Engine combustion control device

Abstract

To suppress an occurrence of abnormal combustion in advance while improving thermal efficiency.SOLUTION: An engine combustion control device: applies bias voltage between plug electrodes of an ignition plug in synchronization with an initiation of a low-temperature oxidation reaction of a mixed gas; estimates combustion property such as an iso-octane ratio based on ion current detected during a detection period, from the time the bias voltage starts being applied until a predetermined time prior to an ignition timing; corrects the ignition timing in an identical cycle with the cycle in which the combustion property is estimated according to the combustion property; and ignites the mixed gas at the corrected ignition timing.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a combustion control device applied to an engine including a cylinder and a spark plug for igniting an air-fuel mixture in the cylinder.

Background Art

[0002] A combustion control device for an engine shown in Patent Document 1 below is known. The combustion control device of Patent Document 1 includes an ignition coil including a primary coil and a secondary coil, a switching element for controlling energization to the primary coil, a spark plug that discharges in response to an induced voltage of the secondary coil, an ion signal detection circuit for detecting an ion current flowing between plug electrodes of the spark plug, and an ECU electrically connected to the switching element and the ion signal detection circuit. When the ignition timing arrives and the energization period to the primary coil ends, the ECU calculates the cumulative value of the ion current from the start of energization to the primary coil, and determines whether pre-ignition (premature ignition) has occurred based on the calculated cumulative value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above Patent Document 1, when the occurrence of pre-ignition is determined, appropriate control for suppressing pre-ignition is to be executed. However, in the above Patent Document 1, pre-ignition is determined based on the cumulative value of the ion current detected during the period from the start of energization to the end of energization (in other words, the ignition timing) of the primary coil. Therefore, at the time when pre-ignition is determined, ignition has already ended, and it is considered that combustion has progressed considerably. For this reason, there has been a problem that substantial pre-ignition suppression control cannot be executed unless at least the next cycle is reached. Also, in order to avoid the surfacing of such problems, it is conceivable to design the engine on the safe side so that abnormal combustion such as pre-ignition does not occur as much as possible. However, if this is done, there is a problem that the thermal efficiency of the engine decreases.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide an engine combustion control device capable of suppressing the occurrence of abnormal combustion while improving the thermal efficiency.

Means for Solving the Problems

[0006] As a solution to the above problems, the present invention is a combustion control device applied to an engine including a cylinder, an injector that injects fuel into the cylinder, and a spark plug that ignites an air-fuel mixture containing the fuel injected from the injector. The combustion control device includes: an ignition coil including a primary coil and a secondary coil; an igniter that induces a high voltage in the secondary coil through energization and de-energization of the primary coil, and causes a discharge to occur between the plug electrodes of the spark plug by the induced high voltage; a bias voltage generation unit that applies a bias voltage for detecting an ion current generated between the plug electrodes due to ions in the cylinder between the plug electrodes; an ion current detection unit that detects the ion current; an ignition control unit that controls the bias voltage generation unit so that the bias voltage is applied between the plug electrodes in accordance with the start of a low-temperature oxidation reaction occurring in the cylinder as the air-fuel mixture is compressed, and controls the igniter so that a discharge occurs between the plug electrodes at an ignition timing set at a time later than the start of the low-temperature oxidation reaction; and an arithmetic unit that estimates the properties of the fuel injected from the injector based on the ion current detected by the ion current detection unit during a detection period that is a period from the time when the application of the bias voltage starts to a predetermined time earlier than the ignition timing. The ignition control unit corrects the ignition timing in the same cycle as the cycle in which the properties of the fuel are estimated according to the properties of the fuel, and controls the igniter so that the discharge is performed at the corrected ignition timing (Claim 1).

[0007] According to the present invention, the fuel properties (hereinafter also referred to as fuel properties) are estimated based on the ion current detected before the ignition timing, and the ignition timing is corrected based on the estimated fuel properties. Therefore, the ignition timing can be adjusted to an appropriate timing considering the differences in fuel properties. That is, since the differences in fuel properties affect the likelihood of knocking, according to the present invention in which the ignition timing is corrected according to such fuel properties, the air-fuel mixture can be ignited at an ignition timing with as high a thermal efficiency as possible within a range where knocking does not occur. Moreover, since the isooctane ratio is estimated before the ignition timing, the ignition timing in the same cycle as the cycle in which the estimation is performed can be adjusted in advance to an appropriate timing considering knocking. Thereby, it is possible to suppress the occurrence of knocking while improving the thermal efficiency.

[0008] Preferably, the calculation unit estimates the ratio of isooctane contained in the fuel as the fuel property, and the ignition control unit corrects the ignition timing to the retard side as the ratio of isooctane is smaller (Claim 2).

[0009] The ratio of isooctane contained in the fuel (hereinafter also referred to as the isooctane ratio) is one of the typical fuel properties that influence the likelihood of knocking. That is, it has the property that the larger the isooctane ratio, the less likely knocking is to occur, and the smaller the isooctane ratio, the more likely knocking is to occur. Therefore, according to this aspect in which the ignition timing is corrected to the retard side as the isooctane ratio is smaller, knocking caused by fuel properties can be effectively suppressed. Conversely, when the isooctane ratio is large, since the ignition timing is set on the advance side, it is possible to improve the thermal efficiency while suppressing knocking.

[0010] Preferably, the calculation unit calculates an ion current feature amount correlated with the fuel property based on the ion current detected during the detection period, and estimates the ratio of isooctane from the calculated ion current feature amount (Claim 3).

[0011] In this aspect, since the ion current feature amount correlated with the isooctane ratio is calculated based on the ion current during the detection period, the isooctane ratio can be appropriately estimated from the ion current feature amount.

[0012] Preferably, the ion current feature amount is the maximum charge amount which is the maximum value of the charge amount between the plug electrodes during the detection period, and the calculation unit estimates that the ratio of isooctane is larger as the maximum charge amount is smaller (Claim 4).

[0013] In this aspect, by utilizing the finding that the isooctane ratio is large when the maximum charge amount is small, the isooctane ratio can be appropriately estimated from the maximum charge amount.

[0014] The ion current feature amount may be the maximum ion current which is the maximum value of the ion current during the detection period. In this case, it is preferable that the calculation unit estimates that the ratio of isooctane is larger as the maximum ion current is smaller (Claim 5).

[0015] Also in this aspect, the isooctane ratio can be appropriately estimated.

[0016] Preferably, the ignition control unit controls the bias voltage generation unit so that the bias voltage gradually increases from the start of the low-temperature oxidation reaction and then gradually decreases (Claim 6).

[0017] In this way, when the bias voltage is changed in a mountain shape, the charge amount between the plug electrodes can be changed in a similar mountain-shaped tendency. This facilitates the calculation of the above-described maximum charge amount which is the maximum value of the charge amount, or the above-described maximum ion current which is the maximum value of the ion current. Further, since the ion current increasing with the start of the low-temperature oxidation reaction is further amplified by the gradual increase of the bias voltage, the sensitivity of the maximum charge amount or the maximum ion current that changes depending on the difference in the isooctane ratio can be improved. Thereby, the estimation accuracy of the isooctane ratio can be enhanced.

[0018] Preferably, the bias voltage generation unit is a capacitor device connected to the secondary coil (Claim 7).

[0019] In this aspect, the bias voltage can be appropriately controlled by adjusting the charge amount of the capacitor device.

[0020] Preferably, the ignition control unit controls the bias voltage generation unit so that the application start of the bias voltage is advanced as the engine speed increases (Claim 8).

[0021] Alternatively, the ignition control unit controls the bias voltage generation unit so that the application start of the bias voltage is advanced as the engine load increases (Claim 9).

[0022] In these aspects, the bias voltage can be applied in accordance with the start of the low-temperature oxidation reaction, which advances as the engine load or engine speed increases, and the ion current that increases with the start of the low-temperature oxidation reaction can be appropriately detected.

[0023] Preferably, the combustion control device further includes an abnormal combustion determination unit that determines the occurrence of pre-ignition based on the ion current detected by the ion current detection unit, and an injection control unit that injects additional fuel into the injector when the occurrence of pre-ignition is determined (Claim 10).

[0024] In this aspect, since the latent heat of vaporization of the additionally injected fuel lowers the internal temperature of the cylinder, the progress of the combustion of the air-fuel mixture can be suppressed, and the influence caused by pre-ignition can be reduced.

Advantages of the Invention

[0025] As described above, according to the engine combustion control device of the present invention, it is possible to suppress the occurrence of abnormal combustion while improving the thermal efficiency.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11A

Figure 11B

Figure 12

Embodiments for Carrying Out the Invention

[0027] (1) Overall Configuration of Engine FIG. 1 is a system diagram showing the overall configuration of an engine to which a combustion control device according to an embodiment of the present invention is applied. The engine shown in this figure is a four-cycle spark-ignition engine mounted on a vehicle as a power source for traveling. The engine includes an engine body 1, an intake passage 20 and an exhaust passage 30 connected to the engine body 1, and an ECU 40 that controls each part of the engine. In this embodiment, the upper and lower directions are defined with reference to FIG. 1 for convenience of explanation, but this is not intended to limit the installation posture of the engine.

[0028] The engine body 1 includes a cylinder block 3 and a cylinder head 4 that define a cylinder 2 inside, and a piston 5 that is reciprocally accommodated in the cylinder 2. A combustion chamber C is formed above the piston 5. Although only one cylinder 2 is shown in FIG. 1, the engine body 1 can be a multi-cylinder type having a plurality of cylinders 2.

[0029] An ignition circuit 10, an ignition plug 11, and an injector 15 are attached to the cylinder head 4. The injector 15 is an injection valve that injects fuel (for example, gasoline fuel) supplied from a fuel tank (not shown) through a fuel supply pipe 15a toward the combustion chamber C. The ignition plug 11 is a plug that ignites the air-fuel mixture generated by the fuel injected from the injector 15 into the combustion chamber C. The ignition circuit 10 is a circuit that applies a high voltage for generating an ignition spark to the ignition plug 11. When the air-fuel mixture in the combustion chamber C burns triggered by the ignition by the ignition plug 11, the piston 5 reciprocates under the expansion force of the combustion.

[0030] FIG. 2 is a view showing an enlarged tip portion of the spark plug 11. As shown in this figure, the spark plug 11 includes a plug body 12, a center electrode 13, and a ground electrode 14. The plug body 12 has a cylindrical shape extending along the cylinder axis X1 which is the central axis of the cylinder 2, and is attached to the cylinder head 4 in a state where the tip portion is exposed to the combustion chamber C. The center electrode 13 is formed so as to protrude downward from the center of the tip portion of the plug body 12. The ground electrode 14 is formed so as to extend downward while being bent in an L shape from the peripheral edge of the tip portion of the plug body 12. The tip of the ground electrode 14 faces the center electrode 13 with a predetermined gap G therebetween.

[0031] The center electrode 13 is connected to a secondary coil 103, which will be described later, of the ignition circuit 10. The ground electrode 14 is connected to the ground via the plug body 12 and the cylinder head 4. At the time of ignition, a high voltage is applied from the ignition circuit 10 to the center electrode 13, and a discharge occurs between the center electrode 13 and the ground electrode 14. Then, the air-fuel mixture is ignited by the spark generated along with this discharge. Incidentally, hereinafter, the center electrode 13 and the ground electrode 14 may be collectively referred to as the plug electrodes 13, 14.

[0032] As shown in FIG. 1, a crankshaft 9, which is an output shaft of the engine, is disposed below the piston 5. The crankshaft 9 is rotatably supported by the cylinder block 3. The reciprocating motion of the piston 5 described above is transmitted to the crankshaft 9 via a crank mechanism including a connecting rod 7 and the like, and the crankshaft 9 is rotated.

[0033] A crank angle sensor SN1 is attached to the cylinder block 3. The crank angle sensor SN1 is a sensor that detects the crank angle, which is the rotation angle of the crankshaft 9, and the engine speed, which is the rotation speed of the crankshaft 9.

[0034] The cylinder head 4 is formed with an intake port 16 and an exhaust port 17. The intake port 16 is a port that communicates the combustion chamber C and the intake passage 20. The exhaust port 17 is a port that communicates the combustion chamber C and the exhaust passage 30. An intake valve 18 and an exhaust valve 19 that open and close the intake port 16 and the exhaust port 17 respectively in conjunction with the rotation of the crankshaft 9 are attached to the cylinder head 4.

[0035] The intake passage 20 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 16. The intake passage 20 is provided with an openable and closable throttle valve 21 for adjusting the intake flow rate. An air flow sensor SN2 for detecting the intake flow rate is provided at a position upstream of the throttle valve 21 in the intake passage 20.

[0036] The exhaust passage 30 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 17. The exhaust passage 30 is provided with a catalyst (not shown) or the like for purifying harmful components in the exhaust gas.

[0037] The ECU 40 is a controller mainly composed of a microcomputer including a processor (CPU) that performs various operations, memories such as a ROM and a RAM, and various input / output buses. The ECU 40 receives input information from sensors provided in the engine. For example, the ECU 40 is electrically connected to the above-described crank angle sensor SN1 and air flow sensor SN2. Detection information from these sensors SN1 and SN2, that is, information such as the crank angle, engine speed, and intake flow rate, is sequentially input to the ECU 40.

[0038] The ECU 40 also receives input information from sensors provided in the vehicle. For example, the ECU 40 is electrically connected to a vehicle speed sensor SN3 and an accelerator sensor SN4 provided in the vehicle. The vehicle speed sensor SN3 is a sensor that detects the running speed of the vehicle, that is, the vehicle speed, and the accelerator sensor SN4 is a sensor that detects the opening degree of the accelerator pedal 50 operated by the driver who drives the vehicle, that is, the accelerator opening degree. The detection information (vehicle speed and accelerator opening degree) from each of these sensors SN3, SN4 is sequentially input to the ECU 40.

[0039] The ECU 40 controls each part of the engine while executing various calculations and determinations based on the input information from the above-mentioned various sensors (SN1 to SN4, etc.). For example, the ECU 40 is electrically connected to the ignition circuit 10 and the injector 15, and appropriately outputs control signals to these elements.

[0040] As functional elements related to the above control, the ECU 40 includes an ignition control unit 41, an injection control unit 42, a calculation unit 43, an ion current detection unit 44, and a storage unit 45. The ignition control unit 41 is a module that controls the ignition operation of the spark plug 11 through energization control of the ignition circuit 10. The injection control unit 42 is a module that controls the injection operation of the injector 15. The calculation unit 43 is a control module that performs various calculations and determinations necessary to determine the contents of control by the ignition control unit 41 and the injection control unit 42. The ion current detection unit 44 is a module that detects the ion current generated between the plug electrodes 13, 14 of the spark plug 11 based on a signal from the ignition circuit 10. The storage unit 45 is a module that stores various data necessary for control or calculation.

[0041] (2) Configuration of the ignition circuit FIG. 3 is a circuit diagram showing the configuration of the ignition circuit 10. As shown in this figure, the ignition circuit 10 includes an ignition coil 101 that applies a high voltage for discharge to the spark plug 11, and a coil driver 105 that realizes operations such as energization and de-energization of the ignition coil 101.

[0042] The ignition coil 101 includes a primary coil 102 connected to a battery (not shown) and a secondary coil 103 connected to the center electrode 13 of the spark plug 11. The primary coil 102 and the secondary coil 103 are wound around a common core (iron core).

[0043] The coil driver 105 includes an igniter 106, a capacitor device 107, a current amplification circuit 110, and a Zener diode 111. The igniter 106 is a transistor interposed between the primary coil 102 and the ground (Gnd), with its collector connected to the primary coil 102 and its emitter connected to the ground. The capacitor device 107 is interposed between the secondary coil 103 and the ground. The Zener diode 111 is connected in parallel with the capacitor device 107. The current amplification circuit 110 is interposed between a terminal 121 connected to the ion current detection unit 44 of the ECU 40 and a terminal 125 on the negative electrode side of the capacitor device 107.

[0044] A resistor 115 and a diode 116 are provided in parallel between the secondary coil 103 and the coil driver 105. That is, the secondary coil 103 is connected to the terminal 122 of the coil driver 105 via the resistor 115 or the diode 116.

[0045] The igniter 106 induces a high voltage in the secondary coil 103 through energization and de-energization of the primary coil 102, and causes a discharge between the plug electrodes 13, 14 of the spark plug 11 due to the induced high voltage.

[0046] Specifically, the igniter 106 is switched to the ON state before the ignition timing arrives. As a result, the flow of current between the collector and the emitter is allowed, and the primary coil 102 is energized. That is, a current flows from the battery through the primary coil 102 and the igniter 106 to the ground. Then, when the ignition timing arrives, the igniter 106 is switched from the ON state to the OFF state. Thereby, the flow of current between the collector and the emitter is prohibited, and the energization of the primary coil 102 is stopped. Then, due to electromagnetic induction accompanying the stop of the energization, a high voltage corresponding to the winding ratio of the primary coil 102 and the secondary coil 103 is induced in the secondary coil 103.

[0047] When a high voltage is induced in the secondary coil 103 as described above, a discharge due to the high voltage occurs between the plug electrodes 13 and 14 of the ignition plug 11, and a spark is generated. By this spark, the air-fuel mixture in the combustion chamber C is ignited. FIG. 4 is a diagram showing the flow of current (discharge current) during this discharge. As shown in this figure, the discharge current flows from the center electrode 13 of the ignition plug 11 to the ground through the secondary coil 103, the diode 116, the Zener diode 111, etc.

[0048] The capacitor device 107 applies a bias voltage for detecting the ion current to the ignition plug 11. That is, ions are generated inside the cylinder 2, that is, in the combustion chamber C, along with the reaction of the air-fuel mixture. When a bias voltage is applied to the ignition plug 11 during the generation of such ions, an ion current as shown in FIG. 5 is generated according to the potential difference between the plug electrodes 13 and 14 due to the bias voltage. The ion current flows toward the center electrode 13 of the ignition plug 11 through the current amplification circuit 110, the capacitor device 107, the resistor 115, the secondary coil 103, etc. The capacitor device 107 functions as a voltage supply source (bias voltage generation unit) that applies a bias voltage leading to the generation of such an ion current to the ignition plug 11.

[0049] The capacitor device 107 includes a capacitor 108 and a voltage control circuit 109 arranged in parallel. The capacitor 108 has a pair of chargeable positive and negative electrode plates. The voltage control circuit 109 supplies charge to the capacitor 108 for generating the bias voltage described above. That is, when charge is supplied from the voltage control circuit 109 and the capacitor 108 is charged, a potential difference is generated between the electrode plates of the capacitor 108, and this potential difference also generates a potential difference between the plug electrodes 13 and 14 of the ignition plug 11, which functions as a bias voltage. The charge amount of the capacitor 108, in other words, the magnitude of the bias voltage, is increased or decreased according to the supply amount of charge from the voltage control circuit 109. In other words, the voltage control circuit 109 can control the bias voltage through the charge supply amount to the capacitor 108.

[0050] The current amplification circuit 110 is a circuit that amplifies the ion current. The current amplified by this current amplification circuit 110 is detected by the ion current detection unit 44.

[0051] The coil driver 105 has a terminal 123 that receives a control signal from the ignition control unit 41 of the ECU 40. The above-described igniter 106 and capacitor device 107 (voltage control circuit 109) operate in response to the control signal input through the terminal 123. That is, the ignition control unit 41 controls the energization and de-energization of the primary coil 102 through the ON / OFF control of the igniter 106, and controls the bias voltage of the ignition plug 11 through the adjustment of the charge amount of the capacitor device 107 (capacitor 108).

[0052] (3) Determination of Ignition Timing Based on Ion Current Here, in a spark-ignition engine such as the present embodiment, there is a need to ignite the air-fuel mixture at a timing with as high a thermal efficiency as possible. However, depending on the properties of the fuel injected into the cylinder 2 (combustion chamber C), if the ignition timing is not retarded from the timing at which the thermal efficiency is optimal, knocking, which is abnormal combustion in which end gas (unburned gas) auto-ignites during the combustion of the air-fuel mixture, may occur. For example, gasoline fuel used in a spark-ignition engine mainly contains isooctane, which is a component that is less likely to cause knocking (has high anti-knock properties). However, if the proportion of isooctane varies, knocking may occur when the air-fuel mixture is ignited at the normal ignition timing. Regarding this, in in-vehicle engines on the market, in many cases, the lower limit value of the octane number, which is an index representing anti-knock properties, is determined. However, the octane number does not necessarily match the actual proportion (volume ratio) of isooctane. Therefore, depending on the actual proportion of isooctane, knocking may occur.

[0053] In recent years, from the perspective of carbon neutrality, for example, biofuels such as bioethanol produced from biomass and synthetic fuels such as e-gasoline produced by synthesizing CO2 and H2 derived from renewable energy have attracted attention. These biofuels and synthetic fuels are expected to be used in a mixture with existing gasoline, additives, etc., especially during the popularization period. When assuming the use of such diverse fuels, the proportion of isooctane may vary significantly depending on the fuel used.

[0054] Thus, in a spark-ignition engine, it is assumed that the proportion of isooctane in the fuel used will vary both currently and in the future. In particular, when considering the use of biofuels and synthetic fuels, the proportion of isooctane may vary significantly. In order to improve the thermal efficiency while allowing the use of fuels with such different properties, it is desirable to adjust the ignition timing according to the fuel properties to suppress knocking and at the same time ignite the air-fuel mixture at a timing with as high a thermal efficiency as possible.

[0055] Therefore, the inventors of the present application focused on the correlation between the ratio of isooctane contained in the fuel (hereinafter also referred to as the isooctane ratio) and the above-described ion current, and came up with the idea of determining the ignition timing after estimating the isooctane ratio based on the ion current. That is, before ignition by the ignition plug 11, the ion current is detected, and from the detected ion current, a predetermined characteristic quantity (the maximum charge amount qmax described later) that represents the isooctane ratio and thus the likelihood of knocking is calculated, and further, the ignition timing in the current cycle is determined based on the calculated characteristic quantity. This will be described in detail below.

[0056] (Correlation between Ion Current and Isooctane Ratio) Since the ion current is derived from ions generated by the ionization of the air-fuel mixture containing vaporized and atomized fuel, it is expected that differences in fuel properties will appear as differences in the ion current. Therefore, as a verification experiment based on this expectation, a discharge simulation was conducted to confirm the correlation between the ion current and the isooctane ratio in the fuel. That is, under various conditions with different isooctane ratios, a virtual discharge was caused between the plug electrodes 13 and 14 using a model that modeled the behavior of charged particles (ions or electrons) between the plug electrodes 13 and 14, and the ion current generated during the period until the discharge was examined. Here, as a value related to the ion current, the charge amount q, which is the space charge between the plug electrodes 13 and 14, was identified, and how the charge amount q changes depending on the isooctane ratio was examined. Note that as the charge amount q, the absolute value of the space charge (negative) of electrons was used.

[0057] FIG. 6 is a graph showing changes in the bias voltage applied between the plug electrodes 13 and 14 with the crank angle to generate an ion current. In this graph, the change in the bias voltage is shown together with the charge signal which is the energization signal to the primary coil 102. Also, the first crank angle CA1 and the third crank angle CA3 on the horizontal axis of this graph are the crank angles when the energization (charging) to the primary coil 102 starts and stops, respectively. That is, the period from the first crank angle CA1 to the third crank angle CA3 is the charging period during which the primary coil 102 is energized. As described above, since the stop of the energization (charging) to the primary coil 102 causes discharge between the plug electrodes 13 and 14, the third crank angle CA3 which is the end point of the charging period is equivalent to the timing of discharge, that is, the ignition timing.

[0058] As shown in FIG. 6, in this verification experiment, the bias voltage was applied from the start to the end of the charging period. That is, the application of the bias voltage was started at the first crank angle CA1 at which the charging period starts, and the application of the bias voltage was stopped at the third crank angle CA3 at which the charging period ends. Further, in this verification experiment, the bias voltage was changed in a mountain shape. That is, the bias voltage was gradually increased from the first crank angle CA1 to the second crank angle CA2 between the first crank angle CA1 and the third crank angle CA3, and the bias voltage was gradually decreased from the second crank angle CA2 to the third crank angle CA3. In other words, in this verification experiment, the bias voltage was applied so that the voltage changes along a mountain-shaped waveform having a peak near the center of the charging period.

[0059] Next, the change in the charge amount q that occurs when the bias voltage is applied as described above was examined, and the results shown in FIG. 7 were obtained. Specifically, under various conditions with different isooctane ratios in the fuel, a bias voltage that changes in a mountain shape as shown in FIG. 6 was applied to the spark plug 11, and the change in the charge amount q at that time was examined. Among the waveforms in FIG. 7, conditions other than the isooctane ratio, such as engine load and engine speed, are the same.

[0060] As shown in Fig. 7, the charge quantity q changes along a mountain-shaped waveform with a peak during the charging period, similar to the bias voltage. Also, the value of the peak, i.e., the maximum charge quantity qmax which is the maximum value of the charge quantity q, changes depending on the isooctane ratio. That is, as is clear from Fig. 7, the maximum charge quantity qmax becomes smaller as the isooctane ratio increases.

[0061] Fig. 8 is a graph directly showing the relationship between the isooctane ratio and the maximum charge quantity qmax obtained from the results of Fig. 7. As can also be understood from this figure, the maximum charge quantity qmax becomes smaller as the isooctane ratio increases, and becomes larger as the isooctane ratio decreases. Here, a large isooctane ratio means that knocking is less likely to occur, and a small isooctane ratio means that knocking is more likely to occur. This suggests that the ignition timing considering knocking can be determined from the maximum charge quantity qmax.

[0062] (4) Actual control Next, the details of the engine combustion control performed based on the above findings will be described. As shown below, in this embodiment, the standard ignition timing Igr determined from the operating state of the engine is corrected according to the isooctane ratio estimated from the maximum charge quantity qmax which is a characteristic quantity of the ion current, and the air-fuel mixture is ignited at the corrected ignition timing. Moreover, since the calculation for such ignition timing determination is performed during the energization of the primary coil 102 (during the charging period), it is possible to correct the ignition timing within the same cycle as the cycle in which the calculation was performed. This will be described in detail below.

[0063] FIG. 9 and FIG. 10 are flowcharts showing details of combustion control performed by the ECU 40 during engine operation. When this combustion control starts, the arithmetic unit 43 of the ECU 40 acquires various information regarding the engine (step S1). Specifically, the arithmetic unit 43 acquires information such as the crank angle, engine speed, intake air flow rate, vehicle speed, and accelerator opening from the detection values of the crank angle sensor SN1, air flow sensor SN2, vehicle speed sensor SN3, and accelerator sensor SN4. Also, based on the acquired accelerator opening and vehicle speed, the load (required torque) of the engine is specified.

[0064] Next, the arithmetic unit 43 determines the fuel injection amount and injection timing (step S2). That is, the arithmetic unit 43 determines the injection amount, which is the amount of fuel to be injected from the injector 15, based on the intake air flow rate and engine load acquired in step S1 above. Also, the arithmetic unit 43 determines the injection timing, which is the timing at which fuel injection from the injector 15 should start, based on the determined injection amount and the engine speed acquired in step S1 above.

[0065] Next, the arithmetic unit 43 determines the standard ignition timing Igr based on the operating conditions including the engine load and engine speed acquired in step S1 above (step S3). The standard ignition timing Igr is determined in advance based on prior experiments and the like for each operating condition of the engine as an ignition timing that maximizes the thermal efficiency as much as possible within the range where knocking does not occur. Also, the standard ignition timing Igr is determined on the premise that the isooctane ratio of the fuel is a predetermined reference value. The reference value of the isooctane ratio can be set as appropriate, but for example, it may be set to any value between 90% and 100% with regular gasoline or high-octane gasoline currently on the market in mind.

[0066] In the storage unit 45 of the ECU 40, map data defining the relationship between the engine operating conditions (such as load and rotational speed) and the standard ignition timing Igr is stored in advance so that the standard ignition timing Igr can be derived from the conditions. The arithmetic unit 43 determines the standard ignition timing Igr from the engine operating conditions by referring to the stored map data. Note that the data stored in the storage unit 45 for deriving the standard ignition timing Igr is not limited to map data, and may be, for example, an arithmetic expression.

[0067] Next, the arithmetic unit 43 predicts the start timing of the low-temperature oxidation reaction that occurs as the air-fuel mixture is compressed (step S4). The low-temperature oxidation reaction is a slow oxidation reaction that occurs before the high-temperature oxidation reaction (substantially the combustion reaction) that generates high thermal energy with a flame, and can occur in the latter half of the compression stroke when the combustion chamber C becomes hot. The start timing of the low-temperature oxidation reaction can be predicted from the engine operating conditions based on prior experiments and the like.

[0068] FIG. 11A is a graph showing the relationship between the engine load and the start timing of the low-temperature oxidation reaction, and FIG. 11B is a graph showing the relationship between the engine rotational speed and the start timing of the low-temperature oxidation reaction. In each graph, it is assumed that the conditions other than the parameter on the horizontal axis (engine load or engine rotational speed) are the same. As shown in FIG. 11A, the low-temperature oxidation reaction starts at a more advanced timing as the engine load increases. Also, as shown in FIG. 11B, the low-temperature oxidation reaction starts at a more advanced timing as the engine rotational speed increases. In the storage unit 45, map data or arithmetic expressions corresponding to FIGS. 11A and 11B are stored in advance. The arithmetic unit 43 predicts the start timing of the low-temperature oxidation reaction from the engine operating conditions (such as load and rotational speed) using the stored map data or arithmetic expression.

[0069] Next, the arithmetic unit 43 determines the charge start timing, which is the timing to start energizing, i.e., charging, the primary coil 102 of the ignition circuit 10 (step S5). In the present embodiment, the charge start timing is set to be substantially simultaneous with the start of the low-temperature oxidation reaction. The arithmetic unit 43 determines the charge start timing based on the start timing of the low-temperature oxidation reaction predicted in step S4 above so that charging is started at such timing.

[0070] Next, the injection control unit 42 of the ECU 40 injects fuel into the injector 15 at the timing when the injection timing determined in step S2 above arrives (step S6). The fuel injection continues until the fuel corresponding to the injection amount determined in step S2 above is completely injected.

[0071] Next, the ignition control unit 41 of the ECU 40 starts energizing, i.e., charging, the primary coil 102 and starts applying a bias voltage to the spark plug 11 at the timing when the charge start timing determined in step S5 above arrives (step S7). That is, the ignition control unit 41 controls the igniter 106 so that energization of the primary coil 102 is started at the timing when the charge start timing substantially simultaneous with the low-temperature oxidation reaction arrives, and controls the capacitor device 107 (voltage control circuit 109) so that a bias voltage is applied between the plug electrodes 13 and 14 of the spark plug 11 at the same time. Thus, in the present embodiment, the energization of the primary coil 102 and the application of the bias voltage are started at the same timing in accordance with the start of the low-temperature oxidation reaction. Applying the bias voltage in accordance with the start of the low-temperature oxidation reaction is to capture the increasing tendency of ions in the cylinder 2 that increases with the start of the low-temperature oxidation reaction.

[0072] Here, as shown in FIGS. 11A and 11B, the start timing of the low-temperature oxidation reaction is more advanced as the engine load or engine speed is higher. From this, the timing when the application of the bias voltage is started in step S7 above is set more advanced as the engine load or engine speed is higher.

[0073] Also, in the above step S7, similar to the verification experiment described above, a bias voltage is applied so that the voltage changes in a mountain shape (see FIG. 6). That is, in the present embodiment, the ignition control unit 41 applies a bias voltage such that the voltage gradually increases and then gradually decreases from the start to the end of charging. More specifically, the ignition control unit 41 starts applying the bias voltage at the first crank angle CA1 corresponding to the charge start timing determined in the above step S5, and gradually increases the bias voltage from there. Further, the ignition control unit 41 adjusts the bias voltage such that the voltage reaches a peak at the second crank angle CA2 near the center of the charge period and gradually decreases toward the third crank angle CA3 at which the charge period ends. Note that the charge end timing corresponding to the third crank angle CA3, in other words, the ignition timing, may be changed (corrected) from the standard ignition timing Igr determined in the above step S3 by the processing of each step described later. Here, however, the bias voltage is adjusted on the assumption that the standard ignition timing Igr is the charge end timing.

[0074] Next, the calculation unit 43 determines whether or not the detection end timing CAx, which is slightly delayed from the peak timing (the second crank angle CA2) of the bias voltage, has arrived (step S8). The detection end timing CAx is the timing at which it is expected that the data of the ion current necessary for calculating the maximum charge amount qmax, which is performed in the next step S9, is obtained, and is set at a timing that is retarded by a predetermined small crank angle from the second crank angle CA2 at which the bias voltage reaches a peak. In other words, the period from the first crank angle CA1 at which the bias voltage is applied to the detection end timing CAx is the detection period of the ion current necessary for calculating the maximum charge amount qmax.

[0075] When it is determined as NO in step S8 above and it is confirmed that the detection end timing CAx has not yet arrived, the arithmetic unit 43 determines whether or not the ignition of the air-fuel mixture has been detected based on the ion current detected by the ion current detector 44 of the ECU 40 (step S12). That the air-fuel mixture has ignited at this stage means that abnormal combustion, that is, pre-ignition, has occurred in which the air-fuel mixture self-ignites before ignition by the spark plug 11. The occurrence of pre-ignition, that is, the self-ignition of the air-fuel mixture during the charge period, appears as a phenomenon in which the ion current rises at an abnormal rate of increase. In step S12, when such an abnormal increase in the ion current is confirmed, the arithmetic unit 43 determines that pre-ignition has occurred. Note that the arithmetic unit 43 that determines the occurrence of pre-ignition corresponds to the "abnormal combustion determination unit" in the present invention.

[0076] When it is determined as YES in step S12 above and the occurrence of pre-ignition is confirmed, the injection control unit 42 causes the injector 15 to inject additional fuel (step S13). That is, for the injector 15 that has once finished injecting a regulated amount of fuel in step S6 above, an additional amount of fuel is further injected. The injected additional fuel causes a temperature drop due to the latent heat of vaporization and plays a role in suppressing the progress of combustion.

[0077] On the other hand, when it is determined as NO in step S12 above and it is confirmed that pre-ignition has not occurred, the arithmetic unit 43 returns to step S8 above and waits for the arrival of the detection end timing CAx.

[0078] When it is determined as YES in step S8 above and the arrival of the detection end time CAx is confirmed at the end of detection, the calculation unit 43 calculates the maximum charge amount qmax, which is the maximum value of the charge amount q between the plug electrodes 13 and 14, based on the ion current detected by the ion current detector 44 so far (step S9). Specifically, the calculation unit 43 calculates the maximum charge amount qmax using a predetermined calculation formula based on the data of the ion current detected by the ion current detector 44 during the detection period (FIG. 6) from the first crank angle CA1, which is the start time of the application of the bias voltage, to the detection end time CAx, and the data of the bias voltage during the same period. The maximum charge amount qmax calculated in this way can be said to be a value characterizing the ion current during the above detection period, that is, one of the ion current characteristic amounts.

[0079] Here, as described above, the detection end time CAx is a time somewhat later than the second crank angle CA2 (FIG. 6) at which the bias voltage reaches its peak. On the other hand, as understood from FIGS. 6 and 7, the charge amount q (space charge) between the plug electrodes 13 and 14 changes along a mountain-shaped waveform similar to the trend of the bias voltage. Therefore, at the timing of step S9 immediately after the detection end time CAx is reached, the time when the charge amount q between the plug electrodes 13 and 14 becomes maximum should already have passed. That is, in the present embodiment, the detection end time CAx is set at a timing slightly later than the time when the charge amount q is predicted to be maximum. For this reason, even at the timing of step S9 during the application of the bias voltage, the maximum charge amount qmax, which is the maximum value of the charge amount q, can be calculated.

[0080] Next, the arithmetic unit 43 estimates the isooctane ratio of the fuel based on the maximum charge amount qmax calculated in step S9 above (step S10). The isooctane ratio is, as described above, the ratio of isooctane contained in the fuel injected into cylinder 2, and is determined with a tendency as shown in FIG. 8 in relation to the maximum charge amount qmax. That is, the isooctane ratio decreases as the maximum charge amount qmax increases. In the storage unit 45, map data or arithmetic expressions corresponding to FIG. 8 are stored in advance for each operating condition including the engine load and the engine speed. The arithmetic unit 43 estimates the isooctane ratio from the maximum charge amount qmax using the map data or arithmetic expression that conforms to the current operating condition.

[0081] Next, the arithmetic unit 43 determines the correction amount ΔIg of the standard ignition timing Igr from the isooctane ratio estimated in step S10 above (step S15). The correction amount ΔIg is set according to the deviation amount between the reference value, which is the assumed isooctane ratio for determining the standard ignition timing Igr, and the estimated value of the isooctane ratio obtained in step S10 above. Specifically, the correction amount ΔIg is set to increase as the deviation amount between these reference value and the estimated value increases.

[0082] Also, the direction of correction by the correction amount ΔIg changes depending on the magnitude relationship between the reference value and the estimated value of the isooctane ratio. For example, when the estimated value of the isooctane ratio is smaller than the reference value, it means that fuel that is more likely to cause knocking than expected is being used. Therefore, the correction amount ΔIg in this case is a retard correction amount for correcting the standard ignition timing Igr to the retard side. On the other hand, when the estimated value of the isooctane ratio is larger than the reference value, it means that fuel that is less likely to cause knocking than expected is being used. Therefore, the correction amount ΔIg in this case is an advance correction amount for correcting the standard ignition timing Igr to the advance side. When the reference value of the isooctane ratio is close to 100%, the correction amount ΔIg is basically all retard correction amounts.

[0083] Next, the ignition control unit 41 determines the timing obtained by correcting the standard ignition timing Igr by ΔIg determined in step S15 above as the ignition timing by the ignition plug 11 (step S16). The ignition timing determined in this way is determined with a tendency as shown in FIG. 12 according to the setting method of the correction amount ΔIg described above. As shown in FIG. 12, the ignition timing determined in step S16, that is, the corrected ignition timing obtained by correcting the standard ignition timing Igr by ΔIg, is set on the retard side as the isooctane ratio is smaller, and is set on the advance side as the isooctane ratio is larger.

[0084] Next, at the timing when the ignition timing determined in step S16 above, that is, the timing obtained by correcting the standard ignition timing Igr by ΔIg arrives, the ignition control unit 41 causes the ignition plug 11 to perform ignition (step S17). That is, the ignition control unit 41 controls the igniter 106 so that the energization (charging) to the primary coil 102 is stopped as the ignition timing arrives. Thereby, a high voltage is induced in the secondary coil 103, and a discharge is performed between the plug electrodes 13 and 14 of the ignition plug 11 in response to the induced high voltage.

[0085] Next, the calculation unit 43 estimates the combustion center of gravity of the combustion generated by the ignition in step S17 (step S18). The combustion center of gravity is the timing when 50% of the mass of the injected fuel has burned. Such a combustion center of gravity can be estimated, for example, through calculation of the heat generation amount accompanying combustion. The method for calculating the heat generation amount is not particularly limited. For example, in the case of an engine equipped with a cylinder pressure sensor that detects the in-cylinder pressure, which is the pressure in the combustion chamber C, the heat generation amount can be calculated from the detection value of the cylinder pressure sensor, and the combustion center of gravity can be estimated from the change in the calculated heat generation amount.

[0086] Next, the arithmetic unit 43 determines whether or not the combustion center of gravity estimated in step S18 deviates from the target combustion center of gravity (step S19). The target combustion center of gravity is determined in advance for each operating condition including the engine load and the engine speed and stored in the storage unit 45. The arithmetic unit 43 compares the stored target combustion center of gravity with the combustion center of gravity estimated in step S18 and determines whether there is a deviation between the two.

[0087] When it is determined as YES in step S19 and it is confirmed that there is a deviation in the combustion center of gravity, the ignition control unit 41 corrects the standard ignition timing Igr according to the deviation (step S20). For example, when the estimated combustion center of gravity deviates to the retard side with respect to the target combustion center of gravity, the ignition control unit 41 corrects the standard ignition timing Igr to the advance side. Conversely, when the estimated combustion center of gravity deviates to the advance side with respect to the target combustion center of gravity, the ignition control unit 41 corrects the standard ignition timing Igr to the retard side.

[0088] On the other hand, when it is determined as NO in step S19 and it is confirmed that there is no deviation in the combustion center of gravity, the standard ignition timing Igr is not corrected and the flow returns to step S1.

[0089] (5) Operational effects As described above, in the present embodiment, a bias voltage is applied between the plug electrodes 13 and 14 of the ignition plug 11 in accordance with the start of the low-temperature oxidation reaction, and based on the ion current detected during the detection period from the start time (CA1) of the application of the bias voltage to the detection end time CAx before the ignition time (CA3), the ratio of isooctane contained in the fuel, that is, the isooctane ratio, is estimated. Then, the ignition timing in the same cycle in which the estimation is performed is corrected according to the isooctane ratio, and ignition is performed by the ignition plug 11 at the corrected ignition timing. According to such a configuration, there is an advantage that the occurrence of knocking can be suppressed while improving the thermal efficiency.

[0090] That is, in the present embodiment, the isooctane ratio of the fuel is estimated based on the ion current detected before the ignition timing, and the ignition timing is corrected according to the estimated isooctane ratio. Therefore, the ignition timing can be adjusted to an appropriate timing considering the difference in the isooctane ratio. Specifically, the isooctane ratio is one of the typical fuel properties that affect the likelihood of knocking. Therefore, according to the present embodiment in which the ignition timing is corrected according to the isooctane ratio, the larger the isooctane ratio, the more the ignition timing can be set on the advanced side, and the air-fuel mixture can be ignited at an ignition timing with better thermal efficiency as much as possible within the range where knocking does not occur. Moreover, since the isooctane ratio is estimated before the ignition timing, the ignition timing in the same cycle as the cycle in which the estimation is performed can be adjusted in advance to an appropriate timing considering knocking. Thereby, it is possible to suppress the occurrence of knocking while improving the thermal efficiency.

[0091] More specifically, in the present embodiment, as an ion current feature amount correlated with the isooctane ratio, the maximum charge amount qmax, which is the maximum value of the charge amount q (space charge) between the plug electrodes 13 and 14 during the detection period, is calculated. It is estimated that the smaller the calculated maximum charge amount qmax, the larger the isooctane ratio (see FIG. 8). According to such a configuration, the isooctane ratio can be appropriately estimated by utilizing the correlation between the maximum charge amount qmax and the isooctane ratio.

[0092] Further, in the present embodiment, the bias voltage is adjusted so that the voltage gradually increases and then gradually decreases during the application of the bias voltage (see FIG. 6). Thus, when the bias voltage is changed in a mountain shape, the charge amount q between the plug electrodes 13 and 14 can be changed in a similar mountain-shaped tendency. This facilitates the calculation of the above-described maximum charge amount qmax, which is the maximum value of the charge amount q. In addition, since the ion current that increases with the start of the low-temperature oxidation reaction is further amplified by the gradual increase of the bias voltage, the sensitivity of the maximum charge amount qmax that changes depending on the difference in the isooctane ratio can be improved. Thereby, the estimation accuracy of the isooctane ratio can be enhanced.

[0093] In addition, in the present embodiment, a capacitor device 107 (Fig. 3) is connected to the secondary coil 103, and a bias voltage is applied between the plug electrodes 13 and 14 due to the charging of the capacitor device 107. According to such a configuration, the bias voltage can be appropriately controlled by adjusting the charge amount of the capacitor device 107.

[0094] In addition, in the present embodiment, the application start timing of the bias voltage is adjusted so that it advances as the engine load or the engine speed increases. According to such a configuration, the bias voltage can be applied in accordance with the start of the low-temperature oxidation reaction that advances as the engine load or the engine speed increases (see Figs. 11A and 11B), and the ion current that increases with the start of the low-temperature oxidation reaction can be appropriately detected.

[0095] In addition, in the present embodiment, the occurrence of pre-ignition is determined based on the detected ion current, and when the occurrence of pre-ignition is determined, additional fuel is injected. According to such a configuration, since the latent heat of vaporization of the additionally injected fuel decreases the internal temperature of the cylinder 2, the progress of the combustion of the air-fuel mixture can be suppressed, and the influence caused by pre-ignition can be reduced.

[0096] (6) Modification As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0097] For example, in the above embodiment, as the ion current feature quantity correlated with the isooctane ratio, the maximum charge quantity qmax, which is the maximum value of the charge quantity q (space charge) between the plug electrodes 13 and 14, was calculated. However, the ion current feature quantity can be calculated from the ion current detected by the ion current detection unit 44 and may be any value correlated with the isooctane ratio, not limited to the maximum charge quantity qmax. For example, the maximum ion current, which is the maximum value of the ion current detected by the ion current detection unit 44, may be calculated as the ion current feature quantity. Even in this case, the isooctane ratio can be estimated from the calculated maximum ion current. That is, it can be estimated that the smaller the maximum ion current, the larger the isooctane ratio.

[0098] Also, in the above embodiment, the isooctane ratio of the fuel was estimated from the ion current (or ion current feature quantity) detected during a predetermined detection period. However, the object of estimation may be any fuel property related to the ease of knocking occurrence, not limited to the isooctane ratio.

[0099] In the above embodiment, the energization (charge) of the primary coil 102 and the application of the bias voltage between the plug electrodes 13 and 14 were started simultaneously. However, these may be started at different timings. That is, a bias voltage may be applied between the plug electrodes 13 and 14 in accordance with the start of the low-temperature oxidation reaction, and the energization of the primary coil 102 may be started a few minutes earlier or later than the start of the application of the bias voltage.

Explanation of Reference Numerals

[0100] 2 cylinders 11 Ignition plug 15 Injector 41 Ignition control unit 42 Injection control unit 43 Arithmetic unit (abnormal combustion determination unit) 44 Ion current detection unit 101 Ignition coil 102 Primary coil 103 Secondary coil 106 Igniter 107 Capacitor device (bias voltage generation unit) qmax Maximum charge amount

Claims

1. A combustion control device applied to an engine including a cylinder, an injector that injects fuel into the cylinder, and a spark plug that ignites an air-fuel mixture including the fuel injected from the injector, comprising: An ignition coil including a primary coil and a secondary coil; An igniter that induces a high voltage in the secondary coil through energization and de-energization of the primary coil, and causes a discharge to occur between the plug electrodes of the spark plug by the induced high voltage; A bias voltage generation unit that applies a bias voltage for detecting an ion current generated between the plug electrodes due to ions in the cylinder between the plug electrodes; An ion current detection unit that detects the ion current; An ignition control unit that controls the bias voltage generation unit so that the bias voltage is applied between the plug electrodes in accordance with the start of a low-temperature oxidation reaction occurring in the cylinder as the air-fuel mixture is compressed, and controls the igniter so that a discharge occurs between the plug electrodes at an ignition timing set at a time later than the start of the low-temperature oxidation reaction; An arithmetic unit that estimates the properties of the fuel injected from the injector based on the ion current detected by the ion current detection unit during a detection period that is a period from the time when the application of the bias voltage starts to a predetermined time earlier than the ignition timing; The ignition control unit corrects the ignition timing in the same cycle as the cycle in which the properties of the fuel are estimated according to the properties of the fuel, and controls the igniter so that the discharge is performed at the corrected ignition timing, a combustion control device for an engine.

2. In the combustion control device for an engine according to Claim 1, The arithmetic unit estimates the ratio of isooctane contained in the fuel as the properties of the fuel, The ignition control unit corrects the ignition timing to the retard side as the ratio of isooctane is smaller, a combustion control device for an engine.

3. In the combustion control device for an engine according to Claim 2, The arithmetic unit calculates an ion current feature amount correlated with the properties of the fuel based on the ion current detected during the detection period, and estimates the ratio of isooctane from the calculated ion current feature amount, a combustion control device for an engine.

4. In the combustion control device for an engine according to Claim 3, The ion current feature amount is the maximum charge amount that is the maximum value of the charge amount between the plug electrodes during the detection period. The calculation unit estimates that the smaller the maximum charge amount is, the larger the proportion of isooctane is, in an engine combustion control device.

5. In the engine combustion control device according to claim 3, The ion current characteristic amount is the maximum ion current that is the maximum value of the ion current during the detection period, The calculation unit estimates that the smaller the maximum ion current is, the larger the proportion of isooctane is, in an engine combustion control device.

6. In the engine combustion control device according to claim 4 or 5, The ignition control unit controls the bias voltage generation unit so that the bias voltage gradually increases from the start of the low-temperature oxidation reaction and then gradually decreases, in an engine combustion control device.

7. In the engine combustion control device according to any one of claims 1 to 5, The bias voltage generation unit is a capacitor device connected to the secondary coil, in an engine combustion control device.

8. In the engine combustion control device according to any one of claims 1 to 5, The ignition control unit controls the bias voltage generation unit so that the start of application of the bias voltage is advanced as the engine speed increases, in an engine combustion control device.

9. In the engine combustion control device according to any one of claims 1 to 5, The ignition control unit controls the bias voltage generation unit so that the start of application of the bias voltage is advanced as the engine load increases, in an engine combustion control device.

10. In the engine combustion control device according to any one of claims 1 to 5, An abnormal combustion determination unit that determines the occurrence of pre-ignition based on the ion current detected by the ion current detection unit, And an injection control unit that injects additional fuel into the injector when the occurrence of the pre-ignition is determined, further provided in the engine combustion control device.

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