Hydrogen engine control device

Abstract

To compensate for deviation of output of an air-fuel ratio sensor due to unburned hydrogen.SOLUTION: An ECU 21 for controlling an air-fuel ratio of a hydrogen engine 10, comprises a processing circuit 23 that performs processes of: calculating an amount of fluctuation in combustion pressure based on a detection result of an in-cylinder pressure sensor 18; and calculating a correction amount for correcting rich deviation in output of an air-fuel ratio sensor 20 due to unburned hydrogen in exhaust based on the amount of fluctuation in combustion pressure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 describes an engine in which air-fuel ratio sensors are installed upstream and downstream of a catalyst in an exhaust passage. Patent Document 1 also describes that a deviation in the output of the air-fuel ratio sensor upstream of the catalyst caused by hydrogen generated during rich combustion is compensated for based on the output of the air-fuel ratio sensor downstream of the catalyst. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-185512 Summary of the Invention [Problem to be solved by the invention]

[0004] Some hydrogen engines that use hydrogen gas as fuel are equipped with an air-fuel ratio sensor. In hydrogen engines, hydrogen may not be completely burned in the combustion chamber and may be discharged into the exhaust passage. Therefore, even in such hydrogen engines, there is a possibility that the output of the air-fuel ratio sensor may be affected by the unburned hydrogen. In such hydrogen engines, it is possible to compensate for the output deviation of the air-fuel ratio sensor caused by unburned hydrogen using the method described in Patent Document 1. However, to do this, it is necessary to install an air-fuel ratio sensor that is not affected by unburned hydrogen, separate from the air-fuel ratio sensor that compensates for the output deviation. [Means for solving the problem]

[0005] A control device for a hydrogen engine that solves the above problem is a control device for a hydrogen engine that is equipped with an in-cylinder pressure sensor and an air-fuel ratio sensor, The system includes a memory device and a processing circuit, and the memory device stores a program for calculating a correction amount for correcting a rich deviation in the output of the air-fuel ratio sensor due to unburned hydrogen in the exhaust gas. The processing circuit executes the program read from the memory device to perform a process of calculating a fluctuation amount of combustion pressure for each fixed combustion cycle based on the in-cylinder pressure sensor, and a process of calculating the correction amount based on the fluctuation amount. [Effects of the Invention]

[0006] The deviation in the output of the air-fuel ratio sensor due to unburned hydrogen can be compensated for. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing a schematic configuration of an embodiment of a control device for a hydrogen engine; [Figure 2] 10 is a flowchart of a compensation routine executed by the control device. [Figure 3] 4 is a graph showing the relationship between combustion pressure fluctuation amount, engine load factor, and unburned hydrogen concentration. [Figure 4] 4 is a graph showing the relationship between the unburned hydrogen concentration and the lean correction amount. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of a control device for a hydrogen engine will be described in detail below with reference to Figures 1 to 4. The hydrogen engine controlled by the control device of this embodiment is mounted on a vehicle. <Configuration of hydrogen engine and its control device> The hydrogen engine 10 shown in FIG. 1 includes an intake passage 11, a combustion chamber 12, and an exhaust passage 13. An air flow meter 14 and a throttle valve 15 are installed in the intake passage 11. The air flow meter 14 is a sensor that detects the intake air amount GA. The throttle valve 15 is a valve that adjusts the amount of air introduced into the combustion chamber 12. An injector 16, an ignition device 17, and an internal cylinder pressure sensor 18 are installed in the combustion chamber 12. The injector 16 injects hydrogen gas into the air introduced into the combustion chamber 12 through the intake passage 11. The ignition device 17 ignites the mixture of hydrogen gas and air by spark discharge. The internal cylinder pressure sensor 18 is a sensor that detects the internal cylinder pressure P of the combustion chamber 12. A NOx sensor 19 and an air-fuel ratio sensor 20 are installed in the exhaust passage 13. The NOx sensor 19 is a sensor that detects the concentration of NOx (nitrogen oxides) in the exhaust gas in the exhaust passage 13. The air-fuel ratio sensor 20 is a sensor for detecting the air-fuel ratio λ of the mixture burned in the combustion chamber 12 .

[0009] The hydrogen engine 10 is controlled by an ECU (electronic control unit) 21 that serves as a control device. The ECU 21 is equipped with a storage device 22 that stores programs and data for controlling the hydrogen engine 10. The ECU 21 also has a processing circuit 23 that executes programs read from the storage device 22. The ECU 21 receives the outputs of the air flow meter 14, NOx sensor 19, and air-fuel ratio sensor 20. The ECU 21 also receives the outputs of other sensors, such as a crank angle sensor 24 that detects the crank angle and an accelerator pedal sensor 25 that detects the accelerator pedal depression amount ACC. The ECU 21 calculates the engine speed NE, which is the rotational speed of the output shaft of the hydrogen engine 10, based on the output of the crank angle sensor 24.

[0010] <Air-fuel ratio control> The ECU 21 controls the air-fuel ratio as part of the control of the hydrogen engine 10. The air-fuel ratio control is performed by manipulating the throttle opening TA, which is the opening rate of the throttle valve 15, and the hydrogen gas injection amount Q of the injector 16.

[0011] During air-fuel ratio control, the ECU 21 first calculates the required torque TE*, which is the torque required for the hydrogen engine 10, based on the accelerator pedal depression amount ACC and the engine rotation speed NE. Next, the ECU 21 calculates the target air-fuel ratio λ*, which is the control target value for the air-fuel ratio λ, based on the required torque TE* and the engine rotation speed NE. Next, the ECU 21 determines the hydrogen gas injection amount Q so that torque equal to the required torque TE* is obtained. Furthermore, the ECU 21 determines the throttle opening TA so that the air-fuel ratio λ is equal to the target air-fuel ratio λ*. The ECU 21 then controls the air-fuel ratio λ of the hydrogen engine 10 by operating the injector 16 and the throttle valve 15 based on the determined hydrogen gas injection amount Q and throttle opening TA. Note that during this control of the air-fuel ratio λ, the ECU 21 performs feedback correction of either or both of the hydrogen gas injection amount Q and the throttle opening TA based on the air-fuel ratio λ detected by the air-fuel ratio sensor 20.

[0012] <Output compensation of air-fuel ratio sensor 20> In the hydrogen engine 10, hydrogen that remains unburned in the combustion chamber 12 may be discharged into the exhaust passage 13. If unburned hydrogen is present in the exhaust, the output of the air-fuel ratio sensor 20 will indicate an air-fuel ratio that is richer than the actual air-fuel ratio λ. The ECU 21 performs processing to compensate for the deviation of the output of the air-fuel ratio sensor 20 to the rich side due to unburned hydrogen.

[0013] 2 shows a flowchart of a compensation routine executed by the ECU 21 to compensate for the output of the air-fuel ratio sensor 20. The ECU 21 repeatedly executes the processing of this routine at predetermined control intervals while the hydrogen engine 10 is operating. The ECU 21 executes this routine by having the processing circuit 23 execute a program read from the storage device 22. This routine ends after the processing of step S140.

[0014] When this routine starts, the ECU 21 first determines in step S100 whether the engine speed NE and the NOx concentration are stable. The ECU 21 determines that the engine speed NE and the NOx concentration are stable if both of the following requirements (A) and (B) continue for a predetermined time or longer. Requirement (A) is that the amount of change in the engine speed NE calculated based on the output of the crank angle sensor 24 is equal to or less than a predetermined value. Requirement (B) is that the amount of change in the NOx concentration in the exhaust detected by the NOx sensor 19 is equal to or less than a predetermined value.

[0015] If the engine speed NE and NOx concentration are stable (S100: YES), in step S110 the ECU 21 calculates the combustion pressure fluctuation COV of the hydrogen engine 10 based on the output of the in-cylinder pressure sensor 18. More specifically, the ECU 21 calculates the indicated mean effective pressure (IMEP) in the combustion chamber 12 for each combustion in the hydrogen engine 10 based on the output of the in-cylinder pressure sensor 18. The ECU 21 then obtains the average value and variance of the indicated mean effective pressure over a fixed cycle, and calculates the ratio of the variance to the average value as the value of the combustion pressure fluctuation COV.

[0016] Next, in step S120, the ECU 21 calculates the unburned hydrogen concentration in the exhaust gas based on the combustion pressure fluctuation COV and the engine load factor KL. The engine load factor KL represents the intake air filling rate of the combustion chamber 12. Next, in step S130, the ECU 21 calculates the lean correction amount Δ based on the unburned hydrogen concentration. Then, in step S140, the ECU 21 calculates the sum of the air-fuel ratio sensor value λs and the lean correction amount Δ as the value of the air-fuel ratio λ. The air-fuel ratio sensor value λs represents the value of the air-fuel ratio λ calculated from the output of the air-fuel ratio sensor 20, assuming that there is no deviation in the output of the air-fuel ratio sensor 20.

[0017] On the other hand, if it is determined in step S100 that the engine rotation speed NE and the NOx concentration are not stable (S100: NO), the ECU 21 skips steps S110 to S130 and proceeds to step S 140. In this case, the ECU 21 calculates the value of the air-fuel ratio λ using the value of the lean correction amount Δ that was last calculated during the previous execution of this routine.

[0018] <Actions and Effects of the Embodiment> In step S110 of Fig. 2, the ECU 21 calculates the combustion pressure fluctuation amount COV of the hydrogen engine 10 based on the output of the in-cylinder pressure sensor 18. In step S120 of Fig. 2, the ECU 21 estimates the unburned hydrogen concentration of the exhaust gas based on the combustion pressure fluctuation amount COV. In step S130 of Fig. 2, the ECU 21 calculates a lean correction amount Δ based on the unburned hydrogen concentration. In step S140 of Fig. 2, the ECU 21 corrects a rich deviation in the output of the air-fuel ratio sensor 20 caused by unburned hydrogen in the exhaust gas based on the lean correction amount Δ. Therefore, in steps S120 and S130, the ECU 21 calculates the lean correction amount Δ for correcting a rich deviation in the output of the air-fuel ratio sensor 20 caused by unburned hydrogen in the exhaust gas based on the combustion pressure fluctuation amount COV.

[0019] FIG. 3 shows the relationship between the unburned hydrogen concentration calculated in step S120 of FIG. 2 and the combustion pressure fluctuation COV and engine load factor KL used in the calculation. When some of the hydrogen gas injected by the injector 16 remains unburned, the combustion pressure is lower than when all of the hydrogen gas is burned. Therefore, when intermittent incomplete combustion occurs and unburned hydrogen is discharged into the exhaust passage 13, the combustion pressure fluctuation COV becomes larger. Therefore, as shown in FIG. 3, when the engine load factor KL is constant, the ECU 21 calculates a value for the unburned hydrogen concentration that is larger when the combustion pressure fluctuation COV is large than when it is small. Furthermore, when the combustion pressure fluctuation COV is constant, the unburned hydrogen concentration tends to increase as the engine load factor KL decreases. Therefore, as shown in FIG. 3, when the engine load factor KL is small, the ECU 21 calculates a value for the unburned hydrogen concentration that is larger than when it is large.

[0020] 4 shows the relationship between the lean correction amount Δ calculated in step S130 in FIG. 2 and the unburned hydrogen concentration. The output of the air-fuel ratio sensor 20 deviates more toward the rich side as the unburned hydrogen concentration in the exhaust gas increases. Therefore, as shown in FIG. 4, the ECU 21 calculates the lean correction amount Δ to be a value that is larger when the unburned hydrogen concentration is high than when it is low. Therefore, by correcting the air-fuel ratio sensor value λs using the lean correction amount Δ, it is possible to appropriately compensate for the rich deviation of the output of the air-fuel ratio sensor 20 due to unburned hydrogen in the exhaust gas.

[0021] According to the control device for the hydrogen engine 10 of this embodiment, the following effects can be achieved. (1) The ECU 21 in the control device of this embodiment is equipped with a processing circuit 23 that performs the following two processes. One of the processes is a process for calculating the combustion pressure fluctuation amount COV based on the in-cylinder pressure sensor 18. The other process is a process for calculating a lean correction amount Δ based on the combustion pressure fluctuation amount COV to correct a rich deviation in the output of the air-fuel ratio sensor 20 due to unburned hydrogen in the exhaust. By performing these processes, the control device of this embodiment can appropriately compensate for the deviation in the output of the air-fuel ratio sensor 20 due to unburned hydrogen.

[0022] (2) The above compensation allows the air-fuel ratio λ to be accurately determined, thereby enabling air-fuel ratio control to be performed with high precision. (3) When the engine load factor KL is small, the processing circuit 23 of the ECU 21 calculates the lean correction amount Δ so that the ratio of the absolute value of the lean correction amount Δ to the combustion pressure fluctuation amount COV is larger than when the engine load factor KL is large. Therefore, if the combustion pressure fluctuation amount COV is constant, it is possible to calculate an appropriate value for the lean correction amount Δ that matches the tendency of the hydrogen engine 10, which is that the unburned hydrogen concentration increases as the engine load factor KL decreases.

[0023] (4) The processing circuit 23 of the ECU 21 calculates the lean correction amount Δ when the fluctuation in the NOx concentration is equal to or less than a predetermined value. If the lean correction amount Δ is calculated based on the combustion pressure fluctuation amount COV when the actual air-fuel ratio λ is fluctuating, the influence of the fluctuation in the air-fuel ratio λ will be reflected in the lean correction amount Δ. On the other hand, when the air-fuel ratio λ fluctuates, the NOx concentration in the exhaust gas also fluctuates. Therefore, if the lean correction amount Δ is calculated when the fluctuation in the NOx concentration is small, the influence of the fluctuation in the air-fuel ratio λ will be less likely to be reflected in the lean correction amount Δ. Therefore, the output deviation of the air-fuel ratio sensor 20 due to the influence of unburned hydrogen can be accurately compensated for.

[0024] (Other embodiments) This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0025] In the above embodiment, the ratio of the variance to the average value of the indicated mean effective pressure was calculated as the value of the combustion pressure fluctuation COV. However, the value of the combustion pressure fluctuation COV may be calculated using another value that indicates the magnitude of fluctuation in the combustion pressure based on the output of the in-cylinder pressure sensor 18. For example, instead of the indicated mean effective pressure, the peak value of the internal pressure of the combustion chamber 12 for each combustion cycle may be obtained, and the difference between the maximum and minimum values ​​of the peak value in a certain combustion cycle may be calculated as the value of the combustion pressure fluctuation COV.

[0026] In the above embodiment, the condition for calculating the lean correction amount Δ based on the combustion pressure fluctuation amount COV is that the engine rotation speed NE and the NOx concentration are stable. However, the condition for this calculation may be changed as appropriate.

[0027] The engine load factor KL may not be used to estimate the unburned hydrogen concentration in step S120 of FIG. In the compensation routine in Figure 2, the unburned hydrogen concentration is estimated from the combustion pressure fluctuation COV, and then the lean correction amount Δ is calculated based on the unburned hydrogen concentration. However, it is also possible to omit the calculation of the unburned hydrogen concentration and calculate the lean correction amount Δ directly from the combustion pressure fluctuation COV. [Explanation of symbols]

[0028] 10 Hydrogen engine 11 Intake passage 12 Combustion chamber 13 Exhaust passage 14 Air flow meter 15 Throttle valve 16 injectors 17 Ignition system 18 Cylinder pressure sensor 19 NOx sensor 20 Air-fuel ratio sensor 21 ECU (control unit) 22 Storage device 23 Processing circuit 24 Crank angle sensor 25 Accelerator pedal sensor

Claims

1. A control device for a hydrogen engine equipped with an in-cylinder pressure sensor and an air-fuel ratio sensor, a storage device and a processing circuit; the storage device stores a program for calculating a correction amount for correcting a rich deviation of the output of the air-fuel ratio sensor due to unburned hydrogen in the exhaust gas, The processing circuit executes the program read from the storage device, a process of calculating a fluctuation amount of combustion pressure for each fixed combustion cycle based on the in-cylinder pressure sensor; a process of calculating the correction amount based on the fluctuation amount; Do Hydrogen engine control device.

2. 2. A control device for a hydrogen engine according to claim 1, wherein the processing circuit calculates the correction amount so that the ratio of the absolute value of the correction amount to the fluctuation amount is larger when the load factor of the hydrogen engine is small than when the load factor is large.

3. the hydrogen engine is equipped with a NOx sensor that detects the NOx concentration in the exhaust gas; The processing circuit calculates the correction amount when the fluctuation in the NOx concentration is equal to or less than a predetermined value. The control device for a hydrogen engine according to claim 1.

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