Bosch 5.3 ABS/EDL system, function: EDL:

The electronic differential lock (EDL) is an aid when driving away from a standstill. An electronically controlled brake application on the spinning driven wheel provides a torque reaction point for the differential. This enables the wheel with better traction to transmit engine power onto the road. The EDL is effective in both forward and reverse directions.

EDL is standard equipment on vehicles with all wheel drive, where it acts on all four wheels (on vehicles with front wheel drive it acts only on the front wheels). A mechanical differential lock is not required.

The EDL active control function can be initiated at road speeds up to 40 km/h. Once the EDL has become active, it cuts out automatically at a predetermined upper speed threshold, which is 40 km/h on vehicles with front wheel drive and 80 km/h on vehicles with all wheel drive.

Suction dampers are installed in the hydraulic unit to assist the build-up of pressure in the corresponding wheel brake cylinders when the EDL is active. The operating range of the pressure limiting valve in the hydraulic unit is 170 +/- 25 bar.

To prevent the brakes from overheating, the EDL control function is suppressed if the temperature of the brakes exceeds a certain value which is defined in the ABS control module (w/EDL) -J104-. The temperature of the brakes is calculated by the control module by means of a simulation formula. The EDL is then reactivated when the calculated temperature drops below a predetermined lower threshold. The operation of the conventional brake system and the ABS function are not affected by this automatic cut-off feature.

When the ignition is switched off, the calculated temperature of the hot brakes is stored in memory until the ignition is switched on again. When the ignition is switched on, the instrument cluster sends a time signal which enables the ABS control module (w/EDL) -J104- to calculate the period the vehicle has been left standing. This period is put into the temperature simulation formula to calculate the new temperature of the brakes. If the vehicle has been left standing for more than one hour, the control module will automatically assume a brake temperature equal to the lowest value in the simulation formula.

If the EDL is switched off because the temperature limit has been exceeded, this will be indicated in the measured value block for a period of 20 ignition cycles. See READ MEASURING VALUE BLOCK (FUNCTION 08)  .