EGR system either at an EGR connection line 24 of an EGR cooler arrangement 38 or can enter the direct EGR line 28 as shown in Fig. 4. Connecting the air bypass 20 with the direct EGR line 28 reduces isolation thickness of the direct EGR line 28 due to controlled mixing of the "hot" exhaust gas with the "cool" charged air. Fire risk and temperature-related damage can be reduced. Fig. 5 shows another embodiment of an engine arrangement 10, wherein the EGR system 22 comprises a direct EGR line 28, such that EGR coolers 38 are not necessary. Due to controlled injections of cold charged air via the air bypass 20 into the direct EGR line 28, a temperature and mixing ratio of the exhaust gas/air mixture can be reached such that an optimal mixed gas can enter the engine cold side 16 at the EGR/air input port 56. The controlling method can help to optimise the lambda value of the engine.

A magnified view of a sub part A of Fig. 5 is shown in Fig. 6. Air 34 is charged by a turbocharger 60 (not shown) and can flow through an airline 30 towards a charge air cooler 14 (also not shown), which can be controlled by a first throttle 42a. The airline 30 is connected at a bypass port 76 to the EGR line 24, whereby air 34 can enter the EGR line 24 through an air-bypass port 26, whereby a second throttle 42b is arranged in the air bypass 20. Both throttles 42a and 42b can control the amount of charged air 34 flowing either towards a charge air cooler 14 or through the air bypass 20 into the EGR system 22 with a short response time. At the air- bypass port 26, charged air mixes with exhaust gas 32 forming an air/exhaust gas mixture 36 which thoroughly mixes during traveling in an EGR line segment 46 acting as a mixing chamber 48. Diameter and internal configuration of the EGR line segment 46 can be adapted to optimize mixing of exhaust gas 32 and charged air 34. The mixed gas 36 is lead to the EGR/air input port 56 of the engine inlet side 16 of the engine 12. Typically, the pressure in the EGR system can reach up to 500 kPa, whereby the pressure in the charged air system pressure is about 15 kPa. Therefore, additional means such as operating valves, non-return valves or active components, such as additional turbines or pressure regulators, can be arranged in the air bypass line 20 to improve mixing of exhaust gas 32 and charged air 34.

Fig. 7 shows a more detailed embodiment of an engine arrangement being similar to the embodiment shown in Figs. 3 and 4, wherein the air bypass 20 is connected to a direct EGR line 28 and to a cooled EGR line 24. A control device 40 comprises a temperature sensor 52 being arranged at the EGR/air input port 56 and evaluating the temperature of the mixed gas entering the engine 12. In order to maintain a predefined temperature T in, which can vary between a minimum and maximum threshold value T_scr and T_ max, the control device 40 controls at least throttles 42a to 42c being arranged in the airline 30 (42a) in the air bypass 20 connected to the direct EGR line 28 (42b) and in the airline 20 connected to the cooled EGR line 24 (42c). Furthermore, a throttle 42d can control the amount of EGR gas recirculating to the cold side 16 of the engine 12. Since a direct temperature measurement of a temperature sensor 52 may be too slow and inaccurate, the control device 40 can be connected to an electronic sensor system of the engine arrangement 10 and can evaluate for instance the angle of a gas accelerator pedal, driving conditions and further engine-related parameters. Thus, during indirect measurement of the engine load, a fast response time and a more accurate control of the temperature and ratio of the air/exhaust gas mixture entering the port 56 can be provided. Typically, the EGR flow is 20% to 30% of the total exhaust gas being released by the engine 12. Fig. 8 finally shows a vehicle 15, wherein an engine arrangement 12 comprises an EGR system 22 having an EGR cooler 38 and a turbocharger 60 with a charge air cooler 14, whereby the charge air cooling system can be bypassed by an air bypass 20 at the hot side 18 of the engine such that charged air can flow through the EGR line 24 of the EGR system 22. The lambda value of the engine 12 can be optimized and the exhaust gas temperature at low load or at an engine start can reach temperature values even at low load or at an engine start, at which a SCR catalyst 54 is enabled to work efficiently.

The engine arrangement can be used for diesel engines and also for gasoline engines, and can be installed in vehicles or in other apparatuses and machines driven by combustion engines, such as electric power generators, working machines or the like. Due to a minimal structural modification of the engine arrangement, improved admission parameters, additional constructional space and enhanced performance of the engines can be attained. The invention can be incorporated into newly built engines and can also be used for remodelling existing engines with little effort. Reference Numerals engine arrangement

engine

charge air cooler

engine inlet side

engine outlet side

air bypass

EGR system

EGR line

air-bypass port

direct EGR line

air line

exhaust gas

air

air/exhaust gas mixture

EGR cooler

a high temperature EGR cooler

b low temperature EGR cooler

control device

throttle

a throttle in air line

b throttle in air-bypass for direct EGR linec throttle in air-bypass for cooled EGR lined throttle in EGR line

e throttle in direct EGR line

EGR bypass

EGR line segment

mixing chamber

vehicle

temperature sensor

SCR catalyst

EGR/air input port

EGR/cooled air mixing port

turbocharger

exhaust pipe

air intake

conventional air bypass

Exhaust gas output port

cooling device

low temperature cooling device

high temperature cooling device

bypass port