JP2003201897A - Control device of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide countermeasures that ensure the combustion stability and improve fuel consumption, in a device in which, the mode is forced to switch to a uniform charge combustion mode from a stratified charge combustion mode that has been carried out, when the variation between actual combustion pressure and target combustion pressure is equal to or larger than a predetermined value. <P>SOLUTION: In a cylinder injection type engine in which combustion modes are switched based on the operational condition of an engine, an ECU sets a target value of pressure of fuel that is supplied to a fuel injection valve, controls a high pressure fuel pump so that the variation of the fuel pressure between the target fuel pressure and the actual fuel pressure becomes small. When the variation of the fuel pressure in the stratified charge combustion mode is equal or larger than the predetermined values ΔF2, ΔF2', the combustion mode is forced to switch to the uniform charge combustion mode. This predetermined value is set larger as the engine revolution speed is higher. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an engine, and more particularly, to a control device for a direct injection engine in which fuel is directly injected into a combustion chamber, and belongs to the technical field of engine control.

[0002]

2. Description of the Related Art Conventionally, there is known an engine in which a combustion mode is switched between a stratified combustion mode and a homogeneous combustion mode based on an operating state of the engine in order to improve fuel efficiency and secure output. With such an engine,
Generally, the fuel injection valve is arranged so as to face the inside of the cylinder, and the fuel is directly injected from the fuel injection valve into the combustion chamber.

In the stratified charge combustion mode, fuel is injected in the compression stroke. The injected fuel is collected around the electrodes of the spark plug using the cavity (wall guide) formed on the piston crown surface and the intake flow (air guide) such as tumble flow, and in an air-fuel ratio state where ignition is possible. Stratify. The average air-fuel ratio of the air-fuel mixture in the entire combustion chamber is larger than the theoretical air-fuel ratio (for example, A / F> 25), and the fuel efficiency is improved in a lean state. The stratified charge combustion mode is executed in a low load low rotation speed region where output is not so required.

On the other hand, in the homogeneous combustion mode, fuel is injected in the intake stroke. The injected fuel is sufficiently mixed with intake air, and the combustion chamber is filled with a homogeneous mixture that is easy to burn. The air-fuel ratio of the air-fuel mixture is almost the theoretical air-fuel ratio (A / F = 14.7),
Alternatively, it is made slightly smaller (for example, A / F = 13), and a high output is secured in a rich state. The homogeneous combustion mode is
It is executed in a high load and high rotation region where high output is required.

In such an in-cylinder injection type engine, it is necessary to directly inject a predetermined amount of fuel into the high pressure combustion chamber within a short time, and therefore, the high pressure (for example, 3 to 13 MPa) is applied to the fuel injection valve.
A high-pressure fuel supply system is provided as a means for supplying the fuel. This fuel supply system includes a high pressure fuel pump, a high pressure regulator, and the like. Then, the pressure of the fuel supplied to the fuel injection valve by this high-pressure fuel supply system is detected by the fuel pressure sensor,
The fuel supply system performs feedback control so that the deviation between the actual fuel pressure and the target fuel pressure that is separately set based on the operating state of the engine (for example, engine rotation speed, fuel injection amount, combustion chamber temperature state, etc.) becomes small. To be done. As a result, when a drive pulse signal with a predetermined pulse width (valve opening time) is output to the fuel injection valve, a predetermined amount of fuel is injected into the combustion chamber, and the optimum air-fuel ratio that matches the operating state or combustion mode of the engine is obtained. To be achieved.

[0006] Such control of the fuel supply system, and further control of the fuel pressure, is achieved by controlling the electric pump when an electric high-pressure pump is used as the high-pressure fuel pump, for example. Alternatively, when a solenoid valve is used as the high-pressure regulator, it is achieved by controlling the solenoid valve.

Therefore, when an abnormality or failure occurs in the fuel supply system such as a high-pressure fuel pump or a high-pressure regulator, the fuel pressure cannot be controlled, and the actual fuel pressure largely deviates from the target fuel pressure, the same pulse is generated. Even if the width is given, the amount of fuel injection from the fuel injection valve fluctuates and the optimum air-fuel ratio cannot be achieved. In particular, if the fuel pressure deviation between the actual fuel pressure and the target fuel pressure becomes large during execution of the stratified charge combustion mode, the following various problems will occur.

That is, in the stratified combustion mode, the air-fuel mixture is made as lean as possible and the fuel spray is unevenly distributed around the plug to obtain explosive combustion energy. Therefore, as mentioned above, the injected fuel is
It is gathered around the plug and stratified by using the intake flow such as the cavity of the piston crown surface and tumble flow. The success of such stratification depends on the penetration force of the fuel spray in addition to the cavity shape and the tumble flow rate.
Therefore, whether the actual fuel pressure supplied to the fuel injection valve deviates from the target fuel pressure to the lower side or the higher side, the fuel injection pressure from the fuel injection valve decreases or becomes excessive, and the penetration force of the fuel spray is increased. In either case, the balance between the penetrating force of the fuel spray and the cavity shape or the tumble flow rate is lost, stratification does not work well, and ignition becomes difficult.

Even if the stratification is successful, if the actual fuel pressure deviates from the target fuel pressure to the lower side, the fuel injection amount becomes insufficient and the air-fuel ratio becomes excessively lean.
The flammability is insufficient and the possibility of misfire increases. However, in this case, it is possible to increase the fuel injection amount by lengthening the pulse width of the drive pulse signal. However, then, as the valve opening time becomes longer, the fuel pressure further decreases, the penetrating force of the fuel spray is further weakened, and it becomes even more difficult to counter the intake flow, making stratification even more difficult. . Further, the fuel pressure further decreases, which causes a problem that the promotion of atomization and atomization of the fuel is hindered.

On the other hand, when the actual fuel pressure deviates from the target fuel pressure to the higher side, the penetrating force of the fuel spray increases, so that the amount of fuel adhering to the piston crown surface and the cavity wall surface increases, and Problems such as an increase in unburned hydrocarbons (HC) also occur. Not only that, because it is not possible to secure the time for vaporization and atomization of the fuel, it becomes difficult for the fuel to get into the intake flow, which is one of the causes of difficulty in stratification.

As a technique capable of coping with this, Japanese Patent Laid-Open No.
Japanese Unexamined Patent Publication No. 0-145517 discloses that when the actual fuel pressure is lower than the target fuel pressure by a predetermined value or more, the combustion mode is fixed to the homogeneous combustion mode. By doing this, even if the stratified charge combustion mode is selected based on the operating condition of the engine,
Switching from homogeneous combustion mode to stratified combustion mode is prohibited. Alternatively, if the stratified combustion mode is being executed, the homogeneous combustion mode is forcibly switched. This allows
As described above, it is possible to avoid problems such as engine stall due to misfire due to poor stratification.

[0012]

However, in the above technique, the above-mentioned predetermined value, which is a criterion for determining whether or not the combustion mode is switched to the homogeneous combustion mode, is a fixed value. Remains.

That is, since the combustion stability of the engine generally tends to decrease as the engine speed decreases, the effect of the decrease in the fuel pressure by the above-mentioned predetermined value is remarkable when the engine speed is lower than when the engine speed is high. Appear in. When the fuel pressure decreases when the engine speed is low, the combustion stability further decreases, and there is a strong possibility that a stable engine operating state cannot be ensured, but since the predetermined value is a fixed value as described above, It is difficult to switch to the homogeneous combustion mode.

On the other hand, when the engine speed is high, the engine operating condition is more stable than when the engine speed is low. Therefore, even if the actual fuel pressure falls below the target fuel pressure by the predetermined value, Little impact. That is, when the engine speed is high, than when the engine speed is low,
Although it is possible to suppress the switching to the homogeneous combustion mode, in the above technology, since the predetermined value is a fixed value as described above, it is possible to switch to the homogeneous combustion mode more than necessary, resulting in the stratified combustion mode. The fuel economy, which is one of the greatest features of the engine, is sacrificed, which is not preferable and the commercialability of the engine deteriorates.

The present invention has been made in view of the above situation, and when the deviation between the actual fuel pressure and the target fuel pressure exceeds a predetermined value during execution of the stratified charge combustion mode, the homogeneous combustion mode is forcibly forced. It is an object of the present invention to provide a countermeasure that can improve fuel efficiency while ensuring combustion stability.

[0016]

That is, the invention according to claim 1 is provided with a fuel injection valve for directly injecting fuel into the combustion chamber, and the combustion mode is changed to the stratified combustion mode and the homogeneous combustion based on the operating state of the engine. A control device for an engine adapted to switch between a fuel injection valve and a fuel injection valve, and fuel pressure detection means for detecting a pressure of fuel supplied to the fuel injection valve by the fuel supply valve. And a target fuel pressure setting means for setting a target value of the pressure of the fuel supplied to the fuel injection valve based on the operating state of the engine, a target fuel pressure set by the setting means, and an actual fuel pressure detected by the detecting means. The fuel pressure control means for controlling the fuel supply means so that the deviation of the fuel pressure is smaller than the first predetermined value during the execution of the stratified charge combustion mode. A combustion mode switching means for switching the forced homogeneous combustion mode regardless of the rotation state, characterized in that is provided with setting means for setting a larger value to the predetermined value the larger the engine rotational speed.

According to the present invention, the predetermined value as the threshold value for forcibly switching the combustion mode to the homogeneous combustion mode during execution of the stratified combustion mode is set to a larger value as the engine speed increases. The smaller the engine speed, the easier it is to switch to the homogeneous combustion mode. That is, when the engine speed is low, the homogeneous combustion mode is relatively quickly switched to ensure combustion stability, and when the engine speed is high, unnecessary switching to the homogeneous combustion mode is reduced, and fuel consumption is improved. .

Next, the invention according to claim 2 relates to claim 1.
In the invention described in (1), when the actual fuel pressure is lower than the target fuel pressure, the setting means sets the predetermined value to a larger value than when the actual fuel pressure is higher than the target fuel pressure.

The present invention, during execution of the stratified charge combustion mode,
If the deviation between the actual fuel pressure and the target fuel pressure exceeds the specified value,
In the case of forcibly switching to the homogeneous combustion mode, the purpose is to improve fuel efficiency while ensuring combustion stability.However, when the actual fuel pressure is higher than the target fuel pressure, the combustion stability and In addition to the problem of fuel economy, problems such as poor stratification and exhaust emission are likely to occur. Therefore, when the actual fuel pressure is higher than the target fuel pressure, it is easier to switch from the normal stratified charge combustion operation to the homogeneous combustion operation than when the actual fuel pressure is low, and the problems of stratification failure and exhaust emission are less likely to occur.

Next, the invention described in claim 3 is the same as claim 1
Alternatively, when the fuel pressure deviation is smaller than a predetermined value but larger than a second predetermined value which is smaller than the predetermined value during execution of the stratified charge combustion mode, the fuel injection by the fuel injection valve is performed. It is characterized in that an injection mode changing means for changing the mode is provided.

As described above, according to the present invention, when the deviation of the fuel pressure between the actual fuel pressure and the target fuel pressure becomes a predetermined value or more during execution of the stratified charge combustion mode, the combustion is stably switched to the homogeneous combustion mode. The purpose of this is to improve fuel efficiency while ensuring fuel economy, but the stratified charge combustion mode is maintained until the fuel pressure deviation exceeds a predetermined value. However, even within the range where this stratified charge combustion mode is maintained, when the fuel pressure deviation is large, the above-mentioned problems of stratification failure and emission reduction become greater than when it is small. Therefore, in the present invention, the fuel pressure deviation between the actual fuel pressure and the target fuel pressure does not increase until switching to the homogeneous combustion mode, but when it has increased to a certain extent, the mode of fuel injection is changed for the time being, as described above. The problems of stratification failure and emission are dealt with to maintain the stratified combustion mode. Hereinafter, the present invention will be described in more detail through embodiments of the invention.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the overall structure of a cylinder injection type engine 1 according to an embodiment of the present invention. The engine 1 has a cylinder block 3 in which a plurality of cylinders 2 ... 2 (only one is shown) are arranged in series, and a cylinder head 4 mounted on the cylinder block 3. A piston 5 is vertically reciprocally fitted in each cylinder 2 to define a combustion chamber 6. A crankshaft 7 is rotatably supported by the cylinder block 3, and a piston 5 is connected to the crankshaft 7 by a connecting rod 8. An electromagnetic pickup type crank angle sensor 9 for detecting a crank angle is provided on one end side of the crank shaft 7.

The combustion chamber 6 is of a pent roof type. The ceiling of the combustion chamber 6 has a roof shape with two inclined surfaces extending to the lower end of the cylinder head 4. Two intake ports 10 and 10 or exhaust ports 11 and 11 (only one of each is shown) are opened on each inclined surface. An intake valve 12 or an exhaust valve 13 is provided at each opening. Intake port 1
Numerals 0 and 10 linearly extend obliquely upward from the combustion chamber 6 and are independently opened on the side surface (the right side surface in FIG. 1) of the engine 1. The exhaust ports 11 and 11 extend horizontally immediately from the combustion chamber 6, merge into one on the way, and open to the other side surface of the engine 1 (left side surface in FIG. 1).

The engine 1 is a well-known variable valve mechanism 1
4 and 14 are provided. That is, the rotation phases of the intake-side and exhaust-side cam shafts (not shown) for opening and closing the intake valve 12 and the exhaust valve 13 with respect to the crankshaft 7 are continuously maintained within a predetermined angle range by the variable valve operating mechanisms 14, 14. Of the intake valve 12 and the exhaust valve 13
The opening / closing operation timing of is changed independently.

At the top of the combustion chamber 6, the above four intake / exhaust valves 1
An ignition plug 16 is arranged surrounded by 2, 12, 13, and 13. The electrode at the tip of the spark plug 16 is located at a position protruding from the ceiling of the combustion chamber 6 by a predetermined length. On the other hand, the base end portion of the ignition plug 16 is connected to an ignition circuit 17, and the ignition circuit 17 energizes each ignition plug 16 at a predetermined ignition timing for each cylinder 2. The crown surface of the piston 5 that forms the bottom of the combustion chamber 6 is shaped so as to follow the ceiling of the combustion chamber 6 that faces it. A concave portion 5a (see FIG. 3) having a predetermined shape is formed in the center of the crown surface of the piston 5.

At the ceiling of the combustion chamber 6, the intake port 1
Injector (fuel injection valve) so that it is sandwiched between 0 and 10
18 is arranged so as to face the combustion chamber 6. The injector 18 directly injects fuel into the combustion chamber 6 from a position slightly below the intake ports 10, 10. This injector 1
Reference numeral 8 is a known swirl injector for ejecting a fuel into a swirling flow from an injection hole at the tip. The injected fuel has a hollow cone shape that is coaxial with the axis of the injector 18.
In this injector 18, the higher the fuel injection pressure and the smaller the spread angle of the spray, the higher the penetration force of the fuel spray.

A base end portion of each injector 18 ... 18 is connected to a fuel distribution pipe 19 common to all the cylinders 2 ... The fuel distribution pipe 19 distributes the high-pressure fuel supplied from the fuel supply system 20 to the cylinders 2 ... The high pressure fuel supply system 20 is configured, for example, as shown in FIG. Fuel distribution pipe 1
A low-pressure fuel pump 23, a low-pressure regulator 24, a fuel filter 25, a high-pressure fuel pump 26, and a high-pressure regulator 27 are arranged in this order from the upstream side to the downstream side of a fuel passage 22 that communicates 9 with the fuel tank 21.

The fuel tank 21 is driven by the low-pressure fuel pump 23.
The fuel sucked up from is regulated by the low pressure regulator 24, filtered by the filter 25, and sent under pressure to the high pressure fuel pump 26. The high pressure fuel pump 26 and the high pressure regulator 27 are connected to the fuel tank 21 through a return passage 29. The return passage 29 is provided with a low pressure regulator 28 for adjusting the pressure of the fuel returned to the fuel tank 21. A part of the fuel boosted by the high-pressure fuel pump 26 is returned to the fuel tank 21 through the return passage 29 while the flow rate is adjusted by the high-pressure regulator 27.

The high pressure regulator 27 is composed of a solenoid valve. That is, the high-pressure regulator 27 is controlled by controlling the energization time and the energization timing for the solenoid valve, and as a result, the pressure state of the fuel supplied to the fuel distribution pipe 19 is set to an appropriate value (for example, 3 to 13 MPa, during stratified charge combustion operation). 4-7 MPa). In the fuel supply system 20 shown in FIG. 2A, the high pressure regulator 27 has the injector 1
The fuel injection pressure by 8, that is, the penetration force of the fuel spray is adjusted. A fuel pressure sensor 53 that detects the fuel pressure supplied from the fuel supply system 20 to the injector 18 is provided in the fuel distribution pipe 19.

Instead of this, a high pressure fuel supply system 20 'having a structure as shown in FIG. 2 (b) may be adopted. In this fuel supply system 20 ', an electrically driven high pressure pump 26' capable of changing the discharge amount of fuel as a high pressure fuel pump over a wide range.
Is used. By controlling the electric pump 26 ', the discharge amount of fuel from the pump 26' to the fuel distribution pipe 19 can be adjusted, whereby the fuel distribution pipe 1
It is possible to control the pressure state of the fuel supplied to 9. In this case, the electric high pressure pump 26 ′ adjusts the fuel injection pressure of the injector 18. In the fuel supply system 20 of FIG. 2B, the high pressure regulator 2
7 and the return passage 29 can be omitted.

Returning to FIG. 1, an intake passage 30 is arranged on the side surface of the engine 1 (right side surface in FIG. 1). Intake passage 30
Communicates with the intake ports 10, 10 of each cylinder 2 and supplies intake air filtered by an air cleaner (not shown) to the combustion chamber 6. In the intake passage 30, a hot wire type air flow sensor 31 for detecting the amount of intake air taken into the engine 1 from the upstream side to the downstream side, an electric throttle valve 32 for adjusting the opening degree of the intake passage 30, and a surge tank. 33 and the like are provided. Although not shown, the throttle valve 32 is not mechanically connected to the accelerator pedal and is driven by an electric drive motor.

Intake passage 3 downstream of the surge tank 33
Reference numeral 0 is an independent passage branched for each cylinder 2. The downstream end of each independent passage is further branched into two, and each intake port 10,
It communicates with 10. Intake flow (air motion, air guide) for adjusting the flow velocity of the tumble flow T (see FIG. 3) generated in the combustion chamber 6 on the upstream side of each intake port 10.
A control valve 34 is provided. This valve 34 has a shape in which a circular butterfly valve is partially cut away, and is preferably precisely opened and closed by a stepping motor. When the intake flow control valve 34 is closed, intake air flows downstream only from the cutout portion of the valve 34, and a strong tumble flow T is generated in the combustion chamber 6. On the other hand, as the intake flow control valve 34 opens, the intake air also flows from other than the cutout portion of the valve 34,
The strength of the tumble flow T is gradually weakened.

As shown in FIGS. 3B to 3C, the cylinder 2
Of the spark plug 16 and the piston 5 in the compression stroke of the
The tumble flow T is flowing toward the injector 18 between the front surface and the crown surface. The intake flow control valve 34 and the stepping motor control the flow rate of the tumble flow T to increase or decrease.

Returning to FIG. 1, the other side surface of the engine 1 (see FIG.
An exhaust passage 36 for exhausting burnt gas (exhaust gas) from the combustion chamber 6 is disposed on the left side surface of the exhaust chamber. An upstream end of the exhaust passage 36 is an exhaust manifold 37 that branches for each cylinder 2 and communicates with the exhaust port 11. A linear O ₂ sensor 3 for detecting the residual oxygen concentration in the exhaust gas at the collecting portion of the exhaust manifold 37
8 are provided. The air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is detected based on the detection result of the sensor 38. The sensor 38 produces a linear output with respect to the oxygen concentration in a predetermined air-fuel ratio range including the stoichiometric air-fuel ratio.

An exhaust pipe 39 is provided at the collecting portion of the exhaust manifold 37.
Is connected to the upstream end of the exhaust pipe 39, and a catalyst device 40 for purifying exhaust gas is connected to the downstream end of the exhaust pipe 39. This catalytic device 4
0 absorbs NOx in an atmosphere where the oxygen concentration in the exhaust is high, while NOx absorbed when the oxygen concentration in the exhaust decreases.
It is a NOx absorption reduction type catalyst device that releases and purifies by reduction. This catalyst device 40 exhibits high exhaust purification performance at the same level as the three-way catalyst in the vicinity of the theoretical air-fuel ratio. A known lambda O ₂ sensor 41 used for determining the deterioration state of the catalyst device 40 is disposed downstream of the catalyst device 40. The output of the sensor 41 reverses stepwise at the stoichiometric air-fuel ratio. A three-way catalyst may be arranged in series with the NOx absorption reduction type catalyst device 40.

An upstream end of the EGR passage 43 opens at an upstream portion of the exhaust pipe 39. The EGR passage 43 recirculates a part of the exhaust gas flowing through the exhaust passage 36 to the intake passage 30. EGR
The downstream end of the passage 43 is connected to the intake passage 30 downstream of the throttle valve 32. An electric EGR valve 44 is disposed near the downstream end of the EGR passage 43, and the EGR valve 44 is used to
The amount of exhaust gas recirculated through the R passage 43 is adjusted.

Engine control unit (ECU)
Reference numeral 50 denotes the variable valve mechanism 14, 14, each of the cylinders 2 ... 2
Ignition circuit 17 of each spark plug 16 ... 16, Injector 18 ... 18, High pressure regulator 27 of fuel supply system 20
(In the case of the configuration of FIG. 2A) or electric high-pressure pump 26 '(in the case of the configuration of FIG. 2B), electric throttle valve 32 (driving motor), intake flow control valve 34 (stepping motor thereof) ), And controls the operation of the electric EGR valve 44 and the like. The ECU 50 receives at least output signals from the crank angle sensor 9, the air flow sensor 31, the linear O ₂ sensor 38, the lambda O ₂ sensor 41, and the like, and also detects the opening degree of the accelerator pedal (accelerator operation amount). Output signal from opening sensor 51, engine 1
The output signal from the rotation speed sensor 52 that detects the rotation speed (rotation speed of the crankshaft 7), the output signal from the fuel pressure sensor 53 that detects the fuel pressure supplied from the fuel supply system 20 to the injector 18, and the like are input.

The ECU 50 determines the intake / exhaust valves 12, 12, 1 based on the operating state of the engine 1 indicated by these input signals.
3, 13 opening / closing operation timing, fuel injection amount / injection timing / injection pressure (injection force of fuel spray) by the injector 18, intake air amount adjusted by the throttle valve 32, and tumble flow adjusted by the intake flow control valve 34. The flow rate / strength of T, the exhaust gas recirculation ratio adjusted by the EGR valve 44, and the like are controlled.

As shown in FIG. 4 by way of example, in the warm state of the engine 1, the operating region on the low load and low rotation side is the region where stratified charge combustion should be executed. In this stratified charge combustion region, the injector 18 is provided at a predetermined timing in the compression stroke of the cylinder 2 (for example, during stratified charge combustion operation, as shown in FIG. 12 (a), a range from 40 ° to 140 ° before compression top dead center BTDC). Fuel is injected from. Spark plug 16 for fuel spray
Are unevenly distributed in layers near the electrodes of the spark plug 1 in this state.
6 is ignited by sparks and burned (stratified combustion mode). In this stratified charge combustion mode, the opening of the throttle valve 32 is relatively increased in order to reduce the intake loss of the engine 1. As a result, the average air-fuel ratio in the combustion chamber 6 becomes leaner (larger value) than the stoichiometric air-fuel ratio (for example, A / F> 25), and fuel efficiency is improved.

On the other hand, the operating region on the high load to high rotation side other than the stratified charge combustion region is a region where homogeneous combustion should be executed.
In this homogeneous combustion region, fuel is injected from the injector 18 in the intake stroke of the cylinder 2. The injected fuel sufficiently mixes with the intake air, and the air-fuel mixture fills the combustion chamber 6 in a homogeneous state, and in this state, spark ignition is performed by the spark plug 16 and combustion (homogeneous combustion mode). In this homogeneous combustion mode, the fuel injection amount, throttle opening degree, etc. are controlled so that the air-fuel ratio of the air-fuel mixture becomes approximately the theoretical air-fuel ratio (A / F≈14.7) in most operating regions. However, in the full load region or the like, the air-fuel ratio is set to a richer state (smaller value) than the stoichiometric air-fuel ratio (for example, A / F = 13). As a result, a high output corresponding to a high load can be obtained.

Further, when the engine 1 is warm, the hatched area in FIG. 4 is the EGR area. In this region, the EGR valve 44 is opened to recirculate a part of the exhaust gas to the intake passage 30 side to suppress the generation of NOx. At this time, EG
The opening degree of the R valve 44 is adjusted according to the load state and the rotation speed of the engine 1 such that the EGR rate (exhaust gas recirculation rate) becomes smaller at least on the higher load side. This allows
When high output is required, insufficient output of the engine 1 and reduction of combustion stability can be prevented. When the engine 1 is cold, the homogeneity combustion mode is set in all operating regions of the engine 1 with the highest priority given to ensuring combustion stability. The EGR region is eliminated and the EGR valve 44 is always fully closed.

Further, as shown in FIG. 5 as an example, in the operating region of relatively low load and low rotation and in the operating region of extremely low load and high rotation, fuel is single-injected from the injector 18.
That is, the injector 18 is opened once so that the entire amount of fuel is injected (see FIG. 12A). Therefore, the single injection region is set to the low load low rotation region where the fuel demand is relatively small. On the other hand, in a relatively high load operation region, the fuel is dividedly injected from the injector 18 regardless of the rotation speed. That is, the injector 18 is opened a plurality of times (typically twice) so that the entire amount of fuel is injected (see FIG. 11A). Therefore, the divided injection region is set to a high load region where the required fuel amount is relatively large. The control map shown in FIG. 4 and the control map shown in FIG. 5 are used to achieve different purposes. Therefore, in the stratified combustion mode, single injection may be performed or divided injection may be performed. The same applies to the homogeneous combustion mode.

In the engine 1, as described above, when operating in the stratified charge combustion mode, the tumble flow T generated in the combustion chamber 6 is fully utilized, and the behavior of the fuel spray is controlled by the tumble flow T. And proper stratification of the air-fuel mixture,
We are also trying to optimize the air-fuel ratio in the stratosphere. That is, when the operating state of the engine 1 is in the stratified charge combustion region,
As shown in FIG. 3A, the tumble flow T generated in the intake stroke of each cylinder 2 is held until the latter half of the compression stroke of the cylinder 2 as shown in FIG. 3B. Then, the fuel is injected from the injector 18 so as to collide with the tumble flow T from a direction substantially facing the tumble flow T.

By doing so, the fuel spray moves toward the ignition plug 16 while being gradually decelerated by the tumble flow T, and during that time, vaporization and atomization of fuel droplets and mixing with air are promoted. Then, at the ignition timing of the cylinder 2, a combustible air-fuel mixture is formed and stays in the vicinity of the electrode of the ignition plug 16 as shown in a dark state in FIG. Therefore, the penetration force of the fuel spray from the injector 18 adjusted by the high-pressure regulator 27 or the electric high-pressure pump 26 'is adjusted according to the flow rate of the tumble flow T adjusted by the intake flow control valve 34. Further, the injector 18 is opened by a predetermined pulse width at a predetermined timing which is calculated back from the ignition timing of the cylinder 2, and a predetermined amount of fuel is injected. Such operation control of the injector 18 is performed by the ECU 50 according to a predetermined control program.

Next, the combustion mode switching control in the engine 1 will be described with reference to the flow charts shown in FIGS. This combustion mode switching control is performed by a plurality of programs such as the high-pressure fuel pump discharge amount feedback control of FIG. 6, the high-pressure fuel pump abnormality determination of FIG. 7, the fuel control mode determination of FIG. 8, each parameter control of FIG. The data detected and calculated by the program is stored in the ECU 50 as needed, the data stored in the ECU 50 is read out as necessary, and is repeatedly executed concurrently in parallel with a predetermined control cycle during operation of the engine 1. It is achieved by Here, various state quantities (engine operating state) such as engine rotation speed, engine load, engine temperature, actual fuel pressure, operation mode (including combustion mode of FIG. 4 and injection mode of FIG. 5) are the fuel of FIG. Control mode determination step S
At 21, it is detected.

First, the high pressure fuel pump discharge amount feedback control shown in FIG. 6 will be described. First, step S
At 1, the actual fuel pressure is input. Next, in steps S2 and S3, the target discharge amount of fuel from the high-pressure fuel pumps 26, 26 'and the target fuel pressure are set based on the actual fuel pressure and the like. Here, this target fuel pressure is set according to the combustion mode and the engine rotation speed. In step S4,
A fuel pressure deviation ΔF between the actual fuel pressure and the target fuel pressure is calculated. In addition,
The fuel pressure deviation ΔF is an absolute value of (actual fuel pressure-target fuel pressure).

Next, at step S5, it is judged from various state quantities whether or not the fuel pressure feedback condition is satisfied. If the fuel pressure feedback condition is satisfied, then at step S6, the actual fuel pressure is equal to the target fuel pressure. The target fuel pressure feedback control is performed so that when the fuel pressure feedback condition is not satisfied, the process bypasses step S6 and returns to the start. In order for the fuel pressure feedback control condition to be satisfied, for example, it is not in the start mode,
The conditions are that the engine is not in the stalled mode, various sensors including the fuel pressure sensor are normal, and the high-pressure fuel pumps 26, 26 'are not abnormal.

At this time, the high-pressure regulator 27 or the electric high-pressure pump 26 'of the high-pressure fuel supply system 20 is feedback-controlled so that the fuel pressure deviation ΔF becomes as small as possible. As a result, the injector 18 outputs the drive pulse signal having the optimized injection pulse width (valve opening time).
When it is output to, the injector 18 injects an appropriate amount of fuel into the combustion chamber 6, and the air-fuel ratio converges to an optimum air-fuel ratio that matches the operating state or combustion mode of the engine.

Next, the high pressure fuel pump abnormality determination shown in FIG. 7 will be described. First, in step S11, it is determined whether or not an abnormality determination condition for the high pressure fuel pumps 26, 26 'is satisfied. Here, the conditions for determining the abnormality of the high-pressure fuel pump include, for example, conditions in which various sensors are normal and are not in the start mode, the engine stall mode, and the fuel cut mode. Then, if the abnormality determination condition is satisfied in step S11, the process proceeds to step S12, and if the condition is not satisfied, it is determined in step S17 that there is no abnormality in the high pressure fuel pump and the high pressure fuel pumps 26, 26 are detected. Reset the error judgment of '.

Then, in step S12, when the stratified charge combustion mode is being executed, the first abnormality determination value used for determining the combustion mode from the stratified charge combustion mode to the homogeneous combustion mode and the determination for changing the injection mode are performed. The second abnormality determination value used is calculated.

Here, as shown in FIGS. 10A and 10B, different values are set for the first and second abnormality determination values depending on whether the actual fuel pressure is higher than the target fuel pressure. That is, when the actual fuel pressure is higher than the target fuel pressure, the first and second
ΔF1 and ΔF2 are set as the abnormality determination values, and when they are smaller, ΔF1 ′ and ΔF2 ′ are set as the first and second abnormality determination values.
Is set.

Further, each abnormality determination value ΔF1, ΔF1 ', Δ
F2 and ΔF2 ′ are set to smaller values as the engine speed is lower. That is, when the engine speed is low, compared to when the engine speed is high, the normal stratified charge combustion operation is switched to the stratified combustion maintenance operation by changing the fuel injection mode, and the stratified combustion maintenance operation is switched to the homogeneous combustion operation. Is likely to occur. This is because the lower the engine speed, the more unstable the combustion (that is, the low engine speed region is the region where the combustion stability is insufficient), and therefore the possibility of misfire or engine stall is eliminated as early as possible. .

Further, as is clear by comparing FIGS. 10A and 10B, the first and second abnormality determination values ΔF1 and ΔF2 when the actual fuel pressure is higher than the target fuel pressure are the corresponding actual fuel pressures. Is smaller than the target fuel pressure, the first and second abnormality determination values ΔF
The value is smaller than 1 ', ΔF2'. That is, when the actual fuel pressure is higher than the target fuel pressure, compared to when it is low, the normal stratified charge combustion operation is switched to the stratified charge combustion maintaining operation by changing the fuel injection mode, and the stratified charge combustion maintaining operation is changed to the homogeneous combustion operation. Switching tends to occur.

This is because, as described above, when the fuel pressure is high, not only the problem of stratification but also the problem of exhaust emission occurs, and the stratified combustion maintaining operation by changing the fuel injection mode is compared. The main reason is that it is difficult. On the other hand, when the fuel pressure is low, the stratification can be maintained by increasing the fuel injection amount by, for example, lengthening the pulse width of the drive pulse signal without changing the fuel injection mode (split injection or injection timing). It is possible to
The range in which the fuel injection mode can be changed to maintain and continue the stratified charge combustion operation is relatively wide.

That is, when the engine speed is low, the homogeneous combustion mode is relatively quickly switched to ensure combustion stability, and when the engine speed is high, unnecessary switching to the homogeneous combustion mode is reduced to reduce fuel consumption. It is possible to improve fuel efficiency and ensure combustion stability at the same time.

Next, at step S13, the fuel pressure deviation ΔF calculated at step S4 of the high pressure fuel pump discharge amount feedback control of FIG. 7 is read. Next, at step S14, this fuel pressure deviation ΔF is compared with the first abnormality determination value ΔF1.
Or ΔF1 '(ΔF1' when the actual fuel pressure is higher than the target fuel pressure
1, ΔF1 'when the actual fuel pressure is lower than the target fuel pressure. Corresponding to the second predetermined value of claim 3. ) It is determined whether or not it is larger, and when it is smaller, it means that the actual fuel pressure is within the allowable range. Therefore, in step S17, the high pressure fuel pumps 26, 2
Reset 6'abnormality judgment. Then, the fuel pressure deviation ΔF
Is greater than the first abnormality determination value ΔF1 or ΔF1 ′, then in step S15, the fuel pressure deviation ΔF is the second abnormality determination value ΔF2 or ΔF2 ′ (if the actual fuel pressure is greater than the target fuel pressure, ΔF2, the actual fuel pressure is the target). Δ when smaller than fuel pressure
F2 '. In the following description, this description will be omitted). Then, step S15
When it is determined that the fuel pressure deviation ΔF is larger than the second abnormality determination value ΔF2, it is determined in step S16 that “high-pressure fuel pump abnormality 2”, and when it is determined that the difference is smaller than the second abnormality determination value ΔF2. In step S15, it is determined that "high-pressure fuel pump abnormality 1".

Next, the fuel control mode determination shown in FIG. 8 will be described. First, as described above, step S21
Then, various state quantities such as engine rotation speed, engine load, engine temperature, actual fuel pressure, operation mode (including the combustion mode of FIG. 4 and the injection mode of FIG. 5) indicating the operating state of the engine are detected.

Next, in step S22, the results of the high-pressure fuel pump abnormality determination of FIG. 7 (high-pressure fuel pump abnormality 1, high-pressure fuel pump abnormality 2, no high-pressure fuel pump abnormality) are input, and in step S23, the stratified charge combustion mode is set. It is determined whether or not the condition to be satisfied is satisfied. If the condition is satisfied, the stratified combustion mode is executed in step S4, and if the condition is not satisfied, the homogeneous combustion mode is executed in step S5. The conditions for determining whether the stratified charge combustion mode is established are that the engine is not in the start & engine mode, the engine speed is equal to or lower than a predetermined speed, the target fuel pressure is equal to or lower than a predetermined value, and the high-pressure fuel pump abnormality input in step S22. The determination result may be that the high-pressure fuel pump abnormality is not 1. That is, from the result of the high-pressure fuel pump abnormality determination, when the high-pressure fuel pump abnormality 2 is input in step S22, the homogeneous combustion mode is set in step S25, and the high-pressure fuel pump abnormality is not input or the high-pressure fuel pump abnormality 1 is input. If so, the stratified charge combustion mode is set in step S24.

Next, each parameter control of FIG. 9 will be described. First, in step S31, similarly to step S23 of the fuel control mode determination in FIG. 8, it is determined whether or not the stratified combustion mode condition is satisfied, and when the condition is not satisfied (for example, when the high pressure fuel pump abnormality 2 is detected). (If determined), the fuel injection timing in the homogeneous combustion mode is set in step S35. On the other hand, when the stratified combustion mode condition is satisfied in step S31 (for example, when the above-mentioned various conditions are satisfied and it is determined that there is no high-pressure fuel pump abnormality or high-pressure fuel pump abnormality 1), step S32 Then, it is determined whether the high pressure fuel pump abnormality 1 is not established, and when the high pressure fuel pump abnormality 1 is not established (Y
In the case of ES), that is, when there is no abnormality in the high-pressure fuel pumps 26, 26 ', the fuel injection timing in the stratified charge combustion mode is set in step S33. Further, in step S32, when the high-pressure fuel pump abnormality 1 is not established (when NO), that is, the high-pressure fuel pump abnormality 1 is established, the injection timing correction amount when the fuel pump is abnormal is calculated. In step S33, the fuel injection timing in the stratified charge combustion mode is set.

The setting of the fuel injection mode in the stratified charge combustion mode in step S33 is determined as whether the high-pressure fuel pumps 26 and 26 'have no abnormality in the high-pressure fuel pump or the abnormality 1 in the high-pressure fuel pump as described above. The fuel pressure deviation ΔF and the first and second abnormality determination values ΔF used in the high pressure fuel pump abnormality determination of FIG.
1, ΔF2, ΔF1 ′, ΔF2 ′ are subdivided.

That is, when the actual fuel pressure is larger than the target fuel pressure, the fuel pressure deviation ΔF is smaller than the first abnormality determination value ΔF1 (ΔF ≦ ΔF1), and when the actual fuel pressure is smaller than the target fuel pressure, the fuel pressure deviation ΔF is ΔF1. When it is smaller than ′ (ΔF ≦ ΔF1 ′), that is, the fuel pressure deviation ΔF is within the allowable range or error range, if any, and there is no high-pressure fuel pump abnormality in the high-pressure fuel pump abnormality determination of FIG. 7. When the determination is made, the injection pulse and the injection timing are optimized, and as shown in FIG.
The stratified combustion mode is normally executed as it is to improve fuel efficiency.

Further, when the actual fuel pressure is higher than the target fuel pressure, when the fuel pressure deviation ΔF is larger than the first abnormality determination value ΔF1 and smaller than ΔF2 (ΔF1 <ΔF ≦ ΔF2
When the actual fuel pressure is smaller than the target fuel pressure, the fuel pressure deviation ΔF is larger than the first abnormality determination value ΔF1 ′ and smaller than ΔF2 ′ (ΔF1 ′ <ΔF ≦ ΔF).
2 '), that is, when the high-pressure fuel pump abnormality determination of FIG. 7 determines that the high-pressure fuel pump abnormality 1, the mode of fuel injection by the injector 18 is changed to continue the stratified charge combustion mode.

That is, in this case, the high pressure fuel supply system 2
0 high-pressure fuel pump 26 or 26 'or regulator 27
As a result, the fuel pressure deviation ΔF is larger than the first predetermined value ΔF1 or ΔF1 ′, but is not larger than the second predetermined value ΔF2 or ΔF2 ′. In other words, the actual fuel pressure deviates from the target fuel pressure to the higher or lower side, and if the normal stratified combustion mode is continued as it is, misfire and eventually engine stall problem or exhaust emission problem may occur. Injector 18 for the time being
This is a state that can be dealt with by changing the mode of fuel injection.

Therefore, as shown in FIG. 11, in such a case, the combustion mode is not immediately switched to the homogeneous fuel mode, but the mode of fuel injection by the injector 18 is changed to change the stratified combustion mode. Try to maintain and continue as much as possible. This allows
One of the greatest features of the stratified charge combustion mode, that is, the good fuel economy is fully utilized, and the commerciality of the engine 1 is not impaired.

Specifically, when the actual fuel pressure is higher than the target fuel pressure, it is assumed that the fuel is dividedly injected (when the single injection region in FIG. 5 is switched to the divided injection, or when it is in the divided injection region, The split injection is maintained as it is), and the injection timing of the earlier injection is accelerated.

For example, as shown in FIG. 12 (a), the fuel is compressed in the normal stratified charge combustion mode before the top dead center BTDC 40 °.
Assuming that a single injection is made in the range of up to 140 °, FIG.
As shown in (b), after the fuel injection is divided into two, the injection timing of the first injection is set to BTDC40.
Advance before °. Alternatively, as shown in FIG. 13A, the fuel is compressed in the normal stratified charge combustion mode before the top dead center B
If split injection is performed in the range of TDC 40 ° to 140 °, the injection start timing of the earlier injection is advanced before BTDC 40 °, as shown in FIG. 13B.

In this way, the actual fuel pressure supplied to the injector 18 (fuel injection pressure and hence fuel spray penetration force)
If the value is high, first by split injection of fuel,
The amount of fuel injected once is reduced, the amount of fuel adhering to the crown surface of the piston 5, the recess 5a, etc. is reduced as much as possible, and the problem of exhaust emission is suppressed. If the split injection is originally performed (for example, twice), it may be further divided (for example, three times).

In addition, by advancing the injection timing of the earlier injection, the fuel of the later injection (the injection amount of which is corrected by the divided injection) has a favorable flow rate of the tumble flow T. The fuel spray is brought close to the electrode of the ignition plug 16 while maintaining the opposing balance to achieve good stratification and optimization of the air-fuel ratio around the plug 16. In addition, the fuel injected early has a time for vaporization and atomization,
A weakly stratified combustion state is reached. From the above, the problem of poor stratification and the problem of exhaust emission when the actual fuel pressure is higher than the target fuel pressure can be suppressed.

On the other hand, when the actual fuel pressure is lower than the target fuel pressure, the fuel is similarly split-injected, and the injection timing is generally advanced.

For example, as shown in FIG. 12A, the fuel is compressed in the normal stratified charge combustion mode before the top dead center BTDC 40 °.
Assuming that a single injection is made in the range of up to 140 °, FIG.
As shown in (c), the fuel injection is divided into two and both injection timings are advanced (the injection end timing of the later injection is advanced before BTDC 140 °). Alternatively, as shown in FIG. 13A, the fuel is compressed in the normal stratified charge combustion mode before the BTD.
If the split injection is performed in the range of C40 ° to 140 °, both injection timings are advanced as shown in FIG. 13 (c).

In this way, the actual fuel pressure supplied to the injector 18 (fuel injection pressure and hence fuel spray penetration force)
If is low, first by split injection of fuel,
The one-time valve opening time is shortened to prevent the fuel injection pressure or the fuel spray penetration force from being excessively reduced. This allows
The opposing balance between the penetration force of the fuel spray and the flow velocity of the tumble flow T is maintained as much as possible to contribute to good stratification. The fuel spray is maintained so as to be able to face the tumble flow T.

In addition, by making the injection timing earlier as a whole, the penetrating force of the fuel spray, which is decreasing, is compensated for in time (when the injection pressure is low, the fuel spray collides with the tumble flow T.
It takes a long time to reach the position to be opposed by covering the time by the early injection), and this also keeps a good opposing balance with the tumble flow T to maintain the fuel spray at the spark plug 16 In order to achieve good stratification and to optimize the air-fuel ratio around the plug 16 by bringing the electrode close to the electrode. As described above, the problem of poor stratification when the actual fuel pressure is lower than the target fuel pressure can be suppressed.

Next, the setting of the fuel injection mode in the homogeneous combustion mode in step S35 will be described. That is,
In this case, when the high-pressure fuel pump abnormality determination determines that the high-pressure fuel pump abnormality 2, the actual fuel pressure is increased due to an abnormality or failure of the high-pressure fuel pump 26 or 26 ′ of the high-pressure fuel supply system 20, the regulator 27, or the like. Is larger than the target fuel pressure, the fuel pressure deviation ΔF is larger than the second predetermined value ΔF2 which is larger than the first predetermined value ΔF1 (ΔF
1 <ΔF2 <ΔF), when the actual fuel pressure is smaller than the target fuel pressure, the fuel pressure deviation ΔF is larger than the second predetermined value ΔF2 ′ which is larger than the first predetermined value ΔF1 ′ (ΔF1 ′ <ΔF2 ′ <. ΔF). In other words, the actual fuel pressure largely deviates from the target fuel pressure to the higher or lower side, and if the stratified charge combustion mode is maintained as it is, misfire will occur, and engine stall will occur, or exhaust emission will decrease. Therefore, as shown in FIG.
In such a case, the combustion mode is switched from the stratified combustion mode to the homogeneous combustion mode without undue effort, and the above-mentioned problem is surely avoided.

Specifically, the proper values of the injection pulse and the injection timing are calculated based on the actual fuel pressure, and as a result, the calculated injection pulse width is not smaller than the predetermined minimum limit value τmin, and the predetermined value is not set. If it is not larger than the maximum limit value τmax, the injection pulse and the injection timing are optimized and the homogeneous combustion mode is executed as usual. Here, the minimum limit value τmin and the maximum limit value τmax of the injection pulse width are determined from the performance / mechanical factors of the injector 18.

On the other hand, the injection pulse width is the minimum limit value τmin
When it is smaller, the injection pulse width is set to the minimum limit value τmi.
n, and the injection timing is an appropriate value calculated above.
At the same time, in the case of no load, increase the engine speed,
When there is a load, the ignition timing and throttle opening are controlled to optimize the torque and air-fuel ratio.

When the injection pulse width is larger than the maximum limit value τmax, the injection pulse width is set to the maximum limit value τmax and the injection timing is set to the appropriate value calculated above.

The engine according to this embodiment is
Fuel was collected around the plug by using intake flow (air motion, air guide) such as tumble flow, and it was distributed unevenly to achieve stratification, but instead, it was formed on the piston crown surface. The fuel may be stratified by using a cavity (wall guide).

[0078]

As described above, according to the present invention, when the deviation between the actual fuel pressure and the target fuel pressure becomes a predetermined value or more during execution of the stratified charge combustion mode, the homogeneous combustion mode is forcibly switched to. In the above, by setting the predetermined value to a larger value as the engine speed is higher, it is possible to provide a countermeasure that can improve fuel efficiency while ensuring combustion stability. INDUSTRIAL APPLICABILITY The present invention can be expected to be widely used in general engines having a configuration in which fuel is directly injected into a combustion chamber and the combustion mode can be switched between a stratified combustion mode and a homogeneous combustion mode.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of an engine according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a fuel supply system of the engine.

FIG. 3 is a state in which a tumble flow is generated in the intake stroke of a cylinder of the same engine, and a combustible mixture stays around the electrode of the spark plug using the tumble flow at the ignition timing in the latter half of the compression stroke of the cylinder. It is explanatory drawing which shows a mode.

FIG. 4 is a diagram showing an example of a control map in which an operating region for setting the engine to a stratified combustion mode or a homogeneous combustion mode is set.

FIG. 5 is a diagram showing an example of a control map in which an operating region in which the engine is set to a single injection mode or a split injection mode is set.

FIG. 6 is an example of a flowchart of high-pressure fuel pump discharge amount feedback control of a combustion mode switching control program for the engine.

FIG. 7 is also an example of a flowchart of high pressure fuel pump abnormality determination of the combustion mode switching control program.

FIG. 8 is an example of a flow chart for fuel control mode determination of the combustion mode switching control program.

FIG. 9 is also an example of a flowchart of each parameter control of the combustion mode switching control program.

FIG. 10 is a map illustrating a relationship between a predetermined value for determining a fuel pressure deviation and an engine rotation speed, and a magnitude relationship between the predetermined values.

FIG. 11 is an explanatory diagram showing a relationship between a positive or negative fuel pressure deviation and a combustion mode.

FIG. 12 is an explanatory diagram showing an example of a change in the fuel injection mode for maintaining / continuing the stratified charge combustion mode, in a case where the engine operating state is in the single injection region.

FIG. 13 is likewise an explanatory diagram showing an example of a change in fuel injection mode, when the operating state of the engine is in the split injection region.

[Explanation of symbols]

1 engine (cylinder injection type) 2 cylinder 5 piston 6 combustion chamber 10 intake port 11 exhaust port 12 intake valve 13 exhaust valve 16 spark plug 18 injector (fuel injection valve) 20 fuel supply system (fuel supply means) 26 high-pressure fuel pump 27 high pressure regulator 50 ECU (target fuel pressure setting means, fuel pressure control means,
Injection mode changing means, combustion mode switching means) 53 fuel pressure sensor (fuel pressure detecting means) T tumble flow ΔF1, ΔF1 ′ first abnormality determination value (second predetermined value) ΔF2, ΔF2 ′ second abnormality determination value (predetermined value)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 37/00 F02M 37/00 C (72) Inventor Kuniko Minatani Shinchi Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Motonori Yoshida 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima F-Term (reference) in Mazda Co., Ltd. 3G023 AA01 AA02 AB01 AC05 AD02 AD06 AD29 AE05 AG01 AG03 3G084 AA04 BA14 BA15 DA02 EA11 EB11 FA10 FA20 FA30 FA38 3G301 HA01 HA04 HA13 HA16 HA17 JA02 JB02 JB09 LA05 LB04 MA19 MA26 NA08 PB08A PB08Z PD09A PD09Z PE03Z PE08Z PF03Z

Claims (3)

[Claims] 1. A control device for an engine, comprising a fuel injection valve for directly injecting fuel into a combustion chamber, and switching a combustion mode between a stratified combustion mode and a homogeneous combustion mode based on an operating state of the engine. A fuel supply means for supplying fuel to the fuel injection valve, and a fuel pressure detection means for detecting the pressure of fuel supplied to the fuel injection valve by the supply means,
Target fuel pressure setting means for setting a target value of the pressure of the fuel supplied to the fuel injection valve based on the operating state of the engine, and a deviation between the target fuel pressure set by the setting means and the actual fuel pressure detected by the detecting means. When the fuel pressure deviation becomes larger than a predetermined value during execution of the stratified charge combustion mode, the combustion mode is forcedly set regardless of the operating state of the engine. An engine control device comprising: combustion mode switching means for switching to a homogeneous combustion mode; and setting means for setting the predetermined value to a larger value as the engine speed increases. 2. The engine according to claim 1, wherein the setting means sets the predetermined value to a large value when the actual fuel pressure is lower than the target fuel pressure as compared to when the actual fuel pressure is higher than the target fuel pressure. Control device. 3. When the fuel pressure deviation is smaller than a predetermined value but is larger than a second predetermined value smaller than the predetermined value during execution of the stratified combustion mode, the mode of fuel injection by the fuel injection valve is changed. The engine control device according to claim 1 or 2, further comprising: an injection mode changing unit that controls the injection mode.