Pre-ignition detection device

Abstract

The invention provides a preignition detection device. The processing circuit calculates a rotational variation amount of the engine and a spontaneous combustion start timing in order to detect the occurrence of pre-ignition in the engine. The engine is of a spark ignition type in which a gas mixture in a combustion chamber is ignited by spark discharge. The spontaneous combustion start timing is the timing at which the temperature of the mixed gas in the combustion chamber during the compression stroke reaches the ignition point of the mixed gas. When the rotational variation amount is equal to or greater than a predetermined threshold value and the spontaneous combustion start timing is earlier than the predetermined timing, it is determined that pre-ignition has occurred in the engine.

Description

[0001] Cross-references of related applications

[0002] This application claims priority to Japanese patent application No. 2023-205275 filed on December 5, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to a pre-ignition detection device. The pre-ignition detection device detects the occurrence of pre-ignition in a spark ignition engine. Background Art

[0004] Spark ignition engines ignite the air-fuel mixture in the combustion chamber by spark discharge. In spark ignition engines, pre-ignition may sometimes occur. Pre-ignition is a phenomenon in which the air-fuel mixture in the combustion chamber ignites spontaneously before the ignition based on the spark discharge is implemented. Japanese Patent Publication No. 2009-275663 discloses a device for detecting the occurrence of pre-ignition based on the rotational variation of the engine. Summary of the invention

[0005] According to one aspect of the present disclosure, a pre-ignition detection device having a processing circuit is provided. The processing circuit calculates the rotational variation and the self-ignition start timing of the engine in order to detect the occurrence of pre-ignition in the engine. The engine is a spark ignition type that ignites the mixture in the combustion chamber by spark discharge. The self-ignition start timing is the timing when the temperature of the mixture in the combustion chamber during the compression stroke reaches the ignition point of the mixture. The processing circuit determines that pre-ignition has occurred in the engine when the rotational variation is greater than a predetermined threshold value and the self-ignition start timing is earlier than a predetermined timing.

[0006] The above-mentioned pre-ignition detection device improves the detection accuracy of pre-ignition in a spark ignition engine.

[0007] However, engine rotation fluctuations may sometimes occur due to poor combustion other than pre-ignition. If pre-ignition is detected based only on the amount of rotation fluctuation, it may be erroneously detected that pre-ignition has occurred when poor combustion other than pre-ignition has occurred. The above structure improves this. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a diagram schematically showing the structure of one embodiment of a pre-ignition detection device.

[0009] Figure 2 yes Figure 1 A flow chart of a pre-ignition detection routine executed by a processor of a pre-ignition detection device.

[0010] Figure 3 The (A) part indicates Figure 1A timing diagram showing changes in the rotation speed of the crankshaft of the engine. Figure 3 Part (B) is a time chart showing the transition of the angular velocity of the crankshaft.

[0011] Figure 4 This is a graph showing changes in cylinder pressure during normal combustion and during pre-ignition in a gasoline engine.

[0012] Figure 5 This is a graph showing changes in cylinder pressure during normal combustion and during the occurrence of pre-ignition in a hydrogen engine. DETAILED DESCRIPTION

[0013] It should be understood that the description “at least one of A and B” herein means “only A” or “only B” or “both A and B”.

[0014] Below, refer to Figure 1~Figure 5 One embodiment of the pre-ignition detection device is described in detail.

[0015] <Structure of Engine 10>

[0016] First, refer to Figure 1 , the structure of the engine 10 to which the pre-ignition detection device of the present embodiment is applied will be described. Figure 1 The engine 10 shown is a hydrogen engine, and its fuel is hydrogen. The engine 10 includes a cylinder 11 and a piston 12 which is freely reciprocatingly accommodated in the cylinder 11. A combustion chamber 13 for burning a mixture is 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 connecting rod mechanism which converts the reciprocating motion of the piston 12 into the rotational motion of the crankshaft 15. In addition, the engine 10 includes an intake passage 16, an injector 17, an ignition device 18, and an exhaust passage 19. A 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 mixture in the combustion chamber 13 is ignited by spark discharge generated by the ignition device 18. Exhaust gas generated by the combustion of the mixture is discharged from the combustion chamber 13 through the exhaust passage 19. The intake passage 16 is provided with an air flow meter 20 for detecting an intake air flow rate GA in the intake passage 16 and a throttle valve 21 for adjusting the intake air flow rate GA.

[0017] <Structure of Pre-ignition Detection Device>

[0018] Next, continue to refer to Figure 1, the structure of the pre-ignition detection device of the present embodiment is described. In the case of the present embodiment, the ECU (Electronic Control Unit: electronic control unit) 30 for engine control constitutes the pre-ignition detection device. Detection signals of various sensors for detecting the operating state of the engine 10 are input to the ECU 30. Examples of such sensors include the above-mentioned air flow meter 20, the crank angle sensor 22 for detecting the rotation angle of the crankshaft 15, that is, the crank angle, and the 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. The memory 32 stores programs and data for engine control in advance. The processor 31 calculates various operation quantities of the engine 10 based on the detection results of each sensor by executing the program read from the memory 32. The processor 31 is a processing device or a processing circuit. Examples of the operation quantities of the engine 10 calculated by the processor 31 are the injection amount and injection timing of hydrogen of the injector 17, the ignition timing of the mixture based on the spark discharge of the ignition device 18, and the opening rate 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 , and the like based on the operation amount calculated by the processor 31 .

[0019] <Pre-ignition Detection Processing>

[0020] Pre-ignition sometimes occurs in the engine 10. In pre-ignition, the air-fuel mixture in the combustion chamber 13 ignites by itself before the ignition device 18 performs ignition based on spark discharge, thereby starting combustion. The ECU 30 detects the occurrence of pre-ignition in the engine 10. The following describes the details of the pre-ignition detection process performed by the ECU 30. The pre-ignition detection process is performed by the processor 31 executing a program for pre-ignition detection read from the memory 32. In the following description, normal combustion refers to the following state. That is, in normal combustion, pre-ignition does not occur. Moreover, in normal combustion, the air-fuel mixture in the combustion chamber 13 starts to burn by the spark discharge of the ignition device 18.

[0021] Figure 2 The following is a processing procedure of a pre-ignition detection routine executed by the processor 31 for the pre-ignition detection process. The processor 31 repeatedly executes this routine every predetermined control cycle while the engine 10 is operating.

[0022] After starting this routine, the processor 31 first calculates the rotational variation RF of the engine 10 (S100). The processor 31 calculates the engine speed NE based on the detection result of the crank angle sensor 22. The processor 31 calculates the angular velocity of the crankshaft 15 by obtaining the differential value of the engine speed NE. The processor 31 calculates the absolute value of the minimum value of the angular velocity per combustion cycle or the variation range of the angular velocity per combustion cycle as the value of the rotational variation RF.

[0023] Next, the processor 31 calculates the timing of the start of autoignition (S110). The timing of the start of autoignition indicates the timing 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. The ignition point of the air-fuel mixture in the present embodiment is the ignition point of hydrogen. The timing of the start of autoignition is represented by the crank angle [BTDC°] before the compression top dead center. The processor 31 calculates the amount of intake air in the combustion chamber 13 based on the intake air flow rate GA, the engine speed NE, the opening rate of the throttle valve 21, etc. The processor 31 calculates the timing of the start of autoignition based on the intake air amount and the intake air temperature THA.

[0024] In the present embodiment, the timing of the start of autoignition is calculated as a case where the air-fuel mixture is adiabatically compressed in the combustion chamber 13 during the compression stroke. The volume of the combustion chamber 13 when the air-fuel mixture is adiabatically compressed to the ignition point can be calculated by using Poisson's law and the first law of thermodynamics. In detail, 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 temperature THA, the specific heat ratio of the air-fuel mixture, etc. The volume of the combustion chamber 13 is determined by the crankshaft angle. Based on these relationships, the timing [BTDC°] when the volume of the combustion chamber 13 becomes the calculated value is calculated. Therefore, the timing of the start of autoignition is obtained.

[0025] When both the next requirement A and the requirement B are satisfied (S120: Yes and S130: Yes), the processor 31 determines that pre-ignition has occurred (S140). Requirement A is that the rotational variation RF calculated in S100 is greater than the predetermined threshold value X. The value of the predetermined threshold value X is set to a value greater than the maximum rotational variation. The maximum rotational variation is the maximum value of the rotational variation RF during normal combustion. Requirement B is that the self-ignition start timing calculated in S110 is earlier than the predetermined timing T. The predetermined timing T is set to a timing earlier than the optimal ignition timing. The torque generated by the engine 10 varies according to the ignition timing. At the optimal ignition timing, the torque generated by the engine 10 is the largest. The ECU 30 controls the ignition timing of the mixture based on the spark discharge of the ignition device 18 to the optimal ignition timing or a timing later than the optimal ignition timing. Therefore, regardless of the control state of the engine 10, the predetermined timing T becomes a timing earlier than the ignition of the ignition device 18. After processor 31 determines in S140 that pre-ignition has occurred, or after a negative determination in either S120 or S130 , it ends the processing of this routine in the current control cycle.

[0026] When the processor 31 determines that pre-ignition has occurred in this routine, it corrects the operation amount of the engine 10 for suppressing the occurrence of pre-ignition. An example of the correction of the operation amount for suppressing the occurrence of pre-ignition is to reduce the opening rate of the throttle valve 21. If the opening rate of the throttle valve 21 is reduced, the intake air amount of the combustion chamber 13 is reduced. As a result, the temperature rise of the air-fuel mixture in the combustion chamber 13 caused by the adiabatic compression in the compression stroke can be suppressed. Therefore, the occurrence of pre-ignition is suppressed.

[0027] <Functions and Effects of Implementation Methods>

[0028] Figure 3 The portion (A) of shows the change in the engine speed NE during the period before and after the occurrence of pre-ignition. Figure 3 Part (B) shows the change in the angular velocity of the crankshaft 15 during the above period.

[0029] The top surface of the piston 12 receives the combustion pressure generated by the combustion of the mixture in the combustion chamber 13. As a result, the engine speed NE accelerates. After reaching the peak, the engine speed NE decelerates until the next combustion. In this way, the engine speed NE repeatedly rises and falls at each combustion.

[0030] If pre-ignition occurs, the piston 12 in the cylinder 11 in the compression stroke is hindered from rising. Therefore, the engine speed NE decreases. Therefore, when pre-ignition occurs, the engine speed NE is greatly decelerated compared to the deceleration of the engine speed NE during normal combustion. As a result, the rotational variation RF of the engine 10 increases. Here, the maximum rotational variation is the maximum value of the rotational variation RF during normal combustion. Therefore, when the rotational variation of the engine 10 exceeds the maximum rotational variation, pre-ignition may occur.

[0031] In the case of this embodiment, the processor 31 Figure 2 The processor 31 calculates the rotational variation RF of the engine 10 in the pre-ignition detection routine (S100). The processor 31 determines that the rotational variation RF is greater than a predetermined threshold value X as one of the conditions for determining that pre-ignition has occurred. The processor 31 determines whether the rotational variation RF of the engine 10 is greater than the threshold value X based on the angular velocity of the crankshaft 15. Specifically, the processor 31 calculates the absolute value of the minimum value of the angular velocity of each combustion of the engine 10 or the variation range of the angular velocity of each combustion as the value of the rotational variation RF of the engine 10. Figure 3 "Δ1" in the portion (B) of represents the absolute value of the minimum angular velocity when pre-ignition occurs. Figure 3 “Δ2” in part (B) indicates the variation range of the angular velocity when pre-ignition occurs.

[0032] However, when poor combustion other than pre-ignition, such as misfire, occurs, the engine speed NE also decreases. Therefore, it may be difficult to distinguish pre-ignition from poor combustion other than pre-ignition based only on the rotational fluctuation amount RF of the engine 10 .

[0033] On the other hand, the condition for the occurrence of pre-ignition includes that the temperature of the air-fuel mixture in the combustion chamber 13 becomes equal to or higher than the ignition point due to the adiabatic compression in the compression stroke. On the other hand, when the pre-ignition occurs near the compression top dead center, the decrease in the engine speed NE becomes smaller than when the pre-ignition occurs at an earlier timing. Therefore, even when the rotation variation of the engine 10 occurs, when the timing when the temperature of the air-fuel mixture reaches the ignition point is after the ignition timing, it is considered that the cause of the rotation variation of the engine 10 is other than the pre-ignition.

[0034] In the case of this embodiment, the processor 31 Figure 2 The auto-ignition start timing is calculated in the pre-ignition detection routine. At the auto-ignition start timing, 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. The processor 31 determines that pre-ignition has occurred when the rotational variation RF is greater than the threshold value X and the auto-ignition time is earlier than the predetermined time T. Therefore, compared with the case where the occurrence of pre-ignition is determined based on the rotational variation RF alone, for example, the present embodiment has a low possibility of misjudging a combustion failure other than pre-ignition as pre-ignition. Therefore, in the pre-ignition detection device of the present embodiment, the detection accuracy of pre-ignition is improved.

[0035] Such a pre-ignition detection device of the present embodiment can also be applied to spark ignition engines other than hydrogen engines such as gasoline engines. Generally, in hydrogen engines, it is difficult to distinguish pre-ignition from other combustion failures compared to gasoline engines. Therefore, the pre-ignition detection device of the present embodiment is particularly suitable for application to hydrogen engines.

[0036] Figure 4 The figure shows the change of the cylinder pressure Pc in each case of normal combustion and pre-ignition in a gasoline engine. The double-dashed line shows the cylinder pressure Pc in normal combustion. The solid line shows the cylinder pressure Pc when pre-ignition occurs. The cylinder pressure Pc shows the pressure in the combustion chamber 13. Figure 4As shown, when pre-ignition occurs, the cylinder pressure Pc rises sharply. In the case of a gasoline engine, when the mixture ignites spontaneously, unlike normal combustion, the flame propagation in the combustion chamber 13 cannot proceed smoothly. As a result, after the pre-ignition occurs, the cylinder pressure Pc fluctuates drastically. Such changes in the cylinder pressure Pc when pre-ignition occurs can be detected by a knock sensor for knock detection, etc. In contrast, such changes in the cylinder pressure Pc do not occur in poor combustion other than pre-ignition. A knock sensor is provided in most gasoline engines. That is, in the case of a gasoline engine, by referring to the rotational variation RF and the detection results of the knock sensor together, it is possible to distinguish between pre-ignition and poor combustion other than pre-ignition.

[0037] Figure 5 Indicates the change of cylinder pressure Pc in each case during normal combustion and when pre-ignition occurs in a hydrogen engine. The double-dotted line indicates the cylinder pressure Pc during normal combustion. The solid line indicates the cylinder pressure Pc when pre-ignition occurs. The ignition point of hydrogen is higher than that of gasoline. The propagation speed of the flame of hydrogen is higher than that of the flame of gasoline. Therefore, in a hydrogen engine, when pre-ignition occurs, the cylinder pressure Pc rises earlier and more sharply than in a gasoline engine. In a hydrogen engine, after pre-ignition occurs, the flame propagates to the entire combustion chamber 13 faster than in a gasoline engine. Therefore, in a hydrogen engine, unlike a gasoline engine, it is difficult for the cylinder pressure Pc to change drastically after pre-ignition occurs. Therefore, in a hydrogen engine, the detection result of the knock sensor cannot be used as circumstantial evidence of the occurrence of pre-ignition. Therefore, it is more difficult to distinguish between pre-ignition and poor combustion other than pre-ignition in a hydrogen engine than in a gasoline engine.

[0038] According to the pre-ignition detection device of the present embodiment described above, the following effects can be achieved.

[0039] (1) The processor 31 detects the occurrence of pre-ignition by the following two processes. One of the two processes is a process of calculating the rotational variation RF of the engine 10 and the auto-ignition start timing. The other process is a process of determining that pre-ignition has occurred when the rotational variation RF is greater than a predetermined threshold value X and the auto-ignition start timing is earlier than a predetermined timing T. Here, at the auto-ignition start timing, 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 auto-ignition start time. In addition, when pre-ignition occurs at a later timing, the rotational variation of the engine 10 becomes smaller than when pre-ignition occurs at an earlier timing. Therefore, pre-ignition accompanied by a large engine rotational variation occurs when the auto-ignition start timing is earlier than a certain degree. Therefore, by referring to both the rotational variation RF and the auto-ignition start timing, it is sometimes possible to distinguish between pre-ignition and poor combustion other than pre-ignition. Therefore, in the pre-ignition detection device of the present embodiment, the detection accuracy of pre-ignition is improved.

[0040] (2) The processor 31 calculates the auto-ignition start timing based on the intake air amount and the intake air temperature THA of the combustion chamber 13. The intake air amount and the intake air temperature THA are the main factors that determine the auto-ignition start timing. Therefore, the calculation accuracy of the auto-ignition start timing is improved, and the detection accuracy of pre-ignition is improved.

[0041] (3) The processor 31 determines whether the rotational fluctuation amount RF is equal to or greater than the predetermined threshold value X based on the angular velocity of the crankshaft 15 of the engine 10. Therefore, the accuracy of determining whether the rotational fluctuation amount RF is equal to or greater than the predetermined threshold value X is improved, thereby improving the accuracy of detecting pre-ignition.

[0042] (4) Generally, it is difficult for a hydrogen engine to distinguish between pre-ignition and combustion failure other than pre-ignition, as compared to a gasoline engine. The present embodiment can also detect pre-ignition with high accuracy in a hydrogen engine.

[0043] (Other Implementations)

[0044] This embodiment can be implemented by being modified as follows. This embodiment and the following modified examples can be implemented in combination with each other within the range that there is no technical contradiction.

[0045] A physical quantity different from that in the above embodiment may be used as the rotation variation RF calculated by the ECU 30. The rotation variation RF may be a physical quantity indicating the magnitude of the rotation variation of the engine 10, such as the variation range of the engine speed NE per combustion.

[0046] The auto-ignition start timing may be calculated by a method different from the above-mentioned embodiment. In addition to the intake air amount and the intake air temperature THA, the injection amount of hydrogen, the wall temperature of the cylinder 11, etc. are also factors that determine the auto-ignition start timing. By performing calculations based on these factors, the calculation accuracy of the auto-ignition start timing can be improved. In addition, the auto-ignition start timing may be calculated without using either the intake air amount or the intake air temperature THA.

[0047] The pre-ignition detection device of the above-described embodiment can also be applied to a gasoline engine or the like, that is, a spark ignition engine using a fuel other than hydrogen.

[0048] The pre-ignition detection device may include a CPU and a ROM to execute software processing. That is, the pre-ignition detection device only needs to include any one of the following structures (a) to (c).

[0049] (a) The pre-ignition detection device includes one or more processors that execute various processes according to a computer program. The processor includes a CPU and a memory such as a RAM and a ROM. The memory stores a program code or an instruction configured to cause the CPU to execute a process. The memory, i.e., a non-transitory computer-readable storage medium, includes all available media that can be accessed by a general-purpose or special-purpose computer.

[0050] (b) The pre-ignition detection device has one or more dedicated hardware circuits that execute various processes. As a dedicated hardware circuit, for example, an integrated circuit for a specific purpose, that is, ASIC or FPGA, can be cited. ASIC is the abbreviation of "Application Specific Integrated Circuit", and FPGA is the abbreviation of "Field Programmable Gate Array".

[0051] (c) The pre-ignition detection device includes a processor that executes a part of various processes according to a computer program and a dedicated hardware circuit that executes the remaining processes among the various processes.

Claims

1. A pre-ignition detection device, comprising a processing circuit, wherein the processing circuit is configured to perform the following processing: Calculating a rotational variation amount and a self-ignition start timing of an engine, wherein the engine is a spark ignition type that ignites a mixture in a combustion chamber by spark discharge, and the self-ignition start timing is a timing when a temperature of the mixture in the combustion chamber during a compression stroke reaches an ignition point of the mixture; and When the rotation variation amount is equal to or greater than a predetermined threshold value and the self-ignition start timing is earlier than a predetermined timing, it is determined that pre-ignition has occurred in the engine, thereby detecting the occurrence of the pre-ignition in the engine.

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

3. The pre-ignition detection device according to claim 1 or 2, wherein: The processing circuit is configured to calculate the auto-ignition start timing based on the intake air amount of the combustion chamber.

4. The pre-ignition detection device according to any one of claims 1 to 3, wherein: The processing circuit is configured to calculate the auto-ignition start timing based on the temperature of intake air sucked into the combustion chamber.

5. The pre-ignition detection device according to any one of claims 1 to 4, wherein: The processing circuit is configured to determine whether the rotational variation amount is equal to or greater than the predetermined threshold value based on an angular velocity of a crankshaft of the engine.

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