In-cylinder pressure detection method, in-cylinder pressure sensor diagnosis method, and internal combustion engine control device

Abstract

The present invention can detect the in-cylinder pressure (p) with good accuracy regardless of the influence of the elongation of the discharge path. In the in-cylinder pressure detection method of the present invention, high-frequency components are removed from the discharge waveform of the secondary coil, and information on the secondary current (I2) and the secondary voltage (V2) is obtained from the discharge waveform from which the high-frequency components have been removed. Then, the in-cylinder pressure (p) is calculated according to the KIM relational expression.

Description

Technical Field

[0001] The present invention relates to an in-cylinder pressure detection method, an in-cylinder pressure sensor diagnosis method, and an internal combustion engine control device. Background Art

[0002] In recent years, in order to improve the fuel consumption of vehicles, a control device for an internal combustion engine has been developed, which incorporates technologies such as making the internal combustion engine operate by burning a mixture gas leaner than the stoichiometric air-fuel ratio, and taking in a part of the exhaust gas after combustion and re-inhaling it.

[0003] When such a control device for an internal combustion engine is adopted, since the amounts of fuel and air in the combustion chamber deviate from the theoretical values, it is easy for the ignition of the fuel by the spark plug to be delayed. The period and frequency of this ignition delay vary depending on component deviations and changes in operating conditions. In an internal combustion engine composed of multiple cylinders, in order to suppress ignition delay in all cylinders, it is necessary to increase the fuel amount for cylinders with a high ignition delay frequency, or reduce the exhaust gas recirculation amount.

[0004] However, increasing the fuel amount or reducing the exhaust gas recirculation amount will suppress the improvement of fuel consumption. Therefore, there is a requirement for combustion control for each cylinder that matches the component characteristics of each cylinder. When controlling the fuel injection device and ignition coil for each cylinder, it is necessary to detect ignition delay based on the in-cylinder pressure of each cylinder. Therefore, it is necessary to detect the in-cylinder pressure of each cylinder with high precision.

[0005] Patent Document 1 discloses a relational expression between ignition discharge and in-cylinder pressure (p). According to this relational expression, the in-cylinder pressure (p) can be calculated based on the discharge voltage (V), discharge current (I), and discharge path length (l).

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-135786 Summary of the Invention

[0009] Technical Problem to be Solved by the Invention

[0010] However, in the relational expression disclosed in Patent Document 1, it is necessary to measure the discharge path length (l). The discharge path is affected by the flow of gas between the spark plug electrodes and elongates. Also, when measuring the discharge path length, it is necessary to visualize the inside of the combustion chamber, which is practically difficult. Moreover, due to the gas flow in the cylinder, the deviation based on the combustion cycle is large, so it is difficult to estimate the gas flow between the spark plug electrodes. Therefore, there is a problem that the in-cylinder pressure (p) of each cylinder cannot be detected with good accuracy regarding the relational expression disclosed in Patent Document 1.

[0011] An object of the present invention is to detect the in-cylinder pressure (p) with good accuracy without being affected by the elongation of the discharge path in view of the above problems.

[0012] Technical solution for solving the technical problem

[0013] In order to solve the above technical problem and achieve the object of the present invention, the in-cylinder pressure detection method of the present invention detects the in-cylinder pressure by using information of a secondary coil of an internal combustion engine, the internal combustion engine having a primary coil, a secondary coil that generates an electromotive force when the energization of the primary coil is cut off, and a spark plug connected to the secondary coil. This in-cylinder pressure detection method removes high-frequency components from the discharge waveform of the secondary coil, obtains information on the secondary current and secondary voltage from the discharge waveform from which the high-frequency components have been removed, and calculates the in-cylinder pressure according to the following formula (1).

[0014] [Mathematical formula 1]

[0015]

[0016] wherein, V2 is the secondary voltage, I2 is the secondary current, p is the in-cylinder pressure, p0 is the atmospheric pressure, and l is the length of the discharge path.

[0017] Advantages of the invention

[0018] According to the in-cylinder pressure detection method having the above structure, the in-cylinder pressure (p) can be detected with good accuracy without being affected by the elongation of the discharge path.

[0019] In addition, other technical problems, structures, and effects than the above can be clarified by the description of the following embodiments. Description of the drawings

[0020] Figure 1 is an overall structure diagram showing a basic structure example of an internal combustion engine according to an embodiment of the present invention.

[0021] Figure 2 is a partially enlarged view of a spark plug according to an embodiment of the present invention for explanation.

[0022] Figure 3 is a functional block diagram showing the functional structure of a control device of an internal combustion engine according to an embodiment of the present invention.

[0023] Figure 4 is a diagram showing the relationship between the operating state of an internal combustion engine and the gas flow velocity around a spark plug according to an embodiment of the present invention.

[0024] Figure 5A , Figure 5BThis is a diagram showing the relationship between the discharge path and the flow velocity between the electrodes of a spark plug according to an embodiment of the present invention.

[0025] Figure 6 This is a diagram showing a circuit including an ignition coil according to an embodiment of the present invention.

[0026] Figure 7 This is a diagram showing an example in which the accuracy of the in-cylinder pressure (p) calculated only using the relational expression is evaluated.

[0027] Figure 8 This is a diagram for explaining an example of the frequency component of the in-cylinder pressure.

[0028] Figure 9 This is a flowchart showing the sequence of in-cylinder pressure detection processing according to an embodiment of the present invention.

[0029] Figure 10 This is a diagram showing an example in which the detection accuracy of the in-cylinder pressure (p) according to an embodiment of the present invention is evaluated. Detailed Embodiment

[0030] 1. Embodiment

[0031] Hereinafter, an internal combustion engine control device according to an embodiment of the present invention will be described. In addition, the same reference numerals are assigned to common components in the respective drawings.

[0032] [Internal Combustion Engine System]

[0033] First, the structure of the internal combustion engine system according to the present embodiment will be described. Figure 1 This is an overall structure diagram showing a basic structure example of an internal combustion engine according to an embodiment of the present invention.

[0034] Figure 1 The internal combustion engine 100 shown may be a single-cylinder or may have multiple cylinders. In the embodiment, the internal combustion engine 100 having 4 cylinders will be described as an example. As Figure 1 shown, the air sucked from the outside in the internal combustion engine 100 flows through the air cleaner 110, the intake pipe 111, and the intake manifold 112. The air after passing through the intake manifold 112 flows into each cylinder 150 when the intake valve 151 is opened. The amount of air flowing into each cylinder 150 is adjusted by the throttle valve 113. The amount of air adjusted by the throttle valve 113 is measured by the flow rate sensor 114.

[0035] A throttle valve opening sensor 113a for detecting the opening of the throttle valve is provided in the throttle valve 113. The opening information of the throttle valve 113 detected by the throttle valve opening sensor 113a is output to the control device (Electronic Control Unit: ECU) 1.

[0036] In the present embodiment, an electronically controlled throttle valve driven by an electric motor is applied as the throttle valve 113. However, as the throttle valve in the present invention, any throttle valve capable of appropriately adjusting the air flow rate may be used, and other types of throttle valves may also be applied.

[0037] The temperature of the gas flowing into each cylinder 150 is detected by an intake air temperature sensor 115.

[0038] A crank angle sensor 121 is provided on the radially outer side of an annular gear 120 attached to a crankshaft 123. The crank angle sensor 121 detects the rotational angle of the crankshaft 123. In the present embodiment, the crank angle sensor 121 detects the rotational angle of the crankshaft 123 every 10° and for each combustion cycle.

[0039] A water temperature sensor 122 is provided in a water jacket (not shown) of the cylinder head. The water temperature sensor 122 detects the temperature of the cooling water of the internal combustion engine 100.

[0040] In addition, an accelerator pedal position sensor (APS) 126 for detecting the displacement amount (depression amount) of an accelerator pedal (throttle pedal) 125 is provided in the vehicle. The accelerator pedal position sensor 126 detects the required torque of the driver. The required torque of the driver detected by the accelerator pedal position sensor 126 is output to a control device 1 described later. The control device 1 controls the throttle valve 113 based on this required torque.

[0041] Fuel stored in a fuel tank 130 is sucked and pressurized by a fuel pump 131. The fuel sucked and pressurized by the fuel pump 131 is adjusted to a specified pressure by a pressure regulator 132 provided in a fuel pipe 133. Then, the fuel adjusted to the specified pressure is injected into each cylinder 150 from a fuel injection device (injector) 134. The remaining fuel after the pressure adjustment by the pressure regulator 132 returns to the fuel tank 130 via a return pipe (not shown).

[0042] The control of the fuel injection device 134 is performed based on a fuel injection pulse (control signal) from a fuel injection control unit 82 of the control device 1 described later.

[0043] An exhaust valve 152 and an exhaust manifold 160 are installed in each cylinder 150. When the exhaust valve 152 is opened, exhaust gas is discharged from the cylinder 150 to the exhaust manifold 160. The exhaust manifold 160 discharges the burned gas (exhaust gas) to the outside of the cylinder 150. A three-way catalyst 161 is provided on the exhaust side of the exhaust manifold 160. The three-way catalyst 161 purifies the exhaust gas. The exhaust gas purified by the three-way catalyst 161 is discharged to the atmosphere.

[0044] An upstream air-fuel ratio sensor 162 is provided on the upstream side of the three-way catalyst 161. The upstream air-fuel ratio sensor 162 continuously detects the air-fuel ratio of the exhaust gas discharged from each cylinder 150.

[0045] In addition, a downstream air-fuel ratio sensor 163 is provided on the downstream side of the three-way catalyst 161. The downstream air-fuel ratio sensor 163 outputs a switch-type detection signal near the stoichiometric air-fuel ratio. The downstream air-fuel ratio sensor 163 in the present embodiment is an O2 sensor.

[0046] Spark plugs 200 are respectively provided on the upper parts of the respective cylinders 150. The spark plugs 200 generate sparks by discharging (igniting), and the sparks ignite in the air-fuel mixture in the cylinders 150. Thereby, an explosion occurs in the cylinders 150, and the pistons 170 are pushed downward. By pushing the pistons 170 downward, the crankshaft 123 rotates. An ignition coil 300 that generates the electric energy (voltage) supplied to the spark plugs 200 is connected to the spark plugs 200.

[0047] Output signals from various sensors such as the throttle opening sensor 113a, the flow rate sensor 114, the crankshaft angle sensor 121, the accelerator pedal position sensor 126, and the water temperature sensor 122 described above are output to the control device 1. The control device 1 detects the operating state of the internal combustion engine 100 based on the output signals from these various sensors. And the control device 1 controls the amount of air sent into the cylinders 150, the fuel injection amount from the fuel injection device 134, the ignition timing of the spark plugs 200, and the like.

[0048] [Spark plug]

[0049] Next, the spark plug 200 will be described with reference to Figure 2 as follows.

[0050] Figure 2 is a partially enlarged view for explaining the spark plug 200.

[0051] As Figure 2 shown, the spark plug 200 has a center electrode 210 and an outer electrode 220. The center electrode 210 is supported by a socket (not shown) via (with) an insulator 230. Thereby, the center electrode 210 is insulated. The outer electrode 220 is grounded.

[0052] In the ignition coil 300 (refer to Figure 1)When a voltage is generated in [], a specified voltage (for example, 20,000 V to 40,000 V in this embodiment) is applied to the center electrode 210. When the specified voltage is applied to the center electrode 210, a discharge (ignition) occurs between the center electrode 210 and the outer electrode 220. And, the spark generated by the discharge ignites in the air-fuel mixture in the cylinder 150.

[0053] In addition, the voltage that causes dielectric breakdown (insulation breakdown) of the gas components in the cylinder 150 and generates a discharge (ignition) varies according to the state of the gas between the center electrode 210 and the outer electrode 220 and the in-cylinder pressure of the cylinder 150. The voltage at which this discharge occurs is called the dielectric breakdown voltage.

[0054] The discharge control (ignition control) of the spark plug 200 is performed by the ignition control unit 83 of the control device 1 described later.

[0055] [Hardware Configuration of the Control Device]

[0056] Next, the overall structure of the hardware of the control device 1 will be described.

[0057] As Figure 1 shown, the control device 1 includes an analog input unit 10, a digital input unit 20, an A / D (Analog / Digital) conversion unit 30, a RAM (Random Access Memory), a MPU (Micro-Processing Unit), a ROM (Read Only Memory), an I / O (Input / Output) port 70, and an output circuit 80.

[0058] Analog output signals from various sensors such as a throttle valve opening sensor 113a, a flow rate sensor 114, an accelerator pedal position sensor 126, an upstream air-fuel ratio sensor 162, a downstream air-fuel ratio sensor 163, and a water temperature sensor 122 are input to the analog input unit 10.

[0059] The A / D conversion unit 30 is connected to the analog input unit 10. The analog output signals from various sensors input to the analog input unit 10 are converted into digital signals by the A / D conversion unit 30 after signal processing such as noise removal. The digital signals obtained by the conversion of the A / D conversion unit 30 are stored in the RAM 40.

[0060] Digital output signals from the crank angle sensor 121 are input to the digital input unit 20.

[0061] The digital input unit 20 is connected to the I / O port 70. The digital output signal input to the digital input unit 20 is stored in the RAM 40 via the I / O port 70.

[0062] Each output signal stored in the RAM 40 is subjected to arithmetic processing in the MPU 50.

[0063] The MPU 50 executes a control program (not shown) stored in the ROM 60, and performs arithmetic processing on the output signals stored in the RAM 40 according to the control program. The MPU 50 calculates a control value according to the control program and temporarily stores the control value in the RAM 40, where the control value specifies the amount of movement of each actuator (such as the throttle valve 113, the pressure regulator 132, the spark plug 200, etc.) for driving the internal combustion engine 100.

[0064] The control value specifying the amount of movement of the actuator stored in the RAM 40 is output to the output circuit 80 via the I / O port 70.

[0065] In the output circuit 80, there is provided an overall control unit 81 (see Figure 3 ) for overall control of the internal combustion engine based on output signals from various sensors (such as the accelerator pedal position sensor 126), a fuel injection control unit 82 (see Figure 3 ) for controlling the driving of the plunger rod (not shown) of the fuel injection device 134, and an ignition control unit 83 (see Figure 3 ) for controlling the voltage applied to the spark plug 200, and other functions.

[0066] [Functional block of the control device]

[0067] Next, with reference to Figure 3 the functional structure of the control device 1 will be described.

[0068] Figure 3 is a functional block diagram for explaining the functional structure of the control device 1.

[0069] Each function of the control device 1 is implemented as various functions of the output circuit 80 by the MPU 50 executing the control program stored in the ROM 60. Various functions in the output circuit 80 include, for example, the control of the fuel injection device 134 by the fuel injection control unit 82 and the discharge control of the spark plug 200 by the ignition control unit 83.

[0070] As Figure 3 shown, the output circuit 80 of the control device 1 has an overall control unit 81, a fuel injection control unit 82, and an ignition control unit 83.

[0071] [Overall control unit]

[0072] The overall control unit 81 is connected to the accelerator pedal position sensor 126 and receives the required torque (acceleration signal S1) from the accelerator pedal position sensor 126. The overall control unit 81 detects the in-cylinder pressure (p) through the in-cylinder pressure detection process described later.

[0073] Based on the required torque (acceleration signal S1) from the accelerator pedal position sensor 126 and the detected in-cylinder pressure (p), the overall control unit 81 performs overall control of the fuel injection control unit 82 and the ignition control unit 83.

[0074] [Fuel injection control unit]

[0075] The fuel injection control unit 82 is connected to the cylinder determination unit 84 that determines each cylinder 150 of the internal combustion engine 100, the angle information generation unit 85 that measures the crank angle of the crankshaft 123, and the rotational speed information generation unit 86 that measures the engine speed. The fuel injection control unit 82 receives the cylinder determination information S3 from the cylinder determination unit 84, the crank angle information S4 from the angle information generation unit 85, and the engine speed information S5 from the rotational speed information generation unit 86.

[0076] In addition, the fuel injection control unit 82 is connected to the intake air amount measurement unit 87 that measures the intake air amount of the air inhaled into the cylinder 150, the load information generation unit 88 that measures the engine load, and the coolant temperature measurement unit 89 that measures the temperature of the engine coolant. The fuel injection control unit 82 receives the intake air amount information S6 from the intake air amount measurement unit 87, the engine load information S7 from the load information generation unit 88, and the coolant temperature information S8 from the coolant temperature measurement unit 89.

[0077] Based on the received various information, the fuel injection control unit 82 calculates the injection amount and injection time of the fuel injected from the fuel injection device 134. The fuel injection control unit 82 sends the fuel injection pulse S9 generated based on the calculated fuel injection amount and injection time to the fuel injection device 134.

[0078] [Ignition control unit]

[0079] In addition to being connected to the overall control unit 81, the ignition control unit 83 is also connected to the cylinder determination unit 84, the angle information generation unit 85, the rotational speed information generation unit 86, the load information generation unit 88, and the coolant temperature measurement unit 89, and receives (accepts) the respective information from them.

[0080] Based on the received various information, the ignition control unit 83 calculates the current amount (energization angle) of energizing the primary coil 310 of the ignition coil 300 (refer to Figure 8 ), the energization start time, and the time (ignition time) for cutting off the current flowing through the primary coil 310.

[0081] The ignition control unit 83 outputs an energization signal SA to the primary coil 310 of the ignition coil 300 based on the calculated energization amount, energization start time, and ignition time, thereby performing discharge control (ignition control) of the spark plug 200.

[0082] [Relationship between the operating state of the internal combustion engine and the gas flow velocity around the spark plug]

[0083] Next, with reference to Figure 4 the relationship between the operating state of the internal combustion engine 100 and the gas flow velocity around the spark plug 200 will be described.

[0084] Figure 4 is a diagram showing the relationship between the operating state of the internal combustion engine 100 and the gas flow velocity around the spark plug 200.

[0085] As Figure 4 shown, generally, the higher the engine speed and load, the higher the gas flow velocity in the cylinder 150 becomes, and the gas around the spark plug 200 becomes a high flow velocity. Therefore, in the case of high engine speed and load, the gas flows at high speed between the center electrode 210 and the outer electrode 220 of the spark plug 200.

[0086] In addition, in the internal combustion engine 100 performing exhaust gas recirculation (EGR: Exhaust Gas Recirculation), the EGR rate is set according to the relationship between the engine speed and the load, for example, as Figure 4 shown. In addition, the higher the EGR rate is set, the wider the high EGR region becomes, and the more fuel consumption reduction and exhaust gas reduction can be achieved. However, in the high EGR region, since the probability of flame kernel growth decreases, misfiring is likely to occur in the spark plug 200.

[0087] [Relationship between the discharge path between the electrodes of the spark plug and the flow velocity]

[0088] Next, with reference to Figure 5A 、 Figure 5B the relationship between the discharge path between the electrodes of the spark plug and the flow velocity will be described.

[0089] Figure 5A 、 Figure 5B is a diagram showing the relationship between the discharge path between the electrodes of the spark plug and the flow velocity.

[0090] As Figure 5A 、 Figure 5BAs shown, when dielectric breakdown occurs between the center electrode 210 and the outer electrode 220 of the spark plug 200, a discharge path 211 is formed between the electrodes 210 and 220 during the period until the current flowing between the electrodes 210 and 220 becomes below a certain value. When the combustible gas comes into contact with this discharge path 211, the flame kernel grows and reaches combustion. Since the discharge path 211 moves under the influence of the gas flow between the electrodes 210 and 220, as Figure 5A shown, the higher the gas flow rate, the longer the discharge path 211 is formed in a short time. On the other hand, as Figure 5B shown, the lower the gas flow rate, the shorter the discharge path 211 becomes.

[0091] When the internal combustion engine 100 operates at a high EGR rate, even if the combustible gas comes into contact with the discharge path 211, the probability of the flame kernel growth decreases. Therefore, it is necessary to increase the chance of the combustible gas coming into contact with the discharge path 211. As described above, the discharge path 211 is generated by breaking down the insulation of the gas. Therefore, if the current required to maintain the discharge path 211 is constant, power corresponding to the length of the discharge path 211 needs to be supplied when maintaining the discharge path 211.

[0092] In the case of a high gas flow rate, the energization control of the ignition coil 300 is performed in such a way that a large amount of power is output from the ignition coil 300 to the spark plug 200 in a short time. Thus, it is possible to form Figure 5A a longer discharge path 211 as shown. As a result, the discharge path 211 can obtain the opportunity to contact the gas in a larger space.

[0093] On the other hand, in the case of a low gas flow rate, the energization control of the ignition coil 300 is performed in such a way that a small amount of power is continuously output from the ignition coil 300 to the spark plug 200 for a long time. Thus, it is possible to maintain Figure 5B the formation of the shorter discharge path 211 as shown. As a result, the discharge path 211 can obtain the opportunity to contact the gas passing near the electrodes of the spark plug 200 for a longer time.

[0094] [Circuit of the ignition coil]

[0095] Next, an ignition coil according to an embodiment will be described with reference to Figure 6 the following.

[0096] Figure 6 is a diagram illustrating the circuit of an ignition coil according to an embodiment.

[0097] Figure 6The circuit 400 shown has an ignition coil 300. The ignition coil 300 includes a primary coil 310 wound with a specified number of turns and a secondary coil 320 wound with more turns than the primary coil 310.

[0098] One end of the primary coil 310 is connected to a DC power supply 330. Thus, a specified voltage (e.g., 12V) can be applied to the primary coil 310. The other end of the primary coil 310 is connected to the collector (C) terminal of an igniter (power supply control circuit) 340 and grounded via the igniter 340. The igniter 340 uses a transistor, a field effect transistor (FET), etc.

[0099] The base (B) terminal of the igniter 340 is connected to the ignition control unit 83. The power supply signal SA output from the ignition control unit 83 is input to the base (B) terminal of the igniter 340. When the power supply signal SA is input to the base (B) terminal of the igniter 340, the collector (C) terminal and the emitter (E) terminal of the igniter 340 become in a conductive state, and current flows between the collector (C) terminal and the emitter (E) terminal. Thus, the power supply signal SA is output from the ignition control unit 83 to the primary coil 310 of the ignition coil 300 via the igniter 340. As a result, current flows in the primary coil 310, and electric power (electrical energy) is stored.

[0100] When the output of the power supply signal SA from the ignition control unit 83 stops, the current flowing in the primary coil 310 is cut off. As a result, a high voltage corresponding to the turns ratio of the coil with respect to the primary coil 310 is generated in the secondary coil 320. In addition, between the spark plug 200 and the secondary coil 320, a voltage detection unit for detecting the secondary voltage and a current detection unit for detecting the secondary current are provided.

[0101] The high voltage generated in the secondary coil 320 is applied to the center electrode 210 of the spark plug 200 (refer to Figure 5A , Figure 5B ). Thus, a potential difference is generated between the center electrode 210 and the outer electrode 220 of the spark plug 200. When the potential difference generated between the center electrode 210 and the outer electrode 220 becomes equal to or higher than the insulation breakdown voltage Vm of the gas (the air-fuel mixture in the cylinder 150), the gas component is insulation broken down, and discharge is generated between the center electrode 210 and the outer electrode 220. As a result, ignition (firing) of the fuel (air-fuel mixture) is performed. The ignition control unit 83 operates the circuit 400 as described above using the power supply signal SA and controls the energization of the ignition coil 300.

[0102] [Relationship between ignition discharge and in-cylinder pressure]

[0103] Next, the relationship between the ignition discharge and the in-cylinder pressure will be described.

[0104] As an example of the relationship between the ignition discharge and the in-cylinder pressure, there is a relationship derived by Kim Anderson et al., generally known as the KIM relationship. The KIM relationship is represented by Equation (2).

[0105] [Mathematical formula 2]

[0106]

[0107] The KIM relationship holds during inductive discharge or glow discharge. In this relationship, V2 represents the secondary voltage, I2 represents the secondary current, p represents the in-cylinder pressure, p0 represents the atmospheric pressure, and l represents the length of the discharge path. Therefore, V2, I2, p, and l are variables, and p0 is a fixed value.

[0108] In the above Equation (2), V2 is calculated based on l, I2, p, and p0. By transforming Equation (2) as shown in Equations (3) to (5), p can be calculated based on l, I2, V2, and p0. In addition, Equation (5) is the same as the above Equation (1).

[0109] [Mathematical formula 3]

[0110]

[0111]

[0112]

[0113] [Calculation of in-cylinder pressure using only the relationship]

[0114] Next, regarding the in-cylinder pressure (p) calculated only using the above Equation (5), refer to Figure 7 for the description.

[0115] Figure 7 is a diagram showing an example of evaluating the accuracy of the in-cylinder pressure (p) calculated only using the above Equation (5).

[0116] Figure 7 The horizontal axis of each of the diagrams shown represents the time [msec] after the start of the discharge. Figure 7 The vertical axis of each of the diagrams shown represents the secondary current (I2) [A], the secondary voltage (V2) [kV], and the in-cylinder pressure (p) [kPa].

[0117] In Figure 7In [the figure], the solid lines representing the secondary current (I2), secondary voltage (V2), and in-cylinder pressure (p) are measured values. The measured values are obtained by continuously discharging two ignition coils with a time difference to extend the discharge period. Thereby, the period during which measurement can be performed can be extended, and the combustion index can be calculated based on more information.

[0118] In addition, the dashed line representing the in-cylinder pressure (p) is a calculated value obtained using the above-mentioned formula (5). Specifically, the length (l) of the discharge path is taken as the distance between the electrodes, and the measured values of the secondary current (I2) and secondary voltage (V2) are substituted into the relational expression, and as a result, the in-cylinder pressure (p) represented by the dashed line is obtained. The solid line representing the in-cylinder pressure (p) is a measured value obtained by measuring the in-cylinder pressure (p) using a combustion pressure sensor.

[0119] As Figure 7 shown, in the waveforms of the secondary current (I2) and secondary voltage (V2), variations in re-discharge can be seen accompanying the elongation of the discharge path. And the calculated value (dashed line) of the in-cylinder pressure (p) repeatedly deviates from and coincides with the measured value (solid line). This is considered to be the case where the above-mentioned formula (5), i.e., the KIM relational expression, holds when the discharge path forms at the shortest distance between the electrodes at the start of re-discharge. And it is considered that after the discharge, due to the influence of the gas flow in the cylinder, the discharge path elongates, and the in-cylinder pressure calculated according to the above-mentioned formula (5) deviates from the measured in-cylinder pressure. Therefore, when simply calculating the in-cylinder pressure (p) using the above-mentioned formula (5), there is a problem of reduced accuracy.

[0120] [Frequency components of in-cylinder pressure]

[0121] Next, the frequency components of the in-cylinder pressure (p) will be described with reference to Figure 8 as follows.

[0122] Figure 8 is a diagram for explaining an example of the frequency components of the in-cylinder pressure (p).

[0123] Figure 8 represents the result obtained by performing FFT (Fast Fourier transform) processing on the waveform of the in-cylinder pressure (p) shown in Figure 7 . The horizontal axis of the chart shown in Figure 8 represents the number (order), and the vertical axis represents the Fourier coefficient (amplitude). In Figure 8 , the solid line represents the result obtained by performing FFT processing on the waveform of the measured value, and the dashed line represents the result obtained by performing FFT processing on the waveform of the calculated value using the above-mentioned formula (5).

[0124] As Figure 8 ​​As shown, three maxima can be confirmed in the dotted line of the calculated value. For each frequency band containing each maximum, starting from the one with the smaller order, they are the low-frequency band A, the medium-frequency band B, and the high-frequency band C. The dotted line in the low-frequency band A roughly coincides with the solid line in the low-frequency band A. Since the solid line is only the component of the in-cylinder pressure, the dotted line in this frequency band (low-frequency band A) is considered to be the component of the in-cylinder pressure.

[0125] On the other hand, in the medium-frequency band B and the high-frequency band C, the dotted line deviates from the solid line. As the reasons for this deviation, the gentle changes in the secondary current (I2) and the secondary voltage (V2) due to the elongation of the discharge path, and the sharp changes in the secondary current (I2) and the secondary voltage (V2) due to re-discharge can be cited. That is, it can be considered that the dotted line in the medium-frequency band B contains the frequency components of the elongation of the discharge path, and the dotted line in the high-frequency band C contains the frequency components of re-discharge.

[0126] In addition, with the insulation breakdown accompanied by re-discharge, capacitive discharge (arc discharge) occurs. As described above, the KIM relation holds in inductive discharge or glow discharge. Therefore, in the high-frequency band C, the KIM relation cannot be applied.

[0127] Then, in this embodiment, the medium-frequency band B and the high-frequency band C (i.e., the high-frequency components) are removed from the waveforms of the secondary current (I2) and the secondary voltage (V2), and then the in-cylinder pressure (p) is calculated using the above formula (5). Thus, a calculated value (in-cylinder pressure (p)) that eliminates the influence of the frequency components of the elongation of the discharge path and re-discharge can be obtained. After removing the frequency components of the elongation of the discharge path, it becomes a hypothetical (imagined) windless state, and the length of the discharge path is fixed to the shortest distance between the electrodes (between the electrodes 210 and 220). In addition, the high-frequency components related to the present invention include the frequency components of the elongation of the discharge path and the frequency components of re-discharge.

[0128] When removing the medium-frequency band B and the high-frequency band C, if a normal analog low-pass filter circuit is used, response delay and phase shift will occur. As a result, the accuracy of the calculated in-cylinder pressure is reduced. For this reason, a cut-off order is set between the low-frequency band A and the medium-frequency band B, and the inverse FFT processing (inverse FFT) is performed with the value of the dotted line above the cut-off order being zero. Thus, response delay and phase shift can be reduced.

[0129] [In-cylinder Pressure Detection Processing]

[0130] Next, regarding the in-cylinder pressure detection processing performed by the overall control unit 81 of this embodiment, reference is made to Figure 9 for explanation.

[0131] Figure 9 is a flowchart showing the sequence of the in-cylinder pressure detection processing of this embodiment.

[0132] First, the overall control unit 81 detects the secondary current (I2) and the secondary voltage (V2) (S1). In the process of S1, the discharge waveforms (the waveforms during the discharge period) of the secondary current (I2) and the secondary voltage (V2) are detected.

[0133] Next, the overall control unit 81 removes the high-frequency components from the discharge waveforms, and obtains the values of the secondary current (I2) and the secondary voltage (V2) from the waveforms after removing the high-frequency components (S2). In the process of S2, FFT processing is performed in such a way that the number of times above a predetermined cut-off number (the number range) becomes zero. After that, by performing inverse FFT processing, the high-frequency components are removed. Here, the cut-off number is set based on the frequency components in the waveform of the in-cylinder pressure obtained by using a combustion pressure sensor (a standard sensor prepared to obtain the measured value).

[0134] Next, the overall control unit 81 calculates the in-cylinder pressure (p) by using the above formula (5) obtained by converting the KIM relation (S3). After the process of S3, the overall control unit 81 ends the in-cylinder pressure detection process. In this way, by removing the high-frequency components from the discharge waveforms of the secondary current (I2) and the secondary voltage (V2), a hypothetical windless state can be formed, and the influence of the elongation of the discharge path can be eliminated. That is, the length of the discharge path can be fixed to the shortest distance between the electrodes. As a result, the in-cylinder pressure (p) can be detected (calculated) with good accuracy.

[0135] Figure 10 It is a diagram showing an example of evaluating the detection accuracy of the in-cylinder pressure (p) of the present embodiment. Figure 10 In the horizontal axes of the respective graphs shown in, the time [msec] after the start of discharge is represented. Figure 7 In the vertical axes of the respective graphs shown in, the secondary current (I2) [A], the secondary voltage (V2) [kV], and the in-cylinder pressure (p) [kPa] are represented.

[0136] In Figure 10 The solid lines representing the secondary current (I2) and the secondary voltage (V2) are obtained by performing the above-mentioned FFT processing and inverse FFT processing to remove the high-frequency components. In addition, the solid line representing the in-cylinder pressure (p) is the measured value obtained by measuring the in-cylinder pressure (p) using a combustion pressure sensor. The dotted line representing the in-cylinder pressure (p) is the calculated value calculated by using the above formula (5). Specifically, taking the length (l) of the discharge path as the distance between the electrodes, and substituting the secondary current (I2) and the secondary voltage (V2) from which the high-frequency components have been removed into the relation, as a result, the in-cylinder pressure (p) represented by the dotted line is obtained.

[0137] The deviation between the calculated value obtained by using the above formula (5), which is the dotted line, and the measured value obtained by using the combustion pressure sensor, which is the solid line, becomes smaller. Thus, it is possible to confirm that the detection accuracy (calculation accuracy) of the in-cylinder pressure (p) is improved. As a result, it is possible to perform combustion control for each cylinder with high accuracy by cylinder, and the fuel consumption of the vehicle can be improved.

[0138] 2. Summary

[0139] As described above, the in-cylinder pressure detection method of the above embodiment detects the in-cylinder pressure (p) using the information of the secondary coil (secondary coil 320). Using this in-cylinder pressure detection method, high-frequency components are removed from the discharge waveform of the secondary coil, and information on the secondary current (I2) and the secondary voltage (V2) is obtained from the discharge waveform from which the high-frequency components have been removed. The in-cylinder pressure (p) is calculated according to the above formula (1) (formula (5)). Thus, it is possible to make the space between the electrodes of the spark plug (spark plug 200) (between the center electrode 210 and the outer electrode 220) a hypothetical windless state, and it is possible to detect the in-cylinder pressure (p) while eliminating the influence of the elongation of the discharge path and re-discharge. As a result, it is possible to detect the in-cylinder pressure (p) with high accuracy, and combustion control corresponding to the component characteristics of the cylinder can be achieved. Therefore, it is possible to improve the fuel consumption performance. In addition, since it is not necessary to use a combustion pressure sensor to detect the in-cylinder pressure (p), the number of components can be reduced, and the cost of the internal combustion engine system can be reduced.

[0140] In addition, in the in-cylinder pressure detection method of the above embodiment, the length (l) of the discharge path in formula (1) is the shortest distance between the electrodes in the spark plug (spark plug 200). Thus, it is possible to use the electrode distance with high reproducibility as the length of the discharge path. In addition, it is not necessary to detect the length of the discharge path.

[0141] In addition, in the in-cylinder pressure detection method of the above embodiment, the removal of the high-frequency components is achieved by performing FFT processing with a predetermined number range set to zero for the waveform data of the secondary current and the secondary voltage, and then performing inverse FFT processing. Thus, it is possible to remove the high-frequency components and reduce the response delay and phase shift.

[0142] In addition, in the in-cylinder pressure detection method of the above embodiment, the predetermined order range is determined according to the frequency components in the pressure waveform of the measured value obtained by using the combustion pressure sensor. Thus, it is possible to correctly determine the high-frequency components to be removed, and it is possible to more reliably remove the frequency components of the elongation of the discharge path and the frequency components of re-discharge.

[0143] In addition, the internal combustion engine control device (control device 1) of the above-described embodiment includes: a primary coil (primary coil 310); a secondary coil that generates an electromotive force when the energization of the primary coil is interrupted; and a spark plug (spark plug 200) connected to the secondary coil. Moreover, it includes a control unit (overall control unit 81) that removes high-frequency components from the discharge waveform of the secondary coil, obtains information on the secondary current and secondary voltage from the discharge waveform from which the high-frequency components have been removed, and calculates the in-cylinder pressure based on the above formula (1) (formula (5)). Thereby, it is possible to detect the in-cylinder pressure (p) while eliminating the influence of the elongation of the discharge path and re-discharge. As a result, it is possible to detect the in-cylinder pressure (p) with good accuracy, and it is possible to achieve combustion control that matches the component characteristics of the cylinder. Therefore, it is possible to improve the fuel consumption performance. In addition, since it is not necessary to use a combustion pressure sensor to detect the in-cylinder pressure (p), it is possible to reduce the number of components and achieve cost reduction of the internal combustion engine system.

[0144] Furthermore, the in-cylinder pressure detection method and the internal combustion engine control device of the present invention can also be applied to an internal combustion engine having an in-cylinder pressure sensor (combustion pressure sensor). In this case, by comparing the output of the in-cylinder pressure sensor with the in-cylinder pressure (p) detected by the in-cylinder pressure detection method, it is also possible to perform diagnosis of the in-cylinder pressure sensor. In addition, when the in-cylinder pressure sensor fails, by controlling the internal combustion engine by detecting the in-cylinder pressure using the in-cylinder pressure detection method of the present invention, it is possible to achieve control for operation after failure (Fail operation).

[0145] As described above, the embodiments of the in-cylinder pressure detection method, the in-cylinder pressure sensor diagnosis method, and the internal combustion engine control device of the present invention have been described, including their effects. However, the in-cylinder pressure detection method, the in-cylinder pressure sensor diagnosis method, and the internal combustion engine control device of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the invention described in the claims.

[0146] In addition, the above-described embodiments are detailed descriptions for facilitating the understanding of the present invention and are not limited to having all the structures described. In addition, a part of the structure of one embodiment can be replaced with the structure of another embodiment, and in addition, the structure of another embodiment can be added to the structure of one embodiment. In addition, regarding a part of the structure of each embodiment, it is also possible to add, omit, or replace other structures.

[0147] For example, in the above-described embodiment, a structure is adopted in which the overall control unit 81 performs the in-cylinder pressure detection process. However, the in-cylinder pressure detection process of the present invention may also be performed by a control unit provided separately from the control device 1, such as a digital signal processor (DNP). In this case, noise in the secondary coil can be prevented from mixing into the control device 1. In addition, when a control unit for performing the in-cylinder pressure detection process is provided outside the control device 1, the control unit and the control device 1 constitute an internal combustion engine control device.

[0148] Description of Reference Numerals

[0149] 1... Control device, 10... Analog input unit, 20... Digital input unit, 30... A / D conversion unit, 40... RAM, 50... MPU, 60... ROM, 70... I / O port, 80... Output circuit, 81... Overall control unit, 82... Fuel injection control unit, 83... Ignition control unit, 84... Cylinder determination unit, 85... Angle information generation unit, 86... Rotational speed information generation unit, 87... Intake air amount measurement unit, 88... Load information generation unit, 89... Water temperature measurement unit, 100... Internal combustion engine, 110... Air cleaner, 111... Intake pipe, 112... Intake manifold, 113... Throttle valve, 115... Intake air temperature sensor, 120... Ring gear, 123... Crankshaft, 125... Accelerator pedal, 130... Fuel tank, 131... Fuel pump, 132... Pressure regulator, 133... Fuel pipe, 134... Fuel injection device, 150... Cylinder, 151... Intake valve, 152... Exhaust valve, 160... Exhaust manifold, 161... Three-way catalyst, 170... Piston, 200... Spark plug, 210... Center electrode, 211... Discharge path, 220... Outer electrode, 230... Insulator, 300... Ignition coil, 310... Primary coil, 320... Secondary coil, 330... DC power supply, 340... Igniter (energization control circuit), 400... Circuit.

Claims

1. An in-cylinder pressure detection method that detects in-cylinder pressure using information from the secondary coil of an internal combustion engine. The internal combustion engine has a primary coil, a secondary coil that generates an electromotive force when the energization of the primary coil is cut off, and a spark plug connected to the secondary coil. The in-cylinder pressure detection method is characterized in that: Remove high-frequency components from the discharge waveform of the secondary coil. Obtain information on the secondary current and secondary voltage from the discharge waveform from which the high-frequency components have been removed, and calculate the in-cylinder pressure according to the following formula (1). (Mathematical formula 1) Among them, V2 is the secondary voltage, I2 is the secondary current, p is the in-cylinder pressure, p0 is the atmospheric pressure, and l is the length of the discharge path.

2. The in-cylinder pressure detection method according to claim 1, characterized in that: The length of the discharge path is the shortest distance between the electrodes of the spark plug.

3. The in-cylinder pressure detection method according to claim 1 or 2, characterized in that: For the waveform data of the secondary current and secondary voltage, perform FFT processing in such a way that a predetermined frequency range becomes zero, and then perform inverse FFT processing to remove the high-frequency components.

4. The in-cylinder pressure detection method according to claim 3, characterized in that: The predetermined frequency range is determined according to the frequency components in the pressure waveform of the measured value obtained using a combustion pressure sensor.

5. An in-cylinder pressure sensor diagnosis method, characterized in that: Perform diagnosis of the in-cylinder pressure sensor using the in-cylinder pressure detected by the in-cylinder pressure detection method according to claim 1 and the output of the in-cylinder pressure sensor.

6. An internal combustion engine control device that controls an internal combustion engine having a primary coil, a secondary coil that generates an electromotive force when the energization of the primary coil is cut off, and a spark plug connected to the secondary coil. The internal combustion engine control device is characterized in that: It includes a control unit that removes high-frequency components from the discharge waveform of the secondary coil, and obtains information on the secondary current and secondary voltage from the discharge waveform from which the high-frequency components have been removed, and calculates the in-cylinder pressure according to the following formula (1). (Mathematical formula 1) Among them, V2 is the secondary voltage, I2 is the secondary current, p is the in-cylinder pressure, p0 is the atmospheric pressure, and l is the length of the discharge path.

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