Ignition timing control apparatus for internal combustion engine

Claim 1

For use with an internal combustion spark ignition engine connected to drive a vehicle through an automatic transmission having a torque converter or fluid coupling, the engine including an intake passage, a throttle valve in said intake passage, and a distributor having a movable spark adjusting base, ignition timing control apparatus for the engine comprising, in combination: a vacuum actuator having a movable wall connected to the spark adjusting base, a spring urging said movable wall toward a spark advance position, an increase of vacuum intensity in said vacuum actuator moving said movable wall toward a spark retard position against said spring, a conduit connecting the vacuum actuator to said intake passage of the engine downstream from said throttle valve, a selector valve in said conduit having a valve element movable to connect the vacuum actuator to either the engine intake passage or to atmosphere, a member responsive to engine temperature connected to operate the selector valve to cause said vacuum actuator to be connected to atmosphere when the engine temperature is below a predetermined value or to cause said vacuum actuator to be connected to the intake passage downstream from the throttle valve when the engine temperature is above said predetermined value, a check valve and a restricted orifice mounted in parallel in said conduit between the selector valve and the vacuum actuator, said check valve permitting flow through the conduit from the vacuum actuator but preventing reverse flow, whereby a reduction of vacuum intensity in the engine intake passage when the engine is warm causes said check valve to close and causes the restricted orifice to delay advance of the ignition timing, but an increase of vacuum intensity in the engine intake passage causes an immediate retarding of the ignition timing.