Steering Gear: Description and Operation

Design
The steering gear is of the rack and pinion type in which both the mechanical and power steering components are combined in a single unit. Among other features, this means that the mechanical steering function remains available if the power steering function is lost for any reason. The mechanical assembly consists of the pinion (18), rack (10) and tie rods (track rods) (19). The pinion is supported in a journal bearing in the steering gear housing. The input shaft is supported in a ball bearing (4). At the right-hand end, the rack is supported in a plain bearing. The rack is actuated in the housing by the pinion (18) and a spring-loaded preloaded piston. A cylindrical tube (11) attached to the steering gear housing (21) also acts as operating cylinder for the power steering piston. The power steering pump fluid is controlled by the rotary valve in the steering gear housing. the steering gear input shaft is attached to the pinion by a torsion rod. The tie rod (track rods), which are provided with ball joints at each end, also form part of the steering gear. The inner joints are located inside the protective boots (gaiters) and are attached directly to the rack, while the outer joints are permanently lubricated and attached to the tie rods (track rods). The mechanical components of the steering gear are lubricated by a semi-liquid grease and are separated from the power steering assembly by seals (6) and (9). During a steering movement, when one boot (gaiter) is compressed and the other extended, air is free to flow between the boots through the drilled-out rack and the unpressurized part of the steering gear housing.





Operation Of Gear And Fluid
A. Neutral position: The power steering fluid flows freely through the steering gear.
B. Steering to left: High-pressure fluid from the pump enters the valve housing through the upper connection. From the valve housing, the fluid flows through the rotary valve into one of the external fluid lines to act on the piston (20), moving the rack (10) to the right.
C. Steering to right: In this case also, high-pressure fluid from the pump enters the valve housing through the upper connection. After flowing through the rotary valve, the fluid is admitted to the other external fluid line and acts on the other side of the piston (20), moving the rack (10) to the left.





Rotary Valve Assembly
The input shaft actuates the pinion through two drivers, each of which is provided with a circumferential clearance on either side. When no steering effort is exerted on the input shaft, a torsion rod connecting the shaft and pinion acts to maintain the drivers in a position in which the clearance is the same on each side. The torsion rod is a press fit in the pinion and is secured to the shaft by means of a pressed-in locking pin. A valve sleeve in the valve housing is attached to the pinion by a locking pin. The fluid flows radially through the valve between six narrow, vertical grooves in the sleeve and six milled grooves in the input shaft. The valve is balanced as a unit and cannot be rebalanced. The valve is open when the engine is running and no steering effort is exerted on the steering gear. In this position, only a small, equalized leakage flow is admitted to the outlets supplying each side of the power piston and hydraulic fluid circulates freely through the valve When the steering wheel is turned to the left and the road wheel friction is sufficient to overcome the resistance of the torsion rod, the input shaft rotates to the left relative to the rod within the clearance afforded by the drivers. This movement of the input shaft interrupts the free flow of fluid through the valve and admits high-pressure fluid to the external (upper) line supplying the left-hand side of the rack piston. The fluid pressure displaces the piston to the right as long as the torsion rod is subject to the steering force providing power assistance. If the steering effort is reduced, the torsion rod will spring back and the valve will return to the position in which the fluid circulates freely through the valve housing. The action is basically the same when steering to the right, the only difference being that the high-pressure fluid is admitted to the right-hand side of the rack piston through the lower external supply line.