Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2000-04-04
2001-01-30
Kwon, John (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S305000
Reexamination Certificate
active
06178945
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system for an internal combustion engine capable of switching combustion modes which are different in injection timing, such as a homogeneous combustion mode and a stratified combustion mode, while performing quick-response torque correction by using different manipulated variables according to the combustion modes.
2. Description of the Related Art
For stabilization control of engine speed at idling, load compensation control, and torque control for meeting various requests during running, it has heretofore been practiced to perform torque correction by using manipulated variables which are higher in responsiveness than intake air quantity. Such torque correction is herein referred to as “quick-response torque correction”.
On the other hand, in recent years direct-injection spark ignition internal combustion engines have attracted public attention. Typical one of such engines performs, in accordance with an engine operating condition, switching of two combustion modes, i.e., a homogeneous combustion mode in which fuel is injected during intake stroke and is dispersed within a combustion chamber to form a homogeneous mixture, and a stratified combustion mode in which fuel is injected during compression stroke to form a stratified mixture which is concentrated around a spark plug, as disclosed in Japanese patent provisional publication No. 59-37236.
SUMMARY OF THE INVENTION
In such a direct-injection spark ignition internal combustion engine, the above described quick-response torque correction may be performed by using as a manipulated variable or variables at least ignition timing during homogenous operation and equivalence ratio during stratified operation. The calculation of the manipulated variable is performed by being synchronized with crank angle (Ref Job), and the calculation of judgement on the request for the combustion mode is performed by being synchronized with time (e.g., 10 ms). This is because in case of the former the idle speed is detected on the basis of a time interval between Ref signals so as to be reflected on the ignition timing immediately after the detection or the fuel injection quantity during stratified operation, and in case of the latter the calculation synchronous with crank angle causes a large calculation load but if the angular interval for the angle synchronization is expanded for making lower the calculation load the interval of the combustion mode switching judgement becomes so large as to disable rapid switching of the combustion modes.
For example, a combustion mode is requested on the basis of a combustion mode request flag (FSTRR) calculated at the interval of 10 ms, and by Ref Job a manipulated variable (ignition timing or equivalence ratio) for quick-response torque correction is requested on the basis of the combustion mode request flag (FSTRR) at that moment.
However, in such a request system for a manipulated variable for torque correction, in case of switching from a stratified combustion mode to a homogeneous combustion mode and in case the flag (FSTRR) is switched between the fuel injection timing and the Ref signal output timing during homogeneous operation of a certain cylinder (#3 cylinder in FIG.
26
), the fuel injection timing during homogeneous operation of #3 cylinder has already been past so stratified operation must be performed at #3 cylinder and therefore switching to a homogeneous combustion mode starts from #4 cylinder. However, at the time when the Ref signal for #3 cylinder is produced, the flag (FSTRR) has already been switched to request a homogeneous combustion mode, so the quick-response manipulated variable has already been switched from equivalence ratio to ignition timing. As a result, the ignition timing is corrected though stratified operation is actually carried out, causing deterioration of combustion and in the worst case a possibility of misfire.
Further, in case of switching from a homogeneous combustion mode to a stratified combustion mode and in case the flag (FSTRR) is switched after fuel injection for homogeneous operation has been carried out at a certain cylinder (e.g., #1 cylinder in
FIG. 27
) and before the Ref signal for that cylinder rises, homogeneous operation is performed at #1 cylinder since fuel injection for homogeneous operation has already been finished. However, since the flag (FSTRR) has already been switched to request a stratified combustion mode at the time when the Ref signal for #1 cylinder is produced, the quick-response manipulated variable is switched from ignition timing to equivalence ratio. In this instance, correction by equivalence ratio is not performed since fuel injection has already been finished. As a result, quick-response torque correction is not reflected on combustion at #1 cylinder.
The quick-response torque control encounters another problem as follows. When a combustion mode is switched from a stratified combustion mode to a homogeneous combustion mode during execution of quick-response torque control by the use of equivalence ratio at the time of stratified operation, a portion of correction executed by equivalence ratio is converted to a correction value by the use of ignition timing so as to carry out correction by ignition timing. In this connection, it is impossible for the reason of the capacity of ROM to prepare equivalence ratio/ignition timing translation tables for a number of operating conditions. When, for the above reason, the tables are reduced in number considerably for the purpose of reducing the capacity of ROM or an arithmetic expression is used to carry out the conversion, the accuracy of torque control at the time of conversion of equivalence ratio/ignition timing is lowered.
For example,
FIG. 25
shows an equivalence ratio correction factor/ignition timing correction quantity translation table which is prepared by the use of a torque correction factor/equivalence ratio correction factor translation table shown in
FIG. 8 and a
torque correction factor/ignition timing correction quantity translation table shown in FIG.
9
. In the table of
FIG. 25
, an actual characteristic may diverge from the solid line curve as indicated by a dotted line curve.
For this reason, a variation of the torque correction factor attained by the use of equivalence ratio at the time of stratified operation and a variation of the torque correction factor attained by the use of ignition timing which is employed in place of equivalence ratio after switching to a homogeneous combustion mode, when regarded as torque value, are not always smoothly consecutive with each other, thus causing a possibility that a jump or sharp drop is caused in variation of torque when a manipulated variable is switched from equivalence ratio to ignition timing.
According to a first aspect of the present invention, there is provided an internal combustion engine, comprising: a first cylinder; a second cylinder; and a controller. The controller comprises a mode requesting section for requesting one of a first combustion mode and a second combustion mode for each of the cylinders, the second combustion mode being later in a fuel injection timing than the first combustion mode; a mode judging section for judging whether an actual combustion mode of each of the cylinders is the first combustion mode or the second combustion mode; a torque requesting section for generating a torque correction request signal for a torque correction according to operation of the engine; and a torque correction section for performing torque correction for each of the cylinders, in response to the torque correction request signal and to the combustion mode of each of the cylinders, by manipulating different manipulated variables in the respective first and second combustion modes.
By the first aspect of the present invention, after one of the combustion modes is requested, a cylinder would be transitionally maintained at the same combustion mode as that before the request, s
Obata Takeaki
Suzuki Keisuke
Takahashi Nobutaka
Foley & Lardner
Kwon John
Nissan Motor Co,. Ltd.
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