Exhaust gas recirculation system with an auxiliary valve

Claim 1

An exhaust gas recirculation control system for an engine which has an intake passage which incorporates a throttle valve, and an exhaust passage, comprising: an exhaust gas recirculation passage which joins between said exhaust passage and said intake passage; means to detect engine operating parameters; an exhaust gas recirculation flow control valve, provided at a middle portion of said exhaust gas recirculating passage, so as to control the cross-sectional area of said exhaust gas recirculation passage according to a control signal; a computing controller comprising a memory means which is adapted to store target values of a control parameter corresponding to opening amounts of said exhaust gas recirculation flow control valve which provide the most desirable amounts of exhaust gas recirculation under various engine operating conditions determined by combinations of said engine operating parameters, wherein said computing contoller computes the target value of said control parameter based upon said engine operating parameters and compares said target value with the actual value of said control parameter and based thereupon produces said control signal; and an auxiliary valve located in said exhaust gas recirculation passage which is linked with said throttle valve and controls the cross-sectional area of said exhaust gas recirculation passage in relation to the opening amount of said throttle valve.