Power Assisted Steering (PAS) Pump

Power Assisted Steering (PAS) Pump

Td4 pump shown, K1.8 and KV6 pumps similar

1 Outlet connection 2 Inlet connection 3 Cover

4 Body 5 Drive flange

The vane type PAS pump supplies hydraulic pressure to the steering rack valve unit. The PAS pump is driven by a Poly Vee belt from the crankshaft pulley. A self adjusting tensioner is fitted to maintain the correct belt tension.

The PAS pump comprises a body and cover which house the internal components of the pump. A pressure relief valve assembly is installed in the body. The relief valve also incorporates a flow control valve. The pressure relief valve limits the maximum pressure to between 90 and 100 bar (1305 and 1450 lbf/in²) on K1.8 models or 120 and 127 bar (1740 and 1842 lbf/in²) on KV6 and Td4 models. The flow control valve limits the maximum flow to between 5.0 and 6.0 l/ min (1.32 and 1.58 US gal/min).

A shaft runs longitudinally through the pump. One end of the shaft has a drive flange which accepts the drive pulley. The opposite end is closed by the cover. The shaft runs in bearings located in the body. Oil seals at each end of the shaft prevent the leakage of hydraulic fluid.

An oval cam ring is located in the body. Ten roller vanes are housed in a carrier and rotate within the cam ring. The carrier is mounted in the centre of the shaft and receives positive drive from the shaft via a drive pin. The carrier is seated against an end plate which is located in the cover. The front of the carrier is covered by a port plate which is located against a seal plate in the body. The port plate controls the fluid flow into and out of the roller vanes during their cycle.