Thermotime switch
Encyclopedia
A thermotime switch, or TTS, is a sensor used to control the cold start enrichment process in some older fuel injection
systems. An extra injector
is placed in the inlet manifold
designed to feed all of the cylinders
, and 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 an engine first starts, the coolant
temperature 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 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 temperature, meaning the cold start routine is not entered.
Fuel injection
Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....
systems. An extra injector
Injector
ʎ̩An injector, ejector, steam ejector, steam injector, eductor-jet pump or thermocompressor is a pump-like device that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that dɯaws in and...
is placed in the inlet manifold
Inlet manifold
In automotive engineering, an inlet manifold or intake manifold is the part of an engine that supplies the fuel/air mixture to the cylinders...
designed to feed all of the cylinders
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...
, and 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 an engine first starts, the coolant
Coolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...
temperature 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 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 temperature, meaning the cold start routine is not entered.