Steering: Description and Operation: Overview

Power Steering

OVERVIEW
The steering system comprises a ZF manufactured rack and pinion Servotronic 2 steering gear, a power steering pump, a fluid reservoir, a fluid cooler (if fitted) and fluid hoses. The steering gear is an end take-off rack and pinion power assisted unit with the addition of road speed proportional ZF Servotronic 2 assistance.
The steering rack is connected to the front wheel knuckles by adjustable tie-rods. The tie-rods allow for adjustment to centralize the steering wheel and also adjust the toe setting of the front wheel geometry.
The steering gear has a variable ratio rack. This provides conventional response when the steering is in the centre, straight ahead position, but provides more direct and faster steering as the turning angle increases. The variable ratio provides precise and rapid steering response at high speeds and provides optimized steering of the vehicle when maneuvering into parking spaces, turning in tight areas and when cornering in extreme conditions.
Fluid is supplied to the steering gear by a fixed displacement vane pump on petrol models and a variable displacement pump on diesel models. The pump is driven by a belt from the crankshaft pulley. On petrol models the pump is mounted on the LH (left-hand) side of the engine. On diesel models the pump is mounted on the RH (right-hand) side of the engine. A fluid reservoir is positioned at the front RH (right-hand) side of the engine compartment, forward of the front suspension housing on diesel models and on the front LH (left-hand) side of the engine compartment, forward of the front suspension housing on petrol models.
On petrol engine vehicles, a fluid cooler is located in front of the engine cooling radiator. Diesel models do not have a fluid cooler.
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 instrument cluster. The software responds to road speed signals and controls the power assistance via a transducer valve located on the steering gear valve housing.