Braking and drive off torque limitation function

To prevent the maximum coolant temperature or oil temperature specified in the turbo clutch control unit (TK) (A125) from being exceeded, the braking torque is reduced accordingly to protect the vehicle cooling system if the coolant or oil temperature in the turbo clutch is exceeded. This is governed by limiting the actuating pressure for the proportional valve (Y151) and therefore by reducing the oil filling capacity in the turbo clutch's working chamber.

The lower oil charge in the working chamber between the impeller and turbine wheel enables a faster reduction in oil temperature or the coolant temperature, because the oil flow to the heat exchanger is not braked and less thermal energy is released.

To determine when the braking torque should be restricted, the turbo clutch control unit (TK) (A125) continuously measures the oil temperature through the oil temperature sensor (B190) and the coolant temperature through the coolant temperature sensor (B191).

The braking torque is reduced if the coolant temperature is too high, the oil temperature too high or if the oil temperature increases too quickly until the retarder function is completely shutdown.

As soon as the brake torque is limited, a message with the information about the reason for triggering is placed on the vehicle CAN (CAN 1)

 The starting torque is not limited or reduced if the coolant temperature is too high, the oil temperature too high or if the oil temperature increases too quickly. A warning message in the display of the instrument cluster (INS) (P2) and a warning buzzer notify the driver of the thermal overload.

In this instance, a change to a lower gear is required.