Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2001-08-10
2003-10-14
Vo, Hieu T. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S698000, C123S299000, C701S104000
Reexamination Certificate
active
06631704
ABSTRACT:
RELATED APPLICATION
This application claims priority to Japanese Patent Application No. 243380/2000, filed on Aug. 10, 2000 in Japan. The contents of the aforementioned application 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 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, a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke, and a two-stage fuel injection combustion mode in which the fuel injection into the cylinder is performed once during the intake stroke and once during the compression stroke during transition between the homogeneous combustion mode and the stratified combustion mode.
2. Description of the Prior Art
Conventionally, a fuel injection control system of the above-mentioned kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 11-82135. In this control system, the combustion mode of the engine is selected from the stratified combustion mode, the homogeneous combustion mode, and the two-stage fuel injection combustion mode, depending on the engine rotational speed and a target torque, and the engine is controlled to enter the two-stage fuel injection combustion mode when the combustion mode is switched between the stratified combustion mode and the homogeneous combustion mode so as to reduce torque steps. In the two-stage fuel injection combustion mode, a final fuel injection amount which is the sum total of two amounts of fuel to be injected during the compression stroke and during the intake stroke, respectively, is determined based on the intake air amount and the engine rotational speed, and one of the two amounts is set to a fixed amount, while the other is determined by subtracting the one amount (fixed amount) from the final fuel injection amount. Then, the fuel injection is performed during the compression stroke and during the intake stroke by using the one and the other amounts of fuel thus determined.
Further, another control system of the same kind has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 11-93731. An internal combustion engine incorporating this control system includes a swirl control valve for control of a swirl of fuel, and an EGR control valve for control of the EGR rate. In this control system as well, similarly to the above control system, the combustion mode of the engine is selected from the stratified combustion mode, the homogeneous combustion mode, and the two-stage fuel injection combustion mode, depending on the engine rotational speed and a target fuel injection amount (target torque). Further, the engine is controlled to enter the two-stage fuel injection combustion mode when the combustion mode is switched between the stratified combustion mode and the homogeneous combustion mode, and the duration period of the two-stage fuel injection combustion mode is determined based on a difference between a target value of the degree of opening of the swirl control valve and an actually detected value of the same.
A still another control system of the same kind has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 11-22508. Similarly to the above control system, this control system also selects the stratified combustion mode or the homogeneous combustion mode depending on the engine rotational speed and engine load, and the engine is controlled to enter the two-stage fuel injection combustion mode when the combustion mode is switched between the stratified combustion mode and the homogeneous combustion mode. In the two-stage fuel injection combustion mode, the target air-fuel ratio (equivalent ratio) is progressively changed between a rich value for the homogeneous combustion mode and a lean value for the stratified combustion mode by using a weighted mean value of the target air-fuel ratio. Further, the total fuel injection amount is divided into respective amounts of fuel for injections during the intake stroke and during the compression stroke such that a ratio between the divided amounts is also progressively changed, to thereby reduce torque steps.
Of the three conventional control systems described above, the first-mentioned control system sets one of the respective amounts of fuel to be injected during the compression stroke and during the intake stroke to a fixed value in the two-stage fuel injection combustion mode, and hence if an operating condition of the engine, particularly the engine rotational speed, has changed during this mode, the state of flow of air within the cylinder is changed to vary the minimum fuel injection amount in which injected fuel can be ignited during the compression stroke, which sometimes hinders an appropriate air-fuel mixture from being formed. As result, the state of combustion of the engine becomes unstable to cause undesired variation in the engine output, which degraded drivability and fuel economy.
Generally, when EGR control is executed, the EGR rate has a significant influence on the combustion of the mixture, and it is necessary to properly control the EGR rate to ensure the stability of combustion of the engine. Also, in general, so long as the torque demanded of the engine is identical, the degree of opening of a throttle valve and the EGR rate set by the EGR control valve are controlled to respective fairly larger values in the stratified combustion mode than in the homogeneous combustion mode, so that during transition from one of these modes to the other, it takes time for the EGR control valve controlled to a target valve lift amount for one of these combustion modes to be changed to a target value lift amount for the other. That is, the EGR control valve has the lowest response of all devices directly related to the fuel combustion of the engine, and at the same time the most significant influence thereon. The second-mentioned control system, however, merely determines the duration period of the two-stage fuel injection combustion mode based on the difference between the target value of the degree of opening of the swirl control valve and the actually detected value of the same, so that shortage or excess of the EGR rate due to delayed response of the EGR control valve can make the combustion unstable upon termination of the two-stage fuel injection combustion mode. This leads, similarly to the case of the first-mentioned control system, to degraded fuel economy, and degraded drivability due to undesired variation of the engine output.
Further, the third-mentioned conventional control system only progressively changes the target air-fuel ratio in the two-stage fuel injection combustion mode between the rich value suitable for the homogeneous combustion mode and the lean value suitable for the stratified combustion mode, so that when an operating condition of the engine has changed during the two-stage fuel injection combustion mode, the torque actually generated can deviate from a target torque. This causes torque steps upon termination of the two-stage fuel injection combustion mode, leading to degraded drivability.
SUMMARY OF THE INVENTION
It is an 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 an amount of fuel to be injected during a two-stage fuel injection combustion mode and a duration period of the two-stage fuel injection fuel combustion mode, such that stable combustion and smooth transition between combustion modes are ensured, thereby attaining excellent drivability and fuel economy.
To attain the above 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
Kimura Toru
Kohda Yutaka
Ogawa Ken
Ueda Kazuhiro
Huynh Hai
Lahive & Cockfield LLP
Vo Hieu T.
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