Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2000-08-29
2003-01-28
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S305000, C123S406470
Reexamination Certificate
active
06510834
ABSTRACT:
The contents of Japanese Patent Applications Nos. 11-245390, with a filing date of Aug. 31, 1999, in Japan, and 11-262260, with a filing date of Sep. 16, 1999, in Japan, are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a technique for controlling a spark-ignited direct fuel injection internal combustion engine.
Recently, the technique of direct fuel injection in a spark ignition engine is under development to improve fuel efficiency and emission control by injecting fuel directly into a combustion chamber (or each combustion chamber). A control system for such a type normally operates combustion of a homogeneous air fuel mixture distributed uniformly throughout the combustion chamber by fuel injection on the intake stroke. In a predetermined engine operating condition (such as a condition of low revolution speed and low load), the control system operates with ultra lean combustion by injecting fuel on the compression stroke so as to produce an ignitable stratified air fuel mixture around an ignition plug.
Japanese Patent Provisional (Kokai) Publications Nos. 62(1987)-191622 and 2(1990)-169834 disclose internal combustion engines of such a type.
Japanese Patent Provisional (Kokai) Publications No. 10(1998)-169488 further discloses a related technology for activating a catalytic converter. According to this technology, there is produced the stratified air fuel mixture that is richer than the stoichiometric air fuel ratio (i.e. theoretical air fuel ratio) locally around the ignition plug so as to produce a region wanting the oxygen in the combustion chamber. The combustion of the stratified air fuel mixture produces the products of incomplete combustion (such as CO) in this region and raises exhaust gas temperature by means of reacting the product of incomplete combustion (CO) and unburned fuel with the oxygen in the background of the oxygen-lacking region after a main combustion (i.e. combustion by spark ignition and flame propagation thereby).
In the technology mentioned above, the homogeneous combustion is necessary at first to start the engine that has not finished its warm-up for achieving the stable combustibility, and then the stratified combustion is operated according to a request for raising the exhaust gas temperature. After the catalytic converter has been activated, the stratified combustion is converted to the homogeneous lean combustion, which is further converted to the stratified lean combustion, or the homogeneous stoichiometric combustion according to the engine operating condition.
However, the stratified combustion has lower thermal efficiency than the homogeneous combustion in which the air fuel mixture is sufficiently mixed throughout the combustion chamber, therefore there is an undesired sudden change of the engine torque (that is referred to as ‘the torque differentiation’ later) when the stratified combustion is converted to the homogeneous combustion, and vice versa. Such torque differentiation may impair the drivability.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a spark-ignited direct fuel injection internal combustion engine that can reduce the torque differentiation mentioned above when a combustion mode is converted according to the engine operating condition.
The above and other objects of the present invention can be accomplished by a control system for an internal combustion engine that comprises an internal combustion engine having a combustion chamber, an injector provided for the combustion chamber to directly inject fuel and produce an air fuel mixture therein, and an ignition plug provided for the combustion chamber to ignite the air fuel mixture. The control system also comprises a controller for operating the internal combustion engine in one of combustion modes selectively between a homogeneous combustion mode and a stratified combustion mode in response to a request according to an engine operating condition. The controller further adjusts a parameter that affects engine torque of the internal combustion engine so as to reduce the torque differentiation when the combustion mode is converted.
The controller may operate the stratified combustion mode by controlling fuel injection quantity, fuel injection timing, and ignition timing so as to produce and combust a stratified air fuel mixture that is of richer-than-stoichiometric air fuel ratio around the ignition plug, operate the homogeneous combustion mode by controlling the fuel injection quantity, the fuel injection timing, and the ignition timing so as to produce and combust homogeneous air fuel mixture that is distributed uniformly throughout the combustion chamber, convert the combustion mode between the stratified combustion mode and the homogeneous combustion mode upon occurrence of the request according to the engine operating condition, and adjust the parameter so as to reduce the torque divergence when the combustion mode is converted.
If there is the request for raising the exhaust gas temperature, the controller produces and combusts the stratified air fuel mixture that is richer than stoichiometric ratio around the ignition plug (by controlling the fuel injection quantity, the fuel injection timing, and the ignition timing by operating the stratified combustion mode). Because of the richer-than-stoichiometric stratified air fuel mixture, the products of incomplete combustion (such as CO) is produced by the main combustion. The product of incomplete combustion is combusted in the combustion chamber and/or an exhaust passage after the main combustion, therefore the controller can raise the exhaust gas temperature and then promote an activation of an exhaust emission control device such as a catalytic converter.
On the other hand, there is generated a request to operate the homogeneous combustion mode in such engine operating conditions that the engine has not finished its warm-up or the exhaust emission control device has been activated. In such conditions, the controller produces and combusts the air fuel mixture distributed uniformly throughout the combustion chamber (by controlling the fuel injection quantity, the fuel injection timing, and the ignition timing by operating the homogeneous combustion mode).
The controller adjusts the parameter that affects the engine torque so as to reduce the torque differentiation (by adjusting the parameter mentioned above) when the combustion mode is converted according to a change of the request between the homogeneous combustion mode and the stratified combustion mode.
In this manner, the torque differentiation can be reduced, and stable drivability can be achieved.
An exhaust system of the control system may comprise an exhaust passage connected to the internal combustion engine and an exhaust emission control device disposed in the exhaust passage. To generate the request for operating the stratified combustion mode, the controller may check activeness or inactiveness of the exhaust emission control device and permit the stratified combustion mode when the exhaust emission control device is inactive.
In operating the stratified combustion mode, it is desirable that an average air fuel ratio in the entirety of the combustion chamber is set at the stoichiometric ratio to achieve the desired emission performance by the emission control device. Especially when the average air fuel ratio is set substantially equal to the stoichiometric ratio, the amounts of CO and residual oxygen are approximately equivalent and the temperature of the exhaust emission control device increases very efficiently.
The stratified combustion mode may be operated by dividing a fuel injection into a first portion injected on an intake stroke for producing a leaner-than-stoichiometric air fuel mixture throughout the combustion chamber and a second portion injected on a compression stroke for producing a richer-than-stoichiometric air fuel mixture around the ignition plug, and combusting the air fuel mixture produced in the combustion chamber.
In this stratified combustion mode, th
Nishizawa Kimiyoshi
Tomita Masayuki
Yoshida Iwao
Argenbright Tony M.
Foley & Lardner
Huynh Hai H.
Nissan Motor Co,. Ltd.
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