JP2002161790A - Combustion control device for direct injection/spark ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out layered combustion while preventing the occurrence of soot or hydrocarbons at homogeneous combustion. SOLUTION: A fuel injection valve 8 is installed in nearly horizontal attitude so as to be suitable mainly for layered combustion with a narrow spray angle and to tend toward the lower part of a spark plug 7. In this case, since there is a risk of a fuel mist colliding with a bore wall face opposed to the fuel mist flow when the homogeneous combustion with a large injection amount is performed, a required injection amount is divided into a plurality of times of injection to be injected to form a fuel mist F which is short in distance to be reached and is apt to go with a tumble flow T. Since a fuel gas flow is changed by the rotation speed of an engine and the injection amount is varied by a load, the number of times of division, time interval in each injection and the like are variably controlled according to the engine operation condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-cycle direct injection spark ignition type internal combustion engine such as a gasoline engine for an automobile, and more particularly to a fuel injection from a suction stroke to a compression stroke during homogeneous combustion. The present invention relates to a combustion control device that obtains a desired spray form by performing a plurality of divided injections.

[0002]

2. Description of the Related Art As a conventional combustion control apparatus for a direct injection spark ignition type internal combustion engine, as described in Japanese Patent Application Laid-Open No. 9-256936, at least two or more times during stratified combustion operation in an engine low speed and low load range. A divided fuel injection is performed, a uniform mixture is formed in the combustion chamber by the fuel injected before the fuel injection at the latest timing, and the fuel injected at the latest timing is passing near the spark plug. By igniting, stratified combustion is realized.On the other hand, when the engine is running at high speed and high load, the fuel is ignited at the timing when the spray has completed passing near the spark plug, thereby improving combustion stability and fuel. There are techniques for reducing unburned hydrocarbon (HC) emissions due to insufficient mixing of air.

[0003]

However, according to the above-described conventional apparatus, the fuel injected before the latest fuel injection is dispersed throughout the combustion chamber to form a lean mixture. When the engine is under low load with a small fuel injection amount, an excessively lean air-fuel mixture is formed, and incomplete combustion may be caused to increase the unburned HC emission.

In addition, when this conventional combustion control device is applied to a direct injection spark ignition type internal combustion engine in which the air-fuel mixture is transported to the vicinity of an ignition plug by a tumble (vertical vortex) flow, the tumble flow is affected by the momentum of the spray. When the engine is running at a low engine speed where the amount of momentum of the mixture is relatively small and it is difficult to transport the mixture in the direction of the spark plug by the tumble flow, or at a low engine load where the fuel injection amount is small and the mixture tends to be lean. Since the period during which the mixture concentration in the vicinity of the plug is within the appropriate range, that is, the ignitable period cannot be increased, the length of the ignitable period may be insufficient in engine performance as a result.

On the other hand, as a method of improving the problem in the stratified operation in the above-mentioned publication, it is conceivable to configure the fuel injection system so that the air-fuel mixture is concentrated near the ignition plug. That is, in a direct-injection spark ignition type internal combustion engine in which the air-fuel mixture is transported to the vicinity of the ignition plug by tumble (vertical vortex) flow, the spray angle of the fuel injection valve is reduced, and the mounting angle of the fuel injection valve with respect to the cylinder horizontal plane is reduced. It is effective to increase the ratio of the spray directly directed to the spark plug by reducing the size. However, in this method, since the spray penetration is increased due to the small spray angle and the spray is sprayed at an angle close to the horizontal, the spray collides with the opposed bore wall surface during the homogeneous operation, soot generation and HC generation. Increase is a problem.

[0006] The present invention has been made in view of such circumstances, and during homogeneous operation, by dividing the injection into a plurality of injections and dispersing the spray, the fuel can be partially concentrated, Prevents soot from adhering to the combustion chamber wall, thereby setting the spray shape and the position of the fuel injection valve so that the appropriate mixture can be concentrated near the ignition plug during stratified operation in a low load range. It is intended to make it possible. Further, it is an object to improve engine combustion stability and exhaust performance both in the stratified operation and the homogeneous operation.

[0007]

According to a first aspect of the present invention, a fuel injection valve for directly injecting fuel into a combustion chamber and a spark plug are provided. Accordingly, in a combustion control device for a direct-injection spark ignition type internal combustion engine, a stratified operation in which the spray is concentrated near the spark plug and a homogeneous operation in which the spray is uniformly dispersed throughout the combustion chamber are performed, and one cycle is performed during the homogeneous operation. Split injection control means for executing a plurality of medium fuel injections is characterized in that the split injection control means makes the time interval and the injection amount ratio of each injection variable according to the engine speed and the load.

[0008] That is, the present invention utilizes the property that the spray length of the spray is smaller than that of the spray having a larger injection amount than the spray having a larger injection amount. Prevents adhesion. The reason why the smaller the spray amount of the spray is, the shorter the arrival length of the spray is because the arrival length of the spray is determined by the momentum of the fuel. Be shorter.

At the time of homogeneous operation in which the fuel injection amount is relatively large, by dividing the number of injections into a plurality of injections, the injection amount per injection becomes small. Thereby, the reaching length of each spray becomes short, and the spray becomes easy to be placed on the in-cylinder flow, thereby preventing the wall surface from adhering and promoting the dispersion of the fuel into the inside of the cylinder.

[0010] In such a homogeneous operation, the fuel can be surely dispersed to prevent HC reduction and soot generation. Therefore, the spray angle and mounting angle of the fuel injection valve are suitable for stratified combustion. It becomes possible. That is, it is possible to set, for example, a relatively narrow spray angle so that the air-fuel mixture is concentrated near the ignition plug.

Further, since the gas flow in the cylinder due to, for example, tumble changes in conjunction with the engine rotation speed, the injection time interval is controlled to prevent the interference of the sprays of the multiple injections and promote the dispersion. It is important to. Control of the fuel injection amount in each injection is also important for promoting the dispersion of fuel in the cylinder, and it is necessary to set the fuel injection amount to an optimum value according to the engine speed and the load.

According to a second aspect of the present invention, the maximum injection pulse time width per injection is preset with respect to the engine speed. The maximum injection pulse time width is set to be shorter on the higher speed side. That is, the number of injections is set so as not to exceed a predetermined maximum injection pulse time width. In addition, the gas flow in the cylinder becomes active when the engine rotation speed increases, but by shortening the maximum injection pulse time width on the high speed side, the spray reach distance is shortened, and collision with the opposing bore wall surface is avoided. Is done.

According to a third aspect of the present invention, the split injection control means keeps an interval of a plurality of injections at a substantially constant crank angle with respect to a change in engine operating conditions. The in-cylinder flow is interlocked with the engine rotation speed at approximately 1: 1. Therefore, if the interval between the injections is maintained at a substantially constant crank angle, the overlap of the sprays is reliably prevented, and the dispersion of the sprays can be promoted.
The time interval becomes longer as the rotation becomes lower.

Further, according to a fourth aspect of the present invention, the split injection control means keeps an interval of a plurality of injections approximately constant at a crank angle with respect to a change in engine operating conditions. It is characterized in that the number of injections in one cycle increases as the load increases. The injection amount required during one cycle increases as the load increases. However, as the engine rotation speed increases, the injection pulse width is limited to be shorter by the maximum injection pulse time width. Then, the number of injections increases according to the load while the injection interval is kept substantially constant at the crank angle.

According to a fifth aspect of the present invention, the split injection control means sets the injection end timing of the last injection to a predetermined crank angle position with respect to an increase in load and rotation speed. In this case, the predetermined injection interval of each injection is corrected to be short so as not to be delayed. In other words, basically, the interval between each injection is kept substantially constant at the crank angle, but especially at a high load and a high rotation speed,
Since the injection amount is large and the crank angle corresponding to the unit time is long, the entire injection period in one cycle is performed over a relatively long crank angle period. As a result, if the injection end timing of the last injection is later than the predetermined crank angle position, the homogeneity in the cylinder may be hindered. Therefore, in this case, the predetermined injection interval of each injection is corrected to be short so that the injection end timing of the final injection is not delayed from the predetermined crank angle position.

Further, in the invention of claim 6, the split injection control means reduces the number of injections so that the injection suspension period does not become shorter than a predetermined suspension period in response to an increase in load and rotational speed. It is characterized in that a predetermined injection interval of injection is corrected to be long. That is, when the load and the rotation speed increase, the injection suspension period becomes relatively short. However, when this period is excessively short, the effect of dividing the injection decreases. Therefore, in this case, the number of injections is reduced and the predetermined injection interval of each injection is corrected to be longer so that the injection pause period is not shorter than the predetermined pause period.

In the invention of claim 7, the split injection control means performs a relatively large pause after performing a plurality of injections between the intake stroke and the compression stroke in the high rotation range and the high load range. It is characterized in that the remaining fuel is injected once or a plurality of times over a period. In other words, when the amount of fuel required during one cycle is large and the entire amount cannot be injected by the preset crank angle, the injection of the remaining amount is more appropriate in the fuel chamber than in the case where the fuel is uniformly dispersed in the cylinder. Arranging them at appropriate positions is more effective in preventing the generation of soot and preventing an increase in HC.

[0018]

According to the first aspect of the present invention, it is possible to disperse the spray to an appropriate position during the homogeneous operation and to prevent the wall from adhering. Therefore, for example, by applying to a direct injection spark ignition type internal combustion engine of a type that realizes stratified combustion by transporting the air-fuel mixture to the vicinity of the ignition plug by tumble flow, in stratified operation, a narrow spray having a strong penetration force is used. In addition, reliable stratified combustion can be realized, and at the same time, soot generation and HC increase in homogeneous combustion can be prevented, and good performance can be obtained.

According to the second aspect of the present invention, by shortening the maximum injection pulse time width with an increase in the engine speed, the arrival length of the spray can be restricted to be short, and increases with an increase in the engine speed. Even under the in-cylinder flow, it is possible to prevent the spray from colliding with the opposed bore wall surface.

According to the third aspect of the present invention, by maintaining the interval between the injections at a substantially constant crank angle, the overlapping of the sprays can be reliably prevented, and the dispersion of the sprays can be promoted.

According to the fourth aspect of the present invention, even under a condition where the load increases, the dispersion of the spray can be promoted by increasing the number of injections while keeping the injection interval constant.

According to the fifth aspect of the invention, even when the load is high and the rotation speed is high, the injection end timing of the final injection is not delayed from the predetermined crank angle position, and the uniform injection in the cylinder is prevented. It is possible to prevent a decrease in degree.

According to the sixth aspect of the invention, when the load and the rotation speed increase, the injection suspension period can be prevented from becoming excessively short, and the fuel dispersing effect by dividing and performing the injection can be reliably maintained. . Further, it is possible to prevent the number of times of operation of the fuel injection valve from excessively increasing, thereby improving the durability of the fuel injection valve.

According to the present invention, when the entire amount cannot be injected by a preset crank angle, the remaining fuel can be arranged at an appropriate position in the combustion chamber, and the occurrence of soot can be prevented. And an increase in HC can be prevented.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a four-cycle type automobile gasoline engine which is a direct injection spark ignition type internal combustion engine will be described below with reference to the drawings.

FIG. 1 is a sectional view of the direct-injection spark ignition type internal combustion engine, particularly showing a state during fuel injection in a compression stroke. In FIG. 1, 1 is a cylinder head, 2
Represents a cylinder, 3 represents a piston, 4 represents a combustion chamber formed by the piston 3 in the cylinder 2, 5 represents an intake port, and 6 represents an exhaust port. Above intake port 5
Two exhaust ports 6 are provided for each cylinder.

The cylinder head 1 includes the combustion chamber 4
The ignition plug 7 is attached so as to be located substantially at the center on the upper surface side of the
A fuel injection valve 8 for directly injecting fuel into the combustion chamber 4 is attached to a lower portion between the fuel injection valves. This fuel injection valve 8
Has a relatively narrow spray angle, and is mounted in such a manner that fuel is directed obliquely downward from the horizontal so as to point near the lower part of the spark plug 7.

Here, in the combustion chamber 4, a tumble (vertical vortex) flow indicated by an arrow T is formed during the intake stroke by the action of the shape of the intake port 5 or the use of an intake control valve (not shown). The top of the piston 3
A concave portion corresponding to the tumble is formed. When performing stratified combustion, the fuel injection valve 8 injects fuel into the combustion chamber 4 (below the ignition plug 7) at a relatively late stage of the compression stroke. The fuel spray by this injection is transported toward the spark plug 7 by the tumble flow in the cylinder,
A combustible air-fuel mixture is formed in a layer around.

Next, the mixture formation according to the present invention will be described in more detail.

When the mounting angle of the fuel injection valve 8 is small and the spray angle is narrow, the spray (indicated by the symbol F in the drawing) is directly directed downward under the ignition plug 7 during the stratified operation as shown in FIG. As a result, a combustible air-fuel mixture can be formed in the vicinity of the ignition plug 7, so that the combustion stability and the exhaust performance in stratified operation are improved. On the other hand, at the time of high load in which homogeneous combustion is performed, as shown in FIG. 2, the spray length is increased by the narrow spray angle, so that the wall surface adhesion to the opposed bore wall surface increases, and HC and soot increase. There's a problem.

FIG. 3 shows the relationship between the spray amount and the spray reaching distance. As shown in the figure, the spray length of the spray having a small spray amount is longer than the spray length of the spray amount. Be shorter. In the present invention, by utilizing such properties, during homogeneous combustion in which the fuel injection amount increases, the fuel injection distance is shortened by dividing the fuel injection into a plurality of times, and the wall surface to the opposed bore wall surface is reduced. This prevents adhesion and prevents an increase in HC and soot. Here, the reason why the smaller the injection amount of the spray is, the shorter the reaching length of the spray is because the reaching length of the spray is determined by the momentum of the fuel,
When the injection amount is small, the momentum is small, so that the spray reaching length becomes short.

FIG. 4 shows a state of formation of the spray F when the number of injections is divided into a plurality of times in a state where the fuel injection amount under a high load is large. As described above, by reducing the injection amount per injection by dividing the injection into a plurality of injections, the spray arrival length of each injection is shortened, and as shown in FIG. Becomes for that reason,
It prevents wall adhesion and promotes the dispersion of fuel in the cylinder,
HC can be reduced and soot generation can be prevented.

Next, the control for forming the air-fuel mixture according to the present invention will be described.

FIG. 5 is a block diagram showing a control device of the fuel injection valve 8 and the like in the direct injection spark ignition type internal combustion engine.

The operation of the fuel injection valve 8 and the spark plug 7 is controlled by an engine control unit (ECU) 10 together with a fuel pump 9 for supplying high-pressure fuel to the fuel injection valve 8. For these controls, the ECU 10 includes a well-known crank angle sensor 1.
1. Signals are input from the cylinder discrimination sensor 12, the throttle sensor 13, the air amount sensor 14, the fuel pressure sensor 15, the air-fuel ratio sensor 16, the water temperature sensor 17, and the like.

The ECU 10 calculates the required fuel injection amount in one cycle according to the engine speed and load based on the signals from these various sensors, and generates the required fuel pressure by controlling the fuel pump 9 to inject the fuel. The engine is controlled by driving the fuel injection valve 8 by a pulse signal to perform fuel injection, and by driving an ignition coil (not shown) by the ignition signal to discharge the ignition plug 7 and perform ignition.

Hereinafter, the fuel injection control will be described.

FIG. 6 shows a basic pattern of fuel injection during homogeneous combustion according to the present invention. The injection pattern at the time of multiple injections includes the injection start timing of the first injection and the injection period τ1,
Injection start timing of the next injection (that is, injection interval τ12, τ2
3) and the injection period (τ2, τ3...) Are controlled. These injection start timing and injection period are variably set according to the engine speed and the load.

FIG. 7 corresponds to the contents of claim 2 and shows a case where the speed is low and a case where the speed is high with the same load. With the increase of the engine speed, the maximum injection pulse time width per injection is set short, so that at high speed, the number of injections increases and the injection pulse time width decreases at high speed so as not to exceed this. I have.

FIG. 8 corresponds to the contents of claim 5, wherein when the number of injections is increased with an increase in load and rotation, the injection end timing of the final injection is set to (A). As described above, there may be a case where it is later than the predetermined crank angle position θ1. In such a case, in order to avoid a decrease in the degree of homogeneity, the preset injection interval (τ12, τ23) is set so that the injection end timing of the final injection becomes the preset crank angle position θ1. Is corrected to be shorter.

FIG. 9 corresponds to the contents of claim 6, in which the injection suspension period becomes shorter than the preset suspension period as the load and rotation increase (see FIG. 9A). ), The number of injections is reduced and the preset injection interval (τ12) is corrected to be longer, as shown in FIG.

FIG. 10 corresponds to the contents of claim 7, in which the fuel injection is performed a plurality of times from the intake stroke to the compression stroke at a high rotation speed and a high load, and thereafter, after a certain period of suspension. The remaining fuel is injected by at least one or more fuel injections.

FIG. 11 shows a control map when the number of injections is switched according to the engine speed and the load. As shown in the figure, stratified charge combustion occurs in the low-speed, low-load region, and at this time, the entire amount is injected at one time. In the homogeneous combustion region, the number of injections is controlled in the range of 1 to 4 times, and the number of injections generally increases on the high-speed, high-load side.

A line A in the figure indicates that, when the injection amount is the same, the number of injections is increased with an increase in the engine speed, and indicates a region in which the control of claim 2 shown in FIG. 7 is performed.

The line B in the figure indicates a line in which the number of injections increases with an increase in the engine speed and load.
9 shows an area where the control of claim 4 is performed.

A line C in the figure indicates a line in which the injection interval is shortened as the engine speed and the load increase, and indicates a region in which the control of claim 5 shown in FIG. 8 is performed.

A line D in the figure indicates a line for reducing the number of injections in order to secure an idle period in response to an increase in the engine speed and the load. Show.

The line E in the figure is a region where the total injection amount per cycle is very large. After a plurality of injections, after a certain pause period, the remaining fuel is injected again. And the region where the control of claim 7 shown in FIG. 10 is performed is shown.

Next, FIG. 12 is a flowchart showing the flow of the fuel injection control described above. The processing shown in this flowchart implements the split injection control means.

In step 1 (referred to as S1 in the figure, the same applies hereinafter), operating conditions such as engine speed, cooling water temperature and the like are detected based on detection signals from the above-mentioned sensors.

In step 2, based on the detected operating state, the fuel injection amount required for one cycle is calculated using a predetermined calculation formula or map. And in step 3,
From the fuel injection amount and the fuel pressure detected by the fuel pressure sensor 15, an injection pulse width (full injection period) τ required in one cycle is calculated.

In step 4, an injection pattern is determined from the engine speed and load with reference to the table shown in FIG. 11, and the number of injections, the maximum injection amount that can be injected once (maximum injection pulse width), Injection start time of the first injection,
The injection interval is read.

In step 5, the pulse width of each injection is calculated according to each injection pattern. For example, when N injections are set, the injection pulse width from the first injection to the (N-1) th injection is set to the maximum injection pulse width per injection at that time, and the Nth injection is performed. Is obtained as “all injection periods− (N−1) * (maximum injection pulse width that can be injected by one rotation in the rotation)”.

In step 6, a correction calculation of the injection interval is performed, and in step 7, the start timing of each injection is calculated from the first injection start timing and the injection interval. Then, in step 8, the ignition timing is calculated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state of a direct injection spark ignition type internal combustion engine according to the present invention during a stratified operation.

FIG. 2 is an explanatory diagram showing a spray state when injection is not divided during homogeneous combustion.

FIG. 3 is a characteristic diagram showing a relationship between a spray tip reaching distance and an injection amount.

FIG. 4 is an explanatory diagram showing a spray state when injection is divided during homogeneous combustion.

FIG. 5 is a block diagram of a control device.

FIG. 6 is an explanatory view showing a basic ejection pattern according to the present invention.

FIG. 7 is an explanatory view showing an injection pattern corresponding to the contents of claim 2;

FIG. 8 is an explanatory view showing an injection pattern corresponding to the contents of claim 5;

FIG. 9 is an explanatory view showing an injection pattern corresponding to the contents of claim 6;

FIG. 10 is an explanatory view showing an injection pattern corresponding to the contents of claim 7;

FIG. 11 is a characteristic diagram showing a table for setting an injection pattern.

FIG. 12 is a flowchart showing the flow of injection control according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cylinder head 2 ... Cylinder 3 ... Piston 4 ... Combustion chamber 5 ... Intake port 6 ... Exhaust port 7 ... Spark plug 8 ... Fuel injection valve 10 ... Engine control control unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/02 301 F02D 41/02 301A (72) Inventor Koichi Yamaguchi 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Within the Automobile Co., Ltd. (72) Inventor Kenmei Kubo 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa F-term (reference) 3G301 HA01 HA04 HA16 JA02 JA03 JA21 JA29 KA06 KA08 KA23 KA24 LB04 LB07 MA11 MA18 MA26 NA07 NC04 ND03 NE11 NE12 NE14 NE15 PA01Z PA11Z PB03A PB05A PB08Z PD02Z PE03Z PE05Z PE09A

Claims (7)

[Claims] 1. A stratified operation in which a fuel injection valve for directly injecting fuel into a combustion chamber and a spark plug are provided, and spray is concentrated near the spark plug in accordance with engine operating conditions. A combustion control apparatus for a direct injection spark ignition type internal combustion engine in which a homogeneous operation for homogeneously dispersing is performed, comprising: a divided injection control means for executing a plurality of fuel injections in one cycle during the homogeneous operation; Is a combustion control apparatus for a direct injection spark ignition type internal combustion engine, wherein a time interval of each injection and an injection amount ratio are made variable according to an engine rotation speed and a load. 2. The split injection control means according to claim 1, wherein a maximum injection pulse time width per injection is preset with respect to an engine rotation speed, and the maximum injection pulse time width is set shorter on a higher speed side. The combustion control device for a direct injection spark ignition type internal combustion engine according to claim 1, wherein: 3. The direct-injection spark ignition according to claim 1, wherein the split injection control means keeps an interval of a plurality of injections at a substantially constant crank angle with respect to a change in engine operating conditions. A combustion control device for an internal combustion engine. 4. The split injection control means keeps an interval of a plurality of injections substantially constant at a crank angle with respect to a change in engine operation conditions, and increases the number of injections in one cycle with an increase in load. The combustion control device for a direct injection spark ignition type internal combustion engine according to claim 2, characterized in that: 5. The split injection control means sets a predetermined injection interval of each injection so that the injection end timing of the last injection is not delayed from a predetermined crank angle position with respect to an increase in load and rotation speed. 4. The combustion control device for a direct injection spark ignition type internal combustion engine according to claim 3, wherein the correction is made short. 6. The split injection control means reduces the number of injections so that the injection suspension period is not shorter than a predetermined suspension period in response to an increase in load and rotation speed.
The combustion control device for a direct injection spark ignition type internal combustion engine according to claim 3, wherein a predetermined injection interval of each injection is corrected to be long. 7. The divided injection control means performs a plurality of injections between an intake stroke and a compression stroke in a high rotation range and a high load range, and then, after a relatively long rest period, The combustion control device for a direct injection spark ignition type internal combustion engine according to claim 1, wherein the fuel is injected once or plural times.