Control device for internal combustion engine

Abstract

Provided is a control device for an internal combustion engine capable of improving accuracy in estimation of a gas pressure in a cylinder using a polytropic change by correcting deviation of the increase start angle of an actual gas pressure in the cylinder with respect to a mechanical valve closing angle of an intake valve. A control device (50) for an internal combustion engine involves: using an arithmetic expression for calculating, for an angle section from a valve closing angle (θivc_cal) for calculation of an intake valve to a valve opening angle (θivc_cal) for calculation of an exhaust valve, a gas pressure by using a polytropic change on the basis of a gas pressure (Pin) in an intake pipe, a crank angle (θd), and the valve closing angle (θivc_cal) for calculation of the intake valve; estimating a gas pressure (Pcyl_unbrn) in a cylinder during non-combustion; correcting a reference value (θivc0) of a valve closing angle of the intake valve on the basis of the operation state of the internal combustion engine; and calculating the valve closing angle (θivc_cal) for calculation of the intake valve.

Description

Control device for internal combustion engine

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

[0002] Patent Document 1 discloses a technique for estimating the gas pressure in a cylinder during uncombusted combustion based on a polytropic change.

[0003] Patent No. 7031028

[0004] As disclosed in the technology of Patent Document 1, it is generally known that after the intake valve closing angle, the gas pressure in the cylinder increases due to a polytropic change. However, after detailed investigation, the inventor discovered a phenomenon in which the angle at which the actual gas pressure in the cylinder starts to increase deviates from the mechanical closing angle of the intake valve, and even if the gas pressure in the cylinder is estimated from the mechanical closing angle of the intake valve due to a polytropic change, it deviates from the actual gas pressure in the cylinder.

[0005] Therefore, the present disclosure aims to provide a control device for an internal combustion engine that can correct the deviation of the angle at which the actual gas pressure in the cylinder starts to increase relative to the mechanical closing angle of the intake valve, thereby improving the accuracy of estimating the gas pressure in the cylinder due to polytropic changes.

[0006] The control device for an internal combustion engine according to the present disclosure comprises: an intake pipe gas pressure detection unit that detects the 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 angle information detection unit that detects a crank angle based on a detection signal of a crank angle sensor that detects the crank angle; and a gas pressure estimation unit that estimates the gas pressure in the cylinder when uncombusted using an equation that calculates gas pressure through a polytropic change based on the gas pressure in the intake pipe, the crank angle, and the intake valve closing angle for calculation in an angle interval from the intake valve closing angle for calculation of the cylinder's intake valve to the exhaust valve opening angle for calculation, and the gas pressure estimation unit calculates the intake valve closing angle for calculation by correcting a reference value of the intake valve closing angle based on the operating state of the internal combustion engine.

[0007] According to the control device for an internal combustion engine of the present disclosure, the deviation between the reference value of the intake valve closing angle and the angle at which the actual increase in gas pressure in the cylinder due to polytropic change begins is corrected based on the operating state of the internal combustion engine, and the intake valve closing angle for calculation is calculated, and the gas pressure in the cylinder when uncombusted is estimated using an equation for polytropic change based on the intake valve closing angle for calculation, thereby improving estimation accuracy.

[0008] 1 is a schematic configuration diagram of an internal combustion engine and a control device for the internal combustion engine according to a first embodiment. FIG. 1 is a schematic configuration diagram of an internal combustion engine and a control device for the internal combustion engine according to a first embodiment. FIG. 2 is a block diagram of the control device for the internal combustion engine according to the first embodiment. FIG. 3 is a hardware configuration diagram of the control device for the internal combustion engine according to the first embodiment. FIG. 4 is a time chart for explaining angle information detection processing according to the first embodiment. FIG. 5 is a diagram for explaining a deviation between an actual increase start angle in a cylinder and a mechanical closing angle of an intake valve according to the first embodiment. FIG. 6 is a diagram for explaining a cause of a deviation in the closing angle of an intake valve according to the first embodiment. FIG. 7 is a diagram for explaining a correction value of the closing angle according to the rotation speed according to the first embodiment. FIG. 8 is a diagram for explaining setting of a polytropic index according to the rotation speed according to the first embodiment. FIG. 9 is a diagram for explaining setting of a polytropic index for a low rotation speed according to the first embodiment. FIG. 10 is a diagram for explaining setting of a polytropic index for a low rotation speed according to the first embodiment. 1 is a diagram for explaining setting of a polytropic index in the case of a high rotation speed according to embodiment 1. FIG. 2 is a diagram for explaining setting of a polytropic index in the case of a high rotation speed according to embodiment 1. FIG. 3 is a diagram for explaining estimation of gas pressure in the case of changing the polytropic index depending on elapsed time according to embodiment 1.

[0009] 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).

[0010] 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.

[0011] An air flow sensor 3 is provided in the intake pipe 23 upstream of the throttle valve 4, and outputs an electric 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 electric signal corresponding to the air-fuel ratio of the exhaust gas in the exhaust pipe 17.

[0012] 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 also provided with a water temperature sensor 34 that detects the coolant temperature Twt of the coolant that cools the cylinders.

[0013] The top of each cylinder 7 is provided with a spark plug that ignites the air-fuel mixture, and an ignition coil 16 that supplies ignition energy to the spark plug. Also provided at the top of each cylinder 7 are an intake valve 14 that adjusts the amount of intake air drawn 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 changes the valve opening / closing angle. The exhaust valve 15 is provided with an exhaust variable valve timing mechanism that changes the valve opening / closing angle. The variable valve timing mechanisms 14, 15 each have an electric actuator.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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 (TDC) 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.

[0018] 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.

[0019] 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, a gas pressure estimation unit 53, an abnormal combustion determination unit 54, and a basic control unit 55. The control units 51 to 55 of the control device 50 are realized by processing circuits included in the control device 50. Specifically, as shown in FIG. 4 , the control device 50 includes, as processing circuits, an arithmetic processing device 90 (computer) such as a CPU (Central Processing Unit), a storage device 91 connected to the arithmetic processing device 90 via a signal line such as a bus, an input circuit 92 that inputs 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.

[0020] 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.

[0021] 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.

[0022] The functions of the control units 51 to 55 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 55 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 55, including the crank angular velocity ωd, crank angular acceleration αd, gas pressure in the cylinder during combustion Pcyl_brn, gas pressure in the cylinder during uncombustion Pcyl_unbrn, and gas pressure increase ΔPcyl_brn due to combustion, are stored in a rewritable storage device 91 such as a RAM.

[0023] 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.

[0024] 1-2-1. Basic Control Unit 55 As a basic control, the basic control unit 55 calculates the fuel injection amount, ignition timing, etc. based on input output signals from various sensors, and controls the injector 13, the ignition coil 16, etc. The basic control unit 55 calculates the output torque of the internal combustion engine 1 required by the driver based on the output signal 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 55 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 55 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 55 calculates the target opening / closing angles of the intake valve and 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 the target opening / closing angles.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] <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.

[0030] 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.

[0031] 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.

[0032] 1-2-4. Gas Pressure Estimation Unit 53 <Estimation of Gas Pressure Based on Polytropic Change> The gas pressure estimation unit 53 estimates the gas pressure Pcyl_unbrn in the cylinder during uncombusted combustion using an equation for calculating gas pressure based on a polytropic change, based on the gas pressure Pin in the intake pipe, the crank angle θd, and the intake valve closing angle θivc_cal for calculation, in the angle interval from the intake valve closing angle θivc_cal for calculation of the intake valve to the exhaust valve opening angle θevo_cal for calculation of the exhaust valve.

[0033] Here, when the internal combustion engine is actually performing combustion, the gas pressure Pcyl_unbrn in the cylinder when combustion is not occurring is an estimated value of the gas pressure assuming that the internal combustion engine is in an uncombusted state where combustion is not occurring, and when the internal combustion engine is not actually performing combustion, the gas pressure Pcyl_unbrn in the cylinder when combustion is not occurring is an estimated value of the gas pressure in the current uncombusted state.

[0034] For each cylinder i, the gas pressure estimation unit 53 determines that the intake valve is open if the crank angle θd_i of each cylinder i is within the angle interval from the intake valve opening angle θivo_cal_i for calculating the intake valve to the intake valve closing angle θivc_cal_i for calculating the intake valve, and otherwise determines that the intake valve is closed. Also, for each cylinder i, the gas pressure estimation unit 53 determines that the exhaust valve is open if the crank angle θd is within the angle interval from the exhaust valve opening angle θevo_cal_i for calculating the exhaust valve to the exhaust valve closing angle θevc_cal_i for calculating the exhaust valve, and otherwise determines that the exhaust valve is closed. For each cylinder i, the angle interval from the intake valve closing angle θivc_cal_i for calculating the intake valve to the exhaust valve opening angle θevo_cal_i for calculating the exhaust valve is the angle interval in which the intake valve and exhaust valve are closed. The crank angle θd_i of each cylinder i and the valve closing angle and valve opening angle for each calculation are set to the crank angle θd and the crank angle obtained by shifting the valve closing angle and valve opening angle so that the top dead center TDC of the compression stroke of each cylinder i is 0 degrees. In this embodiment, the valve closing angle and valve opening angle for calculation of the intake valve and exhaust valve of each cylinder i, which are set so that the top dead center TDC of the compression stroke of each cylinder i is 0 degrees, are the same for all cylinders.

[0035] In the present embodiment, the gas pressure estimation unit 53 calculates the gas pressure Pcyl_unbrn_i in each cylinder i when uncombusted. As shown in the following equation, for each cylinder i, when the crank angle θd_i is within the angle interval from the intake valve closing angle θivc_cal_i for calculating the intake valve to the exhaust valve opening angle θevo_cal_i for calculating the exhaust valve, and the gas pressure estimation unit 53 determines that the intake valve and the exhaust valve are closed, the gas pressure estimation unit 53 calculates the gas pressure Pcyl_unbrn_i in the cylinder when uncombusted, using an equation for calculating gas pressure using a polytropic change, based on the gas pressure Pin in the intake pipe, the intake valve closing angle θivc_cal_i for calculating the intake valve, and the crank angle θd_i of each cylinder i. That is, for each cylinder i, when the crank angle θd_i is within the angle interval from the intake valve closing angle θivc_cal_i for calculating the intake valve to the exhaust valve opening angle θevo_cal_i, the gas pressure estimation unit 53 calculates the gas pressure Pcyl_unbrn_i in the cylinder when uncombusted at each crank angle θd_i by multiplying the value of the polytropic index Nply_i raised to the power of the value obtained by dividing the cylinder volume Vcyl0_i when the intake valve is closed, which is the cylinder volume at the intake valve closing angle θivc_cal_i for calculating the intake valve, by the cylinder volume Vcyl_i at each crank angle θd_i, by the gas pressure Pin in the intake pipe.

[0036] Here, Nply_i is a polytropic index for each cylinder i, and details will be described later. The gas pressure estimation 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 (TDC), Sp is the projected area of ​​the top surface of the piston, r is the crank length, L is the connecting rod length, and φ_i is the angle of the connecting rod of each cylinder i. Note that an equation other than the fourth and fifth equations of equation (3) may be used as the volume calculation function fvcyl, or map data or other mathematical formulas may be used. Furthermore, the gas pressure estimation unit 53 uses the volume calculation function fvcyl to calculate the cylinder volume Vcyl_i of each cylinder i corresponding to the intake valve closing angle θivc_cal_i for calculation of the intake valve of each cylinder i as the cylinder volume Vcyl0_i when the intake valve of each cylinder i is closed. For the gas pressure Pin in the intake pipe, a value obtained after averaging, such as an average value over the stroke period, or a detected value at the intake valve closing angle θivc_cal_i for calculation may be used.

[0037] Furthermore, as shown in the following equation, for each cylinder i, the gas pressure estimation unit 53 calculates the gas pressure Pcyl_unbrn_i in the cylinder when uncombusted based on the gas pressure Pin in the intake pipe when the intake valve is open and the exhaust valve is closed, and calculates the gas pressure Pcyl_unbrn_i in the cylinder when uncombusted based on the gas pressure Pex in the exhaust pipe when the exhaust valve is open. The gas pressure Pex in the exhaust pipe may be a detected value of atmospheric pressure or a predetermined value.

[0038] The gas pressure estimation unit 53 stores each calculated value, such as the gas pressure Pcyl_unbrn_i in each cylinder i when uncombusted, calculated at each crank angle θd, along with angle information such as the corresponding angle identification number n and crank angle θd, in a storage device 91 such as a RAM.

[0039] <Calculation of Intake Valve Closing Angle θivc_cal> As shown in Figure 6 , after the intake valve is closed, the cylinder gas pressure Pcyl increases due to a polytropic change. However, the angle θinc_act at which the actual cylinder gas pressure Pcyl_act begins to increase is more advanced than the mechanical intake valve closing angle θivc_mch. Therefore, if the cylinder volume at the mechanical intake valve closing angle θivc_mch is set as the cylinder volume Vcyl0 when the intake valve is closed and the cylinder gas pressure Pcyl_mch is estimated using a polytropic change, as shown in Figure 6 , the cylinder gas pressure Pcyl_mch estimated based on the mechanical intake valve closing angle θivc_mch deviates from the actual cylinder gas pressure Pcyl_act. This deviation is particularly large at the peak value of the gas pressure at compression top dead center (TDC). As a result of the investigation, it was found that the deviation amount between the increase start angle θinc_act of the actual gas pressure Pcyl_act in the cylinder and the mechanical closing angle θivc_mch of the intake valve changes depending on the operating state of the internal combustion engine.

[0040] Considering this in more detail, as shown in Figure 7, the angle θinc_act at which the actual increase in gas pressure in the cylinder begins has mechanical and dynamic deviations relative to the mechanical closing angle θivc_mch of the intake valve. First, let's explain the mechanical deviation. The mechanical design closing angle θivc_mch of the intake valve is set during design, taking into account the performance of the internal combustion engine, and the rising portion of the cam lobe is designed to be smooth. Therefore, there is a deviation between the mechanical design closing angle θivc_mch and the angle at which the intake valve opening is actually closed by the umbrella portion of the intake valve. Furthermore, there is a valve clearance between the cam lobe and the valve, which causes a deviation between the mechanical design closing angle θivc_mch and the angle at which the valve actually stops being depressed. These deviations are constant deviations that do not change depending on the operating state of the internal combustion engine and are mechanical deviations.

[0041] Next, dynamic deviation will be explained. Just before the intake valve reaches its mechanical closing angle, the effective opening area between the intake valve and the valve seat falls below a predetermined value. At this angle, the increase in gas pressure in the cylinder due to compression exceeds the decrease in gas pressure in the cylinder caused by backflow of gas from the cylinder into the intake pipe, and the gas pressure in the cylinder begins to increase. The effective opening area at which the gas pressure starts to increase is proportional to the rate at which the gas pressure in the cylinder increases, and becomes larger as the rotational speed Ne increases and as the gas pressure Pin in the intake pipe increases. This dynamic deviation is due to the gas flow just before the intake valve reaches its mechanical closing angle and varies depending on the operating conditions of the internal combustion engine, such as the rotational speed Ne and the gas pressure Pin in the intake pipe.

[0042] Therefore, the gas pressure estimation unit 53 corrects the reference value θivc0 of the intake valve closing angle based on the operating state of the internal combustion engine, and calculates the intake valve closing angle θivc_cal for calculation.

[0043] According to this configuration, the deviation between the reference value θivc0 of the intake valve closing angle and the angle θinc_act at which the actual gas pressure in the cylinder Pcyl_act begins to increase due to polytropic change is corrected based on the operating state of the internal combustion engine, and the intake valve closing angle θivc_cal for calculation is calculated, and the gas pressure in the cylinder when uncombusted Pcyl_unbrn is estimated using an equation for polytropic change based on the intake valve closing angle θivc_cal for calculation, thereby improving estimation accuracy.

[0044] The intake valve closing angle θivc_cal for calculation is set so that the top dead center TDC of the compression stroke is 0 degrees, and the intake valve closing angle θivc_cal for calculation is set as is as the intake valve closing angle θivc_cal_i for calculation of the intake valve of each cylinder i.

[0045] In this embodiment, the reference value θivc0 of the intake valve closing angle is the mechanical closing angle of the intake valve. In this embodiment, an intake variable valve timing mechanism is provided to change the opening and closing angle of the intake valve. The gas pressure estimation unit 53 changes the reference value θivc0 of the intake valve closing angle (in this example, the mechanical closing angle) in accordance with changes in the mechanical closing angle of the intake valve caused by the intake variable valve timing mechanism. That is, the gas pressure estimation unit 53 sets the mechanical closing angle θivc_mch of the intake valve changed by the intake variable valve timing mechanism as the reference value θivc0 of the valve closing angle. The gas pressure estimation unit 53 calculates the mechanical closing angle θivc_mch of the intake valve based on the control state of the phase angle of the intake variable valve timing mechanism. If an intake variable valve timing mechanism is not provided, the reference value θivc0 of the intake valve closing angle is set to a predetermined value.

[0046] <Valve Opening Angle and Closing Angle for Other Calculations> In the present embodiment, the gas pressure estimation unit 53 sets the exhaust valve opening angle θevo_cal for calculation to a reference value θevo0 that corresponds to the mechanical valve opening angle θevo_mch of the exhaust valve. For example, the reference value θevo0 may be set to the mechanical valve opening angle θevo_mch itself, or may be set to a value that is fine-tuned from the mechanical valve opening angle θevo_mch based on experimental data. If an exhaust variable valve timing mechanism that changes the opening and closing angle of the exhaust valve is provided, the gas pressure estimation unit 53 changes the reference value θevo0 of the exhaust valve opening angle (in this example, the mechanical valve opening angle) in accordance with changes in the mechanical valve opening angle of the exhaust valve caused by the exhaust variable valve timing mechanism.

[0047] Similarly, the gas pressure estimation unit 53 sets the intake valve opening angle θivo_cal for calculation to a reference value θivo0 corresponding to the mechanical intake valve opening angle θivo_mch. Similarly, if an intake variable valve timing mechanism is provided, the gas pressure estimation unit 53 changes the reference value θivo0 of the intake valve opening angle (in this example, the mechanical valve opening angle) in accordance with changes in the mechanical intake valve opening angle. The gas pressure estimation unit 53 sets the exhaust valve closing angle θevc_cal for calculation to a reference value θevc0 corresponding to the mechanical exhaust valve closing angle θevc_mch. Similarly, if an exhaust variable valve timing mechanism is provided, the gas pressure estimation unit 53 changes the reference value θevc0 of the exhaust valve closing angle (in this example, the mechanical valve closing angle) in accordance with changes in the mechanical exhaust valve closing angle.

[0048] <Correction of θivc_cal According to Rotational Speed ​​Ne> In this embodiment, the gas pressure estimation unit 53 corrects the reference value θivc0 of the intake valve closing angle based on the rotational speed Ne of the internal combustion engine to calculate the intake valve closing angle θivc_cal for calculation. Here, the rotational speed Ne [rpm] is proportional to the crank angular velocity ωd [rad / s].

[0049] As described above, the deviation Δθ between the actual increase start angle θinc_act of the gas pressure in the cylinder and the mechanical closing angle θivc_mch of the intake valve changes depending on the rotation speed Ne of the internal combustion engine. According to the above configuration, the deviation Δθ can be accurately corrected based on the rotation speed Ne of the internal combustion engine, thereby improving the estimation accuracy of the gas pressure Pcyl_unbrn in the cylinder.

[0050] For example, as shown in the following equation, the gas pressure estimator 53 calculates a rotation-variable correction term a1 × Ne based on the engine speed Ne, adds the rotation-variable correction term a1 × Ne to a fixed correction term b1 to calculate a valve closing angle correction value Δθivc, and adds or subtracts (in this example, subtracts) the valve closing angle correction value Δθivc to a reference value θivc0 of the valve closing angle to calculate a valve closing angle θivc_cal for use in calculating the intake valve. The fixed correction term b1 corresponds to the mechanical deviation, and the rotation-variable correction term a1 × Ne corresponds to the dynamic deviation. As shown in FIG. 8 , the gas pressure estimator 53 increases the correction value Δθivc toward the advance side as the engine speed Ne increases, thereby correcting the reference value θivc0 of the intake valve closing angle to a more advanced side, and thereby calculating a valve closing angle θivc_cal for use in calculating the intake valve.

[0051] In this example, the rotation-variable correction term a1 × Ne is calculated by multiplying the rotation speed Ne by a coefficient a1. The coefficient a1 is set in advance based on experimental data, etc. The fixed-value correction term b1 is also set in advance based on experimental data, etc. Note that while equation (5) is a linear equation of the rotation speed Ne, it may be any mathematical expression, such as a polynomial of second or higher order having a zeroth-order term corresponding to the fixed-value correction term, or may be map data. The fixed-value correction term b1 may also be included in the reference value θivc0 of the valve closing angle (mechanical valve closing angle).

[0052] In addition, since the difference between the actual angle θinc_act at which the gas pressure in the cylinder begins to increase and the mechanical closing angle θivc_mch of the intake valve is caused by a combination of factors, it is preferable that the correction value Δθivc of the closing angle be set based on experimental data.

[0053] <Correction of θivc_cal according to the rotation speed Ne and the gas pressure Pin in the intake pipe> Alternatively, the gas pressure estimation unit 53 may correct the reference value θivc0 of the intake valve closing angle based on the rotation speed Ne of the internal combustion engine and the gas pressure Pin in the intake pipe, and calculate the intake valve closing angle θivc_cal for calculation.

[0054] As described above, the dynamic difference between the angle θinc_act at which the actual gas pressure in the cylinder starts to increase and the mechanical intake valve closing angle θivc_mch varies not only with the rotation speed Ne but also with the gas pressure Pin in the intake pipe. In an internal combustion engine that is significantly affected by the gas pressure Pin in the intake pipe, the accuracy of setting the intake valve closing angle θivc_cal used for calculating the intake valve can be improved by making a correction taking into account the gas pressure Pin in the intake pipe.

[0055] For example, as shown in the following equation, the gas pressure estimation unit 53 calculates a rotation-variable correction term a1×Ne based on the rotation speed Ne, calculates a gas-pressure-variable correction term c1×Pin based on the gas pressure Pin in the intake pipe, adds the rotation-variable correction term a1×Ne, the gas-pressure-variable correction term c1×Pin, and a fixed-value correction term b1 to calculate a valve-closing angle correction value Δθivc, and adds or subtracts (in this example, subtracts) the valve-closing angle correction value Δθivc to or from a reference value θivc0 of the valve-closing angle to calculate a valve-closing angle θivc_cal for use in calculating the intake valve. The fixed-value correction term b1 corresponds to the mechanical deviation, and the rotation-variable correction term a1×Ne and the gas-pressure-variable correction term c1×Pin correspond to the dynamic deviation. As the rotation speed Ne increases, the gas pressure estimation unit 53 increases the correction value Δθivc toward the advance side to correct the reference value θivc0 of the intake valve closing angle to a more advance side, and as the gas pressure Pin in the intake pipe increases, the gas pressure estimation unit 53 increases the correction value Δθivc toward the advance side to correct the reference value θivc0 of the intake valve closing angle to a more advance side, and calculates the intake valve closing angle θivc_cal for calculation.

[0056] In this example, the gas pressure variable correction term c1×Pin is calculated by multiplying the gas pressure P in the intake pipe by a coefficient c1. The coefficient c1 is set in advance based on experimental data or the like, and is a positive value in this example. As with equation (5), the correction term may be any mathematical expression, such as a polynomial of degree two or higher that has a zeroth-order term corresponding to a fixed value, or may be map data.

[0057] <Correction of θivc_cal according to the gas pressure Pin in the intake pipe> Alternatively, the gas pressure estimation unit 53 may correct the reference value θivc0 of the intake valve closing angle based on the gas pressure Pin in the intake pipe, and calculate the intake valve closing angle θivc_cal for calculation.

[0058] In an internal combustion engine in which the rotation speed Ne has little effect and the gas pressure Pin in the intake pipe has a large effect, the accuracy of setting the intake valve closing angle θivc_cal used to calculate the intake valve can be improved by making a correction based on the gas pressure Pin in the intake pipe. As described above, the dynamic deviation between the angle θinc_act at which the actual gas pressure in the cylinder starts to increase and the mechanical intake valve closing angle θivc_mch changes depending on the gas pressure Pin in the intake pipe. By making a correction taking into account the gas pressure Pin in the intake pipe, the accuracy of setting the intake valve closing angle θivc_cal used to calculate the intake valve can be improved.

[0059] For example, as shown in the following equation, the gas pressure estimation unit 53 calculates a gas pressure-variable correction term c1×Pin based on the gas pressure Pin in the intake pipe, adds the gas pressure-variable correction term c1×Pin to a fixed-value correction term b1 to calculate a valve closing angle correction value Δθivc, and adds or subtracts (subtracts in this example) the valve closing angle correction value Δθivc to a reference value θivc0 of the valve closing angle to calculate a valve closing angle θivc_cal for use in calculating the intake valve. The fixed-value correction term b1 corresponds to the above-mentioned mechanical deviation, and the gas pressure-variable correction term c1×Pin corresponds to the above-mentioned dynamic deviation. As the gas pressure Pin in the intake pipe increases, the gas pressure estimation unit 53 increases the correction value Δθivc toward the advance side, corrects the reference value θivc0 of the intake valve closing angle to a more advance side, and calculates the intake valve closing angle θivc_cal for calculation.

[0060] <Change in Polytropic Exponent Nply Based on Operating Condition> The polytropic process used to estimate the gas pressure in the cylinder generally involves an adiabatic change, an isothermal change, or a polytropic change, and therefore the polytropic exponent Nply is treated as a constant value. Since there is no heat transfer in an adiabatic change or an isothermal change, there is basically no problem in treating the polytropic exponent Nply as a constant value. However, in the polytropic change of an internal combustion engine, it is taken into account that there is some heat transfer of the working gas, and the polytropic exponent Nply is a value obtained by approximating between an adiabatic change and an isothermal change.

[0061] In an actual engine, an error occurs due to the loss. In the case of an internal combustion engine, the loss is mainly due to heat transfer. In particular, heat is transferred between the cylinder wall and the differential gas inside the cylinder, and the amount of heat transferred Q is proportional to the area and temperature difference. The following equation expresses the instantaneous amount of heat transferred Q. Here, A is the cross-sectional area through which heat passes, λ is the thermal conductivity, Th is the temperature on the high-temperature side, Tc is the temperature on the low-temperature side, and L is the distance the heat passes. The total amount of heat transferred is Q x transfer time ΔT, where transfer time ΔT is the period of the polytropic change. The longer the compression stroke and combustion stroke corresponding to the period of the polytropic change, i.e., the lower the rotational speed Ne, the greater the total amount of heat transferred between the gas inside the cylinder.

[0062] Therefore, as the rotational speed Ne increases, the total amount of heat exchanged between the gases in the cylinder decreases, approaching adiabatic change and approaching polytropic index Nply = 1.4. On the other hand, as the rotational speed Ne decreases, the total amount of heat exchanged between the gases in the cylinder increases, approaching isothermal change and approaching polytropic index Nply = 1.0. Therefore, it is clear that it is better to change the polytropic index Nply according to the rotational speed Ne. Furthermore, because the temperature of the cylinder wall changes according to the coolant temperature Twt that cools the cylinder, it is clear that it is better to change the polytropic index Nply according to the coolant temperature Twt.

[0063] In this embodiment, the gas pressure estimation unit 53 changes the polytropic exponent Nply used in the calculation formula based on the rotation speed Ne of the internal combustion engine.

[0064] As described above, the total amount of heat exchanged between the cylinder wall and the gas in the cylinder changes in accordance with the rotational speed Ne, and the polytropic index Nply also changes. With this configuration, by changing the polytropic index Nply used in the calculation formula based on the rotational speed Ne of the internal combustion engine, it is possible to appropriately change the polytropic index Nply in accordance with the total amount of heat exchanged between the cylinder wall and the gas in the cylinder, which changes in accordance with the rotational speed Ne.

[0065] As shown in FIG. 9, the gas pressure estimation unit 53 increases the polytropic exponent Nply used in the calculation formula as the rotation speed Ne of the internal combustion engine increases.

[0066] With this configuration, as the rotational speed Ne increases, the total amount of heat exchanged between the cylinder wall and the gas in the cylinder decreases, resulting in a change closer to adiabatic than isothermal. Therefore, by increasing the polytropic index Nply to change the gas pressure in the cylinder closer to adiabatic than isothermal, the accuracy of estimating the polytropic change in the gas pressure Pcyl_unbrn can be improved. The upper limit of the polytropic index Nply is 1.4, which corresponds to adiabatic change. For example, map data or an approximate expression is used as the setting data for the relationship between the rotational speed Ne and the polytropic index Nply.

[0067] The setting of the polytropic index Nply for low engine speeds will be described using Figures 10 to 12. Figures 10 and 11 show the calculated values ​​of in-cylinder gas pressure using the polytropic change formula when Nply is set to 1.4 (adiabatic change), 1.3 (reference value), 1.0 (isothermal change), and 1.24 (set value). In Figure 10, the horizontal axis represents the logarithm of the cylinder volume, and the vertical axis represents the logarithm of the in-cylinder gas pressure. In Figure 11, the horizontal axis represents the cylinder volume, and the vertical axis represents the in-cylinder gas pressure. At low engine speeds, the total amount of heat exchanged between the cylinder wall and the gas in the cylinder increases, so the change approaches isothermal change (Nply = 1.0) rather than adiabatic change (Nply = 1.4). It can be seen that the in-cylinder gas pressure Pcyl_unbrn calculated using Nply = 1.24 is closer to the actual in-cylinder gas pressure Pcyl_act. The polytropic index Nply is set to increase the accuracy of estimating the gas pressure near top dead center (TDC). In Figure 12, the horizontal axis represents the crank angle θd, and the vertical axis represents the in-cylinder gas pressure Pcyl. Although an estimation error occurs before top dead center (TDC), after top dead center (TDC), which is important for estimating the combustion state, the in-cylinder gas pressure Pcyl_unbrn calculated using Nply = 1.24 is close to the actual in-cylinder gas pressure Pcyl_act, thereby achieving good estimation accuracy.

[0068] The setting of the polytropic index Nply for high engine speeds will be described using Figures 13 to 15. Figures 13 and 14 show the calculated values ​​of in-cylinder gas pressure using the polytropic change formula when Nply is set to 1.4 (adiabatic change), 1.3 (reference value), 1.0 (isothermal change), and 1.37 (set value). In Figure 13, the horizontal axis represents the logarithm of the cylinder volume, and the vertical axis represents the logarithm of the in-cylinder gas pressure. In Figure 14, the horizontal axis represents the cylinder volume, and the vertical axis represents the in-cylinder gas pressure. At high engine speeds, the total amount of heat exchanged between the cylinder wall and the gas in the cylinder decreases, so the change approaches adiabatic change (Nply = 1.4) rather than isothermal change (Nply = 1.0). It can be seen that the in-cylinder gas pressure Pcyl_unbrn calculated using Nply = 1.37 is closer to the actual in-cylinder gas pressure Pcyl_act. 15, the horizontal axis represents the crank angle θd, and the vertical axis represents the in-cylinder gas pressure Pcyl. Because the amount of heat exchanged is small at high rotational speeds, the estimation accuracy is high even before top dead center (TDC). It can be seen that the in-cylinder gas pressure Pcyl_unbrn calculated using Nply = 1.37 is close to the actual in-cylinder gas pressure Pcyl_act.

[0069] In this calculation method, the set polytropic index Nply is directly set as the polytropic index Nply_i of each cylinder i.

[0070] Alternatively, the gas pressure estimation unit 53 may change the polytropic exponent Nply used in the calculation formula based on the rotation speed Ne of the internal combustion engine and the coolant temperature Twt of the internal combustion engine.

[0071] As described above, the polytropic index Nply varies not only with the rotation speed Ne but also with the coolant temperature Twt of the internal combustion engine. In the case of an internal combustion engine that is significantly affected by the coolant temperature Twt, the setting accuracy of the polytropic index Nply can be improved by changing the polytropic index Nply in consideration of the coolant temperature Twt of the internal combustion engine.

[0072] The gas pressure estimation unit 53 increases the polytropic index Nply used in the calculation formula as the rotation speed Ne of the internal combustion engine increases, and also increases the polytropic index Nply used in the calculation formula as the coolant temperature Twt of the internal combustion engine increases.

[0073] As the coolant temperature Twt of the internal combustion engine increases, the temperature of the cylinder wall increases, and the temperature difference between the cylinder wall and the gas inside the cylinder heated by compression decreases. This reduces the total amount of heat exchanged between the gas inside the cylinder, resulting in a change closer to adiabatic change and a polytropic index Nply of 1.4. Therefore, by increasing the polytropic index Nply used in the calculation formula as the coolant temperature Twt of the internal combustion engine increases, the accuracy of setting the polytropic index Nply can be improved. For example, map data or an approximate formula is used as setting data that presets the relationship between the rotational speed Ne, the coolant temperature Twt, and the polytropic index Nply.

[0074] Alternatively, the gas pressure estimation unit 53 may change the polytropic exponent Nply used in the calculation formula based on the coolant temperature Twt of the internal combustion engine.

[0075] The gas pressure estimation unit 53 increases the polytropic exponent Nply used in the calculation formula as the coolant temperature Twt of the internal combustion engine increases.

[0076] In the case of an internal combustion engine in which the rotation speed Ne has little effect and the coolant temperature Twt of the internal combustion engine has a large effect, the setting accuracy of the polytropic index Nply can be improved by changing the polytropic index Nply based on the coolant temperature Twt of the internal combustion engine. For example, map data or an approximation formula is used as setting data that pre-sets the relationship between the coolant temperature Twt and the polytropic index Nply.

[0077] <Change in Polytropic Exponent Nply Based on Elapsed Time> As explained using Equation (8), the total amount of heat transferred during a polytropic change increases in proportion to the time elapsed from the start of the polytropic change. Therefore, as the elapsed time increases, the total amount of heat transferred increases, the change approaches isothermal change from adiabatic change, and the polytropic exponent Nply decreases from 1.4 for adiabatic change.

[0078] Therefore, the gas pressure estimation unit 53 may calculate the polytropic index Nply for calculation to be used in the calculation formula by decreasing the polytropic index from its initial value Nply0 by a decrease amount ΔNdc per unit time between the intake valve closing angle θivc_cal for calculation and the exhaust valve opening angle θevo_cal for calculation.

[0079] The gas pressure estimation unit 53 also calculates the polytropic exponent Nply for calculation by reducing the value obtained by reducing the initial value Nply0 of the polytropic exponent by the reduction amount ΔNdc per unit time, and then limiting the value by the exponent lower limit value Nmin.

[0080] For example, as shown in the following equation, the gas pressure estimation unit 53 gradually decreases the polytropic index Nply from the initial value Nply0 by a value obtained by multiplying the decrease amount ΔNdc per unit time by the time interval ΔTd between the corresponding crank angles each time the crank angle θd, which calculates the gas pressure in the cylinder, changes from the intake valve closing angle θivc_cal to the exhaust valve opening angle θevo_cal. Also, the gas pressure estimation unit 53 limits the polytropic index Nply to a lower limit Nmin.

[0081] When the crank angle θd is the intake valve closing angle θivc_cal for calculating the intake valve, j is set to 1, and the polytropic index Nply(1) is set to an initial value Nply0. In this embodiment, the initial value Nply0 is set to the adiabatic change value of 1.4. Each time the crank angle θd for calculating the gas pressure increases, j is increased by 1, and Nply(j) is calculated using the second and third equations of equation (9). The calculated Nply(j) is then used to calculate the gas pressure at the corresponding crank angle θd. Here, (j) represents the calculated value at the current crank angle, and (j-1) represents the calculated value at the previous crank angle. max(A, B) is a function that outputs the larger of A and B. Therefore, the larger of Nply(j) calculated by the second equation of equation (9) at the current crank angle and Nmin is set as the final Nply(j) at the current crank angle. In this calculation method, the polytropic index Nply_i of each cylinder i is calculated individually based on the elapsed time from the intake valve closing angle θivc_cal for calculation of the intake valve of each cylinder i.

[0082] This configuration can represent the phenomenon in which the total amount of heat transferred increases in proportion to the elapsed time from the start of the polytropic change, transitioning from adiabatic change to isothermal change, and the polytropic index Nply decreases from 1.4, which is the value of adiabatic change. This can improve the accuracy of estimating the in-cylinder gas pressure Pcyl_unbrn, especially at the beginning of the period. Furthermore, because the polytropic index Nply is limited to its lower limit by the index lower limit value Nmin, the accuracy of setting the polytropic index Nply after the decrease at the beginning of the period can be ensured.

[0083] In this embodiment, the gas pressure estimation unit 53 changes the index lower limit value Nmin based on the rotation speed Ne of the internal combustion engine.

[0084] According to this configuration, the polytropic exponent Nply after the initial decrease can be set based on the engine speed Ne. For example, as described with reference to FIGS. 10 and 12 , the exponent lower limit Nmin may be set so as to improve the estimation accuracy of the gas pressure near top dead center (TDC). For example, at the low engine speeds shown in FIGS. 10 and 12 , the exponent lower limit Nmin may be set to 1.24, and at the high engine speeds shown in FIGS. 13 and 15 , the exponent lower limit Nmin may be set to 1.37. That is, similar to FIG. 9 , the gas pressure estimation unit 53 increases the exponent lower limit Nmin as the engine speed Ne increases. For example, map data or an approximate expression may be used as the setting data for the relationship between the engine speed Ne and the exponent lower limit Nmin.

[0085] Alternatively, the gas pressure estimation unit 53 may change the index lower limit value Nmin based on the rotation speed Ne of the internal combustion engine and the coolant temperature Twt of the internal combustion engine.

[0086] As described above, the polytropic index Nply varies not only with the rotation speed Ne but also with the coolant temperature Twt of the internal combustion engine. In the case of an internal combustion engine that is significantly affected by the coolant temperature Twt, the accuracy of setting the polytropic index Nply can be improved by changing the index lower limit Nmin in consideration of the coolant temperature Twt of the internal combustion engine. As with the polytropic index Nply, the gas pressure estimation unit 53 increases the index lower limit Nmin as the rotation speed Ne of the internal combustion engine increases, and also increases the index lower limit Nmin as the coolant temperature Twt of the internal combustion engine increases. For example, map data or an approximate expression is used as the setting data that pre-sets the relationship between the rotation speed Ne, the coolant temperature Twt, and the index lower limit Nmin.

[0087] Alternatively, the gas pressure estimation unit 53 may change the index lower limit value Nmin based on the coolant temperature Twt of the internal combustion engine. The gas pressure estimation unit 53 increases the index lower limit value Nmin as the coolant temperature Twt of the internal combustion engine increases.

[0088] In the case of an internal combustion engine in which the rotation speed Ne has little effect and the coolant temperature Twt of the internal combustion engine has a large effect, the accuracy of setting the polytropic index Nply can be improved by changing the index lower limit value Nmin based on the coolant temperature Twt of the internal combustion engine. For example, map data or an approximation formula is used as the setting data in which the relationship between the coolant temperature Twt and the index lower limit value Nmin is preset.

[0089] The gas pressure estimation unit 53 may also change the decrease amount ΔNdc per unit time based on the coolant temperature Twt of the internal combustion engine.

[0090] As the coolant temperature Twt of the internal combustion engine increases, the temperature of the cylinder wall increases, and the temperature difference between the cylinder wall and the gas inside the cylinder that rises due to compression decreases. This reduces the amount of heat exchanged per unit time, and the amount of decrease in the polytropic index per unit time decreases. Therefore, by reducing the amount of decrease ΔNdc per unit time as the coolant temperature Twt of the internal combustion engine increases, the accuracy of setting the polytropic index Nply can be improved. For example, map data or an approximate expression is used as setting data that presets the relationship between the coolant temperature Twt and the amount of decrease ΔNdc.

[0091] FIG. 16 shows the case where the polytropic exponent Nply is changed according to elapsed time. In FIG. 12 , where no change is made according to elapsed time, an error occurs in the estimation of the gas pressure in the early period before top dead center TDC. However, in FIG. 16 , the estimation accuracy of the gas pressure before top dead center TDC is improved. Furthermore, by setting the lower limit value Nmin of the exponent according to the rotation speed Ne, etc., the estimation accuracy of the gas pressure after top dead center TDC is obtained, similar to that in FIG. 12 . Therefore, the estimation accuracy of the gas pressure is improved throughout the entire period of polytropic change.

[0092] 1-2-5. Abnormal Combustion Determination Unit 54 The abnormal combustion determination unit 54 calculates the increase in gas pressure in the cylinder due to combustion, ΔPcyl_brn, based on the crank angle θd, the crank angular velocity ωd, and the crank angular acceleration αd. The abnormal combustion determination unit 54 adds the gas pressure in the cylinder during uncombusted state Pcyl_unbrn to the increase in gas pressure in the cylinder due to combustion, to calculate the gas pressure in the cylinder during combustion, Pcyl_brn. The abnormal combustion determination unit 54 calculates combustion parameters that represent the combustion state based on the gas pressure in the cylinder during combustion Pcyl_brn, and determines whether abnormal combustion has occurred based on the combustion parameters.

[0093] <Calculation of Increase ΔPcyl_brn in Gas Pressure in Cylinder Due to Combustion> The abnormal combustion determination unit 54 calculates the increase ΔPcyl_brn in gas pressure in the cylinder due to combustion based on the crank angle θd, the crank angular velocity ωd, and the crank angular acceleration αd.

[0094] In this embodiment, the abnormal combustion determination unit 54 calculates the gas pressure torque Tgas_unbrn in the uncombusted state, which is the axial torque applied to the crankshaft by the gas pressure in the cylinder in the uncombusted state when it is assumed that the combustion is not occurring, at each crank angle θd, based on the gas pressure Pcyl_unbrn in the cylinder in the uncombusted state and the crank angle θd.

[0095] In this embodiment, the abnormal combustion determination unit 54 uses the following equation to convert gas pressure into torque, and calculates the gas pressure torque Tgas_unbrn in the uncombusted state based on the gas pressure Pcyl_unbrn_i in each cylinder i in the uncombusted state and the crank angle θd_i of each cylinder i.

[0096] 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 (10) 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.

[0097] Using the following equation, the abnormal combustion determination unit 54 calculates the reciprocating inertia torque Tpstn, which is the axial torque applied to the crankshaft due to the reciprocating motion of the piston, at each crank angle θd based on the crank angle θd and the crank angular velocity ωd.

[0098] 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 (11) 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 (10).

[0099] As shown in the following equation, the abnormal combustion determination unit 54 calculates the uncombusted shaft torque Tcrk_unbrn by adding the uncombusted gas pressure torque Tgas_unbrn and the reciprocating inertia torque Tpstn at each crank angle θd.

[0100] Alternatively, the abnormal combustion judgment unit 54 may refer to uncombusted map data in which the relationship between the crank angle θd, crank angular velocity ωd, and the state of the intake gas amount in the cylinder and the uncombusted axial torque Tcrk_unbrn is set, and calculate the uncombusted axial torque Tcrk_unbrn corresponding to each crank angle θd, crank angular velocity ωd, and state of the intake gas amount in the cylinder.

[0101] For example, the uncombusted state map data is set for each operating condition (in this example, the state of the crank angular velocity ωd and the amount of intake gas in the cylinder) that affects the gas pressure torque and the reciprocating inertia torque during uncombusted state. The abnormal combustion determination unit 54 refers to the uncombusted state map data corresponding to the current operating condition and calculates the uncombusted state axial torque Tcrk_unbrn corresponding to each crank angle θd. The uncombusted state map data may be set in advance based on experimental data or may be set in advance based on the theoretical formulas (3), (4), and (10) to (12). Furthermore, the uncombusted state map data may be updated based on the actual axial torque Tcrkd that is actually calculated during uncombusted state.

[0102] As shown in the following equation, the abnormal combustion determination unit 54 calculates the actual torque Tcrkd acting on the crankshaft at each crank angle θd based on the crank angular acceleration αd: where Icrk is the moment of inertia of the crankshaft system.

[0103] The abnormal combustion determination unit 54 calculates an external load torque Tload, which is a torque applied to the crankshaft from outside the internal combustion engine, based on the actual torque Tcrkd_tdc calculated at a crank angle θd_tdc near top dead center TDC and the uncombusted torque Tcrk_unbrn_tdc. Here, the vicinity of top dead center TDC is, for example, within an angle interval from 10 degrees before top dead center (BTDC) to 10 degrees after top dead center (ATDC). For example, the crank angle θd_tdc near top dead center TDC is preset to the crank angle at top dead center TDC.

[0104] The abnormal combustion determination unit 54 calculates the external load torque Tload during combustion by subtracting the actual axial torque Tcrkd_tdc near top dead center TDC from the axial torque Tcrk_unbrn_tdc during uncombusted combustion near top dead center TDC, as shown in the following equation.

[0105] Using the following equation, the abnormal combustion determination unit 54 calculates the increase in gas pressure torque ΔTgas_brn due to combustion at each crank angle θd based on the actual torque Tcrkd, the torque Tcrk_unbrn in the uncombusted state, and the external load torque Tload.

[0106] The abnormal combustion determination unit 54 calculates the increase in 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 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 (10).

[0107] <Calculation of Cylinder Gas Pressure Pcyl_brn During Combustion> The abnormal combustion determination unit 54 calculates the cylinder gas pressure Pcyl_brn_i during combustion for each cylinder i by adding the cylinder gas pressure Pcyl_unbrn_i during uncombusted combustion for each cylinder i to the cylinder gas pressure increase ΔPcyl_brn due to combustion, as shown in the following equation, for each crank angle θd. Note that ΔPcyl_brn is zero for cylinders that are not in the combustion stroke.

[0108] The abnormal combustion determination unit 54 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 gas pressure in the cylinder due to combustion ΔPcyl_brn, and the gas pressure in the cylinder at the time of combustion of each cylinder i Pcyl_brn_i, together with angle information such as the corresponding angle identification number n and crank angle θd, in a storage device 91 such as a RAM.

[0109] <Determination of abnormal combustion> The abnormal combustion determination unit 54 calculates combustion parameters that represent the combustion state of each cylinder i based on the gas pressure Pcyl_brn_i inside the cylinder i during combustion, and determines whether abnormal combustion has occurred in each cylinder i based on the combustion parameters of each cylinder i.

[0110] The abnormal combustion determination unit 54 calculates known combustion parameters, such as the heat release rate, mass fraction burned (MFB), and indicated mean effective pressure (IMEP), for each cylinder i using known equations based on the gas pressure (Pcyl_brn_i) in each cylinder i during combustion. The abnormal combustion determination unit 54 then determines the occurrence of abnormal combustion, such as pre-ignition, knocking, misfire, or incomplete combustion, using known methods based on the combustion parameters. The abnormal combustion determination unit 54 may also determine the occurrence of abnormal combustion using the increase in gas pressure (ΔPcyl_brn) in the cylinder due to combustion as the combustion parameter.

[0111] When it is determined that abnormal combustion has occurred, the basic control unit 55 changes various control variables, such as the intake air amount, ignition timing, air-fuel ratio, and EGR amount, to suppress the occurrence of abnormal combustion. Various known methods are used to change the control variables.

[0112] 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.

[0113] (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.

[0114] (3) In the above-described embodiments, the internal combustion engine 1 has been described as a gasoline engine. However, the embodiments of the present disclosure are not limited to this. That is, the internal combustion engine 1 may be various types of internal combustion engines, such as a diesel engine or an engine that performs HCCI (Homogeneous-Charge Compression Ignition Combustion). Furthermore, even in the case of a gasoline engine, the internal combustion engine 1 may be configured in various ways, such as by being provided with a supercharger.

[0115] 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.

[0116] 1: internal combustion engine, 8: gas pressure sensor, 11: crank angle sensor, 14: intake valve, 15: exhaust valve, 50: control device for internal combustion engine, 51: angle information detection unit, 52: intake pipe gas pressure detection unit, 53: gas pressure estimation unit, 54: abnormal combustion determination unit, Ne: rotation speed of internal combustion engine, Nmin: index lower limit value, Nply: polytropic index, Nply0: initial value of polytropic index, Pcyl_brn: gas pressure in cylinder during combustion, Pcyl_unbrn: when uncombusted where Twt is the gas pressure in the cylinder, Twt is the cooling water temperature, ΔNdc is the amount of decrease per unit time, ΔPcyl_brn is the increase in gas pressure in the cylinder due to combustion, Δθivc is the correction value for the valve closing angle, θd is the crank angle, θevo_cal is the exhaust valve opening angle for calculation, θivc0 is the reference value for the intake valve closing angle, θivc_cal is the intake valve closing angle for calculation, θivc_mch is the mechanical intake valve closing angle, ωd is the crank angular velocity, αd is the crank angular acceleration

Claims

1. A control device for an internal combustion engine comprising: an intake pipe gas pressure detection unit that detects the gas pressure in the intake pipe based on the output signal of a gas pressure sensor that detects the gas pressure in the intake pipe; an angle information detection unit that detects the crank angle based on the detection signal of a crank angle sensor that detects the crank angle; and a gas pressure estimation unit that estimates the gas pressure in the cylinder when uncombusted using an equation that calculates gas pressure using a polytropic change based on the gas pressure in the intake pipe, the crank angle, and the intake valve closing angle for calculation in an angle interval from the intake valve closing angle for calculation of the cylinder's intake valve to the exhaust valve opening angle for calculation, wherein the gas pressure estimation unit corrects a reference value of the intake valve closing angle based on the operating state of the internal combustion engine and calculates the intake valve closing angle for calculation.

2. A control device for an internal combustion engine according to claim 1, wherein the gas pressure estimation unit calculates the valve closing angle for calculation by correcting the reference value of the valve closing angle based on the rotation speed of the internal combustion engine.

3. A control device for an internal combustion engine as described in claim 2, wherein the gas pressure estimation unit calculates a rotation-variable correction term based on the rotational speed, calculates a correction value for the valve closing angle by adding the rotation-variable correction term and a fixed value correction term, and calculates the valve closing angle for calculation by adding or subtracting the correction value for the valve closing angle to the reference value of the valve closing angle.

4. A control device for an internal combustion engine according to claim 1, wherein the gas pressure estimation unit calculates the valve closing angle for calculation by correcting the reference value of the valve closing angle based on the gas pressure in the intake pipe.

5. A control device for an internal combustion engine as described in claim 4, wherein the gas pressure estimation unit calculates a gas pressure variable correction term based on the gas pressure in the intake pipe, calculates a correction value for the valve closing angle by adding the gas pressure variable correction term and a fixed value correction term, and calculates the valve closing angle for calculation by adding or subtracting the correction value for the valve closing angle to the reference value of the valve closing angle.

6. A control device for an internal combustion engine as described in claim 1, wherein the gas pressure estimation unit calculates the valve closing angle for calculation by correcting the reference value of the valve closing angle based on the rotation speed of the internal combustion engine and the gas pressure in the intake pipe.

7. A control device for an internal combustion engine as described in claim 6, wherein the gas pressure estimation unit calculates a rotation-variable correction term based on the rotation speed, calculates a gas-pressure-variable correction term based on the gas pressure in the intake pipe, calculates a correction value for the valve closing angle by adding the rotation-variable correction term, the gas-pressure-variable correction term, and a fixed-value correction term, and calculates the valve closing angle for calculation by adding or subtracting the correction value for the valve closing angle from the reference value of the valve closing angle.

8. A control device for an internal combustion engine according to any one of claims 1 to 7, wherein the reference value of the valve closing angle is a mechanical valve closing angle of the intake valve.

9. A control device for an internal combustion engine as described in any one of claims 1 to 8, wherein the intake valve is equipped with an intake variable valve timing mechanism that changes the opening and closing angle of the intake valve, and the gas pressure estimation unit changes the reference value of the valve closing angle in accordance with the change in the intake valve closing angle of the intake valve caused by the intake variable valve timing mechanism.

10. A control device for an internal combustion engine according to any one of claims 1 to 9, wherein the gas pressure estimation unit varies the polytropic exponent used in the arithmetic expression based on the rotation speed of the internal combustion engine.

11. A control device for an internal combustion engine according to any one of claims 1 to 9, wherein the gas pressure estimation unit changes the polytropic index used in the arithmetic expression based on the temperature of the cooling water of the internal combustion engine.

12. A control device for an internal combustion engine according to any one of claims 1 to 9, wherein the gas pressure estimation unit varies the polytropic index used in the calculation formula based on the rotation speed of the internal combustion engine and the coolant temperature of the internal combustion engine.

13. A control device for an internal combustion engine as described in any one of claims 1 to 9, wherein the gas pressure estimation unit calculates a polytropic index for calculation to be used in the calculation formula by decreasing the polytropic index from its initial value by a decrement per unit time between the valve closing angle for calculation and the valve opening angle for calculation.

14. The control device for an internal combustion engine according to claim 13, wherein the gas pressure estimation section changes the amount of decrease per unit time based on the temperature of cooling water of the internal combustion engine.

15. A control device for an internal combustion engine according to claim 13 or 14, wherein the gas pressure estimation unit sets the initial value of the polytropic exponent to 1.

4.

16. A control device for an internal combustion engine as described in any one of claims 13 to 15, wherein the gas pressure estimation unit calculates the polytropic index for calculation by limiting the value obtained by decreasing the initial value of the polytropic index by the decrease amount per unit time with an index lower limit value, and varies the index lower limit value based on the rotational speed of the internal combustion engine.

17. A control device for an internal combustion engine as described in any one of claims 13 to 15, wherein the gas pressure estimation unit calculates the polytropic index for calculation by limiting the value obtained by decreasing the initial value of the polytropic index by the decrease amount per unit time with an index lower limit value, and varies the index lower limit value based on the cooling water temperature of the internal combustion engine.

18. A control device for an internal combustion engine as described in any one of claims 13 to 15, wherein the gas pressure estimation unit calculates the polytropic index for calculation by limiting the value obtained by decreasing the initial value of the polytropic index by the decrease amount per unit time with an index lower limit value, and varies the index lower limit value based on the rotational speed of the internal combustion engine and the cooling water temperature of the internal combustion engine.

19. A control device for an internal combustion engine as claimed in any one of claims 1 to 18, further comprising an abnormal combustion determination unit that calculates an increase in gas pressure in the cylinder due to combustion based on the crank angle, crank angular velocity, and crank angular acceleration, calculates the gas pressure in the cylinder at the time of combustion by adding the gas pressure in the cylinder at the time of uncombustion to the increase in gas pressure in the cylinder due to combustion, calculates combustion parameters representing the combustion state based on the gas pressure in the cylinder at the time of combustion, and determines whether or not abnormal combustion has occurred based on the combustion parameters.

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