Function Survey

The speeds of All wheels are sensed and processed in the Electronic Traction Support (ETS) control module (N47-2). When the ETS control module (N47-2) recognizes from the speed signals that one or more driven wheels tend to spin, the ETS control operation starts.

Brake Torque Control Circuit
We differentiate between two control ranges in the ETS control mode:

A Control Of Rear Axle
If one of the rear wheels starts to spin, the associated wheel brake is applied until the calculated drive slip is reached. This allows the other wheel to transfer a propulsion force increased by the force applied by the brake. The propulsion force at the font wheels increases accordingly corresponding to the torque distribution in the transfer case (locking differential effect), Beginning at a vehicle speed of 10 km/h increasing pressure is built up at the second rear wheel, whereby the pressure level of the spinning rear wheel is reached at 40 km/h.
This prevents the second rear wheel from starting to spin and the rear end from breaking loose to the greatest possible extent. If the second rear wheel also starts to spin, this is regulated analog to the first rear wheel up to a speed of 10 km/h. At vehicle speed greater than 10 km/h the lower of the two brake pressures is matched to the higher (synchronous pressure build-up), in order to avoid yawing motions resulting from different propulsion forces at the rear axle.
ETS control mode is possible on the rear axle within the speed range of 0-80 km/h when the switch-on conditions are fulfilled.
If the switch-on conditions are still present upon exceeding the 80 km/h threshold while accelerating, the ETS control mode remains effective up to 130 km/h.
Brake fluid pressure is applied to the brake calipers in question by the hydraulic unit (pressure build-up) to brake the spinning wheels. The braking force is regulated by pressure build-up, pressure retention and pressure reduction by means of solenoid valves in the ETS hydraulic unit.

B Control Of Front Axle
If one of the front wheels starts to spin, the brakes are applied until the calculated drive slip is reached.
if the second front wheel also starts to spin, it is braked analog to the first front wheel, however only when the brakes are not applied or only on one wheel on the rear axle. The ETS control mode on the front axle is effective within the speed range of 0-40 km/h when the switch-on conditions are fulfilled.
If the switch-on conditions remain fulfilled while accelerating beyond the 40 km/h threshold ETS control mode remains effective up to 80 km/h.
Brake fluid pressure is applied to the brake calipers in question by the hydraulic unit (pressure build-up) to brake the spinning wheels. The braking force is regulated by pressure build-up, pressure retention and pressure reduction by means of solenoid valves in the ETS hydraulic unit.