Engine exhaust gas recirculation system with periodic recalibration of exhaust back pressure reference

Claim 1

In a motor vehicle combustion engine having an induction conduit, an exhaust conduit characterized by an exhaust pressure therein and an EGR conduit effective to selectively return a portion of the exhaust gas from the exhaust conduit to the induction conduit through a flow-restricting orifice and an EGR which define a chamber therebetween characterized by a control pressure therein, the flow of exhaust gas through the EGR conduit depending on the difference between the control pressure and the exhaust pressure, the improvement comprising: means for sensing the control pressure; means effective to control the EGR valve in response to the sensed control pressure, a determined desired control pressure and a reference, said means being further effective to close the EGR valve during engine idle; and means effective at selected occurrences of engine idle to store the valve of the sensed control pressure for use as the reference between said occurrences, whereby the EGR valve control means is periodically recalibrated during engine operation with reference to the exhaust pressure at engine idle.