Function of the engine brake/constant throttle actuation

W30.35-1173-81

0 Basic position

1 Engine brake stage 1

2 Engine brake stage 2

A3 Drive control (FR) control unit

A6 Engine control (MR) control unit

A20 Retarder control (RS) control unit

B1 Foot throttle actuator

CAN 1 Vehicle CAN

CAN 4 Engine CAN

S2 Engine control/permanent brake operating lever

Y1 Pneumatic constant throttle solenoid valve

Y2 Engine brake flap solenoid valve

- Not for code (MZ4) Turbobrake

Y49 Hydraulic constant throttle solenoid valve

- Only for code (MZ4) Turbobrake

General information

Actuation, that is actuation of the respective permanent brake device, always takes place however over the engine control/permanent brake operating lever (S2), whose switch positions are detected either by the drive control (FR) control unit (A3) or the retarder control (RS) control unit (A20) depending in whether the vehicle is fitted with or without code (BA9) Voith secondary retarder R 115.

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Function

Vehicles without code (MZ4) Turbobrake

 Vehicles which are fitted without code (MZ4) Turbobrake are fitted with a pneumatic constant throttle and an engine brake flap.

The switch positions of the engine control/permanent brake operating lever (S2) are, according to vehicle equipment, detected either by the drive control (FR) control unit (A3) or the retarder control (RS) control unit (A20).

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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 actuate the solenoid valve for the pneumatic throttle valve (Y1) on condition that the engine speed exceeds 900 r.p.m. Actuation by the drive control (FR) control unit (A3) opens the pneumatic constant throttle solenoid valve (Y1) and guides compressed air to the constant throttle valves in the cylinder heads.

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 also causes the drive control (FR) control unit (A3) to actuate both the solenoid valve for the pneumatic constant throttle (Y1) and the solenoid valve for the engine brake flap (Y2).

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The engine brake flap solenoid valve (Y2) controls the flow of compressed air to the operating cylinder of the engine brake flap and the braking force increases.

Vehicles with code (MZ4) Turbobrake

 Vehicles which are fitted with code (MZ4) Turbobrake are fitted with an hydraulic constant throttle and a turbobrake which replaces the engine brake flap.

The switch positions of the engine control/permanent brake operating lever (S2) are, as for vehicles without code (MZ4) Turbobrake, detected either by the drive control (FR) control unit (A3) or the retarder control (RDS) control unit (A20) depending on the installed equipment.

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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 hydraulic constant throttle solenoid valve (Y49). The prerequisite is, however, that the motor speed is above 900 rpm and the coolant temperature above 60°C.

The hydraulic constant throttle solenoid valve (Y49) opens a feed hole to the control line of the constant throttle valve which is then opened by the oil pressure of the engine.

Furthermore the drive control (FR) control unit (A3) initiates that the electric-pneumatic converter (EPW) (Y87) of the turbobrake is actuated.

The brake force for vehicles with code (MZ4) Turbobrake is regulated to 50% at the same time via the electric-pneumatic converter (EPW) (Y87).

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While appropriate solenoid valves are being actuated, the drive control (FR) control unit (A3) initiates actuation of the indicator lamp for the permanent brake in the instrument (INS) (P2).

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%. To do this the control unit (FR) (A3) again sends an appropriate message via the engine CAN (CAN 4) to the engine control (MR) control unit (A6) which correspondingly actuates the electric-pneumatic converter (EPW) (Y87) of the turbobrake.

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 Actuation 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 (CAN 4)

 Failure of the charge air temperature and boost pressure combination sensor or one other system component