Metering Pump for the Steering System
Location and Function
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| Illustration 1 | g00928307 |
Metering pump (1) (steering) is located under the operator platform, as shown.
The direction and speed in turning the machine is controlled by the metering pump. The metering pump is connected to the steering wheel. As the operator turns the steering wheel faster, there is an increase in the flow of oil from the metering pump to the steering cylinders. The increased flow causes the cylinders to move faster. Consequently, turning of the machine is faster.
Operation of Metering Pump Components
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| Illustration 2 | g00928963 |
(2) Inner spool (3) Sleeve (4) Outlet port (5) Load sensing line port (6) Inlet port (7) Rotor (8) Rotor ring (9) Drive shaft (10) Centering spring (11) Pin (12) Internal check valve (13) Left turn port (14) Right turn port (15) Housing (A) Control section (B) Metering section | |
The metering pump is made up of the following two sections:
- Control section (A)
- Metering section (B)
The two sections are connected by hydraulics and by mechanics. The two sections work together in order to send oil to the steering cylinders.
Pump oil goes through inlet port (6) into control section (A). When the steering wheel is turned, control section (A) sends oil to metering section (B). Metering section (B) produces a specific amount of oil flow. Metered oil from metering section (B) is then directed by control section (A) to either left turn port (13) or right turn port (14) .
Metering section (B) is a small hydraulic gerotor pump. The hydraulic pump produces a metered amount of oil flow. Then, the metered oil is directed by control section (A) to the steering cylinders.
Oil flows through outlet port (4). When the steering wheel is in the NO STEER position, the oil is stopped by spool (2). The oil cannot flow to the metering pump to the steering cylinders until the steering wheel is turned.
The steering column is connected to spool (2) by a shaft and a spline coupling.
When the steering wheel is turned, spool (2) turns a small amount until springs (10) are compressed. When the drive pinion contacts the ends of the slots, sleeve (3) also turns.
While the steering wheel is turning, the spool and the sleeve are spread apart by a few degrees. The spool and the sleeve rotate as one unit. The centering springs are compressed.
The initial movement of the spool opens the oil passages between the control section and the metering section. This allows the oil flow from inlet port (6) to go to the metering section.
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| Illustration 3 | g00928973 |
(2) Inner spool (11) Pin (16) Slots for centering springs (17) Outer sleeve (18) Grooves for oil flow (19) Holes for pin (20) Small holes for oil flow | |
When the steering wheel is turned, inner spool (2), pin (11) and drive shaft (9) start to turn. Sleeve (17) does not turn at the same time as inner spool (2), because the diameter of holes (19) in sleeve (17) are slightly larger than the diameter of pin (11). Consequently, inner spool (2) turns inside sleeve (17) enough to align small holes (20) in sleeve (17) with grooves (18) in inner spool (2). The alignment of these holes and grooves provides the path for oil flow to the gerotor. The oil now flows to the steering cylinder. Centering springs (10) are compressed when the spool moves in relation to the sleeve. When the steering wheel is no longer turning, the springs bring the spool and the sleeve back to a center position.
The front end of the machine stays in the turned position when the steering stops. The steering wheel must be turned in the opposite direction in order to straighten the machine.
When the machine is off, the metering pump can be manually operated. Metering section (B) operates as a pump. The suction of the metering section opens internal check (12) . When the internal check valve opens, return oil flows from the steering cylinder to the inlet side of the metering section. During power operation, supply pressure keeps the check valve closed.
Internal check valve (12) converts the metering pump into a hand operated pump for limited manual steering.
Oil Flow
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| Illustration 4 | g00934451 |
Schematic for Right Turn (1) Metering pump (21) Line to the steering charge pump (load sense circuit) (22) Line from the steering charge pump (priority valve) (23) Valve envelope (24) Hydraulic cylinder (steering) (25) Hydraulic cylinder (steering) (26) Valve envelope (27) Line to the propel charge filter (28) Line from blade control valve (A) Control section (B) Metering section (AA) System (AB) Charge pressure (AC) Activated components (AD) Load sense | |
Metering pump (1) contains control section (A) (spool) and metering section (B) (pump). Oil from steering charge pump (22) is delivered to control section (A) .
When you turn the steering wheel to the right, control section (A) is rotated so that valve envelope (23) is activated. This will cause oil to go through metering section (B) and to the head end of hydraulic cylinder (25) and the rod end of hydraulic cylinder (24). As a result, a right turn is made. Illustration 4 shows the oil flow for a right turn.
When you turn the steering wheel to the left, control section (A) is rotated so that valve envelope (26) is activated. This will cause oil to go through metering section (B) and to the rod end of hydraulic cylinder (25) and to the head end of hydraulic cylinder (24). As a result, a left turn is made.
Reference: See Specifications, Systems Operation/Testing and Adjusting, "Steering, Fan and Leveling Blade System" for additional information.