Electro Hydraulic Power Steering

Courtesy of VOLVO CARS CORPORATION

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.