Electrical steering system – 4300

9.1.1 Electrical steering servo

The electrical steering servo consists of twin potentiometers connected to an electronic module in the motor compartment. The electronic module, which is also referred to as the EPS (Electrical Power Steering), is directly mounted on a Brush-Less Permanently Magnetised servo motor (BLPM). The motor has a power amplifier that consists of 2-stage planetary gearing with a gear wheel mounted on a trailing journal and locked with a nut. The gear wheel is meshed with the gear ring on the driving wheel gear, and as such the drive unit also handles steering of the truck.

The steering system is electric and uses a "Steer-By-Wire" design. This means there is no mechanical contact between the steering unit and the truck's steering wheel.

The electronic module monitors all electrically connected components. Monitoring is continuous enabling instant detection of possible cable interruptions. Electrical faults detected in potentiometers, cables and the electronic module result in automatic switch-off of the truck's drive mode and application of the electromechanical brake.

An automatic drive reference measurement is performed at each startup after a no-voltage state. During this calibration, the truck cannot be driven. The drive reference mode safety-checks the system and simultaneously calibrates the wheel position.

Steering is progressive, implying slow-down of the travel speed at large steering angle throws. This promotes safe and efficient truck travel. A certain steering response in the steering unit results in an increasingly greater steering response in the steering wheel. The steering unit is limited to a +/- 60 degree steering response which gives the steering wheel +/-100 degree steering response (drive wheel direction) or +/-90 degree steering response (fork direction).