JP2003106188A - Control system for spark ignition type direct injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure good combustion at light load area in stratified combustion area by controlling diffusion of fuel spray while vaporizing and atomizing fuel well and easing for fuel spray to reach adjacent of a spark plug. SOLUTION: In a spark ignition type direct injection engine stratifying air-fuel mixture around a spark plug 16 by injecting fuel from a fuel injection valve 18 to oppose to tumble flow generated in a combustion chamber 6 in stratified combustion operation, an injection rate adjusting means adjusting injection rate of the fuel injection valve 18 is provided, and a control means 51 controlling the fuel injection rate adjusting means is provided. The control means 51 controls the injection rate adjusting means in such a manner that the injection rate is low in an injection start side of a fuel injection period and high in an injection end side of the fuel injection period in the light load area in the stratified combustion area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark ignition type direct injection system in which fuel is injected from a fuel injection valve so as to face a tumble flow during stratified combustion operation of an engine to stratify the air-fuel mixture around a spark plug. The present invention relates to a control device for an injection engine.

[0002]

2. Description of the Related Art Conventionally, in a spark ignition engine, a fuel injection valve for injecting fuel directly into a combustion chamber is provided, and an air-fuel ratio is made lean in an operating region on a low rotation and low load side and a compression stroke is performed from the fuel injection valve. There are various known spark ignition type direct injection engines in which stratified charge combustion is performed by injecting fuel to improve fuel efficiency.

For example, in the engine disclosed in Japanese Patent Laid-Open No. 2000-104550, an intake system is constructed so that a tumble flow is generated in the combustion chamber, and a fuel injection valve for directly injecting fuel is provided in the combustion chamber. The injection direction of the fuel injection valve is set so that the fuel spray collides with the main flow of the tumble flow in a substantially frontal direction during stratified combustion. By providing a pair of standing walls that suppress the diffusion in the direction, a relatively rich air-fuel mixture gathers around the ignition plug so that stratification is performed.

[0004]

In the engine disclosed in the above publication, the pair of standing walls provided on the crown surface of the piston is used to suppress the diffusion of the fuel spray in the left and right directions. However, if the injection timing from the fuel injection valve is too early, for example, it is difficult to sufficiently prevent the fuel spray from diffusing over the standing wall or in directions other than the standing wall by the ignition timing. Therefore, in order to prevent the diffusion of the fuel before the ignition timing, it is desirable that the interval between the fuel injection timing and the ignition timing be relatively short. In particular, in the low load region where the fuel injection amount is small, in order to secure a state in which the rich air-fuel mixture is unevenly distributed around the spark plug at the ignition timing, it is required to make the interval between the fuel injection timing and the ignition timing as short as possible. It

However, if the interval between the fuel injection timing and the ignition timing is shortened only in consideration of such a demand for preventing fuel diffusion, the vaporization and atomization of the fuel become insufficient and the ignitability deteriorates. Further, the fuel injection timing is delayed (close to the compression top dead center) in order to shorten the interval between the fuel injection timing and the ignition timing while setting the ignition timing to the optimum timing for fuel consumption.
Then, the tumble flow is significantly attenuated by the time the fuel injection timing is reached, and on the other hand, the pressure in the combustion chamber becomes high, which makes it difficult for the fuel spray to reach the vicinity of the spark plug.

In view of such a point, the present invention delays the injection end timing to ensure a state in which a rich air-fuel mixture is unevenly distributed around the spark plug at the ignition timing, particularly in the low speed range of the engine, and the time with respect to the ignition timing. Even if the interval is shortened, the vaporization and atomization of the fuel are performed well, and the penetration force of the fuel spray is increased to respond to the pressure increase in the combustion chamber in the latter part of the injection period, and the fuel around the spark plug is increased. Facilitates the arrival of spray,
An object of the present invention is to provide a control device for a spark ignition type direct injection engine that can favorably perform stratified combustion.

[0007]

In order to achieve the above object, the invention according to claim 1 constitutes a fuel for directly injecting fuel into a combustion chamber while constructing an intake system so as to generate a tumble flow in the combustion chamber. An ignition valve is provided, and during stratified charge combustion operation, fuel is injected so as to face the tumble flow from the fuel injection valve at a timing such that the injection ends in the latter half of the compression stroke and before the ignition timing, thereby igniting at the ignition timing. A spark ignition type direct injection engine configured to stratify a mixture around a plug is provided with injection rate adjusting means for adjusting an injection rate which is an injection amount per unit time from a fuel injection valve, and stratified combustion In the low load region in the region, the injection rate is small on the injection start side of the fuel injection period,
The control means is provided to control the injection rate adjusting means so as to increase the injection end side.

According to this structure, in the stratified charge combustion region, the fuel is injected from the fuel injection valve so as to oppose the tumble flow at a timing such that the injection is finished in the latter half of the compression stroke and before the ignition timing. Is done,
In particular, in the low load region within the stratified charge combustion region, fuel injected at a low injection rate in the early part of the injection period is sufficiently vaporized and atomized by the ignition timing to ensure ignitability, and at the latter stage of the injection period. The injection of a large amount of fuel suppresses the diffusion of the fuel spray, and the injection rate is increased at the time when the pressure in the combustion chamber increases, so that the fuel spray can easily reach around the spark plug. Thus, the stratified charge combustion is favorably performed in the state where the rich air-fuel mixture is unevenly distributed around the spark plug.

According to the present invention, in the low speed region in the low load region within the stratified charge combustion region, the injection rate is small on the injection start side and large on the injection end side in the fuel injection period (claim 2), so that the low load is achieved. The stratification and combustibility are improved especially in the low speed region where the tumble flow is weak.

Further, the injection characteristics in the low load region in the stratified charge combustion region are relatively small with respect to the injection characteristics in the high load region in the stratified charge combustion region, and the injection rate on the injection start side is small and the injection rate on the injection end side is small. By setting the injection rate to be large (Claim 3), it is possible to avoid that the air-fuel mixture around the spark plug becomes excessively rich in the region where the fuel injection amount is large in the stratified combustion region, and the fuel injection amount is increased. The stratification and combustibility in the low negative range with less heat can be improved.

Further, the injection characteristic at the low speed region in the low load region in the stratified charge combustion region is compared with the injection characteristic at the high speed region in the low load region in the stratified charge combustion region at the injection start side. Is preferably set to be small and the injection rate on the injection end side is set to be large (claim 4).

Furthermore, a judging means for judging the temperature state in the combustion chamber is provided, and based on the judgment by this judging means,
Even in the same operating range, it is preferable to control the injection start when the temperature in the combustion chamber is high and to shorten the period when the injection rate is small (claim 5).

With this configuration, in a situation where the temperature in the combustion chamber is high and the fuel is easily vaporized and atomized, but the penetration force of the fuel spray is easily reduced, the fuel spray easily reaches the periphery of the spark plug. The jetting properties are adjusted to obtain and the stratification effect is enhanced.

According to a sixth aspect of the present invention, the intake system is configured to generate a tumble flow in the combustion chamber, and a fuel injection valve for directly injecting fuel is provided in the combustion chamber, and the fuel injection is performed during the stratified charge combustion operation. It is configured to stratify the air-fuel mixture around the spark plug at the ignition timing by injecting the fuel so as to face the tumble flow at a timing such that the injection is completed in the latter half of the compression stroke and before the ignition timing from the valve. In the spark ignition type direct injection engine, a determining means for determining the temperature state in the combustion chamber is provided, and based on the determination by the determining means, when the temperature in the combustion chamber is high or low even in the same operating range during stratified charge combustion operation, On the other hand, a control means for controlling the start timing of fuel injection from the fuel injection valve to be delayed is provided.

According to this structure, in the stratified charge combustion region, the fuel is injected from the fuel injection valve so as to oppose the tumble flow at a timing such that the injection is completed in the latter half of the compression stroke and before the ignition timing. In this case, the stratification action is enhanced in the situation where the temperature in the combustion chamber is high and the vaporization and atomization of the fuel are easily performed.

In this invention, there is provided an injection rate adjusting means for adjusting an injection rate which is an injection amount per unit time from the fuel injection valve, and the control means is provided when the temperature in the combustion chamber is high and when it is low. It is preferable to delay the start timing of fuel injection from the fuel injection valve and control the injection rate adjusting means so as to increase the injection rate (Claim 7).

In this way, the tendency that the penetration force of the fuel spray decreases when the temperature in the combustion chamber is high is corrected, and the fuel spray can easily reach around the spark plug, and the stratification is favorably performed.

Further, the control means controls the injection rate adjusting means such that the injection rate is small on the injection start side and large on the injection end side in the fuel injection period in the low load region within the stratified charge combustion region. (Claim 8) is preferred.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall structure of a spark ignition type direct injection engine according to an embodiment of the present invention. In this figure, an engine body 1 has a cylinder block 3 in which a plurality of cylinders 2 are arranged, and a cylinder head 4 arranged on the cylinder block 3, and a piston 5 is vertically arranged in each cylinder 2. It is inserted so as to be reciprocally movable in the direction, and a combustion chamber 6 is formed between the piston 5 and the cylinder head 4.

The piston 5 is connected to a crank shaft 7 rotatably supported on the lower portion of the cylinder block 3 via a connecting rod 8. An electromagnetic crank angle sensor 9 that detects a crank angle (a rotation angle of the crank shaft 7) is arranged on one end side of the crank shaft 7.

The combustion chamber 6 of each cylinder 2 is of a so-called pent roof type in which the ceiling portion is composed of two inclined surfaces extending from the central portion to the lower end of the cylinder head. A plurality of intake ports 10 and exhaust ports 11 are opened in the combustion chamber 6, and in the present embodiment, two intake ports 10 and two exhaust ports 11 are opened in each of the two inclined surfaces forming the ceiling portion. . An intake valve 12 and an exhaust valve 13 are provided at the open ends of the ports 10 and 11, and the intake valve 12 and the exhaust valve 13 are composed of two cam shafts 14 and the like that are axially supported on the cylinder head 4. The valve operating mechanism is adapted to open and close each cylinder at a predetermined timing.

Above the center of the combustion chamber 6, the above-mentioned 4
The spark plug 16 is arranged so as to be surrounded by the intake and exhaust valves, and the tip of the spark plug 16 projects into the combustion chamber 6 from the ceiling portion. An ignition circuit 17 is connected to the ignition plug 16, and the ignition plug 16 is energized at a predetermined timing for each cylinder 2. In addition, two intake ports 10 are provided at the peripheral edge of the combustion chamber 6.
The fuel injection valve 18 is disposed so as to be sandwiched between the fuel injection valve 18 and the fuel injection valve 18, and the fuel is directly injected into the combustion chamber 6 from the fuel injection valve 18.

The structure of the engine body 1 is shown in FIGS.
More specifically, referring to FIG. 2, the intake ports 10 extend linearly from the combustion chamber 6 obliquely upward and are open on one side surface (the left side surface in FIG. 2) of the engine body 1. The two intake ports 10 are formed independently of each other. The tumble flow T flows into the combustion chamber 6 by the air flowing into the combustion chamber 6 through the intake ports 10.
Is generated. The combustion chamber 6 as shown in FIG.
In the cross section in which the intake port 10 is located on the left side and the exhaust port 11 is located on the right side, the tumble flow T is generated in the clockwise direction (arrow direction in FIG. 2).

The two inclined surfaces forming the ceiling of the combustion chamber 6 have a relatively large installation angle (sandwich angle) α for the intake valve 12 and the exhaust valve 13 installed so as to be substantially orthogonal to the inclined surfaces. The inclination angle is set to be a value, for example, 35 ° or more. By setting the angle of the inclined surface to a large value in this way, the intake port 10 and the exhaust port 11 are prevented from being greatly bent, and the flow resistance of intake air and exhaust gas is set to a small value. ing.

The direction of fuel injection from the fuel injection valve 18 is set so as to face the tumble flow T in the combustion chamber 6. That is, in the cross section shown in FIG. 2, the fuel is injected from the fuel injection valve 18 located on the left side of the combustion chamber 6 toward the lower right, so that the injected fuel is tumble flow T on the crown surface of the piston 5. It is designed to go in the opposite direction.

On the crown surface of the piston 5, a concave portion 21 is formed in a predetermined range across the cylinder axis Z in the cross section on both left and right sides. Then, as shown in FIG. 3, the flow along the ceiling of the combustion chamber 6 is tumble forward Ts,
When the flow along the bottom of the combustion chamber 6 is defined as the tumble forward flow Tm, the tumble forward flow Tm and the fuel spray Fa are introduced into the recess 21 from opposite directions, so that The tumble forward flow Tm and the fuel spray Fa collide head-on.

Further, in the illustrated example, a step portion 22 for deflecting the tumble positive flow Tm upward is formed at a position offset to the left side of the cylinder axis Z of the concave portion 21, and an upper end of the step portion 22 is formed. Substantially parallel to the bottom surface of the recess 21,
That is, the shelf portion 23 extending in the substantially horizontal direction is formed.
This is done in the case where the angle of the inclined surface of the combustion chamber ceiling is large and the distance from the piston crown surface to the ignition plug 16 is relatively large, the fuel spray Fa and the tumble forward flow T.
This is because the air-fuel mixture generated by the collision with m is rolled up by the air current (a part of the tumble flow) deflected upward by the step portion 22 and drifts around the spark plug.

As shown in FIG. 4, in plan view, the recess 21 is formed in a substantially elliptical shape with the fuel injection direction as the major axis and the direction orthogonal thereto as the minor axis. The outer peripheral portion 5a of the crown surface of the piston 5 excluding the installation portion of the recess 21
Is formed so as to extend substantially along the inclined surface of the ceiling portion of the combustion chamber 6 facing it, and the crown surface of the piston 5 in a predetermined period before the compression top dead center of the cylinder 2, for example, in the period of BTDC 40 ° CA to TDC. The squish area is formed between the outer peripheral portion 5a and the ceiling of the combustion chamber 6. Note that TDC means top dead center, BTDC means before top dead center, and CA means crank angle.

The fuel injection valve 18 includes injection rate adjusting means for adjusting the injection rate (injection amount per unit time). For example, the injection rate adjustment made of a piezo element stack as shown in FIG. Has built-in means. That is, the fuel injection valve 18 shown in the same figure has an injection port 181 provided at a tip portion (a lower end portion in the figure) of a valve body 180 and a slidable insertion portion that is slidably inserted into the valve body 180 to open and close the injection port 181. A needle-shaped valve body 182, a back pressure chamber 183 formed behind the valve body 182, a return spring 184 arranged in the back pressure chamber 183, and a rear portion (upper side in the figure) of the valve body 180. And a piston 186 connected to the piezo element laminated body 185 housed in the piezo element laminated body 185.

A fuel chamber 187 communicates with the injection port 181, and a fuel introduction passage 188 is connected to the fuel chamber 187. The return spring 184 biases the valve body 182 in the valve closing direction. The back pressure chamber 183 communicates with a chamber 189 that houses a piston 186.

The piezo element stack 185 is formed by stacking several other piezo elements.
It is electrically connected to 50. Then, in response to the application of the voltage to the piezoelectric element laminated body 185, the piezoelectric element laminated body 1
The chamber 189 and the back pressure chamber 183 become a negative pressure due to the contraction of 85 and the withdrawal of the piston 186 accordingly, and this negative pressure acts on the valve body 182 to open the valve body 182 and thereby the injection port. Fuel is injected from 181. In this case, by changing the voltage applied to the piezo element stack 185, the contraction amount of the piezo element stack 185 changes, and the lift amount of the valve body 182 changes accordingly, so that the injection rate can be changed. It is like this.

Fuel introduction passage 188 of the fuel injection valve 18
A common fuel distribution pipe 19 is connected to all the cylinders 2, and distributes the high-pressure fuel supplied from the fuel supply system 20 to the fuel injection valve 18 of each cylinder. In addition,
The fuel supply system 20, although not shown and described in detail, has a low-pressure fuel pump, a low-pressure regulator, a fuel filter, a high-pressure fuel pump, a high-pressure regulator, etc. in the fuel passage between the fuel distribution pipe 19 and the fuel tank. Are installed.

Returning to FIG. 1, the intake passage 3 communicating with the intake port 10 of each cylinder is provided on one side surface of the engine body 1.
On the other hand, the exhaust passage 32 communicating with the exhaust port 11 of each cylinder is connected to the other side surface of the engine body 1.

The intake passage 31 supplies the air filtered by an air cleaner (not shown) to the combustion chamber 6 of each cylinder 2 of the engine body 1, and an air flow sensor for detecting the intake amount in order from the upstream side thereof. 33 and electric motor 3
Electric throttle valve 34 driven by 5 to open and close
And a surge tank 36. The intake passage 31 downstream of the surge tank 36 is an independent intake passage branched for each cylinder 2, and the downstream end of each independent intake passage is further divided into two intake ports. 10 communicate with each.

A tumble adjusting valve 37 for adjusting the strength of the tumble flow in the combustion chamber 6 is arranged on the upstream side of each of the intake ports 10, and the tumble adjusting valve 37 is operated by an actuator 38 which is, for example, a stepping motor. It is designed to be opened and closed. The tumble control valve 37 is formed by cutting out a part of a circular butterfly valve, for example, a part below the valve shaft, and when the tumble control valve 37 is closed, the tumble control valve 37 is inserted through the cutout part. By flowing the intake air to the downstream side, a tumble flow is formed in the combustion chamber 6, and the tumble flow is gradually weakened as the tumble control valve 37 is opened.

The shapes of the intake port 10 and the tumble adjusting valve 37 are not limited to the above-mentioned shapes.
For example, the intake ports 10 may be configured as a so-called common port type that joins together on the upstream side. In this case, the tumble control valve 37 may have a shape corresponding to the cross-sectional shape of the common port as a base, with a part thereof cut out.

On the other hand, the exhaust passage 32 is for exhausting the burnt gas from the combustion chamber 6, and the exhaust manifold 3 communicating with the exhaust port 11 of each cylinder 2 is provided on the upstream end side thereof.
9 is equipped. A linear O ₂ sensor 40 for detecting the oxygen concentration in the exhaust is provided at the collecting portion of the exhaust manifold 39.
Is provided. The linear O ₂ sensor 40 is used to detect the air-fuel ratio based on the oxygen concentration in the exhaust gas, so that a linear output with respect to the oxygen concentration can be obtained in a predetermined air-fuel ratio range including the theoretical air-fuel ratio. Has become.

The upstream end of an exhaust pipe 41 is connected to the collecting portion of the exhaust manifold 39, and the exhaust pipe 41 is provided with a catalyst 43 for purifying the exhaust gas.

On the upstream side of the exhaust pipe 41, part of the exhaust gas flowing through the exhaust passage 32 is returned to the intake passage 31.
The upstream end of the GR passage 45 is connected. The downstream end of the EGR passage 45 is provided with the throttle valve 34 of the intake passage 31.
It is connected further downstream, for example, to the surge tank 36.
An electric EG whose opening can be adjusted is provided in the middle of the EGR passage 45.
An R valve 46 is provided so that the amount of exhaust gas recirculated through the EGR passage 45 can be adjusted.

A motor 35 for driving the ignition circuit 17, the fuel injection valve 18, the fuel supply system 20, and the throttle valve 34,
Actuator 38 of tumble control valve 37, electric EG
The R valve 46 and the like are controlled by an engine control unit 50 (hereinafter referred to as ECU). Signals from the crank angle sensor 9, the air flow sensor 33, the linear O ₂ sensor 40, and the like are input to the ECU 50, and further, from an accelerator opening sensor 48 that detects an accelerator opening (an operation amount of an accelerator pedal). A detection signal, a detection signal from a rotation speed sensor 49 that detects the rotation speed of the engine, and the like are also input.

The ECU 50 functionally includes a fuel injection control means 51, and further includes a temperature state determination means 52 for determining the temperature state of the engine.

The fuel injection control means 51 controls the timing of fuel injection from the fuel injection valve 18, the injection amount and the injection rate. Specifically, as shown in FIG. 6, for example, the low-load and low-speed engine operating region (a) is set to the stratified combustion region,
The other region (b) is set as a uniform combustion region, and in the stratified combustion region (a), a predetermined time (for example, before compression top dead center (BTDC) 40 ° to 140) from the fuel injection valve 18 to the compression stroke.
(Range of °) to inject fuel for stratified combustion. At this time, the air-fuel ratio is lean (for example, A / F> 2).
The intake air amount and the fuel injection amount are controlled so as to be 5). On the other hand, in the uniform combustion region (b), the fuel is injected from the fuel injection valve 18 in the intake stroke to perform uniform combustion. At this time, the air-fuel ratio is approximately the theoretical air-fuel ratio (A / F = 1
The intake air amount and the fuel injection amount are controlled so as to be 4.7). It should be noted that the air-fuel ratio may be richer than the stoichiometric air-fuel ratio (for example, about A / F = 13) particularly in the full load operation state.

In the low load region of the stratified charge combustion region (a), by controlling the voltage applied to the piezo element stack 185, as shown in FIG. 7, the injection rate is changed to the injection start side of the fuel injection period. Is controlled to be small and to be increased on the injection end side. That is, the chain double-dashed line in FIG. 7 is the injection characteristic when the injection rate is constant over the entire fuel injection period as in the conventional case, and the interval between the fuel injection end timing and the ignition timing in this case is the vaporization of fuel. However, it is considered to be necessary to secure ignition performance while avoiding deterioration of atomization. On the other hand, the injection characteristic in the low load region in this embodiment is as shown by the solid line in FIG. 7, and although the injection start timing is about the same as the conventional injection characteristic, the injection rate on the injection start side Is set lower, while the injection rate is increased on the injection end side, and the injection end timing is set to be later than the conventional one.

Further, based on the discrimination by the temperature state discriminating means 52, when the temperature in the combustion chamber is high above a predetermined value, as shown by the broken line in FIG. 7, the injection start timing is longer than that at low temperature (solid line). The period for delaying and reducing the injection rate is shortened, and the period for increasing the injection rate is lengthened.

Further, even in the low load region in the stratified charge combustion region, the injection characteristics are changed on the low speed side and the high speed side, and on the low speed side, the injection rate is extremely lower on the injection start side than on the high speed side, and on the injection end side. To be raised.

In the high load region within the stratified charge combustion region, the injection characteristics are changed so that the injection rate on the injection start side and the injection rate on the injection end side are closer to each other than in the low load region. Therefore, the injection characteristic in the low load region in the stratified charge combustion region is relatively small compared to the injection characteristic in the high load region in the stratified charge combustion region, the injection rate on the injection start side is small, and the injection rate on the injection end side is small. It is set to be large.

The temperature state determination means 52 estimates the temperature in the combustion chamber based on the exhaust temperature detected by, for example, an exhaust temperature sensor (not shown). Alternatively, the temperature in the combustion chamber may be estimated based on the history of operating states (duration of uniform combustion operation, etc.) and the outside air temperature.

In addition to the above fuel injection control, the ECU 50 closes the tumble control valve at least in the stratified charge combustion region or controls the tumble flow to a small opening to strengthen the tumble flow, and at the same time, to strengthen the tumble flow. The fuel pressure (fuel injection pressure from the fuel injection valve) is controlled by controlling the high-pressure pump of the fuel supply system so that the penetration force of the fuel spray is balanced with the penetration force of the fuel spray. EGR valve 46 so that the recirculation is performed
Are in control.

According to the apparatus of this embodiment as described above,
In the stratified charge combustion region, fuel is injected from the fuel injection valve 18 in the compression stroke, a tumble flow is generated in the combustion chamber 6, and the fuel is injected so as to face the tumble flow. The tumble flow and the fuel spray collide with each other in 6 to promote vaporization and atomization of the fuel, and at the ignition timing, a combustible air-fuel mixture is generated in the vicinity of the spark plug 16 to perform stratified combustion.

In this case, in the low load region within the stratified charge combustion region, the latter-stage center of gravity type injection characteristic (injection rate is small on the injection start side and the injection end side is shown on the solid line (broken line at high temperature) in FIG. The fuel vaporization is suppressed while the diffusion of the fuel is suppressed,
Atomization is also performed well, and combustibility is enhanced.

That is, since the ratio of the fuel injected in the latter part of the injection period increases and the injection end timing is delayed due to the latter center of gravity type injection characteristic,
The diffusion of fuel by ignition timing is reduced. Further, by delaying the injection end timing in this way, the tumble flow is greatly attenuated until the injection is ended, while the pressure in the combustion chamber is significantly increased and the resistance to the flow of the fuel spray is increased. However, since the injection rate is increased on the injection end side, that is, the injection amount per unit time increases, the penetration force of the fuel spray increases, so that the fuel spray can easily reach around the spark plug. By these actions, a state in which the rich air-fuel mixture is unevenly distributed around the spark plug is secured.

Moreover, since the injection rate is set to the same level as the conventional one while the injection rate on the injection start side is made small, the fuel injected at the beginning of the injection period is sufficiently vaporized and atomized by the ignition timing. As a result, the ignitability is ensured and the stratified charge combustion is favorably performed.

Further, for example, when the high-speed high-load operation in the uniform combustion region is performed for a relatively long time and then the low-speed low-load region in the stratified combustion region is entered, the temperature in the combustion chamber is high. At such a high temperature, the fuel is more likely to be vaporized and atomized even if the injection start timing is delayed compared to when the temperature is low. Therefore, as shown by the broken line in FIG. 7, the injection start timing is delayed and the injection rate is changed. Stratified combustion is favorably performed by shortening the period for lowering.

The latter-stage center-of-gravity type injection characteristic as described above is particularly effective in a low-load low-speed range where the injection amount is small and the tumble strength is weak. On the other hand, even in the low load region in the stratified charge combustion region, the tumble flow is stronger on the high speed side than on the low speed region, and injection is performed earlier in the injection period without lowering the injection rate on the injection start side in the low speed region. The fuel is sufficiently vaporized and atomized by the tumble flow, and good stratified combustion is performed.

Further, on the high load side in the stratified charge combustion region, the fuel injection amount is large, and when the injection rate on the injection end side is increased, the air-fuel mixture around the spark plug becomes overrich at the ignition timing. The injection start time is advanced compared to
In addition, the injection rate on the injection start side is increased.

The specific structure of the apparatus of the present invention is not limited to the above-mentioned embodiment, but various modifications can be made. Some examples will be described below.

In the above embodiment, the injection rate during the injection period is changed by changing the lift amount of the valve body 182 of the fuel injection valve in the low load region within the stratified charge combustion region. As shown, the fuel injection is divided into a number of times, and the valve lift is constant,
For duty control, the injection rate (injection amount per unit time) may be changed by changing the valve opening time ratio per unit time. In this case, the injection pulse width corresponding to the valve opening time width is injected. It may be smaller on the start side and larger on the injection end side.

In the above-described embodiment, when the temperature in the combustion chamber is high, the injection start timing is delayed compared to when the temperature is low, and the period for decreasing the injection rate is shortened and the period for increasing the injection rate is long. However, as shown by the broken line in FIG. 9, in the latter part of the injection period in which the injection rate is increased, the injection rate is further increased at high temperature than at low temperature (solid line). May be.

The control in which the injection start timing is delayed when the temperature in the combustion chamber is high compared to when the temperature is low is effective even when the injection rate is not changed during the injection period, as shown in FIG. That is, when the fuel injection is performed at a constant injection rate for a predetermined period at a low temperature as shown by a broken line, the injection start timing is delayed and the injection rate is increased at a high temperature as compared with the low temperature. You can control to.
By doing so, vaporization and atomization are favorably maintained due to the high temperature, and a decrease in penetration force is suppressed by increasing the injection rate, and stratified combustion is favorably performed.

[0061]

As described above, the engine of the present invention stratifies the air-fuel mixture around the spark plug by injecting fuel from the fuel injection valve so as to face the tumble flow in the combustion chamber during the stratified charge combustion operation. The injection rate adjusting means for adjusting the injection rate of the fuel injection valve is provided, and the injection rate is small on the injection start side of the fuel injection period in the low load region in the stratified combustion region, and the injection end is completed. Since it is controlled so as to be large on the side, in the low load region in the stratified charge combustion region, the vaporization and atomization of the fuel are favorably performed to secure the ignitability and prevent the diffusion of the fuel spray. be able to.

Therefore, even in the low load region where the fuel injection amount is small, the stratified charge combustion can be favorably performed, and the fuel consumption improving effect can be enhanced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of the entire structure of a spark ignition type direct injection engine to which a control device of the present invention is applied.

FIG. 2 is a sectional view of an engine body.

FIG. 3 is a sectional view showing a specific shape of a piston.

FIG. 4 is a plan view showing the arrangement of pistons, intake ports, fuel injection valves, etc., and the fuel injection state.

FIG. 5 is a sectional view showing an example of a fuel injection valve including an injection rate adjusting unit.

FIG. 6 is a diagram showing an example of a control map in which a stratified combustion region and a uniform combustion region are set.

FIG. 7 is a diagram showing injection characteristics in a low load region within a stratified charge combustion region.

FIG. 8 is a diagram showing another example of injection characteristics in a low load region within the stratified charge combustion region.

FIG. 9 is a diagram showing another example of injection characteristics at low temperature and high temperature.

FIG. 10 is a diagram showing still another example of injection characteristics at low temperature and high temperature.

[Explanation of symbols]

1 engine body 6 Combustion chamber 10 intake ports 16 spark plugs 18 Fuel injection valve 181 Piezo element stack 50 ECU 51 Fuel injection control means 52 Temperature condition determination means

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02B 31/00 301 F02B 31/00 301Z F02D 41/02 325 F02D 41/02 325F 325G (72) Inventor Araki Keiji 3-3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture F-term within Mazda Corporation (reference) 3G023 AA01 AA07 AA18 AB03 AC05 AD02 AD05 AD07 AD08 AD29 AE05 AG01 AG02 AG03 3G301 HA04 HA09 HA13 HA16 HA17 KA08 KA24 LB04 LC05 MA11 MA18 MA27 NE NE06 NE11 NE12 PA01A PA11A PD02A PE03A PE08A

Claims (8)

[Claims] 1. A fuel injection valve that configures an intake system so as to generate a tumble flow in a combustion chamber, and has a fuel injection valve that directly injects fuel into the combustion chamber. A spark ignition direct injection that is configured to stratify the air-fuel mixture around the spark plug at the ignition timing by injecting fuel so as to face the tumble flow at a timing such that the injection is ended before the ignition timing. The engine is equipped with injection rate adjusting means for adjusting the injection rate, which is the injection amount per unit time from the fuel injection valve, and the injection rate is set to the injection start side of the fuel injection period in the low load area in the stratified charge combustion area. A control device for a spark ignition type direct injection engine, characterized in that it comprises control means for controlling the injection rate adjusting means so that the injection rate adjusting means is increased at the injection end side. 2. The injection rate is small on the injection start side and large on the injection end side in the fuel injection period in the low load range in the low-load range in the stratified charge combustion range.
A control device for the spark ignition type direct injection engine described. 3. The injection characteristic in the low load region in the stratified charge combustion region is set relatively small with respect to the injection characteristic in the high load region in the stratified charge combustion region, and the injection rate on the injection start side is small and the injection rate on the injection end side is small. The control device for a spark ignition type direct injection engine according to claim 1, wherein the injection rate is set to be large. 4. The injection characteristic on the injection start side relative to the injection characteristic in the low load region in the stratified charge combustion region in the low speed region relative to the injection characteristic in the high load region in the low load region in the stratified charge combustion region. 3. The control device for a spark ignition type direct injection engine according to claim 2, wherein is set to be small and the injection rate on the injection end side is set to be large. 5. A period in which the injection start is delayed and the injection rate is small even when the temperature in the combustion chamber is high even in the same operating region, based on the determination by the determination unit for determining the temperature state in the combustion chamber. The control device for a spark ignition type direct injection engine according to any one of claims 1 to 4, wherein the control is performed so as to shorten. 6. An intake system is configured to generate a tumble flow in the combustion chamber, and a fuel injection valve for directly injecting fuel into the combustion chamber is provided, and during the stratified charge combustion operation, the fuel injection valve is in the latter half of the compression stroke and A spark ignition direct injection that is configured to stratify the air-fuel mixture around the spark plug at the ignition timing by injecting fuel so as to face the tumble flow at a timing such that the injection is ended before the ignition timing. The engine is equipped with a discriminating means for discriminating the temperature state in the combustion chamber, and based on the discrimination by the discriminating means, the fuel injection valve is used when the temperature in the combustion chamber is high when the temperature is low even in the same operating range during stratified charge combustion operation. 2. A control device for a spark ignition type direct injection engine, comprising: a control unit that controls so as to delay the start timing of the fuel injection. 7. An injection rate adjusting means for adjusting an injection rate, which is an injection amount per unit time from a fuel injection valve, is provided, and the control means controls the fuel injection when the temperature in the combustion chamber is high and when it is low. 7. The control device for a spark ignition type direct injection engine according to claim 6, wherein the injection rate adjusting means is controlled such that the start timing of fuel injection from the valve is delayed and the injection rate is increased. 8. The control means controls the injection rate adjusting means such that the injection rate is small on the injection start side and large on the injection end side in the fuel injection period in a low load region within the stratified charge combustion region. The control device for a spark ignition type direct injection engine according to claim 7.