Introduction

Introduction
The layout of the power steering circuits, both hydraulic and electrical, are detailed and illustrated in the Description and Operation.

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 coaxial 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.