Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
1998-11-25
2001-07-10
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S299000, C123S300000, C123S480000, C123S672000
Reexamination Certificate
active
06257197
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an engine control system for a direct injection-spark ignition type of engine, and, in particular, to a direct injection-spark ignition engine control system which controls a fuel injection timing when the engine operates with an air-fuel ratio of &lgr;>1.
2. Description of the Related Art
Engine control system of this type incorporate in an exhaust line a NOx adsorbing type of lean NOx conversion catalyst which, on one hand, adsorbs NOx in the exhaust gas while the air-fuel mixture is leaner than a stoichiometric mixture and, on the other hand, desorbs or releases the NOx into exhaust gas for catalyzing reduction of the NOx while the air-fuel mixture is richer than a stoichiometric mixture. As is known from, for example, International Patent Application WO93/07363, such an engine control system controls the engine to operate with an enriched mixture under accelerating conditions or full loading operating conditions and with a lean mixture under the remaining operating conditions, so as to improve fuel consumption.
An engine control system for a direct injection-spark ignition type of engine known from, for example, Japanese Unexamined Patent Publication 7-119507 controls the engine to cause stratified charge combustion in a lower engine loading zone and homogeneous charge combustion in a high engine loading zone. While the engine operates with lower speeds in the high loading zone, a given amount of fuel is delivered in two steps through early and late split injection in a intake stroke, so as to diffuse a first half of fuel sprayed through the early split injection in the combustion chamber before the end of a intake stroke and the second half of fuel in the combustion chamber with its volume increased. This prevents a generation of rich or dense mixture over the top of a piston in a subsequent compression stroke that generally occurs when a given amount of fuel is sprayed all at once through non-split injection, which is desirable to prevent generation of smoke.
Another engine control system for a direct injection-spark ignition engine cooperates with a fuel injector which is direct to face the top of a piston and energized to spray a small amount of fuel preparatorily at the beginning of a intake stroke when the engine causes knocking. The fuel partly sticks to the top wall of the piston on a side of an intake port and bounces off the piston wall toward the intake port to cool the piston head and the combustion chamber on the intake port side with the heat of vaporization of the fuel. Such an engine control system is known from, for example, Japanese Unexamined Patent Publication 7-217478.
Although the lean NOx conversion catalyst described in the International Patent Application WO93/07363 lowers the emission level of NOx even while a fuel mixture is lean, NOx conversion performance of the lean NOx conversion catalyst is inferior to that of a three-way catalyst in a condition in which a stoichiometric fuel mixture is burnt and is not always satisfactorily. In view of this circumstances, it is desirable to restrain formation of NOx during lean mixture combustion by making a fuel mixture more leaner. Further, although fuel consumption is improved even more as a fuel mixture is made leaner, if the fuel mixture is lean in excess, the engine encounters sharp aggravation of fuel combustion, which always results in a problem of lean limits that affects drivability.
Concerning this point, it is assumed that even the engine described in International Patent Application WO93/07363 which is operated with homogeneous charge combustion even when a fuel mixture is lean or the engine described in Japanese Unexamined Patent Publication 7-119507 which is operated with homogeneous charge combustion and stratified charge combustion changed from one to another according to operating conditions is operated with lean homogeneous charge combustion in a middle engine loading zone. Since the homogeneous charge combustion does not permit a high lean limit, if the air-fuel ratio is controlled to be under the lean limit, it is hard to improve fuel consumption and lower the emission level of NOx sufficiently.
SUMMARY OF THE INVENTION
It is an objective of the invention to provide an engine control system for a direct injection-spark ignition type of engine that divides a given amount of fuel into two parts which are intermittently delivered through early and late split injection, respectively, in a intake stroke and controls a fuel injector such that the midpoint between points at which the early and late split injection are timed respectively to start is before the midpoint of a intake stroke during operating the engine to make lean homogeneous charge combustion.
According to a preferred embodiment of the invention, the engine control system cooperates with a direct injection-spark ignition type of engine which is equipped with a fuel injector for spraying fuel directly into a combustion chamber and an exhaust system having a lean NOx conversion catalyst for lowering an emission level of nitrogen oxides (NOx) in exhaust gas at an air-fuel ratio of &lgr;>1 and controls the engine to make stratified charge combustion in a zone of lower engine loadings and homogeneous charge combustion in a zone other than the lower engine loading zone. The engine control system, while the engine is monitored to be in the zone other than the lower engine loading zone and to operate with a fuel mixture of &lgr;>1, divides a given amount of fuel into two parts, desirably two substantially equal parts, which are intermittently delivered through early and late split injection respectively in a intake stroke and controls the fuel injector such that the midpoint between points at which the early and late split injection are timed respectively to start is before the midpoint of a intake stroke.
According to another embodiment of the invention, the engine control system cooperates with a direct injection-spark ignition type of engine which is equipped with a fuel injector for spraying fuel directly into a combustion chamber and an exhaust system having a lean NOx conversion catalyst for lowering an emission level of nitrogen oxides (NOx) in exhaust gas at an air-fuel ratio of &lgr;>1 and controls the engine to operate with a fuel charge of &lgr;>1 in a zone of partial engine loadings and with a fuel charge enriched to be &lgr;<1 in a zone other than the partial engine loading zone. The engine control system, while the engine is monitored to be in the partial engine loading zone, divided a given amount of fuel into two parts which are intermittently delivered through early and late split injection respectively in a intake stroke and controls the fuel injector such that the midpoint between points at which the early and late split injection are timed respectively to start is before the midpoint of a intake stroke.
With the engine control system, while a part of fuel delivered through the early split injection is diffused sufficiently homogeneously in the combustion chamber whose volume increases as the piston moves down before the late split injection is started, another part of fuel subsequently delivered through the late split injection is diffused and made homogeneous in the combustion chamber whose volume has sufficiently increased. That is, the split injection makes a fuel mixture homogeneous in the entire combustion chamber without enhancing penetrating force so high. On condition that a given amount of fuel has to be injected within an entire intake stroke, the early split injection can be timed to start at a point at which the piston moves down at a relatively high speed, which is accompanied by generation of a strong intake air stream, accelerating accomplishment of a homogeneous distribution of fuel mixture and evaporation of fuel. The early and late split injection is off as one whole to the early side of a intake stroke and, in consequence, fuel delivered through the late split injection sticks to a cylinder wall near wh
Kuji Youichi
Nishimura Hirofumi
Mazda Motor Corporation
Nixon & Peabody LLP
Studebaker Donald R.
Vo Hieu T.
Yuen Henry C.
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