Exhaust emission control system for internal combustion engines

Claim 1

In a spark ignition internal combustion engine having an exhaust emission control system including; means for withdrawing a proportion of the exhaust gases from the exhaust manifold at a point corresponding to at least one cylinder and for recycling said exhaust gases to the carburetor, and means for admitting additional air directly into the exhaust manifold for the further combustion of any incompletely burnt fuel present in the exhaust gases in the exhaust system of said engine, the improvement wherein, said exhaust gas recycling means includes temperature sensitive valve means connected in circuit therewith, said temperature sensitive valve means being sensitive to the operating temperature of said engine and operating to prevent opening of said exhaust gas recycling valve means to effect recycling of exhaust gas except when the engine has attained a predetermined operating temperature, further valve means connected to a point in the induction manifold of said engine downstream from the carburetor butterfly valve, said further valve means including, means sensitive to the vacuum in said induction manifold, said further valve means operating to admit additional air to said induction manifold when said vacuum sensitive means thereof detects that the pressure in said induction manifold is below a threshold value, and temperature sensitive valve means operating to inhibit the admission of said additional air when the temperature of said engine is below a predetermined threshold value, control valve means connected in circuit with said further valve means, said control valve means being sensitive to energization of the starter motor of said engine and operating to close said further valve means when said starter motor is energized, whereby to prevent the admission of said additional air to said induction manifold when said engine is being started and thus to avoid the occurrence of explosions in the exhaust system due to said additional air, said carburetor being provided with a first pneumatic sensitive valve, a control input to said first pneumatic pressure sensitive valve, a duct connecting said control input to a third point on said induction manifold, a temperature sensitive valve in said duct, said temperature sensitive valve operating to close communication between said control input and said induction manifold when the operating temperature of said engine is below a predetermined threshold thereby inhibiting operation of said valve, and pneumatic delay means connected in series in said duct, said first pneumatic pressure sensitive valve operating to enrich the mixture supplied by said carburetor, when said engine operating temperature is above said predetermined threshold, with a delay, determined by said pneumatic delay means, after said control input of said valve senses a fall in the pressure in said induction manifold.