Page 64
Service Training
09.03
Section 6
RP01 / Chapter 1
115 804 2401.09.03
6.3 STEERING SYSTEM (LES)
CAUTION: It is imperative, that before working on the control system, that the battery is
disconnected, and the steering capacitor voltage is discharged.
The steering capacitor voltage can be safely discharged by operating the horn with the
battery plug DISCONNECTED. Check that the voltage between 3F1 and the main negative is less
than 5V before working on the truck.
Failure to carry out this procedure can lead to damage of the CAN interface drivers. Components
MUST NOT be removed or replaced with the truck live.
An electrically powered steering system is used. The single unit comprises The motor, gearbox and also
the controller. Only a steering wheel unit and two safety sensors are required external to the main unit. The
steering system is “fly by wire”.
Within the main unit, the motor uses brushless technology and a digital position encoder provides an
accurate position to the controller. This position is also sent via CAN to the driver display for the steering
indicator. The position value is confirmed for safety purposes by monitoring two of the safety sensors
(DSS1 and DSS2) which detect a semicircular cutout in the gear ring attached to the main drive unit. The
third safety sensor (DSS3) is monitored by the driver display for an additional level of safety.
The steering wheel unit contains two parts. The wheel position is monitored by a digital encoder providing
two sets of output signals and a brake unit allows the steering controller to vary the force that the driver
must apply. This gives the driver a similar feel to previous power assisted systems.
The steering system provides a separately wired enable signal to the LDC controller to ensure that traction
is not permitted unless the steering system is fully operational.
The steering system also communicates with other truck controllers via CAN. For example, steering
status, drive wheel position information and diagnostic information are all passed via CAN.
CAN bus to other controllers
OK Signal to LDC controller
Controller
Position encoder
Brushless
motor
Gearbox
Drive shaft
Check signals
Driver demand
Position
encoder
Torque
control
+48V
0V
Keyswitch ON signal
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