Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-03-02
2001-11-27
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S568210, C073S117020
Reexamination Certificate
active
06321732
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system and method to measure and control exhaust gas recirculation flow and estimate cylinder air charge for air-fuel ratio control.
BACKGROUND OF THE INVENTION
Many methods are available to estimate cylinder air charge using a manifold pressure sensor. Typically, engine maps are provided that provide a cylinder air charge as a function of measured manifold pressure, manifold temperature, and engine speed. In engines that also utilize exhaust gas recirculation, an improved cylinder air charge estimate is obtained by providing adjustments based on the amount of exhaust gas recirculation.
One particular method is described in U.S. Pat. No. 5,205,260. In this method, an EGR flow is estimated based on differential pressure across a flow control valve and based on a cross-sectional area of the valve. Then, this flow is used in a manifold filling model to estimate a partial pressure of EGR in the intake manifold. Then, based on this partial pressure of EGR and measured manifold pressure, a cylinder air charge value is computed.
The inventors herein have recognized a disadvantage with the above system. In particular, estimating EGR flow in this manner leads to estimation inaccuracies. Since inaccuracies in EGR flow directly affect estimated cylinder air charge, this leads to inaccuracies in calculated fuel injection amount and therefore may degrade air-fuel ratio control.
SUMMARY OF THE INVENTION
An object of the invention claimed herein is to provide an exhaust gas recirculation measurement system and cylinder air charge estimation system with improve accuracy. The above object is achieved, and problems of prior approaches overcome, by a system for estimating engine flows, including exhaust gas flow from an exhaust manifold of an internal combustion engine to an intake manifold of the engine, the system comprising: a flow control valve having a variable orifice positioned in an exhaust gas recirculation path between the exhaust manifold and intake manifold of the engine; a fixed orifice area located in said path and downstream of said valve; and a computer for measuring a first pressure downstream of said measuring orifice, measuring a differential pressure across said measuring orifice, calculating a recirculated exhaust flow based on said first pressure and said differential pressure, and determining a cylinder air amount based on said first pressure and said calculated recirculated exhaust flow.
By using common signals for estimating EGR flow and cylinder air charge, a simplified structure and reduced cost system is obtained. Further, by using a fixed orifice area downstream of a control valve to recirculate exhaust gas along with a differential pressure measurement and a downstream pressure measurement, a more accurate EGR flow estimate is obtained. In particular, the estimation scheme does not have to account for the changing valve area, and thus less affects have to be included. Further yet, the present invention does not need to measure or infer exhaust manifold temperature or exhaust manifold pressure.
An advantage of the above aspect of the invention is that more accurate cylinder air charge estimate is obtained.
Another advantage of the above aspect of the invention is that the more accurate cylinder air estimate yields improved emissions at a reduced system cost.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.
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Gates Freeman Carter
Kotwicki Allan Joseph
Russell John David
Ford Global Technologies Inc.
Lippa Allan J.
Russell John D.
Wolfe Willis R.
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