Air fuel ratio control using time-averaged error signal

Claim 1

An air fuel ratio feedback type fuel supply system for an internal combustion engine comprising: sensing means for sensing the quantity of oxygen within the exhaust emission of the engine at a given repetition rate and for providing an output indicating whether the air/fuel ratio is rich or lean of stoichiometry; control means coupled to receive the output of said sensing means for controlling the rate of supply of fuel to the engine as a function of the quantity of oxygen sensed by said sensing means, said control means responding to said output so that the rate of making the air fuel ratio richer is a function of a first fraction of time a rich air fuel ratio has been indicated by said sensing means and the rate of making the air fuel ratio leaner is a function of a second fraction of time a rich air fuel ratio has been indicated by said sensing means, and said control means not changing the rate of supply of fuel when the fraction of time a rich air fuel ratio has been indicated falls between the first fraction and the second fraction of time; said control means including a biasing means for comparing the fraction of time a rich air fuel ratio occurs to the fraction of time a rich air fuel ratio is desired, and for generating a difference amount which is processed to yield a correction signal for adjusting the rate of supply of fuel to the engine; said biasing means having an output means for supplying a discrete, step correction signal; and said control means being adapted to change the air fuel ratio in accordance with the formula ##EQU3## wherein El is an expression of the sensing means output indicating a rich or lean condition, El new is a rolling average based upon El old , the previous rolling average, KTAU is a filter time constant indicating the transient responsiveness of said control means.