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Longitudinal acceleration, lateral acceleration and yaw rate – via FlexRay from airbag control unit
Brake pressure – internal wiring to three pressure sensors integrated in the hydraulic unit
Steering angle – via FlexRay from steering angle sender G85 (part of steering column electronics control unit J527)
Motor torques – via FlexRay from motor control unit J623
On the basis of the data received, the control unit determines the wheel slip values in relation to the relevant driving state. If it
detects that regulation is required, it activates the control elements (solenoid valves and electric motor for pump units). It also
triggers the driver information displays required.
The software for activating the electromechanical parking brake is also included in the control unit.
Reference
For further information, please refer to SSP 475 "Audi ESC systems".
A new feature is a refresh routine to maintain the friction contact between the brake pad and the brake disc and prevent corrosion,
even when the vehicle is parked for a long time. The reason for this is the relatively low amount of time that the service brakes are
used for. Thanks to the use of recuperation to decelerate the vehicle, a mere 20 % of braking procedures now use the service
brakes, on average. The refresh routine is activated automatically after the vehicle has been stationary for at least six hours. In this
situation, the recuperation is temporarily deactivated in the next driving cycle and the service brakes are activated instead. Active
brake pressure is generated by the ESC to do this for as long as it takes to generate a defined amount of braking energy.
Hydraulic unit
As on other Audi models with ACC/adaptive cruise assist, the hydraulic unit contains six pump units, the electric motor for the
pump drive, the solenoid valves/switching valves, reservoirs and three pressure sensors. The construction and functions/switching
positions of the valves for the functions to generate, maintain and dissipate pressure fundamentally correspond to those of the
systems already in use. Large reservoirs ensure that pressure is dissipated very quickly in the first start-up phase of the return flow
pump.
Reference
For further information, please refer to SSP 475 "Audi ESC systems".
A pressure sensor permanently measures the pressure in the system (at the brake master cylinder output/the input of the hydraulic
unit). The pressure in the brake circuits (one on each axle) is measured by two additional sensors. As a result, it is possible to regu-
late the pressures at the wheel brakes very precisely so that brake blending can be achieved without the driver noticing the transi-
tions.
Operation and driver information
The ESC can be switched off by holding the corresponding button in the centre console for more than three seconds. This deacti-
vates traction control inputs and braking interventions on individual wheels. The system remains switched off during the current
terminal 15 cycle or until it is reactivated when the button is pressed again. The driver is informed of the deactivation via a message
on the display and the activation of the ESC OFF symbol.
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If system faults or malfunctions of certain other systems (e.g. adaptive air suspension, four-wheel drive, axle differential lock) are
diagnosed while the ESC is deactivated, the ESC is reactivated. This cannot be overridden. The ESC is switched on automatically ev-
ery time the drive system is switched on (terminal 15 on).
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