Ignition timing control system for an internal-combustion engine

Abstract

An ignition timing control system for an engine using a vacuum advance unit connected to a distributor and communicated with an intake passage of the engine, which comprises: a throttle valve plate received within the intake passage; first and second ports formed in the wall of the intake passage; conduits connecting the first and second ports with the vacuum advance unit; and heat-sensitive valve means disposed in the conduit connecting the second port and the advance unit. The first port is located upstream of the valve plate and exposed to the substantially atmospheric pressure while the valve plate remains in its idle position, but exposed to the vacuum when the valve plate is opened from the idle position. The second port is kept located downstream of the valve plate and exposed to the vacuum even when the valve plate is opened to its fast-idle position. The second port is exposed to the substantially atmospheric pressure when the valve plate is further opened from the fast-idle position. The heat-sensitive valve means is open while the engine is cold, and closed when the engine is warmed up above a lower limit. With the valve plate in a position other than the fast-idle position while the engine is cold, the substantially atmospheric pressure is applied to the advance unit whereby the ignition timing is retarded permitting efficient warm-up of the engine and the catalyst. While the valve plate is in its fast-idle position and while the engine is cold, the vacuum developed in the intake passage is applied to the advance unit whereby the ignition timing is advanced permitting a smooth fast-idling of the engine.