Idling rpm feedback control method for internal combustion engines

Claim 1

In a method for controlling the quantity of supplementary air being supplied to an internal combustion engine for a vehicle having wheels, said enging having: an intake passage, a throttle valve arranged in said intake passage, an air passage having one end communicating with said intake passage at a location downstream of said throttle valve and another end communicating with the atmosphere, respectively, said supplementary air being supplied to said engine through said air passage and said intake passage, and power transmission means for transmitting torque from said engine to said wheels of said vehicle, wherein (i) the quantity of said supplementary air is controlled in a predetermined deceleration mode control manner when said engine is decelerating with said throttle valve fully closed and from the moment the engine rpm becomes lower than a first predetermined rpm until it reaches a second predetermined rpm, which is an upper limit of a desired idling rpm range and lower than said first predetermined rpm, so as to prevent a sudden drop in the engine rpm even if said power transmission means is disengaged during the deceleration of said engine, and (ii) the quantity of said supplementary air is controlled in a feedback mode control manner responsive to the difference between the actual engine rpm and desired engine rpm once the engine rpm has reached said second predetermined rpm, the improvement comprising the steps of: (a) determining whether or not said power transmission means is in a state of engagement; (b) continuing said control of the quantity of said supplementary air in said predetermined deceleration mode control manner, as long as said power transmission means is maintained in said state of engagement even after the engine rpm has reached said second predetermined rpm while said engine is controlled in said predetermined deceleration mode control manner, to thereby prevent a sudden increase in the engine rpm upon disengagement of said power transmission means after said second predetermined rpm has been reached; and (c) starting said control of the quantity of said supplementary air in said feedback mode control manner, immediately when said power transmission means is disengaged.