Steering (Operation): Description and operation

Operation

Hydraulic fluid is supplied to the PAS pump inlet from the PAS reservoir, the PAS pump draws in and pressurises the fluid. The PAS pump self regulates internal flow rates and operating pressure, and supplies pressurised fluid from the PAS pump outlet to a rotary control valve in the steering box. At neutral the fluid is circulated by the PAS pump and flows around the system at a lower pressure and a constant flow rate. With most of the fluid being returned to the reservoir the pressure inside the system remains very low. When a control input turns the rotary control valve in the steering box, pressure in the system will rise as the control valve directs fluid to give power assistance.

The action of turning the steering wheel turns the steering column and intermediate shaft. The intermediate shaft turns the input shaft of the steering box. The input shaft moves the rotary control valve in the steering box, the rotary valve controls the pressure used inside the steering box for power assistance. The input shaft also turns a worm gear, the worm gear acts on a roller attached to the output shaft. As the worm gear turns the roller, the roller travels along the lands of the worm gear. As the roller is attached to the output shaft the output shaft turns.

As the output shaft of the steering box turns, hydraulic pressure is supplied via the rotary control valve to the steering box. The hydraulic pressure acts on a rack that assists with the movement of the output shaft of the steering box. A drop arm is attached to the output shaft of the steering box. The drop arm is connected to a drag link by a ball joint. The drag link is connected via ball joints to one front steering knuckle and road wheel. A track rod connected to this steering knuckle links the two steering knuckles together. As one steering knuckle and road wheel is turned by the drag link, the other steering knuckle and wheel is moved by the track rod.