Moving off, function

W25.50-1027-76

Power flow diagram when driving off or when maneuvering

1 Flywheel

2 Dry clutch

3 Vibration damper

4 Hollow shaft

5 Turbo clutch

6 Impeller

7 Turbine wheel

8 Turbine wheel brake

9 Brake roller freewheel

10 Transmission input shaft

Drive off function

To drive off, the engine output is transferred hydrodynamically, but without increasing torque in the turbo clutch (5), from the impeller (6) to the turbine wheel (7). Output is transferred to the transmission input shaft (10) through the blocked brake roller freewheel (9) in the turbine wheel (7).

Under normal driving conditions the turbo clutch (5) is not filled with oil. To drive off it is filled with oil to match the accelerator pedal position. The fast change in its fill level enables the turbo clutch (5) to achieve short response times to changing torque requests or the engine torque is converted briskly and perceptibly into traction.

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As soon as the slip between the impeller (6) and turbine wheel (7) has been sufficiently reduced, the clutch actuator closes the dry clutch (2). During this closing procedure this acts as a lockup clutch for the turbo clutch (5). Once the dry clutch (2) has been completely closed, the oil is completely drained from the turbo clutch's (5) working chamber. The brake roller freewheel (9) is decoupled, and the turbine wheel (7) then rotates loosely only on the transmission input shaft (10).

The handling characteristics match those of a conventional clutch/transmission combination, i.e. without any actuation of the accelerator pedal the vehicle will not roll away on a level piece of ground.

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Maneuvering function

After pressing the maneuvering switch, the working chamber in the turbo clutch (5) is partially filled with oil to match the accelerator pedal position so that in the slowest reverse gear or forward gear stage, the vehicle can then creep as required. This partial filling enables an extremely smooth response of the turbo clutch (5) to changes in the accelerator pedal position.

At the same time, the signal range for the accelerator pedal travel is spread apart and the idle speed limited to max. 1300 rpm.

An activated maneuvering mode is displayed by an indicator lamp in the maneuvering switch and the name panel "Maneuvering mode activated".

In the maneuvering mode any closing of the dry clutch (2) is suppressed.

W25.50-1023-79

6 Impeller

7 Turbine wheel

8 Turbine wheel brake

9 Brake roller freewheel

11 Oil separator

12 Shaped breather

13 Check valve

14 Quick drain valve

15 Heat exchanger

16 Outlet restrictor

17 Outlet check valve

18 Inlet check valve

19 Air restrictor

20 Oil supply chamber

A Working chamber oil feed

B Working chamber oil return

C Vent duct

D Coolant circuit

E Oil circuit (turbine wheel brake)

F Compressed air supply

G Unpressurized line

a Ancillary consumer circuit

A3 Vehicle engine control (FMR) control unit

A125 Turbo clutch (TK) control unit

B187 Oil reservoir pressure sensor

B188 Ventilation pressure sensor

B189 Turbine wheel rpm sensor

B190 Oil temperature sensor

B191 Coolant temperature sensor

CAN 1 Vehicle CAN

Y151 Proportioning valve

Y152 Fast emptying solenoid valve

Y153 Turbine wheel brake solenoid valve

P2 Instrument (INS)

P2h13 WSK/TK indicator lamp

Actuation process

When driving off, the specified torque required by the drive control (FR) control unit (A3) is forwarded to the turbo clutch control unit (TK) (A125) over the vehicle CAN (CAN 1). The turbo clutch control unit (TK) (A125) sends an electrical signal with the required amperage rating to the proportional valve (Y151).

The proportional valve (Y151) is connected to the auxiliary consumer circuit (a) of the vehicle's compressed-air system.

As soon as the proportional valve (Y151) receives an electrical input signal from the turbo clutch control unit (TK) (A125), the signal is converted into a pneumatic actuating pressure, which then acts on the oil in the oil reservoir chamber (20) through the vent duct (C).

At the same time, the quick drain solenoid valve (Y152) is activated. The applied air pressure closes the quick drain valve (14), which is located in the outlet duct downstream of the working chamber.

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The oil reservoir chamber pressure sensor (B187) records the pneumatic actuating pressure, and converts it to an electrical signal. This is then made available to the turbo clutch control unit (TK) (A125) for regulation of the required oil filling for the working chamber between the impeller (6) and turbine wheel (7) and thereby also for regulation of the starting torque.

The oil is pumped via the oil feed working chamber (A) and the intake restrictor (19) through intake ports in the impeller (6) to the working chamber between the turbine wheel (7) and impeller (6).

The hollow shaft (4) driven and rotating impeller (6) accepts the oil into its rotary motion and accelerates it. At the turbine wheel (7) the oil is deflected and fed at the inside diameter of the working chamber to the impeller (6) again. This induces the turbine wheel (7) to rotate with the impeller (6) whereupon the outlet pressure is then generated.

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The air in the working chamber is displaced by the oil and routed over the profile ventilation (12) and oil separator (11) to the atmosphere.

The profile ventilation (12) is then closed in the maximum filling range.

From an outlet pressure of approx. 0.1 bar, the outlet check valve (17) opens and the heated oil flows through the working chamber oil return (B) into the heat exchanger (15), where it dissipates the absorbed thermal energy to the coolant circuit.

The cooled oil then flows from the heat exchanger (15) over the inlet check valve (18) into the oil reservoir chamber (20). Depending on the operating condition, the oil is then fed back to the working chamber or it remains in the oil reservoir chamber (20).

The rotary motion of the turbine wheel (7) is transferred through the brake roller freewheel (9) to the transmission input shaft (10) and the vehicle moves off.

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Once the bypass point is reached, the proportional valve (Y151) is deactivated. The actuating pressure in the oil reservoir chamber (20) is reduced through the vent duct (C) and the proportional valve (Y151). It is vented through a separate vent duct in the turbo clutch housing.

The quick drain solenoid valve (Y152) is deactivated and the exhaust air is routed over the profile ventilation (12) into the working chamber.

At the same time, the quick drain valve (14) is opened and the pending outlet pressure is then reduced. The oil flows over a bypass duct into the secondary housing and straight back into the oil reservoir chamber (20), without passing through the heat exchanger (15).

The profile ventilation (12) is now opened again, and the working chamber is connected through the oil separator (11) with the atmosphere.

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The inlet check valve (18) and outlet check valve (17) are now closed again, to prevent any oil draining into the heat exchanger (15) in the oil reservoir chamber (20).

The dry clutch (2) connected to the flywheel (1) is closed. The transmission input shaft speed is then sped up to match the engine rpm and thereby exceeds the speed of the turbine wheel (7). The brake roller freewheel (9) opens and the turbine wheel (7) is decoupled from the transmission input shaft (10).

Throughout the entire drive off process the oil circuit (E) is activated to lubricate the turbine wheel brake. The check valve (13) ensures that the oil maintains the correct flow direction in the oil circuit (E).