JP2020090893A - Engine controller - Google Patents

Abstract

To reliably suppress occurrence of preignition with a catalyst activated early.SOLUTION: An engine having variable valve mechanisms 13 and 14 that changes at least one of the valve closing timing of an exhaust valve 12 and the valve opening timing of an intake valve 11, comprises a combustion control unit 102 that performs catalyst warm-up promotion control for early activating a catalyst device 41a provided in an exhaust passage 40, and a preignition determination unit 101 that predicts and detects preignition. When preignition occurs (when it is predicted to occur), the variable valve mechanisms 13 and 14 are driven in a direction in which an amount of burnt gas remaining in a cylinder 2 is reduced.SELECTED DRAWING: Figure 6

Description

The present invention relates to a device that controls an engine that includes a variable valve mechanism that changes the valve timing of at least one of an intake valve and an exhaust valve.

Some engines are provided with a catalyst device for purifying the exhaust gas discharged from the cylinders in the exhaust passage. In such an engine, when the temperature of the catalyst device is low, an operation is performed to quickly raise the temperature of the catalyst device to an activation temperature, that is, a temperature at which exhaust gas can be purified.

For example, in Patent Document 1, when the temperature of the catalyst device is lower than a predetermined temperature, a relatively large amount of fuel is supplied into the cylinder, and the air-fuel ratio in the cylinder is generated as the stoichiometric air-fuel ratio in the cylinder. In addition to increasing combustion energy, the ignition timing for igniting the mixture of fuel and air is set to a timing retarded from the normal timing so that the high combustion energy generated in the cylinders is efficiently supplied to the exhaust passage. An engine adapted to do so is disclosed.

JP, 2014-196696, A

Here, increasing the compression ratio of the cylinder is one of the configurations for improving the fuel efficiency. Then, it is conceivable to provide the catalyst device in an engine with a high compression ratio of the cylinders and apply the control of the above-mentioned Patent Document 1. However, in an engine with a high compression ratio, if the control of Patent Document 1 is simply applied to introduce a large amount of air and fuel into the cylinder and the air-fuel ratio thereof is close to the theoretical air-fuel ratio, ignition from the ignition device is performed. Pre-ignition may occur in which the air-fuel mixture starts to burn before the ignition.

On the other hand, for example, it is conceivable to set the ignition timing, the amount of air introduced into the cylinder, and the like in advance to a timing and amount at which pre-ignition does not occur. However, the susceptibility to premature ignition, that is, the ignitability of fuel varies depending on the type of fuel. For example, in gasoline, a type having a lower octane has higher ignitability, and premature ignition is more likely to occur. Therefore, when a fuel that is significantly different from the fuel type when the set value is determined is unexpectedly supplied to the engine, it may not be possible to sufficiently avoid premature ignition.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control device for an engine that can more reliably suppress the occurrence of premature ignition while activating the catalyst early.

As a means for solving the above problems, the present invention provides a cylinder, an air-fuel ratio changing device that can change the air-fuel ratio of an air-fuel mixture in the cylinder, an ignition device that ignites the air-fuel mixture in the cylinder, and an intake air to the cylinder. The intake valve for opening and closing the intake port for introducing the exhaust gas, the exhaust valve for opening and closing the exhaust port for exhausting the exhaust gas from the cylinder, and at least one of the exhaust valve closing timing and the intake valve opening timing. A device for controlling an engine, comprising a variable valve mechanism, an exhaust passage through which exhaust gas discharged from a cylinder through an exhaust port circulates, and a catalyst device provided in the exhaust passage for purifying the exhaust gas. A pre-ignition determination unit that predicts whether pre-ignition occurs in which the air-fuel mixture is ignited before ignition by the ignition device, or detects whether pre-ignition occurs, and the catalyst device. When the temperature is less than the preset reference temperature, the air-fuel ratio in the cylinder becomes near the stoichiometric air-fuel ratio or becomes smaller than the stoichiometric air-fuel ratio, and the temperature of the catalyst device is more retarded than when the temperature is above the reference temperature. At this time, ignition of the air-fuel mixture in the cylinder is performed, and catalyst warm-up promotion that controls the air-fuel ratio changing device, the ignition device, and the variable valve mechanism is performed so that burned gas remains in the cylinder. A combustion control unit for performing control, wherein the combustion control unit is predicted to cause premature ignition by the premature ignition determination unit during execution of the catalyst warm-up promotion control, or premature ignition occurs. When it is detected that it has occurred, the variable valve mechanism is driven in a direction in which the amount of burnt gas remaining in the cylinder is reduced (claim 1).

According to the present invention, when the temperature of the catalyst device is lower than the reference temperature, the catalyst warm-up promotion control is executed to make the air-fuel ratio in the cylinder close to or less than the stoichiometric air-fuel ratio, and the ignition timing. Is considered to be on the retard side of the normal time. Therefore, high combustion energy can be generated in the cylinder, and this energy can be efficiently supplied to the catalyst device, so that the catalyst device can be activated early. Further, since the high-temperature burned gas is configured to remain in the cylinder, the temperature inside the cylinder is increased to promote vaporization and atomization of the fuel supplied into the cylinder, and the fuel is appropriately The catalyst can be burned, high combustion energy can be reliably supplied to the catalyst device, and the discharge of unburned fuel can be suppressed.

Moreover, the present invention is provided with the premature ignition determination unit that predicts that premature ignition occurs or detects that premature ignition occurs. Then, when the premature ignition determination unit predicts that premature ignition occurs or when premature ignition is detected, the amount of burnt gas remaining in the cylinder, that is, the amount of internal EGR gas is The variable valve mechanism is controlled so as to decrease the number. Therefore, even when the type of fuel unexpectedly changes to a highly combustible one, it is possible to predict or detect the occurrence of premature ignition, and when this is predicted or detected, the amount of high-temperature internal EGR gas is reduced. As a result, the temperature in the cylinder can be reduced and premature ignition can be suppressed.

In the above configuration, preferably, the variable valve mechanism is an electric variable mechanism that changes an opening/closing phase of the valve by driving an electric motor (claim 2).

According to this configuration, when the occurrence of premature ignition is predicted or detected, at least one of the exhaust valve closing timing and the intake valve opening timing is rapidly changed to reduce the amount of internal EGR gas. be able to.

According to the present invention, premature ignition is suppressed from occurring during the catalyst warm-up control. Therefore, if the present invention is applied to an engine in which the geometrical compression ratio of the cylinder is as high as 13 or more and premature ignition is likely to occur, the geometrical compression ratio of the cylinder can be increased to improve the fuel efficiency and This is effective because the catalyst can be warmed up early while preventing the occurrence of pre-ignition (claim 3).

Here, if the geometric compression ratio of the cylinder is increased, a part of the air-fuel mixture can be burned by self-ignition. Then, in this case, the combustion time of the air-fuel mixture can be shortened to further improve the fuel efficiency.

Therefore, in the above configuration, when at least the temperature of the catalyst device is equal to or higher than the reference temperature, a part of the air-fuel mixture in the cylinder is SI-combusted by the flame propagation from the ignition point by the ignition device, and the other air-fuel mixture is self-burned. By configuring to perform partial compression ignition combustion in which CI combustion is performed by ignition, it is possible to realize a high-performance engine capable of warming up the catalyst early while preventing the occurrence of premature ignition while further improving fuel efficiency. Item 4).

As described above, according to the engine control device of the present invention, it is possible to more reliably suppress the occurrence of premature ignition while activating the catalyst early.

1 is a system diagram schematically showing an overall configuration of a vehicle engine according to an embodiment of the present invention. It is a figure which shows the lift curve of an intake valve and an exhaust valve. It is a block diagram which shows the control system of an engine. 6 is an operation map for explaining a difference in control depending on engine speed/load. It is a graph which shows the waveform of the heat release rate at the time of SPCCI combustion (partial compression ignition combustion). 6 is a flowchart showing a flow of control of an intake/exhaust valve when performing AWS control.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a preferred embodiment of a vehicle engine (hereinafter, also simply referred to as an engine) to which a control device of the present invention is applied. The engine shown in this figure is a 4-cycle gasoline direct injection engine mounted on a vehicle as a power source for traveling, and includes an engine body 1, an intake passage 30 through which intake air introduced into the engine body 1 flows, An exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, and an external EGR device 50 that returns a part of the exhaust gas flowing through the exhaust passage 40 to the intake passage 30 are provided.

The engine body 1 includes a cylinder block 3 having a cylinder 2 formed therein, a cylinder head 4 mounted on an upper surface of the cylinder block 3 so as to close the cylinder 2 from above, and reciprocally slidably inserted into the cylinder 2. And the piston 5 is The engine body 1 is typically a multi-cylinder type having a plurality of (for example, four) cylinders, but here, for simplification, only one cylinder 2 will be focused on the description.

A combustion chamber 6 is defined above the piston 5, and fuel containing gasoline as a main component is supplied to the combustion chamber 6 by injection from an injector 15 described later. Then, the supplied fuel burns while being mixed with air in the combustion chamber 6, and the piston 5 reciprocates up and down in response to the expansion force of the combustion. The combustion chamber 6 is provided with an in-cylinder pressure sensor SN10 that detects the pressure in the combustion chamber 6, that is, the in-cylinder pressure that is the pressure in the cylinder.

Below the piston 5, a crankshaft 7 which is an output shaft of the engine body 1 is provided. The crankshaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis in accordance with the reciprocating motion (vertical motion) of the piston 5.

The geometric compression ratio of the cylinder 2, that is, the ratio between the volume of the combustion chamber 6 when the piston 5 is at the top dead center and the volume of the combustion chamber when the piston 5 is at the bottom dead center is SPCCI combustion (described later) ( A value suitable for partial compression ignition combustion) is set to 13 or more and 30 or less, preferably 14 or more and 18 or less.

The cylinder block 3 is provided with a crank angle sensor SN1 that detects the rotation angle (crank angle) of the crank shaft 7 and the rotation speed (engine speed) of the crank shaft 7.

The cylinder head 4 has an intake port 9 for introducing the air supplied from the intake passage 30 into the combustion chamber 6, and an exhaust port 10 for discharging the exhaust gas generated in the combustion chamber 6 into the exhaust passage 40. An intake valve 11 that opens and closes an opening of the intake port 9 on the combustion chamber 6 side and an exhaust valve 12 that opens and closes an opening of the exhaust port 10 on the combustion chamber 6 side are provided.

The intake valve 11 and the exhaust valve 12 are driven to open and close by being interlocked with the rotation of the crankshaft 7 by a valve operating mechanism including a pair of cam shafts arranged in the cylinder head 4.

The valve operating mechanism for the intake valve 11 includes an intake VVT 13 that can change the opening/closing timing of the intake valve 11. Similarly, the valve operating mechanism for the exhaust valve 12 incorporates an exhaust VVT 14 capable of changing the opening/closing timing of the exhaust valve 12. The intake VVT 13 (exhaust VVT 14) is a so-called phase type variable mechanism, and changes the opening timing and closing timing of the intake valve 11 (exhaust valve 12) simultaneously and by the same amount. Further, the intake VVT 13 (exhaust VVT 14) is an electric type having an electric motor 13a (14a) as a drive source thereof (see FIG. 2), and the intake valve 11 is operated in accordance with the operation of the electric motor 13a (14a). The opening/closing timing of the (exhaust valve 12) is changed. The intake VVT 13 and the exhaust VVT 14 correspond to an example of "variable valve mechanism" in the claims.

FIG. 2 is a diagram showing lift curves of the intake valve 11 and the exhaust valve 12 (IN shows a lift curve of the intake valve 11, and EX shows a lift curve of the exhaust valve 12). As shown in this figure, the intake valve 11 and the exhaust valve 12 may be driven such that the valve opening periods overlap across the exhaust top dead center (TDC in FIG. 2). This overlapping period, that is, the period in which both the intake valve 11 and the exhaust valve 12 are opened is called a valve overlap period. The valve overlap period can be adjusted by controlling the intake VVT 13 and the exhaust VVT 14 described above. The waveform of the solid line in FIG. 2 exemplifies a case where the valve overlap period is made relatively long, and in this case, the exhaust valve 12 remains for a while after the exhaust top dead center is passed (at the beginning of the intake stroke). By opening the valve, the burnt gas is pulled back from the exhaust port 10 to the combustion chamber 6, and an internal EGR in which the burned gas remains in the combustion chamber 6 is realized. On the contrary, as shown by the broken line waveform, when the valve overlap period is shortened, the amount of burned gas withdrawn from the exhaust port 10 is reduced as described above, and as a result, the internal EGR is suppressed or stopped. It

The cylinder head 4 is provided with an injector 15 for injecting fuel (gasoline) into the combustion chamber 6, and an ignition plug 16 for igniting a mixture of the fuel and the intake air injected from the injector 15 into the combustion chamber 6. It is provided. The spark plug 16 corresponds to the "ignition device" in the claims.

The intake passage 30 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9. Air (fresh air) taken from the upstream end of the intake passage 30 is introduced into the combustion chamber 6 through the intake passage 30 and the intake port 9.

In the intake passage 30, an air cleaner 31 for removing foreign matter in the intake air, an openable/closable throttle valve 32 for adjusting the flow rate of the intake air, a supercharger 33 for sending out the intake air while compressing the intake air, and An intercooler 35 for cooling the intake air compressed by the feeder 33 and a surge tank 36 are provided.

An air flow sensor SN2 that detects the flow rate of intake air, an intake air temperature sensor SN3 that detects the temperature of intake air, and an intake pressure sensor SN4 that detects the pressure of intake air are provided in each part of the intake passage 30. The air flow sensor SN2 and the intake air temperature sensor SN3 are provided in a portion of the intake passage 30 between the air cleaner 31 and the throttle valve 32, and detect the flow rate and temperature of intake air passing through the portion. The intake pressure sensor SN4 is provided in the surge tank 36 and detects the pressure of intake air in the surge tank 36.

The supercharger 33 is a mechanical supercharger mechanically linked to the engine body 1. The specific form of the supercharger 33 is not particularly limited, but any known supercharger such as a Risholum type, a roots type, or a centrifugal type can be used as the supercharger 33.

An electromagnetic clutch 34 capable of electrically switching between engagement/disengagement is provided between the supercharger 33 and the engine body 1. When the electromagnetic clutch 34 is engaged, the driving force is transmitted from the engine body 1 to the supercharger 33, and the supercharger 33 performs supercharging. On the other hand, when the electromagnetic clutch 34 is released, the transmission of the driving force is interrupted and the supercharging by the supercharger 33 is stopped.

The intake passage 30 is provided with a bypass passage 38 for bypassing the supercharger 33. The bypass passage 38 connects the surge tank 36 and an EGR passage 51 described later to each other. A bypass valve 39 that can be opened and closed is provided in the bypass passage 38.

The exhaust passage 40 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10. The burnt gas generated in the combustion chamber 6 is discharged to the outside through the exhaust port 10 and the exhaust passage 40.

A catalytic converter 41 is provided in the exhaust passage 40. The catalytic converter 41 includes a three-way catalyst 41a for purifying harmful components (HC, CO, NOx) contained in the exhaust gas flowing through the exhaust passage 40, and a particulate matter (PM) contained in the exhaust gas. And a GPF (gasoline particulate filter) 41b for collecting the gas. A catalyst temperature sensor SN11 for detecting the temperature of the three-way catalyst 41a is attached to the catalytic converter 41. In the present embodiment, the catalyst temperature sensor SN11 is attached to the portion immediately upstream of the three-way catalyst 41a. Hereinafter, the temperature of the three-way catalyst 41a detected by the catalyst temperature sensor SN11 will be referred to as catalyst temperature as appropriate. The three-way catalyst 41a corresponds to an example of a "catalyst device" in the claims.

The external EGR device 50 has an EGR passage 51 that connects the exhaust passage 40 and the intake passage 30, and an EGR cooler 52 and an EGR valve 53 that are provided in the EGR passage 51. The EGR passage 51 connects a portion of the exhaust passage 40 downstream of the catalytic converter 41 and a portion of the intake passage 30 between the throttle valve 32 and the supercharger 33 to each other. The EGR cooler 52 cools the exhaust gas (external EGR gas) recirculated from the exhaust passage 40 to the intake passage 30 through the EGR passage 51 by heat exchange. The EGR valve 53 is openably and closably provided in the EGR passage 51 on the downstream side (closer to the intake passage 30) than the EGR cooler 52, and adjusts the flow rate of the exhaust gas flowing through the EGR passage 51.

(2) Control System FIG. 3 is a block diagram showing a control system of the engine. The PCM 100 shown in this figure is a microprocessor for controlling the engine and the like as a whole, and is composed of a well-known CPU, ROM, RAM and the like.

Detection signals from various sensors are input to the PCM 100. For example, the PCM 100 is electrically connected to the crank angle sensor SN1, the air flow sensor SN2, the intake air temperature sensor SN3, the intake pressure sensor SN4, the in-cylinder pressure sensor SN10, and the catalyst temperature sensor SN11, which are detected by these sensors. Information (that is, crank angle, engine speed, intake flow rate, intake temperature, intake pressure, in-cylinder pressure, catalyst temperature) is sequentially input to the PCM 100.

Further, in the vehicle, an accelerator sensor SN5 that detects an opening degree of an accelerator pedal (hereinafter referred to as an accelerator opening degree) operated by a driver who drives the vehicle, and a traveling speed of the vehicle (hereinafter referred to as a vehicle speed) are detected. A vehicle speed sensor SN6 is provided, and detection signals from these sensors SN5 and SN6 are also sequentially input to the PCM 100.

The PCM 100 controls each part of the engine while executing various determinations and calculations based on the input information from the respective sensors. That is, the PCM 100 is electrically connected to the electric motors 13a and 14a of the intake VVT 13 and the exhaust VVT 14, the injector 15, the spark plug 16, the throttle valve 32, the electromagnetic clutch 34, the bypass valve 39, the EGR valve 53, and the like. , And outputs a control signal to each of these devices based on the result of the above-mentioned calculation.

Specifically, the PCM 100 functionally has a calculation unit 101 and a combustion control unit 102.

The combustion control unit 102 is a control module that controls the combustion of the air-fuel mixture in the combustion chamber 6, and controls each unit (intake/exhaust VVT 13 of the engine) so that the output torque of the engine becomes an appropriate value according to the driver's request. , 14, the injector 15, the spark plug 16... The calculation unit 101 is a control module for executing various calculations such as determining a control target value by the combustion control unit 102 and determining an engine operating state. The calculation unit 101 corresponds to the "premature ignition determination unit" in the claims.

(3) Catalyst warm-up promotion control In the present embodiment, when the temperature of the three-way catalyst 41a is lower than the predetermined reference temperature and the three-way catalyst 41a is not sufficiently activated, the temperature of the three-way catalyst 41a is raised. Catalyst warm-up promotion control is carried out to promote activation of the three-way catalyst 41a. Hereinafter, the catalyst warm-up promotion control will be referred to as AWS control as appropriate. In the present embodiment, the reference temperature is set to an activation temperature at which the purification rate of the three-way catalyst 41a becomes 50%.

The calculation unit 101 determines whether the catalyst temperature detected by the catalyst temperature sensor SN11 is lower than the reference temperature. When the calculation unit 101 determines that the catalyst temperature is lower than the reference temperature, the calculation unit 101 commands the combustion control unit 102 to perform the AWS control, and when it determines that the catalyst temperature is equal to or higher than the reference temperature, the combustion control unit 102 normally operates. Command to execute the control of. In the present embodiment, when the accelerator opening is depressed, the execution of the AWS control is prohibited, and the calculation unit 101 allows the accelerator opening to be depressed even if the catalyst temperature is lower than the reference temperature. If it is determined that the normal control is performed, the combustion control unit 102 is instructed to perform normal control.

In the AWS control, a large amount of air and fuel are supplied into the combustion chamber 6 when the air-fuel ratio in the combustion chamber 6 is near the stoichiometric air-fuel ratio or smaller than the stoichiometric air-fuel ratio, and when the AWS control is not executed, that is, during normal operation. The throttle valve 32, the spark plug 16, the injector 15, the intake VVT 13, and the exhaust VVT 14 are controlled so that the air-fuel mixture is ignited at a timing more retarded than that and the burned gas remains in the combustion chamber 6. To be done. In the present embodiment, when the AWS control is performed, the air-fuel ratio in the combustion chamber 6 is set to the stoichiometric air-fuel ratio.

Specifically, upon receiving an AWS control execution command from the calculation unit 101, the combustion control unit 102 causes the opening degree of the throttle valve 32 to be fully opened and causes the air-fuel ratio in the combustion chamber 6 to become the stoichiometric air-fuel ratio. A large amount of fuel is injected from the injector 15. Specifically, the combustion control unit 102 estimates the amount of air introduced into the combustion chamber 6 based on the detection value of the air flow sensor SN2 and the like, and the air-fuel ratio becomes the stoichiometric air-fuel ratio with respect to the estimated air amount. The amount of fuel is calculated, and the injector 15 is driven so that the calculated amount of fuel is injected into the combustion chamber 6. As described above, in the present embodiment, the throttle valve 32 and the injector 15 function as an air-fuel ratio changing device that changes the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 (in the cylinder 2).

Further, the combustion control unit 102 sets the ignition timing, which is the timing when the spark plug 16 ignites the air-fuel mixture, to a timing that is on the retard side with respect to the timing during normal operation (when the AWS control is not performed). That is, even if the engine speed and the engine load are the same, the ignition timing is set to be retarded when the AWS control is performed as compared with the normal operation. Then, the combustion control unit 102 causes the spark plug 16 to ignite at the set ignition timing. For example, as will be described later, the ignition timing during normal operation is set near the compression top dead center or in the latter half of the compression stroke, whereas the ignition timing during AWS control is 20° CA from the compression top dead center ( The crank angle is set to a timing on the retard side. The ignition timing at the time of executing the AWS control is preset and stored in the combustion control unit 102.

Further, the combustion control unit 102 closes the exhaust valve 12 at a timing on the retard side of the exhaust top dead center, and opens the intake valve 11 at a timing on the advance side of the exhaust top dead center, The intake VVT 13 and the exhaust VVT 14 are driven so that the intake valve 11 and the exhaust valve 12 both open across the exhaust top dead center. When the intake valve 11 and the exhaust valve 12 are opened and closed in this way, the internal EGR is realized and a relatively large amount of burned gas remains in the combustion chamber 6, as described above.

In the present embodiment, the basic opening/closing timing, which is the basic value of the opening/closing timing of the exhaust valve 12 and the opening/closing timing of the intake valve 11 when the AWS control is performed, is preset and stored in the combustion control unit 102. When the execution command of the AWS control is issued from the calculation unit 101, the combustion control unit 102 drives the intake VVT 13 and the exhaust VVT 14 so that the opening/closing timings of the intake/exhaust valves 11 and 12 respectively become the basic values. The basic opening/closing timing is set, for example, so that the valve overlap period of the intake valve 11 and the exhaust valve 12 is about 40°C.

As described above, in the AWS control, a large amount of fuel and air are introduced into the combustion chamber 6, and the air-fuel ratio thereof is set to the stoichiometric air-fuel ratio, whereby the combustion energy generated in the combustion chamber 6 is increased. .. In particular, since the internal EGR gas is realized, the temperature in the combustion chamber 6 is raised and the vaporization and atomization of the fuel is promoted, so that a large amount of fuel is appropriately burned and high combustion energy is reliably generated. It Moreover, the discharge of unburned fuel is also suppressed. Then, since the ignition timing is retarded, the timing at which the combustion energy is generated is close to the opening timing of the exhaust valve 12, and the high combustion energy generated in the combustion chamber 6 enters the exhaust passage 40. Efficiently discharged. As a result, the temperature of the three-way catalyst 41a is raised.

(4) Control during normal operation Next, the control when the AWS control is not performed, that is, the control during normal operation will be described.

First, the control when the engine water temperature is equal to or higher than a predetermined temperature, that is, when the engine temperature is warm will be described.

FIG. 4 is a map diagram for explaining the difference in control depending on the engine speed/engine load during warm time. As shown in the figure, the operating region of the engine is roughly divided into three operating regions A1 to A3. When the first operating area A1, the second operating area A2, and the third operating area A3, respectively, the first operating area A1 is a low-speed/low-load area in which both the rotation speed and the load are low, and the second operating area A2. Indicates a low-speed/high-load region where the rotation speed is low and the load is high, and the third operation region A3 is a high-speed region where the rotation speed is high. Whether it is warm (whether the engine water temperature is equal to or higher than the predetermined temperature), and in which operating region of the first to third operating regions A1 to A3 the engine is operating , Is determined by the arithmetic unit 101.

(A) First operating area A1 and second operating area A2
In the first operating region A1 and the second operating region A2, partial compression ignition combustion (hereinafter referred to as SPCCI combustion) in which SI combustion and CI combustion are combined is executed. SI combustion is a mode in which the air-fuel mixture is ignited by the spark plug 16 and the air-fuel mixture is forcibly combusted by flame propagation that spreads the combustion region from the ignition point to the surroundings, and the CI combustion is This is a mode in which the air-fuel mixture is burned by self-ignition in an environment in which the temperature of the piston 5 is increased by the compression of the piston 5. The SPCCI combustion in which the SI combustion and the CI combustion are combined is SI combustion of a part of the air-fuel mixture in the combustion chamber 6 by spark ignition performed in an environment on the verge of self-ignition of the air-fuel mixture. This is a combustion mode in which after combustion (because of higher temperature and pressure caused by SI combustion), the remaining air-fuel mixture in the combustion chamber 6 is subjected to CI combustion by self-ignition. Note that "SPCCI" is an abbreviation for "Spark Controlled Compression Ignition".

FIG. 5 is a graph showing a combustion waveform when SPCCI combustion occurs, that is, a change in heat generation rate (J/deg) with respect to a crank angle. In SPCCI combustion, heat generation during SI combustion becomes milder than that during CI combustion. For example, in the waveform of the heat release rate when SPCCI combustion is performed, the rising slope is relatively small, as shown in FIG. Further, the pressure fluctuation in the combustion chamber 6 (that is, dP/dθ:P is the in-cylinder pressure θ is the crank angle) is also gentler during SI combustion than during CI combustion. In other words, the waveform of the heat release rate during SPCCI combustion is relative to the first heat release rate portion (the portion indicated by Q1) formed by SI combustion and having a relatively small rising slope, and the relative heat release rate formed by CI combustion. The second heat generating portion having a large rising slope (the portion indicated by Q2) is formed so as to be continuous in this order.

When the temperature and the pressure inside the combustion chamber 6 increase due to the SI combustion, the unburned air-fuel mixture self-ignites accordingly, and the CI combustion is started. As illustrated in FIG. 5, at this self-ignition timing (that is, the timing at which CI combustion starts), the slope of the heat release rate waveform changes from small to large. That is, the waveform of the heat release rate in SPCCI combustion has an inflection point (X in FIG. 5) that appears at the timing θci at which CI combustion starts.

After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since CI combustion generates more heat than SI combustion, the heat generation rate is relatively large. However, since the CI combustion is performed after the compression top dead center, the slope of the heat release rate waveform does not become excessive. That is, after the compression top dead center, the motoring pressure decreases due to the lowering of the piston 5, which suppresses an increase in the heat release rate, and as a result, it is possible to avoid excessive dp/dθ during CI combustion. It As described above, in SPCCI combustion, due to the property that CI combustion is performed after SI combustion, dp/dθ, which is an index of combustion noise, is unlikely to be excessive, and simple CI combustion (when all fuels are CI burned It is possible to suppress combustion noise as compared with (1).

As the CI combustion ends, the SPCCI combustion also ends. Since the CI combustion has a higher combustion speed than the SI combustion, the combustion end timing can be advanced as compared with the simple SI combustion (when all the fuel is SI burned). In other words, in SPCCI combustion, the combustion end timing can be brought close to the compression top dead center within the expansion stroke. As a result, in SPCCI combustion, fuel efficiency can be improved as compared with simple SI combustion.

Here, in order to realize CI combustion, it is necessary to sufficiently increase the temperature and pressure in the combustion chamber 6. On the other hand, in the present embodiment, as described above, the temperature and pressure in the combustion chamber 6 can be increased near the compression top dead center by increasing the geometrical compression ratio of the engine. A part of the air-fuel mixture can be burnt by CI.

(First operating area)
When the calculation unit 101 determines that the engine water temperature is equal to or higher than a predetermined temperature and that the engine is operating in the first operating region A1, each unit of the engine is controlled by the combustion control unit 102 as follows. It

In the first operating region A1, the injector 15 injects all or most of the fuel to be injected during one cycle during the compression stroke. For example, in the first operation region A1, the injector 15 injects the fuel in two times from the middle stage of the compression stroke to the latter stage. Specifically, the combustion control unit 102 calculates the torque required for the engine from the engine speed, the opening degree of the accelerator pedal, and the like, and also calculates the fuel amount necessary to realize this required torque. Then, the combustion control unit 102 drives the injector 15 so that all or most of the calculated amount of fuel is injected during the compression stroke. Hereinafter, fuel injection for achieving the torque required for this engine is referred to as main injection.

In the first operation region A1, the opening of the throttle valve 32 is set near the fully open position so that the air-fuel ratio (A/F) in the combustion chamber 6 becomes higher (lean) than the theoretical air-fuel ratio, and a large amount of air is generated. It is introduced into the combustion chamber 6. For example, the air-fuel ratio in the combustion chamber 6 is about 30 in the first operating region A1.

In the first operating region A1, the spark plug 16 ignites the air-fuel mixture in the vicinity of the compression top dead center. The ignition timing at this time is preset and stored in the combustion control unit 102, as in the case of the AWS control.

In the first operating region A1, the intake VVT 13 and the exhaust VVT 14 are driven so that both the intake/exhaust valves 11 and 12 are opened across the exhaust top dead center to realize the internal EGR. The EGR valve 53 is opened to a predetermined opening degree, and the gas in the exhaust passage 40 is returned to the combustion chamber 6 as the external EGR gas through the EGR passage 51. As described above, in the first operating region A1, the air-fuel ratio (A/F) is set to be leaner than the stoichiometric air-fuel ratio as described above, and the EGR gas (external EGR gas and internal EGR gas) is set in the combustion chamber 6. ) Is introduced, the gas air-fuel ratio (G/F), which is the weight ratio of the total gas in the combustion chamber 6 to the fuel, becomes lean.

The supercharger 33 is turned off on the side where the rotation speed is low in the first operating region A1. That is, the electromagnetic clutch 34 is released to disconnect the supercharger 33 from the engine body 1, and the bypass valve 39 is fully opened to stop supercharging by the supercharger 33. On the other hand, on the side where the rotation speed is high in the operating region A1, the supercharger 33 is turned on. That is, when the electromagnetic clutch 34 is engaged and the supercharger 33 and the engine body 1 are connected, supercharging by the supercharger 33 is performed. At this time, the bypass valve is adjusted so that the pressure (supercharging pressure) in the surge tank 36 detected by the second intake pressure sensor SN7 coincides with the target pressure predetermined for each operating condition (rotation speed/load). The opening degree of 39 is controlled.

(Second operation area)
When the calculation unit 101 determines that the engine water temperature is equal to or higher than the predetermined temperature and that the engine is operating in the second operation region A2, each unit of the engine is controlled by the combustion control unit 102 as follows. It

In the second operating region A2, the opening degree of the throttle valve 32 is set according to the engine speed and the engine load so that the air-fuel ratio in the combustion chamber 6 becomes the stoichiometric air-fuel ratio. Further, the injector 15 carries out the main injection separately in the intake stroke and the compression stroke. That is, the injector 15 injects a part of the fuel of the amount corresponding to the required torque during the intake stroke and injects the remaining fuel during the compression stroke. The spark plug 16 ignites the air-fuel mixture in the vicinity of the compression top dead center, as in the first operating region A1. The ignition timing at this time is also set in advance and stored in the combustion control unit 102, as in the case of the AWS control.

The intake VVT 13 and the exhaust VVT 14 are driven so that the internal EGR is performed only in a part of the second operation region A2 on the low load side (in other words, the internal EGR is stopped on the high load side). The EGR valve 53 is controlled so that the amount of exhaust gas (external EGR gas) recirculated through the EGR passage 51 decreases toward the higher load side. In the vicinity of the maximum engine load, the EGR valve 53 is fully closed and the amount of external EGR gas is set to almost zero. Along with this, even in the second operation region A2, the gas air-fuel ratio (G/F) in the combustion chamber 6 is made lean except in the vicinity of the maximum load of the engine.

The supercharger 33 is turned off in a region of the second operating region A2 where both the rotation speed and the load are low. On the other hand, in the other areas of the second operation area A2, the supercharger 33 is turned on.

(B) Third Operating Region When the calculation unit 101 determines that the engine water temperature is equal to or higher than a predetermined temperature and that the engine is operating in the third operating region A3, normal SI combustion is executed. .. For example, main injection is performed for a predetermined period that at least partially overlaps the intake stroke, and spark ignition by the spark plug 16 is performed in the latter half of the compression stroke. SI combustion is triggered by this spark ignition, and all of the air-fuel mixture in the combustion chamber 6 burns due to flame propagation. The ignition timing at this time is also preset and stored in the combustion control unit 102, as in the case of the AWS control and the like.

(C) During Cold As described above, during warm time, different combustion modes are realized depending on the operating region of the engine. On the other hand, when the calculation unit 101 determines that the engine water temperature is lower than the predetermined temperature, that is, when the engine is cold, the normal SI combustion is performed in the entire operation region as in the third operation region. It The ignition timing at this time is also preset and stored in the combustion control unit 102, as in the case of the AWS control and the like.

(5) Premature Ignition Prevention Control Next, control for preventing premature ignition in which the air-fuel mixture starts combustion at a timing earlier than the ignition timing will be described.

As described above, the ignition timing is preset according to the operating condition of the engine and stored in the combustion control unit 102, and the combustion control unit 102 extracts the value according to the operating condition of the engine to determine the ignition timing. Set to. For example, the ignition timing is set for each of the engine speed and the engine load, and a map is provided, and this map is used for the AWS control, the warm normal operation, and the cold normal operation. Are respectively set and stored in the combustion control unit 102.

The ignition timing stored in the combustion control unit 102 is a timing determined based on an experiment or the like as a timing at which combustion of the air-fuel mixture can be appropriately started in the combustion chamber 6. However, if there is a delay in the introduction of the external EGR gas into the combustion chamber 6 during the transition during warm time, premature ignition may occur. This is because the temperature in the combustion chamber 6 becomes higher than the temperature when the ignition timing is set. Here, premature ignition is considered to occur when the temperature in the combustion chamber 6 is high, such as during warm weather. However, the inventors of the present application have found that premature ignition may occur even during the execution of the AWS control that is performed when the temperature in the combustion chamber 6 is relatively low such as when the engine is started. This is because, in the AWS control, the ignition timing is set to the timing on the relatively retarded side as described above, and when the fuel of the type having an excessively high ignitability is supplied to the engine, the ignition timing is reached. The air-fuel mixture may ignite before.

Thus, in the present embodiment, it is determined whether or not premature ignition occurs during the AWS control and the warm time, and when it is determined that premature ignition occurs, control is performed to prevent this. ..

(Premature ignition determination)
The procedure for determining pre-ignition will be described. This determination is performed by the calculation unit 101.

During the execution of the AWS control, the arithmetic unit 101 determines whether premature ignition has actually occurred. Specifically, the calculation unit 101 calculates the heat generation rate using the in-cylinder pressure detected by the in-cylinder pressure sensor SN10. Then, when the heat release rate becomes equal to or higher than the preset first determination value before the ignition timing, it is determined that the pre-ignition has occurred. The first determination value is set to a value larger than 0.

On the other hand, the arithmetic unit 101 determines whether premature ignition occurs during warming of the engine. Specifically, if the increase rate of the in-cylinder pressure (the amount of increase per unit time) becomes equal to or higher than the second determination value before the ignition timing, then the calculation unit 101 determines that premature ignition occurs. The second determination value is set to a value larger than the maximum value of the increase rate of the in-cylinder pressure during motoring.

(Premature ignition prevention control during warm time)
When the calculation unit 101 determines that pre-ignition occurs during the warm time, the combustion control unit 102 injects fuel from the injector 15 separately from the main injection to supply additional fuel into the combustion chamber 6. ..

When additional fuel is supplied into the combustion chamber 6, the temperature of the air-fuel mixture in the combustion chamber 6 decreases due to the latent heat of vaporization of this fuel. Therefore, the reaction of the air-fuel mixture becomes slow and premature ignition is prevented. Here, a part of the added fuel may be discharged from the combustion chamber 6 without being burned, but the three-way catalyst 41a is basically activated when the AWS control is not performed. Therefore, the unburned fuel is purified by the three-way catalyst 41a, and the exhaust gas performance is maintained excellent.

(Premature ignition prevention control during AWS control implementation)
As described above, when the temperature is warm and the AWS control is not performed, the exhaust gas performance can be favorably maintained while preventing the premature ignition in the additional fuel injection. However, when the AWS control is performed, the three-way catalyst 41a is not sufficiently activated, and therefore, if additional fuel injection is performed, unburned fuel may be discharged without being purified. Therefore, when the AWS control is executed, the temperature in the combustion chamber 6 is lowered by reducing the amount of the internal EGR gas instead of performing additional fuel injection, thereby preventing premature ignition. In the present embodiment, the amount of internal EGR gas is reduced by reducing the valve overlap period between the intake valve 11 and the exhaust valve 12.

Specifically, when the calculation unit 101 determines that pre-ignition has occurred during the execution of the AWS control, the combustion control unit 102 sets the intake VVT 13 so that the opening timing of the intake valve 11 is advanced by a predetermined amount. While driving, the exhaust VVT 14 is driven so that the closing timing of the exhaust valve 12 is retarded by a predetermined amount. In this embodiment, the advance amount of the opening timing of the intake valve 11 and the retard amount of the exhaust valve 12 are set to the same value. For example, these values are set to about 5° CA, and when the determination is made, the valve overlap period is reduced by about 10° CA. As described above, in the present embodiment, since the intake VVT 13 and the exhaust VVT 14 are electrically operated, the combustion controller 102 receives a command for the opening timing of the intake valve 11 and the closing timing of the exhaust valve 12. The valve overlap period is reduced in the combustion cycle subsequent to the combustion cycle that was changed immediately after and was determined to have caused pre-ignition.

The flow of control of the intake/exhaust valves 11 and 12 when the AWS control is executed is shown in the flowchart of FIG.

First, in step S1, the calculation unit 101 determines whether or not the AWS control start condition is satisfied. As described above, in this embodiment, the condition for starting the AWS control is satisfied when the temperature of the catalyst is lower than the determination temperature in the state where the accelerator pedal is not depressed and the AWS control is not started yet. It is judged that it did. If the determination is NO and the AWS control start condition is not satisfied, the process proceeds to step S7. In step S7, the combustion control unit 102 executes normal control and ends the process (returns to step S1).

On the other hand, when the determination in step S1 is YES and the AWS control start condition is satisfied, the process proceeds to step S2. In step S2, the combustion control unit 102 drives the intake VVT 13 and the exhaust VVT 14 so that the opening/closing timing of the intake/exhaust valves 11 and 12 becomes the basic opening/closing timing.

After step S2, the process proceeds to step S3. In step S3, the calculation unit 101 determines whether premature ignition has occurred. When this determination is NO and premature ignition has not occurred, the process proceeds to step S4. In step S4, the combustion control unit 102 does not drive the intake VVT 13 and the exhaust VVT 14, and maintains the opening/closing timing of the intake/exhaust valves 11 and 12 at the current timing.

On the other hand, when the determination in step S3 is YES and premature ignition occurs, the process proceeds to step S5. In step S5, the combustion control unit 102 drives the intake VVT 13 so that the opening timing of the intake valve 11 is advanced by the predetermined amount from the current opening timing (the opening timing of the previous calculation cycle). At the same time, the exhaust VVT 14 is driven so that the valve closing timing of the exhaust valve 12 advances from the current valve closing timing (valve closing timing in the previous calculation cycle) by the above-mentioned predetermined amount. As a result, the valve overlap period of the intake/exhaust valves 11 and 12 is shortened.

After step S5, the process proceeds to step S6. In step S6, the calculation unit 101 determines whether to end the AWS control. Specifically, the calculation unit 101 determines to end the AWS control when the catalyst temperature becomes equal to or higher than the determination temperature or when the accelerator pedal is depressed. When the determination in step S6 is YES and the arithmetic unit 101 determines to end the AWS control, the process proceeds to step S7, the combustion control unit 102 executes the normal control and ends the process (returns to step S1).

On the other hand, when the determination in step S6 is NO and the arithmetic unit 101 determines that the AWS control is still continued, the process returns to step S3, and steps S3 to S6 are repeated. That is, until the AWS control is terminated, the calculation unit 101 repeatedly determines whether or not premature ignition has occurred, and the open timing of the intake valve 11 is set to a predetermined amount each time it is determined that premature ignition has occurred. The exhaust valve 12 is retarded by a predetermined amount.

(6) Functions and Effects As described above, in the present embodiment, when the catalyst temperature is lower than the reference temperature, the AWS control is performed as described above, so that the catalyst is activated early to improve the exhaust gas performance. Can be increased. In particular, the internal EGR is performed when the AWS control is performed, and the high temperature burned gas is configured to remain in the combustion chamber 6, so that the catalyst can be discharged earlier while suppressing the discharge of unburned fuel. It can be activated.

Moreover, it is determined whether the pre-ignition occurs during the execution of the AWS control, and when the pre-ignition occurs during the execution of the AWS control, the valve overlap period of the intake/exhaust valves 11 and 12 is determined. The intake VVT 13 and the exhaust VVT 14 are controlled so that the amount of the internal EGR gas in the combustion chamber 6 decreases and the amount of the internal EGR gas decreases. Therefore, the amount of high-temperature internal EGR gas can be reduced to reduce the temperature in the combustion chamber 6, and it is possible to prevent continuous premature ignition.

Further, in the present embodiment, as the intake/exhaust VVTs 13 and 14, electric VVTs that change the opening/closing phase of the valve by driving the electric motors 13a and 14a are used. Therefore, as compared with the case where a hydraulic VVT is adopted, for example, when it is determined that pre-ignition occurs, the valve overlap period can be shortened quickly, and the internal EGR amount can be reduced with high response. You can

Further, in the present embodiment, the compression ratio of the cylinder 2 is increased to realize SPCCI combustion, so that the fuel efficiency can be improved and the temperature in the combustion chamber 6 easily rises. Early ignition is likely to occur. On the other hand, as described above, it is possible to prevent premature ignition, and it is possible to appropriately burn the air-fuel mixture while improving fuel efficiency.

(7) Modification In the above embodiment, when it is determined that premature ignition occurs during the execution of the AWS control, the intake/exhaust valves 11 and 12 are both opened across the exhaust top dead center. Although the control for shortening the lap period (thereby reducing the internal EGR amount) is executed, it suffices that the valve timing can be changed in the direction in which the internal EGR amount is reduced, and various controls can be adopted within that range. .. For example, as the control for reducing the internal EGR, control may be executed to change the opening/closing timing of the exhaust valve 12 to the advanced side while keeping the opening/closing timing of the intake valve 11 constant. This control also shortens the valve opening period of the exhaust valve 12 during the intake stroke, so that the internal EGR amount can be reduced.

Further, the control for reducing the internal EGR amount is not limited to the above control for shortening the valve overlap period (the period during which both the intake/exhaust valves 11 and 12 are opened). For example, depending on the engine, as control for realizing the internal EGR, a so-called negative overlap period in which both the intake and exhaust valves 11 and 12 are closed across the exhaust top dead center is formed, whereby the burned gas is burned. Can be confined in the combustion chamber 6. In the engine of this type, the valve timing is changed so that the negative overlap period is shortened as the control for reducing the internal EGR when it is determined that the pre-ignition occurs during the execution of the AWS control. It suffices to execute control.

Further, the engine to which the present invention can be applied may be any engine capable of adjusting the internal EGR amount by changing the valve overlap period or the negative overlap period described above, and is not necessarily required for both the intake valve and the exhaust valve. It is not necessary to be able to change the opening/closing timing, and it is not necessary to provide a phase type variable mechanism (VVT) that changes the valve opening timing and the valve closing timing simultaneously and by the same amount. In other words, the variable valve mechanism according to the present invention may be any variable mechanism that can change at least one of the exhaust valve closing timing and the intake valve opening timing.

Further, in the above-described embodiment, an example in which the present invention is applied to an engine capable of SPCCI combustion (partial compression ignition combustion) in which SI combustion and CI combustion are combined has been described, but an engine to which the present invention is applicable is a spark plug. An engine whose output torque can be adjusted according to the ignition timing of an ignition device such as a conventional spark ignition engine that performs SI combustion (combustion by flame propagation from the ignition point) of all the air-fuel mixture The present invention is applicable.

Further, in the above-described embodiment, the case where it is determined whether the pre-ignition has occurred by using the in-cylinder pressure detected by the in-cylinder pressure sensor SN10 during the execution of the AWS control has been described. The determination method is not limited to this. For example, a knock sensor that detects the occurrence of knocking may be used, and whether premature ignition has occurred may be determined based on the detection result of the knock sensor.

Further, even during the execution of the AWS control, it is predicted whether premature ignition occurs or not, not whether the premature ignition actually occurs. Alternatively, the VVTs 13 and 14 may be controlled so that the amount of the internal EGR gas is reduced. For example, when the maximum value of the in-cylinder pressure is greater than or equal to a predetermined value, it may be predicted that premature ignition will occur in the next combustion cycle.

In the above embodiment, the case where the air-fuel ratio in the combustion chamber 6 is set to the stoichiometric air-fuel ratio during the execution of the AWS control has been described. However, as described above, this air-fuel ratio is slightly higher than the stoichiometric air-fuel ratio. Good. Further, it may be smaller than the stoichiometric air-fuel ratio. However, in order to activate the three-way catalyst 41a early, it is desirable that the air-fuel ratio in the combustion chamber 6 during the AWS control is about 15.5 or less.

Further, the catalytic device provided in the exhaust passage and subjected to AWS control is not limited to the three-way catalyst 41a.

2 cylinders 6 combustion chamber 9 intake port 10 exhaust port 11 intake valve 12 exhaust valve 13 intake VVT (variable valve mechanism)
14 Exhaust VVT (Variable valve mechanism)
13a electric motor 14a electric motor 15 injector (air-fuel ratio changing device)
16 Spark plug (ignition device)
32 Throttle valve (air-fuel ratio changing device)
41a Three-way catalyst (catalyst device)
101 Calculation unit (premature ignition determination unit)
102 Combustion control unit

Claims (4)

A cylinder, an air-fuel ratio changing device that can change the air-fuel ratio of the air-fuel mixture in the cylinder, an ignition device that ignites the air-fuel mixture in the cylinder, an intake valve that opens and closes an intake port for introducing intake air into the cylinder, An exhaust valve that opens and closes an exhaust port for exhausting exhaust gas from a cylinder, a variable valve mechanism that changes at least one of the exhaust valve closing timing and the intake valve opening timing, and the exhaust gas that is exhausted from the cylinder through the exhaust port A device for controlling an engine, which includes an exhaust passage through which the exhaust gas flows, and a catalyst device provided in the exhaust passage for purifying exhaust gas,
Predicting whether pre-ignition occurs that the air-fuel mixture is ignited before the ignition by the ignition device is performed, or an pre-ignition determination unit that detects whether pre-ignition has occurred,
When the temperature of the catalyst device is lower than a preset reference temperature, the air-fuel ratio in the cylinder is near the stoichiometric air-fuel ratio or smaller than the stoichiometric air-fuel ratio, and the temperature of the catalyst device is higher than the reference temperature. A catalyst that controls the air-fuel ratio changing device, the ignition device, and the variable valve mechanism so that the air-fuel mixture in the cylinder is ignited at a retarded timing and burned gas remains in the cylinder. With a combustion control unit that performs warm-up promotion control,
The combustion control unit is predicted to cause premature ignition by the premature ignition determination unit during execution of the catalyst warm-up promotion control, or when it is detected that premature ignition occurs, the cylinder An engine control device, characterized in that the variable valve mechanism is driven in a direction in which an amount of burnt gas remaining therein is reduced. In the engine control device according to claim 1,
The engine control device, wherein the variable valve mechanism is an electric variable mechanism that changes an opening/closing phase of a valve by driving an electric motor. The engine control device according to claim 1 or 2,
The engine control device, wherein the geometric compression ratio of the cylinder is set to 13 or more. In the engine control device according to claim 3,
When at least the temperature of the catalyst device is equal to or higher than the reference temperature, the combustion control unit causes a part of the air-fuel mixture in the cylinder to perform SI combustion by the flame propagation from the ignition point by the ignition device, and the other air-fuel mixture itself An engine control device, which executes partial compression ignition combustion in which CI combustion is performed by ignition.

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