Audi A4 2001 Owner's Manual page 33

The function of the brake assistant is
sub-divided into 2 phases:
• Phase 1
If the pressure increase gradient exceeds a
specified value (emergency braking), the ABS
return pump and the relevant solenoid valve
are activated by the ESP control unit and the
brake pressure is thus increased into the ABS
control range, in a similar manner to that of
the control system for an electronic differen-
tial lock.
Brake assistant activated
Phase 1
Brake pressure determined by an
experienced driver
Regulated brake pressure
(brake assistant)
Determined brake pressure
insufficient inexperienced driver
• Phase 2
If the pressure determined by the driver falls
below a certain value after triggering of the
brake assistant, the system pressure is
restored to the pedal pressure determined by
the driver.
Brake pedal unloaded
Phase 2
Time [t]
The integral inlet and outlet valves in the
hydraulic modulator are no longer sim-
ply switched on/off, but are regulated
via supplied voltage.
This enables more precise control on
extremely slippery surfaces, e.g. ice.
Brake assistant
switches off
ABS control
range
SSP254_084
33