Power Steering Pump: Description and Operation

Design





Legend
1- To steering gear
2- From steering gear

The power steering pump is of the vane type and mounted in a bracket on the engine. The pump is driven from the crankshaft by a poly-V belt at the same time.

Function
Pump





Legend

1- Rotor
2- Distancer
3- Outer wall
4- Safety valve
5- Control valve

The pump rotor has 10 loose laminated vanes and rotates in a ring shaped distancer. The laminated vanes are pressed against the walls of the distancer by centrifugal force and oil pressure.

The area of inside the distancer is oval, see A in illustration. Because of this the space between the rotor, distancer wall and two of the vanes changes when the rotor rotates.

When a pair of vanes move from the suction side to the pressure side the space between them increases and oil is sucked in.

The vanes move onto the pressure side. The gap between the vanes decreases at the same time the pressure increases and the oil is forced out into the delivery pipe.

There are two suction and pressure channels that gives the pump double capacity.

Control valve





Legend
1- Delivery pipe
2- Throttle valve
3- Pressure channel
4- Return channel
5- Control valve
6- Safety valve
7- Spring
8- Connecting channel

There is a control valve in the pump housing which regulates the oil quantity and maximum pressure.

When the pump starts the valve (5 A in illustration) is pushed to the left by the spring (7). The oil from the pump passes through the pressure channel (3) via the throttle valve (2) into the pressure pipe (1) and then to the steering gear.

The space to the right of the control valve is connected to the pressure pipe (1) by the connecting channel (8) and has the same pressure.

The throttle valve (2) makes the pressure on the left-hand side of the control valve piston higher than in the pressure pipe and the space to the right of the piston. When the spring pressure is overcome the piston is pushed to the right.

When rotation is sufficiently high in relation to the counter pressure the piston has been moved so much that the surplus oil can pass back to the pump side, see A in illustration. Because the pump is delivering a smaller amount than maximum capacity this valve position can be called normal.

If the pump outlet flow is stopped, by the steering movement being blocked for example, the pressure rises in the pipe (1) and the pressure difference on the ends of the control valve is equalized. The spring then pushes the valve back to the left, the connection with the return channel is closed and the pressure rises again.

At maximum pressure the spring pressure on the safety valve (6), that is the inner part of the control valve, is overcome and oil can pass out to return channels (4), see B in illustration. The pressure on the right-hand side of the piston is decreased and the control valve is moved to the right and opens the connection to return channel.

When the pressure has sunk to a normal value the safety valve shuts and the control valve returns to the normal position.