JP2015057544A - Combustion controller for gasoline engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that it is necessary to grasp the current combustion state in a period of ignition in a cylinder in HCCI in detail, especially, that it is necessary to improve a combustion state by speedily reflecting a fuel injection amount, an EGR supply amount, and control in the period of ignition according to a determination result of the combustion state so as to carry on uniform premixed compression ignition since the ignition can be performed only within specific rotating-speed and load ranges in the HCCI.SOLUTION: A combustion controller for gasoline engine includes: generation period calculation means of calculating generation periods of ion currents detected by a plurality of ion current detection means 30 and 32 in combustion of an internal combustion engine 100; an air fuel ratio sensor which calculates the air fuel ratio of an air fuel mixture in a cylinder 50; and cooling control means of cooling the inside of the cylinder 50 when the generation period of the ion current of a first ignition plug 10 that a calculation result of the generation period calculation means indicates is substantially the same as the generation period of the ion current of the other ignition plug 12 and the air fuel ratio in the cylinder 50 is stoichiometrically rich.

Description

The present invention relates to a control device that controls combustion of an internal combustion engine that operates by switching between spark ignition (SI) and uniform premixed compression ignition (HCCI) in a gasoline engine.

Conventionally, in order to realize further improvement in fuel efficiency of gasoline engines, a large amount of EGR (burned gas) is left to increase the temperature in the cylinder, and the air-fuel mixture supplied into the cylinder is compressed to self-ignite. Uniform premixed compression ignition that is combusted by the above method has been proposed. However, in general, uniform premixed compression ignition can be performed only in the range of low rotation and low load of the internal combustion engine, so that the air-fuel mixture supplied into the cylinder is ignited by the discharge from the spark plug and burned. By switching to ignition, combustion is possible under all operating conditions.

In such uniform premixed compression ignition, self-ignition is performed instead of ignition due to discharge from the spark plug as in spark ignition, so that the ignition timing varies for each combustion. Therefore, for example, Japanese Patent Application Laid-Open No. 2004-197593 (hereinafter “Patent Document 1”) is known as a configuration that detects an ionic current at the time of uniform premixed compression ignition and ignites at an optimal time from the detection result.

In Patent Document 1, the engine is configured by connecting a cylinder head and a cylinder block. The cylinder head is formed with an intake port and an exhaust port, and an intake valve and an exhaust valve that move up and down are provided at the boundary between the intake port and the exhaust port and the inside of the cylinder. Further, the cylinder head is provided with an in-cylinder fuel injection valve and a glow plug for injecting fuel directly into the cylinder.

The intake port is provided with an in-intake fuel injection valve that injects fuel during intake air flowing through the intake port. In addition, two ion sensors are installed on the center side and the outer periphery side of the cylinder, and the degree of stratification is directly determined, and ignition control is performed so that ignition can be performed at an appropriate time even if there is manufacturing variation or deterioration of engine components. . Here, the two ion sensors can be easily mounted on the engine by being integrated with the in-cylinder fuel injection valve and the glow plug, respectively.

Further, the ion sensor provided in the fuel injection valve has two electrodes, and a predetermined voltage is applied between the two electrodes after the start of the engine is completed. When the fuel is burned in the cylinder by such voltage application, an ion current flows between the electrodes due to ions generated when the fuel burns. Further, in the ion sensor provided in the glow plug, a predetermined voltage is applied between the heating element and the cylinder head after completion of the engine start. When fuel is burned in the cylinder by applying such a voltage, an ion current flows between the cylinder head and the heating element due to ions generated when the fuel burns. In this case, the heating element of the glow plug functions as an ion current detection electrode.

Here, if the difference between the ignition timings of the two ion sensors is too large, the combustion period becomes too long, leading to deterioration in fuel consumption and exhaust emission. On the other hand, if the difference in ignition timing is too small, combustion noise is generated due to rapid combustion. Therefore, an internal combustion engine that controls the air-fuel ratio distribution in the cylinder so as to obtain an appropriate difference in ignition timing has been proposed.

JP 2004-197593 A

However, the above-described conventional premixed compression ignition internal combustion engine has the following problems. That is, in Patent Document 1, the air-fuel ratio distribution in the cylinder can be changed so that the output difference between the two ion sensors becomes a predetermined difference, and the ignition timing can be made appropriate. In recent years, it has been known that the propagation of flame in ignition during ignition does not necessarily lead to deterioration of the combustion state. For this reason, it is necessary to grasp the current combustion state in detail at the ignition timing in the cylinder at the time of uniform premixed compression ignition. In particular, since uniform premix compression ignition can be performed only within a specific rotational speed and load range, in order to continue uniform premix compression ignition, the fuel injection amount, EGR supply amount, In addition, it is necessary to quickly reflect the control of the ignition timing and improve the combustion state.

The present invention has been made in view of the above problems, and in combustion by uniform premixed compression ignition, combustion of a gasoline engine that identifies the combustion state in detail from the state of flame propagation of ignition and performs combustion control according to the combustion state The aim is to provide a control device.

In order to solve the above problems, the present invention has the following configuration. That is, an internal combustion engine that performs uniform premixed compression ignition that self-ignites an air-fuel mixture by compression, and is disposed in each of the ignition plugs and at least two ignition plugs provided in a cylinder of the internal combustion engine, An ion current detection means for detecting an ion current generated during combustion of the internal combustion engine, and a combustion control device for a gasoline engine comprising: a plurality of ion current detection timings detected by the plurality of ion current detection means during combustion of the internal combustion engine; A generation timing calculation means for calculating, an air-fuel ratio sensor for calculating the air-fuel ratio of the air-fuel mixture in the cylinder, the generation timing of the ionic current of the first spark plug indicated by the calculation result by the generation timing calculation means, and the other When the generation time of the ion current of the spark plug is substantially the same and the air-fuel ratio in the cylinder is rich with respect to stoichiometry, A cooling control means for cooling the serial cylinder, a combustion control device for a gasoline engine, characterized in that it comprises a.

In the above invention, the difference between the generation timing of the ionic current of the first spark plug and the generation timing of the ionic current of the other spark plug indicated by the calculation result by the generation timing calculation means is larger than desired, and the cylinder When the air-fuel ratio in the engine is rich with respect to stoichiometry, assist control means for performing auxiliary ignition into the cylinder may be provided. Further, the generation timing of the ion current of the first spark plug and the generation timing of the ion current of the other spark plug indicated by the calculation result by the generation timing calculation means are substantially the same, and the air-fuel ratio in the cylinder is An EGR increase control means for increasing the EGR amount into the cylinder may be provided when the engine is lean with respect to the stoichiometry. Further, the difference between the generation timing of the ionic current of the first spark plug and the generation timing of the ionic current of the other spark plug indicated by the calculation result by the generation timing calculation means is larger than desired, and the air-fuel ratio in the cylinder When the engine is lean with respect to stoichiometry, air-fuel ratio rich control means for making the air-fuel ratio in the cylinder rich may be provided.

The cooling control means may be configured by lowering the compression ratio in the cylinder, or the cooling control means may be configured by bringing the air-fuel ratio in the cylinder closer to stoichiometry. Also good. Furthermore, the cooling control means may be configured by reducing the amount of EGR into the cylinder, and the cooling control means is configured by reducing the temperature of EGR into the cylinder. It is good also as a structure to be.

The generation time calculation means may be peak time calculation means for calculating the phase of the peak value of the ion current detected by the ion current detection means.

According to the above configuration, the internal combustion engine performs uniform premixed compression ignition that self-ignites the air-fuel mixture by compression, each of at least two spark plugs provided in a cylinder of the internal combustion engine, and each of the spark plugs An ion current detection means for detecting an ion current generated during combustion of the internal combustion engine, and a plurality of ion current detection means detected during combustion of the internal combustion engine. The generation timing calculation means for calculating the generation timing of current, the air-fuel ratio sensor for calculating the air-fuel ratio of the air-fuel mixture in the cylinder, and the ion current of the first spark plug indicated by the calculation result by the generation timing calculation means The generation timing is substantially the same as the generation timing of the ionic current of the other spark plug, and the air-fuel ratio in the cylinder is rich with respect to the stoichiometry. In some cases, by providing a cooling control means for cooling the inside of the cylinder, the state at the time of combustion by uniform premixed compression ignition is identified in detail with respect to combustion in which knocking may have occurred. A combustion control device for a gasoline engine that performs combustion control according to the combustion state can be realized.

The difference between the generation timing of the ionic current of the first spark plug and the generation timing of the ionic current of the other spark plug indicated by the calculation result by the generation timing calculation means is larger than desired, and the air-fuel ratio in the cylinder When the engine is rich with respect to stoichiometry, an assist control means for performing auxiliary ignition in the cylinder is provided, so that an unstable state in which combustion by uniform premixed compression ignition is difficult to be partially ignited (one of internal combustion engines). It is possible to identify in detail that the part is in an unstable state that is easy to ignite at high temperature, and to improve the stability of ignition. Further, although a part of the internal combustion engine is difficult to ignite, since the air-fuel ratio is rich, the combustion state deteriorates even if control is performed to improve the combustion state by further increasing the fuel injection amount. Therefore, such control can be prevented.

Further, the generation timing of the ion current of the first spark plug and the generation timing of the ion current of the other spark plug indicated by the calculation result by the generation timing calculation means are substantially the same, and the air-fuel ratio in the cylinder is By providing an EGR increase control means for increasing the EGR amount into the cylinder when lean with respect to stoichiometry, knocking is caused even if combustion by uniform premixed compression ignition is normally performed in the present situation It is possible to determine the unstable combustion state that may be possible and improve the stability of ignition. Furthermore, since the internal combustion engine is in an unstable combustion state that may cause knocking at a high temperature, control is performed to improve the combustion state by increasing the fuel injection amount that makes the supply into the cylinder uniform. However, since the combustion state deteriorates, such control can be prevented.

The difference between the generation timing of the ionic current of the first spark plug and the generation timing of the ionic current of the other spark plug indicated by the calculation result by the generation timing calculation means is larger than desired, and the air-fuel ratio in the cylinder Is provided with air-fuel ratio rich control means that makes the air-fuel ratio in the cylinder rich when the engine is lean with respect to stoichiometry, so that even if combustion by uniform premixed compression ignition is normally performed, To identify in detail that the combustion by premixed compression ignition is difficult to ignite partly (an unstable state in which part of the internal combustion engine is ignited easily at high temperature) and improve the stability of ignition Can do. Furthermore, since a part of the internal combustion engine is difficult to ignite, even if control is performed to improve the combustion state by increasing the amount of EGR that causes non-uniform supply to the cylinder, the combustion state deteriorates. Such control can be prevented.

1 is a diagram showing an outline of a gasoline engine according to a first embodiment of the present invention. The ion current output signal waveform and A / F sensor output characteristic when there is no difference in the ion current detection timing and A / F rich in Example 1 are shown. The ion current output signal waveform and A / F sensor output characteristic when there is a difference in the ion current detection timing and A / F rich in Example 1 are shown. The ion current output signal waveform at the time of A / F lean and the A / F sensor output characteristic are shown in FIG. The ion current output signal waveform and the A / F sensor output characteristic at the time of A / F lean are shown in FIG. 2 is a flowchart showing the operation of the combustion control apparatus for a gasoline engine according to the first embodiment.

Hereinafter, an example showing the embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a diagram showing an outline of a gasoline engine according to a first embodiment of the present invention. FIG. 1 shows an ion current output signal waveform and an A / F sensor output characteristic when there is no difference in ion current detection timing and when A / F is rich. 2 shows the ion current output signal waveform and A / F sensor output characteristics when there is a difference in the ion current detection time and when the A / F is rich, and FIG. 3 shows the ion current when there is no difference in the ion current detection time and when the A / F is lean. Fig. 4 shows the output signal waveform and A / F sensor output characteristics. Fig. 5 shows the ion current output signal waveform and A / F sensor output characteristics when there is a difference in the ionic current detection timing and when the A / F is lean. The flowchart which shows operation | movement of a control apparatus is shown in FIG. 6, respectively.

FIG. 1 shows a cross section of a gasoline engine (hereinafter referred to as “internal combustion engine”) 100. The internal combustion engine 100 includes an engine head and an engine block, and the engine head and the engine block are fixed by a plurality of head bolts. . The engine block is opened by a substantially cylindrical cylinder 50 penetrating in the vertical direction, the upper end of the opening is covered with the engine head, and a recess is formed from the lower end of the opening. Further, the cylinder 50 is sealed with a piston 52 fitted in the recess, and the piston 52 is defined as a bottom surface and the engine head is defined as an upper surface.

Further, the compression ratio of the cylinder 50 is preferably set in the range of 11 to 13 so as to be optimal for compressing and pre-igniting the premixed gas in the cylinder 50. Furthermore, the upper end of the cylinder 50 is shaped like a roof by two inclined surfaces, and the two inclined surfaces gradually move from the center of the upper end of the cylinder 50 toward the left and right sides. It extends to approach the mating surface with the inner wall.

An intake port 60 is connected to the inclined surface at the upper end of the cylinder 50 shown on the right side of the drawing, and an exhaust port 70 is connected to the inclined surface at the upper end of the cylinder 50 shown on the left side of the drawing. Further, the internal combustion engine 100 is a four-valve type in which two intake and exhaust ports 60 and 70 are provided for one cylinder 50, and the intake and exhaust ports 60 and 70 and the cylinder are connected to each other. In the connection portion of 50, intake and exhaust valves 62 and 72 are provided.

The intake and exhaust valves 62 and 72 are each provided with a coil spring, and the coil spring is pressed in the direction in which the intake and exhaust valves 62 and 72 are closed. The intake and exhaust valves 62 and 72 are pushed down in the opening direction by the intake and exhaust cams 64 and 74 rotating in conjunction with each other. Further, the intake and exhaust cams 64 and 74 are rotated in synchronization with the intake and exhaust camshafts 66 and 76, respectively, so that the intake and exhaust valves 62 and 72 are opened and closed at predetermined timings, respectively.

Each of the intake and exhaust camshafts 66 and 76 is provided with a variable valve timing mechanism that continuously changes the rotational phase with respect to the crankshaft 56 that rotates the piston 52 in a predetermined angular range. The opening and closing timings of the intake and exhaust valves 62 and 72 are independently changed by the variable valve timing mechanism. Furthermore, although the variable valve timing mechanism is of the hydraulic continuous phase change system, an electromagnetic operation type of continuous phase change system may be used.

Further, by operating the variable valve timing mechanisms of the intake and exhaust camshafts 66 and 76 to the retard side and the advance side, respectively, the overlap of the intake and exhaust valves 62 and 72 can be eliminated. Thus, a large amount of EGR (burned gas) can be retained in the cylinder 50. Furthermore, if the period from when the exhaust valve 72 is closed to when the intake valve 62 is opened becomes short, the amount of EGR gas decreases, and the period from when the exhaust valve 72 is closed to when the intake valve 62 is opened is long. If so, the amount of internal EGR gas increases accordingly.

A first spark plug 10 is provided at the upper end of the cylinder 50 so as to be surrounded by the four intake and exhaust valves 62 and 72. The first spark plug 10 is provided in the cylinder 50. Spark ignition (hereinafter referred to as “SI”) is performed in which the air-fuel mixture supplied to is ignited and burned at a predetermined timing at the end of the compression stroke. Furthermore, a first ignition coil 20 incorporating an igniter is connected to the first spark plug 10.

A second spark plug 12 is provided on the intake side of the cylinder 50 so as to be sandwiched between the two intake valves 62, and the second spark plug 12 is supplied into the cylinder 50. Ignition for assisting self-ignition under predetermined conditions when performing uniform premixed compression ignition (hereinafter referred to as "HCCI") in which the air-fuel mixture is compressed by raising the piston 52 and combusted by self-ignition. Is to do. Further, a second ignition coil 22 incorporating an igniter is connected to the second spark plug 12 in the same manner as the first spark plug 10.

The first and second ignition coils 20 and 22 boost the power supply voltage from the vehicle battery by a transformer composed of a primary coil, a secondary coil, and an iron core. The second spark plugs 10 and 12 are supplied. Further, the second ignition coil 22 is preferably an ignition coil having an output voltage equivalent to that of the first ignition coil 20, but the number of turns of the primary and secondary coils is reduced. For example, an ignition coil in which the voltage generated by the back electromotive force is smaller than that of the first ignition coil 20 may be used.

The first and second ignition coils 20 and 22 have first and second ion currents for detecting ion currents flowing between the electrodes of the first and second spark plugs 10 and 12, respectively. Detection devices 30 and 32 are connected. Further, the first and second ion current detection devices 30 and 32 are composed of a capacitor that acts as a bias power source and an operational amplifier that converts an ion current flowing between the electrodes into an output signal. The ion current detected through the secondary coils of the ignition coils 20 and 22 is converted into an output signal and input to the ECU 40 that performs electrical control of the internal combustion engine 100.

Further, the internal combustion engine 100 is provided with an injector 44 that injects gasoline into the intake port 60. Further, information from a pressure sensor for detecting the pressure in the cylinder 50 and an A / F sensor (described later) for calculating the air-fuel ratio of the air-fuel mixture in the cylinder 50 is input to the intake port 60. The control of the opening / closing of the electric throttle valve provided and the opening / closing time of the injector 44 are adjusted to control the fuel injection amount, thereby controlling the air-fuel ratio of the air-fuel mixture in the cylinder 50.

The ECU 40 controls the overlap period of the intake and exhaust valves 62 and 72 by changing the opening and closing timing of the intake and exhaust valves 62 and 72 by hydraulic control of the variable valve timing mechanism. Further, the ECU 40 switches the ignition signal for changing the ignition timing for the air-fuel mixture by the operation control of the igniter provided in the first and second spark plugs 10 and 12.

Further, the ECU 40 is in a lean state in which the air-fuel ratio (A / F) of the premixed gas in the cylinder 50 is 15 to 30 when the internal combustion engine 100 is in the HCCI operation region of FIG. In addition, the amount of fuel injected by the injector and the opening / closing of the throttle valve are controlled, and self-ignition is performed without ignition by discharge from the first spark plug 10. Further, the ECU 40 tries to increase the temperature in the cylinder 50 by eliminating the overlap of the intake and exhaust valves 62 and 72 and making the amount of EGR gas extremely large during self-ignition, It is possible to improve the stability of self-ignition by compression of the premixed gas.

Further, in the HCCI in the internal combustion engine 100, the temperature in the cylinder 50 is increased by a high compression ratio in the cylinder 50 and a large amount of EGR (burned gas). Further, when the combustion stroke of the internal combustion engine 100 is completed, an A / F sensor 42 is provided that calculates an air-fuel ratio from oxygen ions contained in the exhaust gas passing through the exhaust port 70 and transmits it to the ECU 40. The A / F sensor 42 is attached at a position near the cylinder 50 of the exhaust port 70.

The A / F sensor 42 is composed of a zirconia tube. When the oxygen concentration inside and outside the zirconia tube is large, oxygen ions on the atmosphere side move outward through the zirconia tube. Using this principle, during lean, a large amount of oxygen ions in the exhaust gas moves from the exhaust gas side to the atmosphere side, so that the current increases and the resistance increases the voltage. On the other hand, at the rich time, oxygen ions in the atmosphere forcibly move to the exhaust gas side, and thus the current voltage decreases. Furthermore, at the stoichiometric air fuel ratio (stoichiometry), no current flows because there is no oxygen. Furthermore, the stoichiometry during combustion by HCCI is about 22.

2 (a) and 2 (b) show that in the combustion by the HCCI of the internal combustion engine 100, combustion in the vicinity of the first and second spark plugs 10 and 12 is started substantially simultaneously, and the first and second The output signal waveform when the generation time of the ion current generated between the electrodes of the spark plugs 10 and 12 is t ₁ = t ₂ is shown. FIG. 2C shows the A / F sensor output characteristic indicating the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 100, and represents the rich air-fuel ratio in the shaded area in the figure. ing. Thus, when the ion current detection timings of the first and second spark plugs 10 and 12 are substantially the same and the A / F sensor output characteristic is rich, the cylinder is in a state where fuel injection is large. It is determined that the inside of the engine 50 has become hot and knocking has occurred in the internal combustion engine 100 (a state in which knocking is likely to occur). Further, when the ECU 40 determines that knocking has occurred in the internal combustion engine 100, the ECU 40 executes cooling control means.

Further, the cooling control means controls to lower the compression ratio in the cylinder 50, controls to reduce the amount of gasoline injected from the injector, and brings the air-fuel ratio in the cylinder 50 closer to the stoichiometric, EGR amount into the cylinder 50 And control for lowering the temperature of the EGR supplied into the cylinder 50, and is performed according to the knocking strength. Further, the knocking intensity is identified by the advance angle of the peak value position of the output signal waveform shown in FIGS. 2 (a) and 2 (b). That is, knocking becomes stronger when the peak position of the output signal waveform advances in the arrow advance direction in the figure, and knocking becomes weaker when it returns in the arrow retard direction.

The cooling control means closes the intake valve 62 after the bottom dead center by using the variable valve timing mechanism when the piston 52 moves from bottom dead center to top dead center. Control to lower the compression ratio. Further, the cooling control means includes a cooling mechanism using a heat exchanger such as a radiator in the external EGR that recirculates the exhaust gas by relaying and connecting the intake port 60 and the exhaust port 70, and the flow of engine cooling water. By controlling this, the temperature of the EGR supplied into the cylinder 50 is controlled to be lowered.

In addition, it is known that flame propagation occurs in ignition by HCCI, and when the generation time of ion current generated between the electrodes of the first and second spark plugs 10 and 12 is t ₁ = t ₂ Shows that the inside of the cylinder 50 is in a high temperature state that is very flammable. In addition, if the peak position of the output signal waveform advances in the arrow advance direction in the figure, the temperature in the cylinder 50 becomes higher and the internal combustion engine 100 is likely to be knocked. Furthermore, when the ion current detection timings of the first and second spark plugs 10 and 12 are substantially the same, the rotation angle of the crankshaft 56 of the internal combustion engine 100 is within 0.5 °. In the meantime, ion currents of the first and second spark plugs 10 and 12 are detected, and a crank angle sensor or the like is attached to the crankshaft 56 to detect the rotation angle of the crankshaft 56.

3 (a) and 3 (b) show that in the combustion by the HCCI of the internal combustion engine 100, combustion in the vicinity of the first and second spark plugs 10 and 12 is started with a desired difference. The output signal waveform when the generation time of the ionic current generated between the electrodes of the first and second spark plugs 10 and 12 has a desired interval P and t ₁ <t ₂ is shown. FIG. 3C shows an A / F sensor output characteristic indicating the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 100, and represents the rich air-fuel ratio in the shaded area in the figure. ing. As described above, when the ion current detection timing of the first and second spark plugs 10 and 12 has a difference in the desired interval P and the A / F sensor output characteristic is rich, It is determined that an unstable state in which a part of the cylinder 50 is difficult to ignite (an unstable state in which a part of the cylinder 50 is easily ignited at a high temperature). Further, when the ECU 40 determines that an unstable state in which part of the cylinder 50 is difficult to ignite, the ECU 40 executes assist control means.

The assist control means is a control that performs auxiliary ignition at an optimal ignition timing for combustion by HCCI from the second ignition coil 22 connected to the second spark plug 12. Further, since the air-fuel ratio is calculated to be rich by the A / F sensor 42, a part of the cylinder 50 is in an unstable state in which it is difficult to ignite, but an increase in the combustion injection amount beyond this is Not performed.

Accordingly, although not shown, the generation timing of the ionic current generated between the electrodes of the first and second spark plugs 10 and 12 is t ₁ > t ₂ with a desired interval, and the A / F sensor output characteristics. Is determined to be an unstable state in which a part of the cylinder 50 is not easily ignited (an unstable state in which a part of the cylinder 50 is easily ignited at a high temperature), and the assist control is performed. Executing the means is the same as described above. Further, the desired interval P, which is the difference between the ionic current detection timings of the first and second spark plugs 10 and 12, is that the rotation angle of the crankshaft 56 of the internal combustion engine 100 is 1.5 ° or more. In the meantime, the interval is generated by detecting the ion currents of the first and second spark plugs 10 and 12.

4 (a) and 4 (b) show that in the combustion by the HCCI of the internal combustion engine 100, combustion in the vicinity of the first and second spark plugs 10 and 12 is started substantially simultaneously, and the first and second The output signal waveform when the generation time of the ion current generated between the electrodes of the spark plugs 10 and 12 is t ₁ = t ₂ is shown. FIG. 4C shows an A / F sensor output characteristic indicating the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 100, and represents the lean air-fuel ratio in the shaded area in the figure. Yes. As described above, when the ion current detection timings of the first and second spark plugs 10 and 12 are substantially the same and the A / F sensor output characteristics indicate lean, the combustion by HCCI is normally performed in the present situation. It is determined that the combustion state is unstable but may cause knocking. Further, when it is determined that the internal combustion engine 100 is in an unstable combustion state that may cause knocking, the ECU 40 executes EGR increase control means.

The EGR increase control means is a control for shortening the overlap period by the variable valve timing mechanism. As the overlap period becomes shorter, the EGR amount is increased, and the EGR amount is increased according to an unstable combustion state. adjust. Furthermore, the high possibility of causing knocking is identified based on the advance angle of the output signal waveform shown in FIGS. 4 (a) and 4 (b). That is, if the peak position of the output signal waveform advances in the arrow advance direction in the figure, the possibility of knocking increases, and if it returns to the arrow delay direction, the possibility of knocking decreases.

When the ion current detection timings of the first and second spark plugs 10 and 12 are substantially the same, the rotation angle of the crankshaft 56 of the internal combustion engine 100 is within 0.5 °. It is the same as in FIG. 2 that the ionic currents of the first and second spark plugs 10 and 12 are detected in the meantime.

5 (a) and 5 (b) show that in the combustion by the HCCI of the internal combustion engine 100, combustion in the vicinity of the first and second spark plugs 10 and 12 is started with a desired difference, and the first The output signal waveform when the generation time of the ionic current generated between the electrodes of the first and second spark plugs 10 and 12 has a desired interval P and t ₁ <t ₂ is shown. FIG. 5C shows the A / F sensor output characteristic indicating the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 100, and represents the lean air-fuel ratio in the shaded area in the figure. ing. As described above, when the ion current detection timing of the first and second spark plugs 10 and 12 has a desired interval P difference, and the A / F sensor output characteristics indicate lean, In HCCI, combustion by HCCI is normally performed, but combustion by homogeneous premixed compression ignition is difficult to ignite partly (an unstable state in which part of the internal combustion engine is easily ignited at high temperature) may occur. Judge that there is sex. Further, when the ECU 40 determines that there is a possibility that a part of the cylinder 50 is in an unstable state where it is difficult to ignite, the ECU 40 executes air-fuel ratio rich control means for stabilizing combustion.

The air-fuel ratio rich control means is a control for increasing the amount of gasoline injected from the injector 42 to bring the air-fuel ratio in the cylinder 50 closer to rich. Further, since the degree of ignition in the cylinder 50 can be determined from the difference in the ion current detection timing (desired interval Q) between the first and second spark plugs 10 and 12, the first level of the ignition plug 10 and 12 can be determined. The amount of gasoline injected from the injector 42 is adjusted according to the difference (desired interval Q) in the ion current detection timing of the second spark plugs 10 and 12. That is, the ignition in the cylinder 50 becomes more unstable as the difference (desired interval Q) between the ion current detection timings of the first and second spark plugs 10, 12 increases.

Therefore, although not shown, when the generation timing of the ionic current generated between the electrodes of the first and second spark plugs 10 and 12 has a desired interval and t ₁ > t ₂ , the ECU 40 is currently in the HCCI state. However, there is a possibility that a part of the combustion of the internal combustion engine 100 is not easily ignited (an unstable state in which part of the internal combustion engine is easily ignited at a high temperature). And executing the air-fuel ratio rich control means is the same as described above.

The desired interval Q, which is the difference between the ionic current detection timings of the first and second spark plugs 10 and 12, is the rotation of the crankshaft 56 of the internal combustion engine 100 with a rotation angle of 1.5 ° or more. The interval generated by detecting the ionic currents of the first and second spark plugs 10 and 12 in the meantime is that of the first and second spark plugs 10 and 12 described in FIG. It is the same as the desired interval P as the difference in the ion current detection timing.

In the operation of the combustion control apparatus for the internal combustion engine 100 shown in FIG. 6, the ECU 40 determines whether the combustion of the internal combustion engine 100 is due to HCCI or SI (S1), and the combustion of the internal combustion engine 100 is determined at S1. Is determined to be due to HCCI, the A / F sensor 42 calculates the air-fuel ratio from the exhaust gas resulting from combustion of the internal combustion engine 100 (S2), and the first and second ion current detection devices 30 are calculated. , 32 detect an output signal from an ionic current generated between the electrodes of the first and second spark plugs 10, 12, and supply the detected output signal to the ECU 40 (S3). Further, the ECU 40 determines whether the combustion of the internal combustion engine 100 is performed with a rich air-fuel ratio from the calculation result of S2 (S4), and the combustion of the internal combustion engine 100 is performed with a rich air-fuel ratio in S4. In this case, the ECU 40 determines whether or not the detection timings in the first and second ion current detectors 30 and 32 are substantially the same in the output signal of the ion current detected in S3 (S5). Further, when it is determined in S5 that the detection timings of the output signals of the ion currents in the first and second ion current detectors 30 and 32 are substantially the same, the ECU 40 causes knocking in the internal combustion engine 100. It is determined that knocking is likely to occur, and the cooling control means is executed (S6).

If it is determined in S5 that there is a difference in the detection timing of the output signal of the ion current in the first and second ion current detection devices 30, 32, the ECU 40 is difficult to ignite a part of the cylinder 50. It is determined that the state is unstable (an unstable state in which a part of the cylinder 50 is easily ignited at a high temperature), and the assist control is executed (S11).

In addition, when the vibration caused by knocking is not superimposed other than the vibration due to the combustion of the internal combustion engine 100 in S4, the ECU 40 determines the first and second ion currents in the output signal of the ion current detected in S3. It is determined whether the detection times in the detection devices 30 and 32 are substantially the same (S21). Further, if it is determined in S21 that the detection timings of the output signals of the ion currents in the first and second ion current detectors 30 and 32 are substantially the same, the ECU 40 normally performs combustion by the HCCI. However, it is determined that the internal combustion engine 100 is in an unstable combustion state that may cause knocking, and the EGR increase control means is executed (S22).

If it is determined in S21 that there is a difference between the detection timings of the output signals of the ion currents in the first and second ion current detectors 30 and 32, the ECU 40 normally performs combustion by HCCI. However, it is determined that there is a possibility that a part of the cylinder 50 is in an unstable state in which ignition is difficult, and the air-fuel ratio rich control means is executed (S31).

With the above configuration, when the ion current detection timings of the first and second spark plugs 10 and 12 are substantially the same and the A / F sensor output characteristic is rich, the cylinder is in a state where fuel injection is large. There is a possibility that knocking has occurred by determining that the internal combustion engine 100 has become hot and knocking has occurred in the internal combustion engine 100 (a state in which knocking is likely to occur) and the cooling control means is executed. It is possible to realize a combustion control device for a gasoline engine that recognizes in detail the state at the time of combustion by uniform premixed compression ignition for a certain combustion and performs combustion control according to the combustion state.

Further, when the ion current detection timing of the first and second spark plugs 10 and 12 has a desired interval P difference and the A / F sensor output characteristic is rich, the cylinder 50 Is determined to be in an unstable state in which it is difficult to ignite partly (an unstable state in which part of the cylinder 50 is easily ignited at high temperature), and the assist control means is executed to perform uniform premixed compression ignition It is possible to identify in detail that the combustion caused by the above is an unstable state in which it is difficult to ignite (an unstable state in which a part of the internal combustion engine is easily ignited at a high temperature), and the stability of ignition can be improved. Further, although a part of the internal combustion engine is difficult to ignite, since the air-fuel ratio is rich, the combustion state deteriorates even if control is performed to improve the combustion state by further increasing the fuel injection amount. Therefore, it is possible to prevent such control from being performed.

Further, when the ion current detection timings of the first and second spark plugs 10 and 12 are substantially the same, and the A / F sensor output characteristic shows lean, combustion by HCCI is normally performed in the present situation. However, it is determined that the combustion state is unstable and may cause knocking, and by executing the EGR increase control means, even if combustion by uniform premixed compression ignition is normally performed in the present situation It is possible to determine an unstable combustion state that may cause knocking and improve the stability of ignition. Further, even if an unstable combustion state that may cause knocking at a high temperature in the internal combustion engine is controlled to increase the fuel injection amount that makes the supply into the cylinder uniform, the combustion state is improved. Since the combustion state deteriorates, it is possible to prevent such control from being performed.

Further, when the ion current detection timing of the first and second spark plugs 10 and 12 has a desired interval P difference and the A / F sensor output characteristic indicates lean, HCCI is presently present. Although combustion by normal combustion is normally performed, there is a possibility that the combustion by uniform premixed compression ignition is difficult to ignite partly (an unstable state in which part of the internal combustion engine is easily ignited at high temperature). The air-fuel ratio rich control means is executed, and in the present state, even if the combustion by the uniform premixed compression ignition is normally performed, the combustion by the uniform premixed compression ignition is difficult to be partially ignited. It is possible to identify in detail that it is an unstable state in which a part of the internal combustion engine is easily ignited at a high temperature, and to improve the stability of ignition. Furthermore, although a part of the internal combustion engine is difficult to ignite, even if control is performed to improve the combustion state by increasing the amount of EGR that causes non-uniform supply to the cylinder, the combustion state deteriorates. Thus, it is possible to prevent such control from being performed.

As a modification of the first embodiment, the number of spark plugs provided in the cylinder 50 is increased with respect to the first and second spark plugs 10 and 12, and ion current is detected from three or more spark plugs. You may determine the combustion state at the time of HCCI. In addition, the second spark plug 12 is arranged so as to be sandwiched between the two intake valves 62, but the present invention is not limited to this, and it is arranged so as to be sandwiched between the intake and exhaust valves 62 and 72. You may arrange arbitrarily according to it. Further, as a method of calculating the air-fuel ratio of the internal combustion engine 100, the air-fuel ratio may be calculated from the amount of oxygen in the exhaust port 70 using an O ₂ sensor provided in the exhaust port 70.

Moreover, it is good also as a structure provided with a battery power supply instead of a capacitor | condenser as a bias power supply required for the said 1st and 2nd ion current detection apparatuses 30 and 32 at the time of HCCI. Furthermore, the assist control means may perform control to perform auxiliary ignition at an optimal ignition timing for combustion by HCCI from the first ignition coil 20 connected to the first spark plug 10.

In addition, the air-fuel ratio that is stoichiometric during combustion by HCCI of the internal combustion engine 100 can be appropriately changed according to the design specifications of the internal combustion engine 100 and the like. Further, the ECU 40 compares the ion current detection timings of the first and second spark plugs 10 and 12 from the generation timing of the ion current output signal. The ion current output signals of the first and second spark plugs 10 and 12 may be compared.

When the ion current detection timings of the first and second spark plugs 10 and 12 are substantially the same, the rotation angle of the crankshaft 56 of the internal combustion engine 100 is within 0.5 °. While the ionic currents of the first and second spark plugs 10 and 12 are detected in the meantime, the rotation angle may be changed depending on the specifications of the internal combustion engine 100, and the first and second It may be configured to determine whether or not the time difference at which the ion current detection timings of the two spark plugs 10 and 12 are substantially the same is substantially the same from a map created according to the rotational speed of the internal combustion engine 100. Further, the desired interval P and the desired interval Q, which are the differences between the ion current detection timings of the first and second spark plugs 10 and 12, are set so that the rotation angle of the crankshaft 56 of the internal combustion engine 100 is 1.5. It is assumed that the interval generated by detecting the ion currents of the first and second spark plugs 10 and 12 during the rotation of more than 0 ° is assumed, but the rotation angle is changed depending on the specifications of the internal combustion engine 100 It is also possible to determine whether a desired time difference between the ion current detection timings of the first and second spark plugs 10 and 12 has a desired time difference from a map created according to the rotational speed of the internal combustion engine 100. It is good also as composition to do.

10: First spark plug
12: Second spark plug
20: First ignition coil
22: Second ignition coil
30: 1st ion current detection apparatus (1st ion current detection means)
32: Second ion current detector (second ion current detector)
40: ECU (ignition timing calculation means, combustion state determination means)
42: Air-fuel ratio sensor (A / F sensor)
44: Injector
50: Cylinder
52: Piston
54: Crank
56: Crankshaft
60: Intake port
62: Intake valve
64: Intake cam
66: Intake camshaft
70: Exhaust port
72: Exhaust valve
74: Exhaust cam
76: Exhaust camshaft
100: Gasoline engine (internal combustion engine)

Claims (9)

An internal combustion engine that performs uniform premixed compression ignition that self-ignites a mixture by compression,
At least two spark plugs provided in a cylinder of the internal combustion engine;
In a gasoline engine combustion control apparatus, comprising: an ionic current detection means that is disposed in each of the spark plugs and detects an ionic current generated during combustion of the internal combustion engine;
A generation timing calculation means for calculating a generation timing of ion currents detected by the plurality of ion current detection means during combustion of the internal combustion engine;
An air-fuel ratio sensor for calculating an air-fuel ratio of the air-fuel mixture in the cylinder;
The generation timing of the ion current of the first spark plug and the generation timing of the ion current of the other spark plug indicated by the calculation result by the generation timing calculation means are substantially the same, and the air-fuel ratio in the cylinder is stoichiometric. A combustion control device for a gasoline engine, comprising: a cooling control means for cooling the inside of the cylinder when it is rich. The difference between the generation timing of the ion current of the first spark plug and the generation timing of the ion current of the other spark plug indicated by the calculation result by the generation timing calculation means is larger than desired, and the air-fuel ratio in the cylinder is stoichiometric. The gasoline engine combustion control apparatus according to claim 1, further comprising: assist control means for performing auxiliary ignition in the cylinder when the engine is rich. The generation timing of the ion current of the first spark plug and the generation timing of the ion current of the other spark plug indicated by the calculation result by the generation timing calculation means are substantially the same, and the air-fuel ratio in the cylinder is stoichiometric. The gasoline engine combustion control device according to claim 1 or 2, further comprising an EGR increase control means for increasing an EGR amount into the cylinder when the engine is lean. The difference between the generation timing of the ion current of the first spark plug and the generation timing of the ion current of the other spark plug indicated by the calculation result by the generation timing calculation means is larger than desired, and the air-fuel ratio in the cylinder is stoichiometric. The gasoline engine combustion control device according to any one of claims 1 to 3, further comprising air-fuel ratio rich control means for making the air-fuel ratio in the cylinder rich when the engine is lean. . The gasoline engine combustion control apparatus according to claim 1, wherein the cooling control means is formed by lowering a compression ratio in the cylinder. The gasoline engine combustion control apparatus according to claim 1, wherein the cooling control unit is configured to bring the air-fuel ratio in the cylinder closer to stoichiometry. The gasoline engine combustion control apparatus according to claim 1, wherein the cooling control unit is configured to reduce an EGR amount into the cylinder. 2. The combustion control apparatus for a gasoline engine according to claim 1, wherein the cooling control means is formed by lowering the temperature of EGR into the cylinder. The gasoline according to any one of claims 1 to 8, wherein the generation time calculation means is peak time calculation means for calculating a phase of a peak value of an ion current detected by the ion current detection means. Engine combustion control device.

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