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| Illustration 1 | g00743236 |
Location of Metering Pump (Steering) | |
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| Illustration 2 | g00742919 |
(A) Control section (B) Metering section (1) Spool (2) Sleeve (3) Outlet to the tank (4) Check valve (5) Inlet from the pump (6) Check valve (7) Rotor (8) Stator (9) Centering springs (10) Drive pin (11) Left turn port (12) Right turn port (13) Body (14) Drive shaft (15) Signal port | |
The steering metering pump consists of two sections, control section (A) and metering section (B). Section (A) contains a closed center rotary control valve. Metering section (B) is a gerotor pump.
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| Illustration 3 | g00744660 |
Spool and sleeve of the steering metering pump (1) Spool (2) Sleeve (16) Holes for the drive pin (17) Slots for the drive pin (18) Holes (19) Grooves (20) Slots for the centering springs | |
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 cylinders. The increased flow of oil to the steering cylinders causes the steering cylinder rods to move faster. This causes the machine to make a faster turn.
The steering column is connected to spool (1) by a splined drive shaft. Sleeve (2), spool (1), and drive shaft (14) are connected by drive pin (10). Drive pin (10) is installed through holes (16) in the sleeve and slots (17) in the spool. When the steering wheel is stationary, centering springs (9) position the spool so that the drive pin is in the center of the slots. When spool (1) and sleeve (2) are in this position, the inlet oil at port (5) is blocked by the spool.
When the steering wheel is turned to the right, the spool turns. This compresses the centering springs until the drive pin contacts the ends of the slots in the spool, and the sleeve starts to turn. When the spool and the sleeve are in this position, passages are opened through grooves (19) in the spool and holes (18) in the sleeve. This connects control section (A) to metering section (B). Oil is allowed to flow past check valve (6) in inlet port (5) to rotor (7) and stator (8) in the metering section.
When the steering is turned further, drive pin (10) turns drive shaft (14) and the rotor turns inside the stator. This pumps a metered flow of oil back through the spool and sleeve in the control section of the pump. Oil flows through right turn port (12) to the steering cylinder. Return oil flows into the steering metering pump through the following components to the tank: left turn port (11), spool (1), sleeve (2) and outlet port (3)
When a left turn is made, oil flows to the steering cylinder through left turn port (11). Return oil from the steering cylinder flows back into the metering pump through right turn port (12). The oil then returns to the tank through outlet (3) .
Note: If a pressure spike occurs in the system due to an outside factor, check valve (6) protects the system from damage.
When the steering wheel is stationary, centering springs (9) move the sleeve into alignment with the spool. This stops the oil flow between the control section and the metering section, and the oil flow from the pump (implement and steering) into the steering metering pump is blocked.
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 the engine can not be started again. Check valve (4) and check valve (6) allows steering with an inoperable engine. The makeup valve opens in order to allow return oil to flow between the metering pump and steering cylinder. Check valve (6) prevents the oil from returning to the implement and steering pump.