Pre-ignition 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 preignition detection device for detecting the occurrence of preignition in a spark ignition engine.

Background Art

[0002] In a spark ignition engine that ignites an air-fuel mixture in a combustion chamber by spark discharge, preignition may occur. Preignition 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 preignition based on the engine speed 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 preignition may also cause engine speed fluctuations. Therefore, based only on the speed fluctuation amount, there is a possibility of false detection that preignition has occurred when a combustion failure other than preignition occurs.

Means for Solving the Problems

[0005] A pre-ignition detection device that solves the above problems is a pre-ignition detection device that detects the occurrence of pre-ignition in a spark-ignition type engine that ignites a fuel-air mixture in a combustion chamber by spark discharge, and calculates the auto-ignition start time, which is the time when the temperature of the fuel-air mixture reaches the ignition temperature of the fuel-air mixture due to compression of the fuel-air mixture in the combustion chamber during the compression stroke, and determines that pre-ignition has occurred when the amount of rotational fluctuation of the engine is greater than or equal to a predetermined threshold and the auto-ignition start time is earlier than the predetermined time. [Effects of the Invention]

[0006] The above-mentioned pre-ignition detection device has the effect of improving the accuracy of pre-ignition detection in spark-ignition engines. [Brief explanation of the drawing]

[0007] [Figure 1] This diagram schematically shows the configuration of one embodiment of a pre-ignition detection device. [Figure 2] This is a flowchart of the pre-ignition detection routine executed by the processor of the pre-ignition detection device described above. [Figure 3] (A) is a time chart showing the change in the rotational speed of the engine's crankshaft, and (B) is a time chart showing the change in the angular velocity of the engine's crankshaft. [Figure 4] This graph shows the changes in cylinder pressure during normal combustion and pre-ignition in a gasoline engine. [Figure 5] This graph shows the changes in cylinder pressure during normal combustion and pre-ignition in a hydrogen engine. [Modes for carrying out the invention]

[0008] An embodiment of the pre-ignition detection device will be described in detail below with reference to Figures 1 to 5. <Engine 10 Configuration> First, with reference to Figure 1, the configuration of the engine 10 to which the pre-ignition detection device of this embodiment is applied will be described. The engine 10 shown in Figure 1 is a hydrogen engine, and its fuel is hydrogen. The engine 10 includes a cylinder 11 and a piston 12 that is reciprocally movably housed within the cylinder 11. Within the cylinder 11, a combustion chamber 13 for burning the fuel-air mixture is partitioned by the piston 12. The piston 12 is connected to the crankshaft 15, which is the output shaft of the engine 10, via a connecting rod 14. The connecting rod 14 and the crankshaft 15 constitute a linkage mechanism that converts the reciprocating motion of the piston 12 into the rotational motion of the crankshaft 15. Furthermore, the engine 10 includes an intake passage 16, an injector 17, an ignition device 18, and an exhaust passage 19. A fuel-air 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 fuel-air 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 fuel-air mixture is discharged from the combustion chamber 13 through the exhaust passage 19. The intake passage 16 is equipped with an airflow meter 20 for detecting the intake airflow rate GA of the intake passage 16, and a throttle valve 21 for adjusting the intake airflow rate GA.

[0009] <Configuration of the pre-ignition detection device> Next, referring to Figure 1, the configuration of the pre-ignition detection device of this embodiment will be described. In this embodiment, the ECU (Electronic Control Unit) 30 for engine control constitutes the pre-ignition detection device. The ECU 30 receives detection signals from various sensors for detecting the operating state of the engine 10. Examples of such sensors include the airflow meter 20 mentioned above, the crank angle sensor 22 which detects the crank angle, which is the rotation angle of the crankshaft 15, and the intake air temperature sensor 23 which detects the intake air temperature THA in the intake passage 16. The ECU 30 has a processor 31 and a memory 32. The memory 32 has programs and data for engine control stored in advance. The processor 31 executes the program read from the memory 32 to calculate various control variables of the engine 10 based on the detection results of each sensor. Examples of control variables of the engine 10 calculated by the processor 31 are the amount and timing of hydrogen injection from the injector 17, the ignition timing of the air-fuel mixture due to 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 injectors 17, ignition system 18, throttle valve 21, etc., based on the operation values ​​calculated by the processor 31.

[0010] <Pre-ignition detection process> In engine 10, pre-ignition may occur, where the fuel-air mixture in the combustion chamber 13 self-ignites and begins combustion before the ignition device 18 performs ignition by spark discharge. The ECU 30 detects the occurrence of pre-ignition in engine 10. The details of the pre-ignition detection process performed by the ECU 30 are described below. The pre-ignition detection process is performed by the processor 31 executing a pre-ignition detection program read from memory 32. In the following description, the state in which no pre-ignition has occurred and combustion of the fuel-air mixture in the combustion chamber 13 begins due to spark discharge from the ignition device 18 is described as normal combustion.

[0011] Figure 2 shows the processing procedure of the pre-ignition detection routine executed by the processor 31 for pre-ignition detection. The processor 31 repeatedly executes this routine at predetermined control cycles while the engine 10 is running.

[0012] When this routine is started, the processor 31 first calculates the rotational fluctuation amount RF of the engine 10 (S100). Based on the detection result of the crank angle sensor 22, the processor 31 calculates the engine rotational speed NE and the angular velocity of the crankshaft 15 by finding the derivative of the engine rotational speed NE. Then, the processor 31 calculates the absolute value of the minimum angular velocity for each combustion cycle, or the range of change in angular velocity for each combustion cycle, as the value of the rotational fluctuation amount RF.

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

[0014] In this embodiment, the autoignition start time is calculated assuming that 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 until it reaches the ignition point can be calculated using Poisson's law and the first law of thermodynamics, based on the volume of the combustion chamber 13 at the start of the compression stroke, the intake air volume, the intake air temperature THA, the specific heat ratio of the air-fuel mixture, etc. Since the volume of the combustion chamber 13 is determined by the crank angle, the autoignition start time can be determined by calculating the time [BTDC°] when the volume of the combustion chamber 13 reaches the calculated value based on these relationships.

[0015] And when both of the following requirements A and 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 fluctuation amount RF calculated in S100 is greater than or equal to 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 optimum ignition timing is set as the predetermined timing T. Although the torque generated by the engine 10 changes depending on the ignition timing, the optimum 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 optimum ignition timing or a timing later than that. 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 in 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] <Operations 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. 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. Thus, the engine rotational speed NE repeats ascending and descending 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 engine rotational speed fluctuation amount RF of the engine 10 increases. Thus, when the engine rotational speed fluctuation of the engine 10 exceeds the maximum fluctuation amount, which is the maximum value of the rotational speed fluctuation amount RF during normal combustion, there is a possibility that pre-ignition has occurred.

[0020] In the case of this embodiment, in the pre-ignition detection routine of FIG. 2, the processor 31 calculates the engine rotational speed fluctuation amount RF of the engine 10 (S100). And the processor 31 uses that the rotational speed fluctuation amount RF is equal to or greater than a predetermined threshold value X as one of the requirements for determining that pre-ignition has occurred. The processor 31 determines whether the engine rotational speed 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 engine rotational speed 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 only on the engine rotational speed fluctuation amount RF of the engine 10.

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

[0023] In this embodiment, the processor 31 calculates the autoignition start time, which is the time when the temperature of the air-fuel mixture in the combustion chamber 13 during the compression stroke reaches its ignition point, in the pre-ignition detection routine shown in Figure 2. The processor 31 then determines that pre-ignition has occurred when the rotational fluctuation amount RF is greater than or equal to a threshold X and the autoignition time is earlier than a predetermined time T. Therefore, the possibility of misidentifying a combustion failure other than pre-ignition as pre-ignition is reduced compared to when the determination is based solely on the rotational fluctuation amount RF. Thus, the pre-ignition detection device of this embodiment has the effect of improving the accuracy of pre-ignition detection.

[0024] The pre-ignition detection device of this embodiment can also be applied to spark-ignition engines other than hydrogen engines, such as gasoline engines. However, in the case of hydrogen engines, it is more difficult to distinguish between pre-ignition and other combustion problems compared to gasoline engines, as described below. Therefore, the pre-ignition detection device of this embodiment is particularly suitable for application to hydrogen engines.

[0025] Figure 4 shows the changes in cylinder pressure Pc during normal combustion and pre-ignition in a gasoline engine. Cylinder pressure Pc represents the pressure inside the combustion chamber 13. As shown in Figure 4, when pre-ignition occurs, cylinder pressure Pc rises sharply. In a gasoline engine, if the fuel-air mixture self-ignites, flame propagation in the combustion chamber 13 does not proceed smoothly as in normal combustion. As a result, after pre-ignition occurs, cylinder pressure Pc fluctuates violently. Such fluctuations in cylinder pressure Pc during pre-ignition can be detected by a knock sensor or the like for knock detection. In contrast, such fluctuations in cylinder pressure Pc do not occur in combustion problems other than pre-ignition. Most gasoline engines are equipped with knock sensors. Thus, in the case of a gasoline engine, pre-ignition and other combustion problems can be distinguished by referring to both the rotational speed fluctuation RF and the detection results of the knock sensor.

[0026] Figure 5 shows the changes in cylinder pressure Pc during normal combustion and 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, the cylinder pressure Pc rises earlier and more rapidly when pre-ignition occurs than in a gasoline engine. Furthermore, in a hydrogen engine, the flame propagates throughout the combustion chamber 13 faster after pre-ignition than in a gasoline engine. Therefore, in a hydrogen engine, the drastic fluctuations in cylinder pressure Pc after pre-ignition do not occur as seen in a gasoline engine. Consequently, in a hydrogen engine, the results of the knock sensor cannot be used as corroborating evidence of pre-ignition, making it more difficult to distinguish between pre-ignition and other combustion problems than in a gasoline engine.

[0027] The pre-ignition detection device of this embodiment described above can achieve the following effects. (1) The processor 31 detects the occurrence of pre-ignition through the following two processes. One of the two processes is to calculate the rotational speed fluctuation amount RF of the engine 10 and the autoignition start time. The other is to determine that pre-ignition has occurred if the rotational speed fluctuation amount RF is greater than or equal to a predetermined threshold X and the autoignition start time is earlier than a predetermined time T. The autoignition start time 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 mixture. Pre-ignition occurs after the autoignition start time. Also, if pre-ignition occurs at a later time, the rotational speed fluctuation of the engine 10 will be smaller than if it occurs at an earlier time. Therefore, pre-ignition accompanied by a large rotational speed fluctuation occurs when the autoignition start time is earlier than a certain point. Thus, by referring to both the rotational speed fluctuation amount RF and the autoignition start time, it may be possible to distinguish between pre-ignition and other combustion defects. Therefore, the pre-ignition detection device of this embodiment has the effect of improving the detection accuracy of pre-ignitions.

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

[0029] (3) The processor 31 determines whether the rotational fluctuation amount RF is greater than or equal to a predetermined threshold 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 greater than or equal to a predetermined threshold X, and consequently the accuracy of detecting pre-ignition, can be improved.

[0030] (4) Even in hydrogen engines, where it is more difficult to distinguish between pre-ignition and other combustion failures than in gasoline engines, pre-ignition can be detected with high accuracy. (Other embodiments) This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0031] The rotational fluctuation amount RF calculated by the ECU 30 may be a different physical quantity than that used in the above embodiment. The rotational fluctuation amount RF can be any physical quantity that represents the magnitude of the rotational fluctuation of the engine 10, such as the range of change in engine rotational speed NE for each combustion.

[0032] The autoignition start time may be calculated using a method different from that of the above embodiment. In addition to the intake air volume and intake air temperature THA, the amount of hydrogen injected and the wall temperature of the cylinder 11 are also factors that determine the autoignition start time. By performing calculations based on these factors, the accuracy of the calculation of the autoignition start time can be improved. Alternatively, the autoignition start time may be calculated without using either the intake air volume or the intake air temperature THA.

[0033] The pre-ignition detection device of the above embodiment can also be applied to spark-ignition engines that use fuels other than hydrogen, such as gasoline. (Additional notes) [Note 1] A device for detecting the occurrence of pre-ignition in a spark-ignition type engine that ignites a fuel-air mixture in a combustion chamber by spark discharge, comprising: a process for calculating the amount of rotational fluctuation of the engine and the timing of the start of autoignition; and a process for determining that pre-ignition has occurred when the amount of rotational fluctuation is greater than or equal to a predetermined threshold and the timing of the start of autoignition is earlier than a predetermined time, thereby detecting the occurrence of pre-ignition, wherein the timing of the start of autoignition is the time when the temperature of the fuel-air mixture in the combustion chamber during the compression stroke reaches the ignition point of the fuel-air mixture.

[0034] [Note 2] The pre-ignition detection device described in Note 1, wherein the fuel for the engine is hydrogen. [Note 3] A pre-ignition detection device according to Note 1 or Note 2, which calculates the autoignition start time based on the amount of intake air into the combustion chamber.

[0035] [Note 4] A pre-ignition detection device according to any one of Notes 1 to 3, which calculates the auto-ignition start time based on the temperature of the intake air drawn into the combustion chamber. [Note 5] A pre-ignition detection device according to any one of Notes 1 to 4, which determines whether the rotational fluctuation amount is greater than or equal to a predetermined threshold based on the angular velocity of the crankshaft of the engine. [Explanation of Symbols]

[0036] 10 Engines 11 cylinders 12 pistons 13 Combustion chamber 14 Connecting Rods 15 Crankshaft 16 Intake passage 17 Injectors 18 Ignition system 19 Exhaust passage 20 Airflow Meter 21 Throttle valve 22 Crank angle sensor 23 Intake air temperature sensor 30 ECU 31 processors 32 memory

Claims

1. A device for detecting the occurrence of pre-ignition in a spark-ignition engine that ignites the fuel-air mixture in the combustion chamber by a spark discharge, The process involves calculating the amount of rotational speed fluctuation of the engine and the timing of the start of autoignition, and determining that the pre-ignition has occurred if the amount of rotational speed fluctuation is greater than or equal to a predetermined threshold and the timing of the start of autoignition is earlier than a predetermined time, thereby detecting the occurrence of the pre-ignition. Furthermore, the timing of the start of self-ignition 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 mixture. Pre-ignition detection device.

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, which calculates the auto-ignition start time based on the amount of intake air in the combustion chamber.

4. The pre-ignition detection device according to claim 1, which calculates the autoignition start time based on the temperature of the intake air drawn into the combustion chamber.

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

Images