Patent ID: 6877369

Claim:
An EGR-gas flow rate estimation apparatus for an internal combustion engine which has an exhaust circulation pipe connected between an exhaust passage and an intake passage, and an EGR control valve interposed in the exhaust circulation pipe and having a throttle portion for controlling flow rate of EGR gas flowing through the exhaust circulation pipe, the EGR-gas flow rate estimation apparatus comprising: upstream-gas-pressure obtaining means for obtaining, as an upstream-side gas pressure, a pressure of EGR gas on the upstream side of the EGR control valve; downstream-gas-pressure obtaining means for obtaining, as a downstream-side gas pressure, a pressure of EGR gas on the downstream side of the EGR control valve; provisional-EGR-gas-flow-rate estimation means for estimating, as a provisional EGR gas flow rate, a flow rate of EGR gas passing through the EGR control valve, by use of a general formula which represents a flow rate of a compressible fluid passing through a throttle portion on the basis of an upstream pressure of the compressible fluid at a point immediately before the throttle portion and a downstream pressure of the compressible fluid at a point immediately after the throttle portion, the provisional-EGR-gas-flow-rate estimation means employing the obtained upstream-side gas pressure as the upstream pressure of the compressible fluid in the general formula, and the obtained downstream-side gas pressure as the downstream pressure of the compressible fluid in the general formula; and EGR-gas flow rate estimation means for estimating the flow rate of EGR gas flowing from the exhaust circulation pipe into the intake passage, by correcting an error which is contained in the estimated provisional EGR gas flow rate and which is caused by pipe friction between the exhaust circulation pipe and the EGR gas.