A steering sensor is located on the input shaft where it is bolted to the gearbox housing.
The sensor performs two different functions: Firstly as a torque sensor, it converts steering torque input and direction into voltage signals for the ECU to monitor and convert into a binary code, and secondly as a rotation sensor, which converts the rotation speed and direction into voltage signals for the ECU to monitor and convert into a binary code.
An interfaced ECU circuit that shares the same housing converts the signals from the torque and rotation sensors into signals that the ECU can process and provide an active output.
The microprocessor control unit analyzes inputs from the steering sensor as well as the vehicle’s speed sensor. The sensor inputs are then compared to determine how much power assist is required according to the ‘forces capability map data’ stored in the ECU’s memory. This map data is pre-programmed by the manufacturer.
The ECU then emits the appropriate command to the ‘power unit or current controller’, which supplies the electric motor with the necessary current to activate. The motor then pushes the rack either to the right or left. Direction of rack movement is dependant on which way the voltage flows; reversing the current flow reverses directional rotation of the motor. Increasing current to the motor increases the amount of power assist.
The electric power assistance system has three operating modes:
If the steering wheel is turned and held in the full-lock position and steering assist reaches maximum, the control unit reduces current to the electric motor to prevent an overload situation that might damage the motor. The control unit is also designed to protect the motor against voltage surges from a faulty alternator or charging problem.
The electronic steering control unit is capable of self-diagnosing faults by monitoring the system’s inputs, outputs, and the driving current of the electric motor. If a problem occurs, the control unit turns the system off by actuating a fail-safe relay in the power unit.
This eliminates all power assist, causing the system to revert back to manual steering. An in-dash EPS warning light is also illuminated to alert the driver.
