Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2000-09-05
2002-07-30
Kwon, John (Department: 3754)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S430000, C123S305000
Reexamination Certificate
active
06425366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a control system for an internal combustion engine, and more particularly to a control system for an in-cylinder direct injection internal combustion engine, which controls the operation of the engine such that the combustion mode of the engine is switched between a stratified combustion mode for performing stratified combustion of an air-fuel mixture, and a homogeneous combustion mode for performing homogeneous combustion of the air-fuel mixture, and that torque generated by the engine is controlled based on a desired torque.
2. Description of the Prior Art
Conventionally, a control system for an internal combustion engine, of the above-mentioned kind, was proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 10-103118. This internal combustion engine is installed on an automotive vehicle and includes two kinds of fuel injection valves, one for use in stratified combustion and the other for use in homogeneous combustion. Fuel injection valves for stratified combustion are each mounted in a cylinder head for a corresponding one of cylinders such that fuel is directly injected into a combustion chamber of the corresponding cylinder. Further, a fuel injection valve for homogeneous combustion is mounted in an intake pipe at a location upstream of a throttle valve such that fuel is injected into the intake pipe.
The control system controls the operation of the internal combustion engine such that the combustion mode of the engine is switched between a stratified combustion mode selected when the engine is in a low-load operating condition, and a homogeneous combustion mode selected when the engine is in a high-load operating condition, and that the amount of fuel controlled thereby is injected from the fuel injection valves for homogeneous combustion and stratified combustion to generate a required torque. More specifically, the control system determines as the required torque a total desired injection amount of fuel to be injected from the two kinds of fuel injection valves, based on operating conditions (engine rotational speed, accelerator pedal opening, etc.) of the engine, compares the total desired injection amount with a threshold, and switches the combustion mode between the stratified combustion mode and the homogeneous combustion mode according to results of the comparison.
In the homogeneous combustion mode, fuel injection is carried out by using the two kinds of fuel injection valves, and a desired fuel injection amount (hereinafter referred to as “the homogeneous desired injection amount”) to be injected from the fuel injection valve for homogeneous combustion, and a desired fuel injection amount (hereinafter referred to as “the stratified desired injection amount”) to be injected from one of the fuel injection valves for stratified combustion are determined in the following manner: A correction coefficient is determined based on operating conditions of the engine to multiply the total desired injection amount by the correction coefficient, and the resulting product of the multiplication is set to the homogeneous desired injection amount. Further, based on the homogeneous desired injection amount calculated this time and a smoothing value (averaging value) calculated last time, a present smoothing value is calculated, and a difference calculated by subtracting the present smoothing value from the total desired injection amount is set to the stratified desired injection amount. In the homogeneous combustion mode, the homogeneous desired injection amount and the stratified desired injection amount are set as described above.
On the other hand, in the stratified combustion mode, the homogeneous desired injection amount is set to “0” and the stratified desired injection amount is set to a difference calculated by subtracting the present smoothing value from the total desired injection amount, whereby fuel injection is carried out only by using the fuel injection valve for stratified combustion. When the operating condition of the engine becomes stable after the combustion mode is switched from the homogenous combustion mode to the stratified combustion mode, the smoothing value becomes almost equal to “0”, so that the total desired injection amount is set to the stratified desired injection amount, without any substantial subtraction.
In the control system constructed as above, when the total desired injection amount is increased with an increase in the required torque, the combustion mode of the engine is switched from the stratified combustion mode to the homogeneous combustion mode. As described above, the fuel injection valve for homogeneous combustion is located farther from the combustion chamber than the fuel injection valves for stratified combustion are, so that when the stratified combustion mode is switched to the homogeneous combustion mode, fuel from the fuel injection valve for homogeneous combustion is supplied to the combustion chambers with some delay, i.e. later than fuel from the fuel injection valves for stratified combustion. To eliminate this inconvenience, the homogeneous desired injection amount and the stratified desired injection amount are calculated, as described above, such that the stratified desired injection amount is increased by an amount of fuel corresponding to the above delay. This makes it possible to prevent the air-fuel ratio of an air-fuel mixture supplied to the engine and the output torque generated by combustion of the mixture from being largely changed upon switching of the combustion mode from the stratified combustion mode to the homogeneous combustion mode. Similarly, when the homogeneous combustion mode is switched to the stratified combustion mode in response to a decrease in the required torque, fuel is injected in the stratified desired injection amount which is the difference calculated by subtracting the smoothing value from the total desired injection amount, whereby a large change in the air-fuel ratio can be prevented.
According to the conventional control system, it is possible to prevent a large change in the air-fuel ratio when the combustion mode is switched between the stratified combustion mode and the homogeneous combustion mode, as described above. However, when the engine enters a relatively stable operating condition with the lapse of a transitional time period after the combustion mode is switched e.g. to the homogeneous combustion mode, there no longer occur significant changes in the total desired injection amount or the homogeneous desired injection amount, and the smoothing value also becomes almost constant, so that the smoothing does not produce almost any effect. Similarly, the stratified desired injection amount also ceases to undergo any significant change. For this reason, an actual sum-total desired injection amount which is the sum total of the homogeneous desired injection amount and the stratified desired injection amount both finally determined and injected respectively from the two kinds of fuel injection valves becomes almost identical to the total desired injection amount calculated based on operating conditions of the engine. As a result, the sum-total desired injection amount for actual injection comes to be sensitively changed in response to a slight change in the required torque, e.g. a subtle change in the engine rotational speed or the accelerator pedal opening, so that the air-fuel ratio is too sensitively changed, resulting in degraded drivability. Further, when a transitional time period has elapsed after the combustion mode is switched to the stratified combustion mode, the smoothing value becomes almost equal to “0”, so that the total desired injection amount is directly set to the stratified desired injection amount. Therefore, when a subtle change occurs in the required torque, the air-fuel ratio is sensitively changed in direct response to the subtle change, thereby causing the same problem as in the homogeneous combustion mode.
SUMMARY OF THE INVENTION
It is an object of the inven
Komoriya Isao
Nagatani Shuji
Ogawa Ken
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Kwon John
Vo Hieu T.
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