WO2024224500A1 - Control device for internal combustion engine - Google Patents

Abstract

Provided is a control device of an internal combustion engine capable of determining occurrence of abnormal combustion by using a parameter that has little angle dependency and that is strongly affected by occurrence of abnormal combustion. A control device (50) for an internal combustion engine calculates an increase amount in gas pressure torque due to combustion on the basis of crank angle acceleration (αd) at each crank angle (θd), calculates an increase amount (ΔPcyl_brn) in gas pressure due combustion on the basis of an increase amount (ΔTgas_brn) in gas pressure torque due combustion at each crank angle, and determines whether or not abnormal combustion has occurred in the internal combustion engine on the basis of the increase amount (ΔPcyl_brn) in gas pressure due to combustion at each crank angle (θd) of a determination angle section (Δθdet).

Description

Control device for internal combustion engine

This application relates to a control device for an internal combustion engine.

Pre-ignition, known as abnormal combustion, is a phenomenon in which deposits remaining in the spark plug or cylinder become hot, acting as a heat source and causing self-ignition before ignition by the spark plug. The technology in Patent Document 1 detects pre-ignition based on the range of fluctuations in the rotational speed of the internal combustion engine.

For example, when the ignition timing of a specific cylinder is retarded by a certain angle, the output of the internal combustion engine decreases and the rotation speed of the internal combustion engine fluctuates. At this time, if pre-ignition occurs in a specific cylinder, a flame is generated in the combustion chamber earlier than the ignition timing, and the fluctuation range of the rotation speed of the internal combustion engine becomes smaller. Therefore, the occurrence of pre-ignition is detected by determining whether the fluctuation range of this rotation speed is smaller than a predetermined range (fluctuation range for detecting pre-ignition).

Japanese Patent Application Publication No. 2-136566

In turbocharged internal combustion engines, pre-ignition, including LSPI (Low Speed Pre-Ignition), which occurs especially at low revolutions and high loads, not only advances the timing of the start of combustion, but also involves rapid combustion, which leads to an earlier increase in gas pressure in the cylinder and a sudden increase in gas pressure in the cylinder. The conversion of the force acting on the piston due to the increase in gas pressure caused by pre-ignition into crank angular acceleration is angle-dependent, and near top dead center where pre-ignition occurs, the conversion coefficient approaches 0, and the impact of pre-ignition on crank angular acceleration is small. For this reason, it is difficult to detect the occurrence of pre-ignition with accuracy using detection methods that capture rotational fluctuations. Furthermore, methods that directly detect gas pressure in the cylinder by adding an internal cylinder pressure sensor increase costs.

The present application therefore aims to provide a control device for an internal combustion engine that can determine the occurrence of abnormal combustion using parameters that have little angle dependency and that are strongly influenced by the occurrence of abnormal combustion.

The control device for an internal combustion engine according to the present application comprises:
an angle information detection unit that detects a crank angle and a crank angular acceleration based on an output signal of the crank angle sensor;
a gas pressure calculation unit that calculates, for each of the crank angles, an increment in gas pressure torque due to combustion, among the gas pressure torque applied to the crankshaft by the gas pressure in a cylinder, based on the crank angle and the crank angular acceleration, and calculates, for each of the crank angles, an increment in gas pressure torque due to combustion, based on the increment in gas pressure torque due to combustion and the crank angle;
an abnormal combustion determination unit that determines whether or not abnormal combustion has occurred in the internal combustion engine based on an increment in gas pressure due to the combustion at each crank angle within a determination angle section that is set corresponding to a combustion period;
It is equipped with the following:

In the internal combustion engine control device according to the present application, unlike crank angular acceleration, the increase in gas pressure due to combustion has little angle dependency and is a good indicator of the effects of abnormal combustion. Therefore, the presence or absence of abnormal combustion can be accurately determined based on the increase in gas pressure due to combustion.

1 is a schematic configuration diagram of an internal combustion engine and a control device for the internal combustion engine according to a first embodiment; 1 is a schematic configuration diagram of an internal combustion engine and a control device for the internal combustion engine according to a first embodiment; 1 is a block diagram of a control device for an internal combustion engine according to a first embodiment. 1 is a hardware configuration diagram of a control device for an internal combustion engine according to a first embodiment; 4 is a time chart for explaining an angle information detection process according to the first embodiment. FIG. 2 is a diagram for explaining the determination of the occurrence of pre-ignition according to the first embodiment. FIG. 2 is a diagram for explaining the determination of the occurrence of pre-ignition according to the first embodiment. 5 is a diagram for explaining the behavior of gas pressure in a cylinder during normal combustion according to the first embodiment. FIG. 4 is a diagram for explaining the behavior of gas pressure in a cylinder when pre-ignition occurs in the first embodiment. FIG. FIG. 2 is a diagram for explaining the determination of the occurrence of pre-ignition according to the first embodiment. FIG. 2 is a diagram for explaining the determination of the occurrence of pre-ignition according to the first embodiment. FIG. 4 is a diagram for explaining a misfire occurrence determination according to the first embodiment. FIG. 4 is a diagram for explaining a misfire occurrence determination according to the first embodiment. 5 is a diagram for explaining the behavior of gas pressure in a cylinder when a misfire occurs in the first embodiment. FIG. 5 is a diagram for explaining the behavior of gas pressure in a cylinder according to the first embodiment. FIG. FIG. 11 is a diagram for explaining the determination of the occurrence of pre-ignition according to the second embodiment. FIG. 11 is a diagram for explaining a misfire occurrence determination according to the second embodiment. FIG. 11 is a diagram for explaining the determination of the occurrence of pre-ignition according to the second embodiment. FIG. 11 is a diagram for explaining a misfire occurrence determination according to the second embodiment.

1. First embodiment
A control device 50 for an internal combustion engine 1 according to a first embodiment (hereinafter simply referred to as the control device 50) will be described with reference to the drawings. Figures 1 and 2 are schematic configuration diagrams of the internal combustion engine 1 and the control device 50 according to this embodiment, and Figure 3 is a block diagram of the control device 50 according to this embodiment. The internal combustion engine 1 and the control device 50 are mounted on a vehicle, and the internal combustion engine 1 serves as a driving force source for the vehicle (wheels).

1-1. Configuration of the internal combustion engine 1 First, the configuration of the internal combustion engine 1 will be described. As shown in Fig. 1, the internal combustion engine 1 has a cylinder 7 that burns a mixture of air and fuel. The internal combustion engine 1 has an intake pipe 23 that supplies air to the cylinder 7, and an exhaust pipe 17 that discharges exhaust gas burned in the cylinder 7. The internal combustion engine 1 is a gasoline engine. The internal combustion engine 1 has a throttle valve 4 that opens and closes the intake pipe 23. The throttle valve 4 is an electronically controlled throttle valve that is driven to open and close by an electric motor controlled by a control device 50. The throttle valve 4 is provided with a throttle opening sensor 19 that outputs an electric signal according to the opening of the throttle valve 4.

The intake pipe 23 upstream of the throttle valve 4 is provided with an airflow sensor 3 that outputs an electrical signal according to the amount of intake air drawn into the intake pipe 23. The internal combustion engine 1 is provided with an exhaust gas recirculation device 20. The exhaust gas recirculation device 20 has an EGR flow path 21 that recirculates exhaust gas from the exhaust pipe 17 to the intake manifold 12, and an EGR valve 22 that opens and closes the EGR flow path 21. The intake manifold 12 is the part of the intake pipe 23 downstream of the throttle valve 4. The EGR valve 22 is an electronically controlled EGR valve that is driven to open and close by an electric motor controlled by the control device 50. The exhaust pipe 17 is provided with an air-fuel ratio sensor 18 that outputs an electrical signal according to the air-fuel ratio of the exhaust gas in the exhaust pipe 17.

The intake manifold 12 is provided with a gas pressure sensor 8 that outputs an electrical signal corresponding to the pressure inside the intake manifold 12. An injector 13 that injects fuel is provided in the downstream portion of the intake manifold 12. The injector 13 may be provided so as to inject fuel directly into the cylinders 7. The internal combustion engine 1 is provided with an atmospheric pressure sensor 33 that outputs an electrical signal corresponding to the atmospheric pressure Patm. The internal combustion engine 1 is provided with a water temperature sensor 34 that detects the coolant temperature.

At the top of cylinder 7, there is a spark plug that ignites the air-fuel mixture, and an ignition coil 16 that supplies ignition energy to the spark plug. Also, at the top of cylinder 7, there is an intake valve 14 that adjusts the amount of intake air drawn into cylinder 7 from intake pipe 23, and an exhaust valve 15 that adjusts the amount of exhaust gas discharged from inside the cylinder to exhaust pipe 17. The intake valve 14 is provided with an intake variable valve timing mechanism that varies the valve opening and closing timing. The exhaust valve 15 is provided with an exhaust variable valve timing mechanism that varies the valve opening and closing timing. The variable valve timing mechanisms 14, 15 have electric actuators.

As shown in FIG. 2, the internal combustion engine 1 has a number of cylinders 7 (three in this example). Each cylinder 7 has a piston 5 inside. The piston 5 of each cylinder 7 is connected to the crankshaft 2 via a connecting rod 9 and a crank 32. The crankshaft 2 is rotationally driven by the reciprocating motion of the piston 5. The combustion gas pressure generated in each cylinder 7 presses against the top surface of the piston 5, and rotates the crankshaft 2 via the connecting rod 9 and the crank 32. The crankshaft 2 is connected to a power transmission mechanism that transmits driving force to the wheels. The power transmission mechanism is composed of a transmission, a differential gear, etc. Note that a vehicle equipped with the internal combustion engine 1 may be a hybrid vehicle equipped with a motor generator in the power transmission mechanism.

The internal combustion engine 1 is equipped with a signal plate 10 that rotates integrally with the crankshaft 2. The signal plate 10 has multiple teeth at multiple predetermined crank angles. In this embodiment, the signal plate 10 has teeth arranged at 10 degree intervals. The teeth of the signal plate 10 have missing teeth. The internal combustion engine 1 is equipped with a crank angle sensor 11 that is fixed to the engine block 24 and detects the teeth of the signal plate 10.

The internal combustion engine 1 is equipped with a camshaft 29 connected to the crankshaft 2 by a chain 28. The camshaft 29 drives the intake valve 14 and the exhaust valve 15 to open and close. The camshaft 29 rotates once while the crankshaft 2 rotates twice. The internal combustion engine 1 is equipped with a cam signal plate 31 that rotates together with the camshaft 29. The cam signal plate 31 has a number of teeth at a number of predetermined camshaft angles. The internal combustion engine 1 is equipped with a cam angle sensor 30 that is fixed to the engine block 24 and detects the teeth of the cam signal plate 31.

The control device 50 detects the crank angle based on the top dead center of each piston 5 and determines the stroke of each cylinder 7 based on two types of output signals from the crank angle sensor 11 and the cam angle sensor 30. The internal combustion engine 1 is a four-stroke engine with an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke.

The crank angle sensor 11 and cam angle sensor 30 output an electrical signal according to the change in the distance between each sensor and the teeth due to the rotation of the crankshaft 2. The output signal of each angle sensor 11, 30 is a square wave that turns on and off depending on whether the sensor is close to the teeth or far away. For example, an electromagnetic pickup type sensor is used for each angle sensor 11, 30.

1-2. Configuration of the control device 50 Next, the control device 50 will be described.
The control device 50 is a control device that controls the internal combustion engine 1. As shown in FIG. 3, the control device 50 includes control units such as an angle information detection unit 51, a gas pressure calculation unit 52, an abnormal combustion determination unit 53, an avoidance control unit 54, and a basic control unit 55. The control units 51 to 55 of the control device 50 are realized by processing circuits included in the control device 50. Specifically, as shown in FIG. 4, the control device 50 includes, as processing circuits, an arithmetic processing device 90 (computer) such as a CPU (Central Processing Unit), a storage device 91 connected to the arithmetic processing device 90 via a signal line such as a bus, an input circuit 92 that inputs an external signal to the arithmetic processing device 90, and an output circuit 93 that outputs a signal from the arithmetic processing device 90 to the outside.

The arithmetic processing device 90 may be an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, and various signal processing circuits. In addition, multiple arithmetic processing devices 90 of the same type or different types may be provided, and each process may be shared and executed.

The memory device 91 includes volatile and non-volatile memory devices such as RAM (Random Access Memory), ROM (Read Only Memory), and EEPROM (Electrically Erasable Programmable ROM). The input circuit 92 is connected to various sensors and switches and includes A/D converters and the like that input the output signals of these sensors and switches to the arithmetic processing device 90. The output circuit 93 is connected to electrical loads and includes drive circuits and the like that output control signals from the arithmetic processing device 90 to these electrical loads.

The functions of the control units 51 to 55 of the control device 50 are realized by the arithmetic processing device 90 executing software (programs) stored in a storage device 91 such as a ROM or EEPROM, and working in cooperation with other hardware of the control device 50 such as the storage device 91, input circuit 92, and output circuit 93. The setting data of the thresholds and the like used by the control units 51 to 55 are stored in the storage device 91 such as a ROM or EEPROM. The calculated values of the crank angular velocity ωd, crank angular acceleration αd, gas pressure in the cylinder Pcyl, gas pressure in the cylinder when uncombusted Pcyl_unbrn, and increase in gas pressure due to combustion ΔPcyl_brn, and the data of the detected values, etc., calculated by the control units 51 to 55 are stored in a rewritable storage device 91 such as a RAM.

In this embodiment, the input circuit 92 is connected to the crank angle sensor 11, cam angle sensor 30, water temperature sensor 34, air flow sensor 3, throttle opening sensor 19, gas pressure sensor 8, atmospheric pressure sensor 33, air-fuel ratio sensor 18, accelerator position sensor 26, etc. The output circuit 93 is connected to the throttle valve 4 (electric motor), EGR valve 22 (electric motor), injector 13, ignition coil 16, intake variable valve timing mechanism 14, exhaust variable valve timing mechanism 15, etc. Note that various sensors, switches, actuators, etc. (not shown) are connected to the control device 50. The control device 50 detects the operating state of the internal combustion engine 1, such as the intake air volume, pressure in the intake manifold, atmospheric pressure Patm, air-fuel ratio, and accelerator opening, based on the output signals of the various sensors.

1-2-1. Basic control unit 55
As a basic control, the basic control unit 55 calculates the fuel injection amount, ignition timing, etc. based on the input output signals of various sensors, and drives and controls the injector 13, the ignition coil 16, etc. The basic control unit 55 calculates the output torque of the internal combustion engine 1 required by the driver based on the output signal of the accelerator position sensor 26, etc., and controls the throttle valve 4, etc. so that the intake air amount realizes the required output torque. Specifically, the basic control unit 55 calculates a target throttle opening, and drives and controls the electric motor of the throttle valve 4 so that the throttle opening detected based on the output signal of the throttle opening sensor 19 approaches the target throttle opening. The basic control unit 55 also calculates a target opening of the EGR valve 22 based on the input output signals of various sensors, and drives and controls the electric motor of the EGR valve 22. The basic control unit 55 calculates the target opening/closing timing of the intake valve and the target opening/closing timing of the exhaust valve based on the output signals of various sensors input thereto, and controls the drive of the intake and exhaust variable valve timing mechanisms 14, 15 based on each target opening/closing timing.

1-2-2. Angle information detection unit 51
The angle information detection unit 51 detects the crank angle θd based on the output signal of the crank angle sensor 11, and calculates a crank angular velocity ωd, which is a time rate of change of the detected crank angle θd, and a crank angular acceleration αd, which is a time rate of change of the crank angular velocity ωd. The crank angular velocity ωd corresponds to the rotation speed.

In this embodiment, as shown in FIG. 5, the angle information detection unit 51 detects the crank angle θd based on the output signal of the crank angle sensor 11, and detects the detection time Td at which the crank angle θd is detected. Then, the angle information detection unit 51 calculates the angle interval Δθd and the time interval ΔTd corresponding to the detection angle θd based on the detection angle θd, which is the detected crank angle θd, and the detection time Td.

For example, the angle information detection unit 51 determines the crank angle θd when it detects the falling edge (or rising edge) of the output signal (rectangular wave) of the crank angle sensor 11. Using a known method, the angle information detection unit 51 detects the crank angle θd based on the top dead center of the piston 5 of the first cylinder #1 based on two types of output signals from the crank angle sensor 11 and the cam angle sensor 30, and determines the stroke of each cylinder 7.

<Calculation of crank angular velocity ωd and crank angular acceleration αd>
The angle information detection unit 51 calculates the crank angular velocity ωd based on each crank angle θd and the detection time Td at which each crank angle θd was detected. For example, as shown in the following formula, the angle information detection unit 51 calculates the crank angular velocity ωd(n) of the currently detected angle based on the angle interval Δθd(n) between the currently detected crank angle θd(n) and the previously detected crank angle θd(n-1) and the time interval ΔTd(n) between the currently detected time Td(n) and the previously detected time Td(n-1). Note that various other known methods may be used.

The angle information detection unit 51 calculates the crank angular acceleration αd(n) based on the crank angular velocity ωd. For example, as shown in the following formula, the angle information detection unit 51 calculates the crank angular acceleration αd(n) of the current detection angle based on the crank angular velocity ωd(n) calculated at the current detection angle, the crank angular velocity ωd(n-1) calculated at the previous detection angle, and the time interval ΔTd(n) of the current detection angle. Note that various other known methods may be used.

The angle information detection unit 51 associates the calculated angle information such as the crank angular velocity ωd and the crank angular acceleration αd with the corresponding crank angle θd and stores it in a storage device 91 such as a RAM for at least a period equal to or greater than the determination angle range described below.

1-2-3. Gas pressure calculation unit 52
The gas pressure calculation unit 52 calculates an increment ΔTgas_brn of the gas pressure torque due to combustion, which is included in the gas pressure torque applied to the crankshaft by the gas pressure in the cylinder, based on the crank angle θd and the crank angular acceleration αd at each crank angle θd. The gas pressure calculation unit 52 also calculates an increment ΔPcyl_brn of the gas pressure due to combustion, based on the increment ΔTgas_brn of the gas pressure torque due to combustion and the crank angle θd at each crank angle θd. This will be described in detail below.

<Calculation of shaft torque Tcrk_unbrn when combustion is not yet complete>
The gas pressure calculation unit 52 calculates, at each crank angle θd, the gas pressure Pcyl_unbrn in the cylinder when uncombusted assuming that the combustion is unspent, and the axial torque Tcrk_unbrn when uncombusted, which is the axial torque applied to the crankshaft due to the reciprocating motion of the piston, based on the crank angle θd, the crank angular velocity ωd, and the state of the intake gas amount in the cylinder.

In this embodiment, the gas pressure calculation unit 52 calculates the gas pressure torque Tgas_unbrn at the time of uncombustion, which is the axial torque applied to the crankshaft due to the gas pressure in the cylinder at the time of uncombustion when it is assumed that uncombustion occurs, based on the crank angle θd and the state of the intake gas amount in the cylinder at each crank angle θd. In addition, the gas pressure calculation unit 52 calculates the reciprocating inertia torque Tpstn, which is the axial torque applied to the crankshaft due to the reciprocating motion of the piston, based on the crank angle θd and the crank angular velocity ωd at each crank angle θd. The gas pressure calculation unit 52 adds the gas pressure torque Tgas_unbrn at the time of uncombustion and the reciprocating inertia torque Tpstn at each crank angle θd to calculate the axial torque Tcrk_unbrn at the time of uncombustion. This will be explained in detail below.

The gas pressure calculation unit 52 calculates the gas pressure Pcyl_unbrn in the cylinder when uncombusted, assuming that uncombusted fuel is not yet burned, based on the current state of the amount of intake gas in the cylinder (in this example, the current gas pressure Pin in the intake pipe) and the crank angle θd at each crank angle θd.

In this embodiment, the gas pressure calculation unit 52 calculates the gas pressure Pcyl_unbrn_i in each cylinder i when the combustion is not yet performed by using the following formula. For the cylinder i in which the intake valve and the exhaust valve are closed, a formula for calculating the gas pressure by polytropic change is used to calculate the gas pressure Pcyl_unbrn_i in each cylinder i when the combustion is not yet performed based on the gas pressure Pin in the intake pipe and the crank angle θd. For the cylinder i in which the intake valve is open and the exhaust valve is closed, the gas pressure calculation unit 52 calculates the gas pressure Pcyl_unbrn_i in the cylinder when the combustion is not yet performed based on the gas pressure Pin in the intake pipe, and for the cylinder i in which the exhaust valve is open, calculates the gas pressure Pcyl_unbrn_i in the cylinder when the combustion is not yet performed based on the gas pressure Pex in the exhaust pipe.

Here, Nply is a polytropic index, and a preset value is used. Vcyl0 is the cylinder volume of the combustion cylinder when the intake valve is closed, and a preset value may be used or it may be changed according to the intake valve closing timing by the intake variable valve timing mechanism 14. Vcly_θ_i is the cylinder volume of each cylinder at the crank angle θd_i of each cylinder i, and is a function of the crank angle θd_i of each cylinder i. Note that in the case of an offset crank, an offset may be taken into account in calculating the cylinder volume Vcly_θ. For example, the cylinder volume Vcly_θ_i of each cylinder i may be set based on the third and fourth equations of equation (3). Here, Vcyltop is the cylinder volume when the piston is at top dead center, Sp is the projected area of the top surface of the piston, r is the crank length, L is the connecting rod length, and φ_i is the angle of the connecting rod for each cylinder i. Note that the crank angle θd_i for each cylinder i used in the calculation of trigonometric functions is the crank angle obtained by shifting the crank angle θd so that the top dead center of the compression stroke for each cylinder i is 0 degrees.

The gas pressure calculation unit 52 calculates the gas pressure torque Tgas_unbrn when unburned, which is the shaft torque applied to the crankshaft due to the gas pressure in the cylinder when unburned, assuming that there is no combustion, at each crank angle θd, based on the gas pressure Pcyl_unbrn in the cylinder when unburned and the crank angle θd.

In this embodiment, the gas pressure calculation unit 52 uses the following equation to convert gas pressure into torque, and calculates the gas pressure torque Tgas_unbrn in the uncombusted state based on the gas pressure Pcyl_unbrn_i in each cylinder i in the uncombusted state and the crank angle θd_i of each cylinder i.

Here, R_i is a conversion coefficient that converts the force acting on the piston of each cylinder i into torque, and is a function of the crank angle θd_i of each cylinder i. For example, the conversion coefficient R_i of each cylinder i may be set based on the third and fourth equations of equation (4). Alternatively, map data in which the relationship between the crank angle θd and the conversion coefficient R is preset may be used. Note that in the case of an offset crank, an offset may be taken into consideration when calculating the conversion coefficient R_i of each cylinder i. N is the number of cylinders, and in this embodiment, N=3.

The gas pressure calculation unit 52 calculates the reciprocating inertia torque Tpstn, which is the axial torque applied to the crankshaft due to the reciprocating motion of the piston, at each crank angle θd based on the crank angle θd and the crank angular velocity ωd.

In this embodiment, the gas pressure calculation unit 52 calculates the reciprocating inertia torque Tpstn by using the following equation.

Here, mp is the mass of the piston. Ka_i is a coefficient for calculating the acceleration of the piston based on the crank angular velocity ωd, and is a function of the crank angle θd_i of each cylinder i. For example, the acceleration calculation coefficient Ka_i of each cylinder i may be set based on the third formula of formula (5). The third formula of formula (5) is an approximation, but an exact value may be calculated. Alternatively, map data in which the relationship between the crank angle θd and the acceleration calculation coefficient Ka is preset may be used. In the case of an offset crank, an offset may be taken into account in the calculation of the acceleration calculation coefficient Ka_i of each cylinder i. The conversion coefficient R_i of each cylinder i is the same as formula (4). In addition, an inertia torque generated by the inertia of the connecting rod, etc. may be added to the inertia torque Tin.

As shown in the following equation, the gas pressure calculation unit 52 calculates the shaft torque Tcrk_unbrn in the uncombusted state by adding the gas pressure torque Tgas_unbrn in the uncombusted state and the reciprocating inertia torque Tpstn at each crank angle θd.

Alternatively, the gas pressure calculation unit 52 may refer to uncombusted map data in which the relationship between the crank angle θd, crank angular velocity ωd, and the amount of intake gas in the cylinder and the uncombusted axial torque Tcrk_unbrn is set, and calculate the uncombusted axial torque Tcrk_unbrn corresponding to each crank angle θd, crank angular velocity ωd, and amount of intake gas in the cylinder.

For example, the uncombusted map data is set for each operating state (in this example, the state of the crank angular velocity ωd and the amount of gas intake gas in the cylinder) that affects the gas pressure torque and reciprocating inertia torque in the uncombusted state. The gas pressure calculation unit 52 refers to the uncombusted map data corresponding to the current operating state and calculates the uncombusted axial torque Tcrk_unbrn corresponding to each crank angle θd. The uncombusted map data may be set in advance based on experimental data, or may be set in advance based on the theoretical formulas (3) to (6). In addition, the uncombusted map data may be updated based on the actual axial torque Tcrkd that is actually calculated in an uncombusted state.

<Calculation of actual shaft torque Tcrkd>
The gas pressure calculation unit 52 calculates an actual torque Tcrkd acting on the crankshaft at each crank angle θd based on the crank angular acceleration αd.

In this embodiment, the gas pressure calculation unit 52 calculates the actual shaft torque Tcrkd by multiplying the crank angular acceleration αd by the moment of inertia Icrk of the crankshaft system at each crank angle θd, as shown in the following equation.

<Calculation of external load torque Tload>
The gas pressure calculation unit 52 calculates an external load torque Tload, which is a torque applied to the crankshaft from outside the internal combustion engine, based on the actual torque Tcrkd_tdc calculated at the crank angle θd_tdc near the top dead center and the unburned torque Tcrk_unbrn_tdc. Here, the vicinity of the top dead center is, for example, within an angle range from 10 degrees before the top dead center to 10 degrees after the top dead center. For example, the crank angle θd_tdc near the top dead center is preset to the crank angle at the top dead center.

The gas pressure calculation unit 52 calculates the external load torque Tload during combustion by subtracting the actual shaft torque Tcrkd_tdc near the top dead center from the shaft torque Tcrk_unbrn_tdc near the top dead center during uncombustion, as shown in the following equation.

Since the gas pressure torque of the combustion cylinder is nearly zero near the top dead center of the combustion stroke, the external load torque Tload can be calculated with a small computational load based on the unburned axial torque Tcrk_unbrn_tdc near the top dead center and the actual axial torque Tcrkd_tdc near the top dead center when the engine is burned.

<Calculation of Increase in Gas Pressure Torque ΔTgas_brn Due to Combustion>
The gas pressure calculation unit 52 calculates the increase in gas pressure torque ΔTgas_brn due to combustion based on the actual shaft torque Tcrkd, the shaft torque Tcrk_unbrn in the uncombusted state, and the external load torque Tload at each crank angle θd. In this embodiment, the gas pressure calculation unit 52 calculates the increase in gas pressure torque ΔTgas_brn due to combustion by subtracting the shaft torque Tcrk_unbrn in the uncombusted state from the actual shaft torque Tcrkd and adding the external load torque Tload, as shown in the following formula.

<Calculation of Increase in Gas Pressure Due to Combustion ΔPcyl_brn>
The gas pressure calculation unit 52 calculates the increase in gas pressure due to combustion ΔPcyl_brn based on the increase in gas pressure torque due to combustion ΔTgas_brn and the crank angle θd at each crank angle θd. In this embodiment, the gas pressure calculation unit 52 calculates the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn using the following equation. The conversion coefficient R_brn is the conversion coefficient of the combustion cylinder among the conversion coefficients R_i of each cylinder i in equation (4).

Note that when the crank angle θd at top dead center is 0, the conversion coefficient R_brn for the combustion cylinder is 0, resulting in a zero division. Therefore, the gas pressure calculation unit 52 may calculate the average value of ΔPcyl_brn calculated at the crank angles before and after top dead center as ΔPcyl_brn at top dead center.

<Calculation of In-Cylinder Gas Pressure Pcyl>
The gas pressure calculation unit 52 calculates the gas pressure Pcyl in the cylinder by adding the gas pressure Pcyl_unbrn in the uncombusted cylinder to the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn at each crank angle θd, as shown in the following equation.

The gas pressure calculation unit 52 stores each calculated value, such as the actual shaft torque Tcrkd calculated at each crank angle θd, the shaft torque Tcrk_unbrn when uncombusted, the increase in gas pressure torque due to combustion ΔTgas_brn, the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn, and the gas pressure Pcyl in the cylinder, together with the corresponding angle identification number n and angle information such as the crank angle θd, in a storage device 91 such as a RAM.

1-2-4. Abnormal combustion determination unit 53
<Principle for determining abnormal combustion>
The principle of abnormal combustion determination will be described below.
6 plots the relationship between the peak value dQ/dθ_max of the actual heat release rate and the peak value α_max of the crank angular acceleration in each combustion cycle when there is a mixture of combustion cycles in which pre-ignition occurs and combustion cycles in which pre-ignition does not occur. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder), and the peak value α_max of the crank angular acceleration is a value calculated by the control device 50.

The increase in the peak value of the crank angular acceleration α_max is not proportional to the increase in the peak value of the actual heat release rate dQ/dθ_max. Therefore, to the right of the dashed dotted line, which is the region of the peak value of the actual heat release rate dQ/dθ_max where it is desired to determine that pre-ignition is occurring, the peak value of the crank angular acceleration α_max does not increase proportionally, making it difficult to set a determination threshold value (dashed line in Figure 6) that accurately determines the occurrence of pre-ignition.

This is because the conversion of the force acting on the piston due to the increase in gas pressure caused by pre-ignition into crank angular acceleration α is angle-dependent, and near top dead center where pre-ignition occurs, the conversion coefficient R_brn for the combustion cylinder becomes close to 0, so the impact of pre-ignition on crank angular acceleration α is small.

Figure 7 plots the relationship between the peak value dQ/dθ_max of the actual heat release rate in each combustion cycle and the peak value Pcyl_max of the gas pressure in the cylinder calculated by the control device 50 when there is a mixture of combustion cycles in which pre-ignition occurs and combustion cycles in which pre-ignition does not occur.

Because it is not possible to clearly separate the peak value Pcyl_max of the gas pressure inside the cylinder to the right of the dashed dotted line, which is the region of the actual heat release rate peak value dQ/dθ_max where it is desired to determine that pre-ignition is occurring (above the dashed line in Figure 7), from the peak value Pcyl_max of the gas pressure inside the cylinder to the left of the dashed dotted line, which is the region of the actual heat release rate peak value dQ/dθ_max where it is desired to determine that pre-ignition is not occurring (below the dashed line in Figure 7), it is difficult to set a judgment threshold value (dashed line in Figure 7) that accurately determines the occurrence of pre-ignition.

Figure 8 shows an example of changes in the gas pressure Pcyl in the cylinder relative to the crank angle θd in a combustion cycle (compression stroke and combustion stroke) in which pre-ignition is not occurring. The peak value Pcyl_max of the gas pressure in the cylinder is the gas pressure Pcyl in the cylinder at the position of the dashed dotted line A. The gas pressure Pcyl in the cylinder at the position of the dashed dotted line A is the same as the gas pressure Pcyl_unbrn (dashed line) in the cylinder when uncombusted, assuming that there is no combustion.

Figure 9 shows an example of the change in the gas pressure Pcyl in the cylinder relative to the crank angle θd in a combustion cycle (compression stroke and combustion stroke) in which pre-ignition is occurring. The peak value Pcyl_max of the gas pressure in the cylinder is the gas pressure Pcyl in the cylinder at the position of the two-dot chain line B. Since the difference between the peak value Pcyl_max of the gas pressure in the cylinder in Figure 9 and Figure 8 is small, it becomes difficult to determine whether pre-ignition has occurred.

Figure 10 plots the relationship between the peak value dQ/dθ_max of the actual heat release rate and the gas pressure Pcyl_Δbrnmax in the cylinder at the crank angle corresponding to the peak value of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn in each combustion cycle when there is a mixture of combustion cycles in which pre-ignition occurs and combustion cycles in which pre-ignition does not occur. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder), and ΔPcyl_brn and Pcyl_Δbrnmax are values calculated by the control device 50.

Since it is possible to clearly separate the gas pressure Pcyl_Δbrnmax (above the dashed line in FIG. 10) in the cylinder at the crank angle corresponding to the peak value of ΔPcyl_brn to the right of the dashed line which is the region of the actual heat release rate peak value dQ/dθ_max where it is desired to determine that pre-ignition is occurring, and the gas pressure Pcyl_Δbrnmax (below the dashed line in FIG. 10) in the cylinder at the crank angle corresponding to the peak value of ΔPcyl_brn to the left of the dashed line which is the region of the actual heat release rate peak value dQ/dθ_max where it is desired to determine that pre-ignition is not occurring, it is possible to set a judgment threshold value (dashed line in FIG. 10) that accurately determines the occurrence of pre-ignition. This is because, unlike the crank angular acceleration α, ΔPcyl_brn has little angle dependency and the effects of the occurrence of pre-ignition are clearly apparent.

As shown in Figures 8 and 9, the gas pressure Pcyl_Δbrnmax in the cylinder at the crank angle corresponding to the peak value of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn is the gas pressure Pcyl in the cylinder at the position of the two-dot chain line B. There is a large difference between the gas pressure Pcyl_Δbrnmax in the cylinder corresponding to the peak value of ΔPcyl_brn in Figures 8 and 9. Therefore, as shown in Figure 10, it is possible to determine pre-ignition.

Figure 11 plots the relationship between the crank angle θ_dQ/dθmax corresponding to the peak value dQ/dθ_max of the actual heat release rate and the crank angle θd_Δbrnmax corresponding to the peak value of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn in each combustion cycle when there is a mixture of combustion cycles in which pre-ignition occurs and combustion cycles in which pre-ignition does not occur. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder), and the crank angle θd_Δbrnmax corresponding to the peak value of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn is a value calculated by the control device 50.

Because it is possible to clearly separate the crank angle θd_Δbrnmax (above the dashed line in FIG. 11) corresponding to the peak value of ΔPcyl_brn to the right of the dashed dotted line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate for which it is desired to determine that pre-ignition is occurring, and the crank angle θd_Δbrnmax (below the dashed line in FIG. 11) corresponding to the peak value of ΔPcyl_brn to the left of the dashed dotted line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate for which it is desired to determine that pre-ignition is not occurring, it is possible to set a judgment threshold value (dashed line in FIG. 11) that accurately determines the occurrence of pre-ignition. This is because ΔPcyl_brn has little angle dependency, and the effects of the occurrence of pre-ignition are clearly apparent.

Figure 12 plots the relationship between the peak value dQ/dθ_max of the actual heat release rate and the gas pressure Pcyl_Δbrnmax in the cylinder at the crank angle corresponding to the peak value of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn in each combustion cycle when there is a mixture of combustion cycles in which misfires occur and combustion cycles in which misfires do not occur. Note that the scales of the horizontal and vertical axes in Figure 12 are larger than those of the horizontal and vertical axes in Figure 10. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder), and ΔPcyl_brn and Pcyl_Δbrnmax are values calculated by the control device 50.

Since it is possible to clearly separate the gas pressure Pcyl_Δbrnmax in the cylinder at the crank angle corresponding to the peak value of ΔPcyl_brn to the left of the dashed line, which is the region of the actual heat release rate peak value dQ/dθ_max where it is desired to determine that a misfire is occurring (below the dashed line in FIG. 12), and the gas pressure Pcyl_Δbrnmax in the cylinder at the crank angle corresponding to the peak value of ΔPcyl_brn to the right of the dashed line, which is the region of the actual heat release rate peak value dQ/dθ_max where it is desired to determine that a misfire is not occurring (above the dashed line in FIG. 12), it is possible to set a judgment threshold value (dashed line in FIG. 12) that accurately determines the occurrence of a misfire. This is because, unlike the crank angular acceleration α, ΔPcyl_brn has little angle dependency and is able to clearly indicate the effects of the occurrence of a misfire.

Figure 13 plots the relationship between the crank angle θ_dQ/dθmax corresponding to the peak value dQ/dθ_max of the actual heat release rate and the crank angle θd_Δbrnmax corresponding to the peak value of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn in each combustion cycle when there is a mixture of combustion cycles in which misfires occur and combustion cycles in which misfires do not occur. Note that the scales of the horizontal and vertical axes in Figure 13 are larger than those of the horizontal and vertical axes in Figure 11. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder), and the crank angle θd_Δbrnmax corresponding to the peak value of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn is a value calculated by the control device 50.

The crank angle θd_Δbrnmax (below the dashed line in FIG. 13) corresponding to the peak value of ΔPcyl_brn to the left of the dashed line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate for which it is desired to determine that a misfire is occurring, can be clearly separated from the crank angle θd_Δbrnmax (above the dashed line in FIG. 13) corresponding to the peak value of ΔPcyl_brn to the right of the dashed line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate for which it is desired to determine that a misfire is not occurring. This makes it possible to set a judgment threshold value (dashed line in FIG. 13) that accurately determines the occurrence of a misfire. This is because, unlike the crank angular acceleration α, ΔPcyl_brn has little angle dependency and is more clearly affected by the occurrence of a misfire.

As explained above, the occurrence of abnormal combustion such as pre-ignition and misfire can be determined by the increase in gas pressure in the cylinder due to combustion that has little angle dependency, ΔPcyl_brn.

<Determining abnormal combustion>
Therefore, the abnormal combustion determination unit 53 determines whether or not abnormal combustion has occurred in the internal combustion engine based on the increment ΔPcyl_brn of gas pressure due to combustion at each crank angle θd in the determination angle interval Δθdet set corresponding to the combustion period.

As described above, unlike the crank angular acceleration α, the increase in gas pressure due to combustion ΔPcyl_brn has little angle dependency and is a good indicator of the effects of abnormal combustion. Therefore, the presence or absence of abnormal combustion can be accurately determined based on the increase in gas pressure due to combustion ΔPcyl_brn.

The judgment angle interval Δθdet is set to an angle interval within the compression stroke and the combustion stroke so that it can be determined whether or not abnormal combustion has occurred. Note that the compression stroke does not have to be included.

<Judgment of Preignition>
In this embodiment, the abnormal combustion judgment unit 53 judges the peak value of the increase in gas pressure due to combustion ΔPcyl_brn in the judgment angle interval Δθdet, and determines whether or not pre-ignition has occurred by comparing the gas pressure Pcyl_Δbrnmax in the cylinder at the crank angle θd corresponding to the peak value with the gas pressure threshold value ThP_pre for pre-ignition.

As explained using FIG. 10, a difference in tendency of Pcyl_Δbrnmax occurs between when pre-ignition occurs and when it does not occur. Therefore, by setting the gas pressure threshold value ThP_pre for pre-ignition between Pcyl_Δbrnmax when pre-ignition occurs and Pcyl_Δbrnmax when pre-ignition does not occur, it is possible to accurately determine whether pre-ignition has occurred.

The abnormal combustion determination unit 53 determines that pre-ignition has occurred if the gas pressure Pcyl_Δbrnmax in the cylinder corresponding to the peak value of ΔPcyl_brn exceeds the gas pressure threshold value ThP_pre for pre-ignition, and determines that pre-ignition has not occurred if Pcyl_Δbrnmax falls below the gas pressure threshold value ThP_pre for pre-ignition.

The abnormal combustion determination unit 53 sets the gas pressure threshold value ThP_pre for pre-ignition based on the operating state of the internal combustion engine. For example, the abnormal combustion determination unit 53 references gas pressure threshold value data for pre-ignition in which the relationship between the operating state and the gas pressure threshold value ThP_pre is set, and sets the gas pressure threshold value ThP_pre for pre-ignition that corresponds to the current operating state. The operating state of the internal combustion engine may include the state of the amount of intake gas in the cylinder (e.g., the gas pressure Pin in the intake pipe, the amount of intake air, etc.), the air-fuel ratio, the rotational speed (rotational angular velocity), etc.

Alternatively, the abnormal combustion determination unit 53 may determine the peak value of the increase in gas pressure due to combustion ΔPcyl_brn in the determination angle interval Δθdet, and compare the crank angle θd_Δbrnmax corresponding to the peak value with the angle threshold value for pre-ignition Thθ_pre to determine whether pre-ignition has occurred.

As explained using FIG. 11, a difference in tendency of θd_Δbrnmax occurs between when pre-ignition occurs and when it does not occur. Therefore, by setting the angle threshold value Thθ_pre for pre-ignition between θd_Δbrnmax when pre-ignition occurs and θd_Δbrnmax when pre-ignition does not occur, it is possible to accurately determine whether pre-ignition has occurred.

The abnormal combustion determination unit 53 determines that pre-ignition has occurred if the crank angle θd_Δbrnmax corresponding to the peak value of ΔPcyl_brn exceeds the angle threshold value Thθ_pre for pre-ignition, and determines that pre-ignition has not occurred if θd_Δbrnmax falls below the angle threshold value Thθ_pre for pre-ignition.

The abnormal combustion determination unit 53 sets the angle threshold value Thθ_pre for pre-ignition based on the operating state of the internal combustion engine. For example, the abnormal combustion determination unit 53 references gas pressure threshold data for pre-ignition in which the relationship between the operating state and the angle threshold value Thθ_pre is set, and sets the angle threshold value Thθ_pre for pre-ignition that corresponds to the current operating state. The operating state of the internal combustion engine may include the state of the amount of intake gas in the cylinder (e.g., the gas pressure Pin in the intake pipe, the amount of intake air, etc.), the air-fuel ratio, the rotational speed (rotational angular velocity), etc.

<Judgment of misfire>
The abnormal combustion judgment unit 53 judges the peak value of the increase in gas pressure due to combustion ΔPcyl_brn in the judgment angle range Δθdet, and judges whether or not a misfire has occurred by comparing the gas pressure Pcyl_Δbrnmax in the cylinder at the crank angle corresponding to the peak value with the gas pressure threshold value ThP_mf for misfire.

As explained using Figure 12, there is a difference in tendency of Pcyl_Δbrnmax between when misfire occurs and when it does not occur. Therefore, by setting the gas pressure threshold value ThP_mf for misfire between Pcyl_Δbrnmax when misfire occurs and Pcyl_Δbrnmax when it does not occur, it is possible to accurately determine whether a misfire has occurred.

The abnormal combustion determination unit 53 determines that a misfire has occurred if the gas pressure Pcyl_Δbrnmax in the cylinder corresponding to the peak value of ΔPcyl_brn falls below the gas pressure threshold ThP_mf for misfire, and determines that a misfire has not occurred if Pcyl_Δbrnmax exceeds the gas pressure threshold ThP_mf for misfire.

The abnormal combustion determination unit 53 sets the gas pressure threshold value ThP_mf for misfire based on the operating state of the internal combustion engine. For example, the abnormal combustion determination unit 53 references gas pressure threshold value data for misfire in which the relationship between the operating state and the gas pressure threshold value ThP_mf is set, and sets the gas pressure threshold value ThP_mf that corresponds to the current operating state. The operating state of the internal combustion engine may include the state of the amount of intake gas in the cylinder (e.g., the gas pressure Pin in the intake pipe, the amount of intake air, etc.), the air-fuel ratio, the rotational speed (rotational angular velocity), etc.

Alternatively, the abnormal combustion determination unit 53 may determine the peak value of the increase in gas pressure due to combustion ΔPcyl_brn in the determination angle interval Δθdet, and compare the crank angle θd_Δbrnmax corresponding to the peak value with the angle threshold value for misfire Thθ_mf to determine whether or not a misfire has occurred.

As explained using FIG. 13, there is a difference in the tendency of θd_Δbrnmax between when a misfire occurs and when it does not occur. Therefore, by setting the angle threshold value Thθ_mf for misfire between θd_Δbrnmax when a misfire occurs and θd_Δbrnmax when it does not occur, it is possible to accurately determine whether a misfire has occurred.

The abnormal combustion determination unit 53 determines that a misfire has occurred if the crank angle θd_Δbrnmax corresponding to the peak value of ΔPcyl_brn falls below the angle threshold value Thθ_mf for misfire, and determines that a misfire has not occurred if θd_Δbrnmax exceeds the angle threshold value Thθ_mf for misfire.

The abnormal combustion determination unit 53 sets the angle threshold Thθ_mf for misfire based on the operating state of the internal combustion engine. For example, the abnormal combustion determination unit 53 references gas pressure threshold data for misfire in which the relationship between the operating state and the angle threshold Thθ_mf is set, and sets the angle threshold Thθ_mf for misfire that corresponds to the current operating state. The operating state of the internal combustion engine may include the state of the amount of intake gas in the cylinder (e.g., the gas pressure Pin in the intake pipe, the amount of intake air, etc.), the air-fuel ratio, the rotational speed (rotational angular velocity), etc.

<Calculation of Peak Value of ΔPcyl_brn Taking Misfire into Account>
14 shows an example of changes in the gas pressure Pcyl in the cylinder relative to the crank angle θd in a combustion cycle (compression stroke and combustion stroke) in which a misfire occurs. When a misfire occurs, the increase ΔPcyl_brn in the gas pressure in the cylinder due to combustion becomes close to 0, making it difficult to determine its peak value, and the crank angle θd_Δbrnmax corresponding to the peak value fluctuates for each combustion cycle, making it easy for errors in misfire determination to occur.

The abnormal combustion determination unit 53 therefore determines the peak value of the increase in gas pressure due to combustion ΔPcyl_brn in the determination angle interval Δθdet, and if the peak value is smaller than the misfire state corresponding threshold ThΔP_mf, sets the angle θd_mf corresponding to the misfire state, which is preset within the determination angle interval Δθdet, as the crank angle θd_Δbrnmax corresponding to the peak value.

With this configuration, even if a misfire occurs and the increase in gas pressure inside the cylinder due to combustion ΔPcyl_brn approaches 0, making it difficult to determine its peak value, the angle θd_mf corresponding to the misfire state can be set as the crank angle θd_Δbrnmax corresponding to the peak value, and θd_Δbrnmax can be prevented from fluctuating with each combustion cycle, thereby suppressing the occurrence of errors in misfire determination.

The misfire state corresponding threshold value ThΔP_mf is set to a value greater than 0, taking into consideration the fluctuation range of ΔPcyl_brn due to noise, variation factors, etc., when a misfire occurs. For example, the misfire state corresponding angle θd_mf is set to the end angle of the judgment angle interval Δθdet, or is preset to correspond to the crank angle θd_Δbrnmax that corresponds to the peak value when no misfire occurs.

<Measures to deal with fluctuations in ΔPcyl_brn>
15 is an example of changes in the gas pressure Pcyl in the cylinder with respect to the crank angle θd in a combustion cycle (compression stroke and combustion stroke) in which no misfire occurs. In this example, due to the influence of the tooth angle variation of the signal plate 10, the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn is greater than 0 before the start of combustion (hatched portion). Even in this case, since the peak value of ΔPcyl_brn after the start of combustion is greater, no error in the judgment of abnormal combustion occurs, but it is preferable that there is no increase in ΔPcyl_brn before the start of combustion due to noise, variation factors, etc. Also, it is preferable that there is no increase in ΔPcyl_brn before the start of combustion because it leads to deterioration in the calculation accuracy of the heat release rate dQ/dθ in the second embodiment and the mass fraction burned MFB in the third embodiment, which will be described later.

Therefore, when the crank angle θd is changed to the retard side (changed in the rotational direction) during the compression stroke and the combustion stroke, the gas pressure calculation unit 52 determines the crank angle θd at which the increase in gas pressure due to combustion ΔPcyl_brn becomes greater than the zero-over-zero determination threshold ThΔP_0 for the first time during the compression stroke as the first crank angle θd1, determines the crank angle θd at which the increase in gas pressure due to combustion ΔPcyl_brn becomes equal to or less than the zero-over-zero determination threshold ThΔP_0 after the first crank angle θd1 as the second crank angle θd2, and determines the crank angle θd at which the increase in gas pressure due to combustion ΔPcyl_brn becomes greater than the zero-over-zero determination threshold ThΔP_0 after the second crank angle θd2 in the combustion stroke following the compression stroke as the third crank angle θd3. Then, when the first crank angle θd1 and the third crank angle θd3 exist, the gas pressure calculation unit 52 sets the increase in gas pressure due to combustion ΔPcyl_brn in the angle section corresponding to the first crank angle θd1 to the second crank angle θd2 to 0.

With this configuration, even if ΔPcyl_brn before the start of combustion increases above 0 due to noise, variation factors, etc., it is possible to correct ΔPcyl_brn before the start of combustion to 0. The zero excess determination threshold value ThΔP_0 is set to a value equal to or greater than 0.

1-2-4. Avoidance control unit 54
When the abnormal combustion determination unit 53 determines that abnormal combustion has occurred, the avoidance control unit 54 changes control parameters of the internal combustion engine to suppress the occurrence of abnormal combustion, and controls the internal combustion engine. The control parameters to be changed include one or more of the fuel injection amount, the amount of intake gas in the cylinder, the ignition timing, the EGR amount, and the control amount of the variable valve timing mechanism.

<When pre-ignition occurs>
For example, when the control parameters to be changed include the fuel injection amount, the avoidance control unit 54, when it is determined that pre-ignition has occurred, enriches (increases) the fuel injection amount from the reference injection amount, and suppresses the occurrence of pre-ignition by cooling the fuel. When the control parameters to be changed include the intake gas amount in the cylinder, the avoidance control unit 54, when it is determined that pre-ignition has occurred, reduces the intake gas amount in the cylinder to less than the reference intake gas amount, and suppresses the occurrence of pre-ignition by reducing the temperature of the compressed gas near the top dead center. For example, the throttle valve 4 is controlled to the closing side. When the control parameters to be changed include the ignition timing, the avoidance control unit 54, when it is determined that pre-ignition has occurred, changes the ignition timing to the retard side from the reference ignition timing, and suppresses the occurrence of pre-ignition by reducing the combustion temperature.

If the control parameters to be changed include the EGR amount, the avoidance control unit 54 increases the EGR amount above the reference EGR amount when it is determined that pre-ignition has occurred, thereby suppressing the occurrence of pre-ignition by reducing the ignitability of the mixture and reducing the combustion temperature. For example, the EGR valve 22 is controlled to the open side. If the control parameters to be changed include the control amount of the variable valve timing mechanism, the avoidance control unit 54 changes the control amount of the variable valve timing mechanism to a side that suppresses the occurrence of pre-ignition more than the reference control amount when it is determined that pre-ignition has occurred, thereby suppressing the occurrence of pre-ignition. The control amount of the variable valve timing mechanism becomes the opening and closing timing of the exhaust valve when controlling the variable valve timing mechanism of the exhaust valve, and becomes the opening and closing timing of the intake valve when controlling the variable valve timing mechanism of the intake valve. For example, the control amount is changed so that the overlap period between the opening period of the exhaust valve and the opening period of the intake valve increases, the internal EGR amount is increased, and the occurrence of pre-ignition is suppressed by reducing the ignitability of the mixture and reducing the combustion temperature.

If it is determined that pre-ignition has occurred, the avoidance control unit 54 changes the reference control parameters calculated by the basic control unit 55 for the control parameters to be changed, transmits the changed control parameters to the basic control unit 55, and reflects them in the control of the basic control unit 55. If it is determined that pre-ignition has occurred, the avoidance control unit 54 gradually changes the control parameters to be changed to the side that suppresses the occurrence of pre-ignition, and if it is determined that pre-ignition has not occurred, gradually returns the control parameters to the opposite side from the side that suppresses the occurrence of pre-ignition. Furthermore, the avoidance control unit 54 may increase the amount of change in the control parameters to be changed to the side that suppresses the occurrence of pre-ignition as the intensity of the occurrence of pre-ignition increases. If the control parameters to be changed can be changed for each cylinder, the control parameters to be changed for the cylinder in which pre-ignition has occurred may be changed.

<When a misfire occurs>
For example, if the control parameters to be changed include the fuel injection amount, the avoidance control unit 54 makes the fuel injection amount richer (increases it) than the reference injection amount when it is determined that a misfire has occurred, thereby suppressing the occurrence of a misfire. If the control parameters to be changed include the intake gas amount in the cylinder, the avoidance control unit 54 increases the intake gas amount in the cylinder to more than the reference intake gas amount when it is determined that a misfire has occurred, thereby suppressing the occurrence of a misfire. For example, the throttle valve 4 is controlled to open. If the control parameters to be changed include the ignition timing, the avoidance control unit 54 changes the ignition timing to the advanced side from the reference ignition timing when it is determined that a misfire has occurred, thereby suppressing the occurrence of a misfire.

If the control parameters to be changed include the EGR amount, the avoidance control unit 54 reduces the EGR amount below the reference EGR amount when it is determined that a misfire has occurred, thereby suppressing the occurrence of a misfire. For example, it controls the EGR valve 22 to the closing side. If the control parameters to be changed include the control amount of the variable valve timing mechanism, the avoidance control unit 54 changes the control amount of the variable valve timing mechanism to a side that suppresses the occurrence of a misfire more than the reference control amount when it is determined that a misfire has occurred, thereby suppressing the occurrence of a misfire. The control amount of the variable valve timing mechanism becomes the exhaust valve opening and closing timing when controlling the variable valve timing mechanism of the exhaust valve, and becomes the intake valve opening and closing timing when controlling the variable valve timing mechanism of the intake valve. For example, it changes the control amount so that the overlap period between the exhaust valve opening period and the intake valve opening period is reduced, thereby reducing the internal EGR amount and suppressing the occurrence of a misfire.

If it is determined that a misfire has occurred, the avoidance control unit 54 changes the reference control parameters calculated by the basic control unit 55 for the control parameters to be changed, transmits the changed control parameters to the basic control unit 55, and reflects them in the control of the basic control unit 55. If it is determined that a misfire has occurred, the avoidance control unit 54 gradually changes the control parameters to be changed to the side that suppresses the occurrence of misfire, and if it is determined that a misfire has not occurred, gradually returns the control parameters to the side opposite to the suppression side. Furthermore, the avoidance control unit 54 may increase the amount of change in the control parameters to be changed to the side that suppresses the occurrence of misfire as the frequency of misfire increases. If the control parameters to be changed can be changed for each cylinder, the control parameters to be changed for the cylinder where a misfire has occurred may be changed.

2. Second embodiment
A control device 50 according to a second embodiment will be described with reference to the drawings. Description of components similar to those of the first embodiment will be omitted. The basic configuration of the control device 50 according to this embodiment is similar to that of the first embodiment. This embodiment differs from the first embodiment in that a gas pressure calculation unit 52 calculates the heat release rate dQ/dθd, and an abnormal combustion determination unit 53 uses the heat release rate dQ/dθd to determine whether or not abnormal combustion has occurred.

<Calculation of actual heat release rate dQ/dθ>
A gas pressure calculation unit 52 calculates a heat generation rate dQ/dθd per unit crank angle at each crank angle θd based on the gas pressure Pcyl in the cylinder and the crank angle θd.

In this embodiment, the gas pressure calculation unit 52 calculates the heat release rate dQ/dθd per unit crank angle at each crank angle θd using the following equation.

Here, κ is the specific heat ratio, and Vcly_θ is the cylinder volume of the combustion cylinder at each crank angle θd, and is calculated as described above using equation (3). The calculated heat release rate dQ/dθd for each crank angle θd is stored in a storage device 91 such as a RAM, like other calculated values.

<Principle for determining abnormal combustion>
The principle of determining abnormal combustion based on the heat release rate dQ/dθd will be described below.
16 plots the relationship between the crank angle θ_dQ/dθmax corresponding to the peak value dQ/dθ_max of the actual heat release rate in each combustion cycle and the crank angle θd_dQ/dθdmax corresponding to the peak value dQ/dθd_max of the heat release rate calculated by the control device 50, in the case where there is a mixture of combustion cycles in which pre-ignition occurs and combustion cycles in which pre-ignition does not occur. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder).

Because it is possible to clearly separate the crank angle θd_dQ/dθdmax (above the dashed line in FIG. 16) corresponding to the peak value of the heat release rate to the right of the dashed dotted line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate for which it is desired to determine that pre-ignition is occurring, and the crank angle θd_dQ/dθdmax (below the dashed line in FIG. 16) corresponding to the peak value of the heat release rate to the left of the dashed dotted line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate for which it is desired to determine that pre-ignition is not occurring, it is possible to set a judgment threshold value (dashed line in FIG. 16) that accurately determines the occurrence of pre-ignition. This is because, unlike the crank angular acceleration α, the heat release rate dQ/dθd has little angle dependency and is therefore able to clearly show the effects of the occurrence of pre-ignition.

In FIG. 17, the relationship between the crank angle θ_dQ/dθmax corresponding to the peak value dQ/dθ_max of the actual heat release rate and the crank angle θd_dQ/dθdmax corresponding to the peak value dQ/dθd_max of the heat release rate calculated by the control device 50 is plotted in each combustion cycle when there is a mixture of combustion cycles in which misfires occur and combustion cycles in which misfires do not occur. Note that the scales of the horizontal and vertical axes in FIG. 17 are larger than those of the horizontal and vertical axes in FIG. 16. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder).

It is possible to clearly separate the crank angle θd_dQ/dθdmax (below the dashed line in FIG. 17) corresponding to the peak value of the heat release rate to the left of the dashed line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate for which it is desired to determine that a misfire is occurring, from the crank angle θd_dQ/dθdmax (above the dashed line in FIG. 17) corresponding to the peak value of the heat release rate to the right of the dashed line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate for which it is desired to determine that a misfire is not occurring. This makes it possible to set a judgment threshold value (dashed line in FIG. 17) that accurately determines the occurrence of a misfire. This is because, unlike the crank angular acceleration α, the heat release rate dQ/dθd has little angle dependency and is clearly affected by the occurrence of a misfire.

As explained above, the occurrence of abnormal combustion such as pre-ignition and misfire can be determined by the heat release rate dQ/dθd, which has little angle dependency.

<Determining abnormal combustion>
Therefore, the abnormal combustion judgment unit 53 judges whether or not abnormal combustion has occurred in the internal combustion engine based on the heat generation rate dQ/dθd at each crank angle θd in the judgment angle range Δθdet, which is calculated based on the increase in gas pressure ΔPcyl_brn due to combustion at each crank angle θd.

As described above, unlike the crank angular acceleration α, the heat release rate dQ/dθd has little angle dependency and is highly sensitive to the effects of abnormal combustion. Therefore, the presence or absence of abnormal combustion can be accurately determined based on the heat release rate dQ/dθd calculated based on the increase in gas pressure due to combustion ΔPcyl_brn.

<Judgment of Preignition>
In this embodiment, the abnormal combustion judgment unit 53 judges the peak value of the heat generation rate dQ/dθd in the judgment angle interval Δθdet, and determines whether or not pre-ignition has occurred by comparing the crank angle θd_dQ/dθdmax corresponding to the peak value with the angle threshold value Thθ_pre for pre-ignition.

As explained using FIG. 16, a difference in tendency of θd_dQ/dθdmax occurs between when pre-ignition occurs and when it does not occur. Therefore, by setting the angle threshold value Thθ_pre for pre-ignition between θd_dQ/dθdmax when pre-ignition occurs and θd_dQ/dθdmax when pre-ignition does not occur, it is possible to accurately determine whether pre-ignition has occurred.

The abnormal combustion determination unit 53 determines that pre-ignition has occurred if the crank angle θd_dQ/dθdmax corresponding to the peak value of dQ/dθd exceeds the angle threshold value Thθ_pre for pre-ignition, and determines that pre-ignition has not occurred if θd_dQ/dθdmax falls below the angle threshold value Thθ_pre for pre-ignition.

The abnormal combustion determination unit 53 sets the angle threshold value Thθ_pre for pre-ignition based on the operating state of the internal combustion engine. For example, the abnormal combustion determination unit 53 references gas pressure threshold data for pre-ignition in which the relationship between the operating state and the angle threshold value Thθ_pre is set, and sets the angle threshold value Thθ_pre for pre-ignition that corresponds to the current operating state. The operating state of the internal combustion engine may include the state of the amount of intake gas in the cylinder (e.g., the gas pressure Pin in the intake pipe, the amount of intake air, etc.), the air-fuel ratio, the rotational speed (rotational angular velocity), etc.

<Judgment of misfire>
The abnormal combustion judgment unit 53 judges the peak value of the heat release rate dQ/dθd in the judgment angle range Δθdet, and judges whether or not a misfire has occurred by comparing the crank angle θd_dQ/dθdmax corresponding to the peak value with the angle threshold value Thθ_mf for misfire.

As explained using FIG. 17, there is a difference in the tendency of θd_dQ/dθdmax between when a misfire occurs and when it does not. Therefore, by setting the angle threshold value Thθ_mf for misfire between θd_dQ/dθdmax when a misfire occurs and θd_dQ/dθdmax when a misfire does not occur, it is possible to accurately determine whether a misfire has occurred.

The abnormal combustion determination unit 53 determines that a misfire has occurred if the crank angle θd_dQ/dθdmax corresponding to the peak value of the heat release rate dQ/dθd falls below the angle threshold value Thθ_mf for misfire, and determines that a misfire has not occurred if θd_dQ/dθdmax exceeds the angle threshold value Thθ_mf for misfire.

The abnormal combustion determination unit 53 sets the angle threshold Thθ_mf for misfire based on the operating state of the internal combustion engine. For example, the abnormal combustion determination unit 53 references gas pressure threshold data for misfire in which the relationship between the operating state and the angle threshold Thθ_mf is set, and sets the angle threshold Thθ_mf for misfire that corresponds to the current operating state. The operating state of the internal combustion engine may include the state of the amount of intake gas in the cylinder (e.g., the gas pressure Pin in the intake pipe, the amount of intake air, etc.), the air-fuel ratio, the rotational speed (rotational angular velocity), etc.

<Calculation of Peak Value of dQ/dθd Taking Misfire into Account>
In addition, the abnormal combustion judgment unit 53 judges the peak value of the heat release rate dQ/dθd in the judgment angle interval Δθdet, and if the peak value is smaller than the misfire state corresponding threshold value ThdQ_mf, sets the angle θd_mf corresponding to the misfire state that is preset within the judgment angle interval Δθdet as the crank angle θd_dQ/dθdmax corresponding to the peak value.

With this configuration, even if a misfire occurs and the heat release rate dQ/dθd approaches 0, making it difficult to determine its peak value, the angle θd_mf corresponding to the misfire state can be set as the crank angle θd_dQ/dθdmax corresponding to the peak value, and θd_dQ/dθdmax can be prevented from fluctuating with each combustion cycle, thereby suppressing the occurrence of errors in misfire determination.

3. Third embodiment
A control device 50 according to a third embodiment will be described with reference to the drawings. Descriptions of components similar to those of the first embodiment will be omitted. The basic configuration of the control device 50 according to this embodiment is similar to that of the first embodiment. This embodiment differs from the first embodiment in that a gas pressure calculation unit 52 calculates the heat release rate dQ/dθd and the mass fraction burned MFB, and an abnormal combustion determination unit 53 uses the mass fraction burned MFB to determine whether or not abnormal combustion has occurred.

<Calculation of actual heat release rate dQ/dθ>
As in the second embodiment, the gas pressure calculation unit 52 calculates the heat release rate dQ/dθd per unit crank angle at each crank angle θd based on the gas pressure Pcyl in the cylinder and the crank angle θd.

The gas pressure calculation unit 52 uses equation (12) to calculate the heat generation rate dQ/dθd per unit crank angle at each crank angle θd.

<Calculation of mass fraction burned (MFB)>
The gas pressure calculation unit 52 calculates the mass fraction burned MFB for each crank angle θd by integrating the heat release rate dQ/dθd during the combustion period.

＜異常燃焼の判定原理＞
　以下で、質量燃焼割合ＭＦＢによる異常燃焼の判定の原理について説明する。
　図１８には、プレイグニッションが発生する燃焼サイクルと発生しない燃焼サイクルが混在する場合において、各燃焼サイクルにおける、実熱発生率のピーク値ｄＱ／ｄθ＿ｍａｘに対応するクランク角度θ＿ｄＱ／ｄθｍａｘと、制御装置５０により算出された質量燃焼割合ＭＦＢが判定割合（本例では、９０％）に到達するクランク角度θｄ＿ＭＦＢ９０との関係がプロットされている。ここで、実熱発生率のピーク値ｄＱ／ｄθ＿ｍａｘは、実際の気筒内のガス圧（例えば気筒内のガス圧センサで計測した値）から算出した値である。 In this embodiment, the gas pressure calculation unit 52 uses the following equation to calculate the mass fraction burned MFB for each crank angle θd by dividing an interval integral value obtained by integrating the heat release rate dQ/dθd from the start angle θ0 to each crank angle θd by a total integral value Q0 obtained by integrating the heat release rate dQ/dθd over the entire combustion period. The gas pressure calculation unit 52 performs a calculation process to calculate the mass fraction burned MFB at each crank angle θd. The calculated mass fraction burned MFB for each crank angle θd is stored in the storage device 91, such as a RAM, like other calculated values.

<Principle for determining abnormal combustion>
The principle of determining abnormal combustion based on the mass fraction burned (MFB) will be described below.
18 plots the relationship between the crank angle θ_dQ/dθmax corresponding to the peak value dQ/dθ_max of the actual heat release rate in each combustion cycle and the crank angle θd_MFB90 at which the mass fraction burned MFB calculated by the control device 50 reaches a judgment rate (90% in this example) in a case where some combustion cycles have pre-ignition and others do not, in each combustion cycle. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder).

It is possible to clearly separate the crank angle θd_MFB90 (above the dashed line in FIG. 18) at which the mass burn fraction MFB reaches the determination percentage (90%) on the right side of the dashed line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate at which it is desired to determine that pre-ignition is occurring, and the crank angle θd_MFB90 (below the dashed line in FIG. 18) at which the mass burn fraction MFB reaches the determination percentage (90%) on the left side of the dashed line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate at which it is desired to determine that pre-ignition is not occurring. This makes it possible to set a determination threshold value (dashed line in FIG. 18) that accurately determines the occurrence of pre-ignition. This is because, unlike the crank angular acceleration α, the mass burn fraction MFB has little angle dependency and the effect of the occurrence of pre-ignition is clearly apparent.

Figure 19 plots the relationship between the crank angle θ_dQ/dθmax corresponding to the peak value dQ/dθ_max of the actual heat release rate in each combustion cycle, and the crank angle θd_MFB90 at which the mass fraction burned MFB calculated by the control device 50 reaches the judgment rate (90%) when there is a mixture of combustion cycles in which misfires occur and combustion cycles in which misfires do not occur. Note that the scales of the horizontal and vertical axes in Figure 19 are larger than those of the horizontal and vertical axes in Figure 18. Here, the peak value dQ/dθ_max of the actual heat release rate is a value calculated from the actual gas pressure in the cylinder (for example, a value measured by a gas pressure sensor in the cylinder).

The crank angle θd_MFB90 (below the dashed line in FIG. 19) at which the mass fraction burned MFB reaches the determination percentage (90%) on the left side of the dashed line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate at which it is desired to determine that a misfire is occurring, can be clearly separated from the crank angle θd_MFB90 (above the dashed line in FIG. 19) at which the mass fraction burned MFB reaches the determination percentage (90%) on the right side of the dashed line, which is the region of the crank angle θ_dQ/dθmax corresponding to the peak value of the actual heat release rate at which it is desired to determine that a misfire is not occurring. This makes it possible to set a determination threshold value (dashed line in FIG. 19) that accurately determines the occurrence of a misfire. This is because, unlike the crank angular acceleration α, the mass fraction burned MFB has little angle dependency and is more clearly affected by the occurrence of a misfire.

As explained above, the occurrence of abnormal combustion such as pre-ignition and misfire can be determined by the mass fraction burned (MFB), which has little angle dependency.

<Determining abnormal combustion>
Therefore, the abnormal combustion judgment unit 53 judges whether or not abnormal combustion has occurred in the internal combustion engine based on the mass combustion fraction MFB at each crank angle θd in the judgment angle range Δθdet, which is calculated based on the increase ΔPcyl_brn in gas pressure due to combustion at each crank angle θd.

As described above, unlike the crank angular acceleration α, the mass fraction burned MFB has little angle dependency and is more susceptible to the effects of abnormal combustion. Therefore, the presence or absence of abnormal combustion can be accurately determined based on the mass fraction burned MFB calculated based on the increase in gas pressure due to combustion ΔPcyl_brn.

<Judgment of Preignition>
In this embodiment, the abnormal combustion determination unit 53 determines the crank angle θd_MFB90 at which the mass fraction burned MFB becomes a determination ratio (e.g., 90%) in the determination angle section Δθdet, and compares the crank angle θd_MFB90 corresponding to the determination ratio with the angle threshold value Thθ_pre for pre-ignition to determine whether or not pre-ignition has occurred. The determination ratio may be set to a ratio other than 90%.

As explained using FIG. 18, a difference in tendency of θd_MFB90 occurs between when pre-ignition occurs and when it does not occur. Therefore, by setting the angle threshold value Thθ_pre for pre-ignition between θd_MFB90 when pre-ignition occurs and θd_MFB90 when pre-ignition does not occur, it is possible to accurately determine whether pre-ignition has occurred.

The abnormal combustion determination unit 53 determines that pre-ignition has occurred if the crank angle θd_MFB90 at which the mass burn fraction MFB becomes the determination ratio (90%) exceeds the angle threshold value Thθ_pre for pre-ignition, and determines that pre-ignition has not occurred if θd_MFB90 falls below the angle threshold value Thθ_pre for pre-ignition.

The abnormal combustion determination unit 53 sets the angle threshold value Thθ_pre for pre-ignition based on the operating state of the internal combustion engine. For example, the abnormal combustion determination unit 53 references gas pressure threshold data for pre-ignition in which the relationship between the operating state and the angle threshold value Thθ_pre is set, and sets the angle threshold value Thθ_pre for pre-ignition that corresponds to the current operating state. The operating state of the internal combustion engine may include the state of the amount of intake gas in the cylinder (e.g., the gas pressure Pin in the intake pipe, the amount of intake air, etc.), the air-fuel ratio, the rotational speed (rotational angular velocity), etc.

<Judgment of misfire>
The abnormal combustion judgment unit 53 judges the crank angle θd_MFB90 at which the mass burned fraction MFB becomes a judgment ratio (e.g., 90%) in the judgment angle range Δθdet, and judges whether or not a misfire has occurred by comparing the crank angle θd_MFB90 corresponding to the judgment ratio with the angle threshold value Thθ_mf for misfire.

As explained using FIG. 19, there is a difference in the tendency of θd_MFB90 between when a misfire occurs and when it does not occur. Therefore, by setting the angle threshold value Thθ_mf for misfire between θd_MFB90 when a misfire occurs and θd_MFB90 when a misfire does not occur, it is possible to accurately determine whether a misfire has occurred.

The abnormal combustion determination unit 53 determines that a misfire has occurred if the crank angle θd_MFB90 at which the mass fraction burned MFB becomes the determination ratio (90%) falls below the misfire angle threshold Thθ_mf, and determines that a misfire has not occurred if θd_MFB90 exceeds the misfire angle threshold Thθ_mf.

The abnormal combustion determination unit 53 sets the angle threshold Thθ_mf for misfire based on the operating state of the internal combustion engine. For example, the abnormal combustion determination unit 53 references gas pressure threshold data for misfire in which the relationship between the operating state and the angle threshold Thθ_mf is set, and sets the angle threshold Thθ_mf for misfire that corresponds to the current operating state. The operating state of the internal combustion engine may include the state of the amount of intake gas in the cylinder (e.g., the gas pressure Pin in the intake pipe, the amount of intake air, etc.), the air-fuel ratio, the rotational speed (rotational angular velocity), etc.

<Other embodiments>
(1) In the above embodiments, the angle information detection unit 51 uses the output signal of the crank angle sensor 11. However, another crank angle sensor that detects the teeth of a link gear or the like may be provided, and the angle information detection unit 51 may use the output signal of the other crank angle sensor.

(2) In each of the above embodiments, a three-cylinder engine is used as an example. However, an engine with any number of cylinders (e.g., one, two, four, or six cylinders) may be used.

Although various exemplary embodiments and examples are described in this application, the various features, aspects, and functions described in one or more of the embodiments are not limited to application in a particular embodiment, but may be applied to the embodiments alone or in various combinations. Thus, countless variations not illustrated are anticipated within the scope of the technology disclosed in this specification. For example, this includes cases in which at least one component is modified, added, or omitted, and even cases in which at least one component is extracted and combined with components of another embodiment.

1: internal combustion engine, 11: crank angle sensor, 50: control device for internal combustion engine, 51: angle information detection unit, 52: gas pressure calculation unit, 53: abnormal combustion judgment unit, 54: avoidance control unit, dQ/dθd: heat generation rate, Pcyl: gas pressure in cylinder, Pcyl_Δbrnmax: gas pressure in cylinder at crank angle corresponding to peak value of increase in gas pressure in cylinder due to combustion, Pcyl_unbrn: gas pressure in cylinder when uncombusted, ThΔP_0: exceed-zero judgment threshold, ThΔP_mf: misfire state corresponding threshold, Thθ_mf: angle threshold for misfire, Thθ_pre: angle threshold for pre-ignition, ThP_mf: gas pressure threshold for misfire, ThP _pre: gas pressure threshold for pre-ignition, ThdQ_mf: misfire state corresponding threshold, ΔPcyl_brn: increase in gas pressure due to combustion, Δθdet: judgment angle section, αd: crank angular acceleration, θd: crank angle, θd1: first crank angle, θd2: second crank angle, θd3: third crank angle, θd_Δbrnmax: crank angle corresponding to the peak value of the increase in gas pressure in the cylinder due to combustion, θd_MFB90: crank angle at which the mass combustion ratio reaches the judgment ratio, θd_dQ/dθdmax: crank angle corresponding to the peak value of the heat release rate, θd_mf: angle corresponding to the misfire state, ωd: crank angular velocity

Claims (12)

an angle information detection unit that detects a crank angle and a crank angular acceleration based on an output signal of the crank angle sensor;
a gas pressure calculation unit that calculates, for each of the crank angles, an increment in gas pressure torque due to combustion, among the gas pressure torque applied to the crankshaft by the gas pressure in a cylinder, based on the crank angle and the crank angular acceleration, and calculates, for each of the crank angles, an increment in gas pressure torque due to combustion, based on the increment in gas pressure torque due to combustion and the crank angle;
an abnormal combustion determination unit that determines whether or not abnormal combustion has occurred in the internal combustion engine based on an increment in gas pressure due to the combustion at each crank angle within a determination angle section that is set corresponding to a combustion period;
A control device for an internal combustion engine comprising: the gas pressure calculation unit calculates a gas pressure in the cylinder when uncombusted, assuming that uncombusted fuel is not yet burned, based on a current state of an intake gas amount in the cylinder and the crank angle, at each of the crank angles, and calculates a gas pressure in the cylinder when uncombusted, based on the gas pressure in the cylinder when uncombusted and an increase in gas pressure due to the combustion, at each of the crank angles;
2. The control device for an internal combustion engine as described in claim 1, wherein the abnormal combustion judgment unit judges a peak value of the increase in gas pressure due to the combustion in the judgment angle section, and judges whether or not pre-ignition has occurred by comparing the gas pressure in the cylinder at the crank angle corresponding to the peak value with a gas pressure threshold value for pre-ignition. The control device for an internal combustion engine according to claim 1, wherein the abnormal combustion determination unit determines the peak value of the increase in gas pressure due to the combustion in the determination angle interval, and determines whether pre-ignition has occurred by comparing the crank angle corresponding to the peak value with an angle threshold value for pre-ignition. the gas pressure calculation unit calculates a gas pressure in the cylinder when uncombusted, assuming that uncombusted fuel is not yet burned, based on a current state of an intake gas amount in the cylinder and the crank angle, at each of the crank angles, and calculates a gas pressure in the cylinder when uncombusted, based on the gas pressure in the cylinder when uncombusted and an increase in gas pressure due to the combustion, at each of the crank angles;
2. The control device for an internal combustion engine according to claim 1, wherein the abnormal combustion judgment unit judges a peak value of an increase in gas pressure due to the combustion in the judgment angle section, and judges whether or not a misfire has occurred by comparing the gas pressure in the cylinder at the crank angle corresponding to the peak value with a gas pressure threshold value for misfire. The control device for an internal combustion engine according to claim 1, wherein the abnormal combustion determination unit determines the peak value of the increase in gas pressure due to the combustion in the determination angle range, and determines whether or not a misfire has occurred by comparing the crank angle corresponding to the peak value with an angle threshold value for misfire. the gas pressure calculation unit calculates a gas pressure in the cylinder when uncombusted, assuming that uncombusted fuel is not yet burned, based on a current state of an intake gas amount in the cylinder and the crank angle, at each of the crank angles, and calculates a gas pressure in the cylinder when uncombusted, based on the gas pressure in the cylinder when uncombusted and an increase in gas pressure due to the combustion, at each of the crank angles;
calculating a heat release rate per unit crank angle based on the gas pressure in the cylinder and the crank angle at each of the crank angles;
2. The control device for an internal combustion engine according to claim 1, wherein the abnormal combustion judgment unit judges a peak value of the heat release rate in the judgment angle section, and judges whether or not pre-ignition has occurred by comparing the crank angle corresponding to the peak value with an angle threshold value for pre-ignition. the gas pressure calculation unit calculates a gas pressure in the cylinder when uncombusted, assuming that uncombusted fuel is not yet burned, based on a current state of an intake gas amount in the cylinder and the crank angle, at each of the crank angles, and calculates a gas pressure in the cylinder when uncombusted, based on the gas pressure in the cylinder when uncombusted and an increase in gas pressure due to the combustion, at each of the crank angles;
calculating a heat release rate per unit crank angle based on the gas pressure in the cylinder and the crank angle at each of the crank angles;
2. The control device for an internal combustion engine according to claim 1, wherein the abnormal combustion determination unit determines a peak value of the heat release rate in the determination angle interval, and determines whether or not a misfire has occurred by comparing the crank angle corresponding to the peak value with an angle threshold value for misfire. the gas pressure calculation unit calculates a gas pressure in the cylinder when uncombusted, assuming that uncombusted fuel is not yet burned, based on a current state of an intake gas amount in the cylinder and the crank angle, at each of the crank angles, and calculates a gas pressure in the cylinder when uncombusted, based on the gas pressure in the cylinder when uncombusted and an increase in gas pressure due to the combustion, at each of the crank angles;
calculating a heat release rate per unit crank angle based on the gas pressure in the cylinder and the crank angle at each of the crank angles;
calculating a mass combustion fraction for each of the crank angles by integrating the heat release rate over the combustion period;
2. The control device for an internal combustion engine according to claim 1, wherein the abnormal combustion judgment unit judges the crank angle at which the mass combustion rate becomes a judgment rate in the judgment angle range, and judges whether or not pre-ignition has occurred by comparing the crank angle corresponding to the judgment rate with an angle threshold value for pre-ignition. the gas pressure calculation unit calculates a gas pressure in the cylinder when uncombusted, assuming that uncombusted fuel is not yet burned, based on a current state of an intake gas amount in the cylinder and the crank angle, at each of the crank angles, and calculates a gas pressure in the cylinder when uncombusted, based on the gas pressure in the cylinder when uncombusted and an increase in gas pressure due to the combustion, at each of the crank angles;
calculating a heat release rate per unit crank angle based on the gas pressure in the cylinder and the crank angle at each of the crank angles;
calculating a mass combustion fraction for each of the crank angles by integrating the heat release rate over the combustion period;
2. The control device for an internal combustion engine according to claim 1, wherein the abnormal combustion determination unit determines the crank angle at which the mass combustion rate becomes a determination rate in the determination angle range, and determines whether or not a misfire has occurred by comparing the crank angle corresponding to the determination rate with an angle threshold value for misfire. The gas pressure calculation unit is
When the crank angle is changed to the retard side in the compression stroke and the combustion stroke,
determining, as a first crank angle, the crank angle at which an increase in gas pressure due to the combustion becomes greater than a zero exceedance determination threshold during a compression stroke;
determining, after the first crank angle, the crank angle at which an increase in gas pressure due to the combustion becomes equal to or less than the over-zero determination threshold, as a second crank angle;
In a combustion stroke following the compression stroke, the crank angle at which an increase in gas pressure due to the combustion becomes greater than the over-zero determination threshold after the second crank angle is determined as a third crank angle;
10. The control device for an internal combustion engine according to claim 1, wherein, when the first crank angle and the third crank angle exist, an increase in gas pressure due to the combustion in an angle section corresponding to the first crank angle to the second crank angle is set to 0. The control device for an internal combustion engine according to any one of claims 2, 3, 4, and 5, wherein the abnormal combustion determination unit determines a peak value of the increase in gas pressure due to the combustion in the determination angle range, and if the peak value is smaller than a misfire state corresponding threshold value, sets an angle corresponding to a misfire state that is preset within the determination angle range as the crank angle corresponding to the peak value. The control device for an internal combustion engine according to any one of claims 1 to 11, further comprising an avoidance control unit that, when it is determined that abnormal combustion has occurred, changes the control parameters of the internal combustion engine and controls the internal combustion engine so as to suppress the occurrence of abnormal combustion.

Images