Fire detection method and fire detection device

Abstract

To detect an accidental fire in an engine (internal combustion engine) with high accuracy.SOLUTION: In an accidental fire detection method, during auxiliary chamber ignition operation in which an ignition spark plug for an auxiliary chamber ignites an air-fuel mixture in the auxiliary chamber, an ignition device for a main chamber detects the concentration of ions in the main chamber, and an accidental fire detection unit detects an accidental fire based on the detection result of the ignition device for a main chamber.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for detecting misfires in an internal combustion engine.

Background Art

[0002] Patent Document 1 discloses a pre-chamber type spark ignition engine provided with a main combustion chamber (abbreviated as "main chamber") of an engine and a pre-chamber (abbreviated as "pre-chamber") communicating with the main chamber. In the pre-chamber type spark ignition engine, since the air-fuel mixture generated in the pre-chamber quickly burns the air-fuel mixture in the main chamber by the jet flame generated, high thermal efficiency can be obtained.

[0003] The pre-chamber type spark ignition engine disclosed in Patent Document 1 is provided with a circuit for detecting an ion current generated by combustion in an ignition device that applies a high voltage to the ignition plug of the pre-chamber. Then, misfires and combustion failures are detected based on the magnitude of the ion current. In this method, since the ignition plug and the ignition device have the function as an ion sensor, the combustion state of the engine can be detected at low cost without adding a pressure sensor or the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in a pre-chamber type spark ignition engine, even if the air-fuel mixture in the pre-chamber burns and a jet flame is formed, there is a possibility that ignition of the air-fuel mixture in the main chamber fails and a misfire occurs. In this case, in the pre-chamber type spark ignition engine described in Patent Document 1, a circuit for detecting an ion current provided in an ignition device that applies a high voltage to the ignition plug of the pre-chamber detects the ion current accompanying the combustion in the pre-chamber. As a result, even if a misfire occurs in the main chamber, there is a risk of being determined as "normal combustion".

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a misfire detection method and a misfire detection device that detect misfires in an engine (internal combustion engine) with high accuracy.

Means for Solving the Problems

[0007] In order to solve the above problems and achieve the object of the present invention, the misfire detection method of the present invention includes a main chamber into which an air-fuel mixture flows, a main chamber ignition plug provided in the main chamber, a sub-chamber communicating with the main chamber, a sub-chamber ignition plug provided in the sub-chamber, a main chamber ignition device that applies a voltage for igniting the air-fuel mixture in the main chamber to the main chamber ignition plug, and a sub-chamber ignition device that applies a voltage for igniting the air-fuel mixture in the sub-chamber to the sub-chamber ignition plug, and detects misfires in the internal combustion engine. In this misfire detection method, during sub-chamber ignition operation in which the sub-chamber ignition plug ignites the air-fuel mixture in the sub-chamber, the main chamber ignition device detects the concentration of ions in the main chamber, and the misfire detection unit Compare the concentration of ions in the main chamber with a predetermined ion threshold for the main chamber to determine if there is a partial misfire where ignition of the air-fuel mixture in the main chamber fails despite successful ignition of the air-fuel mixture in the auxiliary chamber, and a complete misfire where ignition of the air-fuel mixture in the auxiliary chamber fails, including misfire whether or not is detected. During sub-chamber ignition operation, the sub-chamber ignition device detects the concentration of ions in the sub-chamber. When the misfire detection unit detects a misfire in the main chamber during sub-chamber ignition operation being and the concentration of ions in the sub-chamber is not less than a pre-determined sub-chamber ion threshold for misfire pattern discrimination in part it is determined as partial misfire, and when the concentration of ions in the sub-chamber is less than or equal to the sub-chamber ion threshold for misfire pattern discrimination completely it is determined as complete misfire.

[0008] Further, the misfire detection device of the present invention detects misfires in an internal combustion engine including a main chamber into which an air-fuel mixture flows, a main chamber ignition plug provided in the main chamber, an auxiliary chamber communicating with the main chamber, an auxiliary chamber ignition plug provided in the auxiliary chamber, a main chamber ignition device that applies a voltage for igniting the air-fuel mixture in the main chamber to the main chamber ignition plug, and an auxiliary chamber ignition device that applies a voltage for igniting the air-fuel mixture in the auxiliary chamber to the auxiliary chamber ignition plug. The main chamber ignition device has a primary coil and a secondary coil that generates an electromotive force when the energization of the primary coil is interrupted. The misfire detection device includes a main chamber power storage unit, an in-main-chamber ion detection unit, and a misfire detection unit. The main chamber power storage unit stores electric charge by the current flowing through the secondary coil of the main chamber ignition device. The in-main-chamber ion detection unit detects the concentration of ions in the main chamber when the main chamber power storage unit applies a voltage to the electrodes of the main chamber ignition plug. The misfire detection unit compares the magnitude of the ion concentration detected by the in-main-chamber ion detection unit with a predetermined main chamber ion threshold value during an auxiliary chamber ignition operation in which the air-fuel mixture in the auxiliary chamber is ignited by the auxiliary chamber ignition plug and , during auxiliary chamber ignition operation including partial misfire during auxiliary chamber ignition operation where ignition of the air-fuel mixture in the main chamber fails despite successful ignition of the air-fuel mixture in the auxiliary chamber, and complete misfire during auxiliary chamber ignition operation where ignition of the air-fuel mixture in the auxiliary chamber fails detects whether or not it is a misfire. The auxiliary chamber ignition device has a primary coil and a secondary coil that generates an electromotive force when the energization of the primary coil is interrupted. Further, the misfire detection device includes an auxiliary chamber power storage unit and an in-auxiliary-chamber ion detection unit. The misfire detection unit, during the auxiliary chamber ignition operation During auxiliary chamber ignition operation misfire being When detecting, if the concentration of ions in the auxiliary chamber is not less than a predetermined auxiliary chamber ion threshold value for misfire pattern discrimination During auxiliary chamber ignition operation it is determined as partial misfire, and when the concentration of ions in the auxiliary chamber is less than or equal to the auxiliary chamber ion threshold value for misfire pattern discrimination During auxiliary chamber ignition operation it is determined as complete misfire.

Advantages of the Invention

[0009] According to the misfire detection method and the misfire detection device having the above configuration, misfires in the engine (internal combustion engine) can be detected with high accuracy. Note that problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0010]

Figure 1

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Figure 16

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Figure 18

Embodiments for Carrying Out the Invention

[0011] Hereinafter, examples of embodiments for carrying out the present invention will be described with reference to the accompanying drawings. Components having substantially the same function or configuration in this specification and the accompanying drawings are denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] 1. First Embodiment <Engine> First, a configuration example of an engine according to the first embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 shows an example of a cross section of an engine according to the first embodiment of the present invention.

[0013] As shown in FIG. 1, the engine 13 includes a cylinder 38, a piston 35 that slides within the cylinder 38, an intake valve 32, an exhaust valve 34, and spark plugs 40a and 40b. A main chamber 37 facing the piston 35 is formed within the cylinder 38. The main chamber 37 communicates with an intake manifold 31, an exhaust manifold 33, and a sub-chamber 42. Further, a spark plug 40b is attached to the cylinder 38.

[0014] The intake valve 32 opens and closes the communication between the intake manifold 31 and the main chamber 37. The exhaust valve 34 opens and closes the communication between the exhaust manifold 33 and the main chamber 37. An injector 36 for injecting fuel is provided in the intake manifold 31. An air-fuel mixture in which the fuel injected by the injector 36 and the air sucked from the intake manifold 31 are mixed is supplied to the main chamber 37.

[0015] The sub-chamber 42 is a space surrounded by the sub-chamber forming member 45. The sub-chamber forming member 45 is formed in a hollow substantially cylindrical shape. A spark plug 40a is attached to one axial end of the sub-chamber forming member 45. The other axial end of the sub-chamber forming member 45 penetrates the cylinder 38 and is disposed in the main chamber 37.

[0016] A plurality of through-holes 43 are provided at the other axial end of the sub-chamber forming member 45. In the compression stroke in which the piston 35 ascends, the air-fuel mixture in the main chamber 37 passes through the through-holes 43 of the sub-chamber forming member 45 and is taken into the sub-chamber 42. That is, the sub-chamber 42 takes in the air-fuel mixture from the main chamber 37.

[0017] The engine 13 also includes a sub-chamber ignition device 50a that applies a high voltage to the spark plug 40a and a main-chamber ignition device 50b that applies a high voltage to the spark plug 40b. When a high voltage is applied from the sub-chamber ignition device 50a, the spark plug 40a generates a spark discharge to ignite the air-fuel mixture in the sub-chamber 42. When a high voltage is applied from the main-chamber ignition device 50b, the spark plug 40b generates a spark discharge to ignite the air-fuel mixture in the main chamber 37.

[0018] The sub-chamber ignition device 50a has an ignition unit 51a. The sub-chamber ignition device 50a is electrically connected to an ECU (Electronic Control Unit) 2. Based on an ignition control signal 59a transmitted from the ECU 2, the ignition unit 51a applies a high voltage to the spark plug 40a through a high-tension cord 48a.

[0019] The ignition device 50b for the main chamber has an ignition unit 51b and an ion current detection unit 90b. The ignition device 50b for the main chamber is electrically connected to the ECU 2. The ignition unit 51b applies a high voltage to the spark plug 40b through the high-tension cord 48b based on the ignition control signal 59b transmitted from the ECU 2. The ion current detection unit 90b detects a main chamber ion signal 98b when the air-fuel mixture in the main chamber 37 burns. The ignition device 50b for the main chamber transmits the main chamber ion signal 98b detected by the ion current detection unit 90b to the ECU 2.

[0020] The spark plug 40a includes electrodes 41a (a ground electrode and a center electrode) disposed in the sub-chamber 42. In the compression stroke in which the piston 35 rises, the air-fuel mixture that has passed through the through-hole 43 of the sub-chamber forming member 45 from the main chamber 37 is taken into the sub-chamber 42. Then, when a high voltage is applied from the ignition device 50a for the sub-chamber to the spark plug 40a near top dead center of compression, the electrodes 41a generate a spark discharge.

[0021] When the electrodes 41a generate a spark discharge, the air-fuel mixture in the sub-chamber 42 ignites and a flame is generated in the sub-chamber 42. The flame in the sub-chamber 42 jets out into the main chamber 37 as a plurality of flame jets through the through-hole 43. As a result, the air-fuel mixture in the main chamber 37 ignites at multiple points. The air-fuel mixture that has burned in the main chamber 37 pushes down the piston 35 and rotates a crankshaft (not shown). As a result, the power generated by the engine 13 is taken out to the outside.

[0022] The spark plug 40b includes electrodes 41b (a ground electrode and a center electrode) disposed in the main chamber 37. When a high voltage is applied from the ignition device 50b for the main chamber to the spark plug 40b near top dead center of compression, the electrodes 41b generate a spark discharge. As a result, the air-fuel mixture in the main chamber 37 ignites. The air-fuel mixture that has burned in the main chamber 37 pushes down the piston 35 and rotates a crankshaft (not shown). As a result, the power generated by the engine 13 is taken out to the outside.

[0023] Thus, the engine 13 performs at least ignition by the spark plug 40a provided in the auxiliary chamber 42 (abbreviated as "auxiliary chamber ignition") and ignition by the spark plug 40b provided in the main chamber 37 (abbreviated as "main chamber ignition"). Hereinafter, the state of performing auxiliary chamber ignition is referred to as the auxiliary chamber ignition mode, and the state of performing main chamber ignition is referred to as the main chamber ignition mode.

[0024] The two ignition modes can be used separately as follows. For example, when the engine 13 is in a warm-up state and the engine load is high, the engine 13 is operated in the auxiliary chamber ignition mode. In the auxiliary chamber ignition mode, since the air-fuel mixture in the main chamber 37 is multi-point ignited by the flame jet generated in the auxiliary chamber 42, the combustion in the main chamber 37 is completed in a short time. Therefore, in the auxiliary chamber ignition mode, the occurrence of knocking can be suppressed in a high-temperature and high-load state where knocking is relatively likely to occur, and a large engine output can be obtained. Also, since the combustion in the main chamber 37 is completed in a short time, the isochoric ratio increases, and a high thermal efficiency can be obtained.

[0025] For example, when the engine 13 is in a cold state or the engine load is low, the engine 13 is operated in the main chamber ignition mode. Generally, the auxiliary chamber 42 has a relatively large specific surface area (surface area relative to volume). Therefore, most of the combustion heat generated in the auxiliary chamber 42 is radiated to the outside of the engine 13 through the wall surface of the auxiliary chamber 42. Therefore, when the wall surface temperature of the auxiliary chamber forming member 45 or the combustion temperature of the engine 13 is low, the air-fuel mixture cannot maintain a high-temperature state for continuous combustion, and even if ignition is performed in the auxiliary chamber 42, the possibility of misfire increases.

[0026] On the other hand, the main chamber 37 has a relatively small specific surface area. Therefore, when the wall surface temperature of the cylinder 38 or the combustion temperature of the engine 13 is low, even if ignition is performed in the main chamber 37, the possibility of misfire is low. Therefore, when the engine 13 is in a cold state or the engine load is low, by operating the engine 13 in the main chamber ignition mode, stable operation with less misfire becomes possible.

[0027] In the main chamber ignition mode, ignition occurs at a single point within the main chamber 37, and the flame propagates over a long distance until combustion is completed. Therefore, the combustion period is longer in the main chamber ignition mode than in the sub-chamber ignition mode. This is a factor that reduces the output and thermal efficiency of the engine 13. Therefore, when the engine 13 reaches the warm-up state and the engine load increases, it is desirable to quickly shift to the main chamber ignition mode or the sub-chamber ignition mode.

[0028] <Sub-chamber ignition device> Next, the configuration of the sub-chamber ignition device 50a will be described with reference to FIG. 2. FIG. 2 is an explanatory diagram showing a configuration example of the sub-chamber ignition device 50a.

[0029] As shown in FIG. 2, the sub-chamber ignition device 50a includes an ignition unit 51a. The ignition unit 51a includes a primary coil 52a, a secondary coil 53a, and an igniter 54a. One end of the primary coil 52a is connected to a battery (DC power source) (not shown). As a result, a predetermined voltage (e.g., 12V) is applied to the primary coil 52a, and a primary current flows.

[0030] The other end of the primary coil 52a is connected to the collector terminal of the igniter 54a and is grounded via the emitter terminal of the igniter 54a. Transistors, field effect transistors (FETs), etc. are used for the igniter 54a. The base terminal of the igniter 54a is connected to the ECU 2.

[0031] The secondary coil 53a shares a magnetic circuit and magnetic flux with the primary coil 52a. The turns ratio of the secondary coil 53a to the primary coil 52a is set to about 100, for example. One end of the secondary coil 53a is connected to the electrode 41a of the spark plug 40a. The other end of the secondary coil 53a is connected to the anode of the diode 57a. The cathode of the diode 57a is grounded via the resistor 58a.

[0032] While the ignition control signal 59a is being transmitted from the ECU 2 to the base terminal of the igniter 54a, that is, while the ignition control signal 59a is on, the collector terminal and the emitter terminal of the igniter 54a are energized. As a result, the primary current is output from the collector terminal to the emitter terminal of the igniter 54a via the primary coil 52a.

[0033] When the transmission of the ignition control signal 59a from the ECU 2 to the base terminal of the igniter 54a stops, that is, when the ignition control signal 59a is turned off, the primary current flowing through the igniter 54a is interrupted. At this time, a magnetic field change occurs in the primary coil 52a, and a primary voltage is generated by self-induction. Then, a high secondary voltage corresponding to the turns ratio is generated in the secondary coil 53a by mutual induction. As a result, the secondary voltage is applied to the electrode 41a of the spark plug 40a, and spark discharge occurs at the electrode 41a. Also, the secondary current generated by inducing the secondary voltage in the secondary coil 53a flows through the diode 57a and the resistor 58a.

[0034] <Main chamber ignition device> Next, the configuration of the main chamber ignition device 50b will be described with reference to FIG. 3. FIG. 3 is an explanatory diagram showing a configuration example of the main chamber ignition device 50b.

[0035] As shown in FIG. 3, the main chamber ignition device 50b includes an ignition unit 51b and an ion current detection unit 90b. The ignition unit 51b includes a primary coil 52b, a secondary coil 53b, and an igniter 54b. One end of the primary coil 52b is connected to a battery (DC power supply) not shown. As a result, a predetermined voltage (for example, 12 V) is applied to the primary coil 52b, and a primary current flows.

[0036] The other end of the primary coil 52b is connected to the collector terminal of the igniter 54b and is grounded via the emitter terminal of the igniter 54b. A transistor, a field effect transistor, or the like is used for the igniter 54b. The base terminal of the igniter 54b is connected to the ECU 2.

[0037] The secondary coil 53b shares the magnetic circuit and magnetic flux with the primary coil 52b. The turns ratio of the secondary coil 53b to the primary coil 52b is set to about 100, for example. One end of the secondary coil 53b is connected to the electrode 41b of the ignition plug 40b. The other end of the secondary coil 53b is connected to the ion current detection unit 90b.

[0038] The ion current detection unit 90b includes a capacitor 91b, a Zener diode 92b for controlling the charging voltage connected in parallel with the capacitor 91b, and a voltage conversion resistor 93b connected to the capacitor 91b.

[0039] Also, the ion current detection unit 90b includes a secondary current path diode 94b and an ion current path diode 95b. The secondary current path diode 94b connects the connection point of the capacitor 91b, the Zener diode 92b, and the voltage conversion resistor 93b to the GND. The ion current path diode 95b connects the capacitor 91b to the GND via the voltage conversion resistor 93b.

[0040] While the ignition control signal 59b is being transmitted from the ECU2 to the base terminal of the igniter 54b, that is, while the ignition control signal 59b is on, the collector terminal and the emitter terminal of the igniter 54b are in a conducting state. As a result, the primary current passes through the primary coil 52b and is output from the collector terminal to the emitter terminal of the igniter 54b.

[0041] When the transmission of the ignition control signal 59b from the ECU2 to the base terminal of the igniter 54b stops, that is, when the ignition control signal 59b is turned off, the primary current flowing through the igniter 54b is interrupted. At this time, a magnetic field change occurs in the primary coil 52b, and a primary voltage is generated by self-induction. Then, a high secondary voltage corresponding to the turns ratio is generated in the secondary coil 53b by mutual induction. As a result, the secondary voltage is applied to the electrode 41b of the ignition plug 40b, and spark discharge occurs at the electrode 41b.

[0042] When a discharge spark occurs in the ignition plug 40b, a secondary current flows in the ion current detection unit 90b in the direction of arrow 96b. Then, when the voltage of the secondary coil 53b decreases and becomes lower than the breakdown voltage of the Zener diode 92b (for example, +100 V), the secondary current flows into the capacitor 91b. As a result, the capacitor 91b is charged with electric charge.

[0043] In the main chamber 37 where the ignition plug 40b is installed, ions such as chemical ions and thermal ions exist as intermediate products of the combustion process. When the spark discharge of the ignition plug 40b disappears and the secondary current stops flowing, the electric charge stored in the capacitor 91b is discharged. As a result, a voltage for detecting ion current (for example, +100 V) is applied to the ignition plug 40b via the secondary coil 53b. As a result, positive ions and electrons in the main chamber 37 are captured by the electrode 41b, and an ion current flows in the ion current detection unit 90b in the direction of arrow 97b.

[0044] The ion current flows through the ion current path diode 95b via the GND and is voltage-converted by the voltage-converting resistor 93b. As a result, a voltage corresponding to the magnitude of the ion current is sent to the ECU2 as the main chamber ion signal 98b.

[0045] <Ignition control signal and ion signal in sub-chamber ignition mode> Next, an example of the ignition control signal and the ion signal when the engine 13 is operated in the sub-chamber ignition mode will be described with reference to FIG. 4. FIG. 4 is an explanatory diagram showing an example of the ignition control signal and the ion signal in the sub-chamber ignition mode.

[0046] The horizontal axis of the graph shown in FIG. 4 indicates the passage of time. Regarding the main chamber ion signal 98b, examples of the change 123 of the main chamber ion signal 98b when the air-fuel mixture in the main chamber 37 burns normally and the change 124 of the main chamber ion signal 98b when the air-fuel mixture in the main chamber 37 misfires are shown.

[0047] The ignition control signal 59b is transmitted to charge the capacitor 91b. However, if the air-fuel mixture in the main chamber 37 ignites prior to the sub-chamber ignition when the ignition control signal 59b is transmitted, the pressure in the main chamber 37 may rise earlier than that in the sub-chamber 42. As a result, there is a risk that the flame jet directed from the sub-chamber 42 to the main chamber 37 will not be generated. Therefore, the transmission timing of the ignition control signal 59b is determined so that the air-fuel mixture in the main chamber 37 does not ignite prior to the sub-chamber ignition.

[0048] The transmission of the ignition control signal 59b is carried out at any timing from the initial stage of the combustion stroke (the stroke from the start of sub-chamber ignition to the start of exhaust) of the engine 13 to the mid-stage of the compression stroke. Here, the initial stage of the combustion stroke is, for example, the timing retarded by 10°CA (Crank Angle) from the sub-chamber ignition timing. Also, the mid-stage of the compression stroke is, for example, the timing advanced by about 60°CA from the compression top dead center.

[0049] If it is after the timing retarded by about 10°CA from the sub-chamber ignition timing, the air-fuel mixture in the main chamber 37 is ignited by the flame jet generated by the sub-chamber ignition. Therefore, the air-fuel mixture in the main chamber 37 does not ignite prior to the sub-chamber ignition due to the spark discharge of the ignition plug 40b in the main chamber 37. Also, if it is before the timing advanced by about 60°CA from the compression top dead center, the temperature of the air-fuel mixture in the main chamber 37 is low. Therefore, the air-fuel mixture in the main chamber 37 does not ignite prior to the sub-chamber ignition due to the spark discharge of the ignition plug 40b in the main chamber 37.

[0050] The ECU 2 transmits the ignition control signal 59a to the ignition device 50a for the sub-chamber in the vicinity of the compression top dead center. After that, when the ECU 2 stops transmitting the ignition control signal 59a, a high voltage is applied to the electrode 41a of the ignition plug 40a, and a spark discharge occurs.

[0051] In the vicinity of top dead center of compression, the ratio of the combustible mixture in the auxiliary chamber 42 and in the main chamber 37 is high, and due to the compression by the piston 35, the temperature of the mixture has become sufficiently high. Therefore, when a spark discharge occurs in the ignition plug 40a, the mixture in the auxiliary chamber 42 ignites. Then, the flame in the auxiliary chamber 42 passes through the through-hole 43 and jets into the main chamber 37 as a plurality of flame jets. As a result, multi-point ignition of the mixture in the main chamber 37 is performed.

[0052] When the mixture in the main chamber 37 burns, ions such as chemical ions and thermal ions are generated in the main chamber 37. The ions generated by combustion are detected as an ion current by the ion current detection unit 90b of the main chamber ignition device 50b. When the ion current detection unit 90b detects the ion current, it transmits a main chamber ion signal 98b to the ECU2.

[0053] The ion current flowing through the ion current detection unit 90b increases as the concentration of ions increases. And when the ion current increases, the main chamber ion signal 98b transmitted by the ion current detection unit 90b increases. When the mixture burns normally, since the concentration of the generated ions is high, the main chamber ion signal 98b shows a relatively large value (see change 123). On the other hand, in the case of misfire, since the ion concentration generated in the main chamber 37 becomes low, the main chamber ion signal 98b becomes smaller compared to when it burns normally (see change 123).

[0054] Therefore, the ECU2 detects the maximum value ibmax of the main chamber ion signal 98b that increases after the ignition control signal 59a for auxiliary chamber ignition becomes OFF, and determines that a misfire has occurred when the maximum value ibmax is less than or equal to the ion threshold ic. Also, the ECU2 determines that normal combustion has occurred when the maximum value ibmax is greater than the ion threshold ic. The ion threshold ic is determined in advance by calibration or the like.

[0055] The misfire determination may be performed based on the integrated value of the main chamber ion signal 98b instead of the maximum value ibmax of the main chamber ion signal 98b. In this case, the ECU 2 calculates the integrated value Si of the main chamber ion signal 98b from time t1 to t2, which occurs after the ignition control signal 59a for the sub-chamber ignition, according to Equation (1).

[0056] [Equation 1] TIFF0007698161000001.tif21168

[0057] In Equation (1), i(t) is the instantaneous value of the main chamber ion signal 98b. Also, t1 is the time between the OFF of the ignition control signal 59a and the rise of the main chamber ion signal 98b, and t2 is the time when the ion signal becomes sufficiently small after t1. For example, t1 is the time 1 ms after the OFF of the ignition control signal 59a, and t2 is the time 5 ms after t1. t1 and t2 are determined in advance by calibration or the like.

[0058] When the integrated value Si is less than or equal to the ion threshold value ic, the ECU 2 determines that a misfire has occurred. Also, when the integrated value Si is greater than the ion threshold value ic, the ECU 2 determines that combustion has occurred normally.

[0059] As described above, when performing the misfire determination based on the integrated value of the main chamber ion signal 98b, the amount of calculation in the ECU 2 increases compared to the case of performing the misfire determination based on the maximum value ibmax of the main chamber ion signal 98b. However, when performing the misfire determination based on the integrated value of the main chamber ion signal 98b, an accurate misfire determination can be made even when short-term fluctuations occur in the main chamber ion signal 98b due to factors such as noise.

[0060] <Misfire determination process in sub-chamber ignition mode> Next, the misfire detection procedure executed during the sub-chamber ignition mode in the first embodiment of the present invention will be described with reference to FIG. 5. FIG. 5 is a flowchart showing an example of the procedure of the misfire determination process during the sub-chamber ignition mode according to the first embodiment.

[0061] First, at any time from the initial stage of the combustion stroke to the middle stage of the compression stroke, the ECU 2 transmits an ignition control signal 59b to the main chamber ignition device 50b (S201). As a result, the capacitor 91b of the ion current detection unit 90b is charged with electric charge.

[0062] Next, the ECU 2 transmits an ignition control signal 59a to the auxiliary chamber ignition device 50a in the vicinity of top dead center of compression (for example, 10°CA before top dead center of compression) (S202). Thereafter, the ECU 2 stops transmitting the ignition control signal 59a. As a result, a spark discharge occurs at the electrode 41a of the spark plug 40a.

[0063] Next, the ECU 2 receives a main chamber ion signal 98b from the ion current detection unit 90b of the main chamber ignition device 50b (S203). Next, the ECU 2 detects the maximum value ibmax of the main chamber ion signal 98b (S204). Subsequently, the ECU 2 determines whether or not the maximum value ibmax of the main chamber ion signal 98b is less than or equal to a predetermined ion threshold value ic (S205).

[0064] In step S205, when it is determined that the maximum value ibmax of the main chamber ion signal 98b is not less than or equal to the ion threshold value ic (when S205 is a NO determination), the ECU 2 determines that the air-fuel mixture in the main chamber 37 has burned normally (S206). On the other hand, in step S205, when it is determined that the maximum value ibmax of the main chamber ion signal 98b is less than or equal to the ion threshold value ic (when S205 is a YES determination), the ECU 2 determines that a misfire has occurred (S207).

[0065] When it is determined that a misfire has occurred in step S207, the ECU 2 performs recovery control for recovering from the misfire (208). Here, the recovery control is, for example, control such as reducing the air-fuel ratio (fuel enrichment), reducing the EGR (Exhaust Gas Recirculation) rates of the auxiliary chamber 42 and the main chamber 37, or increasing the ignition energy of the auxiliary chamber ignition device 50a.

[0066] As described above, the misfire detection method according to the first embodiment of the present invention detects misfires and normal combustion based on the ion signal detected by the main chamber ignition device 50b in the sub-chamber ignition mode. The merits obtained by this misfire detection method will be described below.

[0067] In the sub-chamber ignition mode, misfires include complete misfires and partial misfires. A complete misfire occurs when ignition of the air-fuel mixture in the sub-chamber 42 by the ignition plug 40a fails. A partial misfire occurs when, despite the air-fuel mixture in the sub-chamber 42 being ignited, ignition from the flame jet generated in the sub-chamber 42 to the air-fuel mixture in the main chamber 37 fails, or when the flame in the main chamber 37 is extinguished during propagation.

[0068] A partial misfire occurs, for example, when the air-fuel mixture in the main chamber 37 is non-uniform, so that an air-fuel mixture with an appropriate air-fuel ratio is not formed in the vicinity of the sub-chamber, or when the gas flow in the main chamber 37 is excessively strong, so that the initially formed flame is blown away.

[0069] [Table 1] TIFF0007698161000002.tif29168

[0070] Table 1 shows the general trends of the ion concentrations in the sub-chamber 42 and the main chamber 37 during misfires in the sub-chamber ignition mode. As shown in Table 1, when a complete misfire occurs in the sub-chamber ignition mode, the ion concentrations in both the sub-chamber 42 and the main chamber 37 decrease. This is because during a complete misfire, combustion does not occur sufficiently in either the sub-chamber 42 or the main chamber 37, resulting in a small amount of ion generation in both.

[0071] On the other hand, when a partial misfire occurs in the sub-chamber ignition mode, the ion concentration in the sub-chamber 42 is high and the ion concentration in the main chamber 37 is low. This is because during a partial misfire, normal combustion occurs in the sub-chamber 42, generating a large amount of ions, while combustion does not occur sufficiently in the main chamber 37, resulting in a small amount of ion generation.

[0072] The auxiliary chamber type spark ignition engine disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2021-50724) is provided with an ion current detection circuit in an ignition device that applies a high voltage to the ignition plug in the auxiliary chamber, and misfire is determined based on an ion signal obtained from the ion current detection circuit. In this case, since high-concentration ions generated in the auxiliary chamber are detected during partial misfire, there is a possibility of misjudging misfire as "normal combustion".

[0073] On the other hand, in the misfire detection method according to the above-described first embodiment, in the auxiliary chamber ignition mode, it is determined whether or not there is misfire based on the main chamber ion signal 98b detected by the main chamber ignition device 50b. The ion signals detected by the main chamber ignition device 50b during complete misfire and partial misfire are smaller than those during normal combustion. As a result, misfire can be reliably detected.

[0074] 2. Second Embodiment <Engine> Next, a configuration example of an engine according to a second embodiment of the present invention will be described with reference to FIG. 6. FIG. 6 shows an example of a cross section of an engine according to a second embodiment of the present invention.

[0075] The engine 13b according to the second embodiment has the same configuration as the engine 13 (see FIG. 1) according to the first embodiment. The difference between the engine 13b and the engine 13 is the auxiliary chamber ignition device 501a. Therefore, here, the auxiliary chamber ignition device 501a will be described, and the description of the configuration common to the engine 13 will be omitted.

[0076] The auxiliary chamber ignition device 501a includes an ignition unit 51a and an ion current detection unit 90a. The auxiliary chamber ignition device 501a is electrically connected to the ECU 2. The ignition unit 51a applies a high voltage to the ignition plug 40a through the high-tension cord 48a based on the ignition control signal 59a transmitted from the ECU 2. The ion current detection unit 90a detects an auxiliary chamber ion signal 98a when the air-fuel mixture in the auxiliary chamber 42 burns. The auxiliary chamber ignition device 501a transmits the auxiliary chamber ion signal 98a detected by the ion current detection unit 90a to the ECU 2.

[0077] <Ignition device for auxiliary chamber> Next, the configuration of the ignition device 501a for the auxiliary chamber will be described with reference to FIG. 7. FIG. 7 is an explanatory diagram showing a configuration example of the ignition device 501a for the auxiliary chamber.

[0078] As described above, the ignition device 501a for the auxiliary chamber includes an ignition unit 51a and an ion current detection unit 90a. The ignition unit 51a includes a primary coil 52a, a secondary coil 53a, and an igniter 54a. Since the configuration of this ignition unit 51a is the same as that of the ignition unit 51b (see FIG. 3) of the main chamber ignition device 50b according to the first embodiment, a detailed description thereof will be omitted.

[0079] The ion current detection unit 90a includes a capacitor 91 a and a Zener diode 92 a and a voltage conversion resistor 93 a and a secondary current path diode 94 a and an ion current path diode 95 a Since the configuration of this ion current detection unit 90a is the same as that of the ion current detection unit 90b (see FIG. 3) of the main chamber ignition device 50b according to the first embodiment, a detailed description thereof will be omitted.

[0080] The main chamber ignition device 50b according to the second embodiment has an ion current detection unit 90b. Therefore, it is possible to detect the amount of ion generation (ion concentration) in the main chamber 37 by the main chamber ignition device 50b. Further, the ignition device 501a for the auxiliary chamber has an ion current detection unit 90a. Therefore, it is possible to detect the amount of ion generation (ion concentration) in the auxiliary chamber 42 by the ignition device 501a for the auxiliary chamber.

[0081] <Ignition control signal and ion signal in auxiliary chamber ignition mode> Since the ignition control signal and the ion signal when the engine 13b is operated in the auxiliary chamber ignition mode are the same as those in the first embodiment (see FIG. 4), the description thereof will be omitted.

[0082] <Ignition control signal and ion signal in main chamber ignition mode> Next, an example of the ignition control signal and the ion signal when the engine 13b is operated in the main chamber ignition mode will be described with reference to FIG. 8. FIG. 8 is an explanatory diagram showing an example of the ignition control signal and the ion signal in the main chamber ignition mode.

[0083] The horizontal axis of the graph shown in FIG. 8 indicates the passage of time. Regarding the sub-chamber ion signal 98a, examples of the change 125 of the sub-chamber ion signal 98a when the air-fuel mixture in the sub-chamber 42 burns normally and the change 126 of the sub-chamber ion signal 98a when the air-fuel mixture in the sub-chamber 42 misfires are shown.

[0084] When the ECU 2 transmits the ignition control signal 59a to the sub-chamber ignition device 501a and stops transmitting the ignition control signal 59a after a predetermined time has elapsed (the ignition control signal 59a changes from ON to OFF), a high voltage is applied to the electrode 41a of the spark plug 40a. As a result, a spark discharge occurs at the spark plug 40a. Then, when the voltage of the secondary coil 53a of the sub-chamber ignition device 501a decreases and becomes lower than the breakdown voltage of the Zener diode 92a, the secondary current flows into the capacitor 91a. As a result, the capacitor 91a is charged with electric charge.

[0085] The ignition control signal 59a is transmitted to charge the capacitor 91a. However, if the air-fuel mixture in the sub-chamber 42 ignites prior to the main chamber ignition by transmitting the ignition control signal 59a, the pressure in the sub-chamber 42 rises before the main chamber 37. As a result, there is a risk of inhibiting the flame propagation in the main chamber 37. Therefore, the transmission timing of the ignition control signal 59a is determined so that the air-fuel mixture in the sub-chamber 42 does not ignite prior to the main chamber ignition.

[0086] The transmission of the ignition control signal 59a is performed at any timing from the initial stage of the combustion stroke (the stroke from the start of main chamber ignition to the start of exhaust) of the engine 13b to the middle stage of the compression stroke. Here, the initial stage of the combustion stroke is, for example, the timing that is 10°CA retarded from the main chamber ignition timing. Also, the middle stage of the compression stroke is, for example, the timing that is 60°CA advanced from the compression top dead center.

[0087] After the timing that is about 10°CA retarded from the main chamber ignition timing, ignition in the auxiliary chamber 42 is caused by the combustion gas from the main chamber ignition. Therefore, the air-fuel mixture in the auxiliary chamber 42 does not ignite prior to the main chamber ignition due to the spark discharge of the ignition plug 40a. Also, if it is before the timing advanced by about 60°CA from top dead center of compression, the temperature of the air-fuel mixture in the auxiliary chamber 42 is low. Therefore, the air-fuel mixture in the auxiliary chamber 42 does not ignite prior to the main chamber ignition due to the spark discharge of the ignition plug 40a.

[0088] The ECU 2 transmits an ignition control signal 59b to the main chamber ignition device 50b near top dead center of compression. Then, when the ECU 2 stops transmitting the ignition control signal 59b, a high voltage is applied to the electrode 41b of the ignition plug 40b, and spark discharge occurs.

[0089] Near top dead center of compression, the ratio of the combustible air-fuel mixture in the main chamber 37 and in the auxiliary chamber 42 is high, and due to the compression by the piston 35, the temperature of the air-fuel mixture has become sufficiently high. Therefore, when spark discharge occurs in the ignition plug 40b, the air-fuel mixture in the main chamber 37 ignites. Then, the combustion gas in the main chamber 37 flows into the auxiliary chamber 42 through the through hole 43 of the auxiliary chamber forming member 45. As a result, ignition of the air-fuel mixture in the auxiliary chamber 42 occurs.

[0090] When the air-fuel mixture in the auxiliary chamber 42 burns, ions such as chemical ions and thermal ions are generated in the auxiliary chamber 42. The ions generated by combustion are detected as an ion current by the ion current detection unit 90a of the auxiliary chamber ignition device 501a. When the ion current detection unit 90a detects the ion current, it transmits an auxiliary chamber ion signal 98a to the ECU 2.

[0091] The ionic current flowing through the ionic current detection unit 90a increases as the concentration of ions increases. When the ionic current increases, the sub-chamber ionic signal 98a transmitted by the ionic current detection unit 90a also increases. When the air-fuel mixture burns normally, the concentration of the generated ions is high, so the sub-chamber ionic signal 98a indicates a relatively large value (see change 125). On the other hand, when misfire occurs, the concentration of ions generated in the sub-chamber 42 decreases, so the sub-chamber ionic signal 98a becomes smaller compared to when it burns normally (see change 126).

[0092] Therefore, the ECU 2 detects the maximum value iamax of the sub-chamber ionic signal 98a that increases after the ignition control signal 59b for main chamber ignition becomes OFF, and determines that misfire has occurred when the maximum value iamax is equal to or less than the ionic threshold value ic. Further, when the maximum value iamax is greater than the ionic threshold value ic, the ECU 2 determines that normal combustion has occurred.

[0093] As described in the first embodiment, the misfire determination may be performed based on the integral value of the sub-chamber ionic signal 98a instead of the maximum value iamax of the sub-chamber ionic signal 98a.

[0094] <Misfire determination process during sub-chamber ignition mode> The misfire determination process during sub-chamber ignition mode in the second embodiment is the same as that in the first embodiment (see FIG. 5), and thus the description thereof is omitted.

[0095] <Misfire determination process during main chamber ignition mode> Next, the misfire detection procedure executed during main chamber ignition mode in the second embodiment of the present invention will be described with reference to FIG. 9. FIG. 9 is a flowchart showing an example of the procedure of misfire determination process during main chamber ignition mode according to the second embodiment.

[0096] First, the ECU 2 transmits the ignition control signal 59a to the sub-chamber ignition device 501a at any time from the initial stage of the combustion stroke to the middle stage of the compression stroke (S221). As a result, the capacitor 91a of the ionic current detection unit 90a is charged with electric charge.

[0097] Next, the ECU 2 transmits an ignition control signal 59b to the main chamber ignition device 50b near the compression top dead center (for example, 10°CA before the compression top dead center) (S222). After that, the ECU 2 stops transmitting the ignition control signal 59b. As a result, spark discharge occurs at the electrode 41b of the spark plug 40b.

[0098] Next, the ECU 2 receives a sub-chamber ion signal 98a from the ion current detection unit 90a of the sub-chamber ignition device 501a (S223). Next, the ECU 2 detects the maximum value iamax of the sub-chamber ion signal 98a (S224). Subsequently, the ECU 2 determines whether the maximum value iamax of the sub-chamber ion signal 98a is less than or equal to a predetermined ion threshold value ic (S225).

[0099] In step S225, when it is determined that the maximum value iamax of the sub-chamber ion signal 98a is not less than or equal to the ion threshold value ic (when S225 is a NO determination), the ECU 2 determines that the air-fuel mixture in the main chamber 37 has burned normally (226). On the other hand, in step S225, when it is determined that the maximum value iamax of the sub-chamber ion signal 98a is less than or equal to the ion threshold value ic (when S225 is a YES determination), the ECU 2 determines that a misfire has occurred (S227). And when it is determined that a misfire has occurred in step S227, the ECU 2 performs recovery control to recover from the misfire (S228).

[0100] Thus, the misfire detection method according to the second embodiment of the present invention detects misfires and normal combustion based on the ion signal detected by the sub-chamber ignition device 501a in the main chamber ignition mode. The merits obtained by this misfire detection method will be described below.

[0101] In the case of misfire in the main chamber ignition mode, there are complete misfire and partial misfire. Complete misfire occurs when ignition of the air-fuel mixture in the main chamber 37 by the ignition plug 40b fails. Partial misfire occurs when, despite the air-fuel mixture in the main chamber 37 being ignited, ignition of the air-fuel mixture in the auxiliary chamber 42 by the combustion gas generated in the main chamber 37 fails. This partial misfire occurs, for example, when the air-fuel mixture in the auxiliary chamber 42 is non-uniform or when the residual gas concentration in the auxiliary chamber 42 is too high.

[0102] [Table 2] TIFF0007698161000003.tif29168

[0103] Table 2 shows the general tendency of the ion concentrations in the auxiliary chamber 42 and the main chamber 37 during misfire in the main chamber ignition mode. As shown in Table 2, when complete misfire occurs in the main chamber ignition mode, the ion concentrations in both the auxiliary chamber 42 and the main chamber 37 become low. This is because during complete misfire, combustion is not sufficiently carried out in both the auxiliary chamber 42 and the main chamber 37, and the amount of ions generated in both is small.

[0104] On the other hand, when partial misfire occurs in the main chamber ignition mode, the ion concentration in the main chamber 37 is high and the ion concentration in the auxiliary chamber 42 is low. This is because during partial misfire, normal combustion occurs in the main chamber 37 and a large amount of ions are generated, while combustion is not sufficiently carried out in the auxiliary chamber 42 and the amount of ions generated is small. Therefore, when determining whether there is misfire based on the ion signal detected by the main chamber ignition device 50b in the main chamber ignition mode, there is a risk of misdetecting partial misfire as "normal combustion".

[0105] In the misfire detection method according to the above-described second embodiment, in the main chamber ignition mode, it is determined whether there is misfire based on the auxiliary chamber ion signal 98a detected by the auxiliary chamber ignition device 501a. And the ion signals detected by the auxiliary chamber ignition device 501a during complete misfire and partial misfire are smaller than those during normal combustion. As a result, misfire can be reliably detected.

[0106] 3. Third Embodiment Next, a method for discriminating a fire pattern according to the third embodiment will be described. The engine according to the third embodiment is the same as the engine 13b according to the second embodiment. Therefore, the description of the engine according to the third embodiment will be omitted.

[0107] Similar to the engine 13b according to the second embodiment described above, the engine according to the third embodiment can obtain a main chamber ion signal 98b by the main chamber ignition device 50b. Further, the engine according to the third embodiment can obtain a sub-chamber ion signal 98a by the sub-chamber ignition device 501a.

[0108] [Table 3] TIFF0007698161000004.tif44170

[0109] Table 3 shows the intensity relationship between the sub-chamber ion signal 98a and the main chamber ion signal 98b with respect to the fire patterns in the sub-chamber ignition mode and the main chamber ignition mode. As described in the first and second embodiments, there are two fire patterns, complete misfire and partial misfire, in both the sub-chamber ignition mode and the main chamber ignition mode.

[0110] As shown in Table 3, at the time of complete misfire, the intensities of the sub-chamber ion signal 98a and the main chamber ion signal 98b become small in both the sub-chamber ignition mode and the main chamber ignition mode. However, at the time of partial misfire, the magnitude relationship between the intensities of the sub-chamber ion signal 98a and the main chamber ion signal 98b in the sub-chamber ignition mode and the main chamber ignition mode is reversed.

[0111] That is, in the sub-chamber ignition mode, the intensity of the sub-chamber ion signal 98a is large and the intensity of the main chamber ion signal 98b is small. On the other hand, in the main chamber ignition mode, the intensity of the sub-chamber ion signal 98a is small and the intensity of the main chamber ion signal 98b is large. Therefore, by acquiring both the sub-chamber ion signal 98a and the main chamber ion signal 98b, it is possible to discriminate the fire patterns in the sub-chamber ignition mode and the main chamber ignition mode.

[0112] <Ignition control signal and ion signal in the sub-chamber ignition mode> Next, an example of the ignition control signal and the ion signal when the engine according to the third embodiment is operated in the sub-chamber ignition mode will be described with reference to FIG. 10. FIG. 10 is an explanatory diagram showing an example of the ignition control signal and the ion signal in the sub-chamber ignition mode.

[0113] The horizontal axis of the graph shown in FIG. 10 indicates the passage of time. Regarding the sub-chamber ion signal 98a, a change 127 when the air-fuel mixture in the sub-chamber 42 burns normally is shown. Regarding the main-chamber ion signal 98b, a change 128 when the air-fuel mixture in the main-chamber 37 burns normally is shown.

[0114] In the sub-chamber ignition mode, the ECU 2 first transmits an ignition control signal 59b to the main-chamber ignition device 50b. After that, when the ECU 2 stops transmitting the ignition control signal 59b, a high voltage is applied to the electrode 41b of the spark plug 40b, and a spark discharge occurs. Then, when the voltage of the secondary coil 53b of the main-chamber ignition device 50b decreases and becomes lower than the breakdown voltage of the Zener diode 92b, the secondary current flows into the capacitor 91b. As a result, the capacitor 91b is charged with electric charge.

[0115] As described above, the ignition control signal 59b is transmitted to charge the capacitor 91b. The transmission of the ignition control signal 59b is performed at any timing from the initial stage of the combustion stroke (the stroke from the start of sub-chamber ignition to the start of exhaust) to the middle stage of the compression stroke of the engine 13b so that the air-fuel mixture in the main-chamber 37 does not ignite prior to sub-chamber ignition. The initial stage of the combustion stroke is, for example, a timing that is retarded by 10°CA (Crank Angle) from the sub-chamber ignition timing. The middle stage of the compression stroke is, for example, a timing that is advanced by about 60°CA from top dead center of compression.

[0116] Next, the ECU 2 transmits an ignition control signal 59a to the sub-chamber ignition device 501a in the vicinity of the compression top dead center. After that, when the ECU 2 stops transmitting the ignition control signal 59a, a high voltage is applied to the electrode 41a of the spark plug 40a, and a spark discharge occurs. When a spark discharge occurs in the spark plug 40a, the air-fuel mixture in the sub-chamber 42 ignites. Then, the flame in the sub-chamber 42 passes through the through-hole 43 and jets into the main chamber 37 as a plurality of flame jets. As a result, multi-point ignition of the air-fuel mixture in the main chamber 37 is performed.

[0117] After that, when the voltage of the secondary coil 53a of the sub-chamber ignition device 501a decreases and becomes lower than the breakdown voltage of the Zener diode 92a, the secondary current flows into the capacitor 91a. As a result, the capacitor 91a is charged with electric charge.

[0118] Ions generated in the sub-chamber 42 due to the combustion of the air-fuel mixture in the sub-chamber 42 are detected by the ion current detection unit 90a of the sub-chamber ignition device 501a and transmitted to the ECU 2 as a sub-chamber ion signal 98a. Also, ions generated in the main chamber 37 due to the combustion of the air-fuel mixture in the main chamber 37 are detected by the ion current detection unit 90b of the main chamber ignition device 50b and transmitted to the ECU 2 as a main chamber ion signal 98b.

[0119] <Ignition control signal and ion signal in the main chamber ignition mode> Next, an example of the ignition control signal and the ion signal when the engine according to the third embodiment is operated in the main chamber ignition mode will be described with reference to FIG. 11. FIG. 11 is an explanatory diagram showing an example of the ignition control signal and the ion signal in the main chamber ignition mode.

[0120] The horizontal axis of the graph shown in FIG. 11 indicates the passage of time. Regarding the sub-chamber ion signal 98a, a change 127 when the air-fuel mixture in the sub-chamber 42 burns normally is shown. Also, regarding the main chamber ion signal 98b, a change 128 when the air-fuel mixture in the main chamber 37 burns normally is shown.

[0121] In the main chamber ignition mode, the ECU 2 first transmits an ignition control signal 59a to the sub-chamber ignition device 501a. After that, when the ECU 2 stops transmitting the ignition control signal 59a, a high voltage is applied to the electrode 41a of the spark plug 40a, and spark discharge occurs. Then, when the voltage of the secondary coil 53a of the sub-chamber ignition device 501a decreases and becomes lower than the breakdown voltage of the Zener diode 92a, the secondary current flows into the capacitor 91a. As a result, the capacitor 91a is charged with electric charge.

[0122] As described above, the ignition control signal 59a is transmitted to charge the capacitor 91a. The transmission of the ignition control signal 59a is carried out at any timing from the initial stage of the combustion stroke (the stroke from the start of sub-chamber ignition to the start of exhaust) to the middle stage of the compression stroke of the engine 13b so that the air-fuel mixture in the sub-chamber 42 does not ignite prior to the main chamber ignition. The initial stage of the combustion stroke is, for example, the timing retarded by 10°CA (Crank Angle) from the sub-chamber ignition timing. Also, the middle stage of the compression stroke is, for example, the timing advanced by about 60°CA from the top dead center of compression.

[0123] Next, the ECU 2 transmits an ignition control signal 59b to the main-chamber ignition device 50b in the vicinity of top dead center of compression. After that, when the ECU 2 stops transmitting the ignition control signal 59b, a high voltage is applied to the electrode 41b of the spark plug 40b, and spark discharge occurs. When spark discharge occurs at the spark plug 40b, the air-fuel mixture in the main chamber 37 ignites. Then, the combustion gas in the main chamber 37 flows into the sub-chamber 42 through the through-hole 43 of the sub-chamber forming member 45. As a result, the air-fuel mixture in the sub-chamber 42 is ignited.

[0124] After that, when the voltage of the secondary coil 53b of the main-chamber ignition device 50b decreases and becomes lower than the breakdown voltage of the Zener diode 92b, the secondary current flows into the capacitor 91b. As a result, the capacitor 91b is charged with electric charge.

[0125] Ions generated in the main chamber 37 due to the combustion of the air-fuel mixture in the main chamber 37 are detected by the ion current detection unit 90b of the main chamber ignition device 50b and transmitted to the ECU 2 as the main chamber ion signal 98b. Further, ions generated in the auxiliary chamber 42 due to the combustion of the air-fuel mixture in the auxiliary chamber 42 are detected by the ion current detection unit 90a of the auxiliary chamber ignition device 501a and transmitted to the ECU 2 as the auxiliary chamber ion signal 98a.

[0126] <Misfire pattern determination process> Next, the misfire pattern determination procedure in the third embodiment will be described with reference to FIG. 12. FIG. 12 is a flowchart showing an example of the procedure of the misfire pattern determination process according to the third embodiment.

[0127] First, the ECU 2 determines whether the current ignition mode is the auxiliary chamber ignition mode (S241). In step S241, when it is determined that the current ignition mode is not the auxiliary chamber ignition mode (when S241 is NO), the ECU 2 proceeds to the process of step S247.

[0128] On the other hand, in step S241, when it is determined that the current ignition mode is the auxiliary chamber ignition mode (when S241 is YES), the ECU 2 detects the maximum value ibmax of the main chamber ion signal 98b. Then, it is determined whether the maximum value ibmax of the main chamber ion signal 98b is less than or equal to a predetermined ion threshold value ibc (S242).

[0129] In step S242, when it is determined that the maximum value ibmax of the main chamber ion signal 98b is not less than or equal to the predetermined ion threshold value ibc (when S242 is NO), the ECU 2 determines that the air-fuel mixture in the main chamber 37 has burned normally (S243).

[0130] On the other hand, in step S242, when it is determined that the maximum value ibmax of the main chamber ion signal 98b is equal to or less than a predetermined ion threshold value ibc (when S242 is a YES determination), the ECU 2 detects the maximum value iamax of the sub-chamber ion signal 98a. Then, it is determined whether the maximum value iamax of the sub-chamber ion signal 98a is equal to or less than a predetermined ion threshold value iac (S244).

[0131] In step S244, when it is determined that the maximum value iamax of the sub-chamber ion signal 98a is not equal to or less than a predetermined ion threshold value iac (when S244 is a NO determination), the ECU 2 determines that there is a partial misfire (S245). On the other hand, in step S244, when it is determined that the maximum value iamax of the sub-chamber ion signal 98a is equal to or less than a predetermined ion threshold value iac (when S244 is a YES determination), the ECU 2 determines that there is a complete misfire (S246).

[0132] When S241 is a NO determination, the ECU 2 detects the maximum value iamax of the sub-chamber ion signal 98a. Then, it is determined whether the maximum value iamax of the sub-chamber ion signal 98a is equal to or less than a predetermined ion threshold value iac (S247). In step S247, when it is determined that the maximum value iamax of the sub-chamber ion signal 98a is not equal to or less than a predetermined ion threshold value iac (when S247 is a NO determination), the ECU 2 determines that the air-fuel mixture in the main chamber 37 has burned normally (S248).

[0133] On the other hand, in step S247, when it is determined that the maximum value iamax of the sub-chamber ion signal 98a is equal to or less than a predetermined ion threshold value iac (when S247 is a YES determination), the ECU 2 determines whether the maximum value ibmax of the main chamber ion signal 98b is equal to or less than a predetermined ion threshold value ibc (S249).

[0134] In step S249, when it is determined that the maximum value ibmax of the main chamber ion signal 98b is not less than a predetermined ion threshold value ibc (when S249 is NO), the ECU2 determines that it is a partial misfire (S250). On the other hand, in step S249, when it is determined that the maximum value ibmax of the main chamber ion signal 98b is less than or equal to the predetermined ion threshold value ibc (when S249 is YES), the ECU2 determines that it is a complete misfire (S251).

[0135] As described above, in the third embodiment of the present invention, it is possible to discriminate the misfire patterns in each of the sub-chamber ignition mode and the main chamber ignition mode. Thereby, misfire recovery control suitable for each misfire pattern becomes possible.

[0136] In the case where it is determined that it is a complete misfire in the sub-chamber ignition mode, for example, the ignition energy of the sub-chamber ignition device 501a is increased to improve the ignitability in the sub-chamber 42. Further, control is executed to increase the overlap amount of the intake valve 32 and the exhaust valve 34 to promote scavenging of the sub-chamber 42. On the other hand, in the case where it is determined that it is a partial misfire in the sub-chamber ignition mode, control such as enriching the air-fuel ratio of the main chamber 37 or reducing the EGR rate is executed.

[0137] In the case where it is determined that it is a complete misfire in the main chamber ignition mode, for example, the ignition energy of the main chamber ignition device 50b is increased to improve the ignitability in the main chamber 37. Further, control such as enriching the air-fuel ratio of the main chamber 37 or reducing the EGR rate is executed. On the other hand, in the case where it is determined that it is a partial misfire in the main chamber ignition mode, control is executed to increase the overlap amount of the intake valve 32 and the exhaust valve 34 to promote scavenging of the sub-chamber 42.

[0138] By selecting appropriate recovery control according to the misfire pattern in this way, reliable misfire recovery becomes possible. Thereby, it is possible to improve the fuel consumption of the engine 13b, reduce emissions, and reduce vibrations and noises associated with misfires.

[0139] 4. Fourth Embodiment In the misfire detection method according to the first to third embodiments described above, the ECU detected misfires based on the ion signals received from the main chamber ignition device and the auxiliary chamber ignition device. In this case, the ECU performs processes such as calculating the maximum values ibmax and iamax of the ion signals and the integrated value Si, and comparing the calculation results with the ion threshold value ic. Therefore, there is a problem that the computational load on the ECU increases. In addition, since the ECU has a misfire determination function, there is also a problem that the development man-hours of the control software become relatively large.

[0140] The engine according to the fourth embodiment has the same configuration as the engine 13 (see FIG. 1) according to the first embodiment. The difference between the engine according to the fourth embodiment and the engine 13 according to the first embodiment is the main chamber ignition device 501b having a misfire determination unit. Therefore, here, the main chamber ignition device 501b will be described, and the description of the configuration common to the engine 13 will be omitted.

[0141] <Main chamber ignition device> Next, the configuration of the main chamber ignition device 501b according to the fourth embodiment will be described with reference to FIG. 13. FIG. 13 is an explanatory diagram showing a configuration example of the main chamber ignition device 501b.

[0142] As shown in FIG. 13, the main chamber ignition device 501b includes an ignition unit 51b and an ion current detection unit 901b. Since the configuration of the ignition unit 51b is the same as that of the ignition unit 51b (see FIG. 3) of the main chamber ignition device 50b according to the first embodiment, a detailed description thereof will be omitted.

[0143] The ion current detection unit 901b shows the first example of the misfire detection device in the present invention. The ion current detection unit 901b has the same configuration as the ion current detection unit 90b (see FIG. 3) according to the first embodiment. The difference between the ion current detection unit 901b and the ion current detection unit 90b according to the first embodiment is that it includes a peak hold circuit 80b, voltage dividing resistors 82b and 83b, and a comparator 81b. Therefore, here, the peak hold circuit 80b, the voltage dividing resistors 82b and 83b, and the comparator 81b will be described, and the description of the configuration common to the ion current detection unit 90b according to the first embodiment will be omitted.

[0144] The peak hold circuit 80b, the voltage dividing resistors 82b and 83b, and the comparator 81b constitute a misfire determination unit for determining whether there is a misfire. In the ion current detection unit 901b, the main chamber ion signal 98b voltage-converted by the voltage conversion resistor 93b is input to the peak hold circuit 80b. The peak hold circuit 80b holds the maximum value ibmax of the main chamber ion signal 98b for a certain period and then outputs it to one end of the comparator 81b.

[0145] The period during which the peak hold circuit 80b holds the maximum value ibmax of the main chamber ion signal 98b is shorter than one cycle period of the engine cycle, for example, 10 ms. When the period for holding the maximum value ibmax of the main chamber ion signal 98b has passed, the output of the peak hold circuit 80b becomes 0. As a result, the maximum value ibmax of the main chamber ion signal 98b is input to the comparator 81b every one cycle of the engine cycle.

[0146] The voltage dividing resistors 82b and 83b are supplied with a +12V voltage from a battery (not shown). The voltage dividing resistors 82b and 83b divide the supplied +12V voltage and output it as an ion threshold value ic to the other end of the comparator 81b. The resistance values of the voltage dividing resistors 82b and 83b are appropriately selected so that the ion threshold value ic becomes an appropriate value for misfire detection.

[0147] Comparator 81b compares the maximum value ibmax of the input main chamber ion signal 98b with the ion threshold value ic. When the maximum value ibmax of the main chamber ion signal 98b is less than or equal to the ion threshold value ic, it transmits "1" to ECU2 as the misfire determination signal 88b. Also, when the maximum value ibmax of the main chamber ion signal 98b is greater than the ion threshold value ic, comparator 81b transmits "0" to ECU2 as the misfire determination signal 88b.

[0148] ECU2 receives the misfire determination signal 88b during the period when the peak hold circuit 80b holds the maximum value ibmax of the main chamber ion signal 98b. ECU2 determines that there is a "misfire" when the misfire determination signal 88b is "1", and determines that there is "normal combustion" when the misfire determination signal 88b is "0". Thereby, in the sub-chamber ignition mode, the computational load on ECU2 associated with misfire detection can be reduced. Also, since the control software incorporated in ECU2 is simplified, the man-hours for software development can be reduced.

[0149] In this embodiment, the peak hold circuit 80b is used to detect the maximum value ibmax of the main chamber ion signal 98b. However, as the ion current detection unit according to the present invention, the ion integrated value Si may be detected by changing the peak hold circuit 80b to an integration circuit.

[0150] Also, in this embodiment, an example of a main chamber ignition device provided with a misfire determination unit is shown. However, as the misfire detection device according to the present invention, a sub-chamber ignition device provided with a misfire determination unit, similar to the above-described main chamber ignition device 501b, may be used. In this case, in the main chamber ignition mode, the computational load on ECU2 associated with misfire detection can be reduced. Also, since the control software incorporated in ECU2 is simplified, the man-hours for software development can be reduced.

[0151] 5. Fifth Embodiment During normal combustion, the amount of ions generated, for example, increases as the load increases. Also, during normal combustion, the amount of ions generated, for example, decreases as the air-fuel ratio increases. Thus, the amount of ions generated during normal combustion varies depending on the engine operating conditions. Therefore, it is considered that the appropriate value of the ion threshold ic, which is the misfire determination criterion, changes depending on the operating conditions.

[0152] The appropriate value of the ion threshold ic indicates the ion threshold at which misfires can be detected most accurately. If the ion threshold ic deviates significantly from the appropriate value, there is a risk of misjudging a misfire as "normal combustion" or, conversely, misjudging normal combustion as a "misfire". Therefore, to maintain the accuracy of misfire detection, it is important to set the ion threshold ic to the appropriate value.

[0153] The engine according to the fifth embodiment has the same configuration as the engine 13 according to the first embodiment. The difference between the engine according to the fifth embodiment and the engine 13 according to the first embodiment is the main chamber ignition device 502b that variably controls the ion threshold ic according to the engine operating conditions. Therefore, here, the main chamber ignition device 502b will be described, and the description of the configuration common to the engine 13 will be omitted.

[0154] <Main chamber ignition device> Next, the configuration of the main chamber ignition device 502b according to the fifth embodiment will be described with reference to FIG. 14. FIG. 14 is an explanatory diagram showing a configuration example of the main chamber ignition device 502b.

[0155] The main chamber ignition device 502b has the same configuration as the main chamber ignition device 501b according to the fourth embodiment. The difference between the main chamber ignition device 502b according to the fifth embodiment and the main chamber ignition device 501b according to the fourth embodiment is the ion current detection unit 902b. Therefore, here, the ion current detection unit 902b will be described, and the description of the configuration common to the main chamber ignition device 501b will be omitted.

[0156] The ion current detection unit 902b shows a second example of the misfire detection device in the present invention. The ion current detection unit 902b has the same configuration as the ion current detection unit 901b (see FIG. 13) according to the fourth embodiment. The difference between the ion current detection unit 902b and the ion current detection unit 901b according to the fourth embodiment is that the means for generating the ion threshold value ic is replaced by a variable voltage device 84b from the voltage dividing resistors 82b and 83b. Therefore, here, the variable voltage device 84b will be described, and the description of the configuration common to the ion current detection unit 901b will be omitted.

[0157] As shown in FIG. 14, a voltage of +12V is supplied to the variable voltage device 84b from a battery (not shown). Also, an ion threshold signal 55b is supplied to the variable voltage device 84b from the ECU 2. The variable voltage device 84b transforms the supplied +12V voltage based on the magnitude of the ion threshold signal 55b and outputs it as the ion threshold value ic to the other end of the comparator 81b.

[0158] <Ion Threshold Signal and Ion Threshold Value ic> Next, the relationship between the magnitude of the ion threshold signal 55b input from the ECU 2 to the variable voltage device 84b and the ion threshold value ic output from the variable voltage device 84b will be described with reference to FIG. 15. FIG. 15 is an explanatory diagram showing the relationship between the ion threshold signal and the ion threshold value in the variable voltage device of the main chamber ignition device.

[0159] As shown in FIG. 15, the ion threshold value ic output from the variable voltage device 84b is proportional to the magnitude of the ion threshold signal 55b. Also, the ion threshold value ic output from the variable voltage device 84b is continuously variably set in the range from 0V to the battery voltage of +12V according to the magnitude of the ion threshold signal 55b.

[0160] In this embodiment, the ignition device 502b for the main combustion chamber equipped with a misfire determination unit is configured to variably control the ion threshold value. However, as a misfire detection device according to the present invention, a sub-combustion chamber ignition device equipped with a misfire determination unit may be used in the same manner as the above-described ignition device 502b for the main combustion chamber. Further, in that case, similar to the ignition device 502b for the main combustion chamber, the variable voltage device of the ignition device for the sub-combustion chamber may be configured to variably control the ion threshold value.

[0161] <Change of Ion Threshold Signal> The ECU 2 sets the magnitude of the ion threshold signal 55b according to the operating conditions of the engine according to the fifth embodiment. Next, an example of the change of the ion threshold signal 55b set by the ECU 2 will be described with reference to FIGS. 16 to 18.

[0162] FIG. 16 is an explanatory diagram showing an example of the change of the ion threshold signal 55b with respect to the EGR rate or the air-fuel ratio in the main combustion chamber 37. When the EGR rate or the air-fuel ratio in the main combustion chamber 37 increases, the intensity of the ion signal decreases. Therefore, as shown in FIG. 16, it is desirable to change the ion threshold signal 55b so as to decrease as the EGR rate or the air-fuel ratio increases.

[0163] FIG. 17 is an explanatory diagram showing an example of the change of the ion threshold signal 55b with respect to the engine torque or the volumetric efficiency. When the engine torque or the volumetric efficiency increases, the intensity of the ion signal increases. Therefore, as shown in FIG. 17, it is desirable to change the ion threshold signal 55b so as to increase as the engine torque or the volumetric efficiency increases.

[0164] FIG. 18 is an explanatory diagram showing an example of the change of the ion threshold signal 55b with respect to the coolant temperature (cooling water temperature) or the intake air temperature. When the coolant temperature or the intake air temperature increases, the intensity of the ion signal increases. Therefore, as shown in FIG. 18, it is desirable to change the ion threshold signal 55b so as to increase as the coolant temperature or the intake air temperature increases.

[0165] As described above, in the main chamber ignition device 502b according to the fifth embodiment, the ion threshold can be changed according to the operating conditions of the engine. Thereby, the accuracy of misfire detection can be maintained at a high level.

[0166] As the misfire detection device according to the present invention, the ion threshold for the sub-chamber ignition device and the ion threshold for the main-chamber ignition device may be set to different values, respectively. For example, when normal combustion occurs, it is considered that the ion concentration in the sub-chamber is higher than the ion concentration in the main-chamber. Therefore, if the ion threshold for the sub-chamber ignition device is set higher than the ion threshold for the main-chamber ignition device, more accurate misfire detection becomes possible.

[0167] Further, the ion threshold signal according to the present invention may be determined according to at least one of the operating conditions such as the EGR rate, air-fuel ratio, engine torque, volumetric efficiency, coolant temperature, intake air temperature, etc. in the main chamber 37 described above, or may be determined according to two or more operating conditions.

[0168] Also, as described in the first embodiment and the second embodiment, even when the ECU 2 determines misfire, the ion threshold may be changed based on the operating conditions. Thereby, the detection accuracy of misfire can be improved.

[0169] 6. Summary As described above, the misfire detection method according to the first embodiment described above includes a main chamber (main chamber 37) into which an air-fuel mixture flows, a main chamber ignition plug (ignition plug 40b) provided in the main chamber, a sub-chamber (sub-chamber 42) communicating with the main chamber, a sub-chamber ignition plug (ignition plug 40a) provided in the sub-chamber, a main chamber ignition device (main chamber ignition device 50b) that applies a voltage for igniting the air-fuel mixture in the main chamber to the main chamber ignition plug, and a sub-chamber ignition device (sub-chamber ignition device 50a) that applies a voltage for igniting the air-fuel mixture in the sub-chamber to the sub-chamber ignition plug, and detects misfires in an internal combustion engine (engine 13). In this misfire detection method, when performing a sub-chamber ignition operation (sub-chamber ignition mode) in which the sub-chamber ignition plug ignites the air-fuel mixture in the sub-chamber, the main chamber ignition device detects the concentration of ions (the maximum value ibmax of the ion signal) in the main chamber. Then, the misfire detection unit (ECU2) detects misfires based on the detection result of the main chamber ignition device. During complete misfire and partial misfire in the sub-chamber ignition operation, the concentration of ions generated in the main chamber is lower than that during normal combustion. Therefore, misfires during the sub-chamber ignition operation can be reliably detected from the concentration of ions in the main chamber.

[0170] Further, the misfire detection method according to the third embodiment described above is such that, during a sub-chamber ignition operation (sub-chamber ignition mode), the sub-chamber ignition device (sub-chamber ignition device 501a) detects the concentration of ions (the maximum value iamax of the ion signal) in the sub-chamber (sub-chamber 42). Then, when the misfire detection unit (ECU2) detects a misfire during the sub-chamber ignition operation, it discriminates the misfire pattern (complete misfire and partial misfire) based on the detection result of the sub-chamber ignition device. Thereby, the misfire pattern during the sub-chamber ignition operation can be detected, and misfire recovery control suitable for the misfire pattern can be executed.

[0171] In addition, in the misfire detection method according to the above-described second embodiment, during the main chamber ignition operation (main chamber ignition mode) in which the main chamber ignition plug (ignition plug 40b) ignites the air-fuel mixture in the main chamber (main chamber 37), the sub-chamber ignition device (sub-chamber ignition device 501a) detects the concentration of ions (the maximum value iamax of the ion signal) in the sub-chamber (sub-chamber 42). Then, the misfire detection unit (ECU 2) detects misfires based on the detection result of the sub-chamber ignition device. During complete misfires and partial misfires in the main chamber ignition operation, the concentration of ions generated in the sub-chamber becomes lower than that during normal combustion. Therefore, misfires during the main chamber ignition operation can be reliably detected from the concentration of ions in the sub-chamber.

[0172] In addition, in the misfire detection method according to the above-described third embodiment, during the main chamber ignition operation (main chamber ignition mode), the main chamber ignition device (main chamber ignition device 50b) detects the concentration of ions (the maximum value ibmax of the ion signal) in the main chamber (main chamber 37). Then, when the misfire detection unit (ECU 2) detects a misfire during the main chamber ignition operation, it discriminates the misfire pattern (complete misfire and partial misfire) based on the detection result of the main chamber ignition device. Thereby, the misfire pattern during the main chamber ignition operation can be detected, and misfire recovery control suitable for the misfire pattern can be executed.

[0173] In addition, in the misfire detection methods according to the above-described first and second embodiments, the power storage unit (capacitor 91b) provided in the main chamber ignition device (main chamber ignition device 50b) to detect the concentration of ions in the main chamber (main chamber 37), or the power storage unit (capacitor 91a) provided in the sub-chamber ignition device (sub-chamber ignition device 501a) to detect the concentration of ions in the sub-chamber (sub-chamber 42) accumulates electric charge at any timing from the initial stage of the combustion stroke to the middle stage of the compression stroke. This can prevent the air-fuel mixture in the main chamber from igniting prior to the sub-chamber ignition. As a result, during the sub-chamber ignition operation (sub-chamber ignition mode), it is possible to prevent the pressure in the main chamber from rising before the sub-chamber, and to prevent the generation of a flame jet from the sub-chamber toward the main chamber. Also, it is possible to prevent the air-fuel mixture in the sub-chamber from igniting prior to the main chamber ignition. As a result, during the main chamber ignition operation (main chamber ignition mode), it is possible to prevent the pressure in the sub-chamber from rising before the main chamber, and to prevent the flame propagation in the main chamber from being inhibited.

[0174] Further, the misfire detection device (ion current detection unit 901b) according to the fourth embodiment described above detects misfires in an internal combustion engine (engine 13) including a main chamber (main chamber 37) into which an air-fuel mixture flows, a main chamber ignition plug (ignition plug 40b) provided in the main chamber, a sub-chamber (sub-chamber 42) communicating with the main chamber, a sub-chamber ignition plug (ignition plug 40a) provided in the sub-chamber, a main chamber ignition device (main chamber ignition device 50b) that applies a voltage for igniting the air-fuel mixture in the main chamber to the main chamber ignition plug, and a sub-chamber ignition device (sub-chamber ignition device 50a) that applies a voltage for igniting the air-fuel mixture in the sub-chamber to the sub-chamber ignition plug. The main chamber ignition device of the internal combustion engine has a primary coil (primary coil 52b) and a secondary coil (secondary coil 53b) that generates an electromotive force when the energization of the primary coil is interrupted. The misfire detection device includes a main chamber power storage unit (capacitor 91b), a main chamber ion detection unit (ion current path diode 95b and voltage conversion resistor 93b), and a main chamber misfire detection unit (comparator 81b). Electric charge is stored in the main chamber power storage unit by the current flowing through the secondary coil of the main chamber ignition device. The main chamber ion detection unit detects the concentration of ions (maximum value ibmax of the ion signal) in the main chamber by the main chamber power storage unit applying a voltage to the electrodes of the main chamber ignition plug during the sub-chamber ignition operation (sub-chamber ignition mode) in which the air-fuel mixture in the sub-chamber is ignited by the sub-chamber ignition plug. The main chamber misfire detection unit detects whether or not there is a misfire by comparing the magnitude of the ion concentration detected by the main chamber ion detection unit with a predetermined main chamber ion threshold value (ion threshold value ic). During complete misfire and partial misfire in the sub-chamber ignition operation, the concentration of ions generated in the main chamber is lower than that during normal combustion. Therefore, misfire during sub-chamber ignition operation can be reliably detected from the ion concentration in the main chamber. Also, since the misfire detection device detects misfire in the sub-chamber ignition operation, the computational load on the control device (ECU2) of the internal combustion engine associated with misfire detection can be reduced. Further, since the control software incorporated in the control device of the internal combustion engine is simplified, the man-hours for software development can be reduced.

[0175] Also, the sub-chamber ignition device according to the fourth embodiment described above includes a primary coil and a secondary coil that generates an electromotive force when the energization of the primary coil is interrupted. And the misfire detection device includes a sub-chamber power storage unit, a sub-chamber ion detection unit, and a sub-chamber misfire detection unit. The sub-chamber power storage unit stores charge by the current flowing through the secondary coil of the sub-chamber ignition device. The sub-chamber ion detection unit detects the concentration of ions (the maximum value iamax of the ion signal) in the sub-chamber (sub-chamber 42) by applying a voltage to the electrodes of the sub-chamber ignition plug (ignition plug 40a) by the sub-chamber power storage unit when performing main-chamber ignition operation (main-chamber ignition mode) to ignite the air-fuel mixture in the main chamber (main chamber 37) by the main-chamber ignition plug. The sub-chamber misfire detection unit detects whether there is misfire by comparing the magnitude of the ion concentration detected by the sub-chamber ion detection unit with a predetermined sub-chamber ion threshold value. During complete misfire and partial misfire in the main-chamber ignition operation, the concentration of ions generated in the sub-chamber is lower than that during normal combustion. Therefore, misfire during main-chamber ignition operation can be reliably detected from the ion concentration in the sub-chamber. Also, since the misfire detection device detects misfire in the main-chamber ignition operation, the computational load on the control device (ECU2) of the internal combustion engine associated with misfire detection can be reduced. Further, since the control software incorporated in the control device of the internal combustion engine is simplified, the man-hours for software development can be reduced.

[0176] Also, the misfire detection device (ion current detection unit 902b) according to the fifth embodiment described above includes a main-chamber ion threshold value change unit (variable voltage device 84b) that changes the main-chamber ion threshold value. Accordingly, the ion threshold value used during the sub-chamber ignition operation (sub-chamber ignition mode) can be changed. As a result, the accuracy of misfire detection during the sub-chamber ignition operation can be improved.

[0177] In addition, the misfire detection device according to the fifth embodiment described above includes a sub-chamber ion threshold value changing unit that changes the sub-chamber ion threshold value. Accordingly, the ion threshold value used during the main-chamber ignition operation (main-chamber ignition mode) can be changed. As a result, the accuracy of misfire detection during the main-chamber ignition operation can be improved.

[0178] In addition, the main-chamber ion threshold value changing unit (variable voltage device 84b) or the sub-chamber ion threshold value changing unit according to the fourth and fifth embodiments described above changes the main-chamber ion threshold value (ion threshold value ic) or the sub-chamber ion threshold value according to at least one of the air-fuel ratio, the EGR rate, and the engine torque. Accordingly, the ion threshold value can be changed according to the operating conditions of the internal combustion engine (engine). As a result, the accuracy of misfire detection can be maintained at a high level.

[0179] In addition, the main-chamber ion threshold value and the sub-chamber ion threshold value according to the fourth and fifth embodiments described above are set to different magnitudes. Accordingly, even when the ion concentration in the sub-chamber and the ion concentration in the main-chamber are different after normal combustion, highly accurate misfire detection becomes possible.

[0180] As described above, embodiments of the misfire detection method and the misfire detection device of the present invention have been described including their operational effects. However, the misfire detection method and the misfire detection device of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the invention described in the claims.

[0181] In addition, the above-described embodiments have been described in detail for the purpose of explaining the present invention clearly, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can also be added to the configuration of one embodiment. Further, it is possible to add, delete, or replace other configurations for a part of the configuration of each embodiment.

[0182] For example, in the first to third embodiments described above, the ECU 2 is configured to perform misfire determination processing. However, the misfire determination processing according to the present invention may be a control unit provided separately from the ECU 2, for example, a digital signal processor (DSP).

Explanation of Reference Numerals

[0183] 2... ECU, 13, 13b... Engine, 31... Intake manifold, 32... Intake valve, 33... Exhaust manifold, 34... Exhaust valve, 35... Piston, 36... Injector, 37... Main chamber, 38... Cylinder, 40a, 40b... Spark plug, 41a, 41b... Electrode, 42... Auxiliary chamber, 43... Through hole, 45... Auxiliary chamber forming member, 48a, 48b... High-tension cord, 50a, 501a... Ignition device for auxiliary chamber, 50b, 501b, 502b... Ignition device for main chamber, 51a, 51b... Ignition part, 52a, 52b... Primary coil, 53a, 53b... Secondary coil, 54a, 54b... Igniter, 55b... Ion threshold signal, 57a... Diode, 58a... Resistor, 59a, 59b... Ignition control signal, 80b... Peak hold circuit, 81b... Comparator, 82b... Voltage dividing resistor, 84b... Variable voltage device, 88b... Misfire determination signal, 90a, 90b, 901b, 902b... Ion current detection part, 91a, 91b... Capacitor, 92a, 92b... Zener diode, 93b... Voltage conversion resistor, 94b... Secondary current path diode, 95b... Ion current path diode, 98a... Auxiliary chamber ion signal, 98b... Main chamber ion signal

Claims

1. In a method for detecting misfire in an internal combustion engine, comprising a main chamber into which an air-fuel mixture flows, a main chamber ignition plug provided in the main chamber, a sub-chamber communicating with the main chamber, a sub-chamber ignition plug provided in the sub-chamber, a main chamber ignition device for applying a voltage for igniting the air-fuel mixture in the main chamber to the main chamber ignition plug, and a sub-chamber ignition device for applying a voltage for igniting the air-fuel mixture in the sub-chamber to the sub-chamber ignition plug, during sub-chamber ignition operation in which the sub-chamber ignition plug ignites the air-fuel mixture in the sub-chamber, the main chamber ignition device detects the concentration of ions in the main chamber, a misfire detection unit compares the magnitude of the concentration of ions in the main chamber with a predetermined main chamber ion threshold value, and detects whether it is a misfire during sub-chamber ignition including partial misfire in which ignition of the air-fuel mixture in the main chamber fails despite successful ignition of the air-fuel mixture in the sub-chamber and complete misfire in which ignition of the air-fuel mixture in the sub-chamber fails, during the sub-chamber ignition operation, the sub-chamber ignition device detects the concentration of ions in the sub-chamber, when the misfire detection unit detects misfire during sub-chamber ignition during the sub-chamber ignition operation, if the concentration of ions in the sub-chamber is not less than a predetermined sub-chamber ion threshold value for misfire pattern discrimination, it determines that it is the partial misfire, and if the concentration of ions in the sub-chamber is less than or equal to the sub-chamber ion threshold value for misfire pattern discrimination, it determines that it is the complete misfire A misfire detection method.

2. The main chamber ignition device has a power storage unit for detecting the concentration of ions in the main chamber, the power storage unit accumulates charge at any timing from the initial stage of the combustion stroke to the middle stage of the compression stroke The misfire detection method according to claim 1.

3. In a method for detecting misfire in an internal combustion engine, comprising a main chamber into which an air-fuel mixture flows, a main chamber ignition plug provided in the main chamber, a sub-chamber communicating with the main chamber, a sub-chamber ignition plug provided in the sub-chamber, a main chamber ignition device for applying a voltage for igniting the air-fuel mixture in the main chamber to the main chamber ignition plug, and a sub-chamber ignition device for applying a voltage for igniting the air-fuel mixture in the sub-chamber to the sub-chamber ignition plug, during main chamber ignition operation in which the main chamber ignition plug ignites the air-fuel mixture in the main chamber, the sub-chamber ignition device detects the concentration of ions in the sub-chamber, The fire detection unit compares the concentration of ions in the auxiliary chamber with a predetermined ion threshold for the auxiliary chamber to detect whether it is a misfire during main chamber ignition including a partial misfire where ignition of the air-fuel mixture in the auxiliary chamber fails despite successful ignition of the air-fuel mixture in the main chamber, and a complete misfire where ignition of the air-fuel mixture in the main chamber fails. During the main chamber ignition operation, the main chamber ignition device detects the concentration of ions in the main chamber. When the fire detection unit detects a misfire during main chamber ignition during the main chamber ignition operation, if the concentration of ions in the main chamber is not less than a predetermined main chamber ion threshold for misfire pattern discrimination, it determines that it is a partial misfire, and if the concentration of ions in the main chamber is less than the predetermined main chamber ion threshold for misfire pattern discrimination, it determines that it is a complete misfire. A method for detecting misfire. According to claim 4, the auxiliary chamber ignition device has a power storage unit for detecting the concentration of ions in the auxiliary chamber. The power storage unit accumulates charge at any timing from the initial stage of the combustion stroke to the middle stage of the compression stroke. The misfire detection method according to claim 3. According to claim 5 In an internal combustion engine misfire detection device including a main chamber into which an air-fuel mixture flows, a main chamber ignition plug provided in the main chamber, an auxiliary chamber communicating with the main chamber, an auxiliary chamber ignition plug provided in the auxiliary chamber, a main chamber ignition device for applying a voltage for igniting the air-fuel mixture in the main chamber to the main chamber ignition plug, and an auxiliary chamber ignition device for applying a voltage for igniting the air-fuel mixture in the auxiliary chamber to the auxiliary chamber ignition plug, the main chamber ignition device has a primary coil and a secondary coil that generates an electromotive force when the energization of the primary coil is interrupted. A main chamber power storage unit in which charge is stored by the current flowing through the secondary coil of the main chamber ignition device. A main chamber ion detection unit that detects the concentration of ions in the main chamber by the main chamber power storage unit applying a voltage to the electrodes of the main chamber ignition plug. During the auxiliary chamber ignition operation of igniting the air-fuel mixture in the auxiliary chamber by the auxiliary chamber ignition plug, it compares the magnitude of the concentration of ions detected by the main chamber ion detection unit with a predetermined main chamber ion threshold, and detects whether it is a misfire during auxiliary chamber ignition including a partial misfire during auxiliary chamber ignition where ignition of the air-fuel mixture in the main chamber fails despite successful ignition of the air-fuel mixture in the auxiliary chamber, and a complete misfire during auxiliary chamber ignition where ignition of the air-fuel mixture in the auxiliary chamber fails, and includes a fire detection unit. The ignition device for the auxiliary chamber includes a primary coil and a secondary coil that generates an electromotive force when the energization of the primary coil is interrupted. An auxiliary chamber power storage unit that stores electric charge by the current flowing through the secondary coil of the ignition device for the auxiliary chamber. An in-auxiliary-chamber ion detection unit that detects the concentration of ions in the auxiliary chamber by applying a voltage from the auxiliary chamber power storage unit to the electrodes of the ignition plug for the auxiliary chamber. When the misfire detection unit detects a misfire during ignition in the auxiliary chamber during the auxiliary chamber ignition operation, if the concentration of ions in the auxiliary chamber is not less than a predetermined misfire pattern discrimination auxiliary chamber ion threshold, it is determined as a partial misfire during ignition in the auxiliary chamber, and when the concentration of ions in the auxiliary chamber is less than or equal to the misfire pattern discrimination auxiliary chamber ion threshold, it is determined as a complete misfire during ignition in the auxiliary chamber. A misfire detection device.

6. During the main chamber ignition operation in which the air-fuel mixture in the main chamber is ignited, the misfire detection unit compares the magnitude of the concentration of ions detected by the in-auxiliary-chamber ion detection unit with a predetermined ion threshold for the auxiliary chamber, and determines whether it is a misfire during main chamber ignition including a partial misfire during main chamber ignition in which ignition of the air-fuel mixture in the auxiliary chamber fails despite successful ignition of the air-fuel mixture in the main chamber, and a complete misfire during main chamber ignition in which ignition of the air-fuel mixture in the main chamber fails. When the misfire detection unit detects a misfire during main chamber ignition during the main chamber ignition operation, if the concentration of ions in the main chamber is not less than a predetermined misfire pattern discrimination main chamber ion threshold, it is determined as a partial misfire during main chamber ignition, and when the concentration of ions in the main chamber is less than or equal to the misfire pattern discrimination main chamber ion threshold, it is determined as a complete misfire during main chamber ignition. The misfire detection device according to claim 5.

7. It includes a main chamber ion threshold changing unit that changes the main chamber ion threshold. The main chamber ion threshold changing unit changes the main chamber ion threshold so as to decrease as the air-fuel ratio or the EGR rate increases, and changes the main chamber ion threshold so as to increase as the engine torque increases. The misfire detection device according to claim 6.

8. It includes an auxiliary chamber ion threshold changing unit that changes the auxiliary chamber ion threshold. The auxiliary chamber ion threshold changing unit changes the auxiliary chamber ion threshold so as to decrease as the EGR rate or the air-fuel ratio increases, and changes the auxiliary chamber ion threshold so as to increase as the engine torque increases. The misfire detection device according to claim 7.

9. The ion threshold for the main chamber and the ion threshold for the sub-chamber are set to different magnitudes The fire detection device according to claim 6

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