Throttle Plate Control Motor

Function

The throttle plate control motor, possibly with electrical actuator, is used nowadays in conjunction with a throttle body injection; in earlier times it was used with the carburetor, operating with negative pressure. If it is not operated with the electrical actuator, it could also steer the idle-speed operation of a multipoint injection. This way the control unit may take into consideration the numbers of revolution of the engine, the engine temperature, a possibly switched on air conditioning system and an automatic gearbox. Its goal is to ensure a quiet idle-speed without disruptions.

How it works

On the picture above the throttle plate control motor is visible behind the electrical plug contacts. The actuator works via a worm drive on a tapped with spring (on the picture to the left, at the end of the rubber sleeve). On top of the tappet there is a contact, switching on the idle-speed stabilization, whenever the accelerator pedal is not in use. The removed plug shows it: two of the contacts belong to the engine; two are connected with the switch. The tappet moves in or out, thereby both extending and opening the throttle valve angle, or retracting and reducing the angle of the throttle plate. Which way it goes depends on the polarity applied to the engine. Exchanging plus with minus (a change of polarity) causes the throttle plate to close. The actuator is steered via a clocked tension signal. In the foreground of the picture there is the closing absorber, which is not involved with idle-speed. If a higher idle-speed is necessary, the voltage can be increased from 1/100 seconds clock rate up to continuous voltage. The control unit makes sure that the worm drive does not get hooked up in the end position. Jerks of the vehicle or a dying of the engine might be due to a wrongly adjusted stop screw (to the left, its tip barely visible).