Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2001-08-10
2003-05-06
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S295000, C123S406550
Reexamination Certificate
active
06557525
ABSTRACT:
RELATED APPLICATIONS
This application claims priority to Japanese Patent Application No. 243379/2000, filed on Aug. 10, 2000 in Japan, and Japanese Patent Application No. 243381/2000, filed on Aug. 10, 2000 in Japan. The contents of the aforementioned applications are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a control system and method and an engine control unit for an internal combustion engine, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke.
2. Description of the Prior Art
Conventionally, as a control system for an internal combustion engine of a port injection type, an ignition timing control system, for instance, is known which has been proposed by Japanese Patent Publication (Kokoku) No. 7-59925. In this control system, the ignition timing is determined based on the amount of intake air and the rotational speed of the engine, and at the same time, the ignition timing is more retarded as the engine temperature is higher. The retardation of the ignition timing is carried out for prevention of knocking which tends to more readily occur as the combustion temperature rises with a rise in the engine temperature. Further, in the internal combustion engine of a port injection type, fuel is injected toward an intake port during the intake stroke, and an air-fuel mixture is subjected to homogeneous combustion in a state evenly distributed throughout the combustion chamber.
Further, an internal combustion engine of an in-cylinder injection type is also known which in which the combustion mode of the engine is switched between a homogeneous combustion mode in which fuel is injected during the intake stroke and a stratified combustion mode in which fuel is injected during the compression stroke. In general, in this type of internal combustion engine, in the homogeneous combustion mode, fuel is injected into the cylinder during the intake stroke, similarly to the above port injection-type engine, while in the stratified combustion mode, fuel is injected toward a piston during the compression stroke, and evaporated through thermal exchange with the piston to form an air-fuel mixture, and the mixture is subjected to stratified combustion in the state of the mixture being unevenly distributed or concentrated in the vicinity of the spark plug.
When the retardation of ignition timing by the conventional ignition timing control system described above is applied to the above in-cylinder injection-type engine, in the homogeneous combustion mode, knocking is prevented by the retardation of ignition timing based on the engine temperature since the mixture is subjected to homogeneous combustion similarly to the port injection-type engine. On the other hand, in the stratified combustion mode, since the mixture is subjected to stratified combustion, the ignitionability and conditions of occurrence of knocking ascribable to a rise in the engine temperature are different from those in the homogeneous combustion mode. Therefore, if the same retardation of ignition timing is carried out as in the homogeneous combustion mode, combustion efficiency can be degraded due to delay of ignition caused by the retardation of ignition timing which is carried out even though knocking does not occur. This leads to degraded drivability due to decreased engine output and poor fuel economy.
Further, as the aforementioned control system for an internal combustion engine of an in-cylinder fuel injection type, a control system for controlling the fuel injection timing and the amount of fuel to be injected is disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 10-47111. In this control system, the volumetric efficiency is determined based on the intake air amount, and engine load (target average effective pressure) is determined based on accelerator opening and engine rotational speed. Further, the combustion mode is switched between the stratified combustion and the homogeneous combustion mode, is dependence on the engine rotational speed and engine load. Further, combustion parameters, such as a target air fuel ratio, fuel injection timing, ignition timing, and a target EGR rate, are determined by searching respective maps based on the engine rotational speed and engine load when the engine is in the stratified combustion mode, and based on the engine rotational speed and volumetric efficiency when the engine is in the homogeneous combustion mode.
Generally, in the in-cylinder injection-type engine, to enhance the fuel economy and reduce exhaust emissions, when the engine is in the stratified combustion mode, the EGR rate is controlled to a larger value and the intake pipe pressure is controlled to a higher value close to atmospheric pressure than when the engine is in the homogeneous combustion mode. That is, the valve opening of the EGR valve and the valve opening of the throttle valve are controlled to respective larger values. This can cause the target value of the EGR rate and that of the intake air amount to be largely changed, and in such a case, due to a large change in the intake air amount, the intake air can be unstable. In contrast, in the conventional control system described above, in the homogeneous combustion mode, the combustion parameters are calculated based on the volumetric efficiency determined based on the intake air amount, and therefore if the intake air becomes unstable upon transition to the homogeneous combustion mode, the combustion parameters cannot be calculated properly. This can lead to degraded fuel economy, increased exhaust emissions, and degraded drivability.
Further, in the stratified combustion mode, fuel is more difficult to ignite than in the homogeneous combustion mode, and the combustion is more likely to be unstable. Therefore, in the stratified combustion mode, to ensure stable combustion, the ignition timing is required to be set in a more optimized manner than in the homogeneous combustion mode. The conventional control system, however, in the stratified combustion mode, ignition timing is calculated only based on the accelerator opening and engine rotational speed, and hence it is impossible to set the ignition timing to an appropriate value in which the state of combustion and operating conditions of the engine are properly reflected.
SUMMARY OF THE INVENTION
It is a first object of the invention to provide a control system and method and an engine control unit for an internal combustion engine, which are capable of properly determining ignition timing in both of a homogeneous combustion mode and a stratified combustion mode to attain a high combustion efficiency, thereby improving drivability and fuel economy.
It is a second object of the invention to provide a control system and method and an engine control unit for an internal combustion engine, which are capable of properly determining combustion parameters including ignition timing, based on operating conditions and a state of combustion of the engine, such that stable combustion is ensured, thereby attaining improved fuel economy, excellent drivability, and reduced exhaust emissions.
To attain the first object, according to a first aspect of the invention, there is provided a control system for an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke, wherein the control system controls ignition timing of the engine.
The control system according to the first aspect of the invention is characterized by comprising:
an engine temperature-detecting module for detec
Komoriya Isao
Nagatani Shuji
Ogawa Ken
Tagami Hiroshi
Ueda Kazuhiro
Hoang Johnny H.
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Wolfe Willis R.
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