SMART Series 451 Service Manual page 74

SN_Typ 451_us.book Seite 73 Freitag, 30. November 2007 1:56 13
ESP system
The latest ESP system (version 8.1) is installed next to
the brake pedal module on the underfloor and
features the following functions:
• ABS
• ASR
• HBA
• EBD
• ESP
• EBR
• Start-off assist
Antilock brake system (ABS)
Prevents individual wheels from locking up by regu-
lating the brake pressure at the relevant wheel
brakes. The vehicle remains steerable, enabling the
driver to take evasive action himself to avoid sudden
obstacles during emergency braking.
Acceleration skid control (ASR)
Prevents the drive wheels from spinning by inter-
vening in the engine management and brake pressure
regulation. ASR provides good traction and improves
vehicle stability and steerability when moving off and
accelerating.
Hydraulic brake assist (HBA)
Regulates the pressure buildup in the brake system in
relation to the vehicle speed and the actuation speed
of the brake pedal. When emergency braking is
detected by means of characteristics defined before-
hand, the ESP control unit actuates the return flow
pump that is integrated in the hydraulic unit. The
maximum brake pressure is built up.
Electronic brake force distribution (EBD)
Regulates the brake pressure at the rear wheels in
the partial braking range in order to improve the
stability of the vehicle and the braking effect.
Electronic stability program (ESP)
Minimizes oversteer or understeer by means of
specific intervention by the brake system at each
wheel on the front and rear axles. There may also be
intervention in the engine and transmission control
systems if necessary.
Engine braking regulation (EBR)
Reduces slip of the drive wheels in deceleration mode
and thereby improves directional stability and road
adhesion.
Start-off assist
Maintains the brake pressure for approx. 0.7 s after
the brake pedal is released to facilitate start-off on
uphill slopes.
Rpm sensors
The rpm sensors are active sensors, i.e. they must be
connected to a voltage source in order to operate.
They deliver a signal with an rpm-independent,
constant amplitude, and utilize the Hall effect to
detect the rpm signal.
Yaw rate, lateral and longitudinal acceleration sensor
The yaw rate, lateral and longitudinal acceleration
sensor is a combined sensor of micromechanical
design. It registers the yaw rate (yaw angle velocity)
of the vehicle about the vertical axis, the longitudinal
acceleration and the lateral acceleration.
i Note
In the event of an emergency stop in which the
vehicle is braked to a standstill from a speed in
excess of 43 mph (70 km/h), the SAM control unit
automatically activates the hazard warning
system. Deactivation of the hazard warning func-
tion occurs automatically when the vehicle speed
is detected to have risen above 6 mph (10 km/h) or
manually by actuation of the hazard warning
system switch.
Introduction of the smart fortwo, Model Series 451
Brakes
73