Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2002-03-15
2003-12-30
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S301000, C123S305000
Reexamination Certificate
active
06668792
ABSTRACT:
BACKGROUND OF THE INVENTION
a. Field of the Invention
This invention relates to a control system for an in-cylinder direct injection engine which controls the behavior of fuel spray, directly injected into a combustion chamber in a cylinder, with a tumble to combust a mixture stratified around an electrode of a spark plug, and more particularly relates to the technical field of compensation control for compensating an influence on combustion quality of the mixture resulting from intake air density conditions different than desired.
b. Description of the Prior Art
Conventionally, control systems for in-cylinder direct injection engines of this type include one which is adapted to control the penetration of fuel spray from an injector in accordance with the intensity of a tumble, carry the fuel spray toward a spark plug by means of the tumble and stratify a mixture around an electrode of the spark plug, as disclosed in, for example, Japanese Unexamined Patent publication No. 2000-204954.
Specifically, in the above control system, a tumble control valve (TCV) is provided in an intake passage of the engine downstream of a throttle valve. The TCV is opened or closed by an actuator to control the intensity of the tumble in the combustion chamber. At the same time, the fuel injection pressure of the injector is correspondingly controlled so that the fuel spray penetration is balanced against the tumble. In this manner, the fuel spray from the injector is carried by means of the tumble to reach the vicinity of the electrode of the spark plug, which enables stable stratified combustion.
More specifically, the fuel injection pressure of the injector is experimentally set in advance to change depending upon operating conditions of the engine, and stored as a control map. A value corresponding to the current operating conditions of the engine is read out as a target value for control from the map. Then, the fuel injection pressure of the injector (fuel pressure) is controlled to match the target value so that the fuel spray penetration is balanced against the tumble intensity. The fuel spray is thereby carried by means of the tumble to reach the vicinity of the electrode of the spark plug at the exact ignition timing of the cylinder.
In general, since the temperature of the engine is relatively high as compared with that in the air, the temperature conditions of an intake air taken in the combustion chamber is strongly affected by the engine temperature conditions. In addition, a change in temperature of the intake air involves a change in density thereof, which varies the energy of tumble in the combustion chamber. Therefore, even if attempt is made to control the fuel injection pressure of the injector in accordance with the preset map as in the above-mentioned prior art, the fuel spray and the tumble may be thrown out of balance depending upon the engine temperature conditions so that a mixture may be held against stratification, which invites inconveniences of deterioration in ignitability and combustion quality of the mixture.
Particularly in an engine that performs so-called EGR (Exhaust Gas Recirculation) by recirculating part of an exhaust gas to an intake system, the recirculation rate of exhaust gas to fresh air is generally changed in accordance with the engine operating conditions. This change in recirculation rate of high-temperature exhaust gas causes a significant variation in temperature conditions of the intake air. Accordingly, in the engine of this type, the above inconveniences are more pronounced.
Further, for example, in relatively low atmospheric pressure environments such as highlands, the air density is relatively low as compared with flatlands so that the energy of tumble becomes smaller than that in flatlands. Also in this case, like the above-mentioned prior art, a mixture is held against stratification if the fuel injection pressure of the injector is controlled only in accordance with a preset control map.
The present invention has been made in view of the foregoing points, is directed to a control system for an in-cylinder direct injection engine which controls the behavior of fuel spray with a tumble to provide suitable mixture stratification, and has its object of preventing the fuel spray and the tumble from being thrown out of balance due to a change in intake air temperature or atmospheric pressure and of providing suitable mixture stratification.
SUMMARY OF THE INVENTION
To attain the above object, in the present invention, when an engine is in operation, a value for density conditions of an intake air taken in a combustion chamber is detected, and at least one of the flow rate of ah tumble in the combustion chamber, the fuel injection pressure and the fuel injection timing is compensated so that the intensity of the tumble and the penetration of fuel spray are balanced one against another.
Specifically, a first aspect of the invention has as a precondition a control system (A) for an in-cylinder direct injection engine which includes: a fuel injection valve (
18
) for directly injecting a fuel into a combustion chamber (
6
) in a cylinder (
2
) of an engine (
1
); and tumble generating means (
10
) for generating a tumble in the combustion chamber (
6
), in which the fuel is injected against the tumble in the combustion chamber (
6
) by the fuel injection valve (
18
) during stratified-charge combustion operation of the engine (
1
) so that a flammable mixture stays in the vicinity of an electrode of a spark plug (
16
) at the ignition timing for the cylinder (
2
).
Also, the control system (A) further includes: intake air density detecting means (
50
a
) for detecting a value for density conditions of an intake air taken in the combustion chamber (
6
); revolving speed detecting means (
52
) for detecting the revolving speed of the engine (
1
); intake air flow control means (
34
) for controlling the flow rate of the tumble in the combustion chamber (
6
); fuel pressure control means (
20
) for controlling the fuel injection pressure of the fuel injection valve (
18
); and control means (
50
) for controlling the fuel injection valve (
18
), the intake air flow control means (
34
) and the fuel pressure control means (
20
) based on a value detected by at least one of the intake air density detecting means (
50
a
) and the revolving speed detecting means (
52
), wherein the control means (
50
) sets based on at least the engine revolving speed respective reference target values of the tumble flow rate, fuel injection pressure and fuel injection timing that correspond to the case where the value for density conditions of the intake air is equal to a preset reference value, and the control means (
50
) compensatorily modifies at least one of the reference target values based on a value for the difference between the value detected by the intake air density detecting means (
50
a
) and the reference value.
First, according to part of the control system (A) which constitutes the precondition, the fuel is injected from the fuel injection valve (
18
) against a tumble generated by the tumble generating means (
10
) during stratified-charge combustion operation of the engine (
1
). In this case, the flow rate of the tumble, the fuel injection pressure and the fuel injection timing are basically controlled by the control means (
50
) based on at least the engine revolving speed. Therefore, if the intake air density is equal to the reference value, the penetration of fuel spray from the fuel injector (
18
) is balanced against the tumble so that a mixture is stratified around the electrode of the spark plug (
16
) at the exact ignition timing of the cylinder (
2
).
However, for example, if the engine (
1
) is in higher temperature conditions than normally it is, the intake air will be relatively high in temperature and thereby low in density. In such a case, the energy of tumble becomes relatively small so that the tumble and the fuel spray are thrown out of balance. This inhibits suitable stratification of the mixture and thereby impairs the ignitability a
Mamiya Kiyotaka
Tetsuno Masayuki
Yamauchi Takeo
Castro Arnold
Mazda Motor Corporation
Studebaker Donald R.
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