Controller for hydrogen engine

The ECM calculates a peak value of an in-cylinder pressure before ignition based on the operating state of the hydrogen engine. When the peak value of the in-cylinder pressure before ignition exceeds a threshold value, the ECM performs an advancement correction of the ignition timing such that the peak value becomes less than or equal to the threshold value.

The present disclosure relates to a controller for a hydrogen engine.

2. DESCRIPTION OF RELATED ART

Japanese Laid-Open Patent Publication No. 2012-167582 discloses a technique related to an operating gas circulation engine that uses hydrogen gas as fuel. In this technique, the valve timing or the like is controlled such that the peak value of the combustion pressure does not exceed the upper limit value to avoid a decrease in the thermal efficiency due to an excessive increase in the in-cylinder pressure and the in-cylinder temperature.

In a hydrogen engine that uses hydrogen gas as fuel, metal components around a combustion chamber may become brittle due to permeation of hydrogen.

SUMMARY

An aspect of the present disclosure provides a controller for a hydrogen engine that uses hydrogen gas as fuel. The controller includes a processor configured to calculate a peak value of an in-cylinder pressure before ignition based on an operating state of the hydrogen engine, and, when the peak value is greater than a threshold value, change a control content of the hydrogen engine such that the peak value becomes less than or equal to the threshold value.

DETAILED DESCRIPTION

This description provides a comprehensive understanding of the modes, apparatuses, and/or systems described. Modifications and equivalents of the modes, apparatuses, and/or systems described are apparent to one of ordinary skill in the art. Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted.

A controller for a hydrogen engine according to one embodiment will now be described with reference toFIGS.1to3.

Configuration of Hydrogen Engine

First, the configuration of a hydrogen engine10to which the controller of the present embodiment is applied will be described with reference toFIG.1. The hydrogen engine10is an engine that uses hydrogen gas as fuel and is mounted on a vehicle as a drive source that generates propulsion force.

The hydrogen engine10includes a cylinder11, a piston12, a connecting rod13, and a crankshaft14. The piston12is provided to reciprocate in the cylinder11. The piston12is coupled to a crankshaft14, which is an output shaft of the hydrogen engine10, via a connecting rod13. The connecting rod13and the crankshaft14form a link mechanism that converts reciprocation of the piston12into rotation of the crankshaft14.

Each cylinder11includes a combustion chamber15defined by an inner wall of the cylinder11and the piston12. An injector16and an ignition device17are installed in the combustion chamber15. The injector16injects hydrogen gas into the combustion chamber15. The ignition device17ignites the air-fuel mixture of hydrogen gas and intake air with spark discharge.

The combustion chamber15is connected to the intake passage19by an intake valve18. The intake passage19is a passage through which intake air is drawn into the combustion chamber15. Intake air flows into the combustion chamber15from the intake passage19as the intake valve18opens. The intake passage19is provided with a throttle valve20that changes the flow passage area of intake air. The hydrogen engine10also includes a variable valve timing mechanism21that varies the timing of opening and closing the intake valve18. In the following description, the variable valve timing mechanism21is referred to as a “VVT21”.

The combustion chamber15is connected to an exhaust passage23via an exhaust valve22. The exhaust passage23is a discharge passage for exhaust gas generated by combustion of the air-fuel mixture in the combustion chamber15. Exhaust gas in the combustion chamber15flows out to the exhaust passage23when the exhaust valve22opens.

Configuration of Controller

The configuration of a control device for the hydrogen engine10will now be described with reference toFIG.1. The controller of the present embodiment is configured as an engine control module30including a processor31and a memory32. The memory32stores programs and data used to control the hydrogen engine10in advance. The processor31reads programs from the memory32and executes the read programs. In the following description, the engine control module30is referred to as “the ECM30.”

The ECM30receives detection signals of various types of sensors that detect the operating state of the hydrogen engine10. Such sensors include an air flow meter33, a crank angle sensor34, an intake air temperature sensor35, an atmospheric pressure sensor36, an accelerator pedal sensor37, and a vehicle speed sensor38. The air flow meter33is a sensor that detects an intake air amount GA, which is the flow rate of intake air flowing through the intake passage19. The crank angle sensor34is a sensor that detects a crank angle, which is a rotational angle of the crankshaft14. The intake air temperature sensor35is a sensor that detects an intake air temperature THA, which is the temperature of intake air flowing through the intake passage19. The atmospheric pressure sensor36is a sensor that detects the atmospheric pressure PA. The accelerator pedal sensor37is a sensor that detects an accelerator pedal operation amount ACC, which is the operation amount of the accelerator pedal by the driver of the vehicle. The vehicle speed sensor38is a sensor that detects a vehicle speed SPD, which is the traveling speed of the vehicle. The ECM30calculates an engine rotation speed NE, which is the rotation speed of the crankshaft14, based on a detection signal of the crank angle sensor34. In addition, the ECM30calculates the intake air filling factor n of the combustion chamber15based on detection signals of the air flow meter33and the intake air temperature sensor35and the opening degree of the throttle valve20.

The ECM30sets an operation amount of the hydrogen engine10such as the air-fuel ratio of the air-fuel mixture burned in the combustion chamber15, the injection amount and the injection timing of hydrogen gas, the ignition timing, and the timing of opening and closing the intake valve18. In this case, the ECM30sets the operation amounts to values suitable for improving the fuel economy performance and the emission performance of the hydrogen engine10. The ECM30controls the hydrogen engine10by operating the throttle valve20, the injector16, the ignition device17, and the VVT21based on the set operation amounts.

Hydrogen Embrittlement Limiting Control

The ECM30executes, as part of control of the hydrogen engine10, a hydrogen embrittlement limiting control that limits the progress of hydrogen embrittlement in the metal component around the combustion chamber15. Such a hydrogen embrittlement limiting control will now be described.

FIG.2shows a flowchart of a hydrogen embrittlement limiting control routine executed by the ECM30for hydrogen embrittlement limiting control. The ECM30repeatedly executes this routine at each specified control cycle during the operation of the hydrogen engine10.

When this routine is started, in step S100, the ECM30first calculates the peak value P of the in-cylinder pressure before ignition based on the intake air filling factor n, the intake air temperature THA, the atmospheric pressure PA, the ignition timing, the injection amount and the injection timing of the hydrogen gas, and the like. The memory32stores a calculation map that stores the relationship between the peak value P, which has been obtained in advance through experiments or the like, and parameters used for calculation. The ECM30calculates the peak value P using the calculation map.

Subsequently, in step S110, the ECM30calculates the upper limit value PU of the in-cylinder pressure before ignition based on the air excess ratio2. The upper limit value PU represents the in-cylinder pressure when the hydrogen partial pressure in the combustion chamber15is an allowable limit value. The allowable limit value represents the upper limit of a hydrogen partial pressure capable of limiting the progress of hydrogen embrittlement of the metal component to an allowable range. Specifically, the ECM30calculates the hydrogen molar ratio of the air-fuel mixture in the combustion chamber15based on the air excess ratio2. The ECM30divides the allowable limit value by the hydrogen mole fraction and calculates the value obtained by dividing the allowable limit value as the upper limit value PU.

Next, in step S120, the ECM30determines whether the peak value P is greater than an upper limit value PU. If the peak value P is less than or equal to the upper limit value PU (S120: NO), the ECM30ends the process of this routine in the current control cycle. If the peak value P is greater than the upper limit value PU (S120: YES), the ECM30advances the process to step S130.

In step S130, the ECM30calculates an advancement correction amount A of the ignition timing, which is necessary to lower the peak value P to the upper limit value PU. When the ignition timing is advanced to a point prior to the compression top dead center, the peak value P decreases. Thus, in step S130, the ECM30calculates the value of the advancement correction amount A such that the ignition timing is advanced to a point prior to the compression top dead center.

In the following step S140, the ECM30corrects the ignition timing in accordance with the advancement correction amount A. That is, the ECM30advances the ignition timing by an amount corresponding to the value of the advancement correction amount A. Thereafter, the ECM30ends the process of this routine in the current control cycle.

As a result of the advancement correction of the ignition timing at step S140, the ignition timing may be more advanced than the timing at which the injection of the injector16ends. Further, as a result of the advancement correction of the ignition timing in step S140, the time taken from the end of the injection to the ignition becomes short, and the mixture of hydrogen gas to the intake air may become insufficient. In such a case, in step S140, the ECM30also executes advancement correction of the injection timing as well as advancement correction of the ignition timing.

Operation and Advantages of Present Embodiment

The operation and advantages of the present embodiment will now be described.

In step S100ofFIG.2, the ECM30calculates the peak value P of the in-cylinder pressure before ignition based on the operating state of the hydrogen engine10. Further, in step S120ofFIG.2, the ECM30determines whether the peak value P is greater than a threshold value. When the peak value P is greater than the threshold value (S120: YES), in step S140, the ECM30advances the ignition timing to be a point prior to the compression top dead center such that the peak value P becomes less than or equal to the upper limit value PU. That is, in step S140, the ECM30changes the control content of the hydrogen engine10such that the peak value P becomes less than or equal to the upper limit value PU. In step S110ofFIG.2, the ECM30sets the upper limit value PU to the in-cylinder pressure in which the hydrogen partial pressure in the combustion chamber15is a specified allowable upper limit value. In the present embodiment, the upper limit value PU corresponds to the threshold value.

FIG.3shows solid lines an example of changes in the in-cylinder pressure in the case of the present embodiment. InFIG.3, the long-dash short-dash line shows an example of changes in the in-cylinder pressure in a case of a comparative example of a controller that does not perform the hydrogen embrittlement limiting control. The symbol TDC inFIGS.3to5represents the compression top dead center.

In the case ofFIG.3, the hydrogen gas is injected during the compression stroke from time t1 to time t2. In the comparative example, ignition is performed at time t4, which is subsequent to the compression top dead center. In this case, the in-cylinder pressure increases until the compression top dead center and decreases from the compression top dead center to time t4, at which ignition is performed. Thus, in this case, the in-cylinder pressure before ignition is maximized at the compression top dead center. In this case, the value P1 of the in-cylinder pressure at the compression top dead center is greater than the upper limit value PU. As described above, the upper limit value PU represents the in-cylinder pressure in a case in which the hydrogen partial pressure in the combustion chamber15is an upper limit that limits the progress of hydrogen embrittlement of a metal component. Thus, in this case, the hydrogen embrittlement of the metal component around the combustion chamber15cannot be sufficiently limited.

In the present embodiment, if the control of the hydrogen engine10in the current control content causes the peak value P of the in-cylinder pressure before ignition to exceed the upper limit value PU, the ECM30performs the advancement correction of the ignition timing. In the case ofFIG.3, the ECM30advances the ignition timing to time t3, which is a point prior to the compression top dead center. After ignition, the hydrogen in the combustion chamber15is burned. Thus, the peak value of the hydrogen partial pressure in the combustion chamber15is lower than that in the comparative example. Further, in the present embodiment, the ECM30executes the advancement correction of the ignition timing such that the peak value P becomes less than or equal to the upper limit value PU. Thus, the hydrogen partial pressure in the combustion chamber15is limited to less than or equal to an upper limit value that limits the progress of hydrogen embrittlement of a metal component within an allowable range.

The present embodiment has the following advantages.

(1) When the metal component is exposed to the atmosphere containing hydrogen gas, the higher the pressure, the more easily the hydrogen enters the metal component. Since the hydrogen gas in the combustion chamber15is burned after ignition, the timing at which the hydrogen partial pressure in the cylinder is maximized is earlier than the ignition timing or the ignition timing. Thus, the peak value of the in-cylinder pressure before ignition is lowered to limit the progress of hydrogen embrittlement in the metal component. In this respect, in the present embodiment, the ECM30first calculates the peak value P of the in-cylinder pressure before ignition based on the operating state of the hydrogen engine10. When the peak value P exceeds the upper limit value PU, the ECM30changes the control content of the hydrogen engine10so that the peak value P becomes less than or equal to the upper limit value PU. More specifically, the ECM30changes the control contents to advance the ignition timing such that the ignition timing is advanced to a point prior to the compression top dead center. This limits an increase in the hydrogen partial pressure in the combustion chamber15. This reduces the hydrogen embrittlement in the metal component around the combustion chamber.

(2) The ECM30sets the upper limit value PU to the in-cylinder pressure in which the hydrogen partial pressure in the combustion chamber15is a preset allowable upper limit value. Therefore, the hydrogen partial pressure in the combustion chamber15is controlled not to exceed a limit that limits the progress of hydrogen embrittlement.

Modifications

The present embodiment may be modified as follows. The present embodiment and the following modifications can be combined as long as they remain technically consistent with each other.

Change in Control Content (1)

In the above-described embodiment, the ECM30executes the advancement correction of the ignition timing as a change in the control content for setting the peak value P to be less than or equal to the upper limit value PU in the hydrogen embrittlement limiting control. Instead, the peak value P may be less than or equal to the upper limit value PU by a change in the control content.

FIG.4shows solid lines an example of changes in the in-cylinder pressure in a modified example of the controller. In this modified example, the retardation correction of the injection timing of hydrogen gas is performed as a change in the control content for setting the peak value P to the upper limit value PU or less. InFIG.4, the long-dash short-dash line shows an example of changes in the in-cylinder pressure in a case of a comparative example of a controller that does not perform the hydrogen embrittlement limiting control. In the comparative example, hydrogen gas is injected during the compression stroke from time t1 to time t2. Then, ignition is performed at time t4, which is after the compression stroke. In this case, the in-cylinder pressure before ignition is maximized at the compression top dead center. The value P1 of the in-cylinder pressure at the compression top dead center in this case is greater than the upper limit value PU.

In this modification, the ECM30retards the fuel injection timing such that the end timing of the injection is more retarded than the compression top dead center. In the case ofFIG.4, the fuel injection timing is retarded to inject hydrogen gas from time t11 to time t12. In this case, time t12, which is the end time of the injection, is later than the compression top dead center. In such a case, the amount of hydrogen gas present in the combustion chamber15at the point in time of the compression top dead center is less than that in the case of the comparative example. At time t12, at which the fuel injection ends, the piston12has fallen below the compression top dead center. Thus, even if the fuel injection timing is retarded such that the end timing of the injection is later than the compression top dead center, the peak value P can be set to the upper limit value PU.

When the fuel injection timing is retarded, the time from the end of the injection to the ignition is shortened, and the hydrogen gas may not be sufficiently stirred in the intake air until the ignition is performed. In this case, the ignition timing is preferably retarded with the fuel injection timing. In the case ofFIG.4, the ignition timing is retarded from time t4 to time t5.

Change in Control Content (2)

In the hydrogen embrittlement limiting control, the ECM30may change the control content by setting the timing of closing the intake valve18to be later than the timing prior to the change in the control content.

FIG.5shows a solid line an example of changes in the in-cylinder pressure in a modified example of the control device that changes the valve closing timing of the intake valve18. InFIG.5, the long-dash short-dash line shows an example of changes in the in-cylinder pressure in a case of a comparative example of a controller that does not perform the hydrogen embrittlement limiting control. InFIG.5, BDC represents the intake bottom dead center.

In the case of the comparative example, the intake valve18is closed at time t20, which the intake bottom dead center is reached. Then, the hydrogen gas is injected during the subsequent compression stroke from time t1 to time t2. Further, in the case of the comparative example, ignition is performed at time t4, which is after the compression top dead center. In this case, the in-cylinder pressure before ignition is maximized at the compression top dead center. The value P1 of the in-cylinder pressure at the compression top dead center in this case is greater than the upper limit value PU.

In this modification, the ECM30operates the VVT21to reduce the timing of closing the intake valve18. In the case ofFIG.5, the timing of closing the intake valve18is retarded to time t21, which is later than time t20. In this modification, the fuel injection timing and the ignition timing are the same as those in the comparative example. When the timing of closing the intake valve18is retarded relative to the bottom dead center by a certain amount, some of the intake air drawn into the combustion chamber15is blown back to the intake passage19. As the intake air that has been blown back decreases, the intake air filling factor n of the combustion chamber15decreases. This consequently decreases the peak value P of the in-cylinder pressure before ignition. Thus, by changing the control content so that the timing of closing the intake valve18is more delayed than a point prior to the change in the control content, the peak value P can be set to the upper limit value PU. In the same manner, when the intake air filling factor n is decreased by reducing the open degree of the throttle valve20, the peak value P can be set to the upper limit value PU or less.

Other Modifications

In the above-described embodiment, the ECM30calculates, based on the air excess ratio λ, the in-cylinder pressure, in which the hydrogen partial pressure in the combustion chamber is a specified allowable upper limit value, and sets the upper limit value PU to the calculated value. The upper limit value PU may be a fixed value. For example, when the injection amount of hydrogen gas is the maximum value in the control range, the upper limit value PU may be set to a cylinder internal pressure in which the hydrogen partial pressure in the combustion chamber15is the allowable limit value.

The hydrogen embrittlement limiting control of the above embodiment may be applied to a hydrogen engine that does not include the VVT21as long as the retardation correction is not performed on the timing of closing the intake valve18in the control. Further, the hydrogen embrittlement limiting control of the above embodiment may be applied to a hydrogen engine that injects hydrogen gas into the intake passage19as long as the fuel injection timing is not retarded in the control.

The processor31, which is a controller for the hydrogen engine10, is not limited to a device that includes a CPU and a ROM and executes software processing. For example, at least part of the processes executed by the software in the above embodiment may be executed by hardware circuits (such as ASIC) dedicated to executing these processes. That is, the processor31may be modified to have any one of the following configurations (a) to (c). (a) a configuration including a processor that executes all of the above processes according to programs and a program storage device such as a ROM that stores the programs; (b) a configuration including a processor and a program storage device that execute part of the above-described processes according to the programs and a dedicated hardware circuit that executes the remaining processes; and (c) a configuration including a dedicated hardware circuit that executes all of the above-described processes. There may be multiple software execution devices, each including a processor and a program storage device, and multiple dedicated hardware circuits.