[0001] The present application relates to a simulator maintenance tool for a gaseous fuel system of an internal combustion engine and a method of using it to service the gaseous fuel system.

Background of the Invention

[0002] Gaseous fuels like natural gas, hydrogen, propane, and mixtures thereof are becoming more prevalent for use as fuel for internal combustion engines. In this disclosure, "gaseous fuels" are defined to include fuels that are in a gaseous phase at atmospheric pressure and temperature and that are suitable for combustion in an internal combustion engine. With the volatility in the price of conventional fuels like gasoline and diesel, natural gas fueled vehicles are gaining a greater share of the market. Because natural gas is abundant, broadly distributed around the world, and relatively inexpensive compared to gasoline and diesel, reference is made to natural gas in the description of the preferred embodiments but it will be understood that the same apparatus and methods can be used for engines fueled with any of the aforementioned gaseous fuels and other suitable gaseous fuels.

[0003] While many components of a natural gas fueled engine are the same as those for a gasoline or diesel engine, because natural gas (and other gaseous fuels) have different properties from conventional liquid fuels, there are differences in natural gas engines that introduce new problems that need to be overcome. For example, because gaseous fuels are compressible fluids, versus liquid fuels that are essentially incompressible, this can present challenges with efficiently supplying the desired amount of pressurized gaseous fuel.

[0004] A problem with gaseous fueled engines is that when the engine is switched off, there is compressed gaseous fuel remaining in the fuel system. This compressed gas needs to be drained from the system before fuel system components are removed or opened for maintenance or replacement. This is a not a problem for conventional liquid fueled engines where liquid fuel can simply be drained back to the fuel tank. This is not as easy to do with a gaseous fueled engine. For vehicles that store the fuel as a compressed gas, such as compressed natural gas (CNG), the storage pressure is normally higher than the injection pressure, so that a compressor would be required to return gaseous fuel to the fuel storage tank. For vehicles that store the fuel onboard in a liquefied form, such as liquefied natural gas (LNG), it is not easy to re-liquefy the gas and it is not desirable to introduce a warm high pressure gas into a low pressure storage vessel that stores the LNG at cryogenic temperatures. Prior art gaseous fuel systems provide a means for safely venting the gaseous fuel to atmosphere, but with natural gas and other fuels, even though the amount of fuel that is vented is very small, an alternative to venting to atmosphere is more desirable.

[0005] Modern engines normally have many sensors that assist the engine controller to control engine operation and to detect when there is a problem. Because natural gas is a compressible fluid, it is more difficult to measure the amount of fuel that is flowing to the engine because fluid density and mass (and energy) depend upon pressure and temperature. Accordingly, some fuel management systems for gaseous- fueled engines use fuel temperature and pressure sensors that are not needed in a conventional liquid-fueled engine. Sometimes the fault conditions that indicate a problem are not precise as to the cause of the fault. The detected conditions may simply indicate that there is a problem and there could be several potential causes. If a sensor failure is one of the potential causes, this traditionally means that a service technician will need to remove the sensor, replace it, and then determine if the problem persists. With sensors that have a measuring probe that is in direct contact with the fuel, the pressurized fuel in a gaseous fuel system needs to be removed before the sensor can be removed for testing and/or replacement. If the problem is corrected when a new or reconditioned sensor is installed, then the sensor was the cause, but if the problem remains, then a different potential cause must be investigated, and the sensor was replaced needlessly. Accordingly, because removing a sensor takes time and requires the venting of the gaseous fuel system, it would be useful to employ a method of determining whether the sensor is the cause for the detected problem without needing to remove it.

[0006] The present method and apparatus provide a solution to reduce the amount of fuel that is vented to atmosphere and to facilitate the determination of whether or not a sensor needs to be replaced without removing it.

Summary of the Invention

[0007] An improved method for servicing a gaseous fuel system for an internal combustion engine comprises:

[0008] turning the engine off; [0009] disconnecting a sensor from a wiring harness for an engine;

[0010] instead of the sensor, connecting a simulator maintenance tool to the wiring harness;

[0011] turning the engine on; and

[0012] sending a simulated signal from the simulator maintenance tool to an engine electronic control unit. The simulated signal indicates a normal operating condition that allows the engine to be run.

[0013] In preferred embodiments, the sensor is a pressure sensor, such as one that indicates the pressure in the fuel tank, or in an accumulator vessel. In a bi-fuel vehicle, a function of the tank pressure sensor is to indicate to the electronic control unit when there is insufficient pressure available to continue fueling the engine with gaseous fuel. When it is desirable to run the engine to reduce the pressure in the gaseous fuel system by consuming the residual fuel therein, the method further comprises manually shutting off a gaseous fuel supply to the engine before turning the engine on, and running the engine until it stalls because the gaseous fuel supply is shut off and no gaseous fuel is being supplied to the gaseous fuel system, whereby fuel being delivered to the engine is insufficient to sustain combustion. [0014] After the engine stalls the method can further comprise attempting to restart the engine, which can help to further deplete the gaseous fuel system of residual fuel. Alternatively, the method can further comprise manually energizing the gaseous fuel injection valves after the engine stalls. For diagnosing engine fault conditions after the engine stalls, the method further comprises turning on the electronic control unit and reading signals therefrom.

[0015] An advantage of the present method is that it allows service technicians to determine if a sensor requires servicing by checking for a fault condition when the engine is running with the simulated signal instead of a signal from the sensor. When the sensor is not the cause of any fault conditions, this saves the service technician from unnecessarily removing the sensor and replacing it with one known to be in good working, just to check whether this is the cause of the fault condition.

[0016] Unlike a liquid fuel system, since a gaseous fuel is a compressible fluid, the amount of fuel delivered is a function of temperature and pressure, so measuring both of these parameters is not necessary for liquid fuel engines. Accordingly, in preferred embodiments, the sensors that the simulator maintenance tools replace in a gaseous fuel system are temperature and/or pressure sensors.

[0017] A preferred method of servicing a gaseous fuel system for an internal combustion engine involves depleting the gaseous fuel system of residual fuel after the tank shut off valve is closed. The method comprises:

[0018] turning the engine off;

[0019] closing a manual shut off valve at a fuel tank outlet;

[0020] disconnecting a tank pressure sensor that normally indicates fuel tank pressure from a wiring harness for an engine; [0021] instead of the pressure sensor, connecting a tank pressure simulator maintenance tool to the wiring harness; [0022] disconnecting a fuel rail sensor from the wiring harness;

[0023] instead of the fuel rail sensor, connecting a fuel rail simulator maintenance tool to the wiring harness;

[0024] turning the engine on;

[0025] sending a first simulated signal from the tank pressure simulator maintenance tool to an engine electronic control unit, the tank pressure simulated signal indicating a predetermined fixed pressure;

[0026] sending a second simulated signal from the fuel rail simulator maintenance tool to the engine electronic control unit, the second simulated signal indicating a fixed operating condition for the fuel rail;

[0027] wherein the first and second simulated signals are each respectively representative of an operating condition that allows the engine to run and be fueled with a gaseous fuel; and

[0028] running the engine until it stalls.

[0029] After the engine stalls, the method can further comprises attempting to restart the engine, which has the effect of opening the fuel injectors and further depleting the gaseous fuel from the gaseous fuel system. Alternatively, after the engine stalls, the method further comprises manually energizing the gaseous fuel injection valves.

[0030] In preferred embodiments, the fuel rail sensor measures more than one parameter, and the fuel rail simulator maintenance tool is configured so that it sends a fixed simulated signal for each parameter, which each simulated parameter corresponding to an operating condition that allows the engine to run and be fueled with a gaseous fuel. In preferred embodiments, the two parameters measured by the fuel rail sensor are pressure and temperature, but other parameters that can be used to determine fuel flow rate can be measured instead. [0031] An improved simulator maintenance tool for a gaseous fuel system for an internal combustion engine comprises:

[0032] a circuit for generating a simulated sensor signal indicating a normal operating condition that allows the engine to be run; [0033] an electrical coupling for connecting the simulator maintenance tool to a wiring harness instead of a sensor; and

[0034] a housing for enclosing the circuit.

[0035] As described in relation to the method, for the present gaseous fuel system, the sensors that the simulator maintenance tools are designed to replace are a pressure sensor and/or a temperature sensor for indicating fuel pressure in a fuel tank and fuel pressure and temperature in a fuel rail. The fuel rail sensor can be one that measures both temperature and pressure, such that the simulator maintenance tool has a resistive circuit that modifies the input reference voltage with fixed resistances representative of normal temperature and pressure conditions. [0036] In preferred embodiments, the simulator maintenance tool is one of a set of two simulator maintenance tools, with a first simulator maintenance tool for simulating a tank pressure sensor and a second simulator maintenance tool for simulating a fuel rail sensor, and the respective simulator tools have colour coded housings to facilitate identification of each simulator tool. Preferably the two simulator maintenance tools have respective electrical couplings that each has a different shape thereby preventing the simulator maintenance tools from being connected to the wrong harness coupling.

Brief Description of the Drawings

[0037] FIG. 1 is a schematic view of a simulator maintenance tool. [0038] FIG. 2 is a drawing of a resistive circuit that can be used by a simulator maintenance tool to provide a fixed resistance for a simulated sensor output. [0039] FIG. 3 is a drawing of a resistive circuit that can be used by a simulator maintenance tool to provide a fixed resistance for two simulated sensor outputs.

[0040] FIG. 4 is a schematic drawing of a gaseous fuel system for an internal combustion engine showing a simulator maintenance tool coupled to a wiring harness. [0041] FIG. 5 is a graph that plots sensor voltage output versus pressure for a pressure sensor.

[0042] FIG. 6 is a graph that plots sensor resistance versus temperature for a temperature sensor.

[0043] FIG. 7 is a graph that plots sensor voltage output versus pressure for a pressure sensor.

[0044] FIG. 8 is a flow chart that illustrates a method of using the present simulator maintenance tool with a gaseous fuel system.

[0045] FIG. 9 is a flow chart that illustrates a method of using the present simulator maintenance tool to reduce pressure in the gaseous fuel system. [0046] FIG. 10 is a plot of the gaseous fuel system rail pressure versus time when the present method is employed to lower the pressure in the fuel rail.

Detailed Description of Preferred Embodiment(s)

[0047] Simulator maintenance tool 10 shown in FIG. 1 is used in procedures for maintaining and servicing the gaseous fuel system of an internal combustion engine. Simulator maintenance tool 10 comprises housing 15 and an electrical coupling 20. Housing 15 encloses and protects electrical circuit 30 disposed therein. Coupling 20 is an electrical coupling for connecting to a wiring harness (not shown) at a point where it is normally connected to a sensor associated with the gaseous fuel system. For example, in preferred embodiments, this can be a fuel temperature sensor or a fuel pressure sensor or a sensor that measures both pressure and temperature. For example, such sensors typically include a transducer that converts a measured parameter into an electrical resistance. The wiring harness provides a reference voltage to an input pin of the sensor and a variable voltage received from the sensor correlates to the electrical resistance, from which the electronic control unit can determine the value of the measured parameter. Accordingly, electrical circuit 30 is designed to provide an electrical resistance that modifies the reference voltage. The voltage output is a simulated sensor output based on a known fixed resistance that correlates to a normal operating condition under which the engine is permitted to be run. In FIG. 1 coupling 20 is shown schematically with three pins but any number of pins can be employed as appropriate for the sensor that the simulator maintenance tool is intended to simulate.

[0048] With reference to FIG. 2, resistive circuit 200 is an example of a DC circuit designed to be used as a simulator maintenance tool for providing a simulated sensor output for one measured parameter, such as pressure. In a gaseous fuel system for an internal combustion engine, it is desirable to measure the available pressure, for example in an accumulator vessel or in the main storage tank. The engine's electronic control unit can be programmed to give a warning signal or to change to an economy operational setting if the available fuel, as indicated by a pressure sensor, is below a predetermined threshold. Resistive circuit 200 is designed for a 3-pin electrical coupling. In this FIG. 2, pin 1 is for connection to ground, pin 2 is for the simulated pressure sensor output, and pin 3 is for the reference voltage input. This resistive circuit was proven to work to simulate a CNG fuel tank that was half full, when resistors 210 and 220 each had a respective resistance of 1 kQ, > 0.25 W. The pressure sensor that measured CNG tank pressure was a model 11-09-09-23232 (110R000-123vkv4.2) pressure sensor manufactured by Bosch™, and FIG. 5 is a graph that plots voltage output versus pressure for this pressure sensor. Accordingly, it was determined that to simulate a tank that was half full, a resistance was needed to produce a voltage out that was about half of the voltage in. As with all embodiments of this apparatus and method, while other sensors may have different characteristics, the same apparatus and method can be applied. If the characteristics of another sensor are different, the simulated sensor output may correlate to a different operating condition, and if this results in an operating condition in which the engine is inoperable, then different resistors can be substituted in the disclosed resistive circuit, or a simulator maintenance tool with the requisite resistance can be employed to simulate a sensor output that does correspond to a normal operating condition that allows the engine to be operated with gaseous fuel.

[0049] With reference to FIG. 3, resistive circuit 300 is an example of a circuit designed to be used as a simulator maintenance tool for providing simulated sensor outputs for both pressure and temperature. In a gaseous fuel system for an internal combustion engine, it is desirable to measure both the pressure and temperature in the fuel rail that supplies the natural gas to the fuel injector(s). Natural gas fuel systems can introduce natural gas into the intake air stream before the intake air manifold, or into the air intake port for each engine cylinder. In other embodiments, the natural gas can be injected directly into the combustion chamber so that it does not displace any of the air being induced through the air intake ports. In such natural gas fuel systems, knowing the temperature and pressure in the fuel rail helps to control the fueling rate more accurately. Resistive circuit 200 is designed for a 4-pin electrical coupling. In this FIG. 3, pin 1 is for connection to ground, pin 2 is for the simulated pressure sensor output, pin 3 is for the simulated temperature sensor output and pin 4 is for the reference voltage input. By using the resistances set out in Table 1 below, resistive circuit 300 was proven to work to simulate a fuel rail temperature of approximately 25 degrees Celsius and a fuel rail pressure of approximately 1000 kPa (approximately 150 psi), these operating conditions being representative of normal operating conditions that the electronic control unit would interpret to allow the engine to run fueled with the gaseous fuel. Table 1

Resistor Specification

310 4.2 ΜΩ, > 0.25 W

320 8.2 kQ, > 0.25 W 330 40 kQ, > 0.25 W

340 50 kQ, > 0.25 W

[0050] Referring still to resistive circuit 300, the simulator using this circuit simulated a sensor output from a model 51CP26-01 temperature sensor manufactured by Sansata™, and FIG. 6 is a graph that plots resistance versus temperature for this sensor. The simulator maintenance tool was designed to simulate a temperature for a gaseous fuel in a fuel rail. In this case, from FIG. 6 it can be shown that to simulate a sensor signal for 25 degrees Celsius, the simulator maintenance tool needs to have a resistance of about 10 kQ. Resistive circuit 300 was designed with a dual function to also simulate a signal from a pressure sensor for measuring the pressure in the fuel rail. In this example, the pressure sensor that measured CNG rail pressure was a model 51CP26-01 pressure sensor manufactured by Sansata (this particular sensor combines temperature and pressure sensors in a unitary sensor device), and FIG. 7 is a graph that plots voltage output versus pressure for this pressure sensor. With reference to FIG. 7 it can be seen that to simulate 1000 kPa (150 psi) a resistance to produce a voltage out that is about 75% of the voltage in is what is required. FIG. 7 shows by way of example, that different sensors can have different characteristics, depending upon their design and the range of values that they are designed to measure. This example demonstrates how the apparatus can be adapted to different sensor characteristics to enable the same method. [0051] Referring now to FIG. 4, which is a schematic drawing of a gaseous fuel system for an internal combustion engine, showing only those system components necessary for the understanding of this disclosure, and a simulator maintenance tool coupled to a wiring harness. Features, such as isolation valves and pressure relief systems, which are well known but not essential for the understanding of the present system and its operation are not shown in order to simplify the depiction of the shown systems for better understanding thereof. In this example, gaseous fuel system 400 supplies natural gas or another gaseous fuel from fuel tank 410, which in this embodiment is a tank for storing compressed gaseous fuel such as CNG. When filled to full capacity such CNG storage tanks are typically filled to a pressure of between about 20 MPa and about 25 MPa (between about 3,000 and 3,600 psi). From fuel tank 410 the natural gas flows through pipe 412 to pressure regulator 414, which reduces the fuel pressure to the desired pressure for delivery to the engine through fuel rail 416. In this example, fuel rail 416 delivers the fuel to fuel injection valve 420 which inject the gaseous fuel into the air intake ports for each engine cylinder. In other embodiments, the fuel could be introduced at other locations, for example, it could be injected directly into the combustion chambers or into a mixer further upstream from the air intake ports. Pressure sensor 440 measures the pressure in fuel tank 410 indirectly by measuring the gaseous fuel pressure in pipe 412, but in alternative arrangements, pressure sensor 440 could be mounted directly to a coupling on the tank. Pressure sensor 440 is normally connected to wiring harness 452 to receive a reference voltage and output a voltage out, which the electronic control unit correlates to the pressure measured by sensor 440. However, FIG. 4 shows pressure sensor disconnected from wiring harness 452, which is instead connected to simulator maintenance tool 460, such as the one described in FIG. 2. Fuel rail sensor 442 can be of the type that measures both pressure and temperature. Alternative embodiments could use individual pressure and temperature sensors, in which case separate simulator maintenance tools can be used for each individual sensor. Fuel rail sensor 442 measures the pressure and temperature in fuel rail 416, and fuel rail sensor 442 is shown connected to wiring harness 452. Shown next to the harness coupling is second simulator maintenance tool 462, such as the one described in FIG. 3.

[0052] The method of using the present simulator maintenance tools will be described now with reference to the system shown in FIG. 4 and FIGS. 8-10. FIG. 8 is a flow chart that sets out the method for using a simulator maintenance tool. First engine 430 is turned off. When this is done there is still gaseous fuel at injection pressure in fuel rail 416. One of the fuel system sensors, for example pressure sensor 440, is then disconnected from wiring harness 452, leaving pressure sensor 440 installed on pipe 412. Simulator maintenance tool 460 is then connected to wiring harness 452 instead of pressure sensor 440. Then engine 430 can be turned on again and a reference voltage will be supplied to simulator maintenance tool 460 through the wiring harness so that fixed resistance of simulator maintenance tool 460 will modify the voltage and output a predetermined voltage out, this being a simulated sensor output, with a known value, to engine electronic control unit 450. If this does not resolve the engine fault condition, then it can be concluded that pressure sensor 440 is not the cause of the fault condition, because this determines that the fault condition is still detected even when simulator maintenance tool 460 sends a signal to electronic control unit 450 that is representative of a normal pressure (or temperature, as the case may be if this method is applied using simulator maintenance tool 462 connected to wiring harness 452 in place of sensor 442). In this way, if it is determined that pressure sensor 440 is not the cause of the fault condition, then this procedure makes it unnecessary to vent the gaseous fuel from the system, making it unnecessary to remove pressure sensor 440 for replacement and further testing. If an engine fault condition is resolved by connecting simulator maintenance tool 460, and it is known that there is adequate pressure available in fuel tank 410, then it can be deduced that pressure sensor 440 might be the cause, warranting relieving the pressure in the gaseous fuel system so that pressure sensor 440 can be removed and replaced. [0053] While the method was described with reference to pressure sensor 440 and simulator maintenance tool 460, it will be understood that the same method outlined in the flow chart of FIG. 8 can be employed with fuel rail sensor 442 and simulator maintenance tool 462, to determine whether fuel rail sensor 442 is faulty. An exception is that simulator maintenance tool 462 simulates two sensor signals, one for temperature and one for pressure. Nevertheless, the service procedure is the same, because if simulator maintenance tool 462 is connected to the wiring harness, and the fault condition is not resolved, it can still be determined that fuel rail sensor 442 is not the cause, preventing the need to drain the fuel from the gaseous fuel system so that fuel rail sensor 442 can be replaced. Similarly, if the fault condition is resolved by sending the simulated signals to engine electronic controller 450, then it can still be deduced that the system pressure should be relieved and fuel rail sensor 442 should be removed and replaced.

[0054] If it is determined that maintenance must be done on the gaseous fuel system and that the pressure must be reduced to a level at which it is safe to remove sensors or remove other components, such as the fuel rail, or the pressure regulator, simulator maintenance tools 460 and 462 can be used to enable a novel procedure for bringing down the fuel pressure in the gaseous fuel system without venting gaseous fuel to atmosphere. With this procedure both simulator maintenance tools 460 and 462 are connected to wiring harness 452 in place of sensors 440 and 442 respectively. Before turning the engine on, a manual shut off valve is closed between fuel tank 410 and pipe 412. The engine will start and the engine electronic control unit will want to fuel the engine with natural gas because the simulator maintenance tools are fooling it into detecting natural gas at the requisite pressures and temperatures. However, because no more fuel is being supplied to the gaseous fuel system from the fuel tank, once the residual fuel is consumed to a level that there is too little fuel being delivered to the engine to sustain combustion, the engine will stall. To reduce fuel pressure even more, by trying to start the engine after stalling, more fuel will escape from the gaseous fuel system through the fuel injectors. FIG. 10 is a graph that plots the gaseous fuel system rail pressure versus time when the present method was employed. FIG. 10 shows that the method works to reduce the fuel pressure to a level that is safe for a service technical to remove sensors or other components from the gaseous fuel system. When this method was applied to a Ford™ F-250 bi-fuel truck equipped with a Westport Wing™ fuel system the engine ran for between 30 and 45 seconds before stalling and the simulator maintenance tools prevented the engine electronic control unit from automatically switching to gasoline operation, as it normally would if it detected fuel pressures below predetermined thresholds. When the engine stalled there was a residual fuel rail pressure of about 50 psia. The service procedure can comprise reducing pressure further by manually energizing the gaseous fuel injectors or by attempting to turn the engine back on. [0055] Note that the tank pressure sensor is normally installed on pipe 412 for maintenance purposes, because it allows removal of pressure sensor 440 without emptying fuel tank 410, as would be necessary if the pressure sensor was mounted directly on the fuel tank. The tank shut off valve can be integrated into a manifold block for the fuel tank as long as the shut off valve is fluidly upstream from the pressure sensor.

[0056] An advantage of the simulator maintenance tool is that it provides a known electrical resistance. Previously, service technicians would replace the suspect sensor with a sensor that is known to be in good working order. However, being a sensor instead of a simulator, the signal from the sensor would be a variable depending upon the real time measurements of the measured parameter such as temperature or pressure. It is easier to diagnose fault codes when there are fewer variables, so if the simulator maintenance tool is able to provide a fixed and known value in lieu of a signal from a working sensor this can facilitate the problem diagnosis. [0057] When the simulator maintenance tool is used for a bi-fuel engine, meaning an engine that can be fueled with either one fuel or another fuel, another advantage of the present apparatus and method is that by fooling the controller into thinking that there is enough fuel at the requisite pressure in the fuel rail, the engine electronic control unit will not automatically switch to the other fuel, allowing the engine to be run until it stalls for being starved of fuel. Bi-fuel engines are known for fueling an engine with either natural gas or a liquid fuel such as gasoline or diesel. Bi-fuel engines normally keep the conventional liquid fuel tank and add a natural gas fuel tank, so this gives such bi-fuel vehicles extended range and reduces the risk of running out of gaseous fuel in locations where the natural gas re-fueling infrastructure is not fully built up.

[0058] While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.