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 Engine Oil-Finder

Throttle flap control motor

Bypass or throttle flap control motor

It is found with an electric servo-motor in the central injection and previously it was also found in the carburettor, however, there it was vacuum operated. It can in fact, also regulate the idling in a multi-point injection, if the whole system is not actuated through a servo-motor (E-gas). Thus the control device can take into consideration the RPM, the engine temperature, the possibly activated air-conditioning and the automatic gearbox. The aim is to ensure a secure idling behaviour without ups and downs in the RPM.

Servo-motor operates the throttle flap through a worm-drive

This page will deal with the servo-motor operated throttle flap limit. It can be seen in the picture behind the electric plug-in contact. Through a worm drive, it operates a plunger with a spring (on the left at the end of the rubber sleeve). There is a contact switch mounted on the plunger, which activates the idling stabilization when the gas pedal returns to the neutral position. With the plug removed, this can be be clearly seen: two of the contacts operate the motor and two lead to the switch. The plunger can be driven in- and outwards, thus, changing the stopping point at which the throttle flap closes. The (red) closing damper, which is visible in the foreground, has nothjing to do with the idling.

Regulation by pulse width modulation

The servo-motor for the throttle flap stopper is controlled by a clocked voltage signal. Should a higher idling be required, then the voltage signal can be raised from a minimal 1/100th of a second clock rate, up to permanent voltage (pulse-width modulation). Thus the switching of plus and minus (polarity change) can also cause the closing of the throttle flap. The control device itself takes care that the worm-drive does not become entangled with the stopping point. At this point, when test runs are carried out with an external voltage source, caution is to be excercised.

Setting with a feeler gauge and an Ohm-meter is possible

A frequent mistake is probably making the wrong setting of the adjustment-screw for the contact switch. If it does not enable the contact switch to close, then the idling regulation can also not be effective. Jerking when pulling off or the stalling of the engine can be the result. This is why Bosch and also the other individual vehicle manufacturers supply precise instructions on how the Allen screw can be exactly adjusted, e.g., taking into consideration a certain resistance in the throttle flap potentiometer with a feeler gauge and gthen comparing it with the closed contact switch. 10/12

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