These vehicles use an integral power steering system. The integral power steering system integrates the power cylinder and the control valves into the steering gear unit. A separate power cylinder is not necessary with an integral power steering system.
These vehicles use the Servocom® ZF 8097 variable ratio steering gear and includes the following components:
| • | A manual steering mechanism |
| • | A hydraulic control valve |
| • | A hydraulic power cylinder |
Force is transmitted from the steering wheel to the steering gear input shaft when the wheel is turned. A torsion bar turns with the input shaft. The torsion bar exerts a rotational force on the worm shaft. One end of the torsion bar is pinned to the input shaft. The other end is pinned to the worm shaft.
When rotational force is applied, the worm shaft moves the rack piston axially through the gear housing cylinder bore. The recirculating ball mechanism assists in completing this action.
The rack piston is engaged to the sector shaft. The sector shaft is connected by linkage to the steered wheels. This arrangement causes the rack piston to resist axial movement.
Because of this resistance, the input shaft twists the torsion bar. This actuates the control valve. The control valve directs the pressurized fluids. This action assists in the axial movement of the rack piston through the bore. The rack piston then turns the sector shaft in order to steer the vehicle.
Road shock forces are transmitted through the sector shaft to the rack piston and to the worm shaft. The internal geometry of the gear causes the control valve to send a high pressure fluid to the correct cylinder cavity. This high pressure fluid assists in resisting the shock forces. The steering gear prevents any objectionable kickback at the steering wheel by absorbing the shock forces hydraulically.
The steering gear is equipped with an unloading valve (poppet valve) at each end of the rack piston. The following actions occur when the steered wheels approach the axle stop:
| • | The valve opens |
| • | The gear pressure is reduced |
These actions reduce the buildup of heat.
The unloading valves also reduce the forces on the steering linkage. The unloading valves are automatically set at the assembly facility by turning the steering wheel from full lock right to full lock left position.
A relief valve limits the maximum supply pressure. This protects the power steering pump. The relief valve does not reduce pressure as the steered wheels approach the axle stops.
