Functions and parameters
Steering system 4000
Publication No. Date Valid from serial number T-code
261828-040 2008-08-21 6051502 815, 816
© BT Repair Manual RRE140/160/180/200/250 4 – 13
4.5 Steering system 4000
4.5.1 General
The steering system is fully electric – what is known as a steer-by-wire
system. As a result, there is no mechanical contact between the steer
-
ing wheel and the steering drive wheel.
The steering wheel on the steering column is fitted directly to a twin
pulse generator. Rotating the steering wheel results in an electrical sig
-
nal, a pulse train, being transmitted to the following units:
• CID (Central Information Display), and on to
• MCU (Main Control Unit), and then to
• EPS (Electrical Power Steering), the electronics unit on the steering
servo motor.
Steering is progressive, which means that when the truck is operated at
low speed the steering wheel gearing ratio is higher than at high
speeds. This allows the truck to be operated in a safe and efficient man
-
ner.
Design
The pulse generator in the steering wheel is connected to the CID (A1),
and data is sent via the CAN1 bus to the MCU (A5). In the MCU, incom
-
ing data is logically processed to give the required response. Once
processing is complete, the data is sent via CAN2 to the EPS (A2),
which then makes the wheel rotate.
The EPS is fitted directly on top of the steering servo motor. The motor
has a power booster in the form of a two-stage planetary gear. The
planetary gear's output gear wheel is in constant contact with the gear
rim on the drive gear.
The CID monitors the pulse train from the steering wheel. Monitoring is
continuous, so that any break in the cabling is detected immediately.
The MCU monitors the EPS and CAN buses, so any electrical faults in
the pulse generator, cables or electronic unit result in automatic shut
-
down of the truck drive function.
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