Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-02-03
2001-07-10
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C073S117020
Reexamination Certificate
active
06257214
ABSTRACT:
TECHNICAL FIELD
This invention relates to exhaust gas recirculation (EGR) monitoring and, more particularly, to an EGR monitor utilizing both measured and inferred manifold pressure values.
BACKGROUND OF THE INVENTION
Internal combustion engines typically include an EGR system to recirculate a controlled portion of the engine exhaust gas into an engine intake manifold in order to provide a reduction in NO
x
emissions. Typically, a control mechanism including an EGR valve is provided to vary the EGR rate according to one or more sensed condition, such as engine temperature, air charge entering the intake manifold, and engine speed.
It is desirable to monitor the operation of the EGR system through onboard diagnostic routines to determine whether or not the system is operating as expected. One approach to EGR monitoring terminates the recirculation of exhaust gas by closing the EGR valve during steady state cruise operation and records the change or difference in manifold absolute pressure (MAP) between the value prior to termination and the value a short time period following termination. The waiting period allows the MAP signal from a MAP sensor to settle. This termination of recirculation is usually commanded several times and the MAP difference signal is averaged. A problem with this approach is that under high load, the manifold pressure does not change significantly between the value sensed with EGR ON (EGR valve open) and the value sensed with EGR OFF (EGR valve closed). Relying on the MAP difference value at high load may cause a false indication of a malfunctioning EGR system.
SUMMARY OF THE INVENTION
The aforementioned problem is solved in accordance with the present invention and an exhaust gas recirculation system monitor is provided wherein a more complete system response is obtained by inferring a manifold pressure value from air flow in the intake manifold as measured by a mass air meter (MAF sensor) and adding an inferred pressure difference value to the actual pressure difference value. The effect of adding the inferred pressure difference value to the measured pressure difference value as determined by the MAP sensor has a complementary effect since at high load the difference between measure air flow with EGR ON versus EGR OFF is significant. The effect is also complementary at low loads since recirculating gas significantly changes manifold pressure but does not significantly change air flow.
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Bidner David Karl
Cullen Michael John
Martin Douglas Raymond
Castro Arnold
Dolinar Andrew M.
Drouillard Jerome R.
Ford Global Technologies Inc.
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