Preignition detection device

Abstract

To improve detection accuracy of preignition in a spark ignition engine.SOLUTION: A processor 31 of an ECU 30 detects occurrence of pre-ignition in a spark ignition engine that ignites a mixture in a combustion chamber 13 by spark discharge through a process of calculating a rotational fluctuation amount and self-ignition start timing of the engine 10 and a process of determining that pre-ignition has occurred when the rotational fluctuation amount is equal to or larger than a predetermined threshold value and the self-ignition start timing is earlier than predetermined timing. The self-ignition start timing is the timing when the temperature of the mixture in the combustion chamber 13 during a compression stroke reaches the ignition point of the mixture.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pre-ignition detection device for detecting the occurrence of pre-ignition in a spark ignition engine.

Background Art

[0002] In a spark ignition engine that ignites the air-fuel mixture in the combustion chamber by spark discharge, pre-ignition may occur. Pre-ignition is a phenomenon in which the air-fuel mixture in the combustion chamber self-ignites before spark discharge ignition is carried out. Patent Document 1 describes a device for detecting the occurrence of pre-ignition based on the engine's rotational fluctuation amount.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Combustion failures other than pre-ignition may also cause engine rotational fluctuations. Therefore, based solely on the rotational fluctuation amount, there is a possibility of misdetecting the occurrence of pre-ignition when a combustion failure other than pre-ignition occurs.

Means for Solving the Problems

[0005] The pre-ignition detection device for solving the above problems is a pre-ignition detection device that detects the occurrence of pre-ignition in a spark ignition engine that ignites the air-fuel mixture in the combustion chamber by spark discharge. It calculates the self-ignition start time, which is the time when the temperature of the air-fuel mixture reaches the ignition temperature of the air-fuel mixture due to the compression of the air-fuel mixture in the combustion chamber during the compression stroke. When the rotational fluctuation amount of the engine is equal to or greater than a predetermined threshold value and the self-ignition start time is earlier than a predetermined time, it is determined that pre-ignition has occurred.

Effect of the Invention

[0006] The above pre-ignition detection device has the effect of improving the detection accuracy of pre-ignition in a spark ignition engine.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0008] Hereinafter, an embodiment of the pre-ignition detection device will be described in detail with reference to FIGS. 1 to 5. <Configuration of Engine 10> First, referring to FIG. 1, the configuration of the engine 10 to which the pre-ignition detection device of the present embodiment is applied will be described. The engine 10 shown in FIG. 1 is a hydrogen engine, and its fuel is hydrogen. The engine 10 includes a cylinder 11 and a piston 12 reciprocally accommodated in the cylinder 11. A combustion chamber 13 for burning an air-fuel mixture is partitioned and formed in the cylinder 11 by the piston 12. The piston 12 is connected to a crankshaft 15, which is an output shaft of the engine 10, via a connecting rod 14. The connecting rod 14 and the crankshaft 15 constitute a link mechanism that converts the reciprocating motion of the piston 12 into the rotational motion of the crankshaft 15. Further, the engine 10 includes an intake passage 16, an injector 17, an ignition device 18, and an exhaust passage 19. An air-fuel mixture of intake air flowing in through the intake passage 16 and hydrogen injected by the injector 17 is introduced into the combustion chamber 13. The air-fuel mixture in the combustion chamber 13 is ignited by a spark discharge generated by the ignition device 18. The exhaust gas generated by the combustion of the air-fuel mixture is discharged from the combustion chamber 13 through the exhaust passage 19. An air flow meter 20 for detecting the intake air flow rate GA of the intake passage 16 and a throttle valve 21 for adjusting the intake air flow rate GA are installed in the intake passage 16.

[0009] <Configuration of the Pre-Ignition Detection Device> Next, continuing to refer to FIG. 1, the configuration of the pre-ignition detection device according to this embodiment will be described. In the case of this embodiment, an ECU (Electronic Control Unit) 30 for engine control constitutes the pre-ignition detection device. Detection signals from various sensors for detecting the operating state of the engine 10 are input to the ECU 30. Examples of such sensors are the above-described air flow meter 20, a crank angle sensor 22 for detecting the crank angle which is the rotation angle of the crankshaft 15, and an intake air temperature sensor 23 for detecting the intake air temperature THA in the intake passage 16. The ECU 30 has a processor 31 and a memory 32. Programs and data for engine control are stored in advance in the memory 32. The processor 31 calculates each operation amount of the engine 10 based on the detection results of the respective sensors by executing the program read from the memory 32. Examples of the operation amounts of the engine 10 calculated by the processor 31 are the injection amount and injection timing of hydrogen by the injector 17, the ignition timing of the air-fuel mixture by the spark discharge of the ignition device 18, and the opening ratio of the throttle valve 21. The ECU 30 controls the operating state of the engine 10 by operating the injector 17, the ignition device 18, the throttle valve 21, etc. based on the operation amounts calculated by the processor 31.

[0010] <Pre-ignition Detection Process> In the engine 10, pre-ignition may occur where the air-fuel mixture in the combustion chamber 13 self-ignites and starts combustion before the ignition device 18 performs ignition by spark discharge. The ECU 30 detects the occurrence of pre-ignition in the engine 10. Hereinafter, the details of the pre-ignition detection process executed by the ECU 30 will be described. The pre-ignition detection process is performed by the processor 31 executing a pre-ignition detection program read from the memory 32. In the following description, a state where pre-ignition has not occurred and the combustion of the air-fuel mixture in the combustion chamber 13 starts due to the spark discharge of the ignition device 18 is described as normal combustion.

[0011] FIG. 2 shows the processing procedure of a pre-ignition detection routine executed by the processor 31 for pre-ignition detection processing. The processor 31 repeatedly executes the routine at each predetermined control cycle during the operation of the engine 10.

[0012] When starting this routine, the processor 31 first calculates the rotational fluctuation amount RF of the engine 10 (S100). The processor 31 calculates the engine rotational speed NE based on the detection result of the crank angle sensor 22, and calculates the angular velocity of the crankshaft 15 by obtaining the differential value of the engine rotational speed NE. Then, the processor 31 calculates the absolute value of the minimum value of the angular velocity for each combustion cycle, or the change width of the angular velocity for each combustion cycle, as the value of the rotational fluctuation amount RF.

[0013] Next, the processor 31 calculates the pre-ignition start timing (S110). The pre-ignition start timing represents the time when the temperature of the air-fuel mixture in the combustion chamber 13 during the compression stroke reaches the ignition point of the air-fuel mixture. In the case of this embodiment, the ignition point of the air-fuel mixture is the ignition point of hydrogen. The pre-ignition start timing is represented by the crank angle [BTDC°] before top dead center. The processor 31 calculates the intake air amount of the combustion chamber 13 based on the intake air flow rate GA, the engine rotational speed NE, the opening ratio of the throttle valve 21, etc. Then, the processor 31 calculates the pre-ignition start timing based on the intake air amount and the intake air temperature THA.

[0014] In this embodiment, the pre-ignition start timing is calculated assuming that the air-fuel mixture in the combustion chamber 13 is adiabatically compressed during the compression stroke. When the air-fuel mixture is in a state of being adiabatically compressed until it reaches the ignition point, the volume of the combustion chamber 13 can be calculated based on the volume of the combustion chamber 13 at the start of the compression stroke, the intake air amount, the intake air temperature THA, the specific heat ratio of the air-fuel mixture, etc. using Poisson's law and the first law of thermodynamics. And since the volume of the combustion chamber 13 is determined by the crank angle, based on those relationships, the pre-ignition start timing is obtained by calculating the timing [BTDC°] when the volume of the combustion chamber 13 becomes the calculated value.

[0015] And when both of the following requirements A and B are satisfied (S120: YES and S130: YES), the processor 31 determines that pre-ignition has occurred (S140). Requirement A is that the rotational fluctuation amount RF calculated in S100 is equal to or greater than a predetermined threshold value X. A value greater than the maximum fluctuation amount is set as the value of the threshold value X. The maximum fluctuation amount is the maximum value of the rotational fluctuation amount RF during normal combustion. Requirement B is that the self-ignition start timing calculated in S110 is earlier than a predetermined timing T. A timing earlier than the optimal ignition timing is set as the predetermined timing T. Although the torque generated by the engine 10 changes depending on the ignition timing, the optimal ignition timing is the ignition timing at which the torque is maximized. The ECU 30 controls the ignition timing of the air-fuel mixture by the spark discharge of the ignition device 18 to be the optimal ignition timing or a later timing. Therefore, the predetermined timing T is a timing earlier than when the ignition device 18 ignites regardless of the control state of the engine 10. After the determination in S140 that pre-ignition has occurred, or after a negative determination in either S120 or S130, the processor 31 ends the processing of this routine in the current control cycle.

[0016] When the processor 31 determines that pre-ignition has occurred in this routine, it modifies the operation amount of the engine 10 to suppress the occurrence. An example of the modification of the operation amount to suppress the occurrence of pre-ignition is the reduction of the opening ratio of the throttle valve 21. When the opening ratio of the throttle valve 21 is reduced, the intake air amount of the combustion chamber 13 decreases. As a result, the temperature rise of the air-fuel mixture in the combustion chamber 13 due to adiabatic compression during the compression stroke is suppressed, so the occurrence of pre-ignition is suppressed.

[0017] <Actions and Effects of the Embodiment> FIG. 3(A) shows the transition of the engine rotational speed NE during the period before and after pre-ignition. Further, FIG. 3(B) shows the transition of the angular velocity of the crankshaft 15 during the above period.

[0018] The engine rotational speed NE is accelerated when the top surface of the piston 12 receives the combustion pressure due to the combustion of the air-fuel mixture in the combustion chamber 13. After that, the engine rotational speed NE reaches its peak and then decelerates until the next combustion occurs. In this way, the engine rotational speed NE repeats rising and falling for each combustion.

[0019] When pre-ignition occurs, the upward movement of the piston 12 in the cylinder 11 during the compression stroke is hindered, so the engine rotational speed NE decreases. Therefore, when pre-ignition occurs, a significant deceleration of the engine rotational speed NE occurs compared to normal combustion. As a result, the rotational fluctuation amount RF of the engine 10 increases. Thus, when rotational fluctuations of the engine 10 occur that exceed the maximum fluctuation amount, which is the maximum value of the rotational fluctuation amount RF during normal combustion, there is a possibility that pre-ignition has occurred.

[0020] In the case of this embodiment, the processor 31 calculates the rotational fluctuation amount RF of the engine 10 in the pre-ignition detection routine of FIG. 2 (S100). And the processor 31 sets that the rotational fluctuation amount RF being equal to or greater than a predetermined threshold value X is one of the requirements for determining that pre-ignition has occurred. The processor 31 determines whether the rotational fluctuation amount RF of the engine 10 is equal to or greater than the threshold value X based on the angular velocity of the crankshaft 15. Specifically, the processor 31 calculates, as the value of the rotational fluctuation amount RF of the engine 10, the absolute value of the minimum value of the angular velocity for each combustion of the engine 10, or the change width of the angular velocity for each combustion. "Δ1" in FIG. 3(B) indicates the absolute value of the minimum value of the angular velocity when pre-ignition occurs. Also, "Δ2" in FIG. 3(B) indicates the change width of the angular velocity when pre-ignition occurs.

[0021] By the way, when combustion failures other than pre-ignition, such as misfires, occur, the engine rotational speed NE also decreases. Therefore, it may not be possible to distinguish between pre-ignition and other combustion failures based solely on the rotational fluctuation amount RF of the engine 10.

[0022] On the other hand, pre-ignition occurs when the temperature of the air-fuel mixture in the combustion chamber 13 reaches or exceeds the ignition point due to adiabatic compression during the compression stroke. When pre-ignition occurs near top dead center of compression, the decrease in the engine rotational speed NE is smaller than when pre-ignition occurs at an earlier time. Therefore, even when rotational fluctuations occur in the engine 10, if the time when the temperature of the air-fuel mixture reaches the ignition point is after the ignition timing, the cause is considered to be other than pre-ignition.

[0023] In the case of this embodiment, the processor 31 calculates the self-ignition start time, which is the time when the temperature of the air-fuel mixture in the combustion chamber 13 during the compression stroke reaches the ignition point of the air-fuel mixture, in the pre-ignition detection routine of FIG. 2. Then, when the rotational fluctuation amount RF is equal to or greater than the threshold value X and the self-ignition time is earlier than the predetermined time T, the processor 31 determines that pre-ignition has occurred. Therefore, the possibility of misjudging combustion failure other than pre-ignition as pre-ignition is lower than when determining based only on the rotational fluctuation amount RF. Therefore, the pre-ignition detection device of this embodiment has the effect of improving the detection accuracy of pre-ignition.

[0024] Such a pre-ignition detection device of this embodiment is also applicable to spark ignition engines other than hydrogen engines, such as gasoline engines. However, in the case of a hydrogen engine, it is difficult to distinguish pre-ignition from other combustion failures compared to a gasoline engine as described below. Therefore, the pre-ignition detection device of this embodiment is particularly suitable for application to a hydrogen engine.

[0025] Fig. 4 shows the transition of the in-cylinder pressure Pc in the case of normal combustion and the occurrence of pre-ignition in a gasoline engine. The in-cylinder pressure Pc represents the pressure in the combustion chamber 13. As shown in Fig. 4, when pre-ignition occurs, the in-cylinder pressure Pc rises rapidly. In the case of a gasoline engine, when the air-fuel mixture self-ignites, the flame propagation in the combustion chamber 13 does not proceed smoothly as in the case of normal combustion. As a result, after the occurrence of pre-ignition, the in-cylinder pressure Pc fluctuates violently. Such fluctuations in the in-cylinder pressure Pc at the time of pre-ignition can be detected by a knock sensor or the like for knock detection. On the other hand, in the case of combustion failure other than pre-ignition, such fluctuations in the in-cylinder pressure Pc do not occur. And in many gasoline engines, a knock sensor is installed. Thus, in the case of a gasoline engine, by referring to the rotational fluctuation amount RF and the detection result of the knock sensor together, pre-ignition and other combustion failures can be distinguished.

[0026] Fig. 5 shows the transition of the in-cylinder pressure Pc in the case of normal combustion and the occurrence of pre-ignition in a hydrogen engine. Hydrogen has a higher ignition point and a higher flame propagation speed than gasoline. Therefore, in a hydrogen engine, when pre-ignition occurs, the in-cylinder pressure Pc rises earlier and more rapidly than in the case of a gasoline engine. And in a hydrogen engine, after the occurrence of pre-ignition, the flame propagates throughout the combustion chamber 13 earlier than in the case of a gasoline engine. Therefore, in a hydrogen engine, violent fluctuations in the in-cylinder pressure Pc do not occur after the occurrence of pre-ignition as in the case of a gasoline engine. Therefore, in a hydrogen engine, since the detection result of the knock sensor cannot be used as circumstantial evidence for the occurrence of pre-ignition, it is more difficult to distinguish pre-ignition from other combustion failures than in the case of a gasoline engine.

[0027] According to the pre-ignition detection device of the present embodiment described above, the following effects can be achieved. (1) The processor 31 detects the occurrence of pre-ignition through the following two processes. One of the two processes is a process of calculating the rotational fluctuation amount RF of the engine 10 and the self-ignition start timing. The other is a process of determining that pre-ignition has occurred when the rotational fluctuation amount RF is equal to or greater than a predetermined threshold value X and the self-ignition start timing is earlier than a predetermined time T. Also, the self-ignition start timing is the time when the temperature of the air-fuel mixture in the combustion chamber 13 during the compression stroke reaches the ignition point of the air-fuel mixture. Pre-ignition occurs after the self-ignition start timing. Also, when pre-ignition occurs at a later time, the rotational fluctuation of the engine 10 becomes smaller than when it occurs at an earlier time. Therefore, pre-ignition accompanied by significant rotational fluctuation occurs when the self-ignition start timing is earlier than a certain degree. Thus, by referring to both the rotational fluctuation amount RF and the self-ignition start timing, it may be possible to distinguish pre-ignition from other combustion failures. Therefore, the pre-ignition detection device of the present embodiment has the effect of improving the detection accuracy of pre-ignition.

[0028] (2) The processor 31 calculates the self-ignition start timing based on the intake air amount of the combustion chamber 13 and the intake air temperature THA. These intake air amount and intake air temperature THA are the main factors that determine the self-ignition start timing. Therefore, the calculation accuracy of the self-ignition start timing, and thus the detection accuracy of pre-ignition, can be improved.

[0029] (3) The processor 31 determines whether the rotational fluctuation amount RF is equal to or greater than a predetermined threshold value X based on the angular velocity of the crankshaft 15 of the engine 10. Therefore, the determination accuracy of whether the rotational fluctuation amount RF is equal to or greater than a predetermined threshold value X, and thus the detection accuracy of pre-ignition, can be improved.

[0030] (4) Even in a hydrogen engine where it is more difficult to distinguish pre-ignition from other combustion failures than in a gasoline engine, pre-ignition can be accurately detected. (Other embodiments) This embodiment can be implemented with the following modifications. This embodiment and the following modification examples can be implemented in combination with each other within a technically consistent range.

[0031] · As the rotational fluctuation amount RF calculated by the ECU 30, a physical quantity different from that in the above embodiment may be used. The rotational fluctuation amount RF may be a physical quantity representing the magnitude of the rotational fluctuation of the engine 10, such as the change width of the engine rotational speed NE for each combustion.

[0032] · The self-ignition start timing may be calculated in a method different from that in the above embodiment. In addition to the intake air amount and the intake air temperature THA, the hydrogen injection amount, the wall temperature of the cylinder 11, etc. are also factors that determine the self-ignition start timing. By performing calculations based on them, the calculation accuracy of the self-ignition start timing can be improved. Also, the self-ignition start timing may be calculated without using either the intake air amount or the intake air temperature THA.

[0033] · The pre-ignition detection device of the above embodiment is also applicable to a spark ignition engine using a fuel other than hydrogen such as gasoline. (Supplementary Notes) [Supplementary Note 1] A device for detecting the occurrence of pre-ignition in a spark ignition engine that ignites the air-fuel mixture in the combustion chamber by spark discharge, including a process of calculating the rotational fluctuation amount and the self-ignition start timing of the engine, and a process of determining that pre-ignition has occurred when the rotational fluctuation amount is equal to or greater than a predetermined threshold value and the self-ignition start timing is earlier than a predetermined time, and detecting the occurrence of pre-ignition through these processes, and the self-ignition start timing is the time when the temperature of the air-fuel mixture in the combustion chamber during the compression stroke reaches the ignition point of the air-fuel mixture. A pre-ignition detection device.

[0034] [Supplementary Note 2] The pre-ignition detection device according to Supplementary Note 1, wherein the fuel of the engine is hydrogen. [Supplementary Note 3] The pre-ignition detection device according to Supplementary Note 1 or Supplementary Note 2, which calculates the self-ignition start timing based on the intake air amount of the combustion chamber.

[0035] [Appendix 4] The pre-ignition detection device according to any one of Appendices 1 to 3, which calculates the self-ignition start timing based on the temperature of the intake air inhaled into the combustion chamber. [Appendix 5] The pre-ignition detection device according to any one of Appendices 1 to 4, which determines whether or not the amount of rotational fluctuation is equal to or greater than a predetermined threshold value based on the angular velocity of the crankshaft of the engine.

Explanation of Signs

[0036] 10 Engine 11 Cylinder 12 Piston 13 Combustion Chamber 14 Connecting Rod 15 Crankshaft 16 Intake Passage 17 Injector 18 Ignition Device 19 Exhaust Passage 20 Airflow Meter 21 Throttle Valve 22 Crank Angle Sensor 23 Intake Air Temperature Sensor 30 ECU 31 Processor 32 Memory

Claims

1. An apparatus for detecting the occurrence of pre-ignition in a spark-ignition engine that ignites an air-fuel mixture in a combustion chamber by spark discharge, detecting the occurrence of the pre-ignition through a process of calculating the amount of rotational fluctuation of the engine and the auto-ignition start time, and a process of determining that the pre-ignition has occurred when the amount of rotational fluctuation is equal to or greater than a predetermined threshold value and the auto-ignition start time is earlier than a predetermined time, and the auto-ignition start time is the time when the temperature of the air-fuel mixture in the combustion chamber during the compression stroke reaches the ignition point of the air-fuel mixture Pre-ignition detection device.

2. The pre-ignition detection device according to claim 1, wherein the fuel of the engine is hydrogen.

3. The pre-ignition detection device according to claim 1, wherein the auto-ignition start time is calculated based on the intake air amount of the combustion chamber.

4. The pre-ignition detection device according to claim 1, wherein the auto-ignition start time is calculated based on the temperature of the intake air sucked into the combustion chamber.

5. The pre-ignition detection device according to claim 1, wherein based on the angular velocity of the crankshaft of the engine, it is determined whether the amount of rotational fluctuation is equal to or greater than a predetermined threshold value.

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