Discovery II
STEERING
57-10
DESCRIPTION AND OPERATION
Rotary control valve
The rotary valve assembly comprises of three parts. The valve sleeve is fixed inside one end of the worm gear, the
valve sleeve has ports through it to allow the passage of hydraulic fluid. The input shaft has a valve rotor machined
on one end, the valve rotor also has ports through it and can rotate in the valve sleeve. A torsion bar is attached to
the input shaft by a pin, the torsion bar goes through the input shaft and valve rotor and is engaged by a spline into
the worm gear.
The coarse spline on the end of the valve rotor is loosely engaged in the worm gear, the coarse spline can make
contact and drive the worm gear in some full lock and in no pressure conditions. In the event of a torsion bar failure,
power assistance will be lost, the coarse spline will drive the worm gear and enable the vehicle to be steered and
driver control maintained.
Rotary control valve at neutral
1 Worm gear
2 Torsion bar
3 Valve sleeve
4 Pin
5 Input shaft and valve rotor
6 Piston/rack
7 Coarse spline
8 Spline (torque shaft to worm gear)
When there is no demand for assistance the torsion bar holds the ports in the valve sleeve and valve rotor in a neutral
relationship to one another. The ports in the valve sleeve and the valve rotor are so aligned to allow equal (low) fluid
pressure on each side of the piston. Excess fluid flows through ports in the valve rotor through the valve sleeve and
back to the reservoir.