Combustion state detection device for internal combustion engine

Abstract

Provided is a combustion state detection device for an internal combustion engine capable of detecting misfire regardless of the type of fuel. A combustion state detection device for an internal combustion engine is provided with a discharge characteristic quantity acquisition unit and a determination unit. The discharge characteristic quantity acquisition unit acquires a discharge characteristic quantity on the basis of a voltage value or a current value of an ignition coil connected to a spark plug. The spark plug carries out an ignition spark discharge for igniting the mixture, and a probe spark discharge is carried out in the same engine cycle after the ignition spark discharge. Then, the determination unit determines whether the internal combustion engine is in a misfire state or a non-misfire state on the basis of the result of comparison between the discharge characteristic quantity of the spark discharge for detection and a predetermined determination threshold value.

Description

Technical Field

[0001] The present invention relates to a combustion state detection device for an internal combustion engine. Background Art

[0002] Patent document 1 discloses an ignition device for determining whether a gas mixture is normally ignited. The ignition device disclosed in patent document 1 includes an ignition coil, an igniter unit, a normal discharge control unit, a re-discharge control unit, and a misfire determination unit. The normal discharge control unit implements a normal discharge for igniting the gas mixture. The re-discharge control unit implements re-ignition with a primary current smaller than the normal discharge after the normal discharge. Then, the misfire determination unit detects the presence or absence of re-discharge based on secondary current information or primary voltage information related to the secondary current after the re-ignition, and determines whether the gas mixture is normally ignited based on the presence or absence of discharge.

[0003] When the mixture burns normally, more ions are generated in the combustion chamber. Since the ions generated by combustion have the effect of reducing the insulation breakdown voltage of the ignition gap, it is easy to discharge by re-ignition in the case of normal combustion. On the other hand, in the case of misfire, since no ions are generated, no discharge is performed by re-ignition. The ignition device described in Patent Document 1 determines whether the ignition is normal by detecting the difference in discharge caused by ions in this way.

[0004] Patent Document 2 discloses a misfire detection device that detects misfire by detecting whether or not a spark plug has broken down by additional ignition during a period without assistance from breakdown (insulation breakdown) caused by ions.

[0005] In the misfire detection device disclosed in Patent Document 2, the applied voltage (second applied voltage) during additional ignition is set to an appropriate value lower than the applied voltage (first applied voltage) during normal ignition. The appropriate value of the applied voltage (second applied voltage) is a value that does not cause breakdown if the mixture is normally burned by normal ignition, but causes breakdown if the normal ignition misfires. Whether or not there is breakdown during additional ignition is determined by the voltage or current of the ignition coil. Prior art literature Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-200258 Patent Document 2: Japanese Patent Application Publication No. 2021-162011 Summary of the invention Problem that the invention aims to solve

[0007] However, in recent years, research has been conducted on the use of carbon-neutral fuels such as hydrogen or ammonia generated from renewable energy sources as fuel for internal combustion engines. Ions in the combustion chamber are generated by the reaction of hydrocarbons (CH) and oxygen. In the case of fuels such as gasoline or ethanol, the combustion gas contains a lot of hydrocarbons. Therefore, the amount of ions required to determine the combustion state is generated in the combustion chamber. On the other hand, the combustion gas of hydrogen or ammonia contains almost no hydrocarbons. Therefore, when burning fuels such as hydrogen or ammonia, the amount of ions generated is extremely small.

[0008] In the ignition device described in Patent Document 1, the difference in discharge caused by ions is detected. Therefore, it is difficult to determine whether a fuel such as hydrogen or ammonia, which generates very few ions, is ignited normally.

[0009] In the misfire detection device described in Patent Document 2, misfire detection can be achieved even for fuels that do not generate ions due to combustion. However, the insulation breakdown voltage of the ignition gap portion of the ignition coil is not only affected by the pressure in the combustion chamber, but also by various factors such as temperature, gas composition, gas flow, wear or contamination of the spark plug. Therefore, it is difficult to determine the appropriate value of the applied voltage when additional ignition is performed under various operating conditions or environmental conditions of the engine. That is, the misfire detection device described in Patent Document 2 has low robustness to changes in the operating conditions and environmental conditions of the engine.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a combustion state detection device for an internal combustion engine that can detect misfire regardless of the type of fuel. Technical means of solving problems

[0011] In order to solve the above-mentioned problems and achieve this purpose, a combustion state detection device for an internal combustion engine reflecting one aspect of the present invention comprises: a discharge characteristic quantity acquisition unit, which acquires a discharge characteristic quantity based on a voltage value or a current value of an ignition coil connected to a spark plug of the internal combustion engine; and a determination unit, which compares the discharge characteristic quantity acquired by the discharge characteristic quantity acquisition unit with a prescribed determination threshold value. The spark plug performs an ignition spark discharge for igniting a mixture, and performs a detection spark discharge in the same engine cycle after the ignition spark discharge. The discharge characteristic quantity acquisition unit acquires a discharge characteristic quantity based on a voltage value or a current value of the ignition coil in the detection spark discharge. The determination unit determines whether the internal combustion engine is in a misfire state or a non-misfire state based on a comparison between the discharge characteristic quantity and a prescribed determination threshold value. Effects of the Invention

[0012] According to the present invention, misfire can be detected regardless of the type of fuel. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a diagram showing a configuration example of the internal combustion engine according to the first embodiment. Figure 2 It is a diagram showing a configuration example of an ignition unit and a combustion detection unit according to an embodiment of the present invention. Figure 3 This is a diagram showing an example in which a part of the combustion detection unit according to the embodiment of the present invention is arranged inside the ECU. Figure 4 It is a diagram showing a configuration example of an ignition unit and a combustion detection unit according to the first embodiment. Figure 5 This is a diagram showing an example in which a part of the combustion detection unit of the first embodiment is arranged inside the ECU. Figure 6 It is a diagram showing an example of the circuit configuration of an ignition unit and a voltage detection unit according to the first embodiment. Figure 7 This is an explanatory diagram showing an example of the behavior of the timing of the ignition signal and the coil voltage, current, and cylinder pressure according to the first embodiment. Fig. 8A , Figure 8B This is an explanatory diagram showing an example of the operation of the primary voltage and the secondary current of the detection spark discharge according to the first embodiment. Fig. 9 It is an explanatory diagram showing an example of the extension of a general discharge path. Fig. 10A , Fig. 10B , Fig. 10C This is an explanatory diagram showing an example of the relationship between the cylinder pressure, the elongation of the discharge path, the discharge end peak voltage, and the discharge period according to the first embodiment. Fig.11 It is a diagram showing a configuration example of a peak voltage acquisition unit and a determination unit according to the first embodiment. Fig.12 It is an explanatory diagram showing an operation example of the peak voltage acquisition unit and the determination unit according to the first embodiment. Fig.13 This is a flowchart showing the procedure of the misfire detection process based on the peak voltage according to the first embodiment. Fig.14 It is a diagram showing a configuration example of an ignition unit and a combustion detection unit according to the second embodiment. Fig.15 This is a diagram showing an example in which a part of the combustion detection unit according to the second embodiment is arranged inside the ECU. Fig.16 It is a diagram showing an example of the circuit configuration of an ignition unit and a current detection unit according to the second embodiment. Fig.17 It is a diagram showing a configuration example of a discharge period acquisition unit and a determination unit according to the second embodiment. Fig.18It is an explanatory diagram showing an operation example of the discharge period acquisition unit and the determination unit according to the second embodiment. Fig.19 This is a flowchart showing the procedure of misfire detection processing based on the discharge period according to the second embodiment. Fig. 20 It is a diagram showing a configuration example of an ignition unit and a combustion detection unit according to a third embodiment. Fig.21 This is a diagram showing an example in which a part of the combustion detection unit according to the third embodiment is arranged inside the ECU. Fig. 22 It is a diagram showing a configuration example of a discharge period acquisition unit and a determination unit according to the third embodiment. Fig.23 It is an explanatory diagram showing an operation example of the discharge period acquisition unit and the determination unit according to the third embodiment. Fig.24 This is a flowchart showing the procedure of misfire detection processing based on the discharge period according to the third embodiment. Fig.25 It is a diagram showing a configuration example of an ignition unit and a combustion detection unit according to a fourth embodiment. Fig.26 This is a diagram showing an example in which a part of the combustion detection unit according to the fourth embodiment is arranged inside the ECU. Fig. 27 It is an explanatory diagram showing the averaging period of the primary voltage and the average voltage of the spark discharge for detection according to the fourth embodiment. Fig.28 This is an explanatory diagram showing an example of the relationship between the cylinder internal pressure and the average voltage according to the fourth embodiment. Fig.29 This is a flowchart showing the procedure of the misfire detection process based on the average voltage according to the fourth embodiment. Fig.30 This is a flowchart showing the procedure of calculating the average voltage according to the fourth embodiment. Fig.31 It is an explanatory diagram showing a configuration example of an ignition unit and a combustion detection unit according to a fifth embodiment. Fig.32 This is a flowchart showing the procedure of misfire detection processing based on average voltage and peak voltage according to the fifth embodiment. Fig.33A , Fig.33B This is an explanatory diagram showing an example of the behavior of the primary voltage in the detection spark discharge when the detection spark discharge timing is different according to the fifth embodiment. Fig.34This is an explanatory diagram showing an example of misfire detection accuracy when misfire detection is performed based on peak voltage and when misfire detection is performed based on average voltage with respect to changes in detection spark discharge timing according to the fifth embodiment. Fig.35 It is a diagram showing a configuration example of an ignition unit and a combustion detection unit according to a sixth embodiment. Fig.36A , Fig.36B It is an explanatory diagram showing an example of the operation of the primary voltage of the spark discharge for detection, the time differentiation operation of the primary voltage, and the averaging period of the time differentiation of the primary voltage according to the sixth embodiment. Fig.37 This is an explanatory diagram showing an example of the relationship between the cylinder pressure and the voltage change rate according to the sixth embodiment. Fig.38 This is a flowchart showing the procedure of misfire detection processing based on the voltage change rate according to the sixth embodiment. Fig.39 This is a flowchart showing the procedure of calculating the voltage change rate according to the sixth embodiment. Fig.40A , Fig.40B , Fig.40C It is an explanatory diagram showing a method of changing a peak voltage comparison value and a discharge period comparison value with respect to changes in average engine torque, average engine speed, and average intake pressure according to the present invention. Fig.41A , Fig.41B , Fig.41C It is an explanatory diagram showing a method of changing an average voltage comparison value and a voltage change rate comparison value with respect to changes in average engine torque, average engine speed, and average intake pressure according to the present invention. DETAILED DESCRIPTION

[0014] Hereinafter, examples of the mode for implementing the present invention will be described with reference to the drawings. Components having substantially the same function or configuration in this specification and the drawings are denoted by the same reference numerals, and repeated descriptions are omitted.

[0015] <First embodiment> [Structure of internal combustion engine] First, use Figure 1 The configuration of the internal combustion engine according to the first embodiment will be described. Figure 1 It is an overall configuration diagram showing a configuration example of an internal combustion engine according to a first embodiment of the present invention.

[0016] like Figure 1As shown, the internal combustion engine 13 includes a cylinder 38, a piston 35 sliding in the cylinder 38, an intake valve 32, an exhaust valve 34, and a spark plug 40. A combustion chamber 37 facing the piston 35 is formed in the cylinder 38. The combustion chamber 37 communicates with the intake manifold 31 and the exhaust manifold 33.

[0017] The intake valve 32 opens and closes the communication between the intake manifold 31 and the combustion chamber 37. The exhaust valve 34 opens and closes the communication between the exhaust manifold 33 and the combustion chamber 37. The injector 36 for injecting fuel is provided in the intake manifold 31. A mixed gas of the fuel injected by the injector 36 and the air sucked from the intake manifold 31 is supplied to the combustion chamber 37.

[0018] The fuel supplied to the internal combustion engine 13 by the injector 36 includes, in addition to gasoline, ethanol, etc., combustible liquid fuels or gaseous fuels such as methane gas, propane gas, hydrogen, ammonia, and synthetic hydrocarbon fuel (eFuel). In addition, by using hydrogen, ammonia, eFuel, etc. generated by renewable energy such as solar power generation or wind power generation as fuel, the emission of carbon dioxide in the internal combustion engine can be greatly reduced.

[0019] The internal combustion engine 13 has an ignition device 3. The ignition device 3 has an ignition unit 51 that applies a high voltage to the spark plug 40, and a combustion detection unit 1 that detects the combustion state of the internal combustion engine 13. The combustion detection unit 1 corresponds to the combustion state detection device of the present invention.

[0020] When a high voltage is applied from the ignition unit 51, the spark plug 40 generates a spark discharge to ignite the mixture in the combustion chamber 37. The ignition unit 51 is electrically connected to the ECU (Engine Control Unit) 2. The ignition unit 51 applies a high voltage to the spark plug 40 through the high-voltage line 48 according to the ignition signal sent from the ECU 2. The combustion detection unit 1 receives voltage information or current information from the ignition unit 51, detects the combustion state of the internal combustion engine 13 according to the voltage information or current information, and sends the detection result to the ECU 2.

[0021] When the spark plug 40 generates spark discharge, the air-fuel mixture in the combustion chamber 37 ignites and burns. The air-fuel mixture burning in the combustion chamber 37 presses down the piston 35 to rotate the crankshaft (not shown). As a result, the power generated by the internal combustion engine 13 is extracted to the outside.

[0022] [Configuration of the ignition unit and combustion detection unit] Next, use Figure 2 and Figure 3 The configurations of the ignition unit and the combustion detection unit of the ignition device according to the embodiment of the present invention will be described. Figure 2 It is an explanatory diagram showing a configuration example of the ignition unit 51 and the combustion detection unit 1 in the ignition device 3 according to the embodiment of the present invention. Figure 3 This is an explanatory diagram showing an example in which a part of the components of the combustion detection unit according to the embodiment of the present invention is arranged inside the ECU 2 .

[0023] like Figure 2 As shown, the ignition unit 51 includes an igniter 54 and an ignition coil 52. The igniter 54 receives an ignition signal transmitted from the ECU 2. The ignition coil 52 applies a high voltage to the spark plug 40.

[0024] The combustion detection unit 1 includes a discharge information detection unit 53, a discharge characteristic quantity acquisition unit 55, and a determination unit 56. The discharge information detection unit 53 detects the voltage (primary voltage or secondary voltage) or current (secondary current) of the ignition coil 52, and sends it as discharge information to the discharge characteristic quantity acquisition unit 55. The discharge characteristic quantity acquisition unit 55 acquires the discharge characteristic quantity based on the input discharge information and sends it to the determination unit 56. The determination unit 56 performs misfire determination of the internal combustion engine 13 based on the input discharge characteristic quantity and the comparison value received from the ECU 2, and sends the determination result to the ECU 2.

[0025] exist Figure 2 In FIG. 1 , an example is shown in which all the components of the combustion detection unit 1 are arranged inside the ignition device 3. However, a part of the components of the combustion detection unit may be arranged inside the ECU 2. Figure 3 As shown, the ignition device 3 ′ includes an ignition unit 51 and a discharge information detection unit 53 .

[0026] The combustion detection unit 1' is composed of a discharge information detection unit 53 arranged inside the ignition device 3', a discharge characteristic quantity acquisition unit 55' arranged inside the ECU 2, and a determination unit 56'. The combustion detection unit 1' corresponds to the combustion state detection device of the present invention. The discharge information output from the discharge information detection unit 53 is sent to the ECU 2 via the discharge information output unit 4.

[0027] When the discharge characteristic quantity acquisition unit 55' and the determination unit 56' are arranged inside the ECU 2 as in the combustion detection unit 1', the processing of the discharge characteristic quantity acquisition unit 55' and the determination unit 56' can be executed by software operating in the ECU 2. In this case, for example, the misfire determination condition can be flexibly changed according to the operating state of the internal combustion engine 13. Therefore, the detection of the combustion state (misfire determination) can be optimized.

[0028] <First embodiment> [Configuration of the ignition unit and combustion detection unit] Next, use Figure 4 and Figure 5 The configuration of the ignition unit and the combustion detection unit of the ignition device according to the first embodiment will be described. Figure 4It is an explanatory diagram showing a configuration example of the ignition unit 51 and the combustion detection unit 1a in the ignition device 3A of the first embodiment. Figure 5 This is an explanatory diagram showing an example in which a part of the components of the combustion detection unit of the first embodiment is arranged inside the ECU 2 .

[0029] like Figure 4 As shown, the ignition unit 51 includes an igniter 54 and an ignition coil 52. The igniter 54 receives an ignition signal transmitted from the ECU 2. The ignition coil 52 applies a high voltage to the spark plug 40.

[0030] The combustion detection unit 1a includes a voltage detection unit 53a, a peak voltage acquisition unit 55a, and a determination unit 56a. The voltage detection unit 53a detects the voltage (primary voltage or secondary voltage with reversed polarity) of the ignition coil 52, and sends a voltage signal 62 to the peak voltage acquisition unit 55a. In addition, the voltage detection unit 53a preferably detects the primary voltage of the ignition coil 52 rather than detecting the secondary voltage of the ignition coil 52. The secondary voltage of the ignition coil 52 usually reaches tens of thousands of volts. On the other hand, the primary voltage of the ignition coil 52 is usually hundreds of volts. Therefore, compared with the case where the voltage detection unit 53a detects the secondary voltage of the ignition coil 52, when the voltage detection unit 53a detects the primary voltage of the ignition coil 52, the pressure resistance of the hardware can be reduced, and the cost of the hardware can be reduced. In addition, compared with the case where the voltage detection unit 53a detects the secondary voltage of the ignition coil 52, when the voltage detection unit 53a detects the primary voltage of the ignition coil 52, the safety and reliability can be improved.

[0031] The peak voltage acquisition unit 55a acquires the peak voltage value from the input voltage signal 62 and sends it to the determination unit 56a. The determination unit 56a performs misfire determination of the internal combustion engine 13 based on the input peak voltage value and the peak voltage comparison value received from the ECU2 and sends the determination result to the ECU2.

[0032] exist Figure 4 In FIG. 1 , an example is shown in which all the components of the combustion detection unit 1a are arranged inside the ignition device 3A. However, a part of the components of the combustion detection unit may be arranged inside the ECU 2. Figure 5 As shown, the ignition device 3B includes an ignition unit 51 and a voltage detection unit 53a.

[0033] The combustion detection unit 1b is composed of a voltage detection unit 53a arranged inside the ignition device 3B, a peak voltage acquisition unit 55b arranged inside the ECU2, and a determination unit 56b. The combustion detection unit 1b corresponds to the combustion state detection device of the present invention. The voltage detection unit 53a detects the voltage (primary voltage or secondary voltage with reversed polarity) of the ignition coil 52. The voltage signal 62 output from the voltage detection unit 53a is sent to the ECU2 via the voltage output unit 4b. In addition, the voltage detection unit 53a preferably steps down the voltage signal 62 to an appropriate voltage range (for example, a range of 0 to 5 volts) so that the voltage signal 62 can be easily processed in the ECU2.

[0034] The voltage value of the low voltage side, i.e., the primary side, of the ignition coil 52 usually reaches a maximum of several hundred volts. If this voltage value is directly sent to the ECU 2 as the voltage signal 62, the ECU 2 needs a high voltage resistance or a voltage step-down circuit, and the hardware cost of the ECU 2 increases. Therefore, the voltage detection unit 53a steps down the detected voltage of the ignition coil 52 to a voltage range (0 to 5 volts) that is usually processed inside the ECU 2. Thus, the increase in the hardware cost of the ECU 2 can be suppressed.

[0035] If the peak voltage acquisition unit 55b and the determination unit 56b are arranged inside the ECU 2 as in the combustion detection unit 1b, the processing of the peak voltage acquisition unit 55b and the determination unit 56b can be executed by software running in the ECU 2. In this case, for example, the misfire determination condition can be flexibly changed according to the operating state of the internal combustion engine 13. Therefore, the detection of the combustion state (misfire determination) can be optimized.

[0036] [Circuit Configuration of Ignition Section and Voltage Detection Section] Next, use Figure 6 The circuit configuration of the ignition unit 51 and the voltage detection unit 53a will be described. Figure 6 It is an explanatory diagram showing an example of the circuit configuration of the ignition unit 51 and the voltage detection unit 53a.

[0037] like Figure 6 As shown, the ignition unit 51 includes an ignition coil 52 and an igniter 54. In addition, the voltage detection unit 53a includes a voltage dividing resistor R1 and a voltage dividing resistor R2 connected in series.

[0038] In the ignition unit 51, one end of the primary coil 52a of the ignition coil 52 is connected to a battery (DC power supply) not shown in the figure. As a result, a specified voltage (for example, 12V) is applied to the primary coil 52a, and a primary current flows. The other end of the primary coil 52a is connected to the collector terminal of the igniter 54 and one end of the voltage-dividing resistor R1 of the voltage detection unit 53a. The other end of the primary coil 52a is grounded through the emitter terminal of the igniter 54. The igniter 54 can use a transistor, a field effect transistor (Field Effect Transistor: FET), etc. The base terminal of the igniter 54 is connected to the ECU2.

[0039] The secondary coil 52b of the ignition coil 52 shares a magnetic circuit and a magnetic flux with the primary coil 52a. The turns ratio of the secondary coil 52b to the primary coil 52a is set to about 100, for example. One end of the secondary coil 52b is connected to the electrode of the spark plug 40 via the high-voltage wire 48. The other end of the secondary coil 52b is connected to the anode of the diode D0. The cathode of the diode D0 is grounded.

[0040] While the ignition signal is being transmitted from ECU 2 to the base terminal of igniter 54, that is, while the ignition signal is turned on, the collector terminal and the emitter terminal of igniter 54 are energized so that a primary current is output from the collector terminal of igniter 54 to the emitter terminal via primary coil 52a.

[0041] When the transmission of the ignition signal from the ECU 2 to the base terminal of the igniter 54 stops, that is, when the ignition signal is disconnected, the primary current flowing through the igniter 54 is cut off. At this time, a magnetic field change occurs in the primary coil 52a, and a primary voltage is generated by self-induction. Moreover, a high secondary voltage corresponding to the turns ratio is generated in the secondary coil 52b by mutual inductance. As a result, a secondary voltage is applied to the spark plug 40, and the ignition gap 41 (refer to Fig. 9 ) generates spark discharge. In addition, a secondary current generated by inducing a secondary voltage in the secondary coil 52b flows to the ground via the diode D0.

[0042] When the ignition signal turns from on to off and a secondary voltage is generated, a primary voltage is induced by mutual inductance of the ignition coil 52. The primary current generated by the induction of the primary voltage in the primary coil 52a flows to the ground via the voltage dividing resistors R1 and R2 of the voltage detecting unit 53a.

[0043] The voltage detection unit 53a transmits the voltage between the voltage dividing resistor R1 and the voltage dividing resistor R2 as a voltage signal 62. When the voltage of the primary coil 52a is V1, the voltage Vs of the voltage signal 62 is calculated by the equation (1).

[0044] [Formula 1] Vs=V1×R2 / (R1+R2)…(1)

[0045] The voltage V1 of the primary coil 52a (primary coil voltage V1) generated by mutual inductance during spark discharge generally reaches a maximum of several hundred volts. Therefore, the voltage detection unit 53a reduces the primary coil voltage V1 to a low voltage (e.g., a maximum of about 5 volts) that is easy to handle through the voltage dividing resistors R1 and R2, and sends it as a voltage signal 62.

[0046] [Ignition signal timing and the behavior of coil voltage, current, and cylinder pressure] Next, use Figure 7 An example of the operation of the timing of the ignition signal, the coil voltage, the current, and the cylinder pressure in the present embodiment will be described. Figure 7 This is an explanatory diagram showing an example of the behavior of the timing of the ignition signal, the coil voltage, the current, and the cylinder pressure according to the embodiment of the present invention.

[0047] Figure 7 The horizontal axis of the graph shown represents the crankshaft angle, the left end of the graph represents the compression start time (compression bottom dead center), and the right end of the graph represents the expansion end time (expansion bottom dead center). Figure 7 The graph shown shows, from the upper part, the ignition signal sent from the ECU 2 to the ignition unit 51, the primary current of the coil, the secondary current of the coil, the secondary voltage of the coil, the primary voltage of the coil, and the time variation of the cylinder pressure. In addition, the cylinder pressure shows the normal combustion situation (solid line) and the misfire situation (dashed line).

[0048] like Figure 7 As shown, in this embodiment, first, from the late stage of the compression stroke to the early stage of the expansion stroke (for example, 40° before the compression top dead center to 20° after the compression top dead center), the ECU 2 sends an ignition signal (ignition signal for ignition) for igniting the mixture to the ignition unit 51. When the ignition signal for ignition changes from Low (OFF) to High (ON), the igniter 54 becomes energized, and a primary current flows through the primary coil 52a. When a primary current flows through the primary coil 52a, magnetic energy is stored in the ignition coil 52.

[0049] Next, when the ignition signal for ignition is switched from High to Low, the primary current flowing through the igniter 54 is cut off, and a high voltage is induced in the secondary coil 52b by mutual inductance. Fig. 9) produces insulation breakdown (breakdown) and generates spark discharge for ignition (ignition spark discharge). When the ignition spark discharge is generated, the secondary current flows, and then the primary voltage is induced by the mutual inductance of the coil. At this time, the change in the primary voltage becomes an action corresponding to the change in the secondary voltage. That is, when the secondary voltage increases, the primary voltage also increases accordingly.

[0050] The ignition spark discharge is generated and the secondary current flows, so that the magnetic energy accumulated in the ignition coil 52 decreases. As the magnetic energy decreases, the ignition spark discharge ends when the secondary voltage becomes lower than the insulation breakdown voltage of the ignition gap 41. As a result, the secondary current and the primary voltage become almost zero.

[0051] Then, during the expansion stroke, the ECU 2 sends an ignition signal (detection ignition signal) for detecting misfire to the ignition unit 51. When the detection ignition signal changes from Low (OFF) to High (ON), the igniter 54 becomes energized and a primary current flows through the primary coil 52a. When a primary current flows through the primary coil 52a, magnetic energy is stored in the ignition coil 52.

[0052] Next, when the detection ignition signal is switched from High to Low, the primary current flowing through the igniter 54 is cut off, and a high voltage is applied to the secondary coil 52b through the mutual inductance. Due to the high voltage, insulation destruction (breakdown) is caused in the ignition gap 41 of the spark plug 40, and a spark discharge for detection (spark discharge for detection) is generated. When the spark discharge for detection is generated, a secondary current flows, and then a primary voltage is induced through the mutual inductance of the coil. At this time, the change in the primary voltage becomes an action corresponding to the change in the secondary voltage. That is, when the secondary voltage becomes higher, the primary voltage also becomes higher accordingly.

[0053] The magnetic energy accumulated in the ignition coil 52 decreases by generating the detection spark discharge and flowing the secondary current. As the magnetic energy decreases, the detection spark discharge ends when the secondary voltage becomes lower than the insulation breakdown of the ignition gap 41. As a result, the secondary current and the primary voltage become almost zero.

[0054] The timing for sending the detection ignition signal is preferably after the timing when flame propagation in the combustion chamber is substantially completed during normal combustion and when the difference in cylinder pressure between normal combustion and misfire at the timing of sending the ignition signal is greater than a specified value (for example, greater than 0.1 MPa).

[0055] If the timing of sending the ignition signal for detection is too early, the temperature in the cylinder at the timing of the discharge for detection and the distribution of the gas composition containing ions become uneven, or the turbulence of the gas flow becomes stronger. These have an impact on the voltage and discharge period of the spark discharge for detection. Therefore, if the timing of sending the ignition signal for detection is too early, the reliability of misfire detection may be reduced.

[0056] In addition, if the timing of sending the detection ignition signal is too late, the difference in cylinder pressure during normal combustion and misfire at the detection discharge timing becomes smaller. The SN ratio in misfire detection decreases. Therefore, if the timing of sending the detection ignition signal is too late, the reliability of misfire detection may be reduced.

[0057] According to the experimental results of the inventors, the transmission timing of the detection ignition signal is preferably set within the range from a timing 20° ahead of the period of mass fraction burnt 90% (MFB (Mass Fraction Burnt) 90) to a timing 40° behind the period of MFB90.

[0058] When the timing of sending the detection ignition signal is earlier than the timing that is 20° ahead of the period of MFB90, the temperature in the cylinder at the detection discharge timing and the distribution of the gas composition containing ions become uneven, or the turbulence of the gas flow becomes stronger. As a result, the reliability of misfire detection may be reduced. On the other hand, when the timing of sending the detection ignition signal is later than the timing that is 40° behind the period of MFB90, the difference in the cylinder pressure during normal combustion and during misfire becomes smaller. As a result, the SN ratio in misfire detection decreases, and the reliability of misfire detection may be reduced.

[0059] In addition, the ON time of the detection ignition signal (magnetization time of the coil) is set to be not too long within the range of spark discharge (breakdown) regardless of misfire or normal combustion. According to the experimental results of the inventor, the desired ON time of the detection ignition signal is approximately 0.2ms to 1ms.

[0060] When the ON time of the detection ignition signal is too short (for example, 0.1ms), the secondary voltage generated by the mutual inductance is lower than the insulation breakdown voltage, and spark discharge (breakdown) may not occur. On the other hand, when the ON time of the detection ignition signal is too long (for example, 2ms), the probability of re-discharge (re-breakdown) or the establishment of the discharge path (short circuit) increases with the lengthening of the discharge period, and the reliability of misfire detection may be reduced. In addition, when the ON time of the detection ignition signal is too long, the power consumption caused by the detection spark discharge increases, and the fuel economy may deteriorate. Furthermore, the electrode wear of the spark plug accompanying the discharge increases, and there is a risk that the cost required for maintenance of the internal combustion engine will increase.

[0061] In addition, the ON time of the detection ignition signal is preferably changed according to the timing of sending the detection ignition signal or the load of the internal combustion engine. More specifically, when the timing of sending the detection ignition signal is on the advance angle side of the expansion stroke, the ON time of the detection ignition signal is preferably extended compared to the case where the timing of sending the detection ignition signal is on the delay angle side of the expansion stroke. In addition, when the load (torque) of the internal combustion engine is high, the ON time of the detection ignition signal is preferably extended compared to the case where the load of the internal combustion engine is low.

[0062] Compared to the case where the timing of sending the ignition signal for detection is on the delayed angle side of the expansion stroke, the cylinder pressure at the timing of sending the ignition signal for detection becomes higher when the timing of sending the ignition signal for detection is on the advanced angle side of the expansion stroke. As a result, the insulation breakdown voltage for generating the spark discharge for detection becomes higher. Therefore, compared to the case where the timing of sending the ignition signal for detection is on the delayed angle side of the expansion stroke, when the timing of sending the ignition signal for detection is on the advanced angle side of the expansion stroke, the ON time of the ignition signal for detection is extended. As a result, the risk of spark discharge (breakdown) not occurring can be reduced.

[0063] Compared with the case where the load (torque) of the internal combustion engine is low, the cylinder pressure at the timing of sending the detection ignition signal becomes higher when the load (torque) of the internal combustion engine is high. As a result, the insulation breakdown voltage for generating the detection spark discharge becomes higher. Therefore, compared with the case where the load of the internal combustion engine is low, when the load of the internal combustion engine is high, the ON time of the detection ignition signal is extended. As a result, the risk of spark discharge (breakdown) not occurring can be reduced.

[0064] [Operation of primary voltage and secondary current of spark discharge for detection] Next, use Fig. 8A , Figure 8B The operation of the primary voltage and the secondary current of the detection spark discharge in this embodiment will be described. Fig. 8A , Figure 8B This is an explanatory diagram showing an example of the operation of the primary voltage and the secondary current of the detection spark discharge according to the first embodiment.

[0065] Fig. 8A , Figure 8B The horizontal axis of the graph shown represents the elapsed time. Fig. 8A The primary voltage (voltage signal 62) in the detection spark discharge detected by the voltage detection unit 53a is shown. Figure 8BIndicates the time variation of the secondary current of the detection spark discharge. Here, t0 indicates the start time of the detection spark discharge, and t1 indicates the discharge end time of the detection spark discharge. The start time t0 of the detection spark discharge is defined as the time when the absolute value of the secondary current is greater than the specified value, or the time when the detection ignition signal changes from ON to OFF. The discharge end time t1 of the detection spark discharge is defined as the time when the absolute value of the secondary current is less than the specified value. In addition, the discharge period Td of the detection spark discharge is defined as the difference between t1 and t0.

[0066] like Fig. 8A As shown, it represents the action that the primary voltage (voltage signal 62) vibrates greatly after the start time t0 of the detection spark discharge. This is due to the ringing noise generated by the resonance of the parasitic capacitance and inductance contained in the ignition part 51 and the voltage detection part 53a. The ringing noise decreases in the middle of the discharge period. The primary voltage rises at the end of the detection spark discharge and is approximately 0 at the discharge end time t1. That is, at the end of the detection spark discharge, the peak value of the primary voltage (hereinafter referred to as the discharge end peak voltage Vp) appears. In addition, the so-called end of the detection spark discharge refers to a period of approximately 60% to 100% relative to the discharge period Td (the discharge start time of the detection spark discharge is 0%, and the discharge end time of the detection spark discharge is 100%).

[0067] Thus, the voltage rise at the end of the discharge is caused by the elongation effect of the discharge path. In this embodiment, the combustion state is detected based on the discharge end peak voltage Vp in the detection spark discharge. That is, the peak voltage acquisition units 55a, 55b (see Figure 4 or Figure 5 ) obtains the discharge end peak voltage Vp in the detection spark discharge.

[0068] In addition, the discharge end peak voltage Vp in the detection spark discharge acquired by the peak voltage acquisition units 55a and 55b can also be acquired from the discharge end peak voltage of the secondary voltage of the ignition coil 52. However, since the secondary voltage of the ignition coil 52 reaches a maximum of tens of thousands of volts, it is preferable to acquire the discharge end peak voltage Vp from the primary voltage which is on the low voltage side and easy to operate from the viewpoint of reducing the cost of manufacturing the circuit.

[0069] [Extension of discharge path] Next, use Fig. 9 This illustrates the elongation of the discharge path. Fig. 9 It is an explanatory diagram showing an example of the extension of a general discharge path.

[0070] like Fig. 9As shown, when spark discharge is generated in the ignition gap 41 of the spark plug 40, the gas flows through the ignition gap 41 and the discharge path is extended. Fig. 9 This shows an example where the gas flows from left to right. Therefore, the discharge path extends in the direction of the gas flow, that is, in the right direction.

[0071] If the distance from the electrode center of the spark plug 40 to the farthest part of the discharge path is taken as the elongation, the elongation increases as the discharge time passes and is the largest just before the discharge ends. In addition, the resistance of the ignition gap 41 is roughly proportional to the elongation of the discharge path. The greater the elongation, the higher the resistance of the ignition gap 41.

[0072] The secondary voltage of the ignition coil 52 is determined by the product of the resistance of the ignition gap 41 and the secondary current. At the end of the discharge, the increase in the resistance of the ignition gap 41 due to the elongation of the discharge path becomes significant relative to the decrease in the secondary current, so a peak value is generated in the secondary voltage. In addition, the primary voltage (voltage signal 62) excited by the mutual inductance is roughly proportional to the secondary voltage. Therefore, at the end of the discharge, a peak value is also generated in the primary voltage (voltage signal 62), which becomes the peak voltage Vp at the end of the discharge (refer to Fig. 8A ). That is, there is a positive correlation between the elongation of the discharge path and the peak voltage Vp at the end of discharge. The greater the elongation of the discharge path, the higher the peak voltage Vp at the end of discharge.

[0073] [Relationship between cylinder pressure, elongation, discharge end peak voltage Vp, and discharge period Td] Next, use Fig. 10A , Fig. 10B , Fig. 10C The relationship between the cylinder pressure, the elongation, the peak voltage Vp at the end of discharge, and the discharge period Td is described. Fig. 10A , Fig. 10B , Fig. 10C It is an explanatory diagram showing an example of the relationship between the cylinder pressure, the elongation, the discharge end peak voltage Vp, and the discharge period Td according to the present embodiment.

[0074] Fig. 10A An example of the relationship between the cylinder pressure and the elongation of the discharge path in the detection spark discharge is shown. Fig. 10B An example of the relationship between the cylinder pressure and the discharge end peak voltage Vp in the detection spark discharge is shown. Fig. 10C An example of the relationship between the cylinder pressure and the discharge period Td in the detection spark discharge is shown.

[0075] like Fig. 10AAs shown, the cylinder pressure and the elongation of the discharge path are highly correlated. The lower the cylinder pressure, the smaller the elongation of the discharge path. This is because the elongation of the discharge path is determined by the balance between the advection effect caused by the flow of gas and the diffusion effect of electrons. In more detail, the advection effect acts in the direction of increasing the elongation of the discharge path. In contrast, the diffusion effect of electrons acts in the direction of reducing the elongation of the discharge path. Since the diffusion effect of electrons is greater as the cylinder pressure is lower, if the advection effect is constant (the gas flow rate is constant), the elongation is smaller as the cylinder pressure is lower.

[0076] As mentioned above, there is a positive correlation between the elongation of the discharge path and the peak voltage Vp at the end of discharge. Fig. 10B As shown, there is also a positive correlation between the cylinder pressure and the peak voltage Vp at the end of the discharge.

[0077] like Fig. 10C As shown, the cylinder pressure and the discharge period Td are negatively correlated. That is, the lower the cylinder pressure, the longer the discharge period Td. The discharge output (discharge energy per unit time) is determined by the product of the secondary voltage and the secondary current. If the cylinder pressure drops, the elongation of the discharge path becomes smaller, and the discharge output decreases due to the decrease in secondary voltage. Therefore, when the cylinder pressure drops, the consumption rate of the electromagnetic energy stored in the ignition coil 52 decreases, and the discharge period Td becomes longer.

[0078] The cylinder pressure at the time of spark discharge for misfire detection is lower than that during normal combustion. Therefore, the discharge end peak voltage Vp of spark discharge for misfire detection is lower than that during normal combustion. In addition, the discharge period Td of spark discharge for misfire detection is longer than that during normal combustion.

[0079] Therefore, the upper limit of the discharge end peak voltage Vp during misfire (peak voltage comparison value Vpc for misfire determination) is determined in advance by calibration. If the discharge end peak voltage Vp of the detection spark discharge is less than the peak voltage comparison value Vpc, misfire is determined. On the other hand, if the discharge end peak voltage Vp of the detection spark discharge is greater than the peak voltage comparison value Vpc, normal combustion is determined.

[0080] In addition, the lower limit value of the discharge period Td at the time of misfire (discharge period comparison value Tdc for misfire determination) is determined in advance by calibration. And if the discharge period Td of the detection spark discharge is greater than the discharge period comparison value Tdc, it is determined to be misfire. On the other hand, if the discharge period Td of the detection spark discharge is less than the discharge period comparison value Tdc, it is determined to be normal combustion. In addition, the configuration for detecting misfire based on the discharge period Td will be described in the second embodiment described later.

[0081] [Configuration of Peak Voltage Acquisition Unit and Determination Unit] Next, use Fig.11 The configurations of the peak voltage acquisition unit 55a and the determination unit 56a will be described. Fig.11 It is an explanatory diagram showing a configuration example of the peak voltage acquisition unit 55a and the determination unit 56a according to the first embodiment.

[0082] like Fig.11 As shown, the peak voltage acquisition unit 55a includes a trigger generation circuit 66 and a peak hold circuit 67. The ignition signal (reset signal) transmitted from the ECU 2 is input to the trigger generation circuit 66. In addition, the peak hold circuit 67 is input with the trigger signal generated by the trigger generation circuit 66, the voltage signal 62 transmitted from the voltage detection unit 53a, and the ignition signal (reset signal) transmitted from the ECU 2.

[0083] The determination unit 56a also includes a comparison circuit 68. The discharge end peak voltage Vp output from the peak hold circuit 67 and the peak voltage comparison value Vpc sent from the ECU2 are input to the comparison circuit 68. The determination result (High / Low) output from the comparison circuit 68 is sent to the ECU2.

[0084] [Operations of the Peak Voltage Acquisition Unit and the Determination Unit] Next, use Fig.12 An operation example of the peak voltage acquisition unit 55a and the determination unit 56a will be described. Fig.12 It is an explanatory diagram showing an operation example of the peak voltage acquisition unit 55a and the determination unit 56a according to the first embodiment.

[0085] Fig.12 The horizontal axis of the curve graph represents the passage of time. Fig.12 The curve in the figure represents, starting from the upper section, the ignition signal (reset signal) sent from ECU2, the trigger signal generated by the trigger generating circuit 66, the voltage signal 62 (primary voltage) sent from the voltage detection unit 53a, the output value of the peak holding circuit 67, the peak voltage comparison value Vpc sent from ECU2, and the judgment result output by the comparison circuit 68.

[0086] like Fig.12 As shown, after the falling edge of the ignition signal (reset signal) from ON to OFF passes through Tdelay time, the trigger generation circuit 66 causes the trigger signal to rise from Low to High and maintain the High state until the Tsample period passes. While the trigger signal is High, the peak hold circuit 67 holds the maximum value of the input voltage signal 62 and outputs the maximum value to the comparison circuit 68.

[0087] The Tdelay time is predetermined to be approximately 2 / 3 of the discharge period Td of the detection spark discharge. In addition, the Tsample period is predetermined to be approximately equal to the discharge period Td of the detection spark discharge. In this way, by determining the Tdelay time and the Tsample period, the peak voltage Vp at the end of the discharge of the detection spark discharge can be obtained while avoiding the influence of the ringing noise of the voltage signal 62 in the peak hold circuit 67.

[0088] The comparison circuit 68 compares the discharge end peak voltage Vp obtained in the peak hold circuit 67 with the peak voltage comparison value Vpc. Then, when the discharge end peak voltage Vp is less than the peak voltage comparison value Vpc, the output is High (indicating misfire). On the other hand, when the discharge end peak voltage Vp is greater than the peak voltage comparison value Vpc, the output is Low (indicating normal combustion). The output of the comparison circuit 68 is sent to the ECU 2 as the determination result of the determination unit 56a.

[0089] [Procedure for misfire detection based on peak voltage calculated by ECU software] Next, use Fig.13 The procedure of misfire detection based on the discharge cycle peak voltage Vp calculated by the software of the ECU 2 will be described. Fig.13 This is a flowchart showing the misfire detection process based on the discharge cycle peak voltage Vp calculated by the software of the ECU 2 according to the first embodiment.

[0090] exist Figure 5 In the combustion detection unit 1b shown, the peak voltage acquisition unit 55b and the determination unit 56b are arranged inside the ECU 2. Therefore, the acquisition of the peak voltage and the misfire determination are executed by software running in the ECU 2.

[0091] like Fig.13 As shown, ECU2 sends an ignition signal to the igniter 54 in the ignition unit 51 from the late stage of the compression stroke to the early stage of the expansion stroke to perform spark discharge for ignition (S1). Next, ECU2 sends an ignition signal to the igniter 54 in the ignition unit 51 during the expansion stroke to perform spark discharge for detection (S2). Next, ECU2 takes in the voltage signal 62 in the spark discharge for detection detected by the voltage detection unit 53a of the combustion detection unit 1b (S3).

[0092] Next, the peak voltage acquisition unit 55b of ECU2 acquires the discharge end peak voltage Vp according to the voltage signal 62 (S4). Then, the determination unit 56b of ECU2 determines whether the discharge end peak voltage Vp is less than the predetermined peak voltage comparison value Vpc (S5). In step S5, when it is determined that the discharge end peak voltage Vp is not less than the peak voltage comparison value Vpc (if S5 is "No"), the determination unit 56b of ECU2 determines that it is normal combustion (S6). After the processing of step S6, ECU2 ends the misfire detection processing.

[0093] On the other hand, in step S5, when it is determined that the discharge end peak voltage Vp is smaller than the peak voltage comparison value Vpc (if S5 is determined to be "yes"), the determination unit 56b of the ECU2 determines that there is a misfire (S7). After the processing of step S7, the ECU2 ends the misfire detection processing.

[0094] <Second embodiment> [Configuration of the ignition unit and combustion detection unit] Next, use Fig.14 The configuration of the ignition unit and the combustion detection unit according to the second embodiment will be described. Fig.14 It is an explanatory diagram showing a configuration example of an ignition unit and a combustion detection unit of an ignition device according to a second embodiment.

[0095] In the second embodiment, the combustion state is detected based on the discharge period Td in the detection spark discharge. Fig.14 As shown, the ignition device 3C of the second embodiment includes an ignition unit 51 and a combustion detection unit 1c. The combustion detection unit 1c corresponds to the combustion state detection device of the present invention.

[0096] The ignition unit 51 includes an igniter 54 and an ignition coil 52. The igniter 54 receives an ignition signal transmitted from the ECU 2. The ignition coil 52 applies a high voltage to the spark plug 40.

[0097] The combustion detection unit 1c receives current information from the ignition unit 51 and determines the combustion state of the internal combustion engine 13 based on the current information. The combustion detection unit 1c then sends the determination result to the ECU 2. The combustion detection unit 1c includes a current detection unit 53c, a discharge period acquisition unit 55c, and a determination unit 56c.

[0098] The current detection unit 53c detects the secondary current of the ignition coil 52 and sends a current signal 65 (secondary current value) to the discharge period acquisition unit 55c. The discharge period acquisition unit 55c acquires the discharge period Td of the detection spark discharge. That is, the discharge period acquisition unit 55c acquires the discharge period of the ignition coil 52 based on the input current signal 65 and outputs it to the determination unit 56c. The determination unit 56c performs a misfire determination of the internal combustion engine 13 based on the input discharge period and the discharge period comparison value received from the ECU2, and sends the determination result to the ECU2.

[0099] exist Fig.14 In FIG. 1 , an example is shown in which all the components of the combustion detection unit 1c are arranged inside the ignition device 3C. However, a part of the components of the combustion detection unit may be arranged inside the ECU 2. Fig.15 As shown, the ignition device 3D includes an ignition unit 51 and a current detection unit 53c.

[0100] The combustion detection unit 1d is composed of a current detection unit 53c arranged inside the ignition device 3D, and a discharge period acquisition unit 55d and a determination unit 56d arranged inside the ECU 2. The combustion detection unit 1d corresponds to the combustion state detection means of the present invention.

[0101] The current signal 65 output from the current detection unit 53c is sent to the ECU 2 via the current output unit 4d. The current signal 65 output from the current detection unit 53c is a voltage value proportional to the detected coil current value. The current detection unit 58 preferably regulates the voltage of the current signal 65 in a predetermined voltage range (e.g., 0 to 5 volts) so that the processing of the current signal 65 in the ECU 2 becomes easy.

[0102] When the discharge period acquisition unit 55d and the determination unit 56d are arranged inside the ECU 2 as in the combustion detection unit 1d, the processing of the discharge period acquisition unit 55d and the determination unit 56d can be executed by software operating in the ECU 2. In this case, for example, the misfire determination condition can be flexibly changed according to the operating state of the engine. Therefore, the detection of the combustion state (misfire determination) can be optimized.

[0103] [Circuit Configuration of Ignition Section and Current Detection Section] Next, use Fig.16 The circuit configuration of the ignition unit 51 and the current detection unit 53c will be described. Fig.16 It is an explanatory diagram showing an example of the circuit configuration of the ignition unit 51 and the current detection unit 53c.

[0104] like Fig.16 As shown, the ignition unit 51 includes an ignition coil 52 and an igniter 54. In addition, the current detection unit 53c includes a current detection resistor R3.

[0105] In the ignition unit 51, one end of the primary coil 52a of the ignition coil 52 is connected to a battery (DC power supply) not shown in the figure. As a result, a predetermined voltage (for example, 12V) is applied to the primary coil 52a, and a primary current flows. The other end of the primary coil 52a is connected to the collector terminal of the igniter 54. The other end of the primary coil 52a is grounded through the emitter terminal of the igniter 54. The igniter 54 can use a transistor, a field effect transistor (Field Effect Transistor: FET), etc. The base terminal of the igniter 54 is connected to the ECU2.

[0106] The secondary coil 52b of the ignition coil 52 shares a magnetic circuit and a magnetic flux with the primary coil 52a. The turns ratio of the secondary coil 52b to the primary coil 52a is set to, for example, about 100. One end of the secondary coil 52b is connected to the electrode of the spark plug 40 via the high-voltage wire 48. The other end of the secondary coil 52b is connected to the anode of the diode D0. The cathode of the diode D0 is connected to one end of the current detection resistor R3 of the current detection unit 58 and the cathode of the Zener diode TD0. The anode of the Zener diode TD0 is grounded.

[0107] While the ignition signal is being transmitted from ECU 2 to the base terminal of igniter 54, that is, while the ignition signal is turned on, the collector terminal and the emitter terminal of igniter 54 are energized so that a primary current is output from the collector terminal of igniter 54 to the emitter terminal via primary coil 52a.

[0108] When the transmission of the ignition signal from the ECU 2 to the base terminal of the igniter 54 stops, that is, when the ignition signal is disconnected, the primary current flowing through the igniter 54 is cut off. At this time, a magnetic field change occurs in the primary coil 52a, and a primary voltage is generated by self-induction. Moreover, a high secondary voltage corresponding to the turns ratio is generated in the secondary coil 52b by mutual inductance. Thus, a secondary voltage is applied to the spark plug 40, and a spark discharge is generated in the ignition gap 41 of the spark plug 40. In addition, the secondary current generated by the induction of the secondary voltage in the secondary coil 52b flows to the ground via the diode D0 and the current detection resistor R3.

[0109] The current detection unit 53c transmits the potential difference between both ends of the current detection resistor R3 as a current signal 65. If the magnitude of the secondary current flowing through the secondary coil 52b is denoted by I2, the voltage Vt of the current signal 65 is calculated by equation (2).

[0110] [Formula 2] Vt=I2×R3…(2)

[0111] That is, the current detection unit 53c sends a voltage value proportional to the secondary current to the discharge period acquisition units 55c and 55d as a current signal 65. In order to facilitate processing of the current signal 65, the resistance value of the current detection resistor R3 is determined so that the current signal 65 is about 5 volts at maximum.

[0112] In addition, the Zener diode TD0 of the ignition unit 51 forms a safety circuit when the path of the secondary current in the current detection unit 53c is disconnected. In more detail, if the path to the ground through the current detection resistor R3 of the current detection unit 53c is disconnected for some reason, the voltage applied by the Zener diode TD0 rises. And when the applied voltage of the Zener diode TD0 reaches or exceeds the breakdown voltage of the Zener diode TD0, the secondary current flows to the ground through the Zener diode TD0. Thus, even if the path of the secondary current in the current detection unit 53c is disconnected, the discharge of the ignition coil 52 can be ensured.

[0113] [Configuration of the Discharge Period Acquisition Unit and the Determination Unit] Next, use Fig.17 The configurations of the discharge period acquisition unit 55c and the determination unit 56c will be described. Fig.17 It is an explanatory diagram showing a configuration example of the discharge period acquisition unit 55c and the determination unit 56c according to the second embodiment.

[0114] like Fig.17 As shown, the discharge period acquisition unit 55c includes an absolute value circuit 69, a comparison circuit 68a, a clock generation circuit 70, and an integration circuit 71. In addition, the determination unit 56c includes a comparison circuit 68b.

[0115] The current signal 65 sent from the current detection unit 55c is input to the absolute value circuit 69. The absolute value of the current signal 65 sent from the absolute value circuit 69 and the threshold value 72 are input to the comparison circuit 68a. The integration circuit 71 is input with an integration ON signal sent from the comparison circuit 68a, a clock signal (e.g., a 100 kHz clock signal) sent from the clock generation circuit 70, and an ignition signal sent from the ECU 2.

[0116] The comparison circuit 68b of the determination unit 56c receives the discharge period Td sent from the integration circuit 71 and the discharge period comparison value Tdc sent from the ECU 2. The comparison circuit 68b outputs a determination result (High / Low). The determination result (High / Low) output from the comparison circuit 68b is sent to the ECU 2.

[0117] [Operations of the Discharge Period Acquisition Unit and the Determination Unit] Next, use Fig.18 An operation example of the discharge period acquisition unit 55c and the determination unit 56c will be described. Fig.18 It is an explanatory diagram showing an operation example of the discharge period acquisition unit 55c and the determination unit 56c according to the second embodiment.

[0118] Fig.18 The horizontal axis of the graph in represents the passage of time. Fig.18 The curve in the figure represents, starting from the upper section, the ignition signal sent from ECU2, the current signal 65 (secondary current) sent from the current detection unit 53c, the absolute value of the current signal sent from the absolute value circuit 69, the integral ON signal sent from the comparison circuit 68a, the clock signal sent from the clock generating circuit 70, the integral output value of the integral circuit 71, the discharge period comparison value Tdc sent from ECU2, and the judgment result output by the comparison circuit 68b.

[0119] like Fig.18 As shown, the integration circuit 71 resets the output value to zero when the ignition signal rises from Low to High. The absolute value circuit 69 converts the input current signal 65 into an absolute value and inputs the absolute value of the current signal to the comparison circuit 68a.

[0120] The comparison circuit 68a compares the absolute value of the input current signal with the threshold value 72 (see Fig.17 ), and when the absolute value of the current signal is greater than the threshold value 72, the integration ON signal High (indicating a power-on state) is output. In addition, when the absolute value of the current signal is less than the threshold value 72, the comparison circuit 68a outputs the integration ON signal Low (indicating a non-power-on state).

[0121] The threshold 72 is a value used to determine the energization period of the secondary current. The threshold 72 is a value sufficiently smaller than the average value of the current signal 65 when energized, and is pre-set to a value larger than the fluctuation range of the current signal 65 caused by noise when not energized. The threshold 72 is, for example, the average value of the current signal 65 when energized × 0.01.

[0122] The integration circuit 71 counts the number of clock signals input from the clock generation circuit 70 during the period when the integration ON signal input from the comparison circuit 68a is High. Then, the integration output value calculated based on the number of clocks / clock frequency is output. The period when the integration ON signal is High is the current conduction time, that is, the discharge period Td, so the integration output value after the integration ON signal drops from High to Low is equal to the discharge period Td.

[0123] The comparison circuit 68b compares the discharge period Td obtained by the integration circuit 71 with the discharge period comparison value Tdc. Then, when the discharge period Td is greater than the discharge period comparison value Tdc, the output is High (indicating misfire). On the other hand, when the discharge period Td is less than the discharge period comparison value Tdc, the output is Low (indicating normal combustion). The output of the comparison circuit 68b is sent to the ECU 2 as the determination result of the determination unit 56c.

[0124] [Procedure for misfire detection during discharge based on calculation by ECU software] Next, use Fig.19 The procedure of misfire detection based on the discharge period Td calculated by the software of the ECU 2 will be described. Fig.19 This is a flowchart showing the procedure of misfire detection based on the discharge period Td calculated by the software of the ECU 2 according to the second embodiment.

[0125] exist Fig.15 In the combustion detection unit 1d shown, the discharge period acquisition unit 55d and the determination unit 56d are arranged inside the ECU 2. Therefore, the acquisition of the discharge period Td and the misfire determination are executed by software running in the ECU 2.

[0126] like Fig.19 As shown, the ECU 2 sends an ignition signal to the igniter 54 in the ignition unit 51 from the late stage of the compression stroke to the early stage of the expansion stroke to perform the ignition spark discharge (S11). Then, during the expansion stroke, the ECU 2 sends an ignition signal to the igniter 54 in the ignition unit 51 to perform the detection spark discharge (S12). Next, the ECU 2 takes in the current signal 65 in the detection spark discharge detected by the current detection unit 53c of the combustion detection unit 1d (S13).

[0127] Then, the discharge period acquisition unit 55d of ECU2 acquires the discharge period Td from the current signal 65 (S14). Specifically, after the moment when the ignition signal drops from High to Low, the time when the absolute value of the current signal 65 is greater than the preset threshold value is acquired as the discharge period Td. Then, the determination unit 56d of ECU2 determines whether the discharge period Td is greater than the predetermined discharge period comparison value Tdc (S15). In step S15, when it is determined that the discharge period Td is not greater than the discharge period comparison value Tdc (when S15 is determined to be "No"), the determination unit 56d of ECU2 determines that it is normal combustion (S16). After the processing of step S16, ECU2 ends the misfire detection processing.

[0128] On the other hand, in step S15, when it is determined that the discharge period Td is greater than the discharge period comparison value Tdc (S15: Yes), the determination unit 56d of the ECU2 determines that there is a misfire (S17). After the process of step S17, the ECU2 ends the misfire detection process.

[0129] <Third embodiment> [Configuration of the ignition unit and combustion detection unit] Next, use Fig. 20 The configuration of the ignition unit and the combustion detection unit according to the third embodiment will be described. Fig. 20 It is an explanatory diagram showing a configuration example of an ignition unit and a combustion detection unit of an ignition device according to a third embodiment.

[0130] In the third embodiment, the combustion state is detected based on the discharge period Td in the detection spark discharge. Fig. 20 As shown, the ignition device 3E of the third embodiment includes an ignition unit 51 and a combustion detection unit 1e. The combustion detection unit 1e corresponds to the combustion state detection device of the present invention.

[0131] The ignition unit 51 includes an igniter 54 and an ignition coil 52. The igniter 54 receives an ignition signal transmitted from the ECU 2. The ignition coil 52 applies a high voltage to the spark plug 40.

[0132] The combustion detection unit 1e receives voltage information from the ignition unit 51 and determines the combustion state of the internal combustion engine 13 based on the voltage information. The combustion detection unit 1e then sends the determination result to the ECU 2. The combustion detection unit 1e includes a voltage detection unit 53e, a discharge period acquisition unit 55e, and a determination unit 56c.

[0133] The voltage detection unit 53e detects the primary voltage of the ignition coil 52 and sends the voltage signal 62e to the discharge period acquisition unit 55e. The discharge period acquisition unit 55e acquires the discharge period Td of the detection spark discharge. That is, the discharge period acquisition unit 55e acquires the discharge period of the ignition coil 52 based on the input voltage signal 62e and sends it to the determination unit 56c. The determination unit 56c performs misfire determination of the internal combustion engine 13 based on the input discharge period and the discharge period comparison value received from the ECU2, and sends the determination result to the ECU2.

[0134] In addition, the reason why the voltage detection unit 53e detects the primary voltage of the ignition coil 52 is to easily detect the discharge period of the ignition coil 52. The secondary voltage of the ignition coil 52 becomes an open circuit voltage value after the discharge of the ignition coil 52 ends, and maintains a relatively high negative voltage value (for example, -500V). Therefore, it is difficult to detect the discharge end time of the ignition coil 52 based on the magnitude of the secondary voltage of the ignition coil 52. On the other hand, the primary voltage of the ignition coil 52 becomes a reference voltage (approximately 0V) after the discharge of the ignition coil 52 ends. Therefore, the discharge end time of the ignition coil 52 can be easily detected based on the magnitude of the primary voltage of the ignition coil 52.

[0135] exist Fig. 20 In FIG. 1 , an example is shown in which all the components of the combustion detection unit 1e are arranged inside the ignition device 3E. However, a part of the components of the combustion detection unit may be arranged inside the ECU 2. Fig.21 As shown, the ignition device 3F includes an ignition unit 51 and a voltage detection unit 53e.

[0136] The combustion detection unit 1f is composed of a voltage detection unit 53e arranged inside the ignition device 3F, a discharge period acquisition unit 55f and a determination unit 56d arranged inside the ECU 2. The combustion detection unit 1f corresponds to the combustion state detection means of the present invention.

[0137] The voltage signal 62e output from the voltage detection unit 53e is sent to the ECU 2 via the voltage output unit 4f. The voltage signal 62e output from the voltage detection unit 53e is a voltage value proportional to the detected coil voltage value. The voltage detection unit 53e adjusts the voltage signal 62e to a predetermined voltage range (e.g., 0 to 5 volts) so that the voltage signal 62e can be easily processed in the ECU 2.

[0138] When the discharge period acquisition unit 55f and the determination unit 56d are arranged inside the ECU 2 as in the combustion detection unit 1f, the processing of the discharge period acquisition unit 55f and the determination unit 56d can be executed by software operating in the ECU 2. In this case, for example, the misfire determination condition can be flexibly changed according to the operating state of the engine. Therefore, the detection of the combustion state (misfire determination) can be optimized.

[0139] [Configuration of the Discharge Period Acquisition Unit and the Determination Unit] Next, use Fig. 22 The configurations of the discharge period acquisition unit 55e and the determination unit 56c will be described. Fig. 22 It is an explanatory diagram showing a configuration example of the discharge period acquisition unit 55e and the determination unit 56c according to the third embodiment.

[0140] like Fig. 22As shown, the discharge period acquisition unit 55e includes a low-pass filter circuit 80e, a comparison circuit 68e, a clock generation circuit 70, and an integration circuit 71e. In addition, the determination unit 56c includes a comparison circuit 68b.

[0141] The voltage signal 62e sent from the voltage detection unit 53e is input to the low-pass filter circuit 80e. The low-pass filter circuit 80e is set with an off period to remove the ringing noise of the voltage signal 62e. The off period of the low-pass filter circuit 80e is set to, for example, the detection spark discharge period Td×0.1.

[0142] The filtered voltage signal sent from the low-pass filter circuit 80e and the threshold value 72e are input to the comparison circuit 68e.

[0143] The integration circuit 71e receives an integration ON signal from the comparison circuit 68e, a clock signal (eg, a 100 kHz clock signal) from the clock generation circuit 70, and an ignition signal from the ECU 2.

[0144] The discharge period Td sent from the integration circuit 71e and the discharge period comparison value Tdc sent from the ECU2 are input to the comparison circuit 68b of the determination unit 56c. The comparison circuit 68b outputs a determination result (High / Low). The determination result (High / Low) output from the comparison circuit 68b is sent to the ECU2.

[0145] [Operations of the Discharge Period Acquisition Unit and the Determination Unit] Next, use Fig.23 An operation example of the discharge period acquisition unit 60e and the determination unit 56c will be described. Fig.23 It is an explanatory diagram showing an operation example of the discharge period acquisition unit 55e and the determination unit 56c according to the third embodiment.

[0146] Fig.23 The horizontal axis of the graph in represents the passage of time. Fig.23 The curve in the figure represents, starting from the upper section, the ignition signal sent from ECU2, the voltage signal 62e (primary voltage) sent from the voltage detection unit 53e, the filtered voltage signal sent from the low-pass filter circuit 80e, the integral ON signal sent from the comparison circuit 68e, the clock signal sent from the clock generating circuit 70, the integral output value of the integral circuit 71e, the discharge period comparison value Tdc sent from ECU2, and the judgment result output by the comparison circuit 68b.

[0147] like Fig.23As shown, the integration circuit 71e resets the output value to zero when the ignition signal rises from Low to High. The low-pass filter circuit 80e inputs the filtered voltage signal from which the high-frequency component of the input voltage signal 62e is removed to the comparison circuit 68e. The low-pass filter circuit 80e removes the high-frequency ringing noise generated in the voltage signal 62e. Thus, it is possible to prevent erroneous detection of the discharge period obtained from the filtered voltage signal.

[0148] The comparison circuit 68e compares the input filtered voltage signal with the threshold value 72e (see Fig. 22 ), and when the filtered voltage signal is greater than the threshold value 72e, the integration ON signal of High (indicating a power-on state) is output. In addition, when the filtered voltage signal is below the threshold value 72e, the comparison circuit 68e outputs the integration ON signal of Low (indicating a non-power-on state).

[0149] The threshold value 72e is a value for determining the current conduction period. The threshold value 72e is set in advance to a value sufficiently smaller than the average value of the voltage signal 62e during conduction. The threshold value 72e is, for example, the average value of the voltage signal 62e during conduction×0.01.

[0150] The integration circuit 71e counts the number of clock signals input from the clock generation circuit 70 during the period when the integration ON signal input from the comparison circuit 68e is High. Then, the integration circuit 71e outputs an integration output value calculated based on the number of clocks / clock frequency. The period when the integration ON signal is High is the current conduction time, that is, the discharge period Td. Therefore, the integration output value after the integration ON signal drops from High to Low is approximately equal to the discharge period Td.

[0151] The comparison circuit 68b compares the discharge period Td obtained by the integration circuit 71e with the discharge period comparison value Tdc. And, when the discharge period Td is greater than the discharge period comparison value Tdc, the comparison circuit 68b outputs High (indicating misfire). On the other hand, when the discharge period Td is less than the discharge period comparison value Tdc, the comparison circuit 68b outputs Low (indicating normal combustion). The output of the comparison circuit 68b is sent to the ECU 2 as the determination result of the determination unit 56c.

[0152] [Procedure for misfire detection during discharge based on calculation by ECU software] Next, use Fig.24 The procedure of misfire detection based on the discharge period Td calculated by the software of the ECU 2 will be described. Fig.24 This is a flowchart showing the procedure of the misfire detection process based on the discharge period Td calculated by the software of the ECU 2 according to the third embodiment.

[0153] exist Fig.21 In the combustion detection unit 1f shown, the discharge period acquisition unit 55f and the determination unit 56d are arranged inside the ECU 2. Therefore, the acquisition of the discharge period Td and the misfire determination are executed by software running in the ECU 2.

[0154] like Fig.24 As shown, ECU2 sends an ignition signal to the igniter 54 in the ignition unit 51 from the late stage of the compression stroke to the early stage of the expansion stroke to perform spark discharge for ignition (S20). Next, ECU2 sends an ignition signal to the igniter 54 in the ignition unit 51 during the expansion stroke to perform spark discharge for detection (S21). Next, ECU2 takes in the voltage signal 62e in the spark discharge for detection detected by the voltage detection unit 53e of the combustion detection unit 1f (S22).

[0155] Then, the discharge period acquisition unit 55f of the ECU2 removes the high frequency component from the voltage signal 62e by low pass filtering (S23). The low pass filter of the discharge period acquisition unit 55f of the ECU2 sets a cutoff period to remove the ringing noise of the voltage signal 62e. The cutoff period is set to, for example, the detection spark discharge period Td×0.1. The reason why the discharge period acquisition unit 55f of the ECU2 removes the high frequency component by low pass filtering is to remove the high frequency ringing noise generated in the voltage signal 62e and prevent the erroneous detection of the discharge period obtained thereafter.

[0156] Then, the discharge period acquisition unit 55f of ECU2 acquires the discharge period Td based on the filtered voltage signal (S24). Specifically, the time when the filtered voltage signal is greater than the preset power-on determination threshold after the ignition signal drops from High to Low is taken as the discharge period Td. The power-on determination threshold is a value used to determine the power-on period of the current. The power-on determination threshold is pre-set to a value sufficiently small relative to the average value of the voltage signal 62 at power-on. The power-on determination threshold is, for example, the average value of the voltage signal 62e at power-on × 0.01.

[0157] Then, the determination unit 56d of the ECU2 determines whether the discharge period Td is greater than the predetermined discharge period comparison value Tdc (S25). In step S25, when it is determined that the discharge period Td is not greater than the discharge period comparison value Tdc (if S25 is determined as "No"), the determination unit 56d of the ECU2 determines that the combustion is normal (S27). After the processing of step S27, the ECU2 ends the misfire detection processing.

[0158] On the other hand, when it is determined in step S25 that the discharge period Td is greater than the discharge period comparison value Tdc (if S25 is determined to be YES), the determination unit 56d of the ECU2 determines that there is a misfire (S26). After the process of step S26, the ECU2 ends the misfire detection process.

[0159] <Fourth embodiment> [Configuration of the ignition unit and combustion detection unit] Next, use Fig.25 and Fig.26 The configuration of an ignition unit and a combustion detection unit of an ignition device according to a fourth embodiment of the present invention will be described. Fig.25 It is an explanatory diagram showing a configuration example of an ignition unit 51 and a combustion detection unit 1g in an ignition device 3G according to a fourth embodiment. Fig.26 This is an explanatory diagram showing an example in which a part of the components of the combustion detection unit according to the fourth embodiment is arranged inside the ECU 2 .

[0160] like Fig.25 As shown, the ignition unit 51 includes an igniter 54 and an ignition coil 52. The igniter 54 receives an ignition signal transmitted from the ECU 2. The ignition coil 52 applies a high voltage to the spark plug 40.

[0161] The combustion detection unit 1g includes a voltage detection unit 53a, an average voltage acquisition unit 55g, and a determination unit 56g. The voltage detection unit 53a detects the voltage (primary voltage or polarity-inverted secondary voltage) of the ignition coil 52 and sends a voltage signal 62 to the average voltage acquisition unit 55g. In addition, the voltage detection unit 53a preferably detects the primary voltage of the ignition coil 52 rather than the secondary voltage of the ignition coil 52.

[0162] The average voltage acquisition unit 55g acquires the average voltage value of the input voltage signal 62 and sends it to the determination unit 56g. The determination unit 56g performs misfire determination of the internal combustion engine 13 based on the input average voltage value and the average voltage comparison value received from the ECU2, and sends the determination result to the ECU2.

[0163] exist Fig.25 In FIG. 1 , an example is shown in which all the components of the combustion detection unit 1g are arranged inside the ignition device 3G. However, a part of the components of the combustion detection unit may be arranged inside the ECU 2. Fig.26 As shown, the ignition device 3H includes an ignition unit 51 and a voltage detection unit 53a.

[0164] The combustion detection unit 1h is composed of a voltage detection unit 53a disposed inside the ignition device 3H, an average voltage acquisition unit 55h disposed inside the ECU 2, and a determination unit 56h. The combustion detection unit 1h corresponds to the combustion state detection device of the present invention. The voltage signal 62 output from the voltage detection unit 53a is sent to the ECU 2 via the voltage output unit 4h.

[0165] If the average voltage acquisition unit 55h and the determination unit 56h are arranged inside the ECU 2 as in the combustion detection unit 1h, the processing of the average voltage acquisition unit 55h and the determination unit 56h can be executed by software running in the ECU 2. In this case, for example, the misfire determination condition can be flexibly changed according to the operating state of the internal combustion engine 13. Therefore, the detection of the combustion state (misfire determination) can be optimized.

[0166] [Averaging period and average voltage] Next, use Fig. 27 The averaging period and the average voltage of the primary voltage of the detection spark discharge according to the fourth embodiment will be described. Fig. 27 2 is an explanatory diagram of the average voltage acquired by the average voltage acquisition unit 55g or the average voltage acquisition unit 55h.

[0167] Fig. 27 The horizontal axis of the graph shown represents the elapsed time. Fig. 27 The vertical axis of the graph shown represents an example of a voltage signal 62 (primary voltage) in the detection spark discharge detected by the voltage detection unit 53a. Here, t0 represents the start time of the detection spark discharge, and t1 represents the end time of the detection spark discharge. In addition, t2 represents the start time of averaging the voltage signal 62, and t3 represents the end time of averaging the voltage signal 62.

[0168] The average voltage acquisition unit 55g or the average voltage acquisition unit 55h acquires the average voltage Vm of the voltage signal 62 during the discharge period Td of the detection spark discharge. Here, the average voltage Vm is the collective average value of the voltage (primary voltage or polarity-reversed secondary voltage) during the discharge period Td. In addition, the average voltage Vm may also be the RMS value (square root of the square average value) of the voltage (primary voltage or secondary voltage) during the discharge period Td.

[0169] The period for averaging the voltage signal 62 (averaging period Tm) is preferably within the discharge period Td of the detection spark discharge and is the latter part of the discharge period Td. More specifically, it is preferred that the averaging start time t2 of the voltage signal 62 is after 50% of the discharge period Td. In addition, it is preferred that the averaging end time t3 of the voltage signal 62 is after 90% of the discharge period Td. According to the inventor's experiments, the desired range of the averaging start time t2 of the voltage signal 62 is expressed by formula (3). In addition, the preferred range of the averaging end time t3 of the voltage signal 62 is expressed by formula (4).

[0170] [Formula 3] t0+0.9×Td>t2≧t0+0.5×Td…(3) [Formula 4] t0+Td≧t3≧t0+0.9×Td…(4)

[0171] The reason why the averaging start time t2 of the voltage signal 62 is preferably after 50% of the discharge period is that the voltage becomes unstable due to ringing noise in the first half of the detection spark discharge. The reason why the averaging end time t3 of the voltage signal 62 is preferably after 90% of the discharge period is that the voltage at the end of the detection spark discharge has a strong correlation with the cylinder pressure as described above.

[0172] [In-cylinder pressure and average voltage] Next, use Fig.28 The relationship between the cylinder pressure and the average voltage in the fourth embodiment will be described. Fig.28 It is an explanatory diagram showing the relationship between the cylinder pressure and the average voltage Vm at the spark discharge timing for detection.

[0173] like Fig.28 As shown in FIG. 1 , there is a strong correlation between the cylinder pressure at the time of the detection spark discharge and the average voltage Vm. That is, the average voltage Vm increases as the cylinder pressure at the time of the detection spark discharge increases. The cylinder pressure at the time of the detection spark discharge becomes lower during misfire than during normal combustion. Therefore, misfire and normal combustion can be distinguished based on the size of the average voltage Vm.

[0174] [Procedure for misfire detection based on average voltage calculated by ECU software] Next, use Fig.29 The procedure of misfire detection based on the average voltage Vm calculated by the software of the ECU 2 according to the fourth embodiment will be described. Fig.29 This is a flowchart showing the procedure of the fire detection process according to the fourth embodiment.

[0175] exist Fig.26In the combustion detection unit 1h shown, the average voltage acquisition unit 55h and the determination unit 56h are arranged inside the ECU 2. Therefore, the acquisition of the average voltage Vm and the misfire determination are executed by software running in the ECU 2.

[0176] like Fig.29 As shown, ECU2 sends an ignition signal to the igniter 54 in the ignition unit 51 from the late stage of the compression stroke to the early stage of the expansion stroke, and performs spark discharge for ignition (S30). Then, during the expansion stroke, ECU2 sends an ignition signal to the igniter 54 in the ignition unit 51, and performs spark discharge for detection (S31). Then, the average voltage acquisition unit 55h of ECU2 performs the average voltage Vm acquisition process (S32). In step S32, the average voltage acquisition unit 55h acquires the average voltage Vm based on the voltage signal 62. Then, the determination unit 56h of ECU2 determines whether the average voltage Vm is less than the predetermined average voltage comparison value Vmc (S33).

[0177] In step S33, when it is determined that the average voltage Vm is not less than the average voltage comparison value Vmc (if S33 is determined as "No"), the determination unit 56h of ECU2 determines that the combustion is normal (S35). After the processing of step S35, ECU2 ends the misfire detection processing. On the other hand, when it is determined that the average voltage Vm is less than the average voltage comparison value Vmc in step S33 (if S33 is determined as "Yes"), the determination unit 56h of ECU2 determines that there is a misfire (S34). After the processing of step S34, ECU2 ends the misfire detection processing.

[0178] [Average voltage Vm acquisition process] Next, use Fig.30 Description Fig.29 The misfire detection process shown is the average voltage Vm acquisition process executed in step S32. Fig.30 This is a flowchart showing a procedure for calculating the average voltage Vm using the software of the ECU 2 .

[0179] like Fig.30 As shown, ECU2 determines whether the ignition signal is Low (S321). In step S321, if the ignition signal is not Low (if S321 determines "No"), ECU2 repeats step S321. On the other hand, if the ignition signal is Low (S321 determines "Yes"), ECU2 determines that the detection spark discharge has started and sets the current crank angle as the discharge start time t0 (S322).

[0180] Next, ECU2 takes in the voltage signal 62 in the detection spark discharge detected by the voltage detection unit 53a of the combustion detection unit 1h (S323). Then, ECU2 determines whether the voltage signal 62 is less than the pre-set power-on determination threshold (S324). In step S324, if the voltage signal is not less than the pre-set power-on determination threshold (if S324 is determined to be "No"), ECU2 writes the voltage signal and the current crank angle into the buffer (S325). After processing step S325, ECU2 returns to step S323.

[0181] In step S324, when the voltage signal is less than the pre-set power-on determination threshold (when S324 is determined to be "yes"), ECU2 determines that the detection spark discharge has ended and sets the current crank angle as the discharge end time t1 (S326). The power-on determination threshold is a value used to determine the power-on period of the current. The power-on determination threshold is pre-set to a value that is sufficiently small relative to the average value of the voltage signal 62 when the power is on. The power-on determination threshold is, for example, the average value of the voltage signal 62 when the power is on × 0.01.

[0182] Next, ECU2 calculates the averaging start time t2 of the voltage signal based on the discharge start time t0 and the discharge end time t1 (S327). The averaging start time t2 is calculated, for example, by the above-mentioned formula (3). Next, ECU2 calculates the averaging end time t3 of the voltage signal based on the discharge start time t0 and the discharge end time t1 (S328). The averaging end time t3 is calculated, for example, by the above-mentioned formula (4).

[0183] Next, the ECU 2 calculates the average voltage Vm of the voltage signal from the averaging start time t2 to the averaging end time t3 based on the voltage signal value and the crank angle written to the buffer in step S325 (S329). The average voltage Vm is, for example, the collective average of the voltage signal 62 from the averaging start time t2 to the averaging end time t3. In addition, the average voltage Vm is, for example, the RMS value of the voltage signal 62 from the averaging start time t2 to the averaging end time t3. After the processing of step S329, the ECU 2 ends the average voltage Vm acquisition processing and executes Fig.29 Step S33 of the misfire detection process is shown.

[0184] <Fifth embodiment> [Configuration of the ignition unit and combustion detection unit] Next, use Fig.31 The configuration of an ignition unit and a combustion detection unit of an ignition device according to a fifth embodiment of the present invention will be described. Fig.31 It is an explanatory diagram showing a configuration example of an ignition unit and a combustion detection unit according to a fifth embodiment.

[0185] like Fig.31 As shown, the ignition device 3I includes an ignition unit 51 and a voltage detection unit 53a. The ignition unit 51 includes an igniter 54 and an ignition coil 52. The igniter 54 receives an ignition signal sent from the ECU 2. The ignition coil 52 applies a high voltage to the spark plug 40.

[0186] The voltage detection unit 53 a detects the voltage (primary voltage or polarity-inverted secondary voltage) of the ignition coil 52 . The voltage detection unit 53 a preferably detects the primary voltage of the ignition coil 52 rather than the secondary voltage of the ignition coil 52 .

[0187] The combustion detection unit 1i is composed of a voltage detection unit 53a disposed inside the ignition device 3I, a peak voltage acquisition unit 55b disposed inside the ECU 2, an average voltage acquisition unit 55h, and a determination unit 56i. The combustion detection unit 1i corresponds to the combustion state detection device of the present invention.

[0188] The peak voltage acquisition unit 55b acquires the peak voltage Vp of the input voltage signal 62 and sends it to the determination unit 56i. The average voltage acquisition unit 55h acquires the average voltage Vm of the input voltage signal 62 and sends it to the determination unit 56i. The determination unit 56i performs misfire determination of the internal combustion engine 13 based on the input peak voltage Vp or average voltage Vm and the average voltage comparison value or peak voltage comparison value preset by the ECU2.

[0189] [Steps for ECU software-based misfire detection] Next, use Fig.32 The procedure of misfire detection by software of the ECU 2 according to the fifth embodiment will be described. Fig.32 This is a flowchart showing the procedure of the fire detection process according to the fifth embodiment.

[0190] exist Fig.31 In the combustion detection unit 1i shown, the peak voltage acquisition unit 55b, the average voltage acquisition unit 55h, and the determination unit 56i are arranged inside the ECU 2. Therefore, acquisition of the peak voltage Vp, acquisition of the average voltage Vm, and misfire determination are executed by software running in the ECU 2.

[0191] like Fig.32 As shown in FIG. 1 , ECU 2 sends an ignition signal to the igniter 54 in the ignition unit 51 from the late stage of the compression stroke to the early stage of the expansion stroke to perform spark discharge for ignition (S40). Next, ECU 2 sends an ignition signal to the igniter 54 in the ignition unit 51 during the expansion stroke to perform spark discharge for detection (S41). Then, ECU 2 determines whether the timing θd of the spark discharge for detection is greater than a preset timing comparison value θdc (S42).

[0192] In step S42, when it is determined that the detection spark discharge timing θd is not greater than the preset timing comparison value θdc (if S42 is determined as "No"), the ECU 2 performs misfire determination based on the peak voltage Vp (S43). Fig.13 The misfire determination is performed in the sequence after step S3 of the misfire determination process of the peak voltage Vp shown in FIG. After the process of step S44 , the ECU 2 ends the misfire detection process.

[0193] In step S42, when it is determined that the detection spark discharge timing θd is greater than the preset timing comparison value θdc (if S42 is determined to be "yes"), the ECU 2 performs misfire determination based on the average voltage Vm (S44). Fig.29 The misfire determination is performed in the sequence after step S32 of the misfire determination process of the average voltage Vm shown in FIG. After the process of step S44 , the ECU 2 ends the misfire detection process.

[0194] Thus, in the fifth embodiment, the misfire determination based on the peak voltage Vp and the misfire determination based on the average voltage Vm are switched according to the detection spark discharge timing θd. Fig.33A , Fig.33B and Fig.34 This advantage will be described.

[0195] Fig.33A , Fig.33B 1 is an explanatory diagram showing an example of the operation of one time (voltage signal 62 ) of the detection spark discharge when the detection spark discharge timing θd is different. Fig.33A An example of the behavior of the primary voltage (voltage signal 62 ) when the detection spark discharge timing θd is advanced (for example, the detection spark discharge timing θd is 50° after compression top dead center) is shown. Fig.33B An example of the behavior of the primary voltage (voltage signal 62) is shown when the detection spark discharge timing θd is delayed (for example, the detection spark discharge timing θd is 90° after compression top dead center). Fig.33A and Fig.33B The solid line shows an example of the behavior of the primary voltage (voltage signal 62) during normal combustion, and the dotted line shows an example of the behavior of the primary voltage (voltage signal 62) during misfire.

[0196] like Fig.33AAs shown in FIG. 1 , when the detection spark discharge timing θd is advanced (for example, when the detection spark discharge timing θd is 30° after compression top dead center), the gas flow in the cylinder is relatively strong, and the elongation of the discharge path in the detection spark discharge becomes larger. Therefore, when the detection spark discharge timing θd is advanced, the action of the voltage rise at the end of the detection spark discharge becomes significant. Therefore, when the detection spark discharge timing θd is advanced, normal combustion and misfire can be easily distinguished based on the peak voltage Vp.

[0197] On the other hand, Fig.33B As shown in FIG. 1 , when the detection spark discharge timing θd is delayed (for example, when the detection spark discharge timing θd is 90° after compression top dead center), the gas flow in the cylinder is relatively weak, and the elongation of the discharge path in the detection spark discharge becomes smaller. Therefore, when the detection spark discharge timing θd is delayed, the voltage rise at the end of the discharge becomes smaller than when the detection spark discharge timing θd is advanced. Therefore, when the detection spark discharge timing θd is delayed, normal combustion and misfire can be easily distinguished based on the average voltage Vm.

[0198] Fig.34 This is an explanatory diagram showing an example of misfire detection accuracy when misfire detection is performed based on peak voltage Vp and when misfire detection is performed based on average voltage Vm with respect to changes in detection spark discharge timing θd. Misfire detection accuracy is the ratio of the number of cycles that can correctly distinguish misfire and normal combustion to the number of test cycles.

[0199] like Fig.34 As shown in FIG. 1 , when the detection spark discharge timing θd is advanced, the voltage rise at the end of the detection spark discharge is significant. Therefore, the misfire detection based on the peak voltage Vp tends to have a higher misfire detection accuracy than the misfire detection based on the average voltage Vm. On the other hand, when the detection spark discharge timing θd is delayed, the voltage rise at the end of the detection spark discharge is small. Therefore, the misfire detection based on the average voltage Vm tends to have a higher misfire detection accuracy than the misfire detection based on the peak voltage Vp.

[0200] The detection spark discharge timing θd is implemented after the ignition spark discharge timing. Therefore, the detection spark discharge timing θd depends on the ignition spark discharge timing. The ignition spark discharge timing changes in various ways depending on the operating conditions such as the speed, torque, and exhaust gas recirculation (EGR) amount of the internal combustion engine. That is, the appropriate detection spark discharge timing θd changes in various ways depending on the operating conditions such as the speed or torque, and exhaust gas recirculation (EGR) amount of the internal combustion engine.

[0201] Therefore, the determination unit 56i of the ECU2 of the fifth embodiment compares the spark discharge timing θd for detection and the timing comparison value θdc. Then, the determination unit 56i of the ECU2 performs misfire detection based on the peak voltage Vp when the spark discharge timing θd for detection is not delayed from the timing comparison value θdc. In addition, the determination unit 56i of the ECU2 performs misfire detection based on the average voltage Vm when the spark discharge timing θd for detection is delayed from the timing comparison value θdc. Thus, even if the spark discharge timing θd for detection changes, the misfire determination process of the fifth embodiment can obtain high misfire detection accuracy.

[0202] In order to obtain sufficient misfire detection accuracy in the detection spark discharge timing θd for switching between misfire detection based on the peak voltage Vp and misfire detection based on the average voltage, the timing comparison value θdc is determined to an appropriate value in advance by calibration, etc. The appropriate value of the timing comparison value θdc is, for example, 70° after compression top dead center.

[0203] In addition, the timing comparison value θdc is not necessarily a constant value, and may be changed according to the operating conditions of the internal combustion engine. For example, an appropriate value of the timing comparison value θdc is stored in advance as map data for changes in the speed and torque of the internal combustion engine. Then, the determination unit 56i of the ECU 2 refers to the map data and changes the timing comparison value θdc according to the operating conditions of the internal combustion engine. In this way, by changing the timing comparison value θdc according to the operating conditions of the internal combustion engine, even if the operating conditions of the internal combustion engine change, the misfire detection accuracy can be maintained at a high level.

[0204] <Sixth embodiment> [Configuration of the ignition unit and combustion detection unit] Next, use Fig.35 The configuration of an ignition unit and a combustion detection unit of an ignition device according to a sixth embodiment of the present invention will be described. Fig.35 It is an explanatory diagram showing a configuration example of an ignition unit and a combustion detection unit according to the sixth embodiment.

[0205] like Fig.35 As shown, the ignition device 3J includes an ignition unit 51 and a voltage detection unit 53a. The ignition unit 51 includes an igniter 54 and an ignition coil 52. The igniter 54 receives an ignition signal transmitted from the ECU 2. The ignition coil 52 applies a high voltage to the spark plug 40.

[0206] The voltage detection unit 53 a detects the voltage (primary voltage or polarity-inverted secondary voltage) of the ignition coil 52 . The voltage detection unit 53 a preferably detects the primary voltage of the ignition coil 52 rather than the secondary voltage of the ignition coil 52 .

[0207] The combustion detection unit 1j is composed of a voltage detection unit 53a disposed inside the ignition device 3J, a voltage change rate acquisition unit 55j disposed inside the ECU 2, and a determination unit 56j. The combustion detection unit 1j corresponds to the combustion state detection device of the present invention. The voltage detection unit 53a detects the voltage (primary voltage or secondary voltage with reversed polarity) of the ignition coil 52 and outputs it as a voltage signal 62.

[0208] The voltage change rate acquisition unit 55j disposed inside the ECU2 acquires the voltage change rate dV from the input voltage signal 62 and sends it to the determination unit 56j. The determination unit 56j performs misfire determination of the internal combustion engine 13 based on the input voltage change rate dV and a voltage change rate comparison value preset by the ECU2.

[0209] Fig.36A , Fig.36B 2 is an explanatory diagram of the voltage change rate acquired by the voltage change rate acquisition unit 55j. Fig.36A and Fig.36B The horizontal axis of the graph shown represents the elapsed time. Fig.36A The vertical axis represents the primary voltage (voltage signal 62) detected by the voltage detection unit 53a during the detection spark discharge. Fig.36B The vertical axis represents the time differential value dV / dt of the primary voltage (voltage signal 62) detected by the voltage detection unit 53a during the detection spark discharge.

[0210] The voltage change rate dV acquired by the voltage change rate acquisition unit 55j is calculated by equation (5). That is, the voltage change rate dV acquired by the voltage change rate acquisition unit 55j is the average value of the time differential value dV / dt of the primary voltage (voltage signal 62) in the averaging period Tdm.

[0211] [Formula 5]

[0212] The period for averaging the time differential value of the voltage (averaging period Tdm) is preferably between the middle and end of the detection spark discharge. More specifically, the averaging start time t4 of the time differential value of the voltage is preferably in the range of 40% to 60% of the discharge period Td after the detection spark discharge starts. In addition, the averaging end time t5 of the time differential value of the voltage is preferably in the range of 90% to 100% of the discharge period Td after the detection spark discharge starts. According to the inventor's experiments, the desired range of the averaging start time t4 of the time differential value of the voltage is expressed by formula (6). In addition, the preferred range of the averaging end time t5 of the time differential value of the voltage is expressed by formula (7).

[0213] [Formula 6] t0+0.6×Td≧t4≧t0+0.4×Td…(6) [Formula 7] t0+Td≧t5≧t0+0.9×Td…(7)

[0214] The reason why the averaging start time t4 and the averaging end time t5 are preferably within the above range is that the change in voltage behavior caused by the difference in cylinder pressure becomes significant mainly in the later period of the detection spark discharge period. This is because the accuracy of the time differential value of the voltage decreases due to ringing noise in the early period of the detection spark discharge period.

[0215] [Cylinder pressure and voltage change rate] Next, use Fig.37 The relationship between the cylinder pressure and the voltage change rate dV is explained. Fig.37 This is an explanatory diagram showing an example of the relationship between the cylinder pressure and the voltage change rate dV at the detection spark discharge timing according to the sixth embodiment.

[0216] like Fig.37 As shown, the cylinder pressure and the voltage change rate dV at the timing of the detection spark discharge have a high correlation. That is, the lower the cylinder pressure at the timing of the detection spark discharge, the smaller the voltage change rate dV. This is because the lower the cylinder pressure at the timing of the detection spark discharge, the smaller the elongation of the discharge path in the detection spark discharge, which suppresses the voltage rise in the later stage of the discharge of the detection spark discharge. Therefore, compared with normal combustion when the cylinder pressure at the timing of the detection spark discharge becomes high, the voltage change rate dV of the detection spark discharge becomes smaller during misfire when the cylinder pressure at the timing of the detection spark discharge becomes low.

[0217] Therefore, in the sixth embodiment, the upper limit value of the voltage change rate dV during misfire (voltage change rate comparison value dVc for misfire determination) is determined in advance by calibration or the like. Then, if the voltage change rate dV of the detection spark discharge is smaller than the voltage change rate comparison value dVc, the determination unit 56j of the ECU 2 determines that there is misfire. On the other hand, if the voltage change rate dV of the detection spark discharge is not smaller than the voltage change rate comparison value dVc, the determination unit 56j determines that there is normal combustion.

[0218] [Procedure for misfire detection based on voltage change rate calculated by ECU software] Next, use Fig.38 The procedure of misfire detection based on the voltage change rate dV calculated by the software of the ECU 2 will be described. Fig.38 This is a flowchart showing the procedure of the fire detection process according to the sixth embodiment.

[0219] exist Fig.35In the combustion detection unit 1j shown, the voltage change rate acquisition unit 55j and the determination unit 56j are arranged inside the ECU 2. Therefore, the acquisition of the voltage change rate dV and the misfire determination are executed by software running in the ECU 2.

[0220] like Fig.38 As shown, ECU2 sends an ignition signal to the igniter 54 in the ignition unit 51 from the late stage of the compression stroke to the early stage of the expansion stroke, and performs spark discharge for ignition (S50). Next, ECU2 sends an ignition signal to the igniter 54 in the ignition unit 51 during the expansion stroke, and performs spark discharge for detection (S51). Then, the voltage change rate acquisition unit 55j of ECU2 performs voltage change rate dV acquisition processing (S52). In step S52, the voltage change rate acquisition unit 55j acquires the voltage change rate dV based on the voltage signal 62. Then, the determination unit 56j of ECU2 determines whether the voltage change rate dV is less than the predetermined voltage change rate comparison value dVc (S53).

[0221] In step S53, when it is determined that the voltage change rate dV is not less than the voltage change rate comparison value dVc (when S53 is determined as "No"), the determination unit 56j of ECU2 determines that it is normal combustion (S55). After the processing of step S55, ECU2 ends the misfire detection processing. On the other hand, in step S53, when it is determined that the voltage change rate dV is less than the voltage change rate comparison value dVc (when S53 is determined as "Yes"), the determination unit 56j of ECU2 determines that there is a misfire (S54). After the processing of step S54, ECU2 ends the misfire detection processing.

[0222] [Voltage change rate dV acquisition process] Next, use Fig.39 Description Fig.38 The voltage change rate dV acquisition process is executed in step S52 of the misfire detection process shown. Fig.39 3 is a flowchart showing a procedure for calculating the voltage change rate dV by the software of the ECU 2 in step S52 .

[0223] like Fig.39 As shown, ECU2 determines whether the ignition signal is Low (S521). In step S521, if the ignition signal is not Low (S521 is determined as "No"), step S521 is repeated. In step S521, if the ignition signal is Low (S52a is determined as "Yes"), ECU2 determines that discharge has started and sets the current crank angle as the discharge start time t0 (S522).

[0224] Next, ECU2 takes in the voltage signal 62 in the detection spark discharge detected by the voltage detection unit 53a of the combustion detection unit 1j (S523). Then, ECU2 determines whether the voltage signal 62 is less than the preset power-on determination threshold (S524). In step S524, when the voltage signal 62 is not less than the preset power-on determination threshold (when S524 is determined to be "No"), ECU2 calculates the time differential value dV / dt of the voltage signal 62 (S525). Then, ECU2 writes the time differential value dV / dt of the voltage signal 62 and the current crank angle into the buffer (S526). After processing step S526, ECU2 returns to step S523.

[0225] In step S524, when the voltage signal 62 is less than the pre-set power-on determination threshold (when S524 is determined as "yes"), the ECU 2 determines that the discharge is completed and sets the current crank angle as the discharge end time t1 (S527). The power-on determination threshold is a value used to determine the power-on period of the current. The power-on determination threshold is pre-set to a value that is sufficiently small relative to the average value of the voltage signal 62 when the power is on. The power-on determination threshold is, for example, the average value of the voltage signal 62 when the power is on × 0.01.

[0226] Next, the ECU2 calculates the averaging start time t4 of the voltage differential value based on the discharge start time t0 and the discharge end time t1 (S528). The averaging start time t4 is calculated, for example, by the above-mentioned formula (6). Next, the ECU2 calculates the averaging end time t5 of the voltage differential value based on the discharge start time t0 and the discharge end time t1 (S529). The averaging end time t5 is calculated, for example, by the above-mentioned formula (7).

[0227] Next, ECU2 calculates the voltage change rate dV based on the voltage differential value dV / dt and the crank angle written into the buffer in step S526 (S530). The voltage change rate dV is the average value of the voltage differential value from the time t1 when the voltage differential value is averaged to the time t5 when the voltage differential value is averaged. The voltage change rate dV is calculated, for example, by the above-mentioned formula (5). After the processing of step S530, ECU2 ends the voltage change rate dV acquisition processing and executes Fig.38 Step S53 of the misfire detection process is shown.

[0228] [Changes in Peak Voltage Comparison Value and Discharge Period Comparison Value Depending on the Operating State of the Internal Combustion Engine] Next, use Fig.40A , Fig.40B , Fig.40C Changes in the voltage comparison value and the discharge period comparison value will be described. Fig.40A , Fig.40B, Fig.40C It is an explanatory diagram showing a preferred method of changing the peak voltage comparison value Vpc and the discharge period comparison value Tdc with respect to changes in the engine (internal combustion engine) torque, the engine (internal combustion engine) speed, and the intake pressure.

[0229] In the first, second, third and fifth embodiments described above, the peak voltage comparison value Vpc and the discharge period comparison value Tdc for distinguishing misfire from normal combustion can be appropriately determined according to the operating state of the internal combustion engine 13 (engine). Thus, even when the operating state of the internal combustion engine 13 is changed, the accuracy of misfire detection can be maintained at a high level.

[0230] Fig.40A The graph of φ shows an example of the relationship between the average engine torque and the expected peak voltage comparison value Vpc and the discharge period comparison value Tdc. Fig.40B The graph of φ(t) shows an example of the relationship between the average engine speed and the expected peak voltage comparison value Vpc and the discharge period comparison value Tdc. Fig.40C The graph of shows an example of the relationship between the average intake pressure and the expected peak voltage comparison value Vpc and the discharge period comparison value Tdc. Here, "average" refers to the average value of multiple cycles of the engine (internal combustion engine), for example, the average value of 100 cycles of the engine.

[0231] When the average engine torque is high, the average cylinder pressure in the expansion stroke becomes higher than when the average engine torque is low. Fig.40A As shown, when the average engine torque is high, it is preferable to increase the peak voltage comparison value Vpc and decrease the discharge period comparison value Tdc compared to when the average engine torque is low.

[0232] When the average engine speed is high, the extension of the detection spark discharge becomes larger than when the average engine speed is low. Fig.40B As shown, when the average engine speed is high, it is preferable to increase the peak voltage comparison value Vpc and decrease the discharge period comparison value Tdc compared to when the average engine speed is low.

[0233] When the mean intake pressure is high, the mean cylinder pressure in the expansion stroke becomes higher than when the mean intake pressure is low. Fig.40C As shown, when the average intake pressure is high, it is preferable to increase the peak voltage comparison value Vpc and decrease the discharge period comparison value Tdc, compared with when the average intake pressure is low.

[0234] [Changes to voltage comparison value and voltage change rate comparison value] Next, use Fig.41A , Fig.41B , Fig.41C The following describes changes in the voltage comparison value and the voltage change rate comparison value. Fig.41A , Fig.41B , Fig.41C It is an explanatory diagram showing a preferred method of changing the average voltage comparison value Vmc and the voltage change rate comparison value dVc in response to changes in the engine (internal combustion engine) torque, the engine (internal combustion engine) speed, and the intake pressure.

[0235] In the fourth, fifth and sixth embodiments, the average voltage comparison value Vmc and the voltage change rate comparison value dVc for distinguishing misfire and normal combustion can be appropriately determined according to the operating state of the internal combustion engine 13 (engine). Thus, even when the operating state of the internal combustion engine 13 is changed, the accuracy of misfire detection can be maintained at a high level.

[0236] Fig.41A The graph of shows an example of the relationship between the average engine torque and the desired average voltage comparison value Vmc and the voltage change rate comparison value dVc. Fig.41B The graph of shows an example of the relationship between the average engine speed and the desired average voltage comparison value Vmc and the voltage change rate comparison value dVc. Fig.41C The graph of shows an example of the relationship between the average intake pressure and the expected average voltage comparison value Vmc and the voltage change rate comparison value dVc. Here, "average" refers to the average value of multiple cycles of the engine (internal combustion engine), for example, the average value of 100 cycles of the engine.

[0237] When the average engine torque is high, the average cylinder pressure in the expansion stroke becomes higher than when the average engine torque is low. Fig.41A As shown, when the average engine torque is high, it is preferable to increase the average voltage comparison value Vmc and the voltage change rate comparison value dVc compared to when the average engine torque is low.

[0238] When the average engine speed is high, the extension of the detection spark discharge becomes larger than when the average engine speed is low. Fig.41B As shown, when the average engine speed is high, it is preferable to increase the average voltage comparison value Vmc and the voltage change rate comparison value dVc compared to when the average engine speed is low.

[0239] When the mean intake pressure is high, the mean cylinder pressure in the expansion stroke becomes higher than when the mean intake pressure is low. Fig.41CAs shown, when the mean intake pressure is high, it is preferable to increase the mean voltage comparison value Vmc and the voltage change rate comparison value dVc compared to when the mean intake pressure is low.

[0240] <Conclusion> (1) The combustion state detection device for an internal combustion engine of the first embodiment described above includes peak voltage acquisition units 55a, 55b (peak voltage acquisition units) and determination units 56a, 56b (determination units). The peak voltage acquisition units 55a, 55b acquire the discharge end peak voltage Vp (peak voltage value at the discharge end) based on the voltage of the ignition coil 52 (ignition coil) connected to the spark plug 40 (spark plug) that performs discharge. The determination units 56a, 56b compare the discharge end peak voltage Vp acquired by the peak voltage acquisition units 55a, 55b with the peak voltage comparison value Vpc (peak voltage comparison value). The spark plug 40 performs an ignition spark discharge for igniting the air-fuel mixture, and performs a detection spark discharge in the same engine cycle after the ignition spark discharge. Then, the determination units 56a, 56b determine that there is a misfire when the discharge end peak voltage Vp of the detection spark discharge is less than the peak voltage comparison value Vpc. Thus, even for a fuel that does not generate ions due to combustion, misfire can be easily detected based on the discharge end peak voltage Vp. That is, misfire can be detected regardless of the type of fuel. In addition, since misfire is not detected based on the presence or absence of breakdown (insulation breakdown), it is not necessary to determine the appropriate applied voltage when performing the detection spark discharge, and robustness can be maintained.

[0241] (2) The peak voltage comparison value Vpc (peak voltage comparison value) in the combustion state detection device for an internal combustion engine of the first embodiment is changed according to the operating state of the internal combustion engine. As a result, even if the operating state of the internal combustion engine changes, the accuracy of misfire detection based on the discharge end peak voltage Vp can be maintained at a high level.

[0242] (3) In the combustion state detection device for an internal combustion engine according to the first embodiment, the peak voltage comparison value Vpc (voltage comparison value) increases as the engine torque, engine speed, or intake pressure increases. Thus, even if the engine torque, the engine speed, or the intake pressure changes, the accuracy of misfire detection based on the discharge end peak voltage Vp can be maintained at a high level.

[0243] (4) The combustion state detection device for an internal combustion engine according to the first embodiment described above includes the voltage detection unit 53a (voltage detection unit) that detects the voltage of the ignition coil 52 (ignition coil). Thus, it is possible to easily supply information related to the voltage of the ignition coil 52 to the peak voltage acquisition units 55a and 55b (peak voltage acquisition units). In addition, a combustion state detection device (peak voltage acquisition unit 55a, determination unit 56a, and voltage detection unit 53a) may be provided in the ignition device 3A. In this case, by receiving an ignition signal for implementing a detection spark discharge from the ECU2, the detection result of the misfire state can be supplied to the ECU2.

[0244] (5) The peak voltage acquisition unit 55b (peak voltage acquisition unit) and the determination unit 56b (determination unit) in the combustion state detection device for an internal combustion engine of the first embodiment are included in the ECU 2 (control unit), and the ECU 2 outputs an ignition signal for causing the spark plug 40 (spark plug) to perform spark discharge for ignition and spark discharge for detection. Then, the voltage detection unit 53a (voltage detection unit) detects the voltage value after the primary voltage of the ignition coil 52 (ignition coil) or the secondary voltage after polarity inversion is stepped down, and the detected voltage value is sent to the peak voltage acquisition unit 55b. Thus, the processing of acquiring the peak voltage Vp at the end of the discharge and the processing of detecting the combustion state (misfire determination) can be performed by the software operating in the ECU2. In this case, for example, the conditions for misfire determination (peak voltage comparison value Vpc) can be flexibly changed according to the operating state of the internal combustion engine 13. Therefore, the detection of the combustion state can be optimized, and the cost related to the hardware can be reduced. In addition, since the voltage detection unit 53a detects the voltage value after the primary voltage of the ignition coil 52 or the secondary voltage after the polarity is reversed is stepped down, the voltage sent to the peak voltage acquisition unit 55b can be set to the voltage range normally processed inside the ECU2. Thus, the increase in the hardware cost of the ECU2 can be suppressed.

[0245] (6) The combustion state detection device for an internal combustion engine of the second embodiment includes discharge period acquisition units 55c, 55d (discharge period acquisition units) and determination units 56c, 56d (determination units). The discharge period acquisition units 55c, 55d acquire the discharge period Td (discharge period) based on the current of the ignition coil 52 (ignition coil) connected to the spark plug 40 (spark plug) that performs discharge. The determination units 56c, 56d compare the discharge period Td acquired by the discharge period acquisition units 55c, 55d with the discharge period comparison value Tdc (discharge period comparison value). The spark plug 40 performs an ignition spark discharge for igniting the air-fuel mixture, and performs a detection spark discharge in the same engine cycle after the ignition spark discharge. And, the determination units 56c, 56d determine that there is a misfire when the discharge period Td of the detection spark discharge is greater than the discharge period comparison value Tdc. Thus, even for a fuel that does not generate ions due to combustion, a misfire can be easily detected from the discharge period Td. That is, a misfire can be detected regardless of the type of fuel. In addition, since a misfire is not detected based on the presence or absence of breakdown (insulation breakdown), it is not necessary to determine an appropriate applied voltage when performing a detection spark discharge, and robustness can be maintained.

[0246] (7) The combustion state detection device for an internal combustion engine according to the second embodiment changes the discharge period comparison value Tdc (discharge period comparison value) in accordance with the operating state of the internal combustion engine. Thus, even if the operating state of the internal combustion engine changes, the accuracy of misfire detection based on the discharge period Td can be maintained at a high level.

[0247] (8) In the combustion state detection device for an internal combustion engine according to the second embodiment, the discharge period comparison value Tdc decreases as the engine torque, the engine speed, or the intake pressure increases. Thus, even if the engine torque, the engine speed, or the intake pressure changes, the accuracy of misfire detection based on the discharge period Td can be maintained at a high level.

[0248] (9) The combustion state detection device for an internal combustion engine according to the second embodiment described above includes the current detection unit 53c (current detection unit) that detects the current of the ignition coil 52 (ignition coil). Thus, it is possible to easily supply the information related to the current of the ignition coil 52 to the discharge period acquisition units 55c and 55d (discharge period acquisition units). In addition, a combustion state detection device (discharge period acquisition unit 55c, determination unit 56c, and current detection unit 53c) may be provided in the ignition device 3C. In this case, by receiving an ignition signal for implementing a detection spark discharge from the ECU2, the detection result of the misfire state can be supplied to the ECU2.

[0249] (10) The discharge period acquisition unit 55d (discharge period acquisition unit) and the determination unit 56d (determination unit) in the combustion state detection device for an internal combustion engine of the second embodiment are included in the ECU 2 (control unit), and the ECU 2 outputs an ignition signal for causing the spark plug 40 (spark plug) to perform spark discharge for ignition and spark discharge for detection. Then, the current detection unit 53c (current detection unit) detects the secondary current value of the ignition coil 52 (ignition coil), and sends the detected secondary current value to the discharge period acquisition unit 55d. Thus, the process of acquiring the discharge period Td and the process of detecting the combustion state (misfire determination) can be executed by the software running in the ECU 2. In this case, for example, the misfire determination condition (discharge period comparison value Tdc) can be flexibly changed according to the operating state of the internal combustion engine 13. Therefore, the detection of the combustion state can be optimized and the cost related to the hardware can be reduced.

[0250] (11) The combustion state detection device for an internal combustion engine of the third embodiment includes discharge period acquisition units 55e, 55f (discharge period acquisition units) and determination units 56c, 56d (determination units). The discharge period acquisition units 55e, 55f acquire the discharge period Td (discharge period) based on the primary voltage of the ignition coil 52 (ignition coil) connected to the spark plug 40 (spark plug) that performs discharge. The determination units 56c, 56d compare the discharge period Td acquired by the discharge period acquisition units 55e, 55f with the discharge period comparison value Tdc (discharge period comparison value). The spark plug 40 performs an ignition spark discharge for igniting the air-fuel mixture, and performs a detection spark discharge in the same engine cycle after the ignition spark discharge. And, the determination units 56c, 56d determine that there is a misfire when the discharge period Td of the detection spark discharge is greater than the discharge period comparison value Tdc. Thus, even for a fuel that does not generate ions due to combustion, misfire can be easily detected from the discharge period Td. That is, misfire can be detected regardless of the type of fuel. In addition, since misfire is not detected based on the presence or absence of breakdown (insulation breakdown), it is not necessary to determine the appropriate applied voltage when performing the detection spark discharge. As a result, robustness can be maintained.

[0251] (12) The determination units 56c, 56d (determination unit) of the combustion state detection device for an internal combustion engine in the third embodiment change the discharge period comparison value Tdc (discharge period comparison value) according to the operating state of the internal combustion engine. Thus, even if the operating state of the internal combustion engine changes, the accuracy of misfire detection based on the discharge period Td can be maintained at a high level.

[0252] (13) In the combustion state detection device for an internal combustion engine of the third embodiment, the discharge period comparison value Tdc decreases as the engine torque, the engine speed, or the intake pressure increases. Thus, even if the engine torque, the engine speed, or the intake pressure changes, the accuracy of misfire detection based on the discharge period Td can be maintained at a high level.

[0253] (14) The combustion state detection device for an internal combustion engine according to the third embodiment described above includes the voltage detection unit 53e (voltage detection unit) that detects the primary voltage of the ignition coil 52 (ignition coil). Thus, it is possible to easily supply the discharge period acquisition units 55e and 55f (discharge period acquisition units) with information related to the voltage of the ignition coil 52. In addition, a combustion state detection device (discharge period acquisition unit 55e, determination unit 56c, and voltage detection unit 53e) may be provided in the ignition device 3E. In this case, by receiving an ignition signal for implementing a detection spark discharge from the ECU2, the detection result of the misfire state can be supplied to the ECU2.

[0254] (15) The discharge period acquisition unit 55f (discharge period acquisition unit) and the determination unit 56d (determination unit) in the combustion state detection device for an internal combustion engine of the third embodiment are included in the ECU 2 (control unit), and the ECU 2 outputs an ignition signal for causing the spark plug 40 (spark plug) to perform spark discharge for ignition and spark discharge for detection. Then, the voltage detection unit 53e (voltage detection unit) detects the primary voltage value of the ignition coil 52 (ignition coil), and sends the detected voltage value to the discharge period acquisition unit 55f. Thus, the process of acquiring the discharge period Td and the process of detecting the combustion state (misfire determination) can be executed by the software running in the ECU 2. In this case, for example, the misfire determination condition (discharge period comparison value Tdc) can be flexibly changed according to the operating state of the internal combustion engine 13. Therefore, the detection of the combustion state can be optimized and the cost related to the hardware can be reduced.

[0255] (16) The combustion state detection device of the internal combustion engine of the fourth embodiment includes average voltage acquisition units 55g, 55h (average voltage acquisition units) and determination units 56g, 56h (determination units). The average voltage acquisition units 55g, 55h acquire the average voltage Vm based on the voltage of the ignition coil 52 (ignition coil) connected to the spark plug 40 (spark plug) that performs discharge. The determination units 56g, 56h compare the average voltage Vm acquired by the average voltage acquisition units 55g, 55h with the average voltage comparison value Vmc. The spark plug 40 performs an ignition spark discharge for igniting the air-fuel mixture, and performs a detection spark discharge in the same engine cycle after the ignition spark discharge. Furthermore, the determination units 56g, 56h determine that there is a misfire when the average voltage Vm of the detection spark discharge is smaller than the average voltage comparison value Vmc. Thus, even for a fuel that does not generate ions due to combustion, misfire can be easily detected based on the average voltage Vm. That is, misfire can be detected regardless of the type of fuel. In addition, since misfire is not detected based on the presence or absence of breakdown (insulation breakdown), it is not necessary to determine the appropriate applied voltage when performing the detection spark discharge. As a result, robustness can be maintained.

[0256] (17) In the combustion state detection device for an internal combustion engine of the fourth embodiment, the average voltage comparison value Vmc is changed according to the operating state of the internal combustion engine. Thus, even if the operating state of the internal combustion engine changes, the accuracy of misfire detection based on the average voltage Vm can be maintained at a high level.

[0257] (18) In the combustion state detection device for an internal combustion engine according to the fourth embodiment, the average voltage comparison value Vmc increases as the engine torque, the engine speed, or the intake pressure increases. Thus, even if the engine torque, the engine speed, or the intake pressure changes, the accuracy of misfire detection based on the average voltage Vm can be maintained at a high level.

[0258] (19) The combustion state detection device for an internal combustion engine according to the fourth embodiment includes the voltage detection unit 53a (voltage detection unit) that detects the voltage of the ignition coil 52 (ignition coil). Thus, it is possible to easily provide information related to the voltage of the ignition coil 52 to the average voltage acquisition units 55g and 55h (average voltage acquisition units). In addition, a combustion state detection device (average voltage acquisition unit 55g, determination unit 56g, and voltage detection unit 53a) may be provided on the ignition device 3G. In this case, by receiving an ignition signal for implementing a detection spark discharge from the ECU 2, the detection result of the misfire state can be provided to the ECU 2.

[0259] (20) The average voltage acquisition unit 55h (average voltage acquisition unit) and the determination unit 56h (determination unit) in the combustion state detection device for an internal combustion engine of the fourth embodiment are included in the ECU 2 (control unit), and the ECU 2 outputs an ignition signal for causing the spark plug 40 (spark plug) to perform spark discharge for ignition and spark discharge for detection. Then, the voltage detection unit 53a (voltage detection unit) detects the voltage value after the primary voltage of the ignition coil 52 (ignition coil) or the secondary voltage after polarity inversion is stepped down, and the detected voltage value is sent to the average voltage acquisition unit 55h. Thus, the process of acquiring the average voltage Vm and the process of detecting the combustion state (misfire determination) can be executed by software operating in the ECU2. In this case, for example, the condition for misfire determination (average voltage comparison value Vmc) can be flexibly changed according to the operating state of the internal combustion engine 13. Therefore, the detection of the combustion state can be optimized, and the cost related to the hardware can be reduced. In addition, since the voltage detection unit 53a detects the voltage value after the primary voltage of the ignition coil 52 or the secondary voltage after the polarity is reversed is stepped down, the voltage sent to the average voltage acquisition unit 55h can be set to the voltage range normally processed inside the ECU2. Thus, the increase in the hardware cost of the ECU2 can be suppressed.

[0260] (21) The combustion state detection device for an internal combustion engine of the fifth embodiment includes a peak voltage acquisition unit 55b (peak voltage acquisition unit), an average voltage acquisition unit 55h (average voltage acquisition unit), and a determination unit 56i (determination unit). The peak voltage acquisition unit 55b acquires a peak voltage Vp at the end of discharge (peak voltage value at the end of discharge) based on the voltage of the ignition coil 52 (ignition coil) connected to the spark plug 40 (spark plug) that performs discharge. The average voltage acquisition unit 55h acquires an average voltage Vm (average voltage) based on the voltage of the ignition coil 52 (ignition coil) connected to the spark plug 40 (spark plug) that performs discharge. The spark plug 40 performs an ignition spark discharge for igniting the air-fuel mixture, and performs a detection spark discharge in the same engine cycle after the ignition spark discharge. The determination unit 56i compares the detection spark discharge timing θd (detection spark discharge timing) with the timing comparison value θd (timing comparison value). Furthermore, the determination unit 56i compares the average voltage Vm acquired by the average voltage acquisition unit 55h with the average voltage comparison value Vmc (average voltage comparison value) when the detection spark discharge timing θd is greater than the timing comparison value θd, and determines that there is a misfire when the average voltage Vm of the detection spark discharge is less than the average voltage comparison value Vmc. Furthermore, the determination unit 56i compares the discharge end peak voltage Vp acquired by the peak voltage acquisition unit 55b with the peak voltage comparison value Vpc (peak voltage comparison value) when the detection spark discharge timing θd is not greater than the timing comparison value θd, and determines that there is a misfire when the discharge end peak voltage Vp of the detection spark discharge is less than the peak voltage comparison value Vpc. Thus, even for a fuel that does not generate ions due to combustion, misfire can be easily detected based on the average voltage Vm or the peak voltage Vp at the end of the discharge. That is, misfire can be detected regardless of the type of fuel. In addition, since misfire is not detected based on the presence or absence of breakdown (insulation breakdown), it is not necessary to determine the appropriate applied voltage when performing the detection spark discharge. As a result, robustness can be maintained. In addition, since the misfire judgment based on the peak voltage Vp and the misfire judgment based on the average voltage Vm are switched according to the detection spark discharge timing θd, high misfire detection accuracy can be obtained even when the detection spark discharge timing θd changes.

[0261] (22) In the combustion state detection device for an internal combustion engine according to the fifth embodiment, the average voltage comparison value Vmc and the peak voltage comparison value Vpc are changed according to the operating state of the internal combustion engine. Thus, even if the operating state of the internal combustion engine changes, the accuracy of misfire detection based on the average voltage Vm and the accuracy of misfire detection based on the peak voltage Vp can be maintained high.

[0262] (23) In the combustion state detection device for an internal combustion engine according to the fifth embodiment, the average voltage comparison value Vmc and the peak voltage comparison value Vp increase as the engine torque, the engine speed, or the intake pressure increases. Thus, even if the engine torque, the engine speed, or the intake pressure changes, the accuracy of misfire detection based on the average voltage Vm and the accuracy of misfire detection based on the peak voltage Vp can be maintained high.

[0263] (24) The timing comparison value θd (timing comparison value) in the combustion state detection device for an internal combustion engine of the fifth embodiment is changed according to the operating state of the internal combustion engine. Thus, even if the operating state of the internal combustion engine changes, the accuracy of misfire detection based on the average voltage Vm and the accuracy of misfire detection based on the peak voltage Vp can be maintained high.

[0264] (25) The combustion state detection device for an internal combustion engine of the sixth embodiment includes a voltage change rate acquisition unit 55j (voltage change rate acquisition unit) and a determination unit 56j (determination unit). The voltage change rate acquisition unit 55j acquires the voltage change rate dV (voltage change rate) based on the voltage of the ignition coil 52 (ignition coil) connected to the spark plug 40 (spark plug) that performs discharge. The determination unit 56j compares the voltage change rate dV acquired based on the voltage change rate 55j with a voltage change rate comparison value dVc (voltage change rate comparison value). The spark plug 40 performs an ignition spark discharge for igniting the air-fuel mixture, and performs a detection spark discharge in the same engine cycle after the ignition spark discharge. Then, the determination unit 56j determines that there is a misfire when the voltage change rate dV of the detection spark discharge is less than the voltage change rate comparison value dVc. Thus, even for a fuel that does not generate ions due to combustion, misfire can be easily detected based on the voltage change rate dV. That is, misfire can be detected regardless of the type of fuel. In addition, since misfire is not detected based on the presence or absence of breakdown (insulation breakdown), it is not necessary to determine the appropriate applied voltage when performing the detection spark discharge. As a result, robustness can be maintained.

[0265] (26) In the combustion state detection device for an internal combustion engine of the sixth embodiment, the voltage change rate comparison value dVc (voltage change rate comparison value) is changed according to the operating state of the internal combustion engine. Thus, even if the operating state of the internal combustion engine changes, the accuracy of misfire detection based on the voltage change rate dV can be maintained at a high level.

[0266] (27) In the combustion state detection device for an internal combustion engine according to the sixth embodiment, the voltage change rate comparison value dVc (voltage change rate comparison value) increases as the engine torque, engine speed, or intake pressure increases. Thus, even if the engine torque, the engine speed, or the intake pressure changes, the accuracy of misfire detection based on the voltage change rate dV can be maintained at a high level.

[0267] (28) In the combustion state detection device of the internal combustion engine of the above-mentioned first to sixth embodiments, the timing of the spark discharge for detection is in the range from a timing that is 20° ahead of the period when the combustion mass ratio is 90% to a timing that is 40° behind the period when the combustion mass ratio is 90%. Thus, the detection of the misfire state is not affected by the breakdown assistance caused by the ions generated by combustion. As a result, even a fuel (such as hydrogen or ammonia) that hardly generates ions by combustion can detect misfire.

[0268] (29) With respect to the detection spark discharge of the first to sixth embodiments described above, the time (ON period of the ignition signal) during which magnetic energy is accumulated in the ignition coil 52 (ignition coil) during the detection spark discharge is determined so as to produce a spark discharge accompanied by breakdown regardless of the presence or absence of a misfire. Thus, it is not necessary to determine the applied voltage of the detection spark discharge so that breakdown occurs during misfire and no breakdown occurs during normal combustion. Therefore, it is possible to detect a misfire state robustly to changes in the operating state of the internal combustion engine 13 or the environmental state.

[0269] (30) With respect to the detection spark discharge of the first to sixth embodiments described above, when the timing of sending the detection ignition signal is on the advance angle side of the expansion stroke, the time for accumulating magnetic energy in the ignition coil 52 (ignition coil) during the detection spark discharge (the ON period of the ignition signal) is extended compared to when the timing of sending the detection ignition signal is on the retarded angle side of the expansion stroke. In addition, when the load (torque) of the internal combustion engine is high, the time for accumulating magnetic energy in the ignition coil 52 (ignition coil) during the detection spark discharge (the ON period of the ignition signal) is extended compared to when the load (torque) of the internal combustion engine is low. Thus, when the timing of transmitting the detection ignition signal is on the advance angle side of the expansion stroke or when the load (torque) of the internal combustion engine is high, the risk of spark discharge not occurring (breakdown) can be reduced.

[0270] (31) In the combustion state detection device of the internal combustion engine of the first embodiment and the fourth to sixth embodiments, the voltage detection unit 53 a (voltage detection unit) that detects the voltage of the ignition coil 52 (ignition coil) detects the primary voltage of the ignition coil 52 . This can reduce hardware costs and improve safety and reliability.

[0271] The present invention is not limited to the embodiments described above and shown in the drawings, and various modifications can be made without departing from the gist of the invention described in the claims.

[0272] In addition, the above-mentioned embodiments are embodiments described in detail for easy understanding of the present invention, and are not necessarily limited to embodiments having all the described structures. In addition, a part of the structure of some embodiments can be replaced by the structure of other embodiments, and the structure of other embodiments can be added to the structure of some embodiments. In addition, for a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0273] For example, the combustion detection unit (combustion state detection device for an internal combustion engine) 1a, 1b of the first embodiment described above is provided with a voltage detection unit 53a, but the combustion state detection device for an internal combustion engine of the present invention may not be provided with the voltage detection unit 53a. In this case, for example, the combustion state detection device may be constituted only by the ECU. Then, the ECU obtains the discharge end peak voltage based on the voltage value of the ignition coil supplied from the ignition device, and detects the misfire state (combustion state) based on the discharge end peak voltage.

[0274] In addition, the combustion detection unit (combustion state detection device for the internal combustion engine) 1c, 1d of the second embodiment described above is provided with the current detection unit 53c, but the combustion state detection device for the internal combustion engine of the present invention may not be provided with the current detection unit 53c. In this case, for example, the combustion state detection device may be constituted only by the ECU. Then, the ECU acquires the discharge period based on the current value of the ignition coil supplied from the ignition device, and detects the misfire state (combustion state) based on the discharge period.

[0275] In addition, the combustion detection unit (combustion state detection device of the internal combustion engine) 1e, 1f of the third embodiment has a voltage detection unit 53e. However, as the combustion state detection device of the internal combustion engine of the present invention, it is also possible not to have the voltage detection unit 53e. In this case, for example, the combustion state detection device can be constituted only by the ECU. Then, the ECU obtains the discharge period based on the voltage value of the ignition coil supplied from the ignition device, and detects the misfire state (combustion state) based on the discharge period.

[0276] In addition, the combustion detection unit (combustion state detection device for the internal combustion engine) 1g, 1h of the fourth embodiment has a voltage detection unit 53a. However, the combustion state detection device for the internal combustion engine of the present invention may not have the voltage detection unit 53a. In this case, for example, the combustion state detection device may be constituted only by the ECU. Then, the ECU obtains the average voltage based on the voltage value of the ignition coil supplied from the ignition device, and detects the misfire state (combustion state) based on the average voltage.

[0277] In addition, the combustion detection unit (combustion state detection device of the internal combustion engine) 1i of the fifth embodiment described above has a voltage detection unit 53a. However, as the combustion state detection device of the internal combustion engine of the present invention, it is also possible not to have the voltage detection unit 53a. In this case, for example, the combustion state detection device can be constituted only by the ECU. Then, the ECU obtains the average voltage and the peak voltage based on the voltage value of the ignition coil supplied from the ignition device, and detects the misfire state (combustion state) based on the average voltage and the peak voltage.

[0278] In addition, the combustion detection unit (combustion state detection device for an internal combustion engine) 1j of the sixth embodiment described above has a voltage detection unit 53a. However, the combustion state detection device for an internal combustion engine of the present invention may not have the voltage detection unit 53a. In this case, for example, the combustion state detection device may be constituted only by the ECU. Then, the ECU obtains the voltage change rate based on the voltage value of the ignition coil supplied from the ignition device, and detects the misfire state (combustion state) based on the voltage change rate. Explanation of symbols

[0279] 1, 1', 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j...combustion detection unit (combustion state detection device), 2...ECU (control unit), 3, 3', 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H, 3I, 3J...ignition device, 4...voltage output unit, 5...current output unit, 13...internal combustion engine (engine), 31...intake manifold, 32...intake valve, 33...exhaust manifold, 34...exhaust valve, 35...piston, 36...injector, 37...combustion chamber, 38...cylinder, 40...spark plug, 41...ignition gap, 48...high-voltage wire, 51...ignition unit, 52...ignition coil, 52a...primary coil, 52b...secondary coil, 53... Discharge amount detection unit, 53a, 53e...voltage detection unit, 53c...current detection unit, 54...igniter, 55, 55'...discharge characteristic quantity acquisition unit, 55a, 55b...peak voltage acquisition unit, 55c, 55d, 55e, 55f...discharge period acquisition unit, 55h...average voltage acquisition unit, 55j...voltage change rate acquisition unit, 56, 56', 56a, 56b, 56c, 56d, 56g, 56h, 56i, 56j...determination unit, 62, 62e...voltage signal, 65...current signal, 66...trigger generation circuit, 67...peak hold circuit, 68, 68a, 68b...comparison circuit, 69...absolute value circuit, 70...clock generation circuit, 71...integration circuit

Claims

1. A combustion state detection device for an internal combustion engine, characterized in that: have: a discharge characteristic quantity acquisition unit that acquires the discharge characteristic quantity based on a voltage value or a current value of an ignition coil connected to a spark plug of the internal combustion engine; and a determination unit that compares the discharge characteristic amount acquired by the discharge characteristic amount acquisition unit with a predetermined determination threshold value, The spark plug performs an ignition spark discharge for igniting the mixture, and performs a detection spark discharge in the same engine cycle after the ignition spark discharge. The discharge characteristic value acquisition unit acquires the discharge characteristic value based on a voltage value or a current value of the ignition coil during the detection spark discharge. The determination unit determines whether the internal combustion engine is in a misfire state or a non-misfire state based on a comparison between the discharge characteristic amount and the predetermined determination threshold value.

2. The combustion state detection device for an internal combustion engine according to claim 1, characterized in that: The discharge characteristic value acquisition unit acquires a peak voltage value of the ignition coil at the end of a discharge period of the detection spark discharge based on a voltage value of the ignition coil. The determination unit determines that the internal combustion engine is in a misfire state when the peak voltage value is smaller than a predetermined peak voltage determination threshold value.

3. The combustion state detection device for an internal combustion engine according to claim 1, characterized in that: The discharge characteristic value acquisition unit acquires a discharge period of the detection spark discharge based on a secondary current value of the ignition coil. The determination unit determines that the internal combustion engine is in a misfire state when a discharge period of the detection spark discharge is greater than a predetermined discharge period determination threshold value.

4. The combustion state detection device for an internal combustion engine according to claim 1, characterized in that: The discharge characteristic value acquisition unit acquires a discharge period of the detection spark discharge based on a primary voltage value of the ignition coil. The determination unit determines that the internal combustion engine is in a misfire state when a discharge period of the detection spark discharge is greater than a predetermined discharge period determination threshold value.

5. The combustion state detection device for an internal combustion engine according to claim 1, characterized in that: The discharge characteristic value acquisition unit acquires an average voltage value of the ignition coil during a predetermined averaging period of the detection spark discharge based on the voltage value of the ignition coil. The determination unit determines that the internal combustion engine is in a misfire state when the average voltage value is smaller than a predetermined average voltage determination threshold value.

6. The combustion state detection device for an internal combustion engine according to claim 1, characterized in that: The discharge characteristic value acquisition unit acquires a peak voltage value of the ignition coil at the end of a discharge period of the detection spark discharge and an average voltage value of the ignition coil during a predetermined averaging period of the detection spark discharge based on a voltage value of the ignition coil. When the timing of the detection spark discharge is later than a predetermined timing determination threshold value, and when the average voltage value is smaller than a predetermined average voltage determination threshold value, the determination unit determines that the internal combustion engine is in a misfire state. The determination unit determines that the internal combustion engine is in a misfire state when the timing of the detection spark discharge is not later than a predetermined timing determination threshold value and when the peak voltage value is smaller than a predetermined peak voltage determination threshold value.

7. The combustion state detection device for an internal combustion engine according to claim 6, characterized in that: The determination unit changes the predetermined timing determination threshold value according to an operating state of the internal combustion engine.

8. The combustion state detection device for an internal combustion engine according to claim 5 or 6, characterized in that: When the start time of the detection spark discharge is t0, the start time of the predetermined averaging period is t2, the end time of the predetermined averaging period is t3, and the discharge period of the detection spark discharge is Td, The range of t2 is expressed by the following formula (1), and the range of t3 is expressed by the following formula (2): (Formula 1) t0+0.9×Td>t2≧t0+0.5×Td…(1) (Formula 2) t0+Td≧t3≧t0+0.9×Td…(2).

9. The combustion state detection device for an internal combustion engine according to claim 1, characterized in that: The discharge characteristic value acquisition unit acquires a voltage change rate during a discharge period of the detection spark discharge based on a voltage value of the ignition coil. The determination unit determines that the internal combustion engine is in a misfire state when the voltage change rate is smaller than a predetermined voltage change rate determination threshold value.

10. The combustion state detection device for an internal combustion engine according to claim 9, characterized in that: The voltage change rate is an average value of time-differential values ​​of the voltage in a predetermined averaging period of the detection spark discharge.

11. The combustion state detection device for an internal combustion engine according to claim 10, characterized in that: When the start time of the detection spark discharge is t0, the start time of the predetermined averaging period is t4, the end time of the predetermined averaging period is t5, and the discharge period of the detection spark discharge is Td, The range of t4 is expressed by the following formula (3), and the range of t5 is expressed by the following formula (4): (Formula 3) t0+0.6×Td>t4≧t0+0.4×Td…(3) (Formula 4) t0+Td≧t5≧t0+0.9×Td…(4).

12. The combustion state detection device of an internal combustion engine according to claim 1, characterized in that: The determination unit changes the predetermined determination threshold value according to an operating state of the internal combustion engine.

13. The combustion state detection device for an internal combustion engine according to claim 2 or 6, characterized in that: The determination unit increases the peak voltage determination threshold value as the torque, the rotation speed, or the intake pressure of the internal combustion engine increases.

14. The combustion state detection device for an internal combustion engine according to claim 3 or 4, characterized in that: The determination unit decreases the discharge period determination threshold value as the torque, the rotation speed, or the intake pressure of the internal combustion engine increases.

15. The combustion state detection device for an internal combustion engine according to claim 5 or 6, characterized in that: The determination unit increases the average voltage determination threshold value as the torque, the rotation speed, or the intake pressure of the internal combustion engine increases.

16. The combustion state detection device for an internal combustion engine according to claim 9, characterized in that: The determination unit increases the voltage change rate determination threshold value as the torque, the rotation speed, or the intake pressure of the internal combustion engine increases.

17. The combustion state detection device for an internal combustion engine according to claim 1, characterized in that: An ECU is provided, wherein the ECU outputs an ignition signal for implementing the ignition spark discharge and the detection spark discharge to the spark plug, The ECU includes the discharge characteristic amount acquisition unit and the determination unit.

18. The combustion state detection device of an internal combustion engine according to claim 1, characterized in that: The timing of the detection spark discharge is within a range from a timing that is 20° ahead of the timing when the combustion mass ratio is 90% to a timing that is 40° behind the timing when the combustion mass ratio is 90%.

19. The combustion state detection device for an internal combustion engine according to claim 1, characterized in that: The time for accumulating magnetic energy in the ignition coil during the detection spark discharge is 0.2 ms to 1 ms.

20. The combustion state detection device of an internal combustion engine according to claim 1, characterized in that: When the timing of the detection spark discharge is on the advanced angle side of the expansion stroke, the time for which magnetic energy is accumulated in the ignition coil in the detection spark discharge is longer than when the timing of the detection spark discharge is on the retarded angle side of the expansion stroke.

21. The combustion state detection device of an internal combustion engine according to claim 1, characterized in that: When the torque of the internal combustion engine is high, the time for which magnetic energy is accumulated in the ignition coil in the detection spark discharge is longer than when the torque of the internal combustion engine is low.

22. The combustion state detection device for an internal combustion engine according to claim 1, 5, 6 or 9, characterized in that: A discharge information detection unit is provided, the discharge information detection unit detecting a voltage value or a current value of an ignition coil connected to the spark plug, The discharge information detection unit detects a primary voltage value of the ignition coil.

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