Rotary Valve Assembly

Rotary valve assembly




A. To left side of piston.
B. To right side of piston
C. Inlet flow
D. Fluid return
Steering left Neutral position Steering right
High pressure fluid Low pressure fluid

The steering gear input shaft acts on the steering gear gear drive. The shaft has external lugs. There is radial play between the lugs.

A torsion bar which joins the input shaft to the gear drive holds the lugs in a position where the play is equal on each side when there is no steering input on the shaft. The torsion bar is pressed into the gear drive.The torsion bar is secured to the input shaft with a pressed in locking pin.

A rotary valve is located in the valve assembly and fixed to the gear drive with a lock pin. The valve operating range is radial between six narrow vertical channels in the rotary valve and six milled grooves in the input shaft. The valve is balanced as a complete unit and cannot be rebalanced.

The valve is open when the car engine is running and there is no steering input. In the open position the servo oil flows through the valve freely and none of the ducts to the operating cylinders are blocked.

When the steering wheel is turned to the left and the wheel resistance is so great that the torsion bar inertia is overcome, the steering gear input shaft moves to the left in relation to the torsion bar. The input shaft moves within the play allowed between the lugs. With this movement the input shaft stops the free flow through the valve and sends the fluid through the upper feed pipe to the left-hand side of the piston.

As long as the torsion bar is affected by steering input the oil pressure continues to push the steering rack to the right. If the steering input diminishes the torsion bar springs back and the valve assembly returns to the center position so that the oil can circulate freely within the valve assembly.

The function when turning right is, in principle, the same as to the left. The only difference is that the steering gear input shaft sends the high pressure fluid through the valve's lower feed pipe to the right side of the piston.