Method of controlling exhaust gas recirculation for an internal combustion engine

Claim 1

In a method of controlling exhaust gas recirculation for an internal combustion engine including an intake passage, an exhaust passage, and an exhaust gas recirculation control system having an exhaust gas recirculation passage connecting said exhaust passage with said intake passage, an exhaust gas recirculation valve arranged in said exhaust gas recirculation passage for controlling an amount of exhaust gases returned from said exhaust passage to said intake passage, and valve-operating means for varying valve opening of said exhaust gas recirculation valve, said method including the steps of: detecting an actual value of said valve opening of said exhaust gas recirculation valve; detecting operating conditions of said engine; setting a desired value of said valve opening of said exhaust gas recirculation valve in accordance with a detected operating condition of said engine; calculating a difference between said actual value and said desired value of said valve opening; and controlling said valve-operating means such that said difference is reduced to zero; the improvement comprising the step of determining that there is failure in said exhaust gas recirculation control system when said difference between said actual value and said desired value of said valve opening is equal to or larger than a predetermined value which is dependent on operating conditions of said engine.

Claim 3

A method of controlling exhaust gas recirculation according to claim I, wherein said predetermined value is set to to a larger value when said engine is in a transient operating condition than when it is in a steady operating condition.