EML Throttle Valve (DK)

OPERATION
By way of a servomotor (actuator), the EML throttle valve (DK) is opened by the output stage in the Electronic Throttle Control (EML) control unit against the force of a spring. The output stage activates the servomotor with square-wave voltage which has a fixed frequency. The different settings of the EML throttle valve are achieved by altering the ratio between the cut-in and cut-out duration.

When the EML control unit or the EML throttle valve are renewed, or power is cut to the control unit, the information relating to the lower throttle valve (DK) limit stop is lost or incorrect. The EML control unit therefore has a teaching feature which learns the throttle valve (DK) limit stop position once again. When learning this throttle valve (DK) limit stop, the EML system establishes the relationship between the mechanical limit stop and the throttle valve (DK) potentiometer angle. The learning procedure assumes that the vehicle is in cruising mode, the detected water temperature is > 60° C and the engine speed is> 1600 rpm. When all these conditions are fulfilled, the servomotor (actuator) slowly moves the throttle valve against the lower mechanical limit stop. When this limit stop is reached, the EML system stores this teaching value. This learning procedure is carried out during each vehicle start until the new value can be stored.

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

By way of the 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 EML control unit supplies the throttle valve (DK) potentiometer with a controlled voltage of 5 V. It divides this voltage depending upon 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 microprocessor and further converted into angle degrees. The valid angle range is from approx.-3° to approx. 94°.

The EML control unit performs a switching range check in that it compares the cut-out point of the switch (approx. 17°) with the angle setting of the throttle valve (DK) potentiometer. If 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, i.e. 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 cut-out paths which the EML control unit has available are activated.

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

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

- Deactivation of opening branch of the throttle valve (DK) actuator output stage. When this opening 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. The throttle valve (DK) opening speed is also limited when limiting Dk opening.

A further cutout path which passes the EML control unit is the external safety path. It sends idle signal (LL) to the DME when the pedal position sensor is not operated and the brake pedal is depressed. The brake light test switch switches this 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 deg.).