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| Illustration 1 | g00645189 |
The steering metering pump is located at the base of the steering column. (A) Control section (B) Metering section (1) Spool (2) Sleeve (3) Outlet to the tank (4) Inlet from the pump (5) Rotor (6) Stator (7) Centering springs (8) Drive pin (9) Left turn port (10) Right turn port (11) Body (12) Drive shaft | |
The steering metering pump consists of two parts, control section (A) and metering section (B). Control section (A) is a closed center rotary control valve. Metering section (B) is a rotor pump. The steering column is connected to spool (1) by a splined drive shaft.
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| Illustration 2 | g00645191 |
Spool and sleeve of the steering metering pump (1) Spool (2) Sleeve (13) Holes for the drive pin (14) Slots for the drive pin (15) Holes (16) Grooves (17) Slots for the centering springs | |
Sleeve (2), spool (1), and drive shaft (12) are connected by drive pin (8). Drive pin (8) is installed through holes (13) in the sleeve and slots (14) in the spool. When the steering wheel is stationary, centering springs (7) 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 (4) is blocked by the spool.
When the steering wheel turns, 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 (16) in the spool and holes (15) in the sleeve. This connects control section (A) to metering section (B). Oil is allowed to flow from inlet port (4) in order to fill the spaces between rotor (5) and stator (6) .
When the steering wheel turns further, drive pin (8) turns drive shaft (12) and the rotor turns inside the stator. This pumps a metered flow of oil back through the spool and sleeve to the steering control valve. Oil flows through port (9) or port (10). This depends on the direction of rotation of the steering wheel. Return oil from the opposite side of the steering control valve flows into the steering metering pump through the following components to the tank: the other port, spool (1), sleeve (2) and outlet port (3)
When the steering wheel stops, centering springs (7) 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 into the steering metering pump is blocked.