Moving off, function

W25.50-1070-76

Starting-off function

To drive off, the engine output is transferred hydrodynamically, but without increasing torque in the turbo-retarder clutch (5), from the impeller (6) to the turbine wheel (7). Output is transferred to the transmission input shaft (10) through the blocked sprag clutch (9) in the turbine wheel (7). Under normal driving conditions the turbo retarder clutch (5) is not filled with oil. When starting off, it is charged with the amount of oil to match the accelerator pedal position. The fast change in its volumetric efficiency enables the fluid coupling (5) to achieve short reaction times to changing torque requests. It converts the engine torque into traction swiftly and tangibly. 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 fluid coupling (5). Once the dry clutch (2) has been completely closed, the oil is completely drained from the fluid coupling's (5) working chamber. The sprag clutch (9) is decoupled, and the turbine wheel (7) then rotates loosely only on the transmission input shaft (10). During the starting-off procedure, the fluid coupling (5) actuation is indicated by a symbol in the multifunction display or the instrument cluster control unit screen. The handling characteristics are equivalent to that of a conventional clutch/transmission combination. If the accelerator pedal is not pressed, the vehicle will not roll-start on a level piece of ground.

Maneuvering function

After operating the maneuvering switch, the working chamber in the fluid coupling (5) is partially filled with oil. In the lower start-off gears an intended crawling of the vehicle is made possible by releasing the service brake. In the maneuvering mode, the turbo-retarder clutch (5) responds extremely sensitively to any changes in the accelerator pedal position. At the same time, the signal range of the accelerator pedal travel is spread apart and the engine speed is limited to a maximum 1300 rpm. The actuated maneuvering mode is visually indicated by an indicator lamp on the maneuvering switch. In the maneuvering mode any closing of the dry clutch (2) is suppressed.

W25.50-A010-79

W25.50-A000-79

Actuation process

When driving off the required specified torque is forwarded by the transmission control unit to the fluid coupling control unit over the drive train CAN. The fluid coupling control unit sends an electrical signal with the required amperage to the proportional valve.

The proportional valve is connected to the consumer circuit (a) of the vehicle's compressed air system. As soon as the proportional valve receives an electrical input signal from the fluid coupling control unit, the signal is converted into pneumatic actuating pressure. This acts through the air duct (C) on the oil in the fluid reservoir (18).

The oil reservoir chamber pressure sensor records the pneumatic actuating pressure, and converts it into an electrical signal. This is then made available to the fluid coupling control unit to regulate the desired oil charging process of the working chamber between the impeller (6) and the turbine wheel (7), to therefore also regulate the starting torque.

The opened oil feed shutoff valve (17) and the working chamber oil feed (A) enable the oil to flow through intake ports in the impeller (6) into the working chamber between the turbine wheel (7) and the impeller (6).

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

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.

The heated oil flows through the working chamber oil return (B) and the outlet restrictor (14) into the heat exchanger (15), where it dissipates the absorbed thermal energy into the coolant circuit (D). Depending on the operating condition, the cooled-down oil is then routed back over the heat exchanger (15) and the outlet check valve (16) to the working chamber, or it flows back into the reservoir (18).

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

Once the bypass point is reached, the proportional valve is deactivated. The actuating pressure in the reservoir (18) is reduced through the air duct (C) and the proportional valve. It is vented through a separate air duct in the housing gap between the fluid coupling (5) and the transmission.

At the same time, the quick drain solenoid valve is activated and pressure is applied to the oil feed shutoff valve (17). This causes the oil feed shutoff valve (17) to close whereupon the oil flow to the working chamber is then interrupted. The "residual oil" in the working chamber is returned through the heat exchanger (15) and the outlet check valve (16) in the reservoir (18). Once the working chamber has been drained, the quick drain solenoid valve is deactivated, whereupon the oil feed shutoff valve (17) is opened through a return spring.

The profile ventilation (12) is now opened again, and the working chamber is connected through the oil separator (11) with the atmosphere. The outlet check valve (16) is closed again, to prevent the oil in the heat exchanger (15) draining into the reservoir (18).

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 sprag clutch (9) opens and the turbine wheel (7) is decoupled from the transmission input shaft (10).

Throughout the entire starting-up procedure oil flows to the turbine wheel brake (8) through the oil duct (E). This oil flow ensures that he required lubrication is provided.