Function of the engine brake/constant throttle actuation

W30.35-1083-82

0 Basic position

1 Engine brake stage 1

2 Engine brake stage 2

3 Vehicle CAN bus

A3 Drive control (FR) control unit

A20 Retarder control unit

B1 Foot throttle actuator

S2 Engine control/permanent brake operating lever

Y1 Engine brake solenoid valve 1

Y2 Engine brake solenoid valve 2

Z1 CAN star point cab dash support

General

The engine brake or constant throttle is actuated by the FR control unit (A3), which also detects (provided the vehicle is not equipped with Code (BA9) Voith secondary retarder R 115) the applied positions of the engine control/permanent brake operating lever (S2).

 On vehicles with Code (BA9) Voith secondary retarder R 115, the applied positions of the engine control/permanent brake operating lever (S2) are detected by the retarder control unit (A20), converted into messages and sent over the vehicle CAN bus (3) to the FR control unit (A3).

Function

1 If the engine control/permanent brake operating lever (S2) is moved from the basic position (0) to engine brake stage 1 position (1), the FR control unit (A3) actuates engine brake solenoid valve 1 (Y1), provided that engine speed is over
900 rpm.
Engine brake solenoid valve 1 (Y1) supplies compressed air to the constant throttle valves in the cylinder heads, which then open and start the engine braking process.

Meanwhile, the FR control unit (A3) causes the permanent brake indicator lamp on the instrument cluster (INS) to be actuated.

2 If the engine control/permanent brake operating lever (S2) is moved on from engine brake stage 1 position (1) into engine brake stage 2 position (2), the FR control unit (A3) actuates engine brake solenoid valve 2 (Y2), in addition to engine brake solenoid valve 1 (Y1).
Engine brake solenoid valve 2 (Y2) delivers compressed air to the working cylinder of the engine brake flap, which closes the exhaust pipe and thus increases braking power.

 If the following interventions/events occur, the permanent brake processes are interrupted or braking power is reduced:

 accelerator pedal or foot throttle actuator (B1) is operated

 clutch pedal is operated

 control intervention by the antilock brake system (ABS) or acceleration slip regulation (ASR)

 failure in one of the system components