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| Illustration 1 | g00557813 |
Typical example of the metering pump for the steering (1) Outlet to tank, (2) Metering pump inlet check valve, (3) Inlet from pump, (4) Passage, (5) Passage from Gerotor, (6) Gerotor, (7) Passage to Gerotor, (8) Sleeve, (9) Makeup valve, (10) Drive, (11) Pin, (12) Springs, (13) Shaft spool, (A) Control section and (B) Pump section | |
The metering pump (steering) has two main sections, control section (A) and pump section (B). These two sections work together in order to send oil to the steering cylinder. The metering pump is located in the front of the cab behind a panel near the steering column.
Both the direction of a turn and the speed of a turn are controlled by the metering pump. As the steering wheel is turned faster, there is an increase in the flow of oil to the steering cylinder. The increased flow of oil to the steering cylinder causes the steering cylinder to move farther. The increased flow of oil also causes the steering cylinder to move faster. This causes the machine to turn faster.
When the steering wheel is not being turned, control section (A) is in the NEUTRAL position. The metering pump is a closed center valve so there is no alignment between the passages in the spool and orifices in the sleeve in this position. In the NEUTRAL position, the oil that flows into control section (A) flows through orifices to the hydraulic tank. This allows cooler oil to enter the metering pump.
The pump has a port for the load sensing signal. The line from this port is connected to the priority valve. Some of the flow of the inlet oil that is in the NEUTRAL position also flows back to the priority valve. This oil keeps the spool in the priority valve slightly open. This oil keeps the spool ready for a quick response to steering demands.
When the steering wheel is turned for a right turn, pump oil opens check valve (2) and flows into the metering pump through inlet (3) and passage (4). The oil flows from passage (4) into gerotor (6) through passage (7). As the steering wheel turns, gerotor pump (6) turns. This causes the flow of oil from the pump. The oil flows through passage (5). The oil is then directed to the steering cylinders through the right turn port.
As the oil flows out to the cylinder through the right port for a right turn, return oil from the cylinder is coming back into the metering pump through the left port. This oil is sent to the tank through outlet (1) .
When the steering wheel starts to turn, shaft spool (13), pin (11) and drive (10) also start to turn. Sleeve (8) does not start to turn at the same time as the spool because the diameter of the holes in the sleeve are slightly larger than the diameter of pin (11) .
This allows shaft spool (13) to turn inside sleeve (8). As the shaft turns, the small holes align with the grooves. The alignment of these holes and grooves provides the path for oil flow to gerotor (6) and to the steering cylinder. Centering springs (12) are compressed, when the spool moves in relation to the sleeve.
When the steering wheel is not turning, centering springs move the spool and centering springs move the sleeve to a NEUTRAL position. When the rotation of the steering wheel is stopped, the wheels stay in that position.
The steering wheel must be turned in the opposite direction in order to make a left turn. The steering wheel must be turned in the opposite direction for travel that is straight.
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| Illustration 2 | g00558551 |
Spool And Sleeve (8) Sleeve, (13) Shaft spool, (14) Holes for pin, (15) Small holes for oil flow, (16) Grooves for oil flow and (17) Slots for springs | |
When the steering wheel is turned for a left turn, the components move in the opposite direction for a right turn. Oil flows into inlet (3). Oil flows through passage (4) and oil flows through passage (7) into gerotor (6). Oil flows from gerotor (6) through passage (5) and oil flows through the sleeve. Oil flows through the combination of the shaft and spool.
The sleeve and the shaft spool is turned in the opposite direction of the right hand turn. The movement in the opposite direction allows a different set of holes to line up. The movement in the opposite direction provides a path for oil to the left turn port. Oil flows from the left turn port to the steering cylinder.
If there is a hydraulic pump failure, the metering pump can be manually operated. The metering pump can be manually operated, if the engine stops, and if the engine can not be started again. Makeup valve (9) is mounted between the ports. The makeup valve (9) and check valve (2) allows steering with a dead engine. Makeup valve (9) opens in order to allow return oil to flow between the metering pump and steering cylinder. Check valve (2) prevents this oil from returning to the pump.
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| Illustration 3 | g00558569 |
Pump Gears In The Pump Section (10) Drive, (11) Pin, (18) Rotor and (19) Stator NOTE: The rotor and the stator are part of the gerotor. | |
If the unit is taken apart for any reason, pin (11) and rotor (18) must be aligned, before the unit is reassembled.