Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2002-09-27
2004-08-10
Tran, Binh Q. (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S285000, C060S297000, C123S295000, C123S305000
Reexamination Certificate
active
06772585
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a controller or control system of a compression ignition engine. Particularly, the present invention relates to the controller of the compression ignition engine for preventing any deterioration in exhaust gas purification at a transition between spark ignition operation and compression ignition operation and during the compression ignition.
The conventional lean-burn engines can improve fuel economy as the result of the effect of pumping loss decrease, and the like.
However, there is a problem that NO
x
during the lean operation cannot be purified with three way catalyst. Therefore, the technology of a compression ignition engine which can suppress the NO
x
of engine out to several ppms in the lean mixture condition is proposed as one of the solutions of this problem (for instance, see Japanese Patent Application Laid-Open No. Sho 62-15722 Official Gazette, etc.). The compression ignition engine which has been described in the Official Gazette, by charging a pre-mixed air/fuel mixture for self-ignition, enables combustion at a combustion temperature lower than the temperature 1800° K. at which NO
x
generates (FIG.
1
).
However, it should be difficult to achieve the compression ignition at the time of engine starting, at the time of high load range of engine operation or the like and it is needed to switch the compression ignition range of engine operation, and the spark ignition range by a sparking plug depending upon the operation range or the state of the engine, as pointed out also with the Official Gazette (FIG.
2
). The technology of the controller of the compression ignition engine which achieves this has been proposed (for instance, see Japanese Patent Application Laid-Open No. Hei 11-6435 Official Gazette). The compression ignition engine which has been described in this Official Gazette detects ignition timing based on an ionic current within a combustion chamber. Abnormal combustion is prevented by switching the combustion when a difference between the detected ignition timing and the spark ignition timing of a sparking plug becomes lower than a predetermined value. In another way, NO
x
under exhaust is detected, and the combustion is switched based on the change in the density of NO
x
. This technology prevents the combustion from becoming unstable (as proposed technology, see Japanese Patent Application Laid-Open No. Hei 11-336600). At this time, the deterioration in exhaust gas purification due to the miss-firing can be prevented by appropriately judging the timing of the switching.
By the way, the catalyst which purifies the exhaust is not considered even though the conventional technology can prevent the deterioration in exhaust gas purification due to the abnormal combustion possibly caused in transition between the compression ignition and the spark ignition. Therefore, even in the state that the exhaust cannot be purified with the catalyst, the switching for the combustion is carried out, and it occurs a possibility to deprave the exhaust discharged in atmosphere. Namely, if the air/fuel ratio becomes excessively lean condition at the time of switching when the three way catalyst is provided in an exhaust pipe, NO
x
is exhausted as it is without being purified. On the contrary, if the air/fuel ratio becomes excessively rich condition, HC and CO are exhausted without being purified.
Moreover, when the compression ignition is carried out in a lean air/fuel ratio, NO
x
cannot be purified with the three way catalyst. Therefore, it necessitates any means by which NO
x
exhausted from the engine at this time is prevented from deteriorating.
That is, the inventors of the present invention have found that it is possible to monitor the fact that the exhaust gas is purified with the catalyst at the switching transition between the spark ignition mode operation and the compression ignition mode operation by using a three way catalyst and an NO
x
detector located at the downstream side of the three way catalyst, and it is possible to monitor the fact that the combustion aggravates also at the time of the compression ignition mode operation. They found that on the basis of this knowledge a system which achieves this can be provided with a minimum system structure. The above-mentioned prior art techniques do not have at all special consideration about this.
SUMMARY OF THE INVENTION
The present invention has been worked out in view of the problems set forth above. One object of the present invention is to provide a control system for a compression injection engine which can prevent deterioration in exhaust purification at the time of the switching of combustion between spark ignition and compression ignition, at the time of the spark ignition combustion and the compression injection combustion, and can diagnose any deterioration of an NO x detector and a three way catalyst.
In order to accomplish the above-mentioned object, a control system for a compression ignition engine comprises:
a catalytic converter installed within an exhaust passage of the compression ignition engine for compressing and igniting a pre-mixture of a fuel and air;
an air/fuel ratio detector for detecting an air/fuel ratio at upstream side of the catalytic converter; and
an NO
x
detector for detecting NO
x
at downstream side of the catalytic converter.
The control system for the compression ignition engine according to the present invention, constructed as set forth above, is provided with the NO
x
detector located downstream side of the catalytic converter. Since engine control is performed on the basis of the NO
x
detection value, a minimum system of the compression ignition engine can be constructed. Furthermore, with the construction set forth above, prevention of deterioration of exhaust gas purification performance can be achieved upon switching of combustion mode between spark ignition and compression ignition in addition to combustion in the spark ignition mode and compression ignition mode, and prevention of deterioration of exhaust gas purification performance by diagnosis of the NO
x
sensor, the catalytic converter and so forth.
On the other hand, the particular mode of implementation of the control system of the compression ignition engine according to the present invention may use an output signal of the NO
x
detector for preventing deterioration of exhaust gas purification performance. In the alternative, the control system may prevent deterioration of exhaust gas purification performance upon switching transition of combustion mode between spark ignition and compression ignition, during spark ignition mode combustion and during compression ignition mode combustion.
In another aspect of the invention, the control system may further comprise:
combustion mode switching means for switching between a spark ignition mode and compression ignition mode;
exhaust deterioration factor predicting means for predicting a factor causing deterioration of exhaust gas purification performance on the basis of an NO
x
detection value upon switching transition of the combustion mode; and
switching learning means for leaning control amount and control object of the combustion mode switching means on the basis of the factor causing deterioration of exhaust gas purification performance. More particularly, the switching learning means learns a spark ignition timing, a throttle valve control amount, a fuel injection amount, a fuel cut-off period before switching to the compression ignition mode combustion, one of a target intake air flow rate and a target EGR amount or an engine operational range for switching combustion mode between the spark ignition mode combustion and the compression ignition mode combustion.
In a further aspect of the present invention, the control system performs fuel injection between an expansion stroke and an exhaust stroke in the compression ignition mode combustion. The control system may comprise:
air/fuel ratio control means for controlling an output of the air/fuel ratio detector toward a target air/fuel
Iihoshi Yoichi
Ohsuga Minoru
Yamaoka Shiro
Crowell & Moring LLP
Hitachi , Ltd.
Tran Binh Q.
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