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| Illustration 1 | g00950892 |
(1) Outlet port to the left steering cylinders (2) Load sensing signal port (3) Outlet port to the right steering cylinders (4) Outlet port to the combination valve (5) Inlet port from the combination valve | |
The steering metering pump is made up of two sections:
- The control section that contains the ports
- The metering section that contains stator (8) and rotor (14) .
When the steering wheel is turned, the control section sends oil to the metering section . The metered oil from the metering section is then directed by the control section. The metered oil flows to the outlet port to left steering cylinders (1) or to the outlet port to right steering cylinders (3) .
As the steering wheel is rotated faster, there is an increase in the flow of oil. Inside inlet port (5) is a check valve. The check valve prevents steering wheel kickback that is caused by high-pressure spikes in the steering circuit.
Neutral Position
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| Illustration 2 | g00950893 |
Typical Steering Metering Pump in the NEUTRAL Position (1) Outlet port to the left steering cylinders (3) Outlet port to the right steering cylinders (4) Outlet port to the combination valve (5) Inlet port from the combination valve (6) Outer sleeve (7) Passage (8) Stator (9) Inner spool (10) Centering spring (11) Pin (12) Drive (13) Passage (14) Rotor | |
Note: The steering metering pump is shown without the steering wheel column control or the shaft.
The control section of the steering metering pump is a closed center type. When the steering wheel is in the NEUTRAL position, there is no alignment between the holes in outer sleeve (6) and the passages in inner spool (9) . Oil flows through an internal orifice to the hydraulic tank.
Right Turn
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| Illustration 3 | g00950894 |
Typical Steering Metering Pump (1) Outlet port to the left steering cylinders (3) Outlet port to the right steering cylinders (4) Outlet port to the combination valve (5) Inlet port from the combination valve (6) Outer sleeve (7) Passage (8) Stator (9) Inner spool (10) Centering spring (11) Pin (12) Drive (13) Passage (14) Rotor | |
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| Illustration 4 | g00950895 |
(6) Outer sleeve (9) Inner spool (15) Slots for springs (16) Grooves for oil flow (17) Oil holes (18) Holes for pin | |
When the steering wheel is turned clockwise to make a right turn, inner spool (9) , pin (11) and drive (12) start to rotate. Outer sleeve (6) does not rotate at the same time because the diameter of the holes (18) for pin (11) in sleeve (6) is slightly larger than the diameter of pin (11) . This allows spool (9) to rotate in sleeve (6) . This aligns the holes (17) in sleeve (6) with the grooves (16) in spool (9) . The rotation from the NEUTRAL position of spool (9) and sleeve (6) provide an oil path between outlet port (3) and load sensing signal port (2) from Illustration 1.
The pump oil from inlet port (5) flows through holes (17) in sleeve (6) into grooves (16) in spool (9) . The oil in grooves (16) flows outward through holes (17) in sleeve (6) and flows into passage (13) . Oil flows through passage (13) into metering section (GG) . Then, the oil is directed into a space between stator (8) and rotor (14) .
Rotor (14) is splined to drive (12) . As drive (12) rotates, rotor (14) rotates and pumps oil out passage (7) . The metered oil flows through holes (17) in sleeve (6) into other grooves (16) in spool (9) . The metered oil continues out through sleeve (6) into the outlet port (3) .
When the steering wheel is not used, the rotation of spool (9) , pin (11) , drive (12) and rotor (14) stops. Holes (17) in outer sleeve (6) do not line up with grooves (16) in inner spool (9) . The oil flow from inlet port (5) stops. The flow of metered oil to outlet port (3) stops. When the flow of oil is stopped, the wheels will stay in the fixed position.
Left Turn
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| Illustration 5 | g00950896 |
Typical Steering Metering Pump in the LEFT TURN Position (1) Outlet port to the left steering cylinders (3) Outlet port to the right steering cylinders (4) Outlet port to the combination valve (5) Inlet port from the combination valve (6) Outer sleeve (7) Passage (8) Stator (9) Inner spool (10) Centering spring (11) Pin (12) Drive (13) Passage (14) Rotor | |
When the steering wheel is turned counterclockwise the machine makes a left turn. The same components are used for both the right turn and the left turn. For these sequences, the same components move in opposite direction. Oil comes back into the inlet port from combination valve (5) . Spool (9) and sleeve (6) rotate in the opposite direction. This allows a different set of holes to line up with a different set of grooves. The outlet port to the left steering cylinders (1) is now open to the load sensing signal port (2) from Illustration 1.
Oil flows through inner spool (9) and through outer sleeve (6) into passage (7) and into the metering section. The metered oil flows outward through passage (13) . Then, the oil flows back through inner spool (9) and outer sleeve (6) . Then, the oil flows out of outlet port (1) .
Load Sensing
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| Illustration 6 | g00950893 |
Typical Steering Metering Pump in the NEUTRAL Position (1) Outlet port to the left steering cylinder (3) Outlet port to the right steering cylinder (4) Outlet port to the combination valve (5) Inlet port from the combination valve (6) Outer sleeve (7) Passage (8) Stator (9) Inner spool (10) Centering spring (11) Pin (12) Drive (13) Passage (14) Rotor | |
Note: Refer to Illustration 1 for load sensing signal port (2) location.
In addition to the four ports that have already been described, the steering metering pump has a load sensing signal port (2) . The load sensing signal port connects internally by the rotation of inner spool (9) and outer sleeve (6) to the orifice in outlet port (4) . When this occurs, the steering metering pump is in the NEUTRAL position. Also, the load sensing signal port connects internally to outlet port (3) during a right turn and to outlet port (1) during a left turn.
When signal port (2) is connected to a turn port, signal port (2) senses the resistance pressure to rotation. This resistance creates a specific signal pressure. This signal pressure originates from the signal relief valve that is in the combination valve. The signal pressure plus the margin pressure will provide oil flow to the steering metering pump in order to meet the steering demand. The signal pressure is also communicated to the signal resolver in the combination valve. The signal resolver is compared to the implement signal pressure. The highest signal pressure is sent to the flow compensator valve on the hydraulic pump in order to upstroke the pump. Upstroking the pump will meet the greater oil demand.
Also, the steering metering pump has steering line relief valves with anticavitation valves.