Throttle Valve Synchronization

OPERATION
Synchronization of both throttle valves is conducted at idling speed by the Electronic Throttle Control (EML) control unit. Both Injection Signals (ti) of the Digital Motor Electronic (DME) control units are used for the synchronization procedure. The EML control unit can set a maximum difference of (+/-) 1.7 degrees. It starts the synchronization procedure when

- The EML coolant temperature sensor detects> 80° C

- The engine speed is within the range from 600 rpm to 800 rpm

- The Pedal Value Sender (PWG) is not operated

- 20 min have elapsed since the start

- The two ti signals are sent by the DME control unit

- The EML warning lamp does not light

- The EML Throttle Valve (DK) stop has been taught-in

Synchronization takes approx. 3 minutes and is repeated after 20 min at the earliest. The condition "20 min have elapsed after the start" is no longer applicable if the teach-in values are cleared by a longer interruption in the voltage supply (control unit, instrument cluster or battery disconnected).

CAUTION! The output stage of the EML control unit for the throttle valve DK actuator is not short-circuit-proof.

By way of the EML Throttle Valve (DK) potentiometer, the EML control unit detects the position of the throttle valve and moves the throttle valve to the calculated position with the throttle valve actuator.

The throttle valve (DK) potentiometer (voltage divider) is supplied by the EML control unit with a controlled voltage of 5 V. It divides this voltage depending on the angle of rotation. The part voltage fed back by the potentiometer is converted in an analog/digital converter into a form which can be processed by the microcomputer and is further converted into angle degrees. The valid angle range is from approx. minus 3 degrees to approx. 94 degrees.

The EML control unit performs a switching range check in that it compares the shut-down point of the switch (approx. 17°) with the angle setting of the throttle valve (DK) potentiometer. It the EML control unit finds that the deviation is too great, the output is limited and the EML warning lamp lights.

A further test of both switches, Pedal Value Sender (PWG) switch and DK switch, is the switch plausibility check. The control unit logic checks whether one of the following conditions is fulfilled:

- PWG switch (closes at approx. 9°) closed

- DK switch (opens at approx. 17°) closed

- Cruise control FGR active

If one of the conditions is not fulfilled, all three shut-down paths which the EML control unit has available are activated.

The shut-down paths of the EML control unit all result in engine output limitation or deactivation of the throttle valve (throttle valve closed by actuator (servo motor) or by return spring).The various shut-down paths are activated corresponding to the relevant defect in component operation. The control unit can activate three different shut-down paths:

- Output Idle Signal (LL) to the DME system. The idle (LL) is sent to the DME, this system deactivates cruise mode at a speed > approx. 1500 rpm.

- Deactivation of the opening branch of the throttle valve (DK) actuator output stage. When this operating branch is deactivated, the throttle valve can only be closed via the return spring or the closing branch of the throttle valve (DK) actuator output stage.

- Output limitation by limiting throttle valve (DK) opening range. The throttle valve (DK) opening speed is also limited when limiting DK opening.

A further shut-down path which passes the EML control unit is the external safety path. This sends idle signal (LL) to the DME 1...6 cylinder and 7..12 cylinder when pedal position sensor is not operated and the brake pedal is depressed. The brake light test switch switches the ground signal through to the DME via the switch for the external safety path in the pedal position sensor (switch opens at approx. 2.5°).