Function
Function
Electro hydraulic power steering
1. Hydraulic fluid, pressure side
2. Hydraulic fluid, return side.
The Power Steering Control Module (PSCM) is activated when the control module receives 15 supply via the ignition. This is to diagnose certain functions and at the same time prepare to start the pump motor. When the motor is then started, the control module immediately activates the system's pump motor so that the power steering is activated.
The following is measured when the driver turns the wheel:
- steering angle speed
- the vehicle speed
- engine status (engine running)
- power supply mode.
These input signals, together with the internal signals (pump motor speed, temperature in the control module, power consumption of the pump motor etc) are used by the control module to control and diagnose the electro hydraulic power steering. This gives optimal power steering adaptation.
The control module controls the power consumption of the pump motor using the internal power stage. For efficient control of the pump motor, a pulse width modulated supply is used. By controlling the pulse ratio, the control module is able to regulate the output of the pump motor and therefore the speed which indirectly controls the hydraulic pressure in the power steering system. Principally the control module continuously monitors the following:
- the power consumption of the pump motor
- the speed (RPM) of the pump motor
- the temperature in the control module.
This means that the system is regulated constantly so that the hydraulic pressure is correct. The functionality of the system can also be diagnosed efficiently.
Steering wheel movement speed
The Steering wheel angle sensor module (SAS) (4/68) informs the Power Steering Control Module (PSCM) (6/164) about the actual steering wheel angle speed via the controller area network (CAN). This allows the Power Steering Control Module (PSCM) to calculate the optimum desired value for the pump motor speed for optimum steering assistance, irrespective of the speed of steering wheel movements.
Vehicle speed
While driving, the brake control module (BCM) (4/16) registers the acceleration and deceleration of the wheels. The 4 wheel sensors (7/31-32 and 7/56-57) (one on each wheel) provide the brake control module (BCM) with information about the rotation speed of each wheel. The brake control module (BCM) calculates the actual speed of the car using this information and puts it out on the controller area network (CAN). The vehicle speed signal is used by the Power Steering Control Module (PSCM) (6/164) so that, when combined with other parameters, it can calculate the optimal desired value for the pump motor speed. The system reduces the speed of the pump motor (=reduced hydraulic pressure) when the vehicle speed increases. The pump motor speed increases (=increased hydraulic pressure) as vehicle speed drops. This to obtain optimal steering assistance in relation to vehicle speed. This is speed dependent power steering.
Engine status and engine speed (rpm)
The engine control module (ECM) (4/46) provides information about engine status and engine speed via the controller area network (CAN). This information is used to activate the pump motor when the engine is started.
Fault message
If a fault is registered (certain diagnostic trouble codes (DTCs) only), the Power Steering Control Module (PSCM) (6/164) will inform the central electronic module (CEM) (4/56) that there is a fault in the power steering system via the controller area network (CAN). The central electronic module (CEM) then transmits a request via the controller area network (CAN) to the driver information module (DIM) (5/1) to light the information lamp and to activate a text message in the display. The text message informs the driver that there is a fault in the power steering system. When the fault has been remedied, a request is transmitted in the same way to switch off the information lamp and deactivate the text message.