Ignition device

Abstract

To solve the problem that a circuit for detecting a secondary voltage of an ignition coil is required to have high pressure resistance and high safety, which leads to a high circuit cost.SOLUTION: An igniter comprises: a switch unit 3 that conducts and interrupts, based on an ignition signal input from a controller 70, a primary current flowing from a primary coil 21 of an ignition coil 2 composed of a primary coil 21 and a secondary coil 22 connected to an ignition plug 7 in a cylinder to the ground side; a primary voltage detection unit 8 that detects a primary voltage of the ignition coil 2; and a maximum value detection unit 9 that detects a maximum value of the primary voltage of the ignition coil 2. The maximum value detection unit 9 outputs a first maximum value V1max, which is a first maximum value of the primary voltage of the ignition coil 2 after the start of ignition, to the controller 70.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an ignition device for igniting an air-fuel mixture in a combustion chamber of an internal combustion engine.

Background Art

[0002] In recent years, in vehicles such as automobiles, regulations regarding fuel consumption (fuel efficiency) and harmful components of exhaust gases have been strengthened, and such regulations tend to become even more stringent in the future. In particular, regulations regarding fuel efficiency are extremely concerned due to issues such as soaring fuel prices, the impact on global warming, and depletion of energy resources.

[0003] Under such circumstances, a technique is known in which a control device estimates a combustion state based on the in-cylinder pressure of an engine (the pressure of the air-fuel mixture in the combustion chamber) and controls the engine. By generating an ignition signal according to the current combustion state and appropriately controlling the ignition timing, the gas composition in the combustion chamber, etc., the thermal efficiency of the engine can be increased. It is common to use a combustion pressure sensor using a piezo element for in-cylinder pressure detection. However, there are problems such as cost increase and securing space for sensor installation. Therefore, a technique for estimating the in-cylinder pressure from the voltage value of an ignition coil is known. By using an existing ignition coil as a combustion pressure sensor, it becomes unnecessary to install a dedicated combustion pressure sensor, and it is considered effective for the above problems. An example of such an in-cylinder pressure estimation technique is disclosed in Patent Document 1, for example.

[0004] Patent Document 1 describes estimating the combustion pressure based on the maximum voltage value when the ignition plug is controlled, detected by a voltage detection circuit that detects the voltage between the secondary coil and the ignition plug (hereinafter also referred to as "coil secondary voltage").

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In order to generate a spark discharge with a spark plug, it is necessary to generate a potential difference between the discharge gaps of the spark plug that is equal to or greater than the breakdown voltage of the in-cylinder gas at high pressure. Therefore, the coil secondary voltage may become a high voltage exceeding 10,000 volts. Accordingly, the circuit for detecting the coil secondary voltage has problems in that high withstand voltage and high safety are required, resulting in high circuit costs.

[0007] From the above situation, a method that enables the estimation of the in-cylinder pressure of an internal combustion engine at low cost based on the voltage or current of the ignition coil has been desired.

Means for Solving the Problems

[0008] To solve the above problems, the ignition device according to the first aspect of the present invention includes a switch unit configured to conduct and cut off the primary current flowing from the primary coil of an ignition coil, which is composed of a primary coil and a secondary coil connected to a spark plug in a cylinder, to the ground side based on an ignition signal input from a control device, a primary voltage detection unit configured to detect the primary voltage of the ignition coil, and a maximum value detection unit configured to detect the maximum value of the primary voltage of the ignition coil detected by the primary voltage detection unit. And the maximum value detection unit In the control device outputs the first maximum value, which is the first maximum value of the primary voltage of the ignition coil after the start of ignition, to the control device. In order to estimate the in-cylinder pressure based on the correlation between the first maximum value and the pressure in the cylinder, the primary voltage

Advantages of the Invention

[0013] According to at least one aspect of the present invention, it is possible to estimate the in-cylinder pressure of an internal combustion engine based on the voltage or current of the ignition coil, regardless of the secondary voltage of the ignition coil that becomes a high voltage. Thereby, the combustion state in the cylinder can be detected by an ignition device with low circuit costs. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0014]

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Embodiments for Carrying Out the Invention

[0015] Hereinafter, examples of embodiments for carrying out the present invention will be described with reference to the accompanying drawings. Components having substantially the same function or configuration in this specification and the accompanying drawings are denoted by the same reference numerals, and redundant descriptions are omitted.

[0016] <First Embodiment> First, the first embodiment of the present invention will be described. This embodiment is configured to estimate the in-cylinder pressure based on the maximum value in a predetermined section of the primary voltage of the ignition coil 2.

[0017] [Schematic Configuration of Internal Combustion Engine System] FIG. 1 shows the schematic configuration of an internal combustion engine system equipped with an ignition device according to the first embodiment of the present invention. The illustrated internal combustion engine system includes a spark ignition engine 60, an ignition device 50, and an electronic control unit (ECU) 70. The spark ignition engine 60 is, for example, a multi-cylinder reciprocating gasoline engine. The multi-cylinder reciprocating gasoline engine ignites the compressed air-fuel mixture by the spark plugs provided for each combustion chamber (cylinder), and obtains power from the explosion accompanying combustion.

[0018] The ignition device 50 supplies the electric energy necessary for ignition (hereinafter referred to as "ignition energy") to the spark plug 7 at a predetermined timing based on the ignition signal output from the ECU 70. Further, the ignition device 50 detects the first maximum value V1max of the primary voltage V1 (see FIG. 4) of the ignition coil 2 shown in FIG. 3 described later, and sends the voltage value to the ECU 70.

[0019] The ECU 70 estimates the in-cylinder pressure of the engine 60 based on the first maximum value V1max of the primary voltage V1 of the ignition coil 2, and controls the engine 60 based on the estimated in-cylinder pressure. That is, the ECU 70 includes an estimation unit 71 that estimates the state of the engine 60 such as the in-cylinder pressure, and a control unit 72 that determines the operation amount of the engine 60 based on the estimated state of the engine 60 to control the engine 60, and the control amount of the engine 60 is feedback-controlled.

[0020] For example, in the ECU 70, the estimation unit 71 estimates the in-cylinder pressure based on the first maximum value V1max of the primary voltage V1 of the ignition coil 2, and further estimates the combustion center of gravity position (MFB50) from the cylinder pressure. Then, the control unit 72 controls the ignition timing (ignition timing) of the spark plug 7 so that the combustion center of gravity position reaches the maximum thermal efficiency.

[0021] Also, in the ECU 70, for example, the estimation unit 71 estimates the above in-cylinder pressure, and further estimates the magnitude of the cyclic variation of the combustion torque from the in-cylinder pressure. Then, the control unit 72 controls the ignition timing, the ignition energy amount, the exhaust gas recirculation (EGR) amount, the air-fuel ratio, etc. so that the magnitude of the cyclic variation of the combustion torque becomes equal to or less than a predetermined value.

[0022] Also, in the ECU 70, for example, the estimation unit 71 estimates the above in-cylinder pressure, and further estimates the presence or absence of misfire or the misfire rate from the in-cylinder pressure. Then, the control unit 72 controls the ignition timing, the ignition energy amount, the exhaust gas recirculation (EGR) amount, the air-fuel ratio, etc. according to the presence or absence of misfire or the misfire rate.

[0023] Further, in the ECU 70, for example, the estimation unit 71 estimates the in-cylinder pressure, and further estimates the presence or absence of knocking and pre-ignition (hereinafter abbreviated as "pre-ig"). Then, the control unit 72 controls the ignition timing according to the presence or absence of knocking and pre-ig.

[0024] [Hardware Configuration of ECU] FIG. 2 is a block diagram showing an example of the hardware configuration of the ECU 70. The ECU 70 includes an input circuit 191, an A / D conversion unit 192, a CPU (Central Processing Unit) 193 which is a central processing unit, a ROM (Read Only Memory) 194, a RAM (Random Access Memory) 195, and an output circuit 196. Further, the ECU 70 includes a communication circuit 199. The ECU 70 is constituted by, for example, a micro-controller (MCU: Micro-Control Unit).

[0025] The CPU 193 expands and executes the program stored in the ROM 194 (an example of a storage unit) in the RAM 195, whereby the functions of the estimation unit 71 and the control unit 72 of the ECU 70 described above are realized. The ECU 70 is an example of a control device.

[0026] The input circuit 191 takes in the signals output from the sensors 200 as input signals 190. The sensors 200 are, for example, a throttle sensor, a water temperature sensor, a crank angle sensor, an intake cam angle sensor, an exhaust cam angle sensor, etc. not shown in the figure. The sensors 200 also include each detection unit of the ignition device 50 shown in FIG. 3. When the input signal 190 is an analog signal (for example, signals from a water temperature sensor, a throttle sensor, etc.), the input circuit 191 removes noise components from the input signal 190 and outputs the signal after noise removal to the A / D conversion unit 192.

[0027] The A / D conversion unit 192 converts an analog signal into a digital signal and outputs it to the CPU 193. The CPU 193 captures the digital signal output from the A / D conversion unit 192 and executes various operations, diagnoses, controls, etc. by executing control logic (program) stored in a storage medium such as the ROM 194.

[0028] The calculation result of the CPU 193 and the conversion result of the A / D conversion unit 192 are temporarily stored in the RAM 195. As the ROM 194, a non-volatile memory such as an EEPROM (Electrically Erasable and Programmable Read Only Memory) whose content can be rewritten may be used. For example, a program in which an algorithm for controlling the ignition device 50 according to the first embodiment of the present invention is described is stored in the ROM 194 or an auxiliary storage device (not shown).

[0029] The calculation result of the CPU 193 is output as a control signal 197 from the output circuit 196 and used for controlling a control target 210 composed of an actuator or the like for driving the engine 60. The control target 210 is, for example, an intake valve driving device (not shown), an exhaust valve driving device, a fuel injection valve, an ignition device 50 (ignition plug 7), etc. The control target 210 includes the ignition device 50 (ignition plug 7).

[0030] When the input signal 190 is a digital signal, the input signal 190 is directly sent from the input circuit 191 to the CPU 193 via the signal line 198, and the CPU 193 executes necessary operations and controls, etc.

[0031] The communication circuit 199 is a communication interface configured to be able to transmit and receive data with a communication device (not shown) outside the ECU 70 and other ECUs.

[0032] [Configuration of Ignition Device] Next, the configuration of the ignition device 50 according to the first embodiment will be described. FIG. 3 is a schematic circuit diagram showing a configuration example of the ignition device 50. The illustrated ignition device 50 includes an ignition coil 2 composed of a power source 1, a primary coil 21, and a secondary coil 22, a switch section 3, a primary voltage detection section 8, and a maximum value detection section 9. The number of turns of the secondary coil 22 is, for example, about 100 times the number of turns of the primary coil 21. The ignition coil 2 is configured to have a boosting action from the primary side to the secondary side.

[0033] Further, in the illustrated ignition device 50, one end of the ignition plug 7 is connected to one end of the secondary coil 22, and the anode of the high-voltage diode 6 is connected to the other end of the secondary coil 22. The other end of the ignition plug 7 and the cathode of the high-voltage diode 6 are connected to a grounding conductor.

[0034] The power source 1 is, for example, a battery or the like mounted on a vehicle and supplies a DC voltage. The high-potential side electrode of the power source 1 is connected to one end of the primary coil 21.

[0035] The other end of the primary coil 21 is connected to one end of the open / close contact of the switch section 3 composed of a semiconductor switch such as an IGBT (Insulated Gate Bipolar Transistor) and the input end of the primary voltage detection section 8. The other end of the switch section 3 and the other end of the primary voltage detection section 8 are connected to a grounding conductor. The signal output end of the primary voltage detection section 8 is connected to the input end of the maximum value detection section 9. Further, an ignition signal sent from the ECU 70 is input to the other input end of the maximum value detection section 9.

[0036] The switch section 3 is configured to conduct and cut off the primary current flowing from the primary coil 21 to the grounding conductor based on the ignition signal sent from the ECU 70. Here, the circuit configuration of the switch section 3 is shown in FIG. 21. The switch section 3 includes an IGBT that functions as a switching element, a clamp diode D GC , D GE for protecting the IGBT from overvoltage, and a resistor R G , R GE and is composed of. The clamp diode D GCis connected between the gate and the collector of the IGBT, and the clamp diode D GE is connected between the gate and the emitter of the IGBT. Also, the resistor R G is connected to the gate of the IGBT, and the resistor R GE is connected between the gate and the emitter of the IGBT.

[0037] Note that the circuit configuration of the switch unit 3 is an example and is not limited to this example. Also, the semiconductor switch is not limited to the IGBT, and may be constituted by other semiconductor switches such as MOSFETs and transistors.

[0038] Returning to the description of the ignition device 50 in FIG. 3. The primary voltage detection unit 8 detects the potential difference between one end of the primary coil 21 and the grounding conductor as the primary voltage V1 of the ignition coil 2, and outputs the detection result (primary voltage value) to the maximum value detection unit 9 in time series.

[0039] The maximum value detection unit 9 detects the first maximum value V1max within a predetermined interval of the primary voltage V1 of the ignition coil 2 detected in time series by the primary voltage detection unit 8, and outputs the detection result (first maximum value V1max) to the ECU 70 arranged outside the ignition device 50. The maximum value detection unit 9 is constituted by devices such as a microcontroller (hereinafter abbreviated as "microcomputer") and a memory.

[0040] [Operation of the ignition device] Next, the operation of the ignition device 50 according to the first embodiment will be described. FIG. 4 is a waveform diagram showing an operation example of the ignition device 50. This figure is a timing chart showing the ignition operation within one combustion stroke in a single cylinder. In the figure, the ignition signal input from the ECU 70 is shown in the uppermost row, the primary current I1 flowing through the primary coil 21 in the row below it, the primary voltage V1 of the primary coil 21 detected by the primary voltage detection unit 8 in the row below it, the secondary current I2 output and discharged from the secondary coil 22 in the row below it, and the time series changes of the secondary voltage V2 applied between the discharge gaps of the spark plug 7 in the row below it are shown.

[0041] When the ignition signal input from the ECU 70 transitions from a low level to a high level, the switch unit 3 closes the open contact and energizes the primary coil 21 with the primary current I1. While the switch unit 3 is in the closed state, the primary current I1 flowing through the primary coil 21 increases with the passage of time.

[0042] After that, when the ignition signal transitions from a high level to a low level, the switch unit 3 changes the open contact to an open state and cuts off the primary current I1. When the primary current I1 is cut off, a high voltage is induced in the secondary coil 22. Thereby, a high voltage is applied from the secondary coil 22 to the spark plug 7, and a discharge spark is generated at the spark plug 7, and a secondary current I2 flows through the secondary coil 22. Along with the release of the discharge energy by the spark plug 7, the absolute value of the secondary current I2 decreases and eventually becomes zero, ending the discharge. That is, the period from the fall of the secondary current I2 until the secondary current I2 becomes zero is the discharge period T of the ignition coil 2.

[0043] The absolute value of the secondary voltage V2 increases to near the breakdown voltage between the discharge gaps of the spark plug 7 immediately before discharge and rapidly decreases with the start of discharge. Therefore, a first minimum value appears near the start of discharge in the secondary voltage V2. After that, since the length of the discharge path (arc) increases due to the gas flow in the discharge gap of the spark plug 7, the absolute value of the secondary voltage V2 increases again, and a second minimum value appears near the end of the discharge period T. The first minimum value and the second minimum value of the secondary voltage V2 generally become high voltages of about -10,000V.

[0044] Also, when the current in the secondary coil 22 changes, a back electromotive force is generated in the primary coil 21. Due to this back electromotive force, a first maximum value (V1max) and a second maximum value appear in the primary voltage V1 in synchronization with the generation of the first minimum value and the second minimum value of the secondary voltage V2. Since the ignition coil 2 performs a step-down operation from the secondary coil 22 to the primary coil 21, the first maximum value V1max and the second maximum value of the primary voltage V1 are voltage values (several hundred V) lower than the first maximum value and the second maximum value of the secondary voltage V2.

[0045] Also, due to the back electromotive force generated in the primary coil 21, the clamp diode D of the switch section 3 GC , D GE , and the resistor R G , R GE allows current to flow through the primary coil 21. Then, in synchronization with the generation of the first minimum value and the second minimum value of the secondary voltage V2, the first minimum value (I1min) and the second minimum value appear in the primary current I1, respectively.

[0046] The maximum value detection unit 9 detects the first maximum value V1max of the primary voltage V1. Specifically, the maximum value detection unit 9 reads the value of the primary voltage V1 from the ignition start time t0 (hereinafter referred to as the "ignition start time") when the ignition signal transitions from the high level to the low level until the inspection time Δt has elapsed, and obtains the maximum voltage value as the first maximum value V1max therefrom. Here, the inspection time Δt is determined to be longer than the time when the first maximum value V1max of the primary voltage V1 appears from the ignition start time t0 and sufficiently shorter than the discharge period T of the secondary coil 22. The specific value of the inspection time Δt is, for example, 0.1 ms. Also, the length of the inspection time Δt may be defined as a ratio to the discharge period T, such as setting the inspection time Δt to 10% of the discharge period T. The inspection time Δt is obtained in advance through experiments or the like and stored in a memory (not shown) provided in the maximum value detection unit 9.

[0047] The first maximum value V1max of the primary voltage V1 is sent from the ignition device 50 to the ECU 70, and the ECU 70 estimates the in-cylinder pressure using the first maximum value V1max of the primary voltage V1.

[0048] [Correlation between the first maximum value of the primary voltage and the in-cylinder pressure] FIG. 5 is a characteristic diagram showing the correlation between the first maximum value V1max of the primary voltage V1 of the ignition coil 2 and the in-cylinder pressure. FIG. 5 shows the measurement results of the first maximum value V1max of the primary voltage V1 and the in-cylinder pressure at the ignition start time t0 using a spark ignition engine 60. In the figure, the horizontal axis represents the in-cylinder pressure [Pa], and the vertical axis represents the first maximum value V1max [V].

[0049] It is known that the breakdown voltage in spark discharge depends on the gas pressure in the discharge gap of the ignition plug, and the higher the gas pressure, the greater the breakdown voltage. Since the first minimum value of the secondary voltage V2 of the ignition coil 2 is approximately equal to the breakdown voltage, the first minimum value of the secondary voltage V2 has a strong correlation with the in-cylinder pressure at the ignition timing. Also, since the first maximum value V1max of the primary voltage V1 generated by the back electromotive force is approximately proportional to the first minimum value of the secondary voltage V2, the first maximum value V1max also has a strong correlation with the in-cylinder pressure. As shown in FIG. 5, the in-cylinder pressure is approximately proportional to the first maximum value V1max. Therefore, the ECU 70 can estimate the in-cylinder pressure of the engine 60 based on the first maximum value V1max of the primary voltage V1 sent from the ignition device 50.

[0050] The ECU 70 holds the correlation between the first maximum value V1max of the primary voltage V1 obtained by calibration or the like in advance and the in-cylinder pressure in the ROM 194 as a correlation formula or table data. In calibration or the like, the in-cylinder pressure is actually measured using a pressure sensor. The ECU 70 obtains the in-cylinder pressure from the first maximum value V1max of the primary voltage V1 by referring to this correlation formula or table.

[0051] In this embodiment, since the in-cylinder pressure is obtained based on the voltage on the primary side of the ignition coil 2 with a relatively low voltage value, the withstand voltage of the circuit can be reduced compared to the case where the in-cylinder pressure is obtained based on the secondary voltage V2 of the ignition coil 2. Therefore, the ignition device 50 according to this embodiment can keep the cost of the circuit used for estimating the in-cylinder pressure low.

[0052] Note that the second minimum value of the secondary voltage V2 and the second maximum value of the primary voltage V1 have a low correlation with the in-cylinder pressure. This is due to the following reasons.

[0053] The second minimum value of the secondary voltage V2 and the second maximum value of the primary voltage V1 are generated because the discharge path generated in the discharge gap of the ignition plug 7 is extended by the gas flow, and the electrical resistance value of the discharge path increases. That is, the second minimum value of the secondary voltage V2 and the second maximum value of the primary voltage V1 include the influence of the gas flow in addition to the influence of the in-cylinder pressure. Therefore, when estimating the in-cylinder pressure using the second minimum value of the secondary voltage V2 or the second maximum value of the primary voltage V1, there is a possibility that a large error will occur in the estimation result.

[0054] When the elongation amount of the discharge path is large, the second maximum value of the primary voltage V1 may reach the same level as the first maximum value V1max of the primary voltage V1. Therefore, the maximum value detection unit 9 needs to consider not misdetecting the second maximum value of the primary voltage V1 as the first maximum value V1max. For this reason, in the present embodiment, as described above, the inspection time Δt (FIG. 4) is determined to be longer than the time when the first maximum value V1max of the primary voltage V1 appears from the ignition start time t0 and sufficiently shorter than the discharge period T. Then, by the maximum value detection unit 9 obtaining the maximum value of the primary voltage V1 within the inspection time Δt from the ignition start time t0, misdetection of the first maximum value V1max of the primary voltage V1 is prevented. Thereby, the ECU 70 according to the present embodiment can keep the reliability of the in-cylinder pressure estimation result high.

[0055] As described above, the ignition device (ignition device 50) according to the first embodiment is composed of a primary coil and a secondary coil connected to an ignition plug (ignition plug 7) in a cylinder based on an ignition signal input from a control device (ECU 70). A switch unit (switch unit 3) configured to conduct and cut off the primary current (primary current I1) flowing from the primary coil of the ignition coil (ignition coil 2) to the ground side, a primary voltage detection unit (primary voltage detection unit 8) for detecting the primary voltage (primary voltage V1) of the ignition coil, and a maximum value detection unit (maximum value detection unit 9) for detecting the maximum value of the primary voltage of the ignition coil detected by the primary voltage detection unit. The maximum value detection unit is configured to output to the control device the first maximum value (first maximum value V1max), which is the first maximum value of the primary voltage of the ignition coil after ignition starts.

[0056] <Second Embodiment> Next, an ignition device according to a second embodiment of the present invention will be described. This embodiment is configured to estimate the in-cylinder pressure based on the minimum value of the primary current I1 of the ignition coil 2 in a predetermined section.

[0057] [Schematic Configuration of Internal Combustion Engine System] FIG. 6 shows a schematic configuration of an internal combustion engine system including an ignition device according to a second embodiment of the present invention. The illustrated internal combustion engine system includes a spark ignition engine 60, an ignition device 50A, and an electronic control unit (ECU) 70A.

[0058] The ignition device 50A supplies ignition energy to the spark plug 7 at a predetermined timing based on an ignition signal input from the ECU 70A. Further, the ignition device 50A detects the first minimum value I1min of the primary current I1 of the ignition coil 2 described later, and sends the current value to the ECU 70A.

[0059] The ECU 70A estimates the in-cylinder pressure of the engine 60 based on the first minimum value I1min of the primary current I1 of the ignition coil 2, and controls the engine 60 based on the estimated in-cylinder pressure. Although not shown, the ECU 70A includes an estimation unit 71 and a control unit 72, similar to the ECU 70 in the first embodiment. In the ECU 70A, the estimation unit 71 estimates the state of the engine 60 including at least the in-cylinder pressure based on the first minimum value I1min of the primary current I1 of the ignition coil 2, and the control unit 72 controls the engine 60 based on the estimated state of the engine 60.

[0060] [Configuration of Ignition Device] Next, the configuration of the ignition device 50A according to the second embodiment will be described. FIG. 7 is a schematic circuit diagram showing a configuration example of the ignition device 50A. The illustrated ignition device 50A includes a power source 1 that supplies a DC voltage, an ignition coil 2 composed of a primary coil 21 and a secondary coil 22, a high-voltage diode 6, and a switch unit 3, similar to the ignition device 50 in the first embodiment. Further, the ignition device 50A includes a primary current detection unit 10 and a minimum value detection unit 11.

[0061] The primary current detection unit 10 is provided between the high-potential side of the power source 1 and the primary coil 21. The signal output terminal of the primary current detection unit 10 is connected to the input terminal of the minimum value detection unit 11. Further, an ignition signal sent from the ECU 70A is input to the other input terminal of the minimum value detection unit 11.

[0062] The primary current detection unit 10 detects the current value of the primary current I1 flowing through the primary coil 21, and outputs the detection result (primary current value) to the minimum value detection unit 11 in time series.

[0063] The minimum value detection unit 11 detects the first minimum value I1min (FIG. 4) within a predetermined section of the primary current I1 of the ignition coil 2 detected in time series by the primary current detection unit 10, and outputs the detection result (first minimum value I1min) to the ECU 70A arranged outside the ignition device 50A. The minimum value detection unit 11 is composed of devices such as a microcomputer and a memory, for example.

[0064] [Operation of the Ignition Device] Next, the operation of the ignition device 50A according to the second embodiment will be described. Regarding the behavior of the secondary voltage V2 and secondary current I2 of the secondary coil 22 of the ignition device 50A, and the primary voltage V1 and primary current I1 of the primary coil 21, it is the same as the behavior shown in FIG. 4 in the first embodiment, so the overlapping description will be omitted here.

[0065] The minimum value detection unit 11 detects the first minimum value I1min of the primary current I1 of the primary coil 21. Specifically, the minimum value detection unit 11 reads the current value of the primary current I1 of the primary coil 21 from the ignition start time t0 until the inspection time Δt elapses, and selects the minimum current value as the first minimum value I1min of the primary current I1. Here, the inspection time Δt is determined to be longer than the time when the first minimum value I1min of the primary current I1 appears from the ignition start time t0 and sufficiently shorter than the discharge period T of the secondary coil 22. The specific value of the inspection time Δt is, for example, 0.1 ms. Note that the length of the inspection time Δt may be defined as a ratio to the discharge period T, such as setting the inspection time Δt to 10% of the discharge period T. The inspection time Δt is obtained in advance by experiments or the like and stored in a memory (not shown) provided in the minimum value detection unit 11.

[0066] The first minimum value I1min of the primary current I1 is sent from the ignition device 50A to the ECU 70A arranged outside the ignition device 50A. The ECU 70A estimates the in-cylinder pressure using the first minimum value I1min of the primary current I1.

[0067] [Correlation between the first minimum value of the primary current and the in-cylinder pressure] FIG. 8 is a characteristic diagram showing the correlation between the first minimum value I1min of the primary current I1 of the ignition coil 2 and the in-cylinder pressure. FIG. 8 shows the measurement results of the first minimum value of the primary current I1 and the in-cylinder pressure at the ignition start time t0 (FIG. 4) using a spark ignition engine 60. In the figure, the horizontal axis represents the in-cylinder pressure [Pa], and the vertical axis represents the first minimum value I1min [A].

[0068] According to the new findings of the inventor of the present application, a strong correlation as shown in FIG. 8 is obtained between the in-cylinder pressure at the ignition start time t0 and the first minimum value I1min of the primary current I1. Therefore, the ECU 70A can estimate the in-cylinder pressure of the engine 60 based on the first minimum value I1min of the primary current I1 sent from the ignition device 50A.

[0069] The ECU 70A stores, in the ROM 194 as a correlation formula or table data, the correlation between the first minimum value I1min of the primary current I1 of the ignition coil 2 obtained in advance by calibration or the like and the in-cylinder pressure. The ECU 70A obtains the in-cylinder pressure from the first minimum value I1min of the primary current I1 by referring to this correlation formula or table.

[0070] In this embodiment, since the in-cylinder pressure is obtained based on the current on the primary side of the ignition coil 2 with a relatively low voltage value, the withstand voltage of the circuit can be reduced compared to the case where the in-cylinder pressure is obtained based on the secondary voltage V2 of the ignition coil 2. Therefore, the ignition device 50A according to this embodiment can keep the cost of the circuit used for estimating the in-cylinder pressure low.

[0071] Note that, similar to the second maximum value of the primary voltage V1 in the first embodiment, the second minimum value of the primary current I1 includes the influence of the gas flow in addition to the influence of the in-cylinder pressure. Therefore, the correlation between the second minimum value of the primary current I1 and the in-cylinder pressure becomes low. Thus, if the in-cylinder pressure is estimated using the second minimum value of the primary current I1, there may be a large error in the estimation result.

[0072] When the elongation amount of the discharge path is large, the second minimum value of the primary current I1 may reach the same level as the first minimum value I1min of the primary current I1. Therefore, the minimum value detection unit 11 needs to consider not misdetecting the second minimum value of the primary current I1 as the first minimum value I1min of the primary current I1. For this reason, in this embodiment as described above, the inspection time Δt (FIG. 4) is determined to be longer than the time when the first minimum value I1min of the primary current I1 appears from the ignition start time t0 and sufficiently shorter than the discharge period T. Then, by the minimum value detection unit 11 obtaining the minimum value of the primary current I1 within the inspection time Δt from the ignition start time t0, misdetection of the first minimum value I1min of the primary current I1 is prevented. Thereby, the ECU 70A according to this embodiment can keep the reliability of the in-cylinder pressure estimation result high.

[0073] As described above, the ignition device (ignition device 50A) according to the second embodiment is configured to conduct and cut off the primary current (primary current I1) flowing from the primary coil of the ignition coil (ignition coil 2), which is composed of the primary coil and the secondary coil connected to the ignition plug (ignition plug 7) in the cylinder, to the ground side based on the ignition signal input from the control device (ECU 70A). The ignition device includes a switch unit (switch unit 3), a primary current detection unit (primary current detection unit 10) that detects the primary current of the ignition coil, and a minimum value detection unit (minimum value detection unit 11) that detects the minimum value of the primary current of the ignition coil detected by the primary current detection unit. The minimum value detection unit is configured to output the first minimum value (first minimum value I1min), which is the first minimum value of the primary current of the ignition coil after ignition start, to the control device.

[0074] <Third Embodiment> Hereinafter, the ignition device according to the third embodiment of the present invention will be described. In this embodiment, the in-cylinder pressure is estimated based on the primary power of the ignition coil 2.

[0075] [Schematic Configuration of Internal Combustion Engine System] FIG. 9 shows a schematic configuration of an internal combustion engine system including the ignition device according to the third embodiment of the present invention. The illustrated internal combustion engine system is composed of a spark ignition engine 60, an ignition device 50B, and an electronic control unit (ECU) 70B.

[0076] The ignition device 50B supplies ignition energy to the ignition plug 7 at a predetermined timing based on the ignition signal input from the ECU 70B. Further, the ignition device 50B detects the primary power Pw1 (also referred to as "primary power value Pw1") of the ignition coil 2, which will be described later, and sends the power value to the ECU 70B.

[0077] The ECU 70B estimates the in-cylinder pressure of the engine 60 based on the primary power Pw1 of the ignition coil 2, and controls the engine 60 based on the estimated in-cylinder pressure. Although not shown, the ECU 70B includes an estimation unit 71 and a control unit 72, similar to the ECU 70 in the first embodiment. In the ECU 70B, the estimation unit 71 estimates the state of the engine 60 including at least the in-cylinder pressure based on the primary power Pw1 of the ignition coil 2, and the control unit 72 controls the engine 60 based on the estimated state of the engine 60.

[0078] [Configuration of Ignition Device] Next, the configuration of the ignition device 50B according to the third embodiment will be described. FIG. 10 is a schematic circuit diagram showing a configuration example of the ignition device 50B. The illustrated ignition device 50B includes a power supply 1 that supplies a DC voltage, an ignition coil 2 composed of a primary coil 21 and a secondary coil 22, a high-voltage diode 6, and a switch unit 3, similar to the ignition device 50 in the first embodiment. Further, the ignition device 50B includes a primary voltage detection unit 8, a primary current detection unit 10, and a primary power detection unit 12.

[0079] The signal output terminal of the primary voltage detection unit 8 is connected to the input terminal of the primary power detection unit 12. Also, the signal output terminal of the primary current detection unit 10 is connected to another input terminal of the primary power detection unit 12. Further, an ignition signal sent from the ECU 70B is input to another input terminal of the primary power detection unit 12.

[0080] The primary power detection unit 12 obtains the primary power Pw1 from the voltage value of the time-series primary voltage V1 and the current value of the primary current I1 input from the primary voltage detection unit 8 and the primary current detection unit 10, and is configured to output this power value to the ECU 70B. The primary power detection unit 12 is composed of devices such as a microcomputer and a memory, for example.

[0081] [Operation of Ignition Device] Next, the operation of the ignition device 50B according to the third embodiment will be described. The behavior of the secondary voltage V2 and secondary current I2 of the secondary coil 22 of the ignition device 50B, and the primary voltage V1 and primary current I1 of the primary coil 21 is the same as that shown in FIG. 4 in the first embodiment, so redundant explanations are omitted here.

[0082] The primary power detection unit 12 detects the first minimum value I1min of the primary current I1 of the primary coil 21. Specifically, the primary power detection unit 12 reads the current value of the primary current I1 of the primary coil 21 from the ignition start time t0 until the inspection time Δt elapses, and selects the minimum current value as the first minimum value I1min of the primary current I1.

[0083] Furthermore, the primary power detection unit 12 detects the first maximum value V1max of the primary voltage V1 of the primary coil 21. Specifically, the primary power detection unit 12 reads the voltage value of the primary voltage V1 of the primary coil 21 from the ignition start time t0 until the inspection time Δt elapses, and selects the maximum voltage value as the first maximum value V1max of the primary voltage V1.

[0084] Then, the primary power detection unit 12 outputs the absolute value of the product of the first minimum value I1min of the primary current I1 and the first maximum value V1max of the primary voltage V1 as the primary power Pw1. Here, the inspection time Δt is determined to be longer than the time when the first minimum value I1min of the primary current I1 and the first maximum value V1max of the primary voltage V1 appear from the ignition start time t0, and sufficiently shorter than the discharge period T of the secondary coil 22. The specific value of the inspection time Δt is, for example, 0.1 ms. Similar to the cases of the first and second embodiments, the length of the inspection time Δt may be defined by the ratio to the discharge period T, such as setting the inspection time Δt to 10% of the discharge period T. The inspection time Δt is obtained in advance by experiments or the like and stored in a memory (not shown) provided in the primary power detection unit 12.

[0085] The primary power Pw1 is sent from the ignition device 50B to the ECU 70B arranged outside the ignition device 50B. The ECU 70B estimates the in-cylinder pressure using the primary power Pw1.

[0086] [Correlation between primary power and in-cylinder pressure] FIG. 11 is a characteristic diagram showing the correlation between the primary power Pw1 of the ignition coil 2 and the in-cylinder pressure. In FIG. 11, the measured results of measuring the primary power Pw1 and the in-cylinder pressure at the ignition start time t0 (FIG. 4) using the spark ignition engine 60 are shown. In the figure, the horizontal axis represents the in-cylinder pressure [Pa], and the vertical axis represents the primary power Pw1 [W].

[0087] According to the new findings of the inventor of the present application, a strong correlation is obtained between the in-cylinder pressure at the ignition start time t0 and the primary power Pw1 as shown in FIG. 11. Therefore, the ECU 70B can estimate the in-cylinder pressure of the engine 60 based on the primary power Pw1 sent from the ignition device 50B.

[0088] The ECU 70B holds the correlation between the primary power Pw1 and the in-cylinder pressure obtained in advance by calibration or the like in the ROM 194 as a correlation formula or table data. The ECU 70B obtains the in-cylinder pressure from the primary power Pw1 by referring to this correlation formula or table.

[0089] In the present embodiment, since the in-cylinder pressure is obtained based on the power on the primary side of the ignition coil 2 having a relatively low voltage value, the withstand voltage of the circuit can be reduced as compared with the case where the in-cylinder pressure is obtained based on the secondary voltage V2 of the ignition coil 2. Therefore, the ignition device 50B according to the present embodiment can keep the cost of the circuit used for estimating the in-cylinder pressure low.

[0090] Further, according to the new findings of the inventor of the present application, the correlation between the primary power Pw1 of the ignition coil 2 and the in-cylinder pressure is higher than the correlation between the first maximum value V1max of the primary voltage V1 and the in-cylinder pressure in the first embodiment described above, and the correlation between the first minimum value I1min of the primary current I1 and the in-cylinder pressure in the second embodiment also described above. It has become clear that it has a high correlation.

[0091] [Correlation between the first maximum value of the primary voltage, the first minimum value of the primary current, each of the primary power values, and the in-cylinder pressure] Figure 12 shows an example of the measurement results of the correlation coefficient R between the first maximum value V1max of the primary voltage V1 of the ignition coil 2, the first minimum value I1min of the primary current I1, and the primary power value Pw1, and the in-cylinder pressure at the ignition start time t0.

[0092] As shown in Figure 12, the correlation coefficient between the primary power value Pw1 and the in-cylinder pressure is close to 1, and there is a gap therefrom, and in the order of the correlation coefficient between the first maximum value V1max of the primary voltage V1 and the in-cylinder pressure, and the correlation coefficient between the first minimum value I1min of the primary current I1 and the in-cylinder pressure. That is, the correlation coefficient between the primary power value Pw1 and the in-cylinder pressure is higher than the correlation coefficient between the first maximum value V1max of the primary voltage V1 and the in-cylinder pressure, and the correlation coefficient between the first minimum value I1min of the primary current I1 and the in-cylinder pressure. Therefore, when using the primary power value Pw1, the in-cylinder pressure can be estimated with higher accuracy than when using the first maximum value V1max of the primary voltage V1 and the first minimum value I1min of the primary current I1.

[0093] As described above, the ignition device (ignition device 50B) according to the third embodiment is based on an ignition signal input from a control device (ECU 70B), and is composed of a primary coil of an ignition coil (ignition coil 2) connected to a secondary coil connected to a primary coil and an ignition plug (ignition plug 7) in a cylinder. A switch unit (switch unit 3) configured to conduct and cut off a primary current (primary current I1) flowing from the primary coil to the ground side, a primary voltage detection unit (primary voltage detection unit 8) for detecting the primary voltage (primary voltage V1) of the ignition coil, a primary current detection unit (primary current detection unit 10) for detecting the primary current of the ignition coil, from the first maximum value (first maximum value V1max) of the primary voltage detected by the primary voltage detection unit after ignition start, and the first minimum value (first minimum value I1min) of the primary current detected by the primary current detection unit after ignition start, a primary power detection unit (primary power detection unit 12) for detecting the primary power (primary power Pw1) of the ignition coil and outputting the value of the primary power of the ignition coil to the control device.

[0094] <Fourth Embodiment> Hereinafter, an ignition device according to a fourth embodiment of the present invention will be described. In this embodiment, the in-cylinder pressure is estimated based on the average value of the primary voltage of the ignition coil 2.

[0095] [Schematic Configuration of Internal Combustion Engine System] FIG. 13 shows a schematic configuration of an internal combustion engine system including an ignition device according to a fourth embodiment of the present invention. The illustrated internal combustion engine system includes a spark ignition engine 60, an ignition device 50C, and an electronic control unit (ECU) 70C.

[0096] The ignition device 50C supplies ignition energy to the spark plug 7 at a predetermined timing based on an ignition signal input from the ECU 70C. Further, the ignition device 50C detects the average value V1mean of the primary voltage V1 of the ignition coil 2 described later and sends the voltage value to the ECU 70C.

[0097] The ECU 70C estimates the in-cylinder pressure of the engine 60 based on the average value V1mean of the primary voltage V1 of the ignition coil 2 and controls the engine 60 based on the estimated in-cylinder pressure. Although not shown, the ECU 70C includes an estimation unit 71 and a control unit 72, similar to the ECU 70 in the first embodiment. In the ECU 70C, the estimation unit 71 estimates the state of the engine 60 including at least the in-cylinder pressure based on the average value V1mean of the primary voltage V1 of the ignition coil 2, and the control unit 72 controls the engine 60 based on the estimated state of the engine 60.

[0098] [Configuration of Ignition Device] Next, the configuration of the ignition device 50C according to the fourth embodiment will be described. FIG. 14 is a schematic circuit diagram showing a configuration example of the ignition device 50C. The illustrated ignition device 50C includes a power supply 1 that supplies a DC voltage, an ignition coil 2 composed of a primary coil 21 and a secondary coil 22, a high-voltage diode 6, and a switch unit 3, similar to the ignition device 50 in the first embodiment. Further, the ignition device 50C includes a primary voltage detection unit 8 and a primary voltage averaging processing unit 13.

[0099] The signal output terminal of the primary voltage detection unit 8 is connected to the input terminal of the primary voltage averaging processing unit 13. Further, an ignition signal sent from the ECU 70C is input to the other input terminal of the primary voltage averaging processing unit 13.

[0100] The primary voltage averaging processing unit 13 is configured to obtain the average value V1mean of the primary voltage V1 input from the primary voltage detection unit 8 over a predetermined period and output the average value V1mean to the ECU 70C. The predetermined period is after the vibration amplitude of the primary voltage V1 has become equal to or less than a specified value and is shorter than a specified time within the discharge period T of the ignition coil 2. The primary voltage averaging processing unit 13 is composed of devices such as a microcomputer and a memory, for example.

[0101] [Operation of the Ignition Device] Next, the operation of the ignition device 50C according to the fourth embodiment will be described. FIG. 15 is a waveform diagram showing an operation example of the ignition device 50C, and shows a timing chart of the ignition signal input from the ECU 70C and the primary voltage V1 of the primary coil 21 detected by the primary voltage detection unit 8. Note that this figure is an enlarged view of the vicinity of the occurrence time of the first maximum value V1max in the timing chart of the ignition signal and the primary voltage V1 shown in FIG. 4 in the first embodiment.

[0102] The primary voltage averaging processing unit 13 reads the value of the primary voltage V1 of the primary coil 21 from the primary voltage detection unit 8 from time t1 after the ignition start time t0 until time t2 (t2 > t1) is reached. Then, the primary voltage averaging processing unit 13 obtains the average value V1mean of the primary voltage V1 during the period from time t1 to time t2 by Equation (1). In Equation (1), "dt" is the sampling period of the primary voltage V1.

[0103] [Equation]

[0104] As shown in FIG. 15, in the primary voltage V1 of the primary coil 21, immediately after the occurrence of the first maximum value V1max, high-amplitude vibrations occur due to the resonance of the reactance component L and the capacitance component C included in the primary side of the ignition coil 2 of the ignition device 50C. This vibration may cause an increase in the error of the average value calculation result of the primary voltage V1 by the primary voltage averaging unit 13. Therefore, it is desirable that the time (t1 - t0) from the ignition start time t0 to the start of averaging the primary voltage V1 of the ignition coil 2 be a time when the vibration amplitude of the primary voltage V1 of the ignition coil 2 becomes sufficiently small (less than or equal to a predetermined specified value). The specified value of the sufficiently small vibration amplitude may be set, for example, to 1 / 10 of the amplitude of the maximum value.

[0105] Also, within the discharge period T of the ignition coil 2, due to the elongation of the discharge path caused by gas flow, the primary voltage V1 of the ignition coil 2 increases with the passage of time. Since the correlation between this voltage increase and the in-cylinder pressure is low, when estimating the in-cylinder pressure using the primary voltage V1, the elongation of the discharge path becomes a factor increasing the in-cylinder pressure estimation error. Therefore, in order to reduce the influence of the elongation of the discharge path due to gas flow in the cylinder, it is desirable that the averaging period (t2 - t1) be a sufficiently short time with respect to the discharge period T (FIG. 4). That is, the averaging period (t2 - t1) is set to be after time t1 and shorter than a specified time that satisfies the above conditions at least within the discharge period T. The specified time is obtained in advance through experiments or the like and stored in a memory (not shown) provided in the primary voltage averaging unit 13.

[0106] From the above viewpoints, the preferable values of the time (t1 - t0) from the ignition start time t0 to the start of averaging the primary voltage V1 and the time (t2 - t0) from the ignition start time t0 to the end of averaging the primary voltage V1 are obtained, for example, by t1 = 0.2 ms and t2 = 0.3 ms when the ignition start time t0 is taken as the starting point (0 ms). However, t1 and t2 are not limited to these values, and optimal values are determined variously depending on the discharge period of the ignition coil 2, the gas flow intensity, the sampling period of the coil voltage, and the like. Note that the length of the averaging period (t2 - t1) may be defined as a ratio with respect to the discharge period T, such as setting the averaging period (t2 - t1) to 10% of the discharge period T.

[0107] The average value V1mean of the primary voltage V1 obtained by the primary voltage averaging unit 13 is sent from the ignition device 50C to the ECU 70C. The ECU 70C estimates the in-cylinder pressure using the average value V1mean of the primary voltage V1 of the ignition coil 2.

[0108] [Correlation between average value of primary voltage and in-cylinder pressure] FIG. 16 is a characteristic diagram showing the correlation between the average value V1mean of the primary voltage V1 of the ignition coil 2 and the in-cylinder pressure. FIG. 16 shows the measured results of measuring the average value V1mean of the primary voltage V1 and the in-cylinder pressure at the ignition start time t0 (FIG. 4) using a spark ignition engine 60.

[0109] According to the new findings of the inventor of the present application, a strong correlation as shown in FIG. 16 is obtained between the in-cylinder pressure after the ignition start time t0 and the average value V1mean of the primary voltage V1. Therefore, the ECU 70C can estimate the in-cylinder pressure of the engine 60 based on the average value V1mean of the primary voltage V1 sent from the ignition device 50C.

[0110] The ECU 70C holds the correlation between the average value V1mean of the primary voltage V1 obtained by calibration or the like in advance and the in-cylinder pressure as a correlation formula or table data in the ROM 194. The ECU 70C obtains the in-cylinder pressure from the average value V1mean of the primary voltage V1 by referring to this correlation formula or table.

[0111] In the present embodiment, since the in-cylinder pressure is obtained based on the voltage on the primary side of the ignition coil 2 with a relatively low voltage value, the withstand voltage of the circuit can be reduced compared to the case where the in-cylinder pressure is obtained based on the secondary voltage V2 of the ignition coil 2. Therefore, the ignition device 50C according to the present embodiment can keep the cost of the circuit used for estimating the in-cylinder pressure low.

[0112] Furthermore, when obtaining the in-cylinder pressure using the average value V1mean of the primary voltage V1 of the ignition coil 2, the following advantages exist compared to the method of obtaining the in-cylinder pressure using the first maximum value V1max of the primary voltage V1 (first embodiment), the first minimum value I1min of the primary current I1 (second embodiment), and the primary power Pw1 (third embodiment) described above.

[0113] The maximum value of the primary voltage V1 or the minimum value of the primary current I1 that appears immediately after the discharge of the ignition coil 2 generally occurs in an extremely short period on the order of microseconds. Therefore, in order to accurately capture this maximum value or minimum value, it is necessary to sample the voltage or current of the primary coil 21 at a high speed on the order of megahertz. As a result, the computational load and cost of the circuit may increase.

[0114] On the other hand, the primary voltage V1 after a predetermined time has elapsed since the occurrence of the maximum value (first maximum value V1max) of the primary voltage V1 that appears immediately after the discharge of the ignition coil 2 exhibits relatively low-cycle and low-amplitude fluctuations. Therefore, the average value V1mean of the primary voltage V1 can be accurately obtained even with relatively low-speed sampling on the order of kilohertz. Therefore, the ignition device 50C according to the present embodiment can suppress the computational load and cost of the circuit.

[0115] As described above, the ignition device (ignition device 50C) according to the fourth embodiment includes a switch unit (switch unit 3) configured to conduct and cut off the primary current (primary current I1) flowing from the primary coil of the ignition coil (ignition coil 2) composed of the primary coil and the secondary coil connected to the ignition plug (ignition plug 7) in the cylinder based on the ignition signal input from the control device (ECU 70C), a primary voltage detection unit (primary voltage detection unit 8) for detecting the primary voltage (primary voltage V1) of the ignition coil, and a primary voltage averaging processing unit (primary voltage averaging processing unit 13) that calculates the average value (V1mean) within a predetermined period (t2 - t1) during discharge of the primary voltage of the ignition coil detected by the primary voltage detection unit and outputs the average value of the primary voltage to the control device.

[0116] <Fifth Embodiment> The ignition device according to the fifth embodiment of the present invention will be described below. This embodiment is configured to estimate the in-cylinder pressure based on the average value of the secondary current I2 of the ignition coil 2.

[0117] [Schematic Configuration of Internal Combustion Engine System] FIG. 17 shows a schematic configuration of an internal combustion engine system equipped with the ignition device according to the fifth embodiment of the present invention. The illustrated internal combustion engine system includes a spark ignition engine 60, an ignition device 50D, and an electronic control unit (ECU) 70D.

[0118] The ignition device 50D supplies ignition energy to the spark plug 7 at a predetermined timing based on the ignition signal input from the ECU 70D. Further, the ignition device 50D detects the average value I2mean of the secondary current I2 of the ignition coil 2 described later and sends the average value to the ECU 70D.

[0119] The ECU 70D estimates the in-cylinder pressure of the engine 60 based on the average value I2mean of the secondary current I2 of the ignition coil 2 and controls the engine 60 based on the estimated in-cylinder pressure. Although not shown, the ECU 70B includes an estimation unit 71 and a control unit 72 in the same manner as the ECU 70 in the first embodiment. In the ECU 70D, the estimation unit 71 estimates the state of the engine 60 including at least the in-cylinder pressure based on the average value I2mean of the secondary current I2 of the ignition coil 2, and the control unit 72 controls the engine 60 based on the estimated state of the engine 60.

[0120] [Configuration of Ignition Device] Next, the configuration of the ignition device 50D according to the fifth embodiment will be described. FIG. 18 is a schematic circuit diagram showing a configuration example of an ignition device 50D according to a fifth embodiment. The illustrated ignition device 50D is composed of a power supply 1 that supplies a DC voltage, an ignition coil 2 composed of a primary coil 21 and a secondary coil 22, a high-voltage diode 6, and a switch unit 3 that conducts and interrupts a primary current I1 flowing through the primary coil 21, similar to the ignition device 50 in the first embodiment. Further, the ignition device 50D includes a secondary current detection unit 5 and a secondary current averaging processing unit 14.

[0121] The secondary current detection unit 5 is provided between the cathode of the high-voltage diode 6 and the grounding conductor. The signal output terminal of the secondary current detection unit 5 is connected to the input terminal of the secondary current averaging processing unit 14. Further, an ignition signal sent from the ECU 70D is input to the other input terminal of the secondary current averaging processing unit 14.

[0122] The secondary current detection unit 5 detects the current value of the secondary current I2 flowing through the secondary coil 22 and outputs the detection result (secondary current value) to the secondary current averaging processing unit 14 in time series.

[0123] The secondary current averaging processing unit 14 is configured to obtain an average value I2mean of the secondary current I2 input from the secondary current detection unit 5 for a predetermined period and output the average value I2mean to the ECU 70D. The predetermined period is within the discharge period of the ignition coil 2 and is a certain time from the start of discharge. The secondary current averaging processing unit 14 is composed of devices such as a microcomputer and a memory, for example.

[0124] [Operation of the Ignition Device] Next, the operation of the ignition device 50D according to the fifth embodiment will be described. FIG. 19 is a waveform diagram showing an operation example of the ignition device 50D, and shows a timing chart of the ignition signal input from the ECU 70D and the secondary current I2 of the secondary coil 22 detected by the secondary current detection unit 5. Note that this figure is an enlarged view of the timing chart of the ignition signal and the secondary current I2 shown in FIG. 4 in the first embodiment, showing the discharge period T.

[0125] In the secondary current averaging processing unit 14, the value of the secondary current I2 of the secondary coil 22 is read from the secondary current detection unit 5 between the ignition start time t0 and the time t3 (t3 > t0). Then, the secondary current averaging processing unit 14 obtains the average value I2mean of the secondary current I2 during the period from time t0 to time t3 by Equation (2). In Equation (2), "dt" is the sampling period of the secondary current I2.

[0126]

Number

[0127] Also, regarding the time t3 when the period (averaging period) for obtaining the average value I2mean of the secondary current I2 ends, it is desirable to determine the averaging period (t3 - t0) of the secondary current I2 so that it becomes a time of a predetermined specified ratio of the discharge period T of the ignition coil 2. For example, in this embodiment, the specified ratio is set to about 10%.

[0128] When the averaging period (t3 - t0) of the secondary current I2 becomes significantly shorter than 10% of the discharge period T, the change width of the average value I2mean of the secondary current I2 accompanying the pressure change of the in-cylinder pressure becomes small and the S / N decreases. Also, when the averaging period (t3 - t0) of the secondary current I2 becomes significantly longer than 10% of the discharge period T, the correlation between the average value I2mean of the secondary current I2 and the in-cylinder pressure decreases due to the influence of the discharge path elongation accompanying the gas flow in the cylinder.

[0129] Therefore, in the secondary current averaging processing unit 14, for example, the discharge period T is obtained from the difference between the time when the absolute value of the moving average value of the secondary current I2 becomes equal to or less than a predetermined value and the ignition start time t0, and the time t3 is determined such that the period approximately 10% of the discharge period T becomes the averaging period of the secondary current I2. The number of samples of the secondary current I2 when obtaining the moving average value of the secondary current I2 is set in advance. Further, for example, the time t3 obtained for each engine operating condition (torque, rotational speed, ignition timing, etc.) by calibration is stored as table data in a memory (not shown) provided in the secondary current averaging processing unit 14. Then, by referring to the table by the secondary current averaging processing unit 14, the time t3 that defines the averaging period (t3 - t0) may be determined. In this way, the averaging period (t3 - t0) is set within the discharge period T and at a fixed time from the start of discharge. The fixed time is obtained in advance by experiments or the like and stored in a memory (not shown) provided in the secondary current averaging processing unit 14.

[0130] The average value I2mean of the secondary current I2 obtained by the secondary current averaging processing unit 14 is sent from the ignition device 50D to the ECU 70D. In the ECU 70D, the in-cylinder pressure is estimated using the average value I2mean of the secondary current I2 of the ignition coil 2.

[0131] [Correlation between average value of secondary current and in-cylinder pressure] FIG. 20 is a characteristic diagram showing the correlation between the average value I2mean of the secondary current I2 of the ignition coil 2 and the in-cylinder pressure. FIG. 20 shows the measurement results of the average value I2mean of the secondary current I2 and the in-cylinder pressure at the ignition start time t0 (FIG. 4) using a spark ignition engine 60.

[0132] According to the new findings of the inventor of the present application, it has been found that the rate of decrease in the absolute value of the secondary current I2 immediately after ignition start depends on the in-cylinder pressure, and the higher the in-cylinder pressure, the faster the absolute value of the secondary current I2 decreases immediately after ignition start. Therefore, as shown in FIG. 20, a strong correlation is obtained between the in-cylinder pressure after the ignition start time t0 and the average value I2mean of the secondary current I2. Thus, the ECU 70D can estimate the in-cylinder pressure of the engine 60 based on the average value I2mean of the secondary current I2 sent from the ignition device 50D.

[0133] The ECU 70D holds, in the ROM 194, as a correlation formula or table data, the correlation between the average value I2mean of the secondary current I2 of the ignition coil 2 obtained in advance by calibration or the like and the in-cylinder pressure. The ECU 70D obtains the in-cylinder pressure from the average value I2mean of the secondary current I2 by referring to this correlation formula or table.

[0134] In this embodiment, since the voltage applied to the secondary current detection unit 5 is low, the withstand voltage of the circuit can be reduced compared to the case where the in-cylinder pressure is obtained based on the secondary voltage V2 of the ignition coil 2. Therefore, the ignition device 50D according to this embodiment can keep the cost of the circuit used for estimating the in-cylinder pressure low.

[0135] Furthermore, the secondary current I2 immediately after the discharge of the ignition coil 2 fluctuates with a relatively low cycle number and low amplitude. Therefore, the average value I2mean of the secondary current I2 can be accurately obtained even with a relatively low-speed sampling in the kilohertz order. Therefore, the ignition device 50 according to this embodiment can keep the arithmetic load and cost of the circuit low. Also, this embodiment has the advantage that it directly detects the discharge current on the secondary side without using the back electromotive force acting from the secondary side to the primary side of the ignition coil 2, and is less affected by noise and signal attenuation generated inside the ignition device 50D.

[0136] As described above, the ignition device (ignition device 50D) according to the fifth embodiment is configured to conduct and cut off the primary current (primary current I1) flowing from the primary coil of the ignition coil (ignition coil 2) composed of the primary coil and the secondary coil connected to the ignition plug (ignition plug 7) in the cylinder to the ground side based on the ignition signal input from the control device (ECU 70D). It includes a switch unit (switch unit 3), a secondary current detection unit (secondary current detection unit 5) for detecting the secondary current (secondary current I2) of the ignition coil, and a secondary current averaging processing unit (secondary current averaging processing unit 14) that calculates the average value (I2mean) of the secondary current of the ignition coil detected by the secondary current detection unit within a predetermined period (t3 - t0) during discharge and outputs the average value of the secondary current to the control device.

[0137] <Modification example> Furthermore, the present invention is not limited to the above-described embodiments, and it goes without saying that various other application examples and modification examples can be adopted as long as they do not deviate from the gist of the present invention described in the claims. For example, each of the above-described embodiments describes the configuration of the ignition device in detail and specifically for the purpose of easily explaining the present invention, and is not necessarily limited to those having all the components described. Also, a part of the configuration of one embodiment can be replaced with the components of another embodiment. In addition, it is possible to add the components of another embodiment to the configuration of one embodiment. Also, it is possible to add, replace, or delete other components for a part of the configuration of each embodiment.

[0138] Also, in each of the above-described embodiments, the ignition coil 2 is arranged inside the ignition device, but the ignition coil 2 may be arranged outside the ignition device. Also, in each of the above-described embodiments, the maximum value detection unit 9, the minimum value detection unit 11, the primary power detection unit 12, the primary voltage averaging processing unit 13, the secondary current detection unit 5, and the secondary current averaging processing unit 14 are provided inside the ignition device, but these may be provided inside the ECU.

[0139] Moreover, the ignition device of each of the above-described embodiments is not limited to an engine (internal combustion engine) that includes one ignition coil and one spark plug for each cylinder, but can also be applied to an engine that includes a plurality of ignition coils or spark plugs for each cylinder.

[0140] In addition, each of the above-described configurations, functions, processing units, etc. may be realized in hardware by designing a part or all of them, for example, by using an integrated circuit. As the hardware, a processor device in a broad sense such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used.

Explanation of Reference Numerals

[0141] 1... Power supply, 2... Ignition coil, 3... Switch unit, 5... Secondary current detection unit, 7... Spark plug, 8... Primary voltage detection unit, 9... Maximum value detection unit, 10... Primary current detection unit, 11... Minimum value detection unit, 12... Primary power detection unit, 13... Primary voltage averaging processing unit, 14... Secondary current averaging processing unit, 21... Primary coil, 22... Secondary coil, 50, 50A, 50B, 50C, 50D... Ignition device, 60... Engine, 70, 70A, 70B, 70C, 70D... Electronic control unit (ECU), V1... Primary voltage, V1max... First maximum value, V1mean... Average value, V2... Secondary voltage, I1... Primary current, I1min... First minimum value, I2... Secondary current, I2mean... Average value, Pw1... Primary power, T... Discharge period

Claims

1. A switch unit configured to conduct and interrupt a primary current flowing from a primary coil of an ignition coil, which is composed of the primary coil and a secondary coil connected to an ignition plug in a cylinder, to a ground side based on an ignition signal input from a control device; A primary voltage detection unit configured to detect a primary voltage of the ignition coil; A maximum value detection unit configured to detect a maximum value of the primary voltage of the ignition coil detected by the primary voltage detection unit, and the maximum value detection unit outputs the first maximum value of the primary voltage to the control device in order to estimate the in-cylinder pressure based on a correlation between the first maximum value, which is the first maximum value of the primary voltage of the ignition coil after ignition start in the control device, and the pressure in the cylinder. An ignition device.

2. A period during which the maximum value detection unit detects the first maximum value of the primary voltage is set to be longer than a time from ignition start until the first maximum value of the primary voltage appears and shorter than a discharge period of the secondary coil. The ignition device according to claim 1.

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