Misfire detection device for internal combustion engine

Abstract

The present application provides a misfire detection device of an internal combustion engine, which improves the detection accuracy of the generation of misfire of a level at which the exhaust purification function of a trap is impaired. The generation of misfire of a level at which the exhaust purification function of a catalyst is impaired (OT misfire) is detected. When the generation of OT misfire is detected, a basic OT misfire rate is multiplied by a correction coefficient corresponding to the PM accumulation amount. The basic OT misfire rate is a basic value of the OT misfire rate set based on the operating state of the engine. The more the PM accumulation amount, the smaller the value of the correction coefficient. Therefore, the more the PM accumulation amount, the smaller the value of the OT misfire rate after multiplication. Therefore, it is possible to detect OT misfire due to the combustion of PM at the time of misfire generation with a higher reliability.

Description

Technical Field

[0001] This invention relates to a misfire detection device for internal combustion engines. Background Technology

[0002] Japanese Patent Application Publication No. 5-202799 discloses a misfire detection device that evaluates damage to an exhaust gas purification device caused by a misfire based on the operating state of an internal combustion engine. This conventional device calculates an evaluation value when a misfire occurs during the evaluation period. This evaluation value is calculated in a manner corresponding to the operating state at the time of the misfire. Furthermore, this conventional device aggregates the evaluation values ​​calculated during the evaluation period, and if the aggregated value exceeds a threshold, it determines that a misfire has occurred at a level indicating functional impairment of the exhaust gas purification device.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 5-202799 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] However, the aforementioned conventional devices do not consider the case where an exhaust gas purification device is constructed using a trap (e.g., a trap with a honeycomb structure). In this case, PM (particulate matter) accumulated in the trap can significantly affect the aforementioned determination. This is because if PM accumulates in the trap, the combustion of unburned fuel flowing into the trap during a misfire will induce the combustion of the accumulated PM, causing a sharp rise in exhaust gas temperature. Therefore, in the aforementioned conventional devices, it is possible to fail to detect misfires of a level where the exhaust gas purification function of the trap is impaired.

[0008] The present invention was made in view of the above-mentioned problems, and its object is to provide a misfire detection device for internal combustion engines that can improve the detection accuracy of misfire generation when the exhaust gas purification function of the trap is impaired.

[0009] The first invention is a misfire detection device for an internal combustion engine for solving the above-mentioned problems, and has the following features.

[0010] The fire detection device includes an accumulation estimation unit, a judgment value setting unit, and a fire judgment unit.

[0011] The accumulation estimation section estimates the amount of particulate matter accumulated in the exhaust gas purification trap of the internal combustion engine.

[0012] The determination value setting unit sets the misfire determination value based on the operating state of the internal combustion engine and the amount of particulate matter accumulated.

[0013] If the prescribed conditions for determining the fire fault value are met, the fire fault determination unit determines that a fire has occurred at the level of impaired exhaust purification function of the trap.

[0014] The determination value setting unit sets the fire determination value to a smaller value when the amount of accumulation is greater.

[0015] The second invention, based on the first invention, also has the following features.

[0016] Furthermore, the determination value setting unit sets a basic fire failure determination value based on the operating state, sets a correction coefficient based on the accumulation amount, and sets the fire failure determination value by multiplying the basic fire failure determination value by the correction coefficient.

[0017] The greater the amount of accumulation, the smaller the correction coefficient is set to.

[0018] The third invention, based on the first or second invention, also has the following features.

[0019] The internal combustion engine is a spark-ignition engine equipped with an injector that directly injects fuel into the cylinder.

[0020] Invention Effects

[0021] According to the first invention, the greater the accumulation of particulate matter (i.e., PM), the smaller the misfire determination value should be. Setting the misfire determination value to a smaller value can suppress the false detection of misfires that, although caused by the combustion of PM during a misfire, result in damage to the exhaust gas purification function of the trap, such misfires can be detected with high precision. In other words, misfires that, due to the combustion of PM during a misfire, result in damage to the exhaust gas purification function of the trap can be detected with high accuracy.

[0022] According to the second invention, the greater the amount of PM accumulation, the smaller the correction factor can be set. Therefore, the greater the amount of PM accumulation, the smaller the fire hazard determination value, which is set by multiplying the basic fire hazard determination value by the correction factor, can be.

[0023] In recent years, spark-ignition engines have been required to have smaller displacements and higher compression ratios. When fuel is injected directly into the cylinder of such engines, particulate matter (PM) is more easily expelled compared to when fuel is injected into the intake port. According to the third invention, this allows for the precise detection of misfires that occur at levels where the exhaust gas purification function of the trap in a spark-ignition engine equipped with a direct injection system is impaired. Attached Figure Description

[0024] Figure 1This is a diagram illustrating an example of the structure of a fire detection device according to an embodiment of the present invention.

[0025] Figure 2 This is a block diagram illustrating an example of the setting process for the OT (Overhead Fire Rate).

[0026] Figure 3 This is an example graph showing the relationship between engine speed (or engine load) and basic OT misfire rate.

[0027] Figure 4 This is a graph showing the relationship between PM accumulation and the correction factor.

[0028] Figure 5 This is a flowchart illustrating the process for determining and handling an OT (overhead fire).

[0029] Figure 6 This is a block diagram illustrating another example of the setting process for the OT (Overhead Fire Rate). Detailed Implementation

[0030] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, when the number, quantity, amount, range, etc., of each element are mentioned in the embodiments shown below, the present invention is not limited to the mentioned number unless specifically stated or clearly determined in principle. Furthermore, the structures or steps described in the embodiments shown below are not necessarily essential in the present invention unless specifically stated or clearly determined in principle.

[0031] 1. System Structure Description

[0032] The misfire detection device according to an embodiment of the present invention is a device for detecting misfires in an internal combustion engine installed in a vehicle. Specifically, the internal combustion engine is a spark-ignition engine with multiple cylinders. A GPF (Gasoline Particulate Filter) is provided in the exhaust pipe of this engine. The GPF has a honeycomb structure and traps PM flowing in the exhaust pipe. A catalyst (e.g., a three-way catalyst) for purifying specific components in the exhaust is supported on the surface of the cells constituting the honeycomb. That is, the GPF purifies the exhaust flowing in the exhaust pipe.

[0033] Figure 1 This is a diagram illustrating an example of the structure of the fire detection device according to this embodiment. (As shown...) Figure 1 As shown, the misfire detection device includes a crankshaft angle sensor 10, a throttle sensor 20, an ECU (Electric Control Unit) 30, an injector 40, and a MIL (Malfunction Indicator Light) 50.

[0034] The crankshaft angle sensor 10 is a sensor that detects the rotation angle of the engine crankshaft. The crankshaft angle sensor 10 sends the detected rotation angle information (hereinafter also referred to as "crankshaft angle information") to the ECU 30.

[0035] Throttle sensor 20 is a sensor that detects the opening degree of the engine's throttle valve. Throttle sensor 20 sends the detected opening degree information (hereinafter also referred to as "throttle information") to ECU 30.

[0036] The ECU30 is a microcomputer equipped with a processor, memory, and input / output interfaces. The ECU30 receives various information through these interfaces. Based on this information, the ECU30 performs misfire detection and processing.

[0037] Injectors 40 are installed in each cylinder of the engine. The injectors 40 directly inject fuel into the cylinders of the engine according to instructions from the ECU 30. That is, the internal combustion engine to which the misfire detection device of this embodiment is used is also a direct injection engine.

[0038] The MIL50 is installed on the vehicle's dashboard. The MIL50 is illuminated according to instructions from the ECU30.

[0039] 2. Explanation of ECU30's functions

[0040] As a function for processing engine misfire determination, ECU 30 includes a PM quantity estimation unit 32, an OT (OverTemperature) misfire rate setting unit 34, and an OT misfire determination unit 36. Their functions will be explained below.

[0041] 2.1 PM Estimation Section 32

[0042] The PM quantity estimation unit 32 estimates the amount of PM accumulated in the GPF (hereinafter also referred to as "PM accumulation amount"). The PM accumulation amount is calculated based on the amount of PM captured by the GPF (hereinafter also referred to as "PM capture amount") and the amount of PM oxidized in the GPF (hereinafter also referred to as "PM oxidation amount").

[0043] PM capture rate is calculated by multiplying the amount of PM emitted from the engine (hereinafter also referred to as "PM emission") by a prescribed capture ratio. The PM emission rate is calculated based on the engine's operating conditions. PM oxidation rate is calculated by multiplying a prescribed oxidation ratio by the current PM accumulation rate, which is determined based on, for example, the bed temperature of the cell and the oxygen concentration upstream of the GPF. The PM accumulation rate can be calculated by calculating the difference between the PM capture rate and the PM oxidation rate each cycle and accumulating this difference. It should be noted that the calculation method described here is only one example, and various well-known methods can be applied to the estimation of PM accumulation rate.

[0044] 2.2 OT fire rate setting unit 34

[0045] The OT misfire rate setting unit 34 sets the OT misfire rate. The OT misfire rate is set to detect misfires (hereinafter also referred to as "OT misfires") that impair the exhaust gas purification function of the catalyst due to excessive rise in catalyst bed temperature. The OT misfire rate is set based on a basic OT misfire rate and a correction factor. The basic OT misfire rate is a base value of the OT misfire rate set based on the engine's operating conditions. The OT misfire rate is set by multiplying this base value by a correction factor.

[0046] Figure 2 This is a block diagram illustrating an example of the OT misfire rate setting process performed by the OT misfire rate setting unit 34. In this setting process, the basic OT misfire rate is determined by comparing it with a basic OT misfire rate mapping M1 (hereinafter also simply referred to as "mapping M1"). Mapping M1 is a mapping stored in the memory of ECU 30. Mapping M1 is a mapping that defines the relationship between engine speed and engine load and the basic OT misfire rate.

[0047] Figure 3 This is an example graph showing the relationship between engine speed (or engine load) and basic OT misfire rate. For example... Figure 3 As shown, the higher the engine speed (or engine load), the lower the basic OT misfire rate. The reason for this relationship is that in the low-speed, low-load range, even if some misfires occur, their impact on the rise in bed temperature is small. In contrast, in the high-speed, high-load range, a fewer number of misfires have a greater impact on the rise in bed temperature. It should be noted that the engine speed is calculated based on crankshaft angle information, and the engine load is calculated based on throttle position information and crankshaft angle information.

[0048] Furthermore, during the setting process, the correction factor is determined by comparing it with the correction factor mapping M2 (hereinafter also referred to as "mapping M2"). The comparison of mapping M2 is performed using the latest PM accumulation amount estimated by the PM amount estimation unit 32. Mapping M2 is stored in the memory of ECU 30, just like mapping M1. Mapping M2 is a mapping that defines the relationship between PM accumulation amount and correction factor.

[0049] Figure 4 This is a graph showing the relationship between PM accumulation and the correction factor. (Example) Figure 4 As shown, the greater the PM accumulation, the smaller the correction factor. It should be noted that the correction factor is set to 1.0 when the PM accumulation is zero. That is, the greater the PM accumulation, the smaller the correction factor becomes compared to 1.0. The reason for showing this relationship is that the greater the PM accumulation, the greater the amount of PM burned during a misfire. It should be noted that, as already explained, the combustion of PM during a misfire is induced by unburned fuel flowing into the GPF.

[0050] 2.3 OT Fire Detection Unit 36

[0051] The OT fire detection unit 36 ​​determines whether an OT fire has occurred. Figure 5 This is a flowchart illustrating the process of determining and handling an OT (Operational Time-of-Temperature) misfire based on the OT misfire determination unit 36. It should be noted that... Figure 5 The routine shown is repeated during engine operation.

[0052] exist Figure 5 In the example shown, firstly, a determination is made as to whether the precondition for the determination process is met (step S10). As such preconditions, the following conditions are listed as examples.

[0053] (i) The engine warm-up is complete.

[0054] (ii) The engine is idling or in steady state.

[0055] (iii) There was no sudden change in engine speed.

[0056] (iv) No abnormalities were found in the injectors, ignition devices, and other equipment.

[0057] It should be noted that condition (i) above is determined based on engine coolant temperature. Condition (ii) above is determined based on throttle information or vehicle speed. Condition (iii) above is determined based on crankshaft angle information. Condition (iv) above is determined based on signals generated corresponding to the occurrence of malfunctions in various devices.

[0058] The determination in step S10 is repeated until a positive determination result is obtained. If the determination result in step S10 is positive, the detection allowance counter is incremented to a positive value (step S12). The detection allowance counter counts the engine combustion cycles. The positive value of the detection allowance counter is obtained by incrementing the previous counter value by 1 each time a combustion cycle is performed.

[0059] Next, in step S12, it is determined whether the positive condition of the fire counter is met (step S14). The positive condition of the fire counter is met when the rotational variation value is above a threshold. The rotational variation value is defined as the deviation (standard deviation) of the time required for the crankshaft to rotate a specified rotation angle (e.g., 30°). The rotational variation value is calculated based on the crankshaft angle information.

[0060] If the determination result in step S14 is positive, the fire counter is incremented (step S16). The fire counter counts the number of times the rotational change value is above the threshold. The fire counter is incremented by 1 each time the rotational change value is determined to be above the threshold.

[0061] Next, in step S16, it is determined whether the anomaly detection timer has arrived (step S18). Step S18 is performed even if the determination result in step S14 is negative. The arrival of the anomaly detection timer is determined when the detection allowance counter is above a threshold (e.g., 200 times). If the determination result in step S18 is negative, the process returns to step S12, and the detection allowance counter is incremented to positive.

[0062] If the determination result in step S18 is positive, it is determined whether the positive value condition of the anomaly counter is met (step S20). The positive value condition of the anomaly counter is met if the actual fire rate is higher than the OT fire rate. The actual fire rate is calculated by dividing the current counter value of the fire rate counter by the current counter value of the detection allowance counter. The OT fire rate is the fire rate set by the OT fire rate setting unit 34.

[0063] If the determination result in step S20 is positive, the anomaly counter is incremented (step S22). The anomaly counter counts the number of times the actual fire rate is above the OT fire rate. The anomaly counter is incremented by 1 each time the actual fire rate is determined to be above the OT fire rate.

[0064] If the determination result in step S20 is negative, the anomaly counter counts down (step S24). The anomaly counter counts down by subtracting 1 from the previous counter value each time the actual fire rate is determined to be less than the OT fire rate.

[0065] Next, in step S24, the detection enable counter and the fire counter are initialized (step S26). That is, the counter values ​​of the detection enable counter and the fire counter are set to their initial values ​​(i.e., zero). The processing of step S26 is also performed if the determination result of step S28, which will be described later, is negative.

[0066] Next, in step S22, it is determined whether the anomaly counter is above a threshold (e.g., 3 times) (step S28). In the series of processes from S20 to S24, the anomaly counter is counted positively or negatively based on the determination result of step S20. Therefore, in step S28, an anomaly counter above the threshold means that the anomaly counter has continuously counted positively for a number of times equivalent to the threshold.

[0067] If the determination result in step S28 is positive, MIL50 is illuminated, and fuel injection in the misfired cylinder is stopped (step S30). Illumination of MIL50 is based on an illumination command. Stopping fuel injection in the misfired cylinder is based on a stop injection command to the injector 40 of the misfired cylinder. The injector 40 of the misfired cylinder is determined based on the history of positive values ​​in the misfire counter. For example, the cylinder that contributes most to the positive value of the misfire counter is determined as the misfired cylinder. It should be noted that either an illumination command or a stop injection command can be generated to illuminate MIL50 or stop fuel injection in the misfired cylinder.

[0068] 3. Effects

[0069] According to the embodiment described above, when detecting an OT misfire, a correction factor corresponding to the PM accumulation amount is multiplied by the basic OT misfire rate. The greater the PM accumulation, the smaller the correction factor becomes. Therefore, the greater the PM accumulation, the smaller the OT misfire rate after multiplying by the correction factor. Thus, it is possible to suppress situations where an OT misfire occurs due to PM combustion during a misfire but is falsely detected as not having occurred. In other words, it is possible to detect OT misfires caused by PM combustion during a misfire with high accuracy.

[0070] 4. Correspondence between the above embodiments and the present invention

[0071] PM quantity estimation unit 32 corresponds to the "accumulation quantity estimation unit" of the first invention described above. OT fire failure rate setting unit 34 corresponds to the "judgment value setting unit" of the first invention described above. OT fire failure determination unit 36 ​​corresponds to the "fire failure determination unit" of the first invention described above. OT fire failure rate corresponds to the "fire failure determination value" of the first invention described above. Basic OT fire failure rate corresponds to the "basic fire failure determination value" of the second invention described above.

[0072] 5. Other implementation methods

[0073] The fire detection device described above can also be modified as follows.

[0074] Figure 6 This is a block diagram illustrating another example of the OT misfire rate setting process performed by the OT misfire rate setting unit 34. In this setting process, the OT misfire rate is directly calculated by comparing the OT misfire rate mappings M3, M4, ..., Mn. These mappings M3 to Mn are mappings set according to the relationship between the engine speed and engine load and the basic OT misfire rate based on the PM accumulation amount. It should be noted that the engine speed is calculated based on the crankshaft angle information, the engine load is calculated based on the throttle information and the crankshaft angle information, and the PM accumulation amount is estimated by the PM amount estimation unit 32, which is the same as in the above embodiment.

[0075] The internal combustion engine for which the misfire detection device described above is applied can also be a compression-ignition engine. However, the prerequisite is that the compression-ignition engine has an exhaust gas purification trap and that the exhaust gas purification trap has the same function as the GPF (i.e., PM collection function and exhaust gas purification function). When the compression-ignition engine has such a trap, the occurrence of an OT misfire can be detected through the above-described misfire determination process.

[0076] Label Explanation

[0077] 10 Crankshaft Angle Sensor

[0078] 20 Throttle sensor

[0079] 30 ECU

[0080] 32 PM Estimated Quantity Department

[0081] 34 OT fire rate setting unit

[0082] 36 OT Fire Detection Department

[0083] 40 injectors

[0084] 50 MIL.

Claims

1. A misfire detection device for an internal combustion engine, comprising: The estimated amount of particulate matter accumulated in the exhaust gas purifier of an internal combustion engine is estimated. The judgment value setting unit sets a misfire judgment value based on the operating state of the internal combustion engine and the amount of particulate matter accumulated; and If the prescribed conditions for determining the fire hazard value are met, the fire hazard determination unit determines that a fire has occurred at the level of impaired exhaust purification function of the trap. Its features are, Furthermore, the determination value setting unit sets a basic misfire determination value based on the operating state of the internal combustion engine, sets a correction coefficient based on the accumulation amount, and sets the misfire determination value by multiplying the basic misfire determination value by the correction coefficient. The larger the accumulation amount, the smaller the correction coefficient is set to.

2. The misfire detection device for an internal combustion engine according to claim 1, characterized in that, The internal combustion engine is a spark-ignition engine equipped with an injector that directly injects fuel into the cylinder.

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