JP7155962B2 - engine controller - Google Patents

Description

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

2. Description of the Related Art Some engines have an exhaust passage provided with a catalytic device for purifying exhaust gas discharged from a cylinder. In such an engine, when the temperature of the catalyst device is low, 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 less than a predetermined temperature, a relatively large amount of fuel is supplied to the cylinder and the air-fuel ratio in the cylinder is set to the stoichiometric air-fuel ratio. In addition to increasing the combustion energy, the ignition timing for igniting the mixture of fuel and air is retarded from the normal timing, so that the high combustion energy generated in the cylinder is efficiently supplied to the exhaust passage. An engine is disclosed.

JP 2014-196696 A

Here, increasing the compression ratio of the cylinder is one of the configurations for improving the fuel consumption performance. Then, it is conceivable to provide a catalyst device and apply the control of Patent Document 1 to an engine having a high cylinder compression ratio. However, in an engine with a high compression ratio, simply applying the control of Patent Document 1, introducing a large amount of air and fuel into the cylinder, and bringing the air-fuel ratio close to the stoichiometric air-fuel ratio, causes ignition from the ignition device. There is a risk of pre-ignition, in which the air-fuel mixture begins to burn before the

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 the timing and amount at which pre-ignition does not occur. However, the susceptibility to pre-ignition, ie, the ignitability of fuel, differs depending on the type of fuel. For example, gasoline with a lower octane number is more ignitable, and premature ignition is more likely to occur. Therefore, if the engine is unexpectedly supplied with a fuel that is significantly different from the type of fuel when the set value was determined, there is a possibility that premature ignition cannot be sufficiently avoided.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an engine control apparatus capable of activating a catalyst at an early stage and more reliably suppressing the occurrence of pre-ignition.

To solve the above problems, the present invention provides a cylinder, an air-fuel ratio changing device capable of changing the air-fuel ratio of the air-fuel mixture in the cylinder, an ignition device for igniting the air-fuel mixture in the cylinder, and an air-fuel mixture in the cylinder. At least one of the intake valve that opens and closes the intake port for introducing the exhaust gas, the exhaust valve that opens and closes the exhaust port for discharging the exhaust from the cylinder, and the closing timing of the exhaust valve and the opening timing of the intake valve. 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 flows; and a catalytic device provided in the exhaust passage for purifying the exhaust gas, Predict whether or not pre-ignition will occur, in which the mixture ignites before ignition by the injector that injects fuel into the cylinder and the ignition device, or detect whether pre-ignition has occurred and a combustion control unit that controls the air-fuel ratio changing device, the ignition device, and the variable valve mechanism, wherein the combustion control unit controls the temperature of the catalyst device to a preset reference temperature, the air-fuel ratio in the cylinder becomes close to the stoichiometric air-fuel ratio or becomes smaller than the stoichiometric air-fuel ratio, and the air-fuel mixture in the cylinder is retarded at a timing more retarded than when the temperature of the catalytic device is equal to or higher than the reference temperature. and carry out catalyst warm-up promotion control for controlling the air-fuel ratio changing device, the ignition device, and the variable valve mechanism so that the ignition is performed and the burned gas remains in the cylinder, and the catalyst device is equal to or higher than the reference temperature, the air-fuel ratio in the cylinder becomes larger than the stoichiometric air-fuel ratio, ignition is performed at a predetermined timing, and both the intake valve and the exhaust valve are at exhaust top dead center normal operation control for controlling the air-fuel ratio changing device, the ignition device, and the variable valve mechanism so that the valve is opened for a predetermined period across the When the early ignition determination unit predicts that pre-ignition will occur or detects that pre-ignition has occurred, the variable valve mechanism is driven in the direction in which the amount of burnt gas remaining in the cylinder is reduced. When the pre-ignition determination unit predicts that pre-ignition occurs during the execution of the normal operation control, or detects that pre-ignition has occurred, additional fuel is injected from the injector into the cylinder. ( Claim 1).

According to the present invention, when the temperature of the catalyst device is less than the reference temperature, the catalyst warm-up acceleration control is performed to bring the air-fuel ratio in the cylinder to near the stoichiometric air-fuel ratio or less than the stoichiometric air-fuel ratio. is the timing on the retarded side compared to 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. In addition, since the high-temperature burned gas remains in the cylinder, the temperature inside the cylinder is increased, promoting the vaporization and atomization of the fuel supplied to the cylinder, and the fuel is properly dispensed. Therefore, it is possible to reliably supply high combustion energy to the catalyst device and to suppress the discharge of unburned fuel.

Moreover, the present invention is provided with a pre-ignition determination unit that predicts occurrence of pre-ignition or detects occurrence of pre-ignition. When the pre-ignition determining unit predicts that pre-ignition will occur or detects pre-ignition, the amount of burnt gas remaining in the cylinder, that is, the amount of internal EGR gas is The variable valve mechanism is controlled to reduce Therefore, even when the type of fuel unexpectedly changes to one with high combustibility, the occurrence of pre-ignition can be predicted or detected, and when this is predicted or detected, the amount of high-temperature internal EGR gas can be reduced. As a result, the temperature in the cylinder can be reduced, and the occurrence of premature ignition can be suppressed.

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

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

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

Here, if the geometric compression ratio of the cylinder is increased, it becomes possible to burn part of the air-fuel mixture by self-ignition. 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, at least when the temperature of the catalyst device is equal to or higher than the reference temperature, part of the air-fuel mixture in the cylinder is SI-burned by flame propagation from the ignition point of the ignition device, and the other air-fuel mixture is automatically burned. If it is configured to execute partial compression ignition combustion in which CI combustion is performed by ignition, it is possible to realize a high-performance engine that can warm up the catalyst early while preventing premature ignition while further improving fuel efficiency (claim 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 pre-ignition while activating the catalyst at an early stage.

1 is a system diagram schematically showing the overall configuration of a vehicle engine according to one embodiment of the present invention; FIG. FIG. 4 is a diagram showing lift curves of an intake valve and an exhaust valve; 3 is a block diagram showing a control system of the engine; FIG. 4 is an operation map for explaining differences in control according to engine speed/load; 4 is a graph showing a waveform of heat release rate during SPCCI combustion (partial compression ignition combustion). 4 is a flowchart showing a control flow of intake/exhaust valves when AWS control is performed;

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a preferred embodiment of a vehicle engine (hereinafter simply referred to as an engine) to which the 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 running. It has an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, and an external EGR device 50 that recirculates part of the exhaust gas flowing through the exhaust passage 40 to the intake passage 30 .

The engine body 1 includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to block the cylinder 2 from above, and a reciprocatingly slidable insertion into the cylinder 2. and a piston 5 that is The engine main body 1 is typically of a multi-cylinder type having a plurality of (for example, four) cylinders, but for the sake of simplification, only one cylinder 2 will be described here.

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, which will be described later. The supplied fuel burns while being mixed with air in the combustion chamber 6, and the piston 5 reciprocates vertically by receiving the expansion force due to 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 pressure in the cylinder.

A crankshaft 7 that is an output shaft of the engine body 1 is provided below the piston 5 . The crankshaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis according to the reciprocating motion (vertical motion) of the piston 5 .

The geometric compression ratio of cylinder 2, that is, the ratio between the volume of combustion chamber 6 when piston 5 is at top dead center and the volume of the combustion chamber when piston 5 is at bottom dead center, is the SPCCI combustion ( A suitable value 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 crankshaft 7 and the rotation speed (engine speed) of the crankshaft 7 .

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

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

A valve mechanism for the intake valve 11 incorporates an intake VVT 13 capable of changing the opening/closing timing of the intake valve 11 . Similarly, the valve 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 the closing timing of the intake valve 11 (exhaust valve 12) simultaneously and by the same amount. The intake VVT 13 (exhaust VVT 14) is of an electric type having an electric motor 13a (14a) as its drive source (see FIG. 2). (exhaust valve 12) is changed. The intake VVT 13 and the exhaust VVT 14 correspond to an example of the "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 indicates the lift curve of the intake valve 11 and EX indicates the lift curve of the exhaust valve 12). As shown in this figure, the intake valve 11 and the exhaust valve 12 may be driven so that the valve opening periods overlap across 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 open, 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 solid-line waveform in FIG. 2 illustrates a case where the valve overlap period is relatively long. By opening the valve, the burned gas is drawn back from the exhaust port 10 to the combustion chamber 6, and internal EGR is realized in which the burned gas remains in the combustion chamber 6. Conversely, as shown by the dashed waveform, when the valve overlap period is shortened, the amount of burnt gas drawn back from the exhaust port 10 is reduced as described above, and as a result, internal EGR is suppressed or stopped. be.

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

The intake passage 30 includes, in order from the upstream side thereof, an air cleaner 31 that removes foreign matter from the intake air, a throttle valve 32 that can be opened and closed to adjust the flow rate of the intake air, a supercharger 33 that compresses and delivers the intake air, and a supercharger. An intercooler 35 for cooling the intake air compressed by the feeder 33 and a surge tank 36 are provided.

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

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

Between the supercharger 33 and the engine body 1, an electromagnetic clutch 34 is interposed which can be electrically switched between engagement and disengagement. When the electromagnetic clutch 34 is engaged, driving force is transmitted from the engine body 1 to the supercharger 33, and supercharging by the supercharger 33 is performed. On the other hand, when the electromagnetic clutch 34 is released, the transmission of the driving force is interrupted and supercharging by the supercharger 33 is stopped.

A bypass passage 38 for bypassing the supercharger 33 is provided in the intake passage 30 . The bypass passage 38 connects the surge tank 36 and an EGR passage 51 (to be 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 . Burned 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 particulate matter (PM) contained in the exhaust gas. A GPF (gasoline particulate filter) 41b for collecting is incorporated. A catalyst temperature sensor SN11 is attached to the catalytic converter 41 for detecting the temperature of the three-way catalyst 41a. In this embodiment, a catalyst temperature sensor SN11 is attached to the immediately upstream portion of the three-way catalyst 41a. Hereinafter, the temperature of the three-way catalyst 41a detected by the catalyst temperature sensor SN11 is referred to as catalyst temperature. The three-way catalyst 41a corresponds to an example of the "catalyst device" in the claims.

The external EGR device 50 has an EGR passage 51 connecting the exhaust passage 40 and the intake passage 30 , and an EGR cooler 52 and an EGR valve 53 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 . 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 provided in the EGR passage 51 downstream (closer to the intake passage 30 ) than the EGR cooler 52 so as to be openable and closable, 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 the engine control system. A PCM 100 shown in this figure is a microprocessor for overall control of the engine and the like, 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 aforementioned crank angle sensor SN1, airflow sensor SN2, intake air temperature sensor SN3, intake air pressure sensor SN4, in-cylinder pressure sensor SN10, and catalyst temperature sensor SN11. Information (that is, crank angle, engine speed, intake air flow rate, intake air temperature, intake air pressure, in-cylinder pressure, catalyst temperature) is sequentially input to the PCM 100 .

Further, the vehicle is equipped with an accelerator sensor SN5 for detecting the opening of an accelerator pedal operated by the driver of the vehicle (hereinafter referred to as accelerator opening), and a traveling speed of the vehicle (hereinafter referred to as vehicle speed). A vehicle speed sensor SN6 is provided, and detection signals from these sensors SN5 and SN6 are also input to the PCM 100 sequentially.

The PCM 100 controls each section of the engine while executing various determinations and calculations based on the input information from each sensor. That is, the PCM 100 is electrically connected to the electric motors 13a, 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 control signals to these devices based on the results of the above calculations and the like.

Specifically, the PCM 100 functionally has an arithmetic 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 part of the engine (intake/exhaust VVT 13 , 14, injector 15, spark plug 16, etc.). 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 the operating state of the engine. The calculation unit 101 corresponds to the "premature ignition determination unit" in the claims.

(3) Catalyst Warm-Up Acceleration Control In this 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 increased. Catalyst warm-up acceleration control is performed to promote activation of the three-way catalyst 41a. Hereinafter, the catalyst warm-up acceleration control is appropriately referred to as AWS control. In this embodiment, the reference temperature is set to the activation temperature at which the purification rate of the three-way catalyst 41a is 50%.

The calculation unit 101 determines whether or not the catalyst temperature detected by the catalyst temperature sensor SN11 is lower than the reference temperature. If the calculation unit 101 determines that the catalyst temperature is less than the reference temperature, it commands the combustion control unit 102 to perform AWS control, and if it determines that the catalyst temperature is equal to or higher than the reference temperature, the combustion control unit 102 performs normal operation. order to implement the control of In this embodiment, when the accelerator opening is depressed, the execution of the AWS control is prohibited, and the calculation unit 101 determines whether the accelerator opening is depressed even if the catalyst temperature is lower than the reference temperature. If it is determined that the combustion control unit 102 is in a normal state, it instructs the combustion control unit 102 to perform normal control.

Under the AWS control, a large amount of air and fuel are supplied to the combustion chamber 6 in a state where the air-fuel ratio in the combustion chamber 6 is close to the stoichiometric air-fuel ratio or smaller than the stoichiometric air-fuel ratio. 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 on the retarded side and the burned gas remains in the combustion chamber 6. be done. In this embodiment, the air-fuel ratio in the combustion chamber 6 is set to the stoichiometric air-fuel ratio when AWS control is performed.

Specifically, upon receiving a command to perform AWS control from the computing unit 101, the combustion control unit 102 fully opens the throttle valve 32 and adjusts the air-fuel ratio in the combustion chamber 6 to the stoichiometric air-fuel ratio. A sufficient 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 detected value of the airflow sensor SN2, etc., and the air-fuel ratio of the estimated air amount becomes the stoichiometric air-fuel ratio. 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 . Thus, in this 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 (inside the cylinder 2).

Further, the combustion control unit 102 sets the ignition timing, which is the timing at which the spark plug 16 ignites the air-fuel mixture, to a timing retarded from the timing during normal operation (when 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 the retarded side during execution of AWS control compared to during normal operation. Then, the combustion control unit 102 causes the ignition plug 16 to ignite at the set ignition timing. For example, the ignition timing during normal operation is set near the compression top dead center or in the latter half of the compression stroke, as will be described later, whereas the ignition timing during AWS control is set at 20° CA ( crank angle) is set to a timing on the retard side. The ignition timing during execution of the AWS control is set in advance 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 are both opened 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 burnt gas remains in the combustion chamber 6 as described above.

In the present embodiment, basic opening/closing timings, which are basic values for the opening/closing timing of the exhaust valve 12 and the opening/closing timing of the intake valve 11 when AWS control is performed, are set in advance and stored in the combustion control unit 102 . When a command to perform AWS control is issued from calculation unit 101, combustion control unit 102 drives intake VVT 13 and exhaust VVT 14 so that the opening/closing timings of intake/exhaust valves 11 and 12 are each at this basic value. The basic opening/closing timing is set, for example, so that the valve overlap period between the intake valve 11 and the exhaust valve 12 is approximately 40°CA.

Thus, in the AWS control, a large amount of fuel and air are introduced into the combustion chamber 6, and the air-fuel ratio is set to the stoichiometric air-fuel ratio, thereby increasing the combustion energy generated in the combustion chamber 6. . In particular, when the internal EGR gas is realized, the temperature in the combustion chamber 6 is raised and the vaporization and atomization of the fuel are promoted, so that a large amount of fuel is appropriately burned, and high combustion energy is reliably generated. be. In addition, the discharge of unburned fuel is also suppressed. By retarding the ignition timing, the timing at which the combustion energy is generated becomes closer to the opening timing of the exhaust valve 12, and the high combustion energy generated in the combustion chamber 6 flows into the exhaust passage 40. discharged efficiently. This raises the temperature of the three-way catalyst 41a.

(4) Control during normal operation Next, control during non-execution of AWS control, that is, 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 is warm, will be described.

FIG. 4 is a map diagram for explaining differences in control according to the engine speed/engine load when the engine is warm. As shown in the figure, the operating range of the engine is roughly divided into three operating ranges A1 to A3. A first operating area A1, a second operating area A2, and a third operating area A3, respectively. is a low-speed, high-load region in which the rotational speed is low and the load is high, and the third operating region A3 is a high-speed region in which the rotational speed is high. Whether the engine is warm (whether or not the engine water temperature is equal to or higher than the predetermined temperature), and in which of the first to third operating regions A1 to A3 the engine is being operated are determined. , is determined by the computing unit 101 .

(a) First operating region A1 and second operating region A2
In the first operating region A1 and the second operating region A2, partial compression ignition combustion (hereinafter referred to as SPCCI combustion) combining SI combustion and CI combustion is performed. SI combustion is a form in which the air-fuel mixture is ignited by the ignition plug 16, and the air-fuel mixture is forcibly burned by flame propagation that expands the combustion area from the ignition point to the surroundings. It is a mode in which the air-fuel mixture is combusted by self-ignition in an environment of high temperature and high pressure due to compression of the piston 5. SPCCI combustion, which is a combination of SI combustion and CI combustion, involves SI combustion of part of the air-fuel mixture in the combustion chamber 6 by spark ignition performed in an environment just before the air-fuel mixture self-ignites, and the SI It is a combustion mode in which the remaining air-fuel mixture in the combustion chamber 6 undergoes CI combustion by self-ignition after combustion (due to further increase in temperature and pressure accompanying SI combustion). “SPCCI” is an abbreviation for “Spark Controlled Compression Ignition”.

FIG. 5 is a graph showing combustion waveforms when SPCCI combustion occurs, that is, changes in heat release rate (J/deg) with respect to crank angle. In SPCCI combustion, the heat release during SI combustion is milder than that during CI combustion. For example, the waveform of the heat release rate when SPCCI combustion is performed has a relatively small rising slope as shown in FIG. Also, 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 consists of the first heat release rate portion (portion indicated by Q1) formed by SI combustion and having a relatively small rising slope, and the relative heat release rate portion formed by CI combustion. A second heat generating portion (portion indicated by Q2) having a relatively steep rising slope is formed so as to be continuous in this order.

When the temperature and pressure in the combustion chamber 6 increase due to SI combustion, the unburned air-fuel mixture self-ignites and CI combustion starts. As illustrated in FIG. 5, the slope of the waveform of the heat release rate changes from small to large at the timing of this self-ignition (that is, the timing at which CI combustion starts). 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 release rate is relatively high. However, since CI combustion is performed after compression top dead center, the slope of the heat release rate waveform does not become excessive. That is, when the compression top dead center is passed, the motoring pressure drops due to the descent of the piston 5, which suppresses the rise in the heat release rate, thereby avoiding an excessive increase in dp/dθ during CI combustion. be. In this way, in SPCCI combustion, CI combustion is performed after SI combustion. ), combustion noise can be suppressed.

SPCCI combustion also ends with the end of CI combustion. Since the CI combustion has a higher combustion speed than the SI combustion, it is possible to advance the combustion end timing as compared to the simple SI combustion (when all the fuel is SI-burned). In other words, in SPCCI combustion, the end of combustion can be brought closer to compression top dead center in the expansion stroke. As a result, SPCCI combustion can improve fuel efficiency compared to 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 . In contrast, in the present embodiment, as described above, the geometric compression ratio of the engine is increased, so that the temperature and pressure in the combustion chamber 6 can be increased near the top dead center of the compression stroke. , a portion of the air-fuel mixture can be CI-burned.

(First operating region)
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 being operated in the first operating region A1, the combustion control unit 102 controls the various parts of the engine as follows. be.

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 operating region A1, the injector 15 injects fuel in two stages from the middle to the latter half of the compression stroke. Specifically, the combustion control unit 102 calculates the torque requested of the engine from the engine speed and the degree of opening of the accelerator pedal, and calculates the amount of fuel required to achieve the requested torque. Then, combustion control unit 102 drives injector 15 so that all or most of the calculated amount of fuel is injected during the compression stroke. Hereinafter, the fuel injection for realizing the torque required for this engine will be referred to as main injection.

In the first operating region A1, the opening degree of the throttle valve 32 is near full open so that the air-fuel ratio (A/F) in the combustion chamber 6 becomes higher (lean) than the stoichiometric air-fuel ratio, and a large amount of air is supplied. 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 near the compression top dead center. The ignition timing at this time is set in advance and stored in the combustion control unit 102 in the same manner as during 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 and exhaust valves 11 and 12 are opened across the exhaust top dead center to realize internal EGR. The EGR valve 53 is opened to a predetermined degree of opening, and gas in the exhaust passage 40 is recirculated into the combustion chamber 6 as external EGR gas through the EGR passage 51 . Thus, in the first operating region A1, the air-fuel ratio (A/F) is set leaner than the stoichiometric air-fuel ratio as described above, and EGR gas (external EGR gas and internal EGR gas) is supplied to 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 low rotational speed side of 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, the supercharger 33 is turned on in the operating region A1 on the higher rotational speed side. That is, supercharging by the supercharger 33 is performed by engaging the electromagnetic clutch 34 and connecting the supercharger 33 and the engine body 1 . At this time, the pressure in the surge tank 36 (supercharging pressure) detected by the second intake pressure sensor SN7 matches the predetermined target pressure for each operating condition (rotational speed/load). 39 opening is controlled.

(Second operating region)
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 being operated in the second operating region A2, the combustion control unit 102 controls the various parts of the engine as follows. be.

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 performs the main injection by dividing it into an intake stroke and a compression stroke. That is, the injector 15 injects part of the amount of fuel 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 in the same manner as during the AWS control.

The intake VVT 13 and the exhaust VVT 14 are driven so that internal EGR is performed only in a part of the low load side of the second operating region A2 (in other words, internal EGR is stopped on the high load side). The EGR valve 53 is controlled such that the amount of exhaust gas (external EGR gas) recirculated through the EGR passage 51 decreases as the load increases. Near the maximum load of the engine, the EGR valve 53 is fully closed and the amount of external EGR gas is almost zero. Accordingly, even in the second operating region A2, the gas air-fuel ratio (G/F) in the combustion chamber 6 is made lean except near the maximum load of the engine.

The supercharger 33 is turned off in a region where both the rotation speed and the load are low in the second operating region A2. On the other hand, in other areas of the second operating 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 the predetermined temperature and that the engine is being operated in the third operating region A3, normal SI combustion is executed. . For example, the main injection is performed for a predetermined period that overlaps at least a part of the intake stroke, and spark ignition is performed by the spark plug 16 in the latter half of the compression stroke. This spark ignition initiates SI combustion, and all of the air-fuel mixture in the combustion chamber 6 burns due to flame propagation. Note that the ignition timing at this time is also set in advance and stored in the combustion control unit 102 in the same manner as during the AWS control.

(c) When Cold As described above, when the engine is warm, different combustion modes are realized depending on the operating range of the engine. On the other hand, when the calculation unit 101 determines that the engine coolant temperature is less than the predetermined temperature, that is, that the engine is cold, normal SI combustion is performed in all operating regions in the same manner as in the third operating region. be. Note that the ignition timing at this time is also set in advance and stored in the combustion control unit 102 in the same manner as during the AWS control.

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

As described above, the ignition timing is preset according to the operating conditions of the engine and stored in the combustion control unit 102. The combustion control unit 102 extracts a value according to the operating conditions of the engine and determines the ignition timing. set to For example, the ignition timing is set and mapped for each of the engine speed and the engine load. are respectively set and stored in combustion control unit 102 .

The ignition timing stored in the combustion control unit 102 is the timing determined based on experiments or the like as the timing at which the combustion of the air-fuel mixture in the combustion chamber 6 can be appropriately started. However, if there is a delay in the introduction of the external EGR gas into the combustion chamber 6 during a warm transition, there is a risk of premature ignition. This is because the temperature in the combustion chamber 6 becomes higher than the temperature when the ignition timing is set. Here, it is considered that pre-ignition occurs when the temperature inside the combustion chamber 6 is high, such as when the engine is warm. However, the inventors of the present application have found that pre-ignition may occur even during AWS control, which is performed when the temperature in the combustion chamber 6 is relatively low, such as when the engine is started. This is because the ignition timing is set to a relatively retarded timing in the AWS control as described above. It is possible that the air-fuel mixture will ignite earlier.

Accordingly, in the present embodiment, it is determined whether or not pre-ignition occurs during AWS control and during warm-up, and when it is determined that pre-ignition occurs, control is performed to prevent this. .

(premature ignition judgment)
A procedure for determining premature ignition will be described. This determination is made by the calculation unit 101 .

During execution of AWS control, the calculation unit 101 determines whether or not pre-ignition has actually occurred. Specifically, the calculation unit 101 calculates the heat release 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 a preset first determination value before the ignition timing, it is determined that pre-ignition has occurred. The first determination value is set to a value greater than zero.

On the other hand, the calculation unit 101 determines whether or not pre-ignition occurs when the engine is warm. Specifically, when the rate of increase of the in-cylinder pressure (amount of increase per unit time) reaches or exceeds the second determination value before the ignition timing, the calculation unit 101 determines that pre-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 when warm)
When it is determined by the calculation unit 101 that pre-ignition occurs during warm weather, the combustion control unit 102 causes the injector 15 to inject fuel separately from the main injection to supply additional fuel to the combustion chamber 6. .

When additional fuel is supplied into the combustion chamber 6, the latent heat of vaporization of this fuel causes the temperature of the air-fuel mixture in the combustion chamber 6 to drop. Therefore, the reaction of the air-fuel mixture becomes slow and premature ignition is prevented. Here, part of the added fuel may be discharged from the combustion chamber 6 unburned, but the three-way catalyst 41a is basically activated when the AWS control is not performed. Therefore, unburned fuel is purified by the three-way catalyst 41a, and exhaust gas performance is maintained satisfactorily.

(Premature ignition prevention control when AWS control is implemented)
As described above, when the engine is warm and the AWS control is not performed, the exhaust gas performance can be maintained satisfactorily while preventing premature ignition of the additional fuel injection. However, when AWS control is performed, the three-way catalyst 41a is not sufficiently activated, so if additional fuel injection is performed, unburned fuel may be discharged without being purified. Therefore, during execution of AWS control, the temperature in the combustion chamber 6 is lowered by reducing the amount of internal EGR gas instead of performing additional fuel injection, thereby preventing premature ignition. In this 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 execution of the AWS control, the combustion control unit 102 adjusts the intake VVT 13 so that the opening timing of the intake valve 11 is advanced by a predetermined amount. In addition to 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 valve 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 opening timing of the intake valve 11 and the closing timing of the exhaust valve 12 are determined by a command from the combustion control unit 102. The change is made shortly thereafter, and the valve overlap period is reduced in the combustion cycle following the combustion cycle in which pre-ignition was determined to have occurred.

The flow of control of the intake/exhaust valves 11 and 12 during AWS control is shown in the flow chart of FIG.

First, in step S1, the calculation unit 101 determines whether or not a condition for starting the AWS control is satisfied. As described above, in the present embodiment, when the temperature of the catalyst is less than the determination temperature while the accelerator pedal is not depressed and the AWS control has not yet started, the conditions for starting the AWS control are established. It is determined that If this determination is NO and the condition for starting the AWS control is not satisfied, the process proceeds to step S7. In step S7, the combustion control unit 102 performs normal control and ends the process (returns to step S1).

On the other hand, if 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 timings of the intake/exhaust valves 11 and 12 become the basic opening/closing timings.

After step S2, the process proceeds to step S3. In step S3, the calculation unit 101 determines whether or not pre-ignition has occurred. If the 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 timings of the intake/exhaust valves 11 and 12 at the current timings.

On the other hand, if the determination in step S3 is YES and premature ignition has occurred, 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 advances from the current opening timing (the opening timing in the previous calculation cycle) by the predetermined amount. At the same time, the exhaust VVT 14 is driven so that the closing timing of the exhaust valve 12 advances from the current closing timing (the closing timing in the previous calculation cycle) by the 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 reaches or exceeds the determination temperature, or when the accelerator pedal is depressed. If the determination in step S6 is YES and the calculation unit 101 determines to end the AWS control, the process proceeds to step S7, the combustion control unit 102 performs normal control and ends the process (returns to step S1).

On the other hand, if the determination in step S6 is NO and the calculation unit 101 determines to continue the AWS control, the process returns to step S3, and steps S3 to S6 are repeated. That is, until the AWS control ends, the calculation unit 101 continues to repeatedly determine whether or not pre-ignition has occurred, and each time it is determined that pre-ignition has occurred, the opening timing of the intake valve 11 is changed by a predetermined amount. The closing timing of the exhaust valve 12 is retarded by a predetermined amount.

(6) Effect 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 the catalyst is activated early and the exhaust gas performance is improved. can be enhanced. In particular, the internal EGR is performed when the AWS control is performed, and the high-temperature burned gas remains in the combustion chamber 6, thereby suppressing the discharge of unburned fuel and quickly reactivating the catalyst. can be activated.

Moreover, it is determined whether or not pre-ignition has occurred during the execution of the AWS control. The intake VVT 13 and the exhaust VVT 14 are controlled so that the amount of internal EGR gas in the combustion chamber 6 is reduced. Therefore, it is possible to reduce the temperature in the combustion chamber 6 by reducing the amount of high-temperature internal EGR gas, thereby suppressing the continuous occurrence of pre-ignition.

In this embodiment, as the intake/exhaust VVTs 13 and 14, electric VVTs that change the opening/closing phases of the valves by driving the electric motors 13a and 14a are used. Therefore, compared to the case of adopting a hydraulic VVT, for example, when it is determined that pre-ignition has occurred, the valve overlap period can be shortened quickly, and the internal EGR amount can be reduced with high response. can be done.

Further, in the present embodiment, the compression ratio of the cylinder 2 is increased to achieve SPCCI combustion. Premature ignition is likely to occur. On the other hand, it is possible to prevent the occurrence of pre-ignition as described above, and it is possible to appropriately burn the air-fuel mixture while improving the fuel efficiency.

(7) Modification In the above embodiment, when it is determined that pre-ignition has occurred during AWS control, both the intake and exhaust valves 11 and 12 open across the exhaust top dead center. Although the control for shortening the lap period (thereby reducing the internal EGR amount) is executed, it is sufficient if the valve timing can be changed in the direction to reduce the internal EGR amount, and various control can be adopted as long as it is possible. . For example, as control for reducing the internal EGR, control may be executed to advance the opening/closing timing of the exhaust valve 12 while maintaining the opening/closing timing of the intake valve 11 constant. This control also shortens the open 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 aforementioned control for shortening the valve overlap period (the period during which both the intake and exhaust valves 11 and 12 are open). For example, depending on the engine, as a control for realizing internal EGR, a so-called negative overlap period is formed in which both the intake and exhaust valves 11 and 12 are closed across the exhaust top dead center, thereby is confined in the combustion chamber 6. In this type of engine, when it is determined that pre-ignition has occurred during AWS control, the valve timing is changed to shorten the negative overlap period as the control to reduce the internal EGR. control should be executed.

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. It is not necessary to be able to change the opening and closing timing, and it is not necessary to provide a phase type variable mechanism (VVT) that simultaneously changes the valve opening timing and the valve closing timing by the same amount. In other words, the variable valve mechanism in the present invention may be any variable mechanism that can change at least one of the closing timing of the exhaust valve and the opening timing of the intake valve.

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) combining SI combustion and CI combustion has been described. Any engine that can adjust the output torque according to the ignition timing by an ignition device such as, for example, a conventional spark ignition engine that burns all of the air-fuel mixture with SI combustion (combustion by flame propagation from the ignition point) The present invention is applicable.

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

Furthermore, even during execution of AWS control, it is predicted whether or not pre-ignition will occur, rather than whether or not pre-ignition has actually occurred, and when it is predicted that pre-ignition will occur, the above-described Each VVT 13, 14 may be controlled so that the amount of internal EGR gas is reduced immediately. For example, when the maximum value of the in-cylinder pressure is equal to or greater than a predetermined value, it may be predicted that pre-ignition will occur in the next combustion cycle.

In the above embodiment, the air-fuel ratio in the combustion chamber 6 is set to the stoichiometric air-fuel ratio during AWS control. good too. Also, it may be made smaller than the stoichiometric air-fuel ratio. However, in order to achieve early activation of the three-way catalyst 41a, it is desirable that the air-fuel ratio in the combustion chamber 6 during AWS control is about 15.5 or less.

Further, the catalyst device provided in the exhaust passage and subject to the 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 (catalytic 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 discharging exhaust gas from the cylinder, a variable valve mechanism that changes at least one of the closing timing of the exhaust valve and the opening timing of the intake valve, and the exhaust discharged from the cylinder through the exhaust port. and a catalyst device provided in the exhaust passage for purifying exhaust gas, wherein
an injector that injects fuel into the cylinder;
A pre-ignition determination unit that predicts whether pre-ignition occurs in which the air-fuel mixture ignites before ignition by the ignition device occurs, or detects whether pre-ignition has occurred;
A combustion control unit that controls the air-fuel ratio changing device, the ignition device, and the variable valve mechanism,
The combustion control unit is
When the temperature of the catalyst device is lower than a preset reference temperature, the air-fuel ratio in the cylinder becomes close to the theoretical air-fuel ratio or lower than the theoretical air-fuel ratio, and the temperature of the catalyst device becomes lower than when the temperature of the catalyst device is equal to or 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 the burned gas remains in the cylinder. Carry out warm-up promotion control ,
When the temperature of the catalyst device is equal to or higher than the reference temperature, the air-fuel ratio in the cylinder becomes larger than the stoichiometric air-fuel ratio, ignition is performed at a predetermined timing, and both the intake valve and the exhaust valve are exhausted. Carrying out normal operation control for controlling the air-fuel ratio changing device, the ignition device, and the variable valve mechanism so as to open the valve for a predetermined period across top dead center;
When the pre-ignition determination unit predicts that pre-ignition occurs during the execution of the catalyst warm-up promotion control, or detects that pre-ignition has occurred, the burnt gas remaining in the cylinder is reduced. driving the variable valve mechanism in a direction in which the amount of
When the pre-ignition determination unit predicts that pre-ignition occurs during the execution of the normal operation control or detects that pre-ignition has occurred, the injector injects additional fuel into the cylinder. A control device for an engine , characterized in that In the engine control device according to claim 1,
An engine control device, wherein the variable valve mechanism is an electric variable mechanism that changes the opening/closing phase of a valve by driving an electric motor. The engine control device according to claim 1 or 2,
A control device for an engine, wherein the geometric compression ratio of the cylinder is set to 13 or more. In the engine control device according to claim 3,
At least when the temperature of the catalyst device is equal to or higher than the reference temperature, the combustion control unit causes part of the air-fuel mixture in the cylinder to undergo SI combustion by flame propagation from the ignition point of the ignition device, and the other air-fuel mixture is automatically burned. A control device for an engine, characterized in that it executes partial compression ignition combustion in which CI combustion is performed by ignition.

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