| |
| Illustration 1 | g06165877 |
|
(1) Left turn port
(2) Right turn port (3) Pump port (4) Tank port (5) Load sensing port (6) Port to signal and pressure reducing valve (7) Relief valve (8) Relief valve (9) Metering Pump (10) Rotary spool (B) Rotary spool section (C) Metering pump section | |
| |
| Illustration 2 | g06165892 |
|
The metering pump is located on the front of the cab beneath the windshield. (1) Left turn port (2) Right turn port (3) Pump port (4) Tank port (5) Load sensing port | |
The metering pump meters oil from the piston pump (steering) to the steering cylinders. Left turn port (1) and right turn port (2) are connected to the steering cylinders.
The metering pump consists of rotary spool (B) and a metering pump (9).
The metering pump also contains a makeup valve for each steering cylinder and a relief valve for each steering cylinder. The makeup valves prevent voiding if the steering cylinders are moved by external forces.
The rotary spool, which is infinitely variable, has three positions. The rotary spool is offset when the steering wheel is rotating. The rotary spool is spring centered when the steering wheel is stationary. Oil flow past the rotary spool increases as the rotational speed of the steering wheel increases. The rotary spool has the following functions.
- The rotary spool divides the flow from pump port (3) between the metering pump and an output port.
- The rotary spool allows a load sensing signal to flow from load sensing port (5) into the load sensing line when the steering wheel is turning. The magnitude of the load sensing pressure depends on the rotational speed of the steering wheel and on the resistance to the turn.
- The rotary spool directs oil from load sensing port (5) to tank port (4) when the steering wheel is stationary.
- The rotary spool blocks oil flow to the steering cylinders and from the steering cylinders when the steering wheel is stationary.
| |
| Illustration 3 | g06165896 |
|
Pump gears inside metering section - Right Turn (11) Stator (12) Rotor (13) Pin (14) Drive | |
The metering pump is coupled to the steering wheel. As the steering wheel rotates clockwise, pin (13) and drive (14) begin to turn. Oil from pump port (4) goes through the metering pump which transfers oil to the rotary spool and directs oil to the correct steering cylinder.
Rotor (12) is splined to drive (14). As drive (14) turns, rotor (12) pumps oil through the passage. Metered oil then flows back into right turn port (2). Pilot oil from right turn port (2) goes to the directional spool in the steering control valve.
The amount of oil which bypasses the metering pump depends on the difference in output between the metering pump and the piston pump (steering). As the rotational speed of the steering wheel is increased, the difference in output between the metering pump and the piston pump increases. This action occurs because an increased load sensing signal causes the piston pump to upstroke. More oil will bypass the metering pump and the number of rotations which are required to articulate the machine is reduced.