Internal combustion engine control device

Abstract

The present invention provides an internal combustion engine control device that can estimate an external load torque precisely, even when abnormal combustion occurs. The internal combustion engine control device computes the external load torque for the current combustible angle section on the basis of the crank angle acceleration and the torque in the unburned case at a crank angle near top dead center, smooths a plurality of external load torques computed in previous combustible angle sections to compute an external load torque for computation to be used in the current combustible angle section, computes, at each crank angle, one or both of the in-cylinder gas pressure and the increase in in-cylinder gas pressure due to combustion on the basis of the crank angle acceleration, the torque in the unburned case, and the external load torque for computation, and detects the occurrence of abnormal combustion.

Description

Control device for internal combustion engine

[0001] The present disclosure relates to a control device for an internal combustion engine.

[0002] Pre-ignition, also known as abnormal combustion, is a phenomenon in which deposits remaining in the spark plug or cylinder become so hot that they become a heat source and self-ignite before ignition by the spark plug. The technology in Patent Document 1 detects pre-ignition by the fluctuation range of the rotational speed of the internal combustion engine.

[0003] For example, if the ignition timing of a specific cylinder is retarded by a certain angle, the output of the internal combustion engine decreases and the rotational speed of the internal combustion engine fluctuates. If pre-ignition occurs in this case, a flame is generated in the combustion chamber earlier than the ignition timing, thereby reducing the fluctuation range of the rotational speed of the internal combustion engine. Therefore, the occurrence of pre-ignition is detected by determining whether the fluctuation range of this rotational speed is smaller than a predetermined range (fluctuation range for pre-ignition detection).

[0004] The technology of Patent Document 2 is configured to calculate the crank angular velocity and crank angular acceleration based on the output signal of a crank angle sensor, calculate the gas pressure torque generated by combustion based on the crank angular velocity and crank angular acceleration, and calculate the amount of work due to the gas pressure torque.

[0005] JP 2-136566 A JP 2013-87724 A

[0006] Incidentally, the crank angular acceleration includes an acceleration component due to an external load torque applied to the crankshaft from outside the internal combustion engine. Therefore, unless the external load torque is grasped and the gas pressure torque is calculated based on the crank angular velocity and crank angular acceleration, the calculation accuracy decreases. For this reason, it is conceivable to estimate the external load torque based on the crank angular acceleration, etc. However, when abnormal combustion such as pre-ignition occurs, the crank angular acceleration includes a torque fluctuation component caused by the abnormal combustion, which deteriorates the estimation accuracy of the external load torque and the estimation accuracy of the gas pressure torque.

[0007] Therefore, an object of the present disclosure is to provide a control device for an internal combustion engine that can accurately estimate external load torque even when abnormal combustion occurs.

[0008] The control device for an internal combustion engine according to the present disclosure comprises: an angle information detection unit that detects a crank angle, a crank angular velocity, and a crank angular acceleration based on an output signal of a crank angle sensor; an intake pipe gas pressure detection unit that detects a gas pressure in the intake pipe based on an output signal of a gas pressure sensor that detects the gas pressure in the intake pipe; an uncombusted torque calculation unit that estimates an uncombusted torque, which is a torque applied to the crankshaft by the gas pressure in the cylinder and the reciprocating motion of the piston, using a physical model equation of the crank mechanism based on the gas pressure in the intake pipe, the crank angular velocity, and the crank angular acceleration at each crank angle; and an external load torque calculation unit that calculates an external load torque, which is a torque applied to the crankshaft from outside the internal combustion engine, based on the crank angular acceleration and the uncombusted torque at a crank angle near top dead center of the piston in the combustion stroke for a current combustible angle interval, and smooths a plurality of the external load torques calculated in past combustible angle intervals to calculate an external load torque for calculation to be used in the current combustible angle interval. The system comprises: a cylinder gas pressure calculation unit that calculates, for each crank angle, one or both of the increase in cylinder gas pressure due to combustion and the cylinder gas pressure based on the crank angular acceleration, the torque when uncombusted, and the external load torque for calculation of the current combustible angle range corresponding to the crank angle; and an abnormal combustion detection unit that detects the occurrence of abnormal combustion for the current combustible angle range based on the increase in cylinder gas pressure due to combustion and one or both of the cylinder gas pressure.

[0009] If abnormal combustion such as pre-ignition occurs in the current combustible angle range, the abnormal combustion causes fluctuations in the crank angular acceleration near top dead center, and the influence of the abnormal combustion is included in the external load torque for the current combustible angle range calculated based on the crank angular acceleration. Therefore, if the external load torque for the current combustible angle range is used as the external load torque used to detect the occurrence of abnormal combustion in the current combustible angle range, the occurrence of abnormal combustion cannot be accurately detected. According to the control device for an internal combustion engine disclosed herein, when abnormal combustion occurs in the current combustible angle range, the external load torque used for calculation to detect the occurrence of abnormal combustion in the current combustible angle range is calculated by smoothing multiple external load torques calculated in past combustible angle ranges before the abnormal combustion occurred. Therefore, the external load torque for the current combustible angle range, which includes the influence of the abnormal combustion, is not used, making it possible to accurately determine the occurrence of abnormal combustion.

[0010] 1 is a schematic configuration diagram of an internal combustion engine and a control device for the internal combustion engine according to Embodiment 1. FIG. 1 is a schematic configuration diagram of an internal combustion engine and a control device for the internal combustion engine according to Embodiment 1. FIG. 2 is a block diagram of the control device for the internal combustion engine according to Embodiment 1. FIG. 3 is a hardware configuration diagram of the control device for the internal combustion engine according to Embodiment 1. FIG. 4 is a time chart for explaining angle information detection processing according to Embodiment 1. FIG. 5 is a diagram for explaining a combustible angle range and top dead center of each cylinder according to Embodiment 1. FIG. 6 is a diagram for explaining a comparative example when pre-ignition has not occurred according to Embodiment 1 and an example of this embodiment. FIG. 7 is a diagram for explaining a comparative example when pre-ignition has occurred according to Embodiment 1 and an example of this embodiment. FIG. 8 is a diagram for explaining a holding process after pre-ignition has occurred according to Embodiment 1. FIG. 9 is a diagram for explaining a holding process after misfire has occurred according to Embodiment 1. FIG. 10 is a diagram for explaining a determination of erroneous detection of abnormal combustion after a disturbance has occurred according to Embodiment 1. FIG. 11 is a diagram for explaining a holding process after abnormal combustion has been detected according to Embodiment 1. FIG. 12 is a diagram for explaining a detection process for the occurrence of pre-ignition according to Embodiment 1. FIG. 13 is a diagram for explaining a detection process for the occurrence of misfire according to Embodiment 1.

[0011] 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).

[0012] 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 cylinders 7 that burn a mixture of air and fuel. The internal combustion engine 1 has an intake pipe 23 that supplies air to the cylinders 7, and an exhaust pipe 17 that discharges exhaust gas burned in the cylinders 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 corresponding to the opening of the throttle valve 4.

[0013] An air flow sensor 3 is provided in the intake pipe 23 upstream of the throttle valve 4, and outputs an electrical signal corresponding to the amount of intake air taken into the intake pipe 23. The internal combustion engine 1 is equipped 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 portion 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 equipped with an air-fuel ratio sensor 18 that outputs an electrical signal corresponding to the air-fuel ratio of the exhaust gas in the exhaust pipe 17.

[0014] The intake manifold 12 is provided with a gas pressure sensor 8 that outputs an electric signal corresponding to the pressure inside the intake manifold 12. An injector 13 that injects fuel is provided downstream 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 electric 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.

[0015] A spark plug that ignites the air-fuel mixture and an ignition coil 16 that supplies ignition energy to the spark plug are provided at the top of each cylinder 7. Also provided at the top of each cylinder 7 are an intake valve 14 that adjusts the amount of intake air taken into the cylinder 7 from an intake pipe 23, and an exhaust valve 15 that adjusts the amount of exhaust gas discharged from the cylinder to an 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 each have an electric actuator.

[0016] As shown in FIG. 2 , the internal combustion engine 1 has a plurality 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 a crankshaft 2 via a connecting rod 9 and a crank 32. The crankshaft 2 is rotated by the reciprocating motion of the piston 5. Combustion gas pressure generated in each cylinder 7 presses against the top surface of the piston 5, rotating 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.

[0017] The internal combustion engine 1 is equipped with a signal plate 10 that rotates integrally with the crankshaft 2. The signal plate 10 has a plurality of teeth at a plurality of 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 tooth portions where some of the teeth are missing. 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.

[0018] 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 integrally with the camshaft 29. The cam signal plate 31 has a plurality of teeth at a plurality 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.

[0019] Based on two types of output signals from the crank angle sensor 11 and the cam angle sensor 30, the control device 50 detects the crank angle relative to the top dead center of each piston 5 and determines the stroke of each cylinder 7. The internal combustion engine 1 is a four-stroke engine having an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke.

[0020] The crank angle sensor 11 and the cam angle sensor 30 output electrical signals in response to changes 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 from them. Each angle sensor 11, 30 may be, for example, an electromagnetic pickup type sensor.

[0021] 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, an intake pipe gas pressure detection unit 52, an uncombusted torque calculation unit 53, an external load torque calculation unit 54, an in-cylinder gas pressure calculation unit 55, an abnormal combustion detection unit 56, a disturbance detection unit 57, an avoidance control unit 58, and a basic control unit 59. The control units 51 to 59 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 external signals to the arithmetic processing device 90, and an output circuit 93 that outputs signals from the arithmetic processing device 90 to the outside.

[0022] 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, various signal processing circuits, etc. Furthermore, a plurality of the same or different types of arithmetic processing device 90 may be provided, and each process may be shared and executed.

[0023] The storage device 91 includes volatile and non-volatile storage devices such as RAM (Random Access Memory), ROM (Read Only Memory), EEPROM (Electrically Erasable Programmable ROM), etc. The input circuit 92 is connected to various sensors and switches and includes an A / D converter and the like that inputs output signals of these sensors and switches to the arithmetic processing device 90. The output circuit 93 is connected to electrical loads and includes a drive circuit and the like that outputs control signals from the arithmetic processing device 90 to these electrical loads.

[0024] The functions of the control units 51 to 59 of the control device 50 are realized by an arithmetic processing device 90 executing software (programs) stored in a storage device 91 such as a ROM or EEPROM, in cooperation with other hardware of the control device 50, such as the storage device 91, an input circuit 92, and an output circuit 93. Setting data such as threshold values ​​used by the control units 51 to 59 is stored in the storage device 91 such as a ROM or EEPROM. Data such as calculated values ​​and detected values ​​calculated by the control units 51 to 58, including the crank angular velocity ωd, crank angular acceleration αd, cylinder gas pressure Pcyl, cylinder gas pressure Pcyl_unbrn in the uncombusted state, increment in cylinder gas pressure ΔPcyl_brn due to combustion, external load torque Tload, and external load torque Tload_cal for calculation, are stored in a rewritable storage device 91 such as a RAM.

[0025] 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 also connected to the control device 50. Based on output signals from the various sensors, the control device 50 detects the operating conditions of the internal combustion engine 1, such as the intake air amount, pressure in the intake manifold, atmospheric pressure Patm, air-fuel ratio, and accelerator opening.

[0026] 1-2-1. Basic Control Unit 59 As a basic control, the basic control unit 59 calculates the fuel injection amount, ignition timing, etc. based on input output signals from various sensors, and controls the injector 13, the ignition coil 16, etc. The basic control unit 59 calculates the output torque of the internal combustion engine 1 required by the driver based on the output signal from the accelerator position sensor 26, etc., and controls the throttle valve 4, etc., so as to achieve the intake air amount that realizes the required output torque. Specifically, the basic control unit 59 calculates a target throttle opening and controls the electric motor of the throttle valve 4 so that the throttle opening detected based on the output signal from the throttle opening sensor 19 approaches the target throttle opening. The basic control unit 59 also calculates a target opening of the EGR valve 22 based on input output signals from various sensors, and controls the electric motor of the EGR valve 22. The basic control unit 59 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 operation of the intake and exhaust variable valve timing mechanisms 14, 15 based on each target opening / closing timing.

[0027] 1-2-2. Intake Pipe Gas Pressure Detector 52 The intake pipe gas pressure detector 52 detects the gas pressure Pin in the intake pipe based on the output signal of the gas pressure sensor 8 that detects the gas pressure in the intake pipe.

[0028] 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 the time rate of change of the detected crank angle θd, and a crank angular acceleration αd, which is the time rate of change of the crank angular velocity ωd. The crank angular velocity ωd corresponds to the rotation speed.

[0029] 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 also 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 detected angle θd based on the detected crank angle θd and the detection time Td. Each angle interval Δθd or each time interval ΔTd may be multiplied by a learning correction coefficient obtained by learning tooth variations. Various known methods are used to calculate the learning correction coefficient.

[0030] 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 relative to the top dead center (TDC) 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.

[0031] <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 equation, 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 well-known methods may also be used.

[0032] 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 equation, the angle information detection unit 51 calculates the crank angular acceleration αd(n) of the currently detected angle based on the crank angular velocity ωd(n) calculated for the currently detected angle, the crank angular velocity ωd(n-1) calculated for the previously detected angle, and the time interval ΔTd(n) of the currently detected angle. Note that various other well-known methods may also be used.

[0033] The angle information detection unit 51 stores the calculated angle information such as the crank angular velocity ωd and the crank angular acceleration αd in association with the corresponding crank angle θd in the storage device 91 such as a RAM.

[0034] The uncombusted torque calculation unit 53 estimates the uncombusted torque Tcrk_unbrn, which is the torque applied to the crankshaft due to the gas pressure in the cylinder and the reciprocating motion of the piston, at each crank angle θd, using a physical model equation of the crank mechanism based on the gas pressure Pin in the intake pipe, the crank angular velocity ωd, and the crank angular acceleration αd.

[0035] <Calculation of torque based on in-cylinder gas pressure> In this embodiment, the uncombusted torque calculation unit 53 calculates the uncombusted gas pressure torque Tgas_unbrn, which is the torque applied to the crankshaft due to the in-cylinder gas pressure when uncombusted, assuming that uncombusted fuel is present, at each crank angle θd based on the gas pressure Pin in the intake pipe.

[0036] In this embodiment, the uncombusted torque calculation unit 53 calculates the uncombusted in-cylinder gas pressure Pcyl_unbrn_i of each cylinder i using the following equation: For cylinder i whose intake valve and exhaust valve are closed, the uncombusted in-cylinder gas pressure Pcyl_unbrn_i of each cylinder i is calculated based on the gas pressure Pin in the intake pipe and the crank angle θd using an equation for calculating gas pressure using a polytropic change. For cylinder i whose intake valve is open and whose exhaust valve is closed, the uncombusted in-cylinder gas pressure Pcyl_unbrn_i is calculated based on the gas pressure Pin in the intake pipe, and for cylinder i whose exhaust valve is open, the uncombusted in-cylinder gas pressure Pcyl_unbrn_i is calculated based on the gas pressure Pex in the exhaust pipe.

[0037] Here, Nply is a polytropic index, and for example, a preset value is used. Vcyl0 is the cylinder volume of the combustion cylinder when the intake valve is closed. A preset value may be used, or it may be changed depending on the intake valve closing timing set by the intake variable valve timing mechanism 14. The uncombusted torque calculation unit 53 calculates the cylinder volume Vcyl_i of each cylinder i corresponding to the crank angle θd_i of each cylinder i using a volume calculation function fvcyl, in which the relationship between the crank angle θd_i of each cylinder i and the cylinder volume Vcyl_i of each cylinder i is preset. For example, the fourth and fifth equations of Equation (3) are used as the volume calculation function fvcyl. Here, Vcyltop is the cylinder volume when the piston is positioned 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 connecting rod angle of each cylinder i. The crank angle θd_i of each cylinder i used in the calculation of the trigonometric function is a crank angle obtained by shifting the crank angle θd so that the top dead center of the combustion stroke for each cylinder i is 0 degrees. As the volume calculation function fvcyl, an equation other than the fourth and fifth equations of equation (3) may be used, or map data or other equations may be used.

[0038] The uncombusted torque calculation unit 53 calculates the uncombusted gas pressure torque Tgas_unbrn, which is the torque applied to the crankshaft by the uncombusted in-cylinder gas pressure Pcyl_unbrn at each crank angle θd, based on the uncombusted in-cylinder gas pressure Pcyl_unbrn.

[0039] In this embodiment, the uncombusted fuel torque calculation unit 53 uses the following equation to convert gas pressure into torque, and calculates the uncombusted fuel gas pressure torque Tgas_unbrn based on the uncombusted fuel in-cylinder gas pressure Pcyl_unbrn_i of each cylinder i and the crank angle θd_i of each cylinder i.

[0040] Here, R_i is a conversion coefficient for converting 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. A conversion coefficient calculation function fr is used, in which the relationship between the crank angle θd_i of each cylinder i and the conversion coefficient R_i of each cylinder i is set in advance. For example, the third and fourth equations in equation (4) are used as the conversion coefficient calculation function fr. Map data or other formulas may also be used as the conversion coefficient calculation function fr. N is the total number of cylinders, and in this embodiment, N=3.

[0041] Furthermore, the unburned-fuel torque calculation unit 53 calculates a reciprocating inertia torque Tpstn, which is the torque applied to the crankshaft by the reciprocating motion of the piston, at each crank angle θd based on the crank angular velocity ωd.

[0042] In this embodiment, the unburned-fuel-state torque calculation unit 53 calculates the reciprocating inertia torque Tpstn using the following equation.

[0043] 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. A coefficient calculation function fka is used, in which the relationship between the crank angle θd_i of each cylinder i and the coefficient Ka_i of each cylinder i is set in advance. For example, the third equation of equation (5) is used as the coefficient calculation function fka. Map data or other formulas may also be used as the coefficient calculation function fka. The conversion coefficient R_i of each cylinder i is the same as equation (4).

[0044] <Calculation of Uncombusted Torque Tcrk_unbrn> The uncombusted torque calculation unit 53 calculates the uncombusted torque Tcrk_unbrn by adding the uncombusted gas pressure torque Tgas_unbrn and the reciprocating inertia torque Tpstn at each crank angle θd.

[0045] The uncombusted torque calculation unit 53 stores each calculated value, such as the uncombusted in-cylinder gas pressure Pcyl_unbrn_i for each cylinder i calculated at each crank angle θd, the uncombusted gas pressure torque Tgas_unbrn, the reciprocating inertia torque Tpstn, and the uncombusted torque Tcrk_unbrn, 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.

[0046] 1-2-5. External Load Torque Calculation Unit 54 The external load torque calculation unit 54 calculates, for each combustible angle interval, an external load torque Tload, which is a torque applied to the crankshaft from outside the internal combustion engine, based on the crank angular acceleration αd and the torque Tcrk_unbrn during uncombusted combustion, at a crank angle θd_tdc near the top dead center of the piston in the combustion stroke. The external load torque calculation unit 54 smoothes multiple external load torques Tload calculated in past combustible angle intervals, and calculates an external load torque Tload_cal for calculation to be used in the current combustible angle interval.

[0047] The combustible angle interval is set to an angle interval in the combustion cycle where combustion, including abnormal combustion, is likely to occur. As shown in Fig. 6, the combustible angle interval is set to an angle interval within the compression stroke and combustion stroke, for example, an angle interval from 70 degrees before top dead center (BTDC 70 degrees) to 90 degrees after top dead center (ATDC 90 degrees) during the combustion stroke. Furthermore, the vicinity of top dead center during the combustion stroke is, for example, an angle interval from 10 degrees before top dead center (BTDC 10 degrees) to 10 degrees after top dead center (ATDC 10 degrees) during the combustion stroke. For example, the crank angle θd_tdc near the top dead center during the combustion stroke is set to the crank angle at top dead center TDC during the combustion stroke.

[0048] <Calculation of External Load Torque Tload> The external load torque calculation unit 54 calculates the actual torque Tcrkd acting on the crankshaft for each combustible angle interval at a crank angle θd_tdc near top dead center of the combustion stroke based on the crank angular acceleration αd.

[0049] In this embodiment, the uncombusted fuel torque calculation unit 53 calculates the actual torque Tcrkd_tdc near the top dead center by multiplying the crank angular acceleration αd by the moment of inertia Icrk of the crankshaft system at the crank angle θd_tdc near the top dead center, as shown in the following equation.

[0050] The external load torque calculation unit 54 calculates the external load torque Tload for each combustible angle interval based on the actual torque Tcrkd_tdc calculated at the crank angle θd_tdc near the top dead center of the combustion stroke and the torque Tcrk_unbrn_tdc when combustion is not yet complete.

[0051] The external load torque calculation unit 54 calculates the external load torque Tload for each combustible angle section by subtracting the actual torque Tcrkd_tdc near the top dead center of the combustion stroke from the torque Tcrk_unbrn_tdc when uncombusted near the top dead center of the combustion stroke, as shown in the following equation: Here, the external load torque Tload is the positive / negative inverted value of the torque (e.g., negative torque) acting on the crankshaft from the outside.

[0052] When pre-ignition, which will be described later, does not occur, the gas pressure torque of the combustion cylinder becomes almost zero near the top dead center of the combustion stroke. Therefore, the external load torque Tload can be calculated with a small computational load based on the torque Tcrk_unbrn_tdc when uncombusted near the top dead center and the actual torque Tcrkd_tdc when combusted near the top dead center.

[0053] The external load torque calculation unit 54 stores each calculated value, such as the external load torque Tload, in a storage device 91, such as a RAM, in correspondence with the cylinder number corresponding to the combustible angle range and the history number of the combustible angle range for each cylinder number.

[0054] <Calculation of external load torque Tload_cal for calculation> As described above, the external load torque calculation unit 54 smoothes multiple external load torques Tload calculated in past burnable angle intervals and calculates the external load torque Tload_cal for calculation to be used in the current burnable angle interval.

[0055] If abnormal combustion such as pre-ignition occurs in the current combustible angle range, the abnormal combustion affects the crank angular acceleration αd_tdc near top dead center and the actual torque Tcrkd_tdc, and the external load torque Tload for the current combustible angle range, which is calculated based on the actual torque Tcrkd_tdc, includes the influence of the abnormal combustion. Therefore, if the external load torque Tload for the current combustible angle range is used as the external load torque used to detect the occurrence of abnormal combustion in the current combustible angle range, the occurrence of abnormal combustion cannot be accurately detected. According to the above configuration, when abnormal combustion occurs in the current combustible angle range, the external load torque Tload_cal used for calculation to detect the occurrence of abnormal combustion in the current combustible angle range is calculated by smoothing multiple external load torques Tload calculated in past combustible angle ranges before the abnormal combustion occurred. Therefore, the external load torque Tload for the current combustible angle range, which includes the influence of the abnormal combustion, is not used, and the occurrence of abnormal combustion can be accurately determined.

[0056] 7 shows a comparative example and an example of this embodiment in which pre-ignition has not occurred in the current combustible angle section. In the comparative example, the external load torque Tload of the current combustible angle section is set as the external load torque Tload_cal for calculation used in the current combustible angle section, while in the example of this embodiment, the smoothed value of multiple external load torques Tload of past combustible angle sections is set as the external load torque Tload_cal for calculation. In this case, since pre-ignition has not occurred, the external load torque Tload of the current combustible angle section does not include the influence of abnormal combustion, and there is no difference between the actual torque Tcrkd + the increase in gas pressure torque ΔTgas_brn due to combustion and the in-cylinder gas pressure Pcyl between the comparative example and the example of this embodiment.

[0057] 8 shows a comparative example and an example of this embodiment in which pre-ignition occurs near the top dead center of the current burnable angle section. As in FIG. 7 , in the comparative example, the external load torque Tload of the current burnable angle section is set as the external load torque Tload_cal for calculation used in the current burnable angle section, and in the example of this embodiment, the smoothed value of multiple external load torques Tload of past burnable angle sections is set as the external load torque Tload_cal for calculation. In this case, since pre-ignition occurs near the top dead center, the component of the actual torque Tcrkd that suddenly increased due to the occurrence of pre-ignition is included as a component of the external load torque Toad in the external load torque Tload of the current burnable angle section calculated near the top dead center. Therefore, in the comparative example, when calculating the increase in gas pressure torque ΔTgas_brn due to combustion, the component of the actual torque Tcrkd that suddenly increases due to the occurrence of pre-ignition is canceled out by the external load torque Tload in the current combustible angle section, and the characteristics of the torque and in-cylinder gas pressure that suddenly increase due to the occurrence of pre-ignition are not reflected in Tcrkd+ΔTgas_brn and Pcyl. Therefore, the occurrence of abnormal combustion cannot be detected accurately.

[0058] On the other hand, in the example of this embodiment, when calculating the increase in gas pressure torque ΔTgas_brn due to combustion, a smoothed value of the past external load torque Tload before the occurrence of abnormal combustion is used, so that the component of the actual torque Tcrkd that suddenly increases due to the occurrence of pre-ignition is not canceled out, and the characteristics of the torque and in-cylinder gas pressure that suddenly increase due to the occurrence of pre-ignition are reflected in Tcrkd + ΔTgas_brn and Pcyl. Therefore, the occurrence of abnormal combustion can be detected with high accuracy.

[0059] In this embodiment, the internal combustion engine 1 has a plurality of cylinders (three in this example). The external load torque calculation unit 54 smoothes a plurality of external load torques Tload_i calculated in past burnable angle intervals for the same cylinder as the target cylinder i corresponding to the current burnable angle interval, and calculates an external load torque Tload_cal_i for calculation to be used in the current burnable angle interval of the target cylinder i.

[0060] The external load torque Tload is estimated based on the uncombusted torque Tcrk_unbrn_tdc estimated from the in-cylinder gas pressure and the reciprocating motion of the piston, and the actual torque Tcrkd_tdc. However, although there are actual variations between cylinders in the in-cylinder gas pressure and the reciprocating motion of the piston, the uncombusted torque Tcrk_unbrn_tdc is a value calculated under ideal conditions where there are no variations between cylinders, and the actual torque Tcrkd_tdc is a value that reflects the influence of the variations between cylinders near the top dead center of the target cylinder i. Therefore, the external load torque Tload_i calculated from both includes information on the variations between cylinders that affect the combustible angle range of the target cylinder i. According to the above configuration, for the same cylinder as the target cylinder i corresponding to the current burnable angle range, a plurality of past external load torques Tload_i are smoothed to calculate the external load torque Tload_cal_i for calculation to be used in the current burnable angle range of the target cylinder i. As a result, similar to the external load torque Tload_i, the external load torque Tload_cal_i for calculation can include information on variations between cylinders that affect the burnable angle range of the target cylinder i. Then, as will be described later, when calculating the increase in gas pressure torque due to combustion ΔTgas_brn, the external load torque Tload_cal for calculation of the target cylinder i is added, thereby canceling the influence of variations between cylinders and improving calculation accuracy.

[0061] For example, first-order lag filtering is used as the smoothing process. For example, as shown in the following equation, the external load torque calculation unit 54 calculates the external load torque Tload_cal_i(j_i-1) for calculation used in the current combustible angle interval (j_i-1) of the target cylinder i by adding a value obtained by multiplying the external load torque Tload_cal_i(j_i-1) for calculation calculated in the previous combustible angle interval (j_i-1) of the target cylinder i by a filter coefficient Kflt to a value obtained by multiplying the external load torque Tload_i(j_i-1) calculated in the previous combustible angle interval (j_i-1) of the target cylinder i by (1 - filter coefficient Kflt). The filter coefficient Kflt is set to a value smaller than 1.

[0062] The external load torque Tload_cal_i for calculation is stored in a storage device such as a RAM in association with the cylinder number corresponding to the combustible angle interval and the history number j_i of the combustible angle interval of each cylinder number.

[0063] Alternatively, a moving average is used as the smoothing process. For example, as shown in the following equation, the external load torque calculation unit 54 calculates the average value of the external load torques Tload_i(j_i-1), Tload_i(j_i-2), Tload_i(j_i-3), and Tload_i(j_i-4) calculated in the previous, two, three, and four previous combustible angle intervals (j_i-1), (j_i-2), (j_i-3), and (j_i-4) of the target cylinder i as the external load torque Tload_cal_i(j_i) for calculation to be used in the current combustible angle interval (j_i-1) of the target cylinder i. The number of cycles to be averaged may be any number equal to or greater than 1. Alternatively, a weighted moving average may be used.

[0064] <Holding process when occurrence of abnormal combustion due to gas pressure is detected> When the abnormal combustion detection unit 56 described later detects occurrence of abnormal combustion due to gas pressure based on one or both of the increase in cylinder gas pressure ΔPcyl_brn due to combustion and the cylinder gas pressure Pcyl, the external load torque calculation unit 54 executes holding process to calculate the external load torque Tload_cal for calculation to be used in the current burnable angle interval based on the external load torque Tload calculated in the previous burnable angle interval before the abnormal occurrence burnable angle interval, during the burnable angle interval of the holding cycle number including the abnormal occurrence burnable angle interval, which is the burnable angle interval in which the occurrence of abnormal combustion was detected.

[0065] During and for a while after the occurrence of abnormal combustion, fluctuations in the crank angular velocity ωd and the crank angular acceleration αd may continue due to the influence of the abnormal combustion, which may result in a decrease in the estimation accuracy of the external load torque Tload. According to the above configuration, during the burnable angle interval of the number of holding cycles during and after the occurrence of abnormal combustion, the external load torque Tload_cal for calculation can be prevented from being updated using the external load torque Tload with low estimation accuracy calculated during and after the occurrence of abnormal combustion, and is held at the external load torque Tload calculated in a past burnable angle interval prior to the abnormal combustion occurrence burnable angle interval, thereby preventing a decrease in estimation accuracy due to the occurrence of abnormal combustion.

[0066] <Fluctuation After Abnormal Combustion> Figure 9 shows behavior after the occurrence of pre-ignition. Multiple samples are overlaid in Figure 9. The horizontal axis represents the number of combustible angle intervals (number of combustion cycles), and the vertical axes represent the in-cylinder gas pressure PcylΔmax corresponding to the maximum value used to determine pre-ignition, as described below, the external load torque Tload calculated near top dead center in each combustible angle interval (combustion cycle), and the external load torque deviation ΔTload, which represents fluctuations in the external load torque Tload for each cylinder, as described below.

[0067] As shown in Figure 9, the external load torque Tload and the external load torque deviation ΔTload fluctuate for a while after pre-ignition occurs, and it can be seen that calculation accuracy can be maintained by performing a holding process of the external load torque Tload_cal for calculation during the burnable angle interval of the holding cycle number.

[0068] Figure 10 shows the behavior after a misfire occurs. Multiple samples are plotted in Figure 10. The horizontal axis represents the number of combustible angle intervals (number of combustion cycles), and the vertical axis represents the maximum increase in cylinder gas pressure due to combustion ΔPcyl_brnmax, which is used to determine misfire, as described below; the external load torque Tload calculated near top dead center in each combustible angle interval (combustion cycle); and the external load torque deviation ΔTload, which represents the fluctuation of the external load torque Tload for each cylinder.

[0069] 10, the external load torque Tload and the external load torque deviation ΔTload fluctuate for a while after the occurrence of a misfire, and it can be seen that calculation accuracy can be maintained by holding the external load torque Tload_cal for calculation during the combustible angle interval of the number of hold cycles. The number of hold cycles for misfire can be made smaller than the number of hold cycles for pre-ignition.

[0070] <Retention Calculation> For example, when first-order lag filtering is performed on the external load torque Tload_i of a past combustible angle interval of the same target cylinder i, during the combustible angle interval of the retention number of cycles at the time of occurrence of abnormal combustion and after the occurrence, the external load torque calculation unit 54 calculates the calculation external load torque Tload_cal_i(j_i) to be used in the current combustible angle interval (j_i-1) of the target cylinder i by adding a value obtained by multiplying the calculation external load torque Tload_cal_i(j_i-1) calculated in the previous combustible angle interval (j_i-1) of the target cylinder i by the filter coefficient Kflt to a value obtained by multiplying the external load torque Tload_i(j_i_bf) calculated in the combustible angle interval (j_i_bf) of the target cylinder i immediately before the abnormality-occurring combustible angle interval by (1 - filter coefficient Kflt), as shown in the following equation. During the number of holding cycles, the external load torque Tload_i(j_i_bf) calculated in the combustible angle interval (j_i_bf) of the target cylinder i immediately before the abnormality-occurring combustible angle interval continues to be input to the first-order lag filter processing.

[0071] As shown in Figure 12, when pre-ignition occurs, the external load torque Tload fluctuates significantly and continues to fluctuate for a while thereafter. When pre-ignition occurs and after its occurrence, the external load torque Tload_cal for calculation of each cylinder is calculated using the past external load torque Tload calculated for the same cylinder before pre-ignition occurred. Therefore, the external load torque Tload_cal for calculation can be calculated without being affected by fluctuations in the external load torque Tload due to the occurrence of pre-ignition. Furthermore, because the external load torque Tload_cal for calculation of each cylinder is calculated using the past external load torque Tload for the same cylinder before pre-ignition occurred, information on variations between cylinders can be retained.

[0072] Alternatively, during the combustible angle interval at the time of occurrence of abnormal combustion and the number of cycles held after the occurrence, the external load torque calculation unit 54 may set the external load torque Tload_cal_i(j_i) for calculation of the target cylinder i to the external load torque Tload_cal_i(j_i-1) for calculation calculated in the previous combustible angle interval (j_i-1) of the target cylinder i, and may hold it at the external load torque Tload_cal_i(j_i_bf) for calculation of the target cylinder i calculated in the combustible angle interval (j_i_bf) of the target cylinder i immediately before the abnormality occurrence combustible angle interval, as shown in the following equation.

[0073] <Holding Process When Occurrence of Abnormal Combustion is Detected by Another Detection Method> In this embodiment, as described below, the abnormal combustion detection unit 56 is configured to detect occurrence of abnormal combustion by another detection method other than the method of detecting occurrence of abnormal combustion based on one or both of the increase in cylinder gas pressure ΔPcyl_brn due to combustion and the cylinder gas pressure Pcy. When occurrence of abnormal combustion is detected by the other detection method, the external load torque calculation unit 54 executes holding process to calculate the external load torque Tload_cal for calculation to be used in the current burnable angle interval, based on the external load torque Tload calculated in the previous burnable angle interval before the abnormal-occurrence burnable angle interval, during the burnable angle interval of the hold cycle number for the other detection method, which includes the abnormal-occurrence burnable angle interval in which the occurrence of abnormal combustion was detected.

[0074] According to this configuration, even if the occurrence of abnormal combustion is detected by a detection method other than the gas pressure detection method, the external load torque Tload_cal used for calculation is held at the external load torque Tload calculated in a previous combustible angle interval before the combustible angle interval in which the abnormality occurred using the other detection method, just as in the case of the gas pressure detection method, thereby preventing a decrease in estimation accuracy due to abnormal combustion.

[0075] The number of hold cycles for the other detection method may be different from or the same as the number of hold cycles for the gas pressure detection method. Furthermore, for any of the detection methods, the number of hold cycles for each detection method may be changed depending on the type of abnormal combustion. For example, the number of hold cycles is increased for types of abnormal combustion that have greater fluctuations in gas pressure within the cylinder. The method of hold processing itself is similar to the method of detection using gas pressure, and therefore will not be described here.

[0076] <Holding Process When Occurrence of Abnormal Combustion is Detected by Another Detection Method> In this embodiment, as will be described later, the disturbance detection unit 57 detects the occurrence of a disturbance factor that changes the external load torque Tload. When the occurrence of a disturbance factor is detected, the external load torque calculation unit 54 executes holding process to calculate the external load torque Tload_cal for calculating the current burnable angle interval based on the external load torque Tload calculated in the previous burnable angle interval before the disturbance-occurrence burnable angle interval, during the burnable angle intervals for the number of disturbance-occurrence hold cycles that includes the disturbance-occurrence burnable angle interval, which is the burnable angle interval in which the occurrence of the disturbance factor was detected.

[0077] According to this configuration, even when the occurrence of a disturbance factor is detected, the external load torque Tload_cal for calculation is held at the external load torque Tload calculated in a past burnable angle interval prior to the disturbance-occurring burnable angle interval due to the occurrence of the disturbance factor, as in the case of the gas pressure detection method.

[0078] The number of hold cycles for disturbance occurrence may be different from or the same as the number of hold cycles for the gas pressure detection method. Furthermore, the number of hold cycles for disturbance occurrence may be changed depending on the type of disturbance factor. For example, the number of hold cycles is increased as the type of disturbance factor increases the fluctuation of the external load torque Tload. The method of hold processing itself is the same as the gas pressure detection method, and therefore, a description thereof will be omitted.

[0079] <Determining whether the occurrence of abnormal combustion is erroneously detected> After the occurrence of abnormal combustion is detected, the external load torque calculation unit 54 determines whether the occurrence of abnormal combustion is erroneously detected based on the external load torque Tload of the current and past combustible angle intervals calculated based on the crank angular acceleration αd and the torque Tcrk_unbrn during uncombusted combustion.

[0080] The external load torque calculation unit 54 determines that this is an erroneous detection, and if the holding process is being executed, ends the holding process.

[0081] With this configuration, it is possible to determine whether the occurrence of abnormal combustion detected by the abnormal combustion detection unit 56 is an erroneous detection based on the external load torque Tload in each combustible angle interval. If it is determined to be an erroneous detection, the process of holding the external load torque Tload_cal for calculation is terminated before the combustible angle interval for the number of holding cycles ends, and normal calculation of the external load torque Tload_cal for calculation is resumed, thereby improving the calculation accuracy with respect to changes in the external load torque.

[0082] In this embodiment, the external load torque calculation unit 54 calculates the external load torque deviation ΔTload_i (= Tload_i(j_i) - Tload_i(j_i-1)) by subtracting the external load torque Tload_old_i(j_i-1) calculated in the previous combustible angle interval (j_i-1) from the external load torque Tload_i(j_i) calculated in the current combustible angle interval (j_i) for the same cylinder as the target cylinder i corresponding to the current combustible angle interval, and determines that the occurrence of abnormal combustion was an erroneous detection if the state in which the external load torque deviation ΔTload_i is smaller or larger than 0 continues for a number of consecutive combustible angle intervals equal to the total number of cylinders or more.

[0083] According to this configuration, when abnormal combustion occurs in a specific cylinder but not in the other cylinders, the external load torque deviation ΔTload of the specific cylinder will be different in sign from the external load torque deviation ΔTload of the other cylinders. Conversely, when the external load torque deviation ΔTload of all cylinders is the same in sign, it can be determined that the occurrence of abnormal combustion has been erroneously detected due to fluctuations in the actual external load torque, etc.

[0084] <Example of Determining False Detection> Figure 11 shows the behavior of the alternator after power generation is stopped. The example in Figure 11 is an example of a four-cylinder engine. Multiple samples are overlaid in Figure 11. The horizontal axis represents the number of combustible angle intervals (number of combustion cycles), and the vertical axis represents the in-cylinder gas pressure PcylΔmax corresponding to the maximum value used to determine pre-ignition, as described below, the external load torque Tload calculated near the top dead center of each combustible angle interval (combustion cycle), and the external load torque deviation ΔTload representing the fluctuation of the external load torque Tload of each cylinder.

[0085] Since the external load torque Tload_cal for calculation is calculated by smoothing multiple external load torques Tload calculated in past combustible angle intervals, the fluctuations in the actual external load torque are reflected in the increase in gas pressure torque due to combustion ΔTgas_brn and the in-cylinder gas pressure Pcyl for at least the same number of combustible angle intervals as the total number of cylinders (four in this example) after the fluctuations in the actual external load torque, causing the in-cylinder gas pressure PcylΔmax corresponding to the maximum value to increase, resulting in an erroneous detection of the occurrence of pre-ignition. Note that, as will be described later, if the occurrence of a disturbance factor can be detected with a delay or without omission, erroneous detection can be prevented by stopping detection of the occurrence of abnormal combustion after the detection of the occurrence of the disturbance factor.

[0086] On the other hand, a delay or omission in detecting the occurrence of a disturbance factor may result in a false detection of the occurrence of abnormal combustion such as pre-ignition due to fluctuations in the actual external load torque. Even in this case, it can be determined that the detection was false by using the external load torque deviation ΔTload described above. Specifically, unlike after the occurrence of abnormal combustion in Figures 9 and 10, the actual external load torque remains fluctuating, so after the fluctuation, the external load torque deviation ΔTload remains smaller than 0 for the number of combustible angle intervals equal to the total number of cylinders (4 in this example). Therefore, it can be determined that the occurrence of abnormal combustion was falsely detected by the determination method described above.

[0087] The disturbance detection unit 57 detects the occurrence of a disturbance factor that changes the external load torque Tload. The disturbance detection unit 57 detects the occurrence of a disturbance factor based on at least one of a change in vehicle speed, a change in the operating state of the air conditioner, a change in the amount of power generated by the alternator, a shift in the transmission, recovery from a fuel cut in the internal combustion engine, and a change in the number of fuel injections in each combustible angle interval.

[0088] For example, the disturbance detection unit 57 detects the occurrence of a disturbance factor related to a change in vehicle speed when the absolute value of the amount of change in vehicle speed per determination period is equal to or greater than a determination value. For example, when traveling on a rough road, the wheels may lift off the road surface, and a sudden change in running resistance due to the lifting can be detected from the amount of change in vehicle speed. A sudden change in running resistance changes the external load torque Tload, which becomes a disturbance factor.

[0089] The disturbance detection unit 57 detects the occurrence of a disturbance factor related to a change in the operating state of the air conditioner when the absolute value of the change in the load torque of the air conditioner compressor per determination period is equal to or greater than a determination value. For example, the load torque of the air conditioner is estimated based on the compressor rotation speed, which is proportional to the rotation speed of the internal combustion engine, and the refrigerant pressure increased by the compressor. Because the compressor is driven by the rotational driving force of the crankshaft, changes in the compressor load torque cause changes in the external load torque Tload, which becomes a disturbance factor.

[0090] The disturbance detection unit 57 detects the occurrence of a disturbance factor related to a change in the amount of power generated by the alternator when the absolute value of the amount of change in the power generation torque of the alternator per determination period is equal to or greater than a determination value. For example, the power generation torque of the alternator is estimated based on the rotational speed of the alternator, which is proportional to the rotational speed of the internal combustion engine, and the generated current. Because the alternator is driven by the rotational driving force of the crankshaft, a change in the power generation torque of the alternator causes a change in the external load torque Tload, which becomes a disturbance factor.

[0091] The disturbance detection unit 57 detects the occurrence of a disturbance factor related to a gear shift of the transmission when the gear position of the transmission is changed. The transmission is provided between the crankshaft and the wheels. When the gear position is changed, torque fluctuations are transmitted to the crankshaft, which changes the external load torque Tload and becomes a disturbance factor.

[0092] When the internal combustion engine recovers from a fuel cut, the disturbance detection unit 57 detects the occurrence of a disturbance factor related to the recovery of the internal combustion engine from a fuel cut. When the internal combustion engine recovers from a fuel cut and combustion starts, the generated torque changes, which becomes a disturbance factor.

[0093] When the number of fuel injections in each combustible angle section changes, the disturbance detection unit 57 detects the occurrence of a disturbance factor related to the change in the number of fuel injections. For example, when the number of injections changes, such as when fuel is injected once during the intake stroke, when fuel is injected twice during the exhaust stroke and the intake stroke, or when fuel is injected three times during the exhaust stroke, the intake stroke, and the compression stroke, the combustion state changes, and the generated torque changes, which becomes a disturbance factor.

[0094] 1-2-7. Cylinder Gas Pressure Calculation Unit 55 The cylinder gas pressure calculation unit 55 calculates, for each crank angle θd, one or both of the increase in cylinder gas pressure ΔPcyl_brn due to combustion and the cylinder gas pressure Pcyl based on the crank angular acceleration αd, the torque in an uncombusted state Tcrk_unbrn, and the external load torque Tload_cal for calculating the current combustible angle interval corresponding to the crank angle θd.

[0095] In this embodiment, the cylinder gas pressure calculation unit 55 calculates an increase in gas pressure torque due to combustion ΔTgas_brn, which is part of the gas pressure torque applied to the crankshaft by the cylinder gas pressure, at each crank angle θd based on the crank angular acceleration αd. Also, the cylinder gas pressure calculation unit 55 calculates an increase in cylinder gas pressure due to combustion ΔPcyl_brn, at each crank angle θd, based on the increase in gas pressure torque due to combustion ΔTgas_brn and the crank angle θd.

[0096] In this embodiment, the cylinder internal gas pressure calculation unit 55 calculates the actual torque Tcrkd applied to the crankshaft at each crank angle θd based on the crank angular acceleration αd. Specifically, the cylinder internal gas pressure calculation unit 55 calculates the actual 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.

[0097] Furthermore, the cylinder gas pressure calculation unit 55 calculates the gas pressure torque increase ΔTgas_brn due to combustion at each crank angle θd based on the crank angular acceleration αd, the torque Tcrk_unbrn in the uncombusted state, and the external load torque Tload_cal for calculating the current combustible angle interval corresponding to the crank angle θd. Specifically, the cylinder gas pressure calculation unit 55 calculates the gas pressure torque increase ΔTgas_brn due to combustion by subtracting the torque Tcrk_unbrn in the uncombusted state from the actual torque Tcrkd and adding the external load torque Tload_cal for calculation, as shown in the following equation. In this embodiment, the external load torque Tload_cal_i for calculation calculated for the target cylinder i corresponding to the current combustible angle interval corresponding to the crank angle θd is used as the external load torque Tload_cal for calculation.

[0098] The cylinder gas pressure calculation unit 55 calculates the increase in cylinder gas pressure due to combustion ΔPcyl_brn at each crank angle θd based on the increase in gas pressure torque due to combustion ΔTgas_brn. Specifically, the cylinder gas pressure calculation unit 55 calculates the increase in cylinder gas pressure due to combustion ΔPcyl_brn using the following equation: The conversion coefficient R_brn is the conversion coefficient for the combustion cylinder among the conversion coefficients R_i for each cylinder i in equation (4).

[0099] When the crank angle θd at top dead center is 0, the conversion coefficient R_brn of the combustion cylinder becomes 0, resulting in a division by 0. Therefore, the uncombusted torque calculation unit 53 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.

[0100] The cylinder gas pressure calculation unit 55 calculates the cylinder gas pressure Pcyl by adding the uncombusted cylinder gas pressure Pcyl_unbrn and the increase in cylinder gas pressure ΔPcyl_brn due to combustion at each crank angle θd, as shown in the following equation.

[0101] The cylinder gas pressure calculation unit 55 stores each calculated value such as the actual torque Tcrkd calculated at each crank angle θd, the increase in gas pressure torque due to combustion ΔTgas_brn, the increase in cylinder gas pressure due to combustion ΔPcyl_brn, and the cylinder gas pressure Pcyl in a storage device 91 such as a RAM, along with angle information such as the cylinder number corresponding to the combustible angle range, the corresponding angle identification number n, and the crank angle θd.

[0102] 1-2-8. Abnormal Combustion Detector 56 The abnormal combustion detector 56 detects the occurrence of abnormal combustion for the current combustible angle interval based on one or both of the increase in cylinder gas pressure ΔPcyl_brn due to combustion and the cylinder gas pressure Pcyl.

[0103] The abnormal combustion detection unit 56 determines the maximum value ΔPcyl_brnmax of the increase in cylinder gas pressure due to combustion ΔPcyl_brn calculated at each crank angle θd in the current combustible angle range. The abnormal combustion detection unit 56 then determines whether the maximum increase in cylinder gas pressure due to combustion ΔPcyl_brnmax is smaller than a misfire determination value. If the maximum increase in cylinder gas pressure due to combustion ΔPcyl_brnmax is smaller than the misfire determination value, the abnormal combustion detection unit 56 determines that a misfire has occurred in the target cylinder corresponding to the current combustible angle range. The misfire determination value may be set based on the engine speed and load. The crank angle θd corresponding to the maximum increase in cylinder gas pressure due to combustion ΔPcyl_brnmax may also be taken into consideration when determining whether a misfire has occurred.

[0104] Furthermore, the abnormal combustion detection unit 56 calculates the in-cylinder gas pressure Pcyl at the crank angle θd corresponding to the maximum value ΔPcyl_brnmax of the in-cylinder gas pressure increase due to combustion as the in-cylinder gas pressure PcylΔmax corresponding to the maximum value. Then, the abnormal combustion detection unit 56 determines whether the in-cylinder gas pressure PcylΔmax corresponding to the maximum value is greater than a pre-ignition determination value, and if it is greater than the pre-ignition determination value, determines that pre-ignition has occurred in the target cylinder corresponding to the current combustible angle interval. The pre-ignition determination value may be set according to the rotational speed and load. Furthermore, the crank angle θd corresponding to the maximum value ΔPcyl_brnmax of the in-cylinder gas pressure increase due to combustion may also be taken into consideration when determining the occurrence of pre-ignition.

[0105] <Pre-ignition Determination Example> Figure 13 shows a comparative example and an example of this embodiment for determining pre-ignition. In Figure 13, the determination results of samples of multiple combustible angle intervals when pre-ignition has occurred and when it has not occurred are overlaid. The horizontal axis is the crank angle θd corresponding to the maximum value ΔPcyl_brnmax of the increase in cylinder gas pressure due to combustion, and the vertical axis is the cylinder gas pressure PcylΔmax corresponding to the maximum value, which is the cylinder gas pressure Pcyl at that crank angle θd. As in Figure 8, in the comparative example, the external load torque Tload_cal for calculation used in the current combustible angle interval is set to the external load torque Tload of the current combustible angle interval. In the example of this embodiment, the external load torque Tload_cal for calculation is set to a smoothed value of multiple external load torques Tload of past combustible angle intervals.

[0106] In the comparative example, regardless of whether pre-ignition occurs or not, the in-cylinder gas pressure PcylΔmax corresponding to the maximum value of all samples is smaller than the pre-ignition determination value, and the occurrence of pre-ignition is not detected with high accuracy.

[0107] As described above using Figure 8, in the comparative example, the component of the actual torque Tcrkd that suddenly rises due to the occurrence of pre-ignition is included as a component of the external load torque Toad, and when calculating the increase in cylinder gas pressure ΔPcyl_brn due to combustion and the cylinder gas pressure Pcyl, the characteristics of the torque and gas pressure that suddenly rise due to the occurrence of pre-ignition are lost.

[0108] On the other hand, in the example of this embodiment, in samples where pre-ignition has occurred, the cylinder gas pressure PcylΔmax corresponding to the maximum value is greater than the pre-ignition determination value, and in samples where pre-ignition has not occurred, the cylinder gas pressure PcylΔmax corresponding to the maximum value is smaller than the pre-ignition determination value, and the occurrence of pre-ignition is detected with high accuracy.

[0109] As described above, in the example of this embodiment, a smoothed value of the past external load torque Tload before the occurrence of abnormal combustion is used, so that the component of the actual torque Tcrkd that suddenly rises due to the occurrence of pre-ignition is not canceled out, and the increase in the cylinder gas pressure due to combustion ΔPcyl_brn and the cylinder gas pressure Pcyl reflect the characteristics of the torque and cylinder gas pressure that suddenly rise due to the occurrence of pre-ignition.

[0110] <Example of Misfire Determination> Figure 14 shows an example of misfire determination according to this embodiment. In Figure 14, the determination results for samples of multiple combustible angle intervals when a misfire occurs and when a misfire does not occur are overlaid. The horizontal axis represents the crank angle θd corresponding to the maximum increase ΔPcyl_brnmax in cylinder gas pressure due to combustion, and the vertical axis represents the maximum increase ΔPcyl_brnmax in cylinder gas pressure due to combustion at that crank angle θd.

[0111] In the example of this embodiment, in samples where misfire occurs, the maximum increase in cylinder gas pressure due to combustion, ΔPcyl_brnmax, is smaller than the misfire judgment value, and in samples where misfire does not occur, the maximum increase in cylinder gas pressure due to combustion, ΔPcyl_brnmax, is greater than the misfire judgment value, and the occurrence of misfire is detected with high accuracy.

[0112] Alternatively, the abnormal combustion detection unit 56 may use known arithmetic expressions to calculate known combustion parameters such as the heat release rate dQ / dθ, the mass fraction burned MFB, and the indicated mean effective pressure IMEP based on the in-cylinder gas pressure Pcyl at each crank angle θd in the current combustible angle interval, and detect the occurrence of abnormal combustion such as pre-ignition, misfire, or knocking using known methods based on the combustion parameters.

[0113] <Detection of Abnormal Combustion by Another Detection Method> In this embodiment, the abnormal combustion detection unit 56 detects the occurrence of abnormal combustion by another detection method other than the method of detecting the occurrence of abnormal combustion based on one or both of the increase in cylinder gas pressure ΔPcyl_brn due to combustion and the cylinder gas pressure Pcyl. For example, another detection method is a detection method using a knock sensor, an ion current sensor, or an in-cylinder pressure sensor. The abnormal combustion detection unit 56 determines whether knocking or pre-ignition has occurred in the target cylinder corresponding to the current combustible angle range based on the detection signal of the knock sensor using a known method. The abnormal combustion detection unit 56 determines whether misfire, knocking, or pre-ignition has occurred in the target cylinder corresponding to the current combustible angle range based on the detection signal of the ion current sensor using a known method. The abnormal combustion detection unit 56 determines whether misfire, knocking, or pre-ignition has occurred in the target cylinder corresponding to the current combustible angle range based on the detection signal of the cylinder pressure sensor using a known method.

[0114] <Stopping detection of abnormal combustion due to gas pressure> In this embodiment, when the abnormal combustion detection unit 56 detects the occurrence of abnormal combustion due to gas pressure based on one or both of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn and the gas pressure in the cylinder Pcyl, the abnormal combustion detection unit 56 does not detect the occurrence of abnormal combustion due to gas pressure based on one or both of the increase in gas pressure in the cylinder due to combustion ΔPcyl_brn and the gas pressure in the cylinder Pcyl during the combustible angle interval of the number of stop cycles after the abnormal occurrence combustible angle interval, which is the combustible angle interval in which the occurrence of abnormal combustion was detected.

[0115] For a while after abnormal combustion occurs, the crank angular velocity ωd and crank angular acceleration αd fluctuate due to the influence of the abnormal combustion, which may result in a false detection of abnormal combustion even when abnormal combustion is not occurring.With the above configuration, since detection of abnormal combustion based on gas pressure is stopped for the number of stop cycles after abnormal combustion occurs, false detection of abnormal combustion can be prevented.

[0116] In addition, the abnormal combustion detection unit 56 does not detect the occurrence of abnormal combustion due to gas pressure based on one or both of the increase in cylinder gas pressure due to combustion ΔPcyl_brn and the cylinder gas pressure Pcyl during the combustible angle interval of the number of stop cycles for the other detection method after the abnormal occurrence combustible angle interval, which is the combustible angle interval in which the occurrence of abnormal combustion is detected by the other detection method.

[0117] According to this configuration, even if the occurrence of abnormal combustion is detected by a detection method other than the gas pressure detection method, the detection of the occurrence of abnormal combustion by gas pressure is stopped for the number of stop cycles for the other detection method, just as in the case of the gas pressure detection method, thereby preventing the occurrence of abnormal combustion from being mistakenly detected.

[0118] The number of stop cycles for the other detection method may be different from or the same as the number of stop cycles for the gas pressure detection method. Furthermore, for both detection methods, the number of stop cycles for each detection method may be changed depending on the type of abnormal combustion. For example, the number of stop cycles is increased for types of abnormal combustion that have larger fluctuations in gas pressure within the cylinder.

[0119] In addition, when the occurrence of a disturbance factor is detected, the abnormal combustion detection unit 56 does not detect the occurrence of abnormal combustion during a combustible angle interval of the number of stop cycles for disturbance occurrence, which includes the combustible angle interval for disturbance occurrence, which is the combustible angle interval in which the occurrence of the disturbance factor is detected.

[0120] Since the external load torque Tload_cal for calculation is calculated by smoothing multiple external load torques Tload calculated in past combustible angle intervals, for a while after a sudden change in the actual external load torque, the change in the actual external load torque is reflected in the increase in gas pressure torque ΔTgas_brn due to combustion and the in-cylinder gas pressure Pcyl, which may result in an erroneous detection of the occurrence of abnormal combustion.With the above configuration, the occurrence of abnormal combustion is not detected during the combustible angle interval of the disturbance-generating stop cycle number, which includes the disturbance-generating combustible angle interval, so that erroneous detection can be prevented.

[0121] 1-2-9. Avoidance Control Unit 58 When the occurrence of abnormal combustion is detected by the abnormal combustion detection unit 56, the avoidance control unit 58 changes the control parameters of the internal combustion engine and controls the internal combustion engine so as to suppress the occurrence of abnormal combustion. 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.

[0122] <When Pre-ignition Occurs> For example, when pre-ignition is detected, the avoidance control unit 58 enriches (increases) the fuel injection amount relative to the reference injection amount, thereby suppressing pre-ignition through fuel cooling. When pre-ignition is detected, the avoidance control unit 58 reduces the amount of intake gas in the cylinder below the reference intake gas amount, thereby suppressing pre-ignition through a decrease in the temperature of the compressed gas near top dead center. When pre-ignition is detected, the avoidance control unit 58 retards the ignition timing relative to the reference ignition timing, thereby suppressing pre-ignition through a decrease in combustion temperature. When pre-ignition is detected, the avoidance control unit 58 increases the EGR amount relative to the reference EGR amount, thereby suppressing pre-ignition through a decrease in the ignitability of the air-fuel mixture and a decrease in combustion temperature. When pre-ignition is detected, the avoidance control unit 58 changes the control amount of the variable valve timing mechanism relative to the reference control amount to suppress pre-ignition, thereby suppressing pre-ignition.

[0123] <When a misfire occurs> For example, when a misfire is detected, the avoidance control unit 58 enriches (increases) the fuel injection amount relative to the reference injection amount to suppress the occurrence of the misfire. When a misfire is detected, the avoidance control unit 58 increases the amount of intake gas in the cylinder relative to the reference intake gas amount to suppress the occurrence of the misfire. When a misfire is detected, the avoidance control unit 58 advances the ignition timing relative to the reference ignition timing to suppress the occurrence of the misfire. When a misfire is detected, the avoidance control unit 58 reduces the EGR amount relative to the reference EGR amount to suppress the occurrence of the misfire. When a misfire is detected, the avoidance control unit 58 changes the control amount of the variable valve timing mechanism relative to the reference control amount to suppress the occurrence of the misfire, to suppress the occurrence of the misfire.

[0124] 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.

[0125] (2) In the above embodiments, a three-cylinder engine is used as an example. However, an engine with any number of cylinders (for example, one, two, four, or six) may be used.

[0126] Although exemplary embodiments are described in the present disclosure, the various features, aspects, and functions described in the embodiments are not limited to specific embodiments, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are anticipated within the scope of the technology disclosed in the present disclosure specification. For example, variations in, addition to, or omission of at least one component are included.

[0127] 1: internal combustion engine, 2: crankshaft, 50: control device for internal combustion engine, 51: angle information detection unit, 52: intake pipe gas pressure detection unit, 53: uncombusted torque calculation unit, 54: external load torque calculation unit, 55: cylinder gas pressure calculation unit, 56: abnormal combustion detection unit, 57: disturbance detection unit, Pcyl_unbrn: cylinder gas pressure when uncombusted, Pin: gas pressure in intake pipe, Tload: external load torque, Tload_cal: external load torque for calculation, ΔPcyl_brn: increase in cylinder gas pressure due to combustion, ΔTgas_brn: increase in gas pressure torque due to combustion, ΔTload: external load torque deviation, αd: crank angular acceleration, θd: crank angle, ωd: crank angular velocity

Claims

1. An angle information detection unit that detects the crank angle, crank angular velocity, and crank angular acceleration based on the output signal of the crank angle sensor, An intake manifold gas pressure detection unit detects the gas pressure in the intake manifold based on the output signal of a gas pressure sensor that detects the gas pressure in the intake manifold, An unburned torque calculation unit estimates the torque applied to the crankshaft due to the gas pressure in the cylinder and the reciprocating motion of the piston, based on the gas pressure in the intake manifold, the crank angular velocity, and the crank angular acceleration at each crank angle, using a physical model equation of the crank mechanism. For the current combustible angle section, an external load torque calculation unit calculates the external load torque, which is the torque applied to the crankshaft from outside the internal combustion engine, based on the crank angle near the top dead center of the piston during the combustion stroke, and the torque during the unburned period. The unit then smooths the multiple external load torques calculated in previous combustible angle sections to calculate the external load torque to be used in the current combustible angle section. A cylinder gas pressure calculation unit calculates, for each crank angle, the increase in cylinder gas pressure due to combustion and / or the cylinder gas pressure based on the crank angular acceleration, the torque during unburned combustion, and the external load torque for calculation in the current combustible angle section corresponding to the crank angle, For the current combustible angle range, an abnormal combustion detection unit detects the occurrence of abnormal combustion based on the increase in in-cylinder gas pressure due to the combustion and / or the in-cylinder gas pressure, A control device for the internal combustion engine.

2. An internal combustion engine has multiple cylinders, The control device for an internal combustion engine according to claim 1, wherein the external load torque calculation unit smooths out a plurality of external load torques calculated in past combustible angle intervals for the same cylinder as the target cylinder corresponding to the current combustible angle interval, and calculates the external load torque for calculation to be used in the current combustible angle interval of the target cylinder.

3. The control device for an internal combustion engine according to claim 1, wherein when the occurrence of abnormal combustion is detected, the external load torque calculation unit performs a holding process to calculate the external load torque to be used in the current combustible angle section based on the external load torque calculated in a past combustible angle section prior to the abnormal combustible angle section, within the combustible angle section of the number of holding cycles that includes the abnormal combustion occurring combustible angle section, which is the combustible angle section in which the occurrence of abnormal combustion was detected.

4. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein the abnormal combustion detection unit, when it detects the occurrence of abnormal combustion, does not detect the occurrence of abnormal combustion during the combustible angle section of the number of stop cycles after the combustible angle section where the occurrence of abnormal combustion was detected.

5. The abnormal combustion detection unit detects the occurrence of abnormal combustion by a detection method other than the method for detecting the occurrence of abnormal combustion based on the increase in in-cylinder gas pressure due to the combustion and or both of the in-cylinder gas pressure, The control device for an internal combustion engine according to claim 1, wherein the external load torque calculation unit, when the occurrence of abnormal combustion is detected by the other detection method, performs a holding process to calculate the external load torque to be used in the current combustible angle section based on the external load torque calculated in a past combustible angle section prior to the abnormal combustion occurring combustible angle section, within a combustible angle section of a holding cycle number for the other detection method, which includes the abnormal combustion occurring combustible angle section, which is the combustible angle section in which the occurrence of abnormal combustion was detected.

6. The abnormal combustion detection unit detects the occurrence of abnormal combustion by a detection method other than the method for detecting the occurrence of abnormal combustion based on the increase in in-cylinder gas pressure due to the combustion and or both of the in-cylinder gas pressure, A control device for an internal combustion engine according to any one of claims 1 to 3, wherein, during a combustible angle interval for a number of stop cycles for the other detection method, after the combustible angle interval for abnormal combustion which is the combustible angle interval for which the occurrence of abnormal combustion was detected by the other detection method, detection of the occurrence of abnormal combustion based on the increase in in-cylinder gas pressure due to the combustion and the in-cylinder gas pressure, or both.

7. The system includes a disturbance detection unit that detects the occurrence of disturbance factors that change the external load torque, The control device for an internal combustion engine according to claim 1, wherein when the occurrence of the disturbance factor is detected, the external load torque calculation unit performs a holding process to calculate the external load torque to be used in the current combustible angle section based on the external load torque calculated in a past combustible angle section prior to the disturbance-generating combustible angle section, within the combustible angle section of the number of holding cycles for disturbance generation, which is the combustible angle section in which the occurrence of the disturbance factor was detected.

8. The system includes a disturbance detection unit that detects the occurrence of disturbance factors that change the external load torque, The control device for an internal combustion engine according to claim 1, wherein the abnormal combustion detection unit, when the occurrence of the disturbance factor is detected, does not detect the occurrence of abnormal combustion during the disturbance-generating burnable angle section for the number of stop cycles for disturbance generation, which is the burnable angle section for disturbance generation in which the occurrence of the disturbance factor was detected.

9. Internal combustion engines are used as the power source for vehicles. The control device for an internal combustion engine according to claim 7 or 8, wherein the disturbance detection unit detects the occurrence of the disturbance factor based on at least one of the following: a change in vehicle speed, a change in the operating state of the air conditioner, a change in the amount of power generated by the alternator, a gear change of the transmission, recovery from fuel cut-off of the internal combustion engine, and a change in the number of fuel injections in each combustible angle section.

10. After detecting the occurrence of abnormal combustion, the external load torque calculation unit determines whether the detection of abnormal combustion is false based on the external load torque for the current and past combustible angle intervals calculated based on the crank angular acceleration and the torque during non-combustion. The control device for an internal combustion engine according to any one of claims 3, 5, and 7, wherein if it is determined to be a false detection and the holding process is being executed, the holding process is terminated.

11. An internal combustion engine has multiple cylinders, The control device for an internal combustion engine according to claim 10, wherein the external load torque calculation unit calculates a torque deviation by subtracting the external load torque calculated in the previous combustible angle section from the external load torque calculated in the current combustible angle section for the same cylinder as the target cylinder corresponding to the current combustible angle section, and determines that the occurrence of abnormal combustion was a false detection if the state in which the torque deviation is less than or greater than 0 continues for a number of combustible angle sections equal to the total number of cylinders.