Steering: Testing and Inspection

Introduction

The layout of the power steering circuits, both hydraulic and electrical, are detailed and illustrated in the Description and Operation. Refer to the overall system diagram.

There are two major components of the Servotronic rack which provide the unique, variable effort control, based on vehicle speed. The first is the Servotronic Valve which provides the variable steering effort and the second is the Positive Center Feel Torsion Bar. The Servotronic Valve is controlled electronically by a Power Steering Control Module.

The Servotronic valve provides hydraulic reaction to oppose normal movement of the power piston. The benefit of this is to give increased stiffness and feel to the system at higher vehicle speeds.

To achieve the hydraulic reaction, a co-axial piston assembly has been incorporated into the valve housing, which is linked to the inner valve rotor and to the outer valve sleeve, via a series of ball bearings.

The Servotronic valve consists of a variable size orifice (effectively) which varies in size depending on the position of a needle valve. The position of the needle valve is controlled by a solenoid, the armature of which will remain at any fixed point within its overall limit of travel, dependent on the amount of current supplied to the solenoid windings.

As the speed of the vehicle increases, the current supplied to the valve is reduced in stages and the needle moves off its seat which allows pressurized oil to pass into the reaction circuit. The driver subsequently, has to apply more torque to the steering wheel to overcome the added reaction pressure.

Power Steering Pressure Test





Test Equipment

Installing Test Equipment

To install the pressure test equipment:
- Place a suitable drain tray below the PAS pump.
- Install a hose clamp on the reservoir to pump hose prior to disconnecting any hoses, to avoid unnecessary loss of fluid.
- Disconnect the hose from the PAS pump high pressure outlet.
- Install the pump outlet to hose adapter (5). Do not omit the O-ring (9).
Connect the pump adapter to control valve hose (6) of the test equipment.
- Install the adapter (4) in the high pressure hose previously removed from the pump outlet.
- Connect the connector (3) of the test equipment hose (2) to the adapter (4).
- Remove the hose clamp from the reservoir hose.
- Start the engine.

With the control valve (7) OPEN and the engine idling, the following system pressures may be checked:
- During turning.
- When the steering is held on full lock.
- With the steering at rest.

WARNING: TO AVOID EXCESSIVE HEATING OF THE PAS PUMP, DO NOT CLOSE THE VALVE FOR LONGER THAN NECESSARY.

WARNING: DO NOT DRIVE THE VEHICLE WITH THE TEST EQUIPMENT INSTALLED.

With the control valve (7) CLOSED the pump maximum output pressure can be checked.

Removing Test Equipment

To remove the test equipment:
- Install a hose clamp on the reservoir to pump hose.
- Removing the test equipment is a reversal of the installation instructions.
- Install a new O-ring (9) to the PAS pump high pressure outlet to hose connection.
- Install the original hose to the PAS pump.
- Remove the clamp from the reservoir to pump hose.
- Top-up the reservoir fluid.
- Bleed the PAS system.