Internal combustion engine control device

Abstract

To provide an internal combustion engine control device capable of suppressing deterioration of properties of exhaust gas.SOLUTION: A control device 60 is applied to an internal combustion engine 10 that uses hydrogen as fuel. A processing circuit 61 of the control device 60 calculates a basic value of a fuel injection amount of a fuel injection valve 13 on the basis of request torque, sets an upper limit value of fuel injection amount corresponding to an engine load factor or the basic value of the fuel injection amount, whichever is smaller, as a target value of the fuel injection amount, and operates the fuel injection valve 13 on the basis of the target value. The processing circuit 61 corrects relation between the engine load factor and the upper limit value so that the upper limit value corresponding to the engine load factor becomes small when a difference between an NOx concentration in exhaust gas and a reference value of the NOx concentration is a concentration difference threshold value or larger.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an internal combustion engine control device that is applied to an internal combustion engine that uses hydrogen as fuel. [Background technology]

[0002] Patent Document 1 discloses a control device that corrects the fuel injection amount of a fuel injection valve based on the detection value of an air-fuel ratio sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-220833 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the development of internal combustion engines that use hydrogen as fuel has been progressing. In such internal combustion engines, the accuracy of fuel injection amount correction based on the detection value of the air-fuel ratio sensor tends to be low, and the degree of change in NOx concentration in the exhaust gas relative to the change in the air-fuel ratio is relatively large. In other words, in internal combustion engines that use hydrogen as fuel, the effect of the exhaust gas properties on the change in the air-fuel ratio to the rich side is large. [Means for solving the problem]

[0005] An internal combustion engine control device for solving the above problem is applied to an internal combustion engine that uses hydrogen as fuel, and controls the fuel injection amount of a fuel injection valve provided in the internal combustion engine. The internal combustion engine control device includes a processing circuit. The processing circuit executes the following operations: calculating a basic value of the fuel injection amount based on a required torque that is a required value of engine torque, setting the smaller of the upper limit value of the fuel injection amount corresponding to an engine load factor and the basic value of the fuel injection amount as a target value of the fuel injection amount, operating the fuel injection valve based on the target value of the fuel injection amount, and correcting the relationship between the engine load factor and the upper limit value so that the upper limit value corresponding to the engine load factor becomes smaller when the difference between the NOx concentration in the exhaust gas and a reference value of the NOx concentration is equal to or greater than a concentration difference threshold value. Effect of the Invention

[0006] The above-described internal combustion engine control device has an effect of suppressing deterioration of exhaust properties. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic configuration diagram showing a control device which is one embodiment of an internal combustion engine control device, and an internal combustion engine to which the control device is applied. [Diagram 2] FIG. 2 is a block diagram showing a number of processes executed by the control device shown in FIG. [Diagram 3] FIG. 3 is a map showing the relationship between the engine load factor and the excess air ratio. [Figure 4] FIG. 4 is a flowchart showing the upper limit correction process shown in FIG. [Diagram 5] FIG. 5 is a timing chart during operation of the internal combustion engine shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, one embodiment of an internal combustion engine control device will be described with reference to Figs. 1 illustrates an internal combustion engine 10 mounted on a vehicle, a detection system 50 of the internal combustion engine 10, and a control device 60 applied to the internal combustion engine 10. The control device 60 corresponds to an "internal combustion engine control device."

[0009] <Internal combustion engine> The internal combustion engine 10 is a hydrogen engine that uses hydrogen as fuel. The internal combustion engine 10 includes a plurality of cylinders 11, an intake passage 12, a plurality of fuel injection valves 13, and an exhaust passage 14. Only one of the plurality of cylinders 11 is shown in FIG. 1. A piston 15 is housed in each of the plurality of cylinders 11. The plurality of pistons 15 are each connected to a crankshaft 17 via a connecting rod 16. The reciprocating motion of the pistons 15 in the plurality of cylinders 11 causes the crankshaft 17 to rotate.

[0010] The intake passage 12 is connected to the multiple cylinders 11. The intake passage 12 is a passage through which air flows to be introduced into the multiple cylinders 11. A throttle valve 18 that adjusts the amount of air introduced into the multiple cylinders 11 is provided in the intake passage 12.

[0011] The multiple fuel injection valves 13 each inject hydrogen to be supplied into the cylinder 11. In the example shown in Fig. 1, the fuel injection valve 13 is an in-cylinder injection valve that directly injects fuel into the cylinder 11. The internal combustion engine 10 may be equipped with a port injection valve as the fuel injection valve 13, which injects hydrogen into a portion of the intake passage 12 downstream of the throttle valve 18.

[0012] In each of the cylinders 11, a mixture containing air and hydrogen is burned by spark discharge from an ignition plug (not shown). This generates exhaust gas in each of the cylinders 11. The exhaust gas is discharged from the cylinders 11 into an exhaust passage 14. The exhaust gas flows through the exhaust passage 14.

[0013] The internal combustion engine 10 is equipped with an exhaust-driven supercharger 40. The supercharger 40 has a turbine 41 arranged in the exhaust passage 14 and a compressor 42 arranged in the intake passage 12. The turbine 41 is operated by the flow of exhaust gas flowing through the exhaust passage 14. The compressor 42 is arranged in the intake passage 12, upstream of the throttle valve 18. The compressor 42 pressurizes the air flowing through the intake passage 12 by operating in synchronization with the turbine 41.

[0014] <Detection system for internal combustion engines> The detection system 50 includes a plurality of sensors that output signals according to the detection results to the control device 60. The plurality of sensors include, for example, an accelerator opening sensor 51, a crank angle sensor 52, an air flow meter 53, and a NOx sensor 54. The accelerator opening sensor 51 detects the amount of accelerator pedal operation by the driver of the vehicle. The crank angle sensor 52 outputs a signal according to the rotation speed of the crankshaft 17. The air flow meter 53 detects the amount of air flowing through a portion of the intake passage 12 upstream of the compressor 42. The NOx sensor 54 detects the NOx concentration of exhaust gas flowing through the exhaust passage 14.

[0015] In this embodiment, the amount of accelerator pedal operation based on the detection signal of accelerator position sensor 51 is referred to as "accelerator position AC." The rotational speed of crankshaft 17 based on the detection signal of crank angle sensor 52 is referred to as "engine speed NE." The air flow rate based on the detection signal of air flow meter 53 is referred to as "intake air amount GA." The concentration of NOx in the exhaust gas based on the detection signal of NOx sensor 54 is referred to as "NOx concentration FN."

[0016] <Control device> The control device 60 includes a processing circuit 61. One example of the processing circuit 61 is an electronic control device. In this case, the processing circuit 61 includes a CPU 62, a first memory 63, and a second memory 64. The first memory 63 stores various control programs executed by the CPU 62. The second memory 64 stores the calculation results of the CPU 62. The CPU 62 executes the control program, and the processing circuit 61 controls the operation of the internal combustion engine 10 by adjusting the throttle opening SL, which is the opening of the throttle valve 18, and the fuel injection amount QF of the multiple fuel injection valves 13.

[0017] <Processing contents of the processing circuit> A number of processes executed by the processing circuit 61 will be described with reference to FIGS. 2, the CPU 62 executes a control program, whereby the processing circuit 61 executes a plurality of processes for controlling the operation of the internal combustion engine 10. The plurality of processes include a required torque calculation process M13, a target load factor calculation process M15, a throttle opening control process M17, an actual load factor calculation process M19, an upper limit value setting process M21, an injection amount determination process M23, an injector control process M27, and an upper limit value correction process M29.

[0018] In the required torque calculation process M13, the processing circuit 61 calculates the required torque TQR, which is a required value of the engine torque TQ. For example, the processing circuit 61 calculates the required torque TQR so that the value increases as the accelerator opening AC increases. The engine torque TQ is the output torque of the internal combustion engine 10.

[0019] In the target load ratio calculation process M15, the processing circuit 61 calculates a target load ratio KLTr, which is a target value of the engine load ratio. The engine load ratio is the load ratio of the internal combustion engine 10. The engine load ratio represents the ratio of the current amount of air flowing into the cylinders to the amount of air flowing into the cylinders when the internal combustion engine 10 is steadily operated in a full load state. The amount of air flowing into the cylinders is the amount of air flowing into each cylinder 11 during the intake stroke.

[0020] For example, in the target load ratio calculation process M15, the processing circuit 61 calculates the target load ratio KLTr based on the engine speed NE and the required torque TQR. At this time, the processing circuit 61 may calculate the target load ratio KLTr so that the higher the engine speed NE, the larger the target load ratio KLTr. Also, the processing circuit 61 may calculate the target load ratio KLTr so that the higher the required torque TQR, the larger the target load ratio KLTr.

[0021] In the throttle opening control process M17, the processing circuit 61 calculates a throttle opening command value, which is a command value for the throttle opening SL. For example, the processing circuit 61 calculates a throttle opening command value that increases as the target load factor KLTr increases. Then, the processing circuit 61 operates the throttle valve 18 so that the throttle opening SL becomes the throttle opening command value.

[0022] The processing circuit 61 calculates the engine load factor KL in an actual load factor calculation process M19. The processing circuit 61 calculates the engine load factor KL based on the engine speed NE and the intake air amount GA. For example, the processing circuit 61 calculates the engine load factor KL so that the value increases as the engine speed NE increases. Also, for example, the processing circuit 61 calculates the engine load factor KL so that the value increases as the intake air amount GA increases.

[0023] In an upper limit value setting process M21, the processing circuit 61 sets an upper limit value QFL of the fuel injection amount. The processing circuit 61 sets the upper limit value QFL based on the engine load factor KL. 3 shows an example of a map that is referred to when setting the upper limit value QFL. This map shows the relationship between the engine load ratio KL and the excess air ratio λ. The excess air ratio λ is equal to a value obtained by dividing the air-fuel ratio by the stoichiometric air-fuel ratio. When the air-fuel ratio coincides with the stoichiometric air-fuel ratio, the excess air ratio λ is 1. When the excess air ratio λ is greater than 1, this indicates that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio.

[0024] The processing circuit 61 obtains the excess air ratio λ corresponding to the current engine load ratio KL from the map. Then, the processing circuit 61 calculates the upper limit value QFL based on the intake air amount GA and the excess air ratio λ. For example, the processing circuit 61 calculates the fuel injection amount that makes the actual excess air ratio equal to the excess air ratio λ based on the intake air amount GA. The fuel injection amount that is the result of this calculation is the upper limit value QFL.

[0025] The processing circuit 61 determines a target injection amount QFTr, which is a target of the fuel injection amount QF, in an injection amount determination process M23. The injection amount determination process M23 includes a basic injection amount calculation process M24 and a target injection amount calculation process M25.

[0026] In a base injection amount calculation process M24, the processing circuit 61 calculates a base injection amount QFB that is a base value of the fuel injection amount QF. The processing circuit 61 calculates the base injection amount QFB so that the base injection amount QFB increases as the required torque TQR increases.

[0027] The processing circuit 61 calculates the target injection amount QFTr in a target injection amount calculation process M25. The processing circuit 61 sets the smaller one of the base injection amount QFB and the upper limit value QFL as the target injection amount QFTr.

[0028] In the injector control process M27, the processing circuit 61 controls the plurality of fuel injectors 13 based on the target injection amount QFTr. The processing circuit 61 extends the energization time of the solenoid of the fuel injector 13 as the target injection amount QFTr increases.

[0029] The processing circuit 61 changes the upper limit value QFL in the upper limit value correction processing M29. Specifically, the processing circuit 61 changes the map shown in Fig. 3, that is, the relationship between the engine load factor KL and the excess air factor λ.

[0030] The upper limit correction process M29 will be described with reference to Fig. 4. The processing circuit 61 repeatedly executes the upper limit correction process M29 for each predetermined cycle. In step S11, the processing circuit 61 acquires the NOx concentration FN.

[0031] In the next step S13, the processing circuit 61 acquires a reference concentration FNB, which is a reference value of the NOx concentration. The reference concentration FNB is a NOx concentration set based on the specifications of the internal combustion engine 10. A value at which it is possible to determine that the exhaust properties of the internal combustion engine 10 have deteriorated based on the deviation between the reference concentration FNB and the NOx concentration FN is set as the reference concentration FNB. Note that the reference concentration FNB changes depending on the engine load ratio KL. Therefore, the processing circuit 61 acquires the reference concentration FNB according to the current engine load ratio KL.

[0032] In the next step S15, the processing circuit 61 judges whether or not the concentration difference ΔFN, which is the value obtained by subtracting the reference concentration FNB from the NOx concentration FN, is equal to or greater than the concentration difference threshold ΔFNth. The concentration difference threshold ΔFNth is set as a criterion for judging whether or not the map needs to be changed. If the concentration difference ΔFN is equal to or greater than the concentration difference threshold ΔFNth, it is considered that the exhaust properties have deteriorated and that it is better to change the map. If the concentration difference ΔFN is less than the concentration difference threshold ΔFNth, it is considered that it is not necessary to change the map. If the concentration difference ΔFN is equal to or greater than the concentration difference threshold ΔFNth (S15: YES), the processing circuit 61 shifts the processing to step S17. On the other hand, if the concentration difference ΔFN is less than the concentration difference threshold ΔFNth (S15: NO), the processing circuit 61 does not change the map and temporarily ends the upper limit correction processing M29.

[0033] In step S17, the processing circuit 61 judges whether the duration of the state in which the concentration difference ΔFN is equal to or greater than the concentration difference threshold ΔFNth is equal to or greater than a predetermined time. As the predetermined time, a criterion for judging whether the reference concentration FNB and the NOx concentration FN actually diverge is set. If the above-mentioned duration is equal to or greater than the predetermined time, it is assumed that the reference concentration FNB and the NOx concentration FN actually diverge. On the other hand, if the above-mentioned duration is less than the predetermined time, it is assumed that there is a possibility that the deviation between the reference concentration FNB and the NOx concentration FN does not actually occur. If the processing circuit 61 judges that the above-mentioned duration is equal to or greater than the predetermined time (S17: YES), it shifts the processing to step S19. On the other hand, if the processing circuit 61 judges that the above-mentioned duration is less than the predetermined time (S17: NO), it temporarily ends the upper limit correction processing M29 without changing the map.

[0034] In step S19, the processing circuit 61 updates the correction coefficient α, which is a coefficient for correcting the map. For example, the processing circuit 61 calculates the sum of the correction coefficient α and the offset value Δα as the latest value of the correction coefficient α.

[0035] In the next step S21, the processing circuit 61 corrects the map by using the correction coefficient α. Specifically, the processing circuit 61 shifts the line indicating the map in the graph shown in Fig. 3 in a direction to increase the excess air ratio λ. For example, in Fig. 3, the line L1 indicating the map set based on the specifications of the internal combustion engine 10 is shown by a solid line. In this case, as shown by the arrow in Fig. 3, the processing circuit 61 shifts the line L1 indicating the map by the correction coefficient α in a direction to increase the excess air ratio λ. After correcting the map in this way, the processing circuit 61 temporarily ends the upper limit correction process M29.

[0036] <Actions and Effects of the Present Embodiment> The operation of this embodiment will be described with reference to FIG. 5. FIG. 5(A) shows the transition of engine torque TQ. FIG. 5(B) shows the transition of target load factor KLTr, while the dashed line shows the transition of engine load factor KL. FIG. 5(C) shows the transition of basic injection amount QFB, while the solid line shows the transition of target injection amount QFTr. FIG. 5(D) shows the transition of target excess air factor λTr, which is the target of excess air factor λ, and the solid line shows the transition of actual excess air factor λS, which is the actual value of excess air factor λ, and further the two-dot chain line shows the transition of excess air factor λa in the comparative example. FIG. 5(E) shows the transition of NOx concentration FN, while the two-dot chain line shows the transition of NOx concentration FNa in the comparative example.

[0037] The comparative example is a case in which the target injection amount QFTr is set without setting the upper limit value QFL. At timing T11 during steady operation, the engine torque TQ starts to increase. This causes the engine load factor KL to increase. When the engine load factor KL increases, the target injection amount QFTr increases.

[0038] When the engine load ratio KL becomes high in this manner, the supercharging pressure by the supercharger 40 starts to rise. However, as shown after timing T12, a deviation occurs between the target load ratio KLTr and the actual engine load ratio KL due to a response delay of the supercharging pressure of the supercharger 40.

[0039] Here, when the upper limit value QFL is not set as in the comparative example, the basic injection amount QFB is set as the target injection amount QFTr. The basic injection amount QFB is a fuel injection amount based on the required torque TQR. Therefore, the fuel injection amount QF becomes excessive with respect to the intake air amount GA. As a result, the excess air ratio λa changes to the rich side as shown by the two-dot chain line in FIG. 5(D). In other words, the air-fuel ratio changes to the rich side. When the excess air ratio λa changes to the rich side, the NOx concentration FNa in the exhaust gas suddenly increases as shown by the two-dot chain line in FIG. 5(E).

[0040] In contrast, in this embodiment, an upper limit value QFL is set. Therefore, when the basic injection amount QFB exceeds the upper limit value QFL, the upper limit value QFL is set as the target injection amount QFTr. Therefore, as shown in FIG. 5(D), the actual excess air ratio λS is suppressed from changing to the rich side. In other words, the deviation between the target excess air ratio λTr and the actual excess air ratio λS is less likely to occur. As a result, as shown in FIG. 5(E), an increase in the NOx concentration FNa in the exhaust gas is suppressed. In other words, the control device 60 can suppress the deterioration of the exhaust properties.

[0041] In this embodiment, the following effects can be further obtained. (1) Even if the upper limit value QFL is set, deterioration of the exhaust properties may not be sufficiently suppressed due to aging of the characteristics of the internal combustion engine 10. When the concentration difference ΔFN is equal to or greater than the concentration difference threshold value ΔFNth, the control device 60 corrects the relationship between the engine load factor KL and the upper limit value QFL so that the upper limit value QFL corresponding to the engine load factor KL becomes smaller. In this embodiment, the map shown in FIG. 3 is corrected.

[0042] The upper limit value QFL is set using the map corrected in this manner. Then, the target injection amount QFTr is set so as not to exceed the upper limit value QFL. Therefore, even if the characteristics of the internal combustion engine 10 change over time, the control device 60 can suppress deterioration of the exhaust properties.

[0043] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.

[0044] In the above embodiment, the offset value Δα used to update the correction coefficient α is a constant value regardless of the magnitude of the density difference ΔFN, but this is not limited to this. For example, the offset value Δα may be set to a larger value as the density difference ΔFN increases.

[0045] The internal combustion engine to which the control device 60 is applied does not have to be equipped with the turbocharger 40. The processing circuit 61 is not limited to a circuit having a CPU and a ROM and executing software processing. In other words, the processing circuit 61 may have any one of the following configurations (a), (b), and (c).

[0046] (a) The processing circuit 61 includes one or more processors that execute various processes according to a computer program. The processor includes a CPU and memory such as RAM and ROM. The memory stores program codes or instructions configured to cause the CPU to execute processes. The memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or special-purpose computer.

[0047] (b) The processing circuit 61 includes one or more dedicated hardware circuits for executing various processes. Examples of the dedicated hardware circuits include application specific integrated circuits, i.e., ASIC and FPGA. ASIC is an abbreviation for "Application Specific Integrated Circuit" and FPGA is an abbreviation for "Field Programmable Gate Array."

[0048] (c) The processing circuitry 61 includes a processor that executes some of the various processes in accordance with a computer program, and a dedicated hardware circuit that executes the remaining processes among the various processes. [Explanation of symbols]

[0049] 10... internal combustion engine, 13... fuel injector, 40... turbocharger, 60... control device, 61... processing circuit, 62... CPU, 63... first memory, 64... second memory.

Claims

1. An internal combustion engine control device that is applied to an internal combustion engine that uses hydrogen as fuel and controls a fuel injection amount of a fuel injection valve provided in the internal combustion engine, A processing circuit is provided, The processing circuitry includes: calculating a base value of the fuel injection amount based on a required torque which is a required value of an engine torque; setting the smaller one of an upper limit value of the fuel injection amount corresponding to an engine load factor and a basic value of the fuel injection amount as a target value of the fuel injection amount; activating the fuel injection valve based on the target value of the fuel injection amount; When the difference between the NOx concentration in the exhaust gas and the reference value of the NOx concentration is equal to or greater than the concentration difference threshold, the relationship between the engine load factor and the upper limit value is corrected so that the upper limit value corresponding to the engine load factor becomes smaller. Internal combustion engine control device.

2. The internal combustion engine is equipped with a supercharger, The processing circuit operates the fuel injection valve based on the target value of the fuel injection amount. The internal combustion engine control device according to claim 1.

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