Electronic traction system (ETS), function survey - GF42.35-P-0001-04C

The speeds of all wheels are registered and conditioned in the ETS/SPS control module (N47-2). A vehicle reference speed is calculated from them.

If the ETS/SPS control module (N47-2) recognizes from the speed signals that one or more drive wheels are tending to spin, ETS control mode begins. A brake pressure build up at all 4 wheels simultaneously is possible at the lowest coefficients of friction.

A distinction is made between:

1. Closed-loop control in a road gear  (comfort-orientated)
2. Closed-loop control in an off-road gear  (traction-orientated)

1. ETS function when road gear is engaged 

   The spinning drive wheel(s) is/are braked via the associated wheel brakes until the calculated drive slip (approx. 5 km/h above reference speed) is reached. Only as much slip is permitted at each wheel as is required for optimum traction.

   To brake the spinning wheel, the brake fluid pressure is led into the brake caliper (pressure build-up) via a pressure system in the hydraulic unit.

   The brake moment is controlled by pressure build-up, pressure holding, pressure reduction via solenoid valves in the ASR/ETS/ ESP hydraulic unit (A7/3).

   This ETS control mode is permitted only in the speed range of 0-60 km/h when the engagement conditions are met.

   If the engagement conditions are maintained beyond the 60 km/h threshold during an acceleration process, ETS control mode is effective up to approx. 80 km/h.

2. ETS function when off-road gear is engaged (LOW RANGE) 

   The basic function as when a road gear is engaged. However starting at the 5 km/h specified slip requirement, the specified slip is reduced to 2km/h, if there is a greater loss of traction and the vehicle speed is < 20 km/h. Pressure modulation is also influenced.