SMART Series 451 Service Manual page 79

SN_Typ 451_us.book Seite 78 Freitag, 30. November 2007 1:56 13
Steering
Steering centering
This function returns the steering to the center posi-
tion once the driver stops applying steering torque.
The power steering motor is actuated accordingly by
the power steering control unit.
"Active center feeling" function
When the steering wheel is registered in the center
position and there are no steering movements, the
power steering motor is energized by the steering
assist control unit so that a sufficient torque is
produced to hold the steering in the straightahead
position. This actuation conveys an improved steering
center feel to the driver. The system is continuously
calibrated and learns the center position automati-
cally. The long-term calibration is performed via the
ESP wheel sensor system.
Limp-home function
The steering assist control unit constantly checks all
the input signals for plausibility. In the case of a faulty
component the steering, power assistance is shut
down and a fault is stored in the steering assist
control unit. The steering then continues to function
as a conventional rack-and-pinion steering.
78 Introduction of the smart fortwo, Model Series 451
i Note
If the electric steering suffers a function failure,
the electric steering indicator lamp in the instru-
ment cluster lights up to indicate this.
To comply with EMC requirements, the energy line
from the power steering control unit to the power
steering motor is 85 % shielded against external influ-
ences.
The power steering control unit is a CAN bus
subscriber in the overall network. The vehicle speed,
the steering angle and other data are read in over
CAN.
i Note
The steering power assistance is at a maximum at
low speeds and when the vehicle is stationary and
decreases as the vehicle speed increases.
Once the vehicle stops and the engine is switched
off, the steering power assistance is deactivated
in stages after approx. 3 s.