Exhaust gas recirculation system for internal combustion engines

Claim 1

An exhaust gas recirculation system for an internal combustion engine having an induction passage for conducting air-fuel mixture into a combustion chamber of said engine, an exhaust passage for discharging exhaust gases from the combustion chamber, and a recirculation passage leading said exhaust passage to said induction passage to recirculate exhaust gases into the combustion chamber of said engine therethrough, said system comprising: a pneumatically operated servomotor to be operated by negative pressure applied thereto from said induction passage; flow control means disposed within said recirculation passage and associated with said servomotor for controlling the flow quantity of exhaust gases through said recirculation passage in accordance with changes of the negative pressure applied to said servomotor; throttle means disposed within said recirculation passage upstream of said flow control means to form a space between said flow control means and said throttle means; pressure responsive means for modulating negative pressure applied to said servomotor in response to pneumatic pressure applied thereto and pressure appearing in said space; first means for producing a first electric binary signal indicative of rotational speed of said engine; second means for producing a second electric binary signal indicative of negative pressure in said induction passage; third means for producing a first electric analog signal indicative of pneumatic pressure applied to said pressure responsive means; a digital computer for repetitively calculating a value indicative of optimum pneumatic pressure to be applied to said pressure responsive means in accordance with the first and second binary signals, said computer being programmed to calculate the optimum value from a function describing a desired relationship among optimum pneumatic pressure, rotational speed of said engine and negative pressure in said induction passage; fourth means for converting a third electric binary signal indicative of the calculated optimum value from said computer into a second electric analog signal; fifth means for comparing a level of said first analog signal with first and second levels derived from said second analog signal to produce a first output signal therefrom when said first level is higher than the level of said first analog signal and to produce a second output signal therefrom when said second level is lower than the level of said first analog signal, said fifth means ceasing the output signals when the level of said first analog signal is between said first and second levels; and first and second electrically operated valves to selectively apply negative pressure and the atmospheric pressure respectively from said induction passage and the exterior to said pressure responsive means when energized in response to one of said first and second output signals from said fifth means.