Secondary air control system for internal combustion engine

Claim 1

In an internal combustion engine having an intake passage, an exhaust passage and a catalytic converter disposed in said exhaust passage, a secondary air feeding system comprising: an electric air pump of a type which varies a pumping ability thereof in accordance with a voltage applied thereto; a secondary air inlet passage connected to said air pump for feeding the same with a first amount of fresh air; a secondary air outlet passage extending from said air pump to said exhaust passage at a position upstream of said catalytic converter; an electrically controlled valve disposed in said secondary air outlet passage, said valve being opened only when said air pump is energized; intake air amount measuring means for measuring a second amount of fresh air which is fed to combustion chambers of said engine through said intake passage, said intake air amount measuring means being substantially unaffected by said first amount of fresh air flowing in said secondary air inlet passage; voltage determining means for determining a voltage applied to said electric pump in such a manner that said first amount of fresh air fed to said exhaust passage by said pump through said secondary air outlet passage is proportional to said second amount of fresh air measured by said intake air amount measuring means; and voltage applying means for applying the voltage determined by said voltage determining means to said air pump.