Thermotime switch
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A thermotime switch is a sensor used in some older fuel injection system designs. On certain types of fuel injection cold start enrichment is achieved with an extra injector placed in the inlet tract and designed to feed all of the cylinders. Whilst the other injectors have flow rates controlled by pulse duration, the cold start injector stays on during the initial cold starting procedure. This duration is controlled by the Thermotime switch, which is a bimetallic strip based device placed in the water jacket. When the engine starts the water is cold, and the bimetallic strip is closed, which in turn supplies the cold start injector with current. A small heater coil is built in to the thermotime switch which heats up when current is allowed to flow through it, which after a short time opens the bimetallic switch. This effectively gives a timed output to the cold start injector with the timing duration dependent on the temperature of the engine. If the engine is started whilst warm the bimetallic strip remains open due to the higher coolant temperature, meaning the cold start condition is not entered.
