Hydrogen engine control system

Abstract

This suppresses both the occurrence of torque shock and the increase in NOx emissions when switching between stoichiometric and lean combustion. [Solution] The processing circuit 22 of the electronic control unit 21 that controls the hydrogen engine 10 is configured to inject the amount of fuel necessary to generate engine torque according to the required torque as the main injection during the air amount adjustment period for switching between stoichiometric combustion and lean combustion, and to inject the amount of fuel as the post injection such that the total injection amount of the main injection and the post injection is the amount obtained by dividing the actual air amount by the stoichiometric air-fuel ratio.

Description

Technical Field

[0001] The present invention relates to a control device for a hydrogen engine.

Background Art

[0002] Patent Document 1 describes that in a hydrogen engine that burns hydrogen to generate power, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber is changed according to the operating conditions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the hydrogen engine as described above, in order to suppress the emission of NOx (nitrogen oxides), it may be required to temporarily change the air-fuel ratio greatly. However, when the air-fuel ratio is suddenly changed, torque shock occurs, resulting in deteriorated drivability.

Means for Solving the Problems

[0005] The control device for a hydrogen engine that solves the above problems is a control device applied to a hydrogen engine that uses hydrogen as fuel, and includes a process for calculating the required torque, which is the required value of the engine torque; a process for switching between lean combustion, in which the air-fuel ratio of the mixture burned in the combustion chamber is leaner than the stoichiometric air-fuel ratio, and stoichiometric combustion, in which the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio; a process for adjusting the amount of air in the mixture from the amount required for combustion before switching to the amount required for combustion after switching, when switching between stoichiometric combustion and lean combustion is required; and the stoichiometric combustion and The system includes a processing circuit that performs the following steps during the period from when a switch to lean combustion is requested until the adjustment of the amount of air is completed: a process of dividing fuel injection into a main injection during the period from the intake stroke to the compression stroke and a post injection during the period from the expansion stroke to the exhaust stroke; a process of calculating the amount of fuel injection necessary to generate engine torque according to the requested torque as the amount of fuel injection for the main injection; and a process of calculating the amount of fuel injection for the post injection so that the total amount of injection for the main injection and the post injection is equal to or greater than the value obtained by dividing the actual amount of air in the combustion chamber by the stoichiometric air-fuel ratio. [Effects of the Invention]

[0006] The control device for the hydrogen engine described above has the effect of suppressing both the occurrence of torque shock and the increase in NOx emissions when switching between stoichiometric and lean combustion. [Brief explanation of the drawing]

[0007] [Figure 1] This diagram schematically shows the configuration of one embodiment of a control device for a hydrogen engine. [Figure 2] Figure 1 is a flowchart of the combustion switching routine executed by the control device. [Figure 3]Figure 2 is a time chart showing the changes in combustion requirements, target air volume and actual air volume, fuel injection volume, fuel mixture and exhaust air excess ratio, engine torque, and ignition timing when switching from lean combustion to stoichiometric combustion without performing the combustion switching routine. (a) shows the changes in combustion requirements, (b) shows the changes in target air volume and actual air volume, (c) shows the changes in fuel injection volume, (d) shows the changes in air excess ratio of the air mixture and exhaust, (e) shows the changes in engine torque, and (f) shows the changes in ignition timing. [Figure 4] Figure 1 shows a time chart illustrating the changes in combustion requirements, target air volume and actual air volume, fuel injection volume, fuel mixture and exhaust air ratio, engine torque, and ignition timing when switching from stoichiometric to lean combustion in the control device. (a) shows the changes in combustion requirements, (b) shows the changes in target air volume and actual air volume, (c) shows the changes in fuel injection volume, (d) shows the changes in air mixture and exhaust air ratio, (e) shows the changes in engine torque, and (f) shows the changes in ignition timing. [Figure 5] Figure 1 shows a time chart illustrating the changes in combustion requirements, target air volume and actual air volume, fuel injection volume, fuel mixture and exhaust air ratio, engine torque, and ignition timing when switching from lean combustion to stoichiometric combustion in the control device. (a) shows the changes in combustion requirements, (b) shows the changes in target air volume and actual air volume, (c) shows the changes in fuel injection volume, (d) shows the changes in air mixture and exhaust air ratio, (e) shows the changes in engine torque, and (f) shows the changes in ignition timing. [Modes for carrying out the invention]

[0008] Hereinafter, with reference to Figures 1 to 5, one embodiment of the control device for a hydrogen engine will be described in detail. <Configuration of hydrogen engine 10 and its control device> First, the configuration of this embodiment will be described with reference to Figure 1. The hydrogen engine 10 shown in Figure 1 is mounted on a vehicle.

[0009] The hydrogen engine 10 comprises a combustion chamber 11 for burning a fuel-air mixture, an intake passage 12 which is the path for introducing air into the combustion chamber 11, and an exhaust passage 13 which is the path for discharging exhaust gas from the combustion chamber 11. The intake passage 12 is equipped with an air cleaner 14, an air flow meter 15, and a throttle valve 16. The air cleaner 14 is a filtration device that filters out dust and other particles from the air. The air flow meter 15 is a detector that detects the flow rate of air in the intake passage 12. The throttle valve 16 is a valve that adjusts the flow rate of air by changing the flow area of ​​the air in the intake passage 12. The combustion chamber 11 is equipped with an injector 17 that injects hydrogen into the air introduced into the combustion chamber 11 through the intake passage 12. The combustion chamber 11 is also equipped with an ignition device 18 that ignites the fuel-air mixture by spark discharge. The exhaust passage 13 is equipped with an air-fuel ratio sensor 19 for detecting the air-fuel ratio of the fuel-air mixture burned in the combustion chamber 11. Furthermore, a three-way catalytic converter 20, which supports a three-way catalytic converter, is installed in the portion of the exhaust passage 13 downstream of the air-fuel ratio sensor 19.

[0010] The hydrogen engine 10, configured as described above, is controlled by an electronic control unit 21. The electronic control unit 21 includes a processing circuit 22 and a memory device 23. The memory device 23 pre-stores programs and data used to control the hydrogen engine 10. In this embodiment, the electronic control unit 21 corresponds to the control device of the hydrogen engine 10.

[0011] The electronic control unit 21 receives detection signals from the airflow meter 15 and the air-fuel ratio sensor 19. The electronic control unit 21 also receives detection signals from the crank angle sensor 24 and the accelerator pedal sensor 26. The crank angle sensor 24 detects the rotation angle of the crankshaft 25, which is the output shaft of the hydrogen engine 10. The accelerator pedal sensor 26 detects the amount the accelerator pedal 27 is depressed. Based on the detection results from these sensors, the electronic control unit 21 determines the control parameters for the hydrogen engine 10. These parameters include the opening of the throttle valve 16, the amount and timing of hydrogen injection from the injector 17, and the ignition timing of the fuel-air mixture from the ignition device 18. The electronic control unit 21 then controls the hydrogen engine 10 by operating the throttle valve 16, the injector 17, and the ignition device 18 according to the determined control parameters. The control of the hydrogen engine 10 by the electronic control unit 21 is performed by various processes executed by the processing circuit 22. The processing circuit 22 performs various processes by executing a program read from the storage device 23.

[0012] Furthermore, the processing circuit 22 determines the engine speed NE, which is the rotational speed of the crankshaft 25, based on the detection result of the crank angle sensor 24. The processing circuit 22 also determines the amount of air that fills the combustion chamber 11, that is, the amount of air in the fuel-air mixture that burns in the combustion chamber 11, based on the detection result of the airflow meter 15, the opening degree of the throttle valve 16, the engine speed NE, etc.

[0013] <Relationship between air-fuel ratio and NOx emissions in hydrogen engine 10> In the case of a hydrogen engine 10 installed in a vehicle, it is required to keep the amount of NOx (nitrogen oxides) emitted into the outside air within an acceptable range. When the combustion temperature is high, the amount of NOx produced by the combustion of the air-fuel mixture in the combustion chamber 11 is greater than when the combustion temperature is low. If combustion is performed with an air-fuel ratio leaner than a certain point, the combustion temperature decreases and the amount of NOx produced decreases. Furthermore, when combustion is performed with a lean air-fuel ratio, the fuel consumption of the hydrogen engine 10 is suppressed due to the reduction of heat loss, etc. Therefore, in order to suppress both fuel consumption and NOx emissions, it is desirable to make the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 11 of the hydrogen engine 10 leaner, within a range that does not worsen combustion.

[0014] However, lean combustion may not be possible in all operating ranges of the hydrogen engine 10. The reason for this is as follows: There is a limit to the amount of air that can be filled into the combustion chamber 11. Therefore, during high-load operation where a large amount of fuel is burned, it may not be possible to fill the combustion chamber 11 with the amount of air necessary for lean combustion.

[0015] In contrast, a three-way catalytic converter 20, which supports a three-way catalytic converter, is installed in the exhaust passage 13 of the hydrogen engine 10. The three-way catalytic converter 20 has the ability to purify NOx in the exhaust. The three-way catalytic converter 20 exhibits a high NOx purification capacity when combustion is performed at the stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio. Therefore, when combustion is performed at the stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio, the three-way catalytic converter 20 purifies NOx, thereby suppressing the emission of NOx into the outside air. In the following explanation, combustion at the stoichiometric air-fuel ratio will be referred to as stoichiometric combustion, and combustion at an air-fuel ratio leaner than the stoichiometric air-fuel ratio will be referred to as lean combustion. The processing circuit 22 controls the air-fuel ratio of the mixture burned in the combustion chamber 11 of the hydrogen engine 10 so that stoichiometric combustion is performed in the high-load operating range and lean combustion is performed in other operating ranges in order to suppress NOx emissions.

[0016] <Air-fuel ratio control of hydrogen engine 10> Next, we will explain the air-fuel ratio control of the hydrogen engine 10 performed by the processing circuit 22. During air-fuel ratio control, the processing circuit 22 first calculates a required torque TE* based on the detection result of the accelerator pedal sensor 26. The required torque TE* represents the engine torque necessary to satisfy the driving force of the vehicle required by the driver through depressing the accelerator pedal 27.

[0017] Next, the processing circuit 22 sets a target air-fuel ratio, which is the target value of the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber 11, based on the required torque TE* and the engine rotational speed NE. For example, the processing circuit 22 sets the stoichiometric air-fuel ratio in the high load / high rotation operation range, and sets an air-fuel ratio on the lean side of the stoichiometric air-fuel ratio in other operation ranges as the value of the target air-fuel ratio. In the following description, the operation range where the stoichiometric air-fuel ratio is set as the target air-fuel ratio is referred to as the stoichiometric combustion range, and the operation range where an air-fuel ratio on the lean side of the stoichiometric air-fuel ratio is set as the target air-fuel ratio is referred to as the lean combustion range.

[0018] Subsequently, the processing circuit 22 calculates the value of the target air amount M* as the air amount necessary to generate an engine torque corresponding to the required torque TE* with the air-fuel ratio being the target air-fuel ratio. Then, the processing circuit 22 operates the opening degree of the throttle valve 16 so that the actual air amount M, which is the actual air amount filled in the combustion chamber 11, becomes equal to the target air amount M*. Further, the processing circuit 22 calculates the fuel injection amount at which an air-fuel ratio corresponding to the target air-fuel ratio can be obtained with respect to the actual air amount M. Then, the processing circuit 22 operates the injector 17 to inject fuel corresponding to the calculated fuel injection amount. Furthermore, the processing circuit 22 sets the ignition timing based on the required torque TE* and the engine rotational speed NE. Then, the processing circuit 22 operates the ignition device 18 to perform ignition at the set ignition timing.

[0019] 〈Combustion Switching Routine〉 When the operating point of the hydrogen engine 10 changes across the boundary between the stoichiometric combustion region and the lean combustion region, the combustion of the hydrogen engine 10 is switched between stoichiometric combustion and lean combustion. At the boundary between the stoichiometric combustion region and the lean combustion region, the target air-fuel ratio changes discontinuously. Therefore, when switching between stoichiometric combustion and lean combustion, it is necessary to significantly change the amount of air filled into the combustion chamber 11. The processing circuit 22 performs processing for performing such combustion switching while suppressing both torque shock and NOx emissions.

[0020] Hereinafter, referring to FIGS. 2 to 5, the details of the processing performed by the processing circuit 22 when switching between stoichiometric combustion and lean combustion will be described. FIG. 2 shows a flowchart of a combustion switching routine executed by the processing circuit 22 for the processing at the time of combustion switching. When either a switch from stoichiometric combustion to lean combustion or a switch from lean combustion to stoichiometric combustion is requested, the processing circuit 22 starts the processing of this routine.

[0021] When starting this routine, the processing circuit 22 first switches the target air amount M* from the value corresponding to the combustion before switching to the value corresponding to the combustion after switching in step S100. Subsequently, the processing circuit 22 calculates the total injection amount Q based on the actual air amount M in step S110. The processing circuit 22 calculates the amount at which the air-fuel ratio of the air-fuel mixture becomes the theoretical air-fuel ratio when fuel corresponding to the total injection amount Q is injected as the value of the total injection amount Q. In the case of this embodiment, the processing circuit 22 divides the actual air amount M by the theoretical air-fuel ratio and calculates the divided value as the value of the total injection amount Q.

[0022] Next, the processing circuit 22 calculates the main injection amount Qm based on the required torque TE* and the actual air amount M. Specifically, the processing circuit 22 calculates the amount of fuel injection necessary to generate engine torque corresponding to the required torque TE* in relation to the actual air amount M as the value of the main injection amount Qm. Furthermore, in the following step S130, the processing circuit 22 subtracts the main injection amount Qm from the total injection amount Q and calculates the subtracted value as the value of the post-injection amount Qp. Then, in step S140, the processing circuit 22 commands the injector 17 to perform a main injection of an amount equivalent to the main injection amount Qm and a post-injection of an amount equivalent to the post-injection amount Qp. The main injection is fuel injection performed during the period from the intake stroke to the compression stroke. The post-injection is fuel injection performed during the period from the expansion stroke to the exhaust stroke. The fuel injected in the main injection is burned in the combustion chamber 11 to generate engine torque. In contrast, the post-injection is performed from the end of combustion in the combustion chamber 11 to after it has finished. Therefore, post-injection is a type of fuel injection that contributes very little to the generation of engine torque.

[0023] Subsequently, in step S150, the processing circuit 22 determines whether the adjustment of the air quantity from the amount required for combustion before switching to the amount required for combustion after switching has been completed. In this embodiment, the processing circuit 22 determines that the adjustment of the air quantity is complete when the actual air quantity M converges to the target air quantity M*. If the processing circuit 22 determines that the adjustment of the air quantity is complete (S150: YES), it terminates the processing of this routine for this combustion switching. On the other hand, if the processing circuit 22 determines that the adjustment of the air quantity is not complete (S150: NO), it repeats the processing from step S110 to step S150 after a predetermined control cycle.

[0024] <Effect of the Embodiment> During operation of the hydrogen engine 10, the processing circuit 22 of the electronic control unit 21 calculates the required torque TE*, which is the required value of engine torque to be generated by the hydrogen engine 10. Based on the required torque TE*, the processing circuit 22 also switches the combustion of the air-fuel mixture in the combustion chamber 11 between lean combustion and stoichiometric combustion. Lean combustion is combustion in which the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 11 is leaner than the stoichiometric air-fuel ratio. Stoichiometric combustion is combustion in which the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 11 is the stoichiometric air-fuel ratio. In stoichiometric combustion, NOx emissions are suppressed by burning at a stoichiometric air-fuel ratio in which the three-way catalytic converter 20 can effectively purify the NOx generated by combustion. In lean combustion, NOx emissions are suppressed by burning at a lean air-fuel ratio in which the combustion temperature is lower and NOx generation is suppressed.

[0025] In stoichiometric combustion and lean combustion, the air-fuel ratio of the mixture burned in the combustion chamber 11 is significantly different, and the amount of air required for each type of combustion is also significantly different. When a switch between stoichiometric and lean combustion is required, the processing circuit 22 adjusts the amount of air in the mixture from the amount required for the combustion before the switch to the amount required for the combustion after the switch.

[0026] Furthermore, in this embodiment, the processing circuit 22 performs the combustion switching routine shown in Figure 2 for processing during combustion switching. Here, we will first explain the case where lean combustion and stoichiometric combustion are switched without performing the routine.

[0027] Figure 3 shows the control behavior of the hydrogen engine 10 when switching from stoichiometric combustion to lean combustion without performing a combustion switching routine. Figure 3(a) shows the changes in combustion demand, Figure 3(b) shows the changes in target air amount M* and actual air amount M, and Figure 3(c) shows the changes in fuel injection amount. Figure 3(d) shows the changes in the air-fuel ratio of the air-fuel mixture, Figure 3(e) shows the changes in engine torque, and Figure 3(f) shows the changes in ignition timing. The combustion demand indicates whether the combustion of the hydrogen engine 10 requested by the processing circuit 22 is stoichiometric combustion or lean combustion. The air-fuel ratio represents the ratio of the air-fuel ratio to the stoichiometric air-fuel ratio. In Figure 3 and Figures 4 and 5 described later, the demanded torque TE* and engine rotational speed NE are kept constant during the period shown in the figures.

[0028] In Figure 3, at time t1, a switch from stoichiometric combustion to lean combustion is required. Accordingly, the processing circuit 22 changes the value of the target air amount M* from the value for stoichiometric combustion to the value for lean combustion. Then, the processing circuit 22 starts adjusting the air amount from this time t1. There is a large difference in the target air-fuel ratio between stoichiometric and lean combustion, requiring a significant adjustment of the air amount. In Figure 3, the adjustment of the air amount is completed at the subsequent time t2.

[0029] Here, we consider controlling the fuel injection amount during the air volume adjustment period from time t1 to time t2 so as to generate engine torque corresponding to the required torque TE*. Figures 3(c) to (e) show the changes in fuel injection amount, air excess ratio, and engine torque in this case, respectively, as solid lines. In Figure 3, since the required torque TE* is constant, the engine torque in this case is maintained at a constant level. On the other hand, as the air-fuel ratio is changed from the stoichiometric air-fuel ratio towards the lean side, combustion efficiency improves. Therefore, the amount of fuel injection required to generate engine torque corresponding to the required torque TE* decreases as the actual air volume M increases. The air-fuel ratio of the mixture burned in the combustion chamber 11 changes towards the lean side as the actual air volume M increases. Thus, as the actual air volume M increases, the air excess ratio of the mixture also increases.

[0030] As described above, the three-way catalytic converter 20 effectively purifies NOx in the exhaust gas when combustion is performed near the stoichiometric air-fuel ratio. On the other hand, as the air-fuel ratio of the mixture burning in the combustion chamber 11 is changed from the stoichiometric air-fuel ratio to a leaner state, the amount of NOx generated by combustion gradually decreases. When the air-fuel ratio becomes leaner than a certain point, the amount of NOx emissions decreases to an acceptable range. The value of the excess air ratio "LM" shown in Figure 3(d) indicates the value of the excess air ratio when the air-fuel ratio is leaned to an acceptable range for NOx emissions. Therefore, when the excess air ratio of the mixture burning in the combustion chamber 11 is in the range near "1" or in the range of "LM" or higher, the emission of NOx into the outside air can be suppressed. Conversely, Figure 3(d) shows, in hatched areas, the range of excess air ratio values ​​for which NOx emissions cannot be sufficiently suppressed. As shown by the solid line in Figure 3(d), when the fuel injection amount is controlled to generate engine torque corresponding to the required torque TE*, the value of the excess air ratio changes through the range of values ​​indicated by the hatching. Therefore, in this case, there is a possibility that NOx exceeding the acceptable amount will be discharged into the outside air when the combustion switches.

[0031] The increase in NOx emissions during such combustion switching can be suppressed by controlling the fuel injection amount to maintain the air-fuel ratio of the mixture burning in the combustion chamber 11 at the stoichiometric air-fuel ratio until the air volume adjustment is complete. Figures 3(c) and 3(d) show the changes in fuel injection amount and air excess ratio in this case, respectively, as indicated by dashed lines. As shown by the dashed line in Figure 3(d), in this case, during the air volume adjustment period from time t1 to time t2, the air excess ratio of the mixture is "1", i.e., combustion is performed at the stoichiometric air-fuel ratio. Therefore, in such cases, it is possible to suppress the increase in NOx emissions during combustion switching. However, in this case, as shown by the dashed line in Figure 3(c), it is necessary to increase the fuel injection amount along with the increase in the actual air volume M. And, as shown by the dashed line in Figure 3(e), the engine torque increases along with the fuel injection amount. Therefore, in this case, excessive engine torque exceeding the required torque TE* is generated during combustion switching. Retarding the ignition timing reduces combustion efficiency and decreases engine torque. Therefore, as shown by the dashed line in Figure 3(f), it is conceivable to offset the excess engine torque by retarding the ignition timing. However, in the latter half of the air volume adjustment period, the excess engine torque becomes large, requiring a significant retardation of the ignition timing to offset it. As a result, combustion becomes unstable, which may cause torque shocks in the hydrogen engine 10 due to misfires, potentially worsening drivability.

[0032] The increase in NOx emissions and deterioration of drivability during combustion switching described above can also occur when switching from lean combustion to stoichiometric combustion. In response to this, the processing circuit 22 performs main injection and post injection during the period from when a combustion switching is requested until the adjustment of the air volume is completed (S140) in the combustion switching routine shown in Figure 2. In addition, in the combustion switching routine, the processing circuit 22 calculates the amount of fuel injection required to generate engine torque according to the requested torque TE* as the value of the main injection amount Qm (S120). Furthermore, in the combustion switching routine, the processing circuit 22 calculates the value of the post injection amount Qp so that the total injection amount Q of the main injection and post injection becomes the value obtained by dividing the actual amount of air M in the combustion chamber 11 by the stoichiometric air-fuel ratio (S110, S130).

[0033] Figure 4 shows the control behavior of the hydrogen engine 10 when a combustion switching routine is performed to switch from stoichiometric combustion to lean combustion. Figure 4(a) shows the changes in combustion demand, Figure 4(b) shows the changes in target air amount M* and actual air amount M, and Figure 4(c) shows the changes in total injection amount Q and main injection amount Qm. Furthermore, Figure 4(d) shows the changes in the air surplus ratios λm and λe of the air-fuel mixture and exhaust, Figure 4(e) shows the changes in engine torque, and Figure 4(f) shows the changes in ignition timing. The air surplus ratio λm of the air-fuel mixture represents the air surplus ratio of the air-fuel mixture relative to the fuel that contributes to the generation of engine torque. Specifically, the air surplus ratio λm of the air-fuel mixture represents the value obtained by dividing the actual air amount M by the main injection amount Qm (=M / Qm), and then dividing that by the stoichiometric air-fuel ratio. On the other hand, the air surplus ratio λe of the exhaust represents the air surplus ratio relative to the total amount of fuel injected into the combustion chamber 11. Specifically, the exhaust air excess ratio λe represents the value obtained by dividing the actual air volume M by the total injection volume Q (=M / Q) and then further dividing that by the stoichiometric air-fuel ratio.

[0034] In the case of Figure 4, a switch from stoichiometric combustion to lean combustion is required at time t1. During the period from time t1 to time t2, the amount of air required for the combustion switch is adjusted.

[0035] In this embodiment, during the air volume adjustment period, the processing circuit 22 divides fuel injection into main injection and post injection. The difference between the total injection amount Q, shown by the solid line in Figure 4(c), and the main injection amount Qm, shown by the dashed line, corresponds to the post injection amount Qp. Since all fuel injection before and after the air volume adjustment is performed by main injection, the total injection amount Q for the period before time t1 and the period after time t2 is equal to the main injection amount Qm, and the post injection amount Qp is "0".

[0036] In the combustion switching routine shown in Figure 2, the processing circuit 22 calculates the amount of fuel required to generate engine torque corresponding to the required torque TE* in relation to the actual air amount M, using the main injection amount Qm as the value. In contrast, post-injection contributes almost nothing to the generation of engine torque. Therefore, in this embodiment, as shown in Figure 4(e), excessive engine torque exceeding the required torque TE* will not be generated even during the air amount adjustment period. Consequently, the generation of excessive engine torque can be suppressed without retarding the ignition timing.

[0037] On the other hand, the fuel injected in post-injection does not contribute to the generation of engine torque, but it is burned before it flows into the three-way catalytic converter 20. The processing circuit 22 then calculates the post-injection amount Qp so that the ratio of the total injection amount Q to the actual air amount M is equal to the stoichiometric air-fuel ratio. Therefore, the exhaust air excess ratio λe becomes "1", and the properties of the exhaust flowing into the three-way catalytic converter 20 are substantially the same as when combustion is performed at the stoichiometric air-fuel ratio. As a result, in this case, the three-way catalytic converter 20 exhibits the same high NOx purification capacity as during stoichiometric combustion, even during the air amount adjustment period.

[0038] Figure 5 shows the control behavior of the hydrogen engine 10 when a combustion switching routine is performed to switch from lean combustion to stoichiometric combustion. Figure 5(a) shows the changes in combustion demand, Figure 5(b) shows the changes in target air amount M* and actual air amount M, and Figure 5(c) shows the changes in total injection amount Q and main injection amount Qm. Figure 5(d) shows the changes in the air excess ratio λm and λe of the air-fuel mixture and exhaust, Figure 5(e) shows the changes in engine torque, and Figure 5(f) shows the changes in ignition timing.

[0039] In the case of Figure 5, a switch from lean combustion to stoichiometric combustion is required at time t3. During the period from time t3 to time t4, the amount of air for the combustion switch is adjusted. In this case as well, as in the case of Figure 4, during the air amount adjustment period, the amount of fuel injection necessary to generate engine torque according to the required torque TE* is performed as the main injection. Then, the amount of fuel injection necessary to bring the air-fuel ratio of the exhaust flowing into the three-way catalytic converter 20 to the stoichiometric air-fuel ratio is performed as a post-injection. Therefore, even when switching from lean combustion to stoichiometric combustion, an increase in NOx emissions and the generation of excessive engine torque are suppressed.

[0040] <Effects of the Embodiment> As described above, the control device for the hydrogen engine 10 of this embodiment has the effect of suppressing both the occurrence of torque shock and the increase in NOx emissions when switching between stoichiometric combustion and lean combustion.

[0041] <Other Embodiments> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0042] In step S110 of Figure 2, the total injection amount Q may be calculated so that it is equal to or greater than the value obtained by dividing the actual amount of air M in the combustion chamber 11 by the stoichiometric air-fuel ratio. In this case, the air-fuel ratio of the exhaust gas flowing into the three-way catalytic converter 20 during the air volume adjustment period will be richer than the stoichiometric air-fuel ratio. The three-way catalytic converter 20 can effectively purify NOx if the exhaust gas air-fuel ratio is equal to or richer than the stoichiometric air-fuel ratio. Therefore, even in this case, it is possible to suppress both the occurrence of torque shock and the increase in NOx emissions when switching between stoichiometric and lean combustion.

[0043] In the above embodiment, the post-injection amount Qp was calculated by first calculating the total injection amount Q and the main injection amount Qm, and then subtracting the main injection amount Qm from the total injection amount Q. If the total injection amount Q can be calculated to be equal to or greater than the value obtained by dividing the actual amount of air M in the combustion chamber 11 by the stoichiometric air-fuel ratio, then the post-injection amount Qp may be calculated by a different procedure. For example, the value of the post-injection amount Qp can also be calculated in the same way as in the above embodiment by the following procedure. That is, the main injection amount Qm is calculated using the same procedure as in the above embodiment, and the value "Mm" is calculated by multiplying the main injection amount Qm by the stoichiometric air-fuel ratio. Next, Mm is subtracted from the actual amount of air M, and the subtracted value is calculated as the value of the excess air amount Me. Then, the excess air amount Me is divided by the stoichiometric air-fuel ratio, and the divided value is calculated as the value of the post-injection amount Qp.

[0044] The combustion switching routine may be applied only when switching from lean combustion to stoichiometric combustion, or when switching from stoichiometric combustion to lean combustion. [Explanation of symbols]

[0045] 10 Hydrogen engine 11 Combustion chamber 12 Intake passage 13 Exhaust passage 14. Air cleaner 15. Airflow meter 16 Throttle valve 17 Injectors 18 Ignition system 19. Air-fuel ratio sensor 20 Three-way catalyst device 21 Electronic control unit 22 Processing Circuit 23 Storage device 24 Crank angle sensor 25 Crankshaft 26. Accelerator pedal sensor 27. Accelerator pedal

Claims

[Claim 1] A control device applied to a hydrogen engine that uses hydrogen as fuel, The process of calculating the required torque, which is the required value of the engine torque, A process for switching between lean combustion, in which the air-fuel ratio of the fuel mixture burned in the combustion chamber is leaner than the stoichiometric air-fuel ratio, and stoichiometric combustion, in which the air-fuel ratio of the fuel mixture is the stoichiometric air-fuel ratio. When a switch between the stoichiometric combustion and the lean combustion is required, the process of adjusting the amount of air in the mixture from the amount required for the combustion before the switch to the amount required for the combustion after the switch is performed. From the time when the switching between stoichiometric combustion and lean combustion is requested until the adjustment of the amount of air is completed, the fuel injection process is divided into a main injection during the period from the intake stroke to the compression stroke and a post injection during the period from the expansion stroke to the exhaust stroke. A process to calculate the amount of fuel injection required to generate engine torque corresponding to the requested torque as the amount of fuel injection for the main injection, A process for calculating the fuel injection amount for post-injection such that the total injection amount of the main injection and post-injection is equal to or greater than the value obtained by dividing the actual amount of air in the combustion chamber by the stoichiometric air-fuel ratio, It includes a processing circuit that performs the following actions. Control device for a hydrogen engine.

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