Steering: Description and Operation

Design And Function Of Recirculating Ball Power Steering Unit





The housing contains a complete mechanical steering gear, containing a control valve and the operating cylinder. The steering spindle (1) is connected flexibly via a torsion bar (2) to the worm (3) and to the valve pistons (4 and 5) with zero backlash. The valve pistons are installed transversely in the head of the worm. The connection between piston (6) and worm (3) is made by an endless ball chain. When the worm rotates, the balls at one end of the chain engage in a recirculating tube (7) and are directed towards the other end. The piston (6) and the segment shaft (8) splines are in mesh. The special tooth shape on the segment shaft makes it possible to obtain zero backlash adjustment with one adjusting screw.
When in neutral, the oil delivered by the pump flows through valves (4) and (5) and the steering unit and has free access through the opened intake and return control edges to the cylinder chamber and return line. Hydraulic assistance cuts in if valve pistons (4) and (5) are moved out of neutral position. This occurs whenever force is transmitted from steering wheel or the pitman arm to the worm via segment shaft and piston. The torsion bar (2) acts as a connecting link during this operation. It distorts flexibly and, whenever the steering wheel is released, it moves the valve piston back into neutral setting. When the valves (4) and (5) are adjusted, the oil flow is only directed into one operating cylinder chamber, assisting the rotational motion of the steering spindle and counteracting any impact from the road surface.

Steering wheel in neutral position:





Oil flows from the vane pump to the worm head, through inlet grooves (9) and (10) to radial grooves (11) and (12). From here, via connecting bores to the right and left cylinder chambers and via opened return flow grooves (13) and (14) back to the oil container. The valve is also illustrated in cross section.

Steering wheel turned to right:





The valve piston (4) is adjusted to the right and the inlet groove (9) is open. The valve piston (5) is adjusted to the left and the inlet groove (10) is closed. This enables pressurized oil to enter the right cylinder chamber. The oil in the left cylinder chamber is forced out and flows back to the oil container.

Steering wheel turned to left:





The valve piston (5) is adjusted to the right and the inlet groove (10) is open. The valve piston (4) is adjusted to the left and the inlet groove (9) is closed. Pressurized oil can now enter the left cylinder chamber. The oil in the right cylinder chamber is forced out and flows back to the oil container.