JP3692745B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection control device for a direct injection spark ignition type internal combustion engine, and more particularly to a fuel injection control device that changes a fuel injection rate in accordance with engine operating conditions.
[0002]
[Prior art]
A conventional fuel injection control device for a direct injection spark ignition type internal combustion engine is disclosed in Japanese Patent Laid-Open No. 7-63061.
In this, in a direct injection spark ignition type internal combustion engine in which fuel is directly injected from a fuel injection valve into a combustion chamber and is directly ignited by an ignition plug, the combustion chamber includes a main combustion chamber and the main combustion chamber. And an outer combustion chamber formed in an annular shape so as to surround the fuel, and fuel injection from the fuel injection valve is performed toward the main combustion chamber when the load is low, and toward the main combustion chamber and the outer combustion chamber when the load is high Is set to be done.
[0003]
The fuel injection valve is disposed at the outer peripheral edge of the combustion chamber, has a first injection hole directed to the main combustion chamber, and a second injection hole directed to the outer combustion chamber, and corresponds to a fuel injection amount from the first injection hole. The ratio of the fuel injection amount from the second nozzle hole is increased when the engine load is large compared to when the engine load is small.
For such control, the fuel injection valve has a variable lift valve that is lifted according to the engine load, and the first injection hole and the second injection hole are arranged offset in the lift direction of the variable lift valve. It is installed.
[0004]
[Problems to be solved by the invention]
However, such a conventional fuel injection control device has the following problems.
When the fuel injection rate is controlled, a variable lift valve is used. However, a variable mechanism for the lift amount is technically difficult, and the possibility of practical use is extremely low.
[0005]
Further, although a plurality of injection holes in the hole nozzle type fuel injection valve are assumed, it is impossible to use a plurality of injection holes offset in the lift direction when a swirl nozzle type fuel injection valve is used.
In addition, in stratified combustion of a direct-injection spark ignition internal combustion engine, combustion instability due to fuel diffusion on the high rotation side, combustion instability due to overconcentration on the high load side, and plug smoldering are in a trade-off relationship. It is a difficult problem to solve.
[0006]
In view of such a situation, the present invention provides a fuel injection control device capable of improving combustion performance in a direct-injection spark-ignition internal combustion engine by changing the fuel injection rate according to engine operating conditions in a simpler manner. The purpose is to provide.
[0007]
[Means for Solving the Problems]
For this reason, as a result of diligent research, the present inventors, in a direct injection spark ignition internal combustion engine, inject fuel at a high pressure, and therefore the injection time is relatively short. It has been found that by changing the voltage, the fuel injection rate can be changed by changing the valve opening speed during the valve opening operation of the fuel injection valve, leading to the following invention.
[0008]
In a first aspect of the invention, in a direct injection spark ignition internal combustion engine having an electromagnetic fuel injection valve that directly injects fuel into the combustion chamber, the valve opening speed of the fuel injection valve is changed according to engine operating conditions . Therefore, the provided driving voltage varying means for varying a driving voltage for opening operation of the fuel injection valve, a fuel injection control apparatus.
The driving voltage referred to here is the former among the relatively large valve opening operation voltage for opening the fuel injection valve and the relatively small valve opening holding voltage for holding the fuel injection valve open. is there.
[0009]
In the invention according to claim 2, the drive voltage varying means is used for engine combustion during stratified combustion (stratified combustion performed by intensively forming a stratified mixture around the spark plug by injecting fuel in the compression stroke). The drive voltage is changed according to the rotation speed and the load.
The invention according to claim 3 is characterized in that the drive voltage varying means increases the drive voltage as the engine speed increases and the engine load decreases during stratified combustion.
[0010]
In the invention according to claim 4, the drive voltage varying means is high during homogeneous combustion (homogeneous combustion in which fuel is diffused into the combustion chamber by injecting fuel during the intake stroke to form a homogeneous mixture). It is characterized in that the driving voltage is increased as the rotation and the load become higher.
The invention according to claim 5 is characterized in that pulse width correction means for correcting a pulse width for determining the ejection time is provided in accordance with a change in drive voltage by the drive voltage variable means.
[0011]
【The invention's effect】
According to the first aspect of the present invention, in the direct injection spark ignition internal combustion engine, the valve opening speed during the valve opening operation of the fuel injector is changed by changing the drive voltage to the fuel injector according to the engine operating conditions. By changing the fuel injection rate, the fuel injection rate can be changed. Therefore, it is possible to improve the combustion performance by making the fuel injection rate variable according to the engine operating conditions by an extremely simple method.
[0012]
According to the second aspect of the present invention, during stratified combustion, the drive voltage is changed in accordance with the engine speed and the load, so that the stratified combustion generally has a relatively small amount of fuel injection at low rotation and low load. Since it is performed in the region, the change in the fuel injection rate due to the drive voltage is significant, and the degree of stratification (the degree of fuel clumping) greatly affects the combustion performance, which is extremely effective.
[0013]
According to the invention of claim 3, the trade-off relationship can be solved by increasing the drive voltage as the engine speed increases and the engine load decreases during stratified combustion. In other words, on the high speed side, the fuel is more likely to diffuse due to the influence of flow, but by increasing the drive voltage and the fuel injection rate, fuel diffusion is prevented and good stratified combustion is achieved. it can. On the high load side, since the fuel injection amount is relatively large, the fuel may concentrate too much around the spark plug, causing smoldering of the plug, etc., but the drive voltage is reduced to reduce the fuel injection rate. By doing so, the fuel can be diffused to some extent and smoldering of the plug can be prevented.
[0014]
According to the fourth aspect of the present invention, the combustion performance can be improved to some extent by increasing the drive voltage at higher rotation speed and higher load during homogeneous combustion, although the effect is not as good as during stratified combustion.
According to the fifth aspect of the present invention, by correcting the pulse width that determines the injection time in accordance with the change of the drive voltage, it is possible to reliably prevent the deviation of the air-fuel ratio. .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram showing an embodiment of the present invention.
In the direct-injection spark-ignition internal combustion engine 1, a recess (cavity) 3 is formed at an eccentric position of the top surface of the piston 2, and a combustion chamber 5 is formed between the cylinder head 4. A spark plug 6 is attached to a substantially central position of the cylinder head 4 and faces the combustion chamber 5. On the other hand, the fuel injection valve 7 is attached to the cylinder wall and faces the combustion chamber 5.
[0016]
Here, by injecting fuel from the fuel injection valve 7 in the compression stroke, a stratified mixture can be formed intensively around the spark plug 6 to cause stratified combustion, and in the intake stroke By injecting the fuel, the fuel is diffused into the combustion chamber 5 to form a homogeneous air-fuel mixture, and homogeneous combustion can be performed.
The fuel injection valve 7 is of an electromagnetic type (solenoid drive type) and is configured as shown in FIGS.
[0017]
Referring to FIG. 2, when a voltage signal is applied to the coil 12 via the terminal 11, a current flows through the coil 12, and a magnetic circuit is formed by the core 13, the yoke 14, and the plunger 15. The core 13 is sucked against it. When the plunger 16 moves, the ball valve 17 integrated with it moves away from the seat surface 19 of the nozzle 18 and opens the nozzle hole 20. Thereby, fuel injection is performed.
[0018]
A cylindrical swirler 21 is provided surrounding the ball valve 17. As shown in FIGS. 3 and 4, the swirler 21 is formed with a plurality of fuel grooves 22 that guide the fuel in the tangential direction, thereby imparting a turning force to the injected fuel.
The voltage signal to the fuel injection valve 7 is applied from the drive circuit 8 in FIG.
The drive circuit 8 outputs an injection pulse signal (according to engine operating conditions) output from the control unit 9 in FIG. 1 at a fuel injection timing synchronized with engine rotation (compression stroke during stratified combustion, intake stroke during homogeneous combustion). A signal with a pulse width calculated in response) and the command value of the drive voltage, and a comparatively large drive voltage (valve opening voltage) commanded for a certain period of time at the rising edge of the pulse, the subsequent part is compared A voltage signal (see FIG. 5), which is a small constant valve-opening holding voltage, is generated and applied to the fuel injection valve 7.
[0019]
Here, the drive voltage is variably controlled according to the engine operating conditions by the drive voltage varying means 9A configured in software in the control unit 9. Further, the pulse width is corrected by the pulse width correcting means 9B in accordance with the change of the driving voltage.
FIG. 5 shows a case where the drive voltage is increased and a case where the drive voltage is reduced, and FIG. 6 shows a valve lift characteristic when the drive voltage is large and a valve lift characteristic when the drive voltage is small.
[0020]
When the drive voltage is variable, the moving speed of the valve is variable, and as a result, the fuel injection rate is variable. Specifically, when the drive voltage is increased, the moving speed of the valve is increased and the fuel injection rate is increased.
When injecting the same amount of fuel, if the drive voltage is large, the fuel injection rate increases, so the pulse width (injection time) is shortened (see FIG. 5).
[0021]
FIG. 7 shows the movement of in-cylinder fuel during stratified combustion depending on the fuel injection rate. The spatial density of fuel varies depending on the injection rate. When the injection rate is large, as shown in FIG. 7A, the fuel is difficult to diffuse into the cylinder, and as a result, stratified combustion is stabilized. When the injection rate is small, as shown in FIG. 7 (B), the fuel in the cylinder is likely to diffuse, preventing excessive fuel concentration on the high load side in stratified combustion and preventing smoldering of the plug. In addition, mixing of fuel in the cylinder is promoted during homogeneous combustion, leading to stable combustion and reduced exhaust emissions.
[0022]
A specific control example will be described below.
FIG. 8 is a flowchart of the control example 1.
In step 1 (denoted as S1 in the figure, the same applies hereinafter), the engine speed and load (for example, intake air amount) are read.
In step 2, the drive voltage is set with reference to the map of FIG. 9A in which the drive voltage is determined using the engine speed and the load as parameters. This portion corresponds to drive voltage varying means.
[0023]
In step 3, the pulse width is set with reference to the map of FIG. 9B in which the pulse width is determined using the engine speed and the load as parameters in correspondence with the map of FIG. 9A. This part corresponds to the pulse width correction means.
Here, in the map of FIG. 9A, at the time of stratified combustion in the low rotation / low load region, the drive voltage is increased as the engine speed increases and the engine load decreases.
[0024]
As a result, on the high rotation side during stratified combustion, fuel tends to diffuse due to the influence of flow, but by increasing the drive voltage and increasing the fuel injection rate, fuel diffusion is prevented and good Stratified combustion can be realized. On the high load side during stratified combustion, the amount of fuel injected is relatively large, so fuel may concentrate too much around the spark plug and cause smoldering of the plug. By reducing the injection rate, fuel can be diffused to some extent and smoldering of the plug can be prevented.
[0025]
Also, during homogeneous combustion, increasing the drive voltage at higher speeds and loads makes it possible to improve the combustion performance to some extent, although not as effective as during stratified combustion.
Further, the map of FIG. 9B is set so that the basic pulse width corresponding to the engine speed and the load includes a correction corresponding to the driving voltage at that time, and the pulse is generated when the driving voltage is high. When the width is short and the driving voltage is low, the pulse width is lengthened.
[0026]
FIG. 10 is a flowchart of the control example 2.
In step 11, the engine speed and load (for example, intake air amount) are read.
In step 12, the basic pulse width is determined by referring to the map of FIG. 11A in which the basic pulse width is determined assuming that the drive voltage is constant (basic drive voltage) using the engine speed and load as parameters. Set.
[0027]
In step 13, the voltage correction coefficient is set with reference to the map of FIG. 11B in which the voltage correction coefficient is determined using the engine speed and the load as parameters in correspondence with the map of FIG.
In step 14, the basic drive voltage (constant) is multiplied by a voltage correction coefficient to set the drive voltage. This portion corresponds to drive voltage varying means.
[0028]
In step 15, the pulse width is set by dividing the basic pulse width by the voltage correction coefficient (multiplying the basic pulse width by the inverse of the voltage correction coefficient) and further multiplying by the correction coefficient (a constant that is matched by experiment etc.). To do. This part corresponds to the pulse width correction means.
This control example 2 is the same in characteristics as the control example 1 except for the method.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of the present invention. FIG. 2 is a cross-sectional view of a fuel injection valve. FIG. 3 is an enlarged view of a nozzle portion of the fuel injection valve. FIG. 5 is an explanatory diagram of drive voltage. FIG. 6 is a diagram showing valve lift characteristics depending on the magnitude of the drive voltage. FIG. 7 is a diagram showing movement of in-cylinder fuel during stratified combustion by the magnitude of the injection rate. Flowchart of Example 1 [FIG. 9] Diagram showing a map used in Control Example 1. [FIG. 10] Flowchart of Control Example 2. [FIG. 11] Diagram showing a map used in Control Example 2. [Explanation of Symbols]
DESCRIPTION OF SYMBOLS 1 Direct injection spark ignition internal combustion engine 5 Combustion chamber 6 Spark plug 7 Fuel injection valve 8 Drive circuit 9 Control 9A Drive voltage variable means 9B Pulse width correction means

Claims (5)

In a direct-injection spark-ignition internal combustion engine equipped with an electromagnetic fuel injection valve that directly injects fuel into a combustion chamber,
When fuel injection is performed, a drive voltage that is a relatively large voltage is first applied to a valve opening coil of the fuel injection valve to open the fuel injection valve, and then a valve that is relatively small in voltage is opened. It is configured to hold the fuel injection valve in an open state by applying a holding voltage,
In order to change the valve opening speed of the fuel injection valve according to the engine operating conditions, the drive voltage of the drive voltage for opening the fuel injection valve and the valve opening holding voltage thereafter is the magnitude of the drive voltage. the fuel injection control device for an internal combustion engine, characterized in that a driving voltage varying means for varying a of. 2. The fuel injection control device for an internal combustion engine according to claim 1, wherein the drive voltage varying means changes the drive voltage according to the engine speed and load during stratified combustion. 3. The fuel injection for an internal combustion engine according to claim 2, wherein the drive voltage varying means increases the drive voltage as the engine speed increases and the engine load decreases during stratified combustion. Control device. 4. The fuel injection control device for an internal combustion engine according to claim 3, wherein the drive voltage varying means increases the drive voltage at higher revolutions and higher loads during homogeneous combustion. The pulse width correction means for correcting the pulse width for determining the ejection time in accordance with the change in the drive voltage by the drive voltage variable means is provided. Fuel injection control device for internal combustion engine.

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