JP7652990B2 - Internal combustion engine control device and internal combustion engine control method - Google Patents

Description

The present invention relates to an internal combustion engine control device and an internal combustion engine control method.

It has been known that internal combustion engines generate a large amount of hydrocarbons (HC) during cold start when the temperatures of each part are approximately the same as the outside air temperature. There are two main factors that cause hydrocarbons to be generated during cold start. The first is that the low in-cylinder temperature causes unvaporized fuel to be discharged as hydrocarbons without being oxidized (unburned). The second is that the low in-cylinder temperature reduces the amount of fuel that is vaporized before the ignition timing, causing the air-fuel ratio of the in-cylinder mixture to increase (fuel becomes lean). In this case, the required ignition energy increases, causing more ignition failures and flame outs (misfires), resulting in more hydrocarbons.

Furthermore, during cold engine start-up, the fuel injection amount is controlled to be greater than the fuel injection amount after warm-up. As a result, the amount of hydrocarbons generated during cold engine start-up increases even more.

Incidentally, an exhaust catalyst is installed in the exhaust pipe to purify hydrocarbons and other substances generated by the internal combustion engine. Expensive precious metals such as platinum are used in exhaust catalysts. If more precious metals than conventional are used in the exhaust catalyst to improve exhaust performance, the manufacturing cost of the exhaust catalyst will increase significantly. For this reason, attempts have been made to reduce the amount of hydrocarbons generated by controlling the ignition device to reduce misignition and flame quenching in response to the increased ignition energy required during cold engine start.

For example, Patent Document 1 discloses a control device for an internal combustion engine in which an additional ignition is performed immediately after the normal ignition timing (main ignition) near the compression top dead center during one combustion cycle of the internal combustion engine. This technology reduces ignition failures and flame quenching compared to when discharge is performed only once per combustion cycle with normal ignition timing. It also reduces the amount of hydrocarbons generated during cold start.

JP 2020-165352 A

However, when two or more discharges are performed for the purpose of ignition during one combustion cycle of one cylinder, the amount of heat generated by the ignition coil increases. This can cause damage to the ignition coil due to heat damage.

In the control device for an internal combustion engine disclosed in Patent Document 1, when a multi-ignition permission condition is met that executes discharge two or more times during one combustion cycle, the length of time that current is applied to the ignition coil is shortened. As a result, the current application time of the main ignition, i.e., the charging energy to the ignition coil, is reduced compared to when ignition is executed only once during one cycle.

In this way, when the charging energy to the ignition coil is reduced, there are cases where insulation breakdown does not occur during discharge or where the required ignition energy is not reached. As a result, ignition failure (extinction) occurs. Therefore, the internal combustion engine control device described in Patent Document 1 is prone to ignition failure (extinction) under multi-ignition permission conditions, making it difficult to suppress the generation of hydrocarbons.

In view of the above problems, the present invention aims to provide an internal combustion engine control device and an internal combustion engine control method that suppress the generation of hydrocarbons during cold start of an internal combustion engine.

In order to solve the above problems and achieve the present object, an internal combustion engine control device of the present invention controls an internal combustion engine including an ignition device having an ignition plug and an ignition coil that causes the ignition plug to discharge. The internal combustion engine control device includes a control unit that outputs an output signal to the ignition device. The output signal includes a multiple ignition signal for preheating the ignition plug, a main ignition signal that has a frequency different from that of the multiple ignition signal and ignites the mixture by discharging the ignition plug, a precharge signal for precharging the ignition coil , and an overheat detection signal for detecting the state of the ignition coil . The control unit further includes a return detection function that detects a return signal for performing self-diagnosis of the output signal. The control unit compares the overheat detection signal with the return signal to determine whether the overheat detection signal has been blocked by the filter unit. Then, when it is determined that the overheat detection signal has been blocked, it determines that the temperature of the ignition coil is equal to or higher than a first temperature. On the other hand, when it is determined that the overheat detection signal has not been blocked, it determines that the temperature of the ignition coil is lower than the first temperature.

According to the present invention, the charging energy to the ignition coil can be increased as much as possible to ensure proper implementation of ignition control during cold start-up, thereby suppressing the generation of hydrocarbons from the internal combustion engine.

1 is an overall configuration diagram showing an example of a basic configuration of an internal combustion engine according to an embodiment; FIG. 2 is a partial enlarged view illustrating an ignition plug according to an embodiment. 1 is a functional block diagram illustrating a functional configuration of an internal combustion engine control device according to an embodiment. FIG. 4 is a diagram illustrating the relationship between the electrode temperature, the minimum ignition energy, and the air-fuel ratio. FIG. 2 is a circuit diagram showing an example of an electric circuit including an ignition coil. 1 is an example of a discharge waveform of multiple ignition. FIG. 4 is a diagram illustrating the relationship between the number of misfires and the amount of hydrocarbon emissions. FIG. 4 is a diagram showing the relationship between the number of misfires and the environmental temperature. FIG. 1 is a diagram showing the relationship between hydrocarbons and environmental temperature. FIG. 1 illustrates a transition when performing multiple ignition and main ignition. 4 is a conceptual diagram showing the relationship between the amount of heat generated and ignition ability relative to the frequency of an ignition signal. FIG. FIG. 11 is a conceptual diagram showing the relationship between transition time and ignition coil temperature in the cases with and without multiple ignition. 4 is a timing chart showing changes in temperature and HC concentration of a conventional ignition coil. FIG. 2 is a circuit diagram showing an example of an electric circuit including an ignition coil according to an embodiment. 5 is a flowchart showing a multiple ignition switching process according to one embodiment. 5 is a flowchart showing a fuel injection amount switching process according to one embodiment. 5 is a timing chart showing a multiple ignition switching process according to one embodiment. 5 is a flowchart illustrating an example of a fuel injection amount switching process according to an embodiment. 1 is a timing chart showing the relationship between the operating state of an internal combustion engine mounted in a typical automobile and a multiple discharge permission period. 1 is a correlation graph showing the relationship between equivalence ratio and minimum ignition energy.

<Embodiment>
An internal combustion engine control device according to an embodiment will be described below. Note that the same reference numerals are used to designate the same components in the various drawings.

[Internal Combustion Engine System]
First, the configuration of an internal combustion engine system according to an embodiment of the present invention will be described. Fig. 1 is an overall configuration diagram showing an example of the basic configuration of an internal combustion engine according to an embodiment of the present invention.

The internal combustion engine 100 shown in FIG. 1 may have a single cylinder or multiple cylinders, but in the embodiment, an internal combustion engine 100 having four cylinders will be described as an example.

As shown in Figure 1, in an internal combustion engine 100, air drawn in from the outside (intake air) flows through an air cleaner 110, an intake pipe 111, and an intake manifold 112. The air that passes through the intake manifold 112 flows into each cylinder 150 when an intake valve 151 opens. The amount of air flowing into each cylinder 150 is adjusted by a throttle valve 113. The amount of air adjusted by the throttle valve 113 is measured by a flow sensor 114.

The throttle valve 113 is provided with a throttle opening sensor 113a that detects the throttle opening. The throttle valve 113 opening information detected by the throttle opening sensor 113a is output to the control device (Electronic Control Unit: ECU) 1.

In this embodiment, an electronic throttle valve driven by an electric motor is used as the throttle valve 113. However, other types of throttle valves may be used as the throttle valve of the present invention as long as they can appropriately adjust the air flow rate.

The temperature of the air flowing into each cylinder 150 is detected by the intake air temperature sensor 115.

A crank angle sensor 121 is provided radially outward of the ring gear 120 attached to the crankshaft 123. The crank angle sensor 121 detects the rotation angle of the crankshaft 123. In this embodiment, the crank angle sensor 121 detects the rotation angle of the crankshaft 123 every 10° and every combustion cycle.

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

The vehicle is also provided with an accelerator position sensor 126 that detects the amount of displacement (depression) of the accelerator pedal 125. The accelerator position sensor 126 detects the torque required by the driver. The torque required by the driver detected by the accelerator position sensor 126 is output to the internal combustion engine control device 1, which will be described later. The internal combustion engine control device 1 controls the throttle valve 113 based on this torque required.

Fuel stored in the fuel tank 130 is sucked in and pressurized by the fuel pump 131. The fuel sucked in and pressurized by the fuel pump 131 is adjusted to a predetermined pressure by a pressure regulator 132 provided in the fuel pipe 133. The fuel adjusted to the predetermined pressure is then injected into each cylinder 150 from a fuel injection device (injector) 134. Any excess fuel after pressure adjustment by the pressure regulator 132 is returned to the fuel tank 130 via a return pipe (not shown).

The fuel injection device 134 is controlled based on a fuel injection pulse (control signal) from the fuel injection control unit 82 (see Figure 3) of the internal combustion engine control device 1 described later.

An in-cylinder pressure sensor (also called a combustion pressure sensor) 140 is provided in the cylinder head (not shown) of the internal combustion engine 100. The in-cylinder pressure sensor 140 is provided in the cylinder 150 and detects the pressure (combustion pressure) within the cylinder 150. The in-cylinder pressure sensor 140 is, for example, a piezoelectric or gauge type pressure sensor. This makes it possible to detect the in-cylinder pressure within the cylinder 150 over a wide temperature range.

Each cylinder 150 is fitted with an exhaust valve 152 and an exhaust manifold 160. When the exhaust valve 152 opens, exhaust gas is discharged from the cylinder 150 to the exhaust manifold 160. The exhaust manifold 160 discharges the post-combustion 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 into the atmosphere.

An upstream air-fuel ratio sensor 162 is provided upstream of the three-way catalyst 161. The upstream air-fuel ratio sensor 162 continuously (linearly) detects the air-fuel ratio of the exhaust gas discharged from each cylinder 150. In this embodiment, the upstream air-fuel ratio sensor 162 is a linear air-fuel ratio sensor.

In addition, a downstream air-fuel ratio sensor 163 is provided downstream of the three-way catalyst 161. The downstream air-fuel ratio sensor 163 outputs a detection signal that changes in two values according to whether the air-fuel ratio is richer or leaner than the theoretical air-fuel ratio. In this embodiment, the downstream air-fuel ratio sensor 163 is an O2 sensor.

An ignition plug 200 is provided at the top of each cylinder 150. The spark plug 200 generates a spark by discharging (ignition), and the spark ignites the mixture of air and fuel inside the cylinder 150. This causes an explosion inside the cylinder 150, pushing the piston 170 down. Pushing the piston 170 down causes the crankshaft 123 to rotate. An ignition coil 300 that generates electrical energy (voltage) to be supplied to the spark plug 200 is connected to the spark plug 200.

The output signals from various sensors, such as the throttle opening sensor 113a, flow sensor 114, crank angle sensor 121, accelerator position sensor 126, water temperature sensor 122, and in-cylinder pressure sensor 140, are output to an internal combustion engine control device 1 (hereinafter referred to as "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. The control device 1 then controls the amount of air drawn into the cylinder 150, the amount of fuel injected from the fuel injection device 134, the ignition timing of the spark plug 200, and the like.

[Spark plug]
Next, the spark plug 200 will be described with reference to FIG.
FIG. 2 is a partially enlarged view illustrating the spark plug 200. As shown in FIG.

As shown in Figure 2, the spark plug 200 has a center electrode 210 and an outer electrode 220. The center electrode 210 is supported on a plug base (not shown) via an insulator 230. This insulates the center electrode 210. The outer electrode 220 is grounded.

When a voltage is generated in the ignition coil 300 (see FIG. 1), a predetermined voltage (e.g., 20,000 V to 40,000 V) is applied to the center electrode 210. When the predetermined voltage is applied to the center electrode 210, a discharge (ignition) occurs between the center electrode 210 and the outer electrode 220. The spark generated by the discharge then ignites the mixture of air and fuel (gas components) in the cylinder 150.

The voltage at which a discharge (ignition) occurs due to dielectric breakdown of the gas components in the cylinder 150 varies depending on the state of the gas (air-fuel mixture in the cylinder) present between the center electrode 210 and the outer electrode 220 and the internal pressure of the cylinder 150. The voltage at which this discharge occurs is called the dielectric breakdown voltage.

Discharge control (ignition control) of the spark plug 200 is performed by the ignition control unit 83 (see Figure 3) of the control device 1 described later.

[Hardware configuration of the control device]
Next, the overall hardware configuration of the control device 1 will be described.

As shown in FIG. 1, the control device 1 has an analog input section 10, a digital input section 20, an A/D (Analog/Digital) conversion section 30, a RAM (Random Access Memory) 40, an MPU (Micro-Processing Unit) 50, a ROM (Read Only Memory) 60, an I/O (Input/Output) port 70, and an output circuit 80.

Analog output signals from various sensors such as the throttle opening sensor 113a, flow sensor 114, accelerator position sensor 126, upstream air-fuel ratio sensor 162, downstream air-fuel ratio sensor 163, in-cylinder pressure sensor 140, and water temperature sensor 122 are input to the analog input section 10.

An A/D conversion unit 30 is connected to the analog input unit 10. 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. The digital signals converted by the A/D conversion unit 30 are then stored in the RAM 40.

A digital output signal from the crank angle sensor 121 is input to the digital input unit 20.

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

Each output signal stored in RAM 40 is processed by MPU 50.

The MPU 50 executes a control program (not shown) stored in the ROM 60 to process the output signals stored in the RAM 40 in accordance with the control program. In accordance with the control program, the MPU 50 calculates control values that define the operating amounts of each actuator (e.g., the throttle valve 113, the fuel pump 131, the spark plug 200, etc.) that drives the internal combustion engine 100, and temporarily stores the control values in the RAM 40.

The control value that specifies the amount of actuator operation stored in RAM 40 is output to the output circuit 80 via the I/O port 70.

The output circuit 80 is provided with functions such as an overall control unit 81, a fuel injection control unit 82, and an ignition control unit 83 (see FIG. 3). The overall control unit 81 performs overall control of the internal combustion engine based on output signals from various sensors (e.g., the cylinder pressure sensor 140). The fuel injection control unit 82 controls the drive of the plunger rod (not shown) of the fuel injection device 134. The ignition control unit 83 controls the voltage applied to the spark plug 200.

[Control device function block]
Next, the functional configuration of the control device 1 will be described with reference to FIG.
FIG. 3 is a functional block diagram illustrating the functional configuration of the control device 1.

The functions of the control device 1 are realized as various functions in the output circuit 80 by the MPU 50 executing a control program stored in the ROM 60. The various functions in the output circuit 80 include, for example, control of the fuel injection device 134 by the fuel injection control unit 82 and control of the ignition coil 300 by the ignition control unit 83.

As shown in FIG. 3, 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.

[Overall control unit]
The overall control unit 81 receives the required torque (acceleration information S 1 ) from the accelerator position sensor 126 and the in-cylinder pressure information S 2 from the in-cylinder pressure sensor 140 , both of which are stored in the RAM 40 .

The overall control unit 81 performs overall control of the fuel injection control unit 82 and the ignition control unit 83 based on the required torque (acceleration information S1) from the accelerator position sensor 126 and the in-cylinder pressure information S2 from the in-cylinder pressure sensor 140.

[Fuel injection control unit]
The fuel injection control unit 82 is connected to an angle information generation unit 85 that measures the crank angle of the crankshaft 123, a cylinder discrimination unit 84 that determines which of the strokes of each cylinder 150 of the internal combustion engine (for example, the expansion, compression, intake or compression stroke as shown in FIG. 6) the measured current crank angle corresponds to, and a revolution speed information generation unit 86 that measures the engine revolution speed. The fuel injection control unit 82 receives cylinder discrimination information S3 from the cylinder discrimination unit 84, crank angle information S4 from the angle information generation unit 85, and engine revolution speed information S5 from the revolution speed information generation unit 86.

The fuel injection control unit 82 is also connected to an intake air volume measurement unit 87 that measures the intake volume of air taken into the cylinder 150, a load information generation unit 88 that measures the engine load, and a water temperature measurement unit 89 that measures the temperature of the engine coolant. The fuel injection control unit 82 receives intake air volume information S6 from the intake air volume measurement unit 87, engine load information S7 from the load information generation unit 88, and coolant temperature information S8 from the water temperature measurement unit 89.

Based on the received information, the fuel injection control unit 82 calculates the amount and duration of fuel injected from the fuel injection device 134. The fuel injection control unit 82 then transmits a fuel injection pulse S9 generated based on the calculated amount and duration of fuel injection to the fuel injection device 134.

[Ignition control unit]
The ignition control unit 83 is connected to the overall control unit 81, as well as to a cylinder discrimination unit 84, an angle information generation unit 85, a rotation speed information generation unit 86, a load information generation unit 88, and a water temperature measurement unit 89, and receives information from each of these.

Based on the received information, the ignition control unit 83 calculates the amount of current to be passed through the primary coil 310 (see Figure 5) of the ignition coil 300, the time when current begins to flow (current angle), and the time when the current passed through the primary coil 310 is cut off (ignition time).

The ignition control unit 83 performs discharge control (ignition control) by the spark plug 200 by outputting an ignition signal SA to the primary coil 310 of the ignition coil 300 based on the calculated amount of current, the start time of current flow, and the ignition time.

[Electrode temperature, minimum ignition energy and air-fuel ratio]
Next, the relationship between the electrode temperature of the spark plug 200, the minimum ignition energy, and the air-fuel ratio will be described with reference to FIG.
FIG. 4 is a diagram illustrating the relationship between the electrode temperature, the minimum ignition energy, and the air-fuel ratio.

Figure 4 shows the air-fuel ratio values corresponding to the minimum ignition energy values. In Figure 4, the up-down direction indicates the voltage scale value corresponding to the minimum ignition energy of the mixture, and the left-right direction indicates the air-fuel ratio scale value corresponding to the air-fuel ratio of the mixture. The air-fuel ratio P1 shown in Figure 4 is the air-fuel ratio value corresponding to a predetermined value of the minimum ignition energy that can ignite the mixture when the electrode temperature of the ignition plug is low (e.g., minus 7 deg C). On the other hand, the air-fuel ratio P2 is the air-fuel ratio value corresponding to a predetermined value of the minimum ignition energy that can ignite the mixture when the electrode temperature of the ignition plug is high (e.g., 25 deg C).

As shown in Figure 4, in the internal combustion engine 100, the higher the air-fuel ratio (the leaner the fuel), the higher the value of the minimum ignition energy of the mixture, making it more difficult to ignite the mixture by discharge (ignition) from the spark plug. Also, the lower the electrode temperature of the spark plug, the higher the value of the minimum ignition energy of the mixture, making it more difficult to ignite the mixture by discharge (ignition) from the spark plug.

For example, suppose that a value equivalent to the minimum ignition energy corresponding to the air-fuel ratio P2 when the electrode temperature of the spark plug is high is obtained when the electrode temperature of the spark plug is low. In this case, the discharge (ignition) from the spark plug 200 cannot exceed the minimum ignition energy unless the air-fuel ratio is set to an air-fuel ratio P1, which is a value smaller (richer) than the air-fuel ratio P2. Therefore, in the past, a rich air-fuel ratio (P1) was set in the fuel injection control unit 82 on the assumption that the electrode temperature of the spark plug 200 was always low, as a setting with a safety margin that would not cause problems such as misfires in the internal combustion engine 100. As a result, in the internal combustion engine 100, the amount of hydrocarbons (HC) generated during combustion increased as the proportion of fuel in the mixture increased.

On the other hand, the higher the electrode temperature of the spark plug 200 during cold start (see the thick arrow in Figure 4), the lower the minimum ignition energy required to ignite the mixture. Therefore, even if the air-fuel ratio is increased (the fuel is diluted), the discharge (ignition) from the spark plug exceeds the minimum ignition energy, making it possible to ignite the mixture. As a result, the generation of hydrocarbons (HC) in the internal combustion engine 100 can be reduced. Therefore, in the internal combustion engine 100, the electrode temperature of the spark plug 200 during cold start is increased before discharge (ignition), as described below. This increases the air-fuel ratio during cold start, suppressing the generation of hydrocarbons (HC).

[Electrical circuit including ignition coil]
Next, an electric circuit including the ignition coil will be described with reference to FIG.
FIG. 5 is a diagram illustrating an electric circuit including an ignition coil.

The electric circuit 500 shown in Figure 5 has an ignition coil 300. The ignition coil 300 is composed of a primary coil 310 wound with a predetermined number of turns and a secondary coil 320 wound with a greater number of turns than the primary coil 310.

One end of the primary coil 310 is connected to a DC power supply 330. This allows a predetermined voltage (e.g., 12 V) to be applied to the primary coil 310. The other end of the primary coil 310 is connected to the drain (D) terminal of an igniter (current control circuit) 340, and is grounded via the igniter 340. The igniter 340 may be a transistor or a field effect transistor (FET).

The gate (G) terminal of the igniter 340 is connected to the ignition control unit 83 via the temperature switch unit 350. The temperature switch unit 350 is installed to prevent damage due to overheating of the ignition coil 300. The temperature switch unit 350 includes a temperature detection unit 351. The temperature detection unit 351 detects the temperature of the ignition coil 300 via the igniter 340. When the temperature detected by the temperature detection unit 351 becomes equal to or higher than a predetermined threshold value A (first temperature), the temperature switch unit 350 cuts off the ignition signal SA output from the ignition control unit 83 to the igniter 340.

When the temperature switch unit 350 cuts off the ignition signal SA, the current to the primary coil 310 is stopped, thereby preventing the igniter 340 from overheating. When the temperature detected by the temperature detection unit 351 is less than the first temperature, the ignition signal SA output from the ignition control unit 83 is input to the gate (G) terminal of the igniter 340.

When an ignition signal SA is input to the gate (G) terminal of the igniter 340, the drain (D) terminal and the source (S) terminal of the igniter 340 are energized, and a current flows between the drain (D) terminal and the source (S) terminal. This causes the ignition signal SA to be output from the ignition control unit 83 to the primary coil 310 of the ignition coil 300 via the igniter 340. As a result, a current flows through the primary coil 310, and power (electrical energy) is accumulated.

When the output of the ignition signal SA from the ignition control unit 83 stops, the current flowing through the primary coil 310 is interrupted. As a result, a high voltage corresponding to the ratio of the number of turns of the coil to the primary coil 310 is generated in the secondary coil 320.

The high voltage generated in the secondary coil 320 is applied to the center electrode 210 (see FIG. 2) of the spark plug 200. This generates a potential difference 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 exceeds the breakdown voltage Vm of the surrounding gas (air-fuel mixture in the cylinder 150), the gas components undergo dielectric breakdown and a discharge occurs between the center electrode 210 and the outer electrode 220. As a result, the fuel (air-fuel mixture) is ignited. The spark plug 200 and the electric circuit 500 having the ignition coil 300 correspond to the ignition device according to the present invention.

The discharge path generated between the center electrode 210 and the outer electrode 220 reaches a high temperature of several thousand degrees Celsius. Because the discharge path is in contact with the surrounding gas and the electrodes 210, 220, the heat energy of the discharge is distributed to the surrounding gas and the electrodes 210, 220. The heat energy distributed to the surrounding gas heats (preheats) the surrounding gas and the electrodes 210, 220, promoting ignition.

[Discharge waveform of multiple ignition]
Next, the discharge waveform of the multiple ignition will be described with reference to FIG.
FIG. 6 shows an example of a discharge waveform for multiple ignition.

As shown in Figure 6, by repeatedly turning the ignition signal ON and OFF, multiple discharges are added to perform multiple ignitions. This allows the temperature of the electrodes 210, 220 of the spark plug 200 to be increased before the discharge (ignition) that preheats the electrodes of the spark plug 200. This multiple ignition due to additional discharge can be performed at a timing that does not overlap with the ignition timing of the main ignition. In other words, multiple ignition due to additional discharge can be performed at least in the period from after the ignition (start of discharge) of the main ignition to the start of fuel injection (the period from the expansion stroke to the intake stroke in the embodiment of Figure 6).

[Air-fuel ratio and required ignition energy]
Next, the number of misfires and the amount of hydrocarbon emissions will be described with reference to FIGS.
Fig. 7 is a diagram for explaining the relationship between the number of misfires counted in 15 seconds and the amount of hydrocarbon emission (accumulated mass) emitted in the same 15 seconds. Fig. 8 is a diagram showing the relationship between the number of misfires counted in the period from the start of the internal combustion engine to the time 60 seconds have elapsed and the multiple ignition period (heating period) due to additional discharge executed in the same period. Fig. 9 is a diagram showing the relationship between the cumulative mass of hydrocarbons emitted from the start of the internal combustion engine to the time 60 seconds have elapsed and the heating period.

As shown in Figure 7, there is a one-dimensional correlation between the number of misfires and the amount of hydrocarbon emissions. In other words, the main cause of hydrocarbon generation is misfire. Misfires occur when the flame kernel generated by ignition is unable to grow and goes out. In order to grow the flame kernel and suppress the generation of hydrocarbons (HC), it is necessary to suppress misfires.

In order to grow the flame kernel and suppress misfires, it is necessary to suppress the amount of heat transferred (escaping) from the surrounding gas in the discharge path facing the electrodes 210, 220 of the spark plug 200 and the flame kernel to the electrodes 210, 220. For example, if multiple ignition is performed in the ignition device to preheat the electrodes 210, 220 of the spark plug 200, the temperature difference between the discharge path and the flame kernel and the electrodes 210, 220 is reduced. As a result, the amount of heat transferred from the discharge path and the flame kernel to the electrodes 210, 220 can be suppressed.

As shown by the dashed line in Figure 8, there is an inverse proportional relationship between the heating period of the electrodes 210, 220 and the number of misfires, and the longer the heating period, the more the number of misfires can be reduced. The temperature of the electrodes 210, 220 changes depending on the ambient temperature. Therefore, the higher the ambient temperature, the higher the temperature of the electrodes 210, 220 of the spark plug 200. Therefore, as shown in Figure 8, the number of misfires when the ambient temperature is 80 degC is lower than the number of misfires when the ambient temperature is 20 degC. And, as shown by the dashed line in Figure 9, the longer the heating period and the higher the ambient temperature, the more the amount of hydrocarbon emissions can be reduced.

[Ignition signal frequency and ignition coil temperature]
Next, the relationship between the frequency of the ignition signal SA and the temperature of the ignition coil will be described with reference to FIGS.
Fig. 10 is a diagram showing the transition when multiple ignition and main ignition are executed. Fig. 11 is a conceptual diagram showing the relationship between the amount of heat generated and ignitability with respect to the frequency of the ignition signal. Fig. 12 is a conceptual diagram showing the relationship between the transition time and the temperature of the ignition coil in the case where multiple ignition is performed and in the case where multiple ignition is not performed. Fig. 13 is a timing chart showing the change in temperature of a conventional ignition coil and the HC concentration.

The purpose of the multiple ignition performed in this embodiment is to preheat the electrodes of the spark plug 200 before the main ignition. Therefore, multiple ignition is performed before the main ignition. Multiple ignition can also be considered preheating ignition. As shown in FIG. 10, main ignition can improve ignition performance by increasing the ignition energy per discharge. On the other hand, preheating by multiple ignition can improve the amount of electrode heating by increasing the discharge duration per unit time.

As shown in FIG. 10, the main ignition is set so that the ignition energy per discharge is equal to or greater than the breakdown voltage Vm described above. This causes a discharge between the center electrode 210 and the outer electrode 220, and ignites the mixture (flame kernel formation). On the other hand, the multiple ignition (preheat ignition) performed in this embodiment is intended to cause a discharge between the center electrode 210 and the outer electrode 220 before the main ignition, thereby preheating the electrodes 210, 220 of the spark plug 200. Therefore, the multiple ignition (preheat ignition) is performed chronologically earlier than the main ignition.

In multiple ignition (preheating ignition), the amount of power conversion of the ignition coil 300 is increased by repeatedly performing multiple ignitions (discharges), thereby increasing the duration of discharge per unit time. This allows the amount of heating (preheating) of the electrodes 210, 220 to be increased. Therefore, in multiple ignition (preheating ignition), the switching frequency of the ignition signal SA needs to be set higher than in main ignition. That is, the ignition control unit 83 (see FIG. 3) outputs a low-frequency main ignition signal for executing main ignition and a high-frequency multiple ignition signal for executing multiple ignition (preheating ignition). Thus, as shown in FIG. 11, increasing the frequency of the ignition signal SA increases the amount of heat generated by the electrodes 210, 220 of the ignition plug 200. As a result, the ignition ability of the ignition plug 200 is improved.

As described above, in order to reduce hydrocarbons during cold start, it is necessary to perform multiple ignition (preheating ignition) to preheat the electrodes 210, 220 during the period until the internal combustion engine warms up (for example, about 60 seconds after the internal combustion engine is started). However, as shown in FIG. 12, the amount of heat generated by the ignition coil 300 due to multiple ignition (preheating ignition) is greater than that due to main ignition. For this reason, when performing multiple ignition (preheating ignition), as shown in FIG. 13, when the temperature of the ignition coil 300 detected by the temperature detection unit 351 (see FIG. 5) (hereinafter referred to as the "coil temperature") reaches a predetermined threshold A (first temperature), it is preferable to cut off the multiple ignition signal from the ignition control unit 83 to the igniter 340 to adjust the amount of heat generated.

[Electrical circuit including ignition coil]
Next, an electric circuit including an ignition coil according to the present invention will be described with reference to FIG.
FIG. 14 is a circuit diagram showing an example of an electric circuit including an ignition coil according to the present invention.

As shown in Fig. 14, the electric circuit 501 according to the present invention has an ignition coil 300. The ignition coil 300 includes a primary coil 310 wound with a predetermined number of turns, and a secondary coil 320 wound with a greater number of turns than the primary coil 310.

One end of the primary coil 310 is connected to a DC power supply 330. This allows a predetermined voltage (e.g., 12 V) to be applied to the primary coil 310. The other end of the primary coil 310 is connected to the drain (D) terminal of an igniter (current control circuit) 340, and is grounded via the igniter 340. The igniter 340 may be a transistor or a field effect transistor (FET).

The gate (G) terminal of the igniter 340 is connected to the ignition control unit 83 via the temperature switch unit 360 or the temperature switch unit 360 and the filter unit 370. The filter unit 370 is, for example, a low-pass filter. The filter unit 370 passes the main ignition signal, which is a low frequency. The filter unit 370 blocks the multiple ignition signal, which is a high frequency.

The temperature switch unit 360 is installed for the purpose of regulating the temperature of the ignition coil 300. The temperature switch unit 360 is equipped with a temperature detection unit 351. The temperature switch unit 360 switches the connection destination depending on the range of the coil temperature detected by the temperature detection unit 351 (low temperature range, medium temperature range, high temperature range).

The medium temperature range is a range equal to or higher than the above-mentioned threshold A (first temperature) and lower than a predetermined threshold B (second temperature). When the coil temperature is in the medium temperature range, the temperature switch unit 360 connects the ignition control unit 83 and the igniter 340 via the filter unit 370. As a result, the multiple ignition signal, which is a high frequency signal output from the ignition control unit 83, is blocked by the filter unit 370. On the other hand, the main ignition signal, which is a low frequency signal output from the ignition control unit 83, passes through the filter unit 370 and is transmitted to the igniter 340.

The high temperature range is a range above the threshold B (second temperature) and below the upper limit of the rated design temperature of the ignition coil 300. When the coil temperature is in the high temperature range, the temperature switch unit 360 disconnects the ignition control unit 83 from the igniter 340. As a result, the multiple ignition signal and the main ignition signal output from the ignition control unit 83 are not transmitted to the igniter 340.

The low temperature range is a range below the threshold A (first temperature) described above. When the coil temperature is in the low temperature range, the temperature switch unit 360 directly connects the ignition control unit 83 to the igniter 340. As a result, the multiple ignition signal and the main ignition signal output from the ignition control unit 83 are transmitted to the igniter 340.

That is, in the low temperature range, the coil temperature is lower than in the medium or high temperature range, and the temperature difference (temperature margin) from the upper limit of the rated temperature designed for the ignition coil 300 is large. Therefore, in addition to the main ignition for igniting the mixture, multiple ignition (preheating ignition) in which the ignition coil 300 generates a large amount of heat can be performed. Moreover, in this embodiment, the coil temperature is accurately detected by the temperature detection unit 351, and multiple ignition (preheating ignition) is performed until the coil temperature reaches the medium temperature range where the temperature is equal to or higher than the threshold value B (second temperature). This minimizes the temperature margin from the upper limit of the rated temperature and makes it possible to set the period for performing multiple ignition as long as possible, compared to performing multiple ignition (preheating ignition) in the estimated low temperature range without providing the temperature detection unit 351.

Thus, when the coil temperature detected by the temperature detection unit 351 is less than the threshold B (second temperature), the ignition signal SA (main ignition signal only, or main ignition signal and multiple ignition signal) output from the ignition control unit 83 is input to the gate (G) terminal of the igniter 340 via the temperature switch unit 360. When the ignition signal SA is input to the gate (G) terminal of the igniter 340, the drain (D) terminal and the source (S) terminal of the igniter 340 are energized, and a current flows between the drain (D) terminal and the source (S) terminal. As a result, the ignition 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, a current flows in the primary coil 310 and power (electrical energy) is accumulated.

When the output of the ignition signal SA from the ignition control unit 83 stops, the current flowing through the primary coil 310 is interrupted. As a result, a high voltage corresponding to the ratio of the number of turns of the coil to the primary coil 310 is generated in the secondary coil 320.

The high voltage generated in the secondary coil 320 is applied to the center electrode 210 (see FIG. 2) of the spark plug 200. This generates a potential difference 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 exceeds the breakdown voltage Vm of the surrounding gas (air-fuel mixture in the cylinder 150), the gas components undergo dielectric breakdown and a discharge occurs between the center electrode 210 and the outer electrode 220. As a result, the fuel (air-fuel mixture) is ignited. The spark plug 200 and the electric circuit 500 having the ignition coil 300 correspond to the ignition device according to the present invention.

The ignition control unit 83 has an energization control circuit 831 and an output monitor circuit 832. The energization control circuit 831 controls the output of the ignition signal SA. The output monitor circuit 832 corresponds to a return detection function that detects the ignition signal SA output from the energization control circuit 831 as a return signal, and transmits the detection result of the return signal to the energization control circuit 831.

The current control circuit 831 transmits the output state of the ignition signal SA and the detection result of the return signal corresponding to the ignition signal SA to the overall control unit 81 (see FIG. 3). The overall control unit 81 compares the output state of the ignition signal SA with the detection result of the return signal, and if the states of the ignition signal SA and the return signal are different, it determines that the multiple ignition signal and the overheat detection signal described below have been blocked in the filter unit 370. Furthermore, if the ignition signal SA and the return signal are the same, the overall control unit 81 determines that the multiple ignition signal and the overheat detection signal have not been blocked in the filter unit 370.

As described above, in cold start, in order to reduce hydrocarbons, multiple ignition must be performed until the internal combustion engine has finished warming up (for example, for a period of about 60 seconds). However, in multiple ignition (preheating ignition), the amount of heat generated by the ignition coil 300 is greater than in normal ignition, so the actual temperature of the ignition coil 300 reaches the medium temperature range in a relatively short time. Then, when the actual temperature of the ignition coil 300 reaches the medium temperature range, the temperature switch unit 360 cuts off the transmission of the multiple ignition signal to the igniter 340.

Therefore, in this embodiment, as described above, it is determined whether the main ignition signal or the multiple ignition signal has been blocked in the filter unit 370. Furthermore, based on the determination result, it detects the point in time when the actual temperature of the ignition coil 300 reaches the medium temperature range and only the multiple ignition signal is blocked, or the point in time when the actual temperature of the ignition coil 300 returns to the low temperature range and the main ignition signal and the multiple ignition signal are again transmitted to the igniter 340. Then, the coil temperature of the temperature detection unit 351 is calibrated by assuming that the coil temperature at the detected point is threshold value A (first temperature).

When the multiple ignition (preheating ignition) of the spark plug 200 is stopped, the ignition coil 300 is cooled due to the temperature difference with its surroundings (see FIG. 13). As a result, the temperature detected by the temperature detection unit 351 returns to the low temperature range. In the low temperature range, the temperature switch unit 360 selects a path for transmitting the ignition signal SA to the igniter 340 without passing through the filter unit 370. As a result, the main ignition signal and the multiple ignition signal are transmitted to the igniter 340 again. Therefore, multiple ignition can be repeated while suppressing misfires, and the generation of hydrocarbons can be suppressed.

Next, fuel injection control will be described. For example, the fuel injection amount after warming up an internal combustion engine that is not cold started is T. During cold start, the amount of fuel vaporized by the main ignition timing is reduced due to the low temperature in the cylinder, so the amount of fuel involved in the combustion after ignition is reduced. As a result, in order to compensate for the lean air-fuel ratio of the mixture in the cylinder, the fuel injection amount is increased during cold start compared to the injection amount T after warming up. If this increase is a, the fuel injection amount during cold start is T+a. Then, by performing multiple ignition (preheating ignition) in the low temperature range during cold start, the amount of fuel vaporized by the main ignition timing and involved in the combustion after ignition is substantially increased. If the contribution of this multiple ignition (preheating ignition) is b1, the fuel injection amount when multiple ignition is performed is T+a-b1.

When the coil temperature reaches the medium temperature range, multiple ignition is discontinued and only main ignition is performed, the value of the contribution b1 of the above-mentioned multiple ignition (preheat ignition) is reduced, for example, to b2 (b2 < b1). Then, when multiple ignition is performed, the fuel amount is increased by the amount reduced, and the fuel injection amount is set to T + a - b2. This makes it possible to prevent misfires by suppressing the increase in the minimum ignition energy of the mixture that accompanies a decrease in the temperature of the electrodes 210, 220 (see Figure 4). As a result, it is possible to suppress the generation of hydrocarbons overall.

It is also possible to configure the temperature of the electrodes 210, 220 of the spark plug 200 to be inferred based on the coil temperature detected by the temperature detection unit 351 described above, or on the operating state of the internal combustion engine 100, such as the water temperature or the intake air temperature. For example, the temperature of the electrodes 210, 220 at the time when the coil temperature reaches the medium temperature range and the multiple ignition is interrupted is set based on the above-mentioned threshold A (first temperature). Then, based on the elapsed time since the multiple ignition was interrupted or the progress of the combustion cycle (such as the number of times the main ignition was performed), the temperature of the electrodes 210, 220 is inferred to be gradually lowered.

[Multiple ignition switching process]
Next, the multiple ignition switching process according to this embodiment will be described with reference to FIG.
FIG. 15 is a flowchart showing an example of a multiple ignition switching process.

When the multiple ignition switching process is started, the temperature detection unit 351 acquires the coil temperature of the ignition coil 300. Then, the temperature switch unit 360 determines whether the coil temperature detected by the temperature detection unit 351 is equal to or higher than a predetermined threshold value B (second temperature) (S110).

When it is determined in step S110 that the coil temperature is equal to or higher than the predetermined threshold value B (YES in S110), the temperature switch unit 360 selects a path (circuit) that cuts off all ignition signals SA (S120). As a result, the ignition signal SA output from the ignition control unit 83 is not transmitted to the igniter 340, and ignition (ignition) by the spark plug 200 is stopped. After processing in step S120, the ignition device (electrical circuit 501) moves the process to step S110.

On the other hand, when it is determined in step S110 that the coil temperature is not equal to or higher than the predetermined threshold value B (if S110 is determined as NO), the temperature switch unit 360 determines whether the coil temperature is equal to or higher than the predetermined threshold value A (first temperature) (S130).

When it is determined in step S130 that the coil temperature is equal to or higher than the predetermined threshold A (YES in S130), the temperature switch unit 360 selects a path through which the ignition signal SA passes through the filter unit 370 (S140). This causes the multiple ignition signals in the ignition signal SA to be blocked by the filter unit 370, and only the main ignition signal is transmitted to the igniter 340. As a result, in the ignition plug 200, multiple ignition for the purpose of preheating is not performed, and only main ignition is performed. After processing in step S140, the ignition device proceeds to step S110.

On the other hand, when it is determined in step S130 that the coil temperature is not equal to or higher than the predetermined threshold A (if S130 is a NO determination), the temperature switch unit 360 selects a path for transmitting the ignition signal SA to the igniter 340 without passing through the filter unit 370 (S150). This causes the multiple ignition signal and main ignition signal in the ignition signal SA to be transmitted to the igniter 340. As a result, in the ignition plug 200, multiple ignition for the purpose of preheating and main ignition are performed. After processing in step S150, the ignition device proceeds to step S110.

[Fuel injection amount switching process]
Next, the fuel injection amount switching process according to this embodiment will be described with reference to FIG.
FIG. 16 is a flowchart showing an example of the fuel injection amount switching process.

When the fuel injection amount switching process is started, the overall control unit 81 (see FIG. 3) acquires the time that has elapsed since the start of the internal combustion engine to the present. The overall control unit 81 then determines whether the time that has elapsed since the start to the present is within a predetermined value (S210). The predetermined value corresponds to the period until the warm-up described above is completed.

When it is determined in step S210 that the time elapsed from start-up to the present is not within a predetermined value (if S210 is determined as NO), the overall control unit 81 terminates the fuel injection amount switching process (S220).

On the other hand, when it is determined in step S210 that the time elapsed from the start to the present is within a predetermined value (if S210 is determined as YES), the overall control unit 81 outputs an ignition signal SA including multiple ignition signals (S230). Next, the overall control unit 81 determines whether the ignition signal SA and the return signal obtained from the output monitor circuit 832 are different (S240).

When it is determined in step S240 that the ignition signal SA and the return signal are different (YES in S240), the overall control unit 81 sets the fuel injection amount to the first fuel injection amount (S250). When the ignition signal SA and the return signal are different, the overall control unit 81 determines that the filter unit 370 has blocked the multiple ignition signal. When the filter unit 370 has blocked the multiple ignition signal, the ignition coil 300 is equal to or higher than the threshold A (first temperature). After processing step S250, the overall control unit 81 moves the process to step S210.

On the other hand, when it is determined in step S240 that the ignition signal SA and the return signal match (if S240 is a NO determination), the overall control unit 81 sets the fuel injection amount to the second fuel injection amount (S260). When the ignition signal SA and the return signal match, the overall control unit 81 determines that the multiple ignition signal has been transmitted to the igniter 340. After processing step S260, the overall control unit 81 proceeds to step S210.

The first fuel injection amount is the fuel injection amount when the multiple ignition signal is blocked during cold start. The first fuel injection amount corresponds to T+a described above. On the other hand, the second fuel injection amount is the fuel injection amount when the multiple ignition signal is transmitted to the igniter 340 during cold start. The second fuel injection amount corresponds to T+a-bn (n=1, 2) described above. Therefore, the second fuel injection amount is less than the first fuel injection amount.

[Multiple ignition switching process]
Next, the multiple ignition switching process according to this embodiment will be described with reference to FIG.
FIG. 17 is a timing chart showing the multiple ignition switching process.

To improve ignition performance, it is effective to keep the flame kernel generated by the spark discharge warm. In order to keep the flame kernel warm, it is necessary to raise the temperature of the electrode in contact with the flame kernel. As mentioned above, preheating through multiple ignition (discharge) can improve the amount of electrode heating by increasing the discharge duration per unit time. On the other hand, increasing the ignition energy through multiple ignition increases power consumption, which also affects fuel efficiency.

To mitigate the trade-off between improved ignition performance and increased power consumption, a method is needed to efficiently raise the temperature of the electrodes without unnecessarily increasing the ignition energy of multiple ignition. For example, by shortening the interval between multiple ignitions as much as possible within the range in which the discharge is sustained (making it high frequency), the discharge duration per unit time can be extended, and the time it takes for the electrodes 210, 220 to cool between the discharges of the multiple ignitions can be shortened as much as possible (see the first row of Figure 17). As a result, the heating efficiency of multiple ignitions can be improved, and the temperature of the electrodes after the discharge period can be efficiently raised.

A typical passive ignition coil has the function of storing a certain amount of charge. Therefore, the amount of charge increases up to a certain charging time. As the amount of charge increases, the output voltage and output current during discharge increase, and the electrodes 210, 220 are strongly heated. Therefore, by outputting a low-frequency pre-charge pulse (pre-charge signal) with sufficient pre-charging immediately before outputting a high-frequency multiple discharge pulse (multiple ignition signal) for multiple ignition, the temperature of the electrodes 210, 220 can be further increased while keeping the interval between multiple ignitions as high frequency as possible as described above (see the second row of Figure 17). In other words, the pre-charge pulse is a current waveform that has a lower frequency than the multiple discharge pulse and has an output period that ensures that the capacitive discharge of the ignition coil works reliably.

Incidentally, the electric circuit 501 including the ignition coil 300 described above cuts only the high-frequency components of the ignition signal SA when the temperature of the ignition coil 300 is equal to or higher than the threshold A (first temperature). Therefore, the electric circuit 501 continues the low-frequency pre-charge signal even when the temperature of the ignition coil 300 is equal to or higher than the threshold A (first temperature). As a result, high-frequency multiple ignition is not possible (the multiple ignition signal is cut), and the heating efficiency of the electrodes 210, 220 is reduced.

As described above, the control device (ECU) 1 has a return detection function (output monitor circuit 832) that performs self-diagnosis of the ignition signal SA output to the ignition coil 300. This return detection function allows the control device 1 to detect the cutting of high-frequency components performed by the electric circuit 501 in the high-temperature range or medium-temperature range of the ignition coil 300. Thus, by detecting the cutting of high-frequency components, the control device 1 recognizes that the temperature state of the ignition coil 300 is above threshold A (first temperature) and cuts off the output of the pre-charge pulse and the multiple discharge pulse following the pre-charge pulse from the ignition signal SA. In other words, the control device 1 outputs only the main ignition signal when the coil temperature is above threshold A (first temperature). As a result, the amount of heat generated by the ignition coil 300 can be suppressed.

However, when the control device 1 is in a state where only the main ignition signal is output, it cannot detect the cutting of high-frequency components by the electric circuit 501. Therefore, even if the temperature state of the ignition coil 300, which has once risen, converges to below threshold A (first temperature), the control device 1 may not be able to resume output of the multiple ignition signal. Therefore, after the coil temperature reaches or exceeds threshold A (first temperature) and the control device 1 transitions to a state where only the main ignition signal is output, it outputs an overheat detection pulse (overheat detection signal) (see the third row of Figure 17).

The overheat detection pulse is at least one high-frequency pulse (single pulse). This can reduce unnecessary charging and unnecessary signal output operations. The frequency of the overheat detection pulse is set to a frequency band that exceeds the rated frequency at which the filter unit 370 of the electric circuit 501 cuts off the ignition signal SA, while being in a range in which the return signal of the ignition signal SA can be detected by the return detection function (output monitor circuit 832) of the control device 1. As a result, the overheat detection pulse is cut by the filter unit 370 in the medium temperature range, and is not cut by the filter unit 370 in the low temperature range. Therefore, the control device 1 can correctly recognize the temperature state of the ignition coil 300 by detecting whether the overheat detection pulse is cut by the filter unit 370 using the return detection function (see the fourth row of FIG. 17).

When the control device 1 recognizes that the coil temperature is below the threshold A (first temperature), it resumes output of the ignition signal SA, which includes the pre-charge signal and the multiple ignition signal (see the fifth row in FIG. 17). After resuming output of the pre-charge signal and the multiple ignition signal, it stops outputting the overheat detection pulse (see the fifth row in FIG. 17). This makes it possible to reduce the amount of heat generated by the ignition coil 300 while reducing the computational load of the control device 1 and the burden on the ignition control unit 83.

The phase of the overheat detection pulse is set to a timing that is later than the previous main ignition signal and before the next pre-charge signal, and that ensures the time required for switching the ignition signal of the control device 1. The time required for switching the ignition signal is the sum of the time required for the control device 1 to output the overheat detection pulse, detect the return signal of the overheat detection pulse, and determine whether pre-charging can be performed. This allows the control device 1 to switch the output of the pre-charge pulse and multiple discharge pulses within a cycle.

In addition, the phase of the overheat detection pulse should be as late as possible within the period in which the time required for the above-mentioned ignition signal switching can be secured. In other words, the overheat detection pulse should be output at a time during the internal combustion engine stroke that is earlier than the planned timing for outputting the above-mentioned pre-charge signal by the time required for the ignition signal switching (see rows 3 to 5 in FIG. 17). This allows the return signal of the overheat detection pulse to reflect the most recent (most recent) state of the temperature of the ignition coil 300 due to the previous main ignition signal, shortening the delay in switching the ignition signal and enabling the pre-charge pulse and multiple discharge pulse output to be implemented efficiently.

The overheat detection pulse may be output at each predetermined cycle of the combustion cycle of the internal combustion engine. For example, when the temperature of the ignition coil 300 exceeds the threshold value B (second temperature) (high temperature range) and the main ignition signal is cut off, the output of the pre-charge pulse, the multiple discharge pulse, and the main ignition signal from the control device 1 is stopped (not shown), and only the overheat detection pulse is output (intermittently) at regular intervals. This reduces the computational load of the control device 1 and the load of the ignition control unit 83, and it is possible to quickly detect that the temperature of the ignition coil 300 has dropped and the mixture can be ignited again. In addition, such output control of the overheat detection pulse at regular intervals (intermittent) can be performed asynchronously with the combustion cycle when the internal combustion engine is stopped by the idle stop control described later.

[Fuel injection amount switching process]
Next, the fuel injection amount switching process according to this embodiment will be described with reference to FIG.
FIG. 18 is a flowchart showing an example of the fuel injection amount switching process.

When the fuel injection amount switching process is started, the overall control unit 81 (see FIG. 3) of the control device 1 acquires the time that has elapsed since the start of the internal combustion engine to the present. The overall control unit 81 then determines whether the time that has elapsed since the start to the present is within a predetermined value (S310). The predetermined value corresponds to the period until the warm-up described above is completed.

When it is determined in step S310 that the time elapsed from start-up to the present is not within a predetermined value (if S310 is determined as NO), the overall control unit 81 terminates the fuel injection amount switching process (S320).

On the other hand, when it is determined in step S310 that the time elapsed from start-up to the present is within a predetermined specified value (if S310 is determined to be YES), the overall control unit 81 outputs an ignition signal SA including a pre-charge signal and a multiple ignition signal (S330).

Next, the overall control unit 81 determines whether the multiple ignition signal portion of the ignition signal SA is different from the portion of the return signal obtained from the output monitor circuit 832 that corresponds to the multiple ignition signal (S340). If it is determined in step S340 that the ignition signal SA and the return signal are different, the overall control unit 81 determines that the filter unit 370 has blocked the multiple ignition signal. As described above, when the filter unit 370 has blocked the multiple ignition signal, the coil temperature of the ignition coil 300 is at least equal to or higher than the threshold A (first temperature).

When it is determined in step S340 that the ignition signal SA and the return signal are different (if S340 is determined as YES), the overall control unit 81 sets the fuel injection amount to the first fuel injection amount (S350).

Next, the overall control unit 81 turns off the pre-charge signal and the multiple ignition signal, and turns on the overheat detection pulse (overheat detection signal) (step S360). That is, the overall control unit 81 stops outputting the pre-charge signal and the multiple ignition signal, and outputs the overheat detection signal. By the overall control unit 81 stopping outputting the pre-charge signal and the multiple ignition signal, the amount of heat generated by the ignition coil 300 can be reduced, and the coil temperature can be lowered.

Next, the overall control unit 81 determines whether the overheat detection signal portion of the ignition signal SA and the portion of the return signal corresponding to the above-mentioned overheat detection signal are different (S370). If it is determined in step S370 that the ignition signal SA and the return signal are different, the overall control unit 81 determines that the filter unit 370 has blocked the overheat detection pulse. If the filter unit 370 has blocked the overheat detection pulse, the coil temperature of the ignition coil 300 is still equal to or higher than the threshold A (first temperature).

When it is determined in step S370 that the ignition signal SA and the return signal are different (YES in S370), the overall control unit 81 repeats step S370. That is, the overall control unit 81 repeats step S370 until the coil temperature becomes less than the threshold A (first temperature).

On the other hand, when it is determined in step S370 that the ignition signal SA and the return signal match (if S370 returns NO), the overall control unit 81 determines that the coil temperature is below the threshold A (first temperature). Then, the overall control unit 81 stops outputting the overheat detection pulse and outputs the pre-charge signal and the multiple ignition signal (S380).

After processing step S380, or when it is determined in step S340 that the ignition signal SA and the return signal match (if S340 is a NO determination), the overall control unit 81 sets the fuel injection amount to the second fuel injection amount (S390). After processing step S390, the overall control unit 81 proceeds to step S310.

[Period during which multiple ignitions can be performed]
Next, the period during which multiple ignition according to this embodiment can be performed will be described with reference to FIG.
FIG. 19 is a timing chart showing the relationship between the operating state of an engine (internal combustion engine) mounted on a typical automobile and the multiple ignition permitted period.

Some recent engine (internal combustion engine) controls are equipped with idle stop control. When idle stop control is implemented, the engine stops when the vehicle is stopped, resulting in an increase in the number of engine starts. On the other hand, the lower the temperature of the electrodes immediately before multiple ignition is performed, the greater the difference in electrode temperature between when multiple ignition is performed and when it is not. Therefore, the lower the temperature of the electrodes immediately before multiple ignition is performed, the greater the heat retention effect of the flame kernel when multiple ignition is performed. For this reason, it is desirable to perform multiple ignition when the electrodes are cold when the engine is started or restarted.

Specifically, by performing multiple ignitions after the initial or re-initial explosion following the start of fuel injection, as well as for a certain period of time before the initial explosion, it is possible to expect a further increase in the temperature of the electrode. Note that, since no combustion occurs before the start of fuel injection, it is possible to perform continuous multiple ignitions (multiple discharge control) specifically aimed at increasing the temperature of the electrode.

However, consecutive multiple ignitions generate more heat than multiple ignitions after fuel injection. For this reason, if the period during which consecutive multiple ignitions are performed is extended, the ignition coil 300 will overheat before the start of fuel injection. As a result, multiple ignitions cannot be performed after the start of fuel injection. Therefore, it is advisable to estimate the temperatures of the ignition coil 300 and the electrodes 210, 220 from the engine's operating history, outside air temperature, cooling water temperature, etc., and to determine in advance the periods during which multiple ignitions are performed before and after the start of fuel injection.

In particular, during a cold start in cold regions, the temperatures of the ignition coil 300 and the electrodes 210, 220 become sufficiently low. Therefore, it is possible to start multiple ignition before the engine starts rotating. In this case, since there is no air flow inside the cylinder, a high temperature rise effect can be expected from multiple ignition.

[Relationship between ignition performance, equivalence ratio, and multiple ignition]
Next, the relationship between the ignition performance, the equivalence ratio, and the multiple ignition according to this embodiment will be described with reference to FIG.
FIG. 20 is a correlation graph showing the relationship between the equivalence ratio and the minimum ignition energy.

The horizontal axis of the graph shown in Figure 20 is the equivalence ratio of the mixture. The equivalence ratio indicates the mass ratio of air to fuel. When the equivalence ratio is large, the fuel becomes rich, and when the equivalence ratio is small, the fuel becomes lean. And when the equivalence ratio is 1, it is the theoretical air-fuel ratio.

The vertical axis of the graph shown in Figure 20 is the minimum ignition energy for main ignition. The minimum ignition energy is a representative indicator of ignition performance. The common unit of minimum ignition energy is joules. Minimum ignition energy is the minimum discharge energy required to burn the mixture. If the minimum ignition energy is large, the ignition performance will be low, and if the minimum ignition energy is small, the ignition performance will be high.

Here, the main determining factors for ignition performance are the equivalence ratio of the mixture and multiple ignition. As shown in Figure 20, when the equivalence ratio deviates from the stoichiometric mixture ratio (air-fuel ratio), the minimum ignition energy increases and ignition performance decreases. In the case of a cold start, fuel vaporization is delayed, so the equivalence ratio of the mixture is smaller than the stoichiometric mixture ratio. Therefore, in the case of a cold start, the minimum ignition energy increases as the temperature of the engine (internal combustion engine) and the environment decreases.

On the other hand, when the electrodes are heated by multiple ignition, the heat absorption from the flame kernel by the electrodes decreases, improving ignition performance. Therefore, as shown by the dotted line in Figure 20, it is possible to burn the mixture with less ignition energy than when multiple ignition is not performed. In other words, if the minimum ignition energy at engine start can be satisfied even when multiple ignition is not performed, the improvement in ignition performance due to multiple ignition can be converted into a reduction in the equivalence ratio of the mixture. This makes it possible to reduce the amount of fuel injection while satisfying the minimum ignition energy. As a result, improved fuel economy and reduced hydrocarbons can be achieved.

If the minimum ignition energy cannot be met, a misfire will occur, resulting in the emission of an unburned mixture containing a large amount of hydrocarbons, and a deterioration in exhaust and fuel economy. Therefore, switching between the presence and absence of multiple ignition must be performed while maintaining a state in which the minimum ignition energy is met. For this reason, it is advisable to stop multiple ignition after increasing the equivalence ratio of the mixture (increasing the fuel injection amount), or to start multiple ignition and then decrease the equivalence ratio of the mixture (reducing the fuel injection amount).

In this manner, the control device 1 (internal combustion engine control device) according to this embodiment controls an internal combustion engine including an ignition device having the spark plug 200 and the ignition coil 300 that causes the spark plug 200 to discharge. The control device 1 includes an overall control unit 81 (control unit) that outputs output signals to the ignition device. The output signals include a multiple ignition signal for preheating the spark plug 200, a main ignition signal that has a frequency different from that of the multiple ignition signal and is for igniting the air-fuel mixture by discharging the spark plug 200, and a pre-charge signal for pre-charging the ignition coil 300.
This increases the temperature of the electrodes 210, 220, and in turn reduces the minimum ignition energy as much as possible to improve ignition performance. As a result, the ignition performance of the spark plug 200 during main ignition can be improved, and the generation of hydrocarbons can be suppressed.

The overall control unit 81 (control unit) according to this embodiment outputs a multiple ignition signal before outputting a main ignition signal, and outputs a pre-charge signal before outputting the multiple ignition signal.
As a result, before the air-fuel mixture is ignited by the discharge of the spark plug 200, the electrodes 210, 220 and the intake air around the electrodes 210, 220 can be efficiently warmed.

The pre-charge signal in this embodiment is at a lower frequency than the multiple ignition signals.
This makes it possible to increase the charging energy of the ignition coil 300 as much as possible.

The overall control unit 81 (control unit) according to this embodiment outputs a pre-charge signal when the temperature of the ignition coil 300 is below a threshold A (predetermined temperature).
This makes it possible to increase the charging energy of the ignition coil 300 when the temperature of the ignition coil 300 is below the threshold A and the ignition coil 300 is not in an overheated state.

The overall control unit 81 (control unit) in this embodiment stops outputting the pre-charge signal when the temperature of the ignition coil 300 is equal to or higher than threshold value A (predetermined temperature), and increases the amount of fuel injection compared to when the pre-charge signal is output.
This makes it possible to suppress an increase in the temperature of the ignition coil 300 when the temperature of the ignition coil 300 is equal to or higher than the threshold value A and the ignition coil 300 is in an overheated state. Furthermore, by increasing the fuel injection amount, it is possible to prevent the breakdown voltage from increasing even if the temperature of the ignition coil 300 drops. As a result, misfires can be suppressed, and the generation of hydrocarbons can be suppressed.

The overall control unit 81 (control unit) according to this embodiment reduces the fuel injection amount when the pre-charge signal is being output, compared to when the pre-charge signal is not being output.
This makes it possible to suppress the generation of hydrocarbons.

The output signal according to this embodiment includes an overheat detection signal for detecting the state of the ignition coil 300. The ignition device has a temperature detection unit 351 for detecting the temperature of the ignition coil 300, and a filter unit 370 for blocking the multiple ignition signal and the overheat detection signal among the output signals when the temperature of the ignition coil 300 becomes equal to or higher than a threshold A (first temperature). The control device 1 (internal combustion engine control device) has an output monitor circuit 832 (return detection function) for detecting a return signal for performing self-diagnosis of the output signal. The overall control unit 81 (control unit) compares the overheat detection signal with the return signal to determine whether the overheat detection signal has been blocked by the filter unit. Then, when it is determined that the overheat detection signal has been blocked, it is determined that the temperature of the ignition coil 300 is equal to or higher than the threshold A (first temperature). On the other hand, when it is determined that the overheat detection signal has not been blocked, it is determined that the temperature of the ignition coil 300 is lower than the threshold A (first temperature).
This allows the overall control unit 81 to accurately determine whether the temperature of the ignition coil 300 is equal to or higher than the threshold A (first temperature). As a result, pre-charging and multiple ignition can be maximized while avoiding thermal damage to the ignition coil 300.

The overall control unit 81 (control unit) according to this embodiment outputs an overheat detection signal at a timing after outputting a main ignition signal.
This allows the ignition signal to be switched within a cycle. Also, the latest temperature of the ignition coil 300 is reflected in the return signal of the overheat detection pulse, making it possible to reduce the delay in switching the ignition signal.

The overall control unit 81 (control unit) according to this embodiment outputs an overheat detection signal for each predetermined cycle of the combustion cycle of the internal combustion engine.
This makes it possible to output an overheat detection pulse intermittently when the ignition coil 300 becomes overheated to the extent that the main ignition signal is cut off, for example, and as a result, it is possible to quickly detect when the temperature of the ignition coil 300 has dropped and the air-fuel mixture can be ignited again.

The overall control unit 81 (control unit) according to this embodiment outputs a pre-charge signal when it determines that the temperature of the ignition coil 300 is lower than the threshold A (first temperature).
As a result, when the temperature of the ignition coil 300 is below threshold A and the ignition coil 300 is not overheated, the charging energy of the ignition coil 300 is increased to initiate discharge between the electrodes 210, 220, and the temperature of the electrodes 210, 220 can be increased by this discharge.

The overall control unit 81 (control unit) in this embodiment stops output of at least one of the pre-charge signal and the multiple ignition signal when it determines that the temperature of the ignition coil 300 is equal to or higher than threshold value A (first temperature).
As a result, when the temperature of the ignition coil 300 is equal to or higher than the threshold value A and the ignition coil 300 is in an overheated state, the temperature of the ignition coil 300 can be prevented from increasing.

The overall control unit 81 (control unit) according to this embodiment outputs an overheat detection signal before outputting a main ignition signal when idle stop control is performed (when the internal combustion engine is restarted within a predetermined period of time). Then, when it is determined that the temperature of the ignition coil 300 is lower than the threshold A (first temperature), it outputs a pre-charge signal and a multiple ignition signal.
This makes it possible to increase the charging energy of the ignition coil 300 as much as possible when the internal combustion engine is restarted and the ignition coil 300 is not in an overheated state. Also, it is possible to increase the temperature of the electrodes 210, 220 of the spark plug 200 without increasing the ignition energy caused by multiple ignition. As a result, it is possible to improve the ignition ability of the spark plug 200 and suppress the generation of hydrocarbons.

When the overall control unit 81 (control unit) in this embodiment determines that the temperature of the ignition coil 300 is equal to or higher than threshold value A (first temperature), it stops outputting the pre-charge signal and increases the amount of fuel injection compared to when the pre-charge signal is output.
This makes it possible to suppress an increase in the temperature of the ignition coil 300 when the temperature of the ignition coil 300 is equal to or higher than the threshold value A and the ignition coil 300 is in an overheated state. Furthermore, by increasing the fuel injection amount, it is possible to prevent the breakdown voltage from increasing even if the temperature of the ignition coil 300 drops. As a result, misfires can be suppressed, and the generation of hydrocarbons can be suppressed.

The overheat detection signal according to this embodiment is a single pulse signal.
This makes it possible to reduce unnecessary charging and unnecessary signal output operations, and also makes it possible to prevent the overheat detection signal from affecting the temperature rise of the ignition coil 300. Note that the overheat detection signal according to the present invention is not limited to a single pulse, and can be set to a number of pulses within a range that does not affect the temperature rise of the ignition coil.

The overheat detection signal according to this embodiment has a frequency that can be detected by the output monitor circuit 832 (return detection function) and can be cut off by the filter section 370 .
As a result, by detecting that the overheat detection signal is not blocked by the filter unit 370, it is possible to detect that the coil temperature is below the threshold A (first temperature). In addition, even if the overheat detection signal is input to the igniter 340, it is possible to prevent sparks from flying between the electrodes 210 and 220. As a result, it is possible to prevent the overheat detection signal from affecting the temperature rise of the ignition coil 300.

The internal combustion engine control method according to this embodiment is a method for controlling an internal combustion engine including an ignition device having an ignition plug 200 and an ignition coil 300 that causes discharge in the ignition plug 200. In this internal combustion engine control method, an overall control unit 81 (control unit) outputs to the ignition device a multiple ignition signal for preheating the ignition plug 200, a main ignition signal that has a frequency different from that of the multiple ignition signal and is for igniting the air-fuel mixture by discharging the ignition plug 200, and a pre-charge signal for pre-charging the ignition coil 300.
This makes it possible to maximize the charging energy of the ignition coil 300. Also, it is possible to increase the temperature of the electrodes 210, 220 of the spark plug 200 without increasing the ignition energy caused by multiple ignition. As a result, it is possible to improve the ignition performance of the spark plug 200 and suppress the generation of hydrocarbons.

The present invention is not limited to the embodiments described above and shown in the drawings, and various modifications are possible without departing from the spirit of the invention described in the claims.

The above-mentioned embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

1...internal combustion engine control device, 10...analog input section, 20...digital input section, 30...A/D conversion section, 40...RAM, 50...MPU, 60...ROM, 70...I/O port, 80...output circuit, 81...overall control section, 82...fuel injection control section, 83...ignition control section, 84...cylinder discrimination section, 85...angle information generation section, 86...rotation speed information generation section, 87...intake amount measurement section, 88...load information generation section, 89...water temperature measurement section, 100...internal combustion engine, 110...air cleaner, 111...intake pipe, 112...intake manifold, 113...throttle valve, 113a...throttle opening sensor, 114...flow rate sensor, 115...intake air temperature sensor, 120...ring gear, 121...crank angle sensor, Description of the Related Art 122...water temperature sensor, 123...crankshaft, 125...accelerator pedal, 126...accelerator position sensor, 130...fuel tank, 131...fuel pump, 132...pressure regulator, 133...fuel piping, 134...fuel injector, 140...cylinder pressure sensor, 150...cylinder, 151...intake valve, 152...exhaust valve, 160...exhaust manifold, 161...three-way catalyst, 162...upstream air-fuel ratio sensor, 163...downstream air-fuel ratio sensor, 170...piston, 200...spark plug, 210...center electrode, 220...outer electrode, 230...insulator, 300...ignition coil, 310...primary coil, 320...secondary coil, 330...DC power source, 340: Igniter; 350, 360: Temperature switch section; 351: Temperature detection section; 370: Filter section; 500, 501: Electric circuit; 831: Current supply control circuit; 832: Output monitor circuit

Claims (15)

An internal combustion engine control device that controls an internal combustion engine including an ignition device having an ignition plug and an ignition coil that causes the ignition plug to generate a discharge,
a control unit that outputs an output signal to the ignition device;
the output signals include a multiple ignition signal for preheating the ignition plug, a main ignition signal having a frequency different from that of the multiple ignition signal for igniting an air-fuel mixture by discharging the ignition plug, a pre-charge signal for pre-charging the ignition coil, and an overheat detection signal for detecting a state of the ignition coil ,
the ignition device includes a temperature detection unit that detects a temperature of the ignition coil, and a filter unit that blocks the multiple ignition signal and the overheat detection signal from among the output signals when the temperature of the ignition coil becomes equal to or higher than a first temperature,
A return detection function for detecting a return signal for performing self-diagnosis of the output signal is further provided.
The control unit is
comparing the overheat detection signal with the return signal to determine whether the overheat detection signal is blocked by the filter unit;
If it is determined that the overheat detection signal is interrupted, it is determined that the temperature of the ignition coil is equal to or higher than the first temperature;
If it is determined that the overheat detection signal is not interrupted, it is determined that the temperature of the ignition coil is lower than the first temperature.
Internal combustion engine control device. The internal combustion engine control device according to claim 1 , wherein the control unit outputs the multiple ignition signal before outputting the main ignition signal, and outputs the pre-charge signal before outputting the multiple ignition signal. 2. The internal combustion engine control system of claim 1, wherein the precharge signal has a lower frequency than the multiple ignition signals. The internal combustion engine control device according to claim 1 , wherein the control unit outputs the pre-charge signal when a temperature of the ignition coil is lower than a predetermined temperature. The internal combustion engine control device according to claim 1 , wherein the control unit stops outputting the pre-charge signal and increases the fuel injection amount compared to when the pre-charge signal is outputted, when the temperature of the ignition coil is equal to or higher than a predetermined temperature. The internal combustion engine control device according to claim 1 , wherein the control unit reduces the fuel injection amount when the pre-charge signal is being outputted, compared to when the pre-charge signal is not being outputted. The internal combustion engine control device according to claim 1 , wherein the control unit outputs the overheat detection signal at a timing after outputting the main ignition signal. The internal combustion engine control device according to claim 7 , wherein the control unit outputs the overheat detection signal for each predetermined cycle of the combustion cycle of the internal combustion engine. The internal combustion engine control device according to claim 1 , wherein the control unit outputs the pre-charge signal when it determines that the temperature of the ignition coil is lower than the first temperature. The internal combustion engine control device according to claim 1 , wherein the control unit stops output of at least one of the pre-charge signal and the multiple ignition signal when it determines that the temperature of the ignition coil is equal to or higher than the first temperature. 2. The internal combustion engine control device according to claim 1, wherein the control unit outputs the overheat detection signal before outputting the main ignition signal when the internal combustion engine is restarted within a predetermined period of time, and outputs the pre-charge signal and the multiple ignition signal when it determines that the temperature of the ignition coil is lower than the first temperature. 2. The internal combustion engine control device according to claim 1, wherein the control unit, when determining that the temperature of the ignition coil is equal to or higher than the first temperature, stops outputting the pre-charge signal and increases the fuel injection amount compared to when the pre-charge signal is output. The internal combustion engine control device according to claim 1 , wherein the overheat detection signal is a single pulse signal. The internal combustion engine control device according to claim 1 , wherein the overheat detection signal has a frequency that can be detected by the return detection function and can be cut off by the filter section. 1. A method for controlling an internal combustion engine including an ignition device having an ignition plug and an ignition coil that causes the ignition plug to discharge, comprising:
a control unit outputs to the ignition device a multiple ignition signal for preheating the ignition plug, a main ignition signal having a frequency different from that of the multiple ignition signal for igniting the mixture by discharging the ignition plug, a pre-charge signal for pre-charging the ignition coil , and an overheat detection signal for detecting a state of the ignition coil ;
The control unit is
It is equipped with a return detection function that detects return signals to perform self-diagnosis of output signals.
comparing the overheat detection signal with the return signal, and determining whether the overheat detection signal is blocked by a filter unit that blocks the multiple ignition signal and the overheat detection signal from among the output signals when the temperature of the ignition coil becomes equal to or higher than a first temperature;
If it is determined that the overheat detection signal is interrupted, it is determined that the temperature of the ignition coil is equal to or higher than the first temperature;
If it is determined that the overheat detection signal is not interrupted, it is determined that the temperature of the ignition coil is lower than the first temperature.
A method for controlling an internal combustion engine.

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