Internal-combustion engines – Engine speed regulator – Open loop condition responsive
Reexamination Certificate
2001-11-05
2002-12-24
Vo, Hieu T. (Department: 3754)
Internal-combustion engines
Engine speed regulator
Open loop condition responsive
C123S478000, C701S104000
Reexamination Certificate
active
06497214
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a control apparatus for an internal combustion engine using an improved method for calculating an air amount charged into a cylinder of an engine.
To meet the recent severe law regulations relating to purification of exhaust gas, it is necessary to accurately perform an air-fuel ratio control (i.e., a fuel injection control). To this end, it is necessary to accurately calculate an air amount charged into an engine cylinder (i.e., a charged air amount) and appropriately set a fuel injection amount in accordance with the charged air amount.
One of two conventional methods for calculating a charged air amount is referred to as a mass flow method according to which an airflow meter is provided at an upstream side of a throttle valve to measure an intake airflow amount and then a charged air amount is calculated based on the measured intake airflow amount. The other conventional method is referred to as a speed density method according to which an intake pressure sensor is provided at a downstream side of a throttle valve to measure an intake pressure and then a charged air amount is calculated based on the measured intake pressure and an engine speed.
It is however impossible to accurately determine the charged air amount before an intake valve is completely closed (this timing is referred to as an intake valve close timing that corresponds to termination of an intake stroke). On the other hand, a timing for calculating a fuel injection amount (i.e., a fuel injection amount calculating timing) is earlier than the intake valve close timing because a fuel injector injects fuel into an intake passage upstream of the intake valve and therefore the fuel injection must be completed before the intake valve is closed.
In general, the charged air amount varies widely during a transient state of engine operating conditions. Accordingly, the charged air amount causes a significant change even in a short period of time between the fuel injection amount calculating timing to the intake valve close timing. As a result, a ratio of an actual charged air amount to the injected fuel amount (i.e., an actual air-fuel ratio) will possibly deviate from a target value (i.e., a target air-fuel ratio). In other words, the accuracy of the air-fuel control will be worsened during such a transient state of the engine operation.
SUMMARY OF THE INVENTION
In view of the foregoing problems of the prior art, the present invention has an object to provide a control apparatus for an internal combustion engine capable of improving the accuracy of the air-fuel ratio control during a transient state of the engine operating conditions.
To accomplish the above and other related objects, the present invention predicts a throttle opening degree at the intake valve close timing (i.e., a charged air amount determining timing), then predicts a charged air amount based on the predictive throttle opening degree, and finally calculates a fuel injection amount based on the predictive charged air amount. The reason why the present invention uses the throttle opening degree as a parameter for predicting the charged air amount is that a variation of the charged air amount originates from a change of the throttle opening degree. Thus, it is believed that any variation of the charged air amount is accurately and responsively predictable based on a change of the throttle opening degree.
To this end, the present invention provides a first control apparatus for an internal combustion engine comprising an electronic throttle system for controlling a throttle opening degree, including a throttle actuator for driving a throttle valve. An opening degree command calculating means is provided for calculating an opening degree command value based on an accelerator depression amount. A delay means is provided for delaying an output timing of the opening degree command value calculated by the opening degree command calculating means sent to the throttle actuator. A throttle opening degree predicting means is provided for obtaining a predictive throttle opening degree based on a non-delayed opening degree command value being not delayed by the delay means and response delay characteristics of the electronic throttle system, at a timing prior to outputting a delayed opening degree command value. A charged air amount predicting means is provided for obtaining a predictive charged air amount charged into an engine cylinder based on the predictive throttle opening degree obtained by the throttle opening degree predicting means. And, a fuel injection amount calculating means is provided for calculating a fuel injection amount based on the predictive charged air amount obtained by the charged air amount predicting means.
With this arrangement, it becomes possible to predict the throttle opening degree at an intake valve close timing (i.e., at the charged air amount determining timing) by appropriately delaying the output timing of the opening degree command sent to the throttle actuator. In general, an electronic throttle system includes a response delay (or a response lag) in its operation. Thus, the throttle opening degree is predicted based on the non-delayed opening degree command value being not delayed by the delay means and response delay characteristics of the electronic throttle system, at a timing prior to outputting the delayed opening degree command value. Thus, the first control apparatus for an internal combustion engine of the present invention can accurately predict the throttle opening degree at the intake valve close timing, and accurately predict the charged air amount charged into the engine cylinder based on the predicted throttle opening degree. As a result, the air-fuel ratio control accuracy can be improved during a transient state of engine operation.
Predicting a charged air amount based on the predictive throttle opening degree is advantageous in that good response is assured during the transient state. However, merely relying on the predictive charged air amount is not desirable in that a predictive charged air amount in a stationary state tends to deviate from the actual value due to dispersion or aging of the electronic throttle system or due to driving conditions. Furthermore, the charged air amount does not vary in a stationary condition. In other words, a charged air amount calculated based on present operating parameters (intake airflow amount, intake pressure etc.) substantially agrees with the charged air amount determined at a succeeding intake valve close timing.
In view of the above, it is preferable that the charged air amount predicting means obtains a predictive change of charged air amount during a predetermined predictive time terminating at an intake valve close timing based on the predictive throttle opening degree obtained by the throttle opening degree predicting means. The obtained predictive change of charged air amount is added to a base charged air amount obtained based on present operating parameters to obtain the predictive charged air amount.
This makes it possible to accurately predict a charged air amount charged into the engine cylinder in each intake stroke in both of stationary and transient states.
Furthermore, it is preferable that the charged air amount predicting means uses an intake system model according to which a throttle opening is regarded as an orifice and the law of mass conservation is applied to a throttled air amount and an intake air flowing in a throttle downstream intake passage, and the predictive change of charged air amount is obtained by integrating an output of this intake system model during the predictive time terminating at an intake valve close timing. By using this intake system model, it becomes possible to accurately predict the change of charged air amount through a relatively simple calculation.
Furthermore, it is preferable that the throttled air amount is obtained in the intake system model according to the following expression
Gin
=
μ
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A
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Pa
R
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T
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f
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Denso Corporation
Nixon & Vanderhye P.C.
Vo Hieu T.
LandOfFree
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