Steering: Description and Operation

Steering System

Steering System Component Layout

NOTE: 2.7L TdV6 Left Hand Drive shown

Steering System Component Layout (Part 1):

Steering System Component Layout (Part 2):

GENERAL
The steering system on all models comprises the following components:
^ Steering gear with Servotronic valve
^ Servotronic software integrated into air suspension control module
^ Power steering pump
^ Reservoir
^ Lower collapsible shaft
^ Intermediate shaft
^ Upper column assembly with electrical adjustment
^ Steering column multifunction switches
^ Steering column adjustment switch
^ Steering wheel.

The steering system uses a ZF rack and pinion steering gear with a conventional end take-off and a pinion power assisted unit with the addition of ZF Servotronic 2 assistance. The steering gear is handed depending on vehicle drive hand but is common to all three engine variants.

Servotronic 2 adds electronic control and speed sensitive steering to the steering gear. The Servotronic 2 feature provides easy and comfortable steering operation when parking, improved 'road feel' at increased road speeds and adds an integrated, positive center feel feature which optimizes steering wheel torque during high speed driving. The Servotronic 2 system is controlled by software which is incorporated into the air suspension control module. The software responds to steering torque inputs and road speed signals and controls the assistance via a transducer valve located on the steering gear valve.

The steering column features fully electrical adjustment for tilt and reach. On vehicles fitted with memory seats, the steering wheel position control is incorporated into the memory module.

Each steering system uses an engine mounted power steering pump which is driven by an auxiliary belt. The location and attachment of the pump differs between engine variants. A power steering fluid reservoir is mounted near to each pump and provides fluid supply to the pump via a suction hose.

The steering system incorporates a fluid cooler in the hydraulic pipe layout. The cooler is routed near to the front of the vehicle to benefit from the increased airflow when the vehicle is moving. The power steering fluid is cooled as it returns from the gear to the reservoir via the cooler by air flowing over the cooler.

The upper column components are common to all models and drive hands. A collapsible lower shaft is located on the gear pinion shaft by two flats. An intermediate shaft is located between the lower collapsible shaft and the upper column assembly.

The column assembly, which is attached to the vehicle cross-car beam, provides the location for the steering column reach and rake adjustment switch, the steering column multifunction switches, the steering wheel, the steering column lock and the ignition switch. The column assembly comprises a number of components which are designed to allow the column to collapse in a controlled manner in the event of a frontal impact (reducing occupant loads). The lower collapsible shaft is designed to telescope, and the intermediate shaft to de-couple, to prevent excessive frontal impact loads/displacements being transmitted to the steering column.