Steering Gear: Description and Operation

DESCRIPTION






This vehicle is equipped with a rack-and-pinion power steering gear. The gear is a center take-off type gear. Center-take-off means that the tie rods are connected to the steering gear via a rack guide located at the center of the gear.
The power steering gear is mounted on the crossmember behind the engine. The steering column intermediate shaft connects to the pinion shaft of the gear. The outer ends of the outer tie rods attach to steering arms on the suspension's front struts.
Three different power steering gears are available: a base gear, a firm feel gear, and a speed proportional gear. The base gear and firm feel gear are serviced the same. The speed proportional steering gear is physically very similar to the standard gear except for the solenoid control valve extending from its housing. For information and service procedures on the speed proportional power steering gear or its individual components, refer to the SPEED PROPORTIONAL POWER STEERING GEAR.

NOTE: The power steering gear should not be serviced or adjusted. If a malfunction or oil leak occurs within the steering gear, the complete steering gear needs to be replaced.

OPERATION
Turning of the steering wheel is converted into lateral (side-to side) travel through the meshing of the helical pinion teeth with the rack teeth within the steering gear. This lateral travel pushes and pulls the tie rods to change the direction of the vehicle's front wheels.
Power assist steering provided by a pump is controlled by an open-center, rotary type control valve. It directs fluid to either side of the gear's integral steering rack piston. Depending on the rotation of the steering wheel, fluid pressure is transferred to one side of the rack piston over the other.
Road feel is controlled by the diameter of a torsion bar which initially steers the vehicle. As steering effort increases as in a turn, the torsion bar twists, causing relative rotary motion between the rotary valve body and valve spool. This movement restricts fluid flow to one side of the integral rack piston and redirects fluid behind the other side of the integral rack piston, building up hydraulic pressure, thus assisting in the turning effort.
Manual steering control of the vehicle can be maintained if power steering assist is lost. However, under this condition, steering effort is significantly increased.