Function of the engine brake/constant throttle actuation

W30.35-1079-81

0 Basic position

1 Engine brake stage 1

2 Engine brake stage 2

3 Engine CAN bus

4 Vehicle CAN bus

A3 Vehicle engine control (FMR) control unit

A6 MR/PLD control unit

A20 Retarder control unit

B1 Foot throttle actuator

S2 Engine control/permanent brake operating lever

Y1 Solenoid valve exhaust brake 1

Y2 Engine brake 2 solenoid valve
- Not for engine 457.9 with code (MZ4) Turbobrake

Y49 Solenoid valve for the constant throttle
- Only for engine 906.9 and engine 457.9 with code (MZ4) Turbobrake

* Engine 457.9 with code (MZ4) Turbobrake

** Engine 906.9

General information

Actuation of the engine brake or constant throttle varies according to the engine model and vehicle equipment.

Operation, that is activation of the respective permanent brake system always takes place, however, via the operating lever for the engine control/permanent brake (S2), whose switching positions, are detected by the drive control (FR) control unit (A3) or the retarder control unit (A20) depending on whether the vehicle is fitted with or without code (BA9) Voith secondary retarder R 115.

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Function sequences

Vehicles with engine 904.9

 All vehicles fitted with engine 904.9 are fitted with a pneumatic constant throttle and an engine brake flap.
The applied positions of the engine control/permanent brake operating lever (S2) are always detected by the drive control (FR) control unit (A3) since code (BA9) Voith secondary retarder R 115 is not obtainable for vehicles with engine 904.9.

1 Bringing the engine control/permanent brake operating lever (S2) from its base position (0) into the engine brake stage 1 (1) position causes the drive control (FR) control unit (A3) to activate the solenoid valve for engine brake 1 (Y1) on condition that the engine speed is greater than 900 r.p.m. Activation by the drive control (FR) control unit (A3) causes the solenoid valve to open and control the flow of compressed air to the constant throttle in the cylinder head.

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The drive control (FR) control unit (A3) also initiates actuation of the indicator lamp for the permanent brake in the instrument (INS) at the same time.

2 Bringing the engine control/permanent brake operating lever (S2) from the engine brake stage 1 (1) position into the engine brake stage 2 (2) position activates the drive control (FR) control unit (A3) as well as the solenoid valve for engine brake 1 (Y1) and solenoid valve for engine brake 2 (Y2).
The solenoid valve for engine brake 2 (Y2) controls the flow of compressed air to the operating cylinder of the engine brake flap and the braking force increases.

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Vehicles with engine 906.9

 All vehicles fitted with engine 906.9 are fitted with a pneumatic constant throttle and an engine brake flap.
The applied positions of the engine control/permanent brake operating lever (S2) are detected for vehicles with code (BA9) Voith secondary retarder R 115 by the drive control (FR) control unit (A3) and for vehicles with code (BA9) Voith secondary retarder R 115 by the retarder control unit (A20). The latter device passes on the applied positions of the operating lever in the form of messages via the vehicle CAN bus (4) on the drive control (FR) control unit (A3).

1 Bringing the engine control/permanent brake operating lever (S2) from its base position (0) into the engine brake stage 1 (1) position causes the drive control (FR) control unit (A3) to activate the solenoid valve for engine brake (Y49) on condition that the engine speed is greater than 900 r.p.m.

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Here the drive control (FR) control unit (A3) sends an appropriate message via the engine CAN bus (3) to the MR/PLD control unit (A6) which then activates the solenoid valve on the constant throttle (Y49).
The solenoid valve on the constant throttle (Y49) opens a feed hole to the control line on the constant throttle valves which are then opened by the oil pressure of the engine.
The drive control (FR) control unit (A3) also initiates actuation of the indicator lamp for the permanent brake in the instrument (INS) at the same time.

2 Bringing the engine control/permanent brake operating lever (S2) from the engine brake stage 1 (1) position into the engine brake stage 2 (2) position causes the drive control (FR) control unit (A3) to also activate the solenoid valve on engine brake 2 (Y2). The solenoid valve for engine brake 2 (Y2) controls the flow of compressed air to the operating cylinder of the engine brake flap and the braking force increases.

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Vehicles with engine 457.9, without code (MZ4) Turbobrake

 All vehicles fitted with engine 457.9 but without code (MZ4) Turbobrake are fitted with a pneumatic constant throttle and an engine brake flap.
The applied positions of the engine control/permanent brake operating lever (S2) are, as for engine 906.9, detected either by the drive control (FR) control unit (A3) or the retarder control unit (A20) depending on the installed equipment.

1 Bringing the engine control/permanent brake operating lever (S2) from its base position (0) into the engine brake stage 1 (1) position causes the drive control (FR) control unit (A3) to activate the solenoid valve for engine brake 1 (Y1) on condition that the engine speed is greater than 900 r.p.m. Activation by the drive control (FR) control unit (A3) causes the solenoid valve to open and control the flow of compressed air to the constant throttle valves in the cylinder heads.

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The drive control (FR) control unit (A3) also initiates actuation of the indicator lamp for the permanent brake in the instrument (INS) at the same time.

2 Bringing the engine control/permanent brake operating lever (S2) from the engine brake stage 1 (1) position into the engine brake stage 2 (2) position activates the drive control (FR) control unit (A3) as well as the solenoid valve for engine brake 1 (Y1) and solenoid valve for engine brake 2 (Y2).
The solenoid valve for engine brake 2 (Y2) controls the flow of compressed air to the operating cylinder of the engine brake flap and the braking force increases.

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Vehicles with engine 457.9 with code (MZ4) Turbobrake

 All vehicles fitted with engine 457.9 and also with code (MZ4) are fitted with an hydraulic constant throttle and turbobrake which replaces the engine brake flap.
The applied positions of the engine control/permanent brake operating lever (S2) are, as for engine 457.9 without code (MZ4) Turbobrake, detected either by the drive control (FR) control unit (A3) or the retarder control unit (A20) depending on the installed equipment.

1 Bringing the engine control/permanent brake operating lever (S2) from the basic position (0) into the position engine brake stage 1 (1) causes the drive control (FR) control unit (A3) to initially actuate the engine brake solenoid valve 1 (Y1). The prerequisite is, however, that the motor speed is above 900 rpm and the coolant temperature above 60 °C.
The solenoid valve for engine brake 1 (Y1) controls the flow of compressed air to the operating cylinder on the turbobrake whereby the bracket for the sliding grid slides out completely.

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The drive control (FR) control unit (A3) also initiates activation of the solenoid valve on the constant throttle (Y49) and the electrical-pneumatic-converter (EPW) on the turbobrake.
It sends appropriate messages via the engine CAN bus (3) to the MR/PLD control unit (A6) which then activates the solenoid valve on the constant throttle (Y49) and the electrical-pneumatic-converter (EPW) on the turbobrake.
The solenoid valve on the constant throttle (Y49) opens a feed hole to the control line on the constant throttle valves which are then opened by the oil pressure of the engine.
The electrical-pneumatic-converter (EPW) also regulates the braking force of the turbobrake to 50% at the same time.

While appropriate solenoid valves are being activated, the drive control (FR) control unit (A3) initiates activation of the indicator lamp for the permanent brake in the instrument (INS).

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2 Bringing the engine control/permanent brake operating lever (S2) from the engine brake stage 1 (1) position into the engine brake stage 2 (2) position causes the drive control (FR) control unit (A3) to initiate an increase of braking force of the turbobrake to 100%. It again sends an appropriate message via the engine CAN bus (3) to the MR/PLD control unit (A6) which then appropriately activates the electrical-pneumatic-converter (EPW) on the turbobrake.

 Activation of the permanent brake system is discontinued or the brake force is reduced for the following interventions/events:

 Actuation of the gas pedal or the foot throttle actuator (B1)

 Pressing down the clutch pedal

 A regulating intervention by the Antilocking System (ABS) or the Acceleration Slip Regulation (ASR)

 Failure of the engine CAN bus (3)

 Failure of the charge air combination sensor (temperature, pressure) or another system component