Vehicle engine air and fuel mixture controller with engine overrun control

Claim 1

An air and fuel mixture control apparatus for a motor vehicle internal combustion engine having an intake space into which air and fuel are supplied, comprising in combination: an engine fuel supply means effective to supply fuel to the engine intake space at a vehicle operator controlled fuel flow rate; an engine air supply means including a throttle operable between wide open and closed positions to regulate the air flow rate into the engine intake space, the throttle closed position defining a minimum available air flow rate into the engine and a maximum vacuum in the intake space; means responsive to the fuel flow rate effective to provide an engine air flow rate signal representing the air flow rate required to produce a predetermined air/fuel ratio; means effective to monitor the actual air flow rate into the engine; air control means responsive to the air flow rate signal and the monitored air flow rate effective to position the throttle to a position at which the actual air flow rate is substantially equal to the air flow rate represented by the air flow rate signal; means effective to sense engine speed; and means responsive to the sensed engine speed effective to limit the minimum value of the fuel flow rate independent of the vehicle operator controlled fuel flow rate in accord with the value of engine speed to a fuel flow rate whereat the engine air flow rate represented by the air flow rate signal is greater than the minimum available air flow rate, the throttle position being limited in the closed direction by the air control means in accord with the limited minimum value of the fuel flow rate to maintain the vacuum in the intake space at a value less than the maximum value to provide improved engine operation during engine deceleration and coast conditions.