Electronic closed loop air-fuel ratio control system for use with internal combustion engine

Claim 1

A mixture control system for controlling the air-fuel mixture ratio of an internal combustion engine for operation in an open and closed loop mode of operation comprising: (a) an exhaust gas sensor for generating an output voltage signal representing the concentration of a predetermined constituent gas emitted from aid internal combustion engine, said exhaust gas sensor generating different output voltage signals as a function of temperature, (b) command signal generating means for generating a command signal in response to said sensor output voltage signals, said command signal generating means operative for controlling said air-fuel mixture ratio and comprising: (i) means for generating a control signal in response to the sensor output voltage signals, said control signal representative of sensed gas concentration, (ii) comparator means, having a first input terminal biased at a variable reference voltage and a second input terminal responsive to said control signal, for generating a closed-loop mode enabling signal to permit said mixture control system to operate in a closed loop mode of operation when said control signal is above said variable reference voltage and a closed loop mode disabling signal to permit said mixture control system to operate in an open loop mode of operation when said control signal is below said variable reference voltage, and (iii) variable voltage reference setting means, responsive to said closed loop mode enabling signal, for varying said variable reference voltage from a first reference voltage corresponding to a relatively low temperature of said exhaust gas sensor to a second reference voltage corresponding to a relatively higher temperature of said exhaust gas sensor and responsive to said closed loop mode disabling signal for varying said variable reference voltage from said second to said first reference voltages.