Flow Control Valve Open (page 4 of 4)

In the power steering unit, the method used to direct a single source of fluid pressure in either of two directions (for left or right turns) involves the pinion gear transferring a "message" of direction to the fluid in the 4-way valve.

The pinion is mounted slightly off-centre in a pair of bearings, which are in turn mounted in a pinion holder cylinder that rotates, centred in its own outer bearings. At the bottom of the pinion holder is a pin, which fits in a slot in the 4-way valve. As the pinion is turned (to turn left or right), because it is off-centre, it also moves slightly along the rack. This movement is transferred to the holder. The pin in the holder then moves the 4-way valve, to direct fluid pressure to either side of the rack in the power cylinder.

The back edges of the pinion holder (facing away from the rack) hit the stops cast into both sides of the gear housing to avoid pushing the 4-way valve too far in either direction. The front edge of the pinion holder cuts off assist at full lock, as described on the next page.