Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2001-06-12
2003-09-02
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S478000, C123S436000, C701S104000, C701S115000
Reexamination Certificate
active
06612291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel injection controlling system for a diesel engine. More particularly, it relates to a fuel injection controlling system for not exclusively but preferably a multi-cylinder type diesel engine having an exhaust gas recirculating system (an EGRsystem), i.e., a system used for recirculating a part of the exhaust gas into an intake passage of the multi-cylinder type diesel engine. The recirculated exhaust gas will be hereinafter referred to as EGR gas.
2. Background Information
Generally, in a diesel engine, when an amount of fuel injection is increased, there often occurs a lack of air to be supplied to the engine together with the increased fuel to thereby result in a generation of smoke. Therefore, a limit to the increase in the amount of fuel injection is predetermined as a smoke-generating limit, and a controlling is conducted to prevent an amount of fuel injection from increasing beyond the smoke-generating limit. In other words, an amount of fuel injection is always controlled lest it should exceed a limitative smoke generating fuel injection amount. At this stage, combustion is usually taken place in the diesel engine under such a condition that the air-fuel ratio is somewhat leaner than the stoichiometric air-fuel ratio, that is the amount of the intake air into the diesel engine is somewhat larger than that necessary for constituting the stoichiometric air-fuel ratio. Thus, a part of the fresh intake air remains in the EGR gas while permitting some amount of residue oxygen gas to be left in the EGR gas. Therefore, a fuel injection controller has been proposed by which computation of the limitative smoke generating fuel injection amount is performed by taking into account the remaining amount of fresh air in the EGR gas, which produces the above-mentioned residue oxygen gas (Japanese laid-open Patent Publication No. 9-242595 should be referred to).
In the fuel injection controller of the prior art, an amount of intake air Qac entering each cylinder (it will be hereinafter referred to as a cylinder intake air) with respect to an amount of air measured by an airflow meter is computed by using approximation of dynamics of air according to a distance from the air-flow meter to the cylinder, made by a primary delay. Similarly, a suction amount Qec of the ERG gas for each cylinder (it will be hereinafter referred to as a cylinder suction amount of ERG gas) is computed by using approximation of dynamics of air according to a distance from an ERG valve to the cylinder (this distance is smaller than the foregoing distance), made by a primary delay. Then, assuming that the residue amount of air within the cylinder suction amount of EGR gas Qec and the afore-mentioned cylinder intake air amount Qac are both used again for the cylinder combustion, the total amount of the fresh intake air per each cylinder (=Qac+Qec×KOR, where KOR is a constant indicating a ratio of the residue fresh air) is computed. Further, on the basis of the computed total amount of the fresh intake air, the amount of fuel injection determined by a limitative excess coefficient of air is computed to obtain the smoke-generating limit of the fuel injection amount. Thus, when an objective or target amount of fuel injection for each cylinder computed in response to driving conditions of a vehicle exceeds the above-mentioned smoke-generating limit of the fuel injection amount, a controlling is performed so as to suppress the objective amount of fuel injection for each cylinder to the smoke-generating limit of the fuel injection amount.
Nevertheless, unlike a gasoline engine, a diesel engine is constructed and operated so that supply of fuel by injection occurs ahead of supercharging of the air. Thus, when a vehicle mounting thereon the diesel engine is accelerated, the rotating speed of the engine is increased in advance of an increase in the amount of the air due to the supercharging. As a result, the total amount of the fresh air per each cylinder is reduced at an initial stage of the vehicle acceleration. Further, since the airflow meter and the ERG valve are disposed at different positions with regard to the engine, a distance from each cylinder to the airflow meter is different from that from each cylinder to the ERG valve. Thus, when the dynamics of the air is taken into account with respect to the above-mentioned distances from the cylinder to the airflow meter and the ERG valve, the cylinder suction amount of ERG gas Qec is reduced before the cylinder intake air amount Qac is increased. Therefore, the total amount of air as per each cylinder changes so that it is once reduced and thereafter increased. Thus, if the amount of fuel injection is suppressed to the limitative smoke generating amount of the fuel injection which is computed based on the above-mentioned total amount of air as per each cylinder, the suppressed limitative smoke-generating amount of the fuel injection must also change in such a manner that it is temporarily reduced after the fuel injection under a given limitative smoke generating amount of the fuel injection is once carried out, and thereafter it is increased. Therefore, the temporary reduction in the amount of fuel injection during engine acceleration will causes a change in a torque exhibited by the engine, and accordingly an accelerating drivability of a vehicle, especially a vehicle with a manual transmission is deteriorated.
A further description of the prior art fuel injection controller will be provided hereinbelow with reference to FIG.
22
.
As shown in
FIG. 22
, when an accelerator pedal is pressed down at a time t
1
, a corresponding response occurs rather quickly in the cylinder suction ERG amount Qec by taking into account the dynamics of the air, and terminates at a time t
5
. However, in comparison with the above-mentioned cylinder suction ERG amount Qec, a response occurs at a later time t
3
in the cylinder intake air amount Qac. A difference in the starting times between the respective responses causes a temporary reduction in the total amount of the fresh air as per each cylinder as depicted by a fourth curve from the top in FIG.
22
. Thus, when the limitative smoke generating fuel injection amount QSMOKEN in proportion to the above total amount of the fresh air as per each cylinder is computed, a temporary reduction in the limitative smoke-generating fuel injection amount QSMOKEN occurs as depicted by a fifth curve in solid line from the top in FIG.
22
. Therefore, if a requested amount of fuel injection (an objective fuel injection amount Qsol
1
indicated by a single dotted and dashed line) in compliance with an opening degree of an accelerator system of a vehicle is limited to the limitative smoke-generating fuel injection amount QSMOKEN, the limitative smoke-generating fuel injection amount QSMOKEN corresponds to an actual fuel amount injected into each cylinder. Since an output torque exerted by the engine is in proportion to the actual fuel amount, a temporary reduction appears in the output torque exerted by the engine. As a result, in the case of a vehicle provided with a manual transmission, the temporary reduction in the output torque, that is the torque fluctuation causes an operating shock, i.e., a so-called stumbling which is unfavorable to a vehicle driver and/or a passenger.
In the case of a vehicle provided with a torque converter, torque fluctuation is absorbed by the torque converter, and accordingly a temporary reduction in the output torque does not provide any adverse affect on the motion of the vehicle. However, when the lockup mechanism is in operation, the vehicle provided with the torque converter may be exposed to the operating shock in a manner similar to the vehicle provided with the manual transmission.
Although the foregoing description of the prior art fuel injection controller is directed to the case where a diesel engine is in its accelerating operation, a like problem such as the stumbling phenomenon and the unfavorable sm
Foley & Lardner
Huynh Hai
Nissan Motor Co,. Ltd.
Yuen Henry C.
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