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| Illustration 1 | g03703336 |
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Steering pump (left turn) (1) Drive shaft (2) Swashplate (3) Actuator piston (4) Feedback lever (5) Notch (6) Pump control solenoid (7) Lever arm (8) Pump control spool (9) Pump control valve (10) Crossover relief valve (11) Passage to the steering motor (12) Passage to the steering motor (13) Pressure override valve (POR valve) (14) Barrel assembly (15) Piston (BB) Cutaway section (CC) Component surface (FF) Activated components (GG) Tank pressure (KK) High pressure (LL) First pressure reduction (RR) Charge pressure (SS) Reduced charge pressure | |
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| Illustration 2 | g03703339 |
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Steering pump (left turn) (1) Drive Shaft (10) Crossover relief valve (11) Passage to the steering motor (12) Passage to the steering motor (13) Pressure override valve (POR valve) (16) Passage from the steering charge pump (17) Resolver (BB) Cutaway section (CC) Component surface (FF) Activated components (GG) Tank pressure (KK) High pressure (LL) First pressure reduction (RR) Charge pressure (SS) Reduced charge pressure | |
When the engine is running, the charge pump produces flow to the following components: pump control valve (9) and crossover relief and makeup valves (10). The makeup valves open and both sides of the drive loop fill with oil at charge pressure. In pump control valve (9), the charge pressure is blocked at pump control spool (8).
Springs keep actuator piston (3) in the center position in order to hold swashplate (2) in the NEUTRAL position.
When the steering control lever is moved to LEFT TURN, the upper pump control solenoid (6) is energized. Pump control spool (8) shifts downward in order to send oil to the upper end of actuator piston (3). The actuator piston moves down and the swashplate angle increases in proportion to the movement of the actuator piston. As a result, the steering pump sends flow through the closed loop in a direction that rotates the steering motor for LEFT TURN.
When the steering control lever is moved to RIGHT TURN, the lower pump control solenoid (6) is energized. Pump control spool (8) shifts upward in order to send oil to the lower end of actuator piston (3). The actuator piston moves up and the swashplate angle increases in proportion to the movement of the actuator piston in order to reverse the direction of the pump. Oil now flows through the closed loop in a direction that rotates the steering motor for RIGHT TURN.
The hydraulic steering pump is a bidirectional variable displacement axial piston pump. The displacement of the pump and the direction of oil flow is controlled by the pump control valve.
The steering hydraulic pump has the following components:
Pump control valve (9) - The pump control valve regulates the flow of charge oil to the ends of actuator piston (3). Actuator piston (3) is mechanically connected to the swashplate. The actuator piston adjusts the angle of swashplate (2). The pump control valve responds proportionally to the movement of the steering control lever in the cab. The pump control valve contains two solenoids (6), pump control spool (8), lever arm (7), and feedback lever (4).
Feedback lever (4) - The feedback lever joins pump control valve (9) and actuator piston (3). Feedback lever (4) provides resistance against the pump control solenoid in order to meter oil to actuator piston (3).
Actuator piston (3) - The actuator piston adjusts the angle of swashplate (2). Oil from pump control valve (9) moves the actuator piston. Centering springs are used to maintain a neutral position when the steering control lever is not sending a turning signal.
Notch (5) - The notch is the mechanical connection between actuator piston (3) and feedback lever (4). When the actuator piston moves, the feedback lever moves in order to increase the tension in the spring that is connected between the lever arms.
POR valve (13) - Resolver (17) shifts in order to allow the highest pressure in the drive loop to act against the spring in the POR valve. When this drive loop pressure overcomes the spring in the POR valve, pressure from either side of actuator piston (3) is drained to the pump case. When the pressure of the oil in the drive loop exceeds the pressure setting of the POR valve, the pump will destroke.
Barrel assembly (14) - The barrel contains nine pistons. Barrel assembly (14) rotates whenever the engine is running. Pistons (15) move oil into the barrel and out of the barrel.
Swashplate (2) - The displacement of the pump is controlled by the angle of the swashplate. When the swashplate is at a maximum angle, the pistons move the maximum volume of oil in and out of the rotating barrel. The swashplate can angle to either side in order to change the direction of the flow of oil.
Drive shaft (1) - The rotation of the pump is clockwise when the pump is viewed from the drive end. The piston and barrel assembly are splined to the drive shaft.
Crossover relief and makeup valves (10) - The crossover relief valves relieve high-pressure spikes in the drive loop. Each valve also contains a makeup valve. The makeup valve allows charge oil to replenish the closed drive loop.
Resolver (17) - The resolver ensures that the highest pressure in the drive loop reaches POR valve (13).
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| Illustration 3 | g01391582 |
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(18) Spring
(19) Passage from the actuator piston (20) Passage to pump case (21) Passage from the drive loop (22) Passage from the drive loop (23) Slug (24) Chamber (25) Piston (26) Valve | |
The POR valve limits the maximum pressure in both sides of the closed drive loop. When the valve opens, the valve drains oil from the actuator piston in the steering pump. As the actuator piston is drained, the centering springs in the actuator piston move the swashplate in order to reduce pump output.
Slug (23) serves as a resolver. Oil from the high-pressure side of the closed loop enters the POR valve through either passage (21) or passage (22). Slug (23) is moved left if the high pressure is in passage (22). Slug (23) is moved right if the high pressure is in passage (21). The high-pressure oil is sent to chamber (24).
When the pressure in chamber (24) is high enough to overcome spring (18), piston (25) and valve (26) move to the left against spring (18). The valve connects passage (19) to passage (20). The oil from the actuator piston is then allowed to drain to the pump case.
The pressure setting of the POR valve is adjustable.
Crossover Relief and Makeup Valve
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| Illustration 4 | g01391612 |
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(27) Passage from the drive loop
(28) Passage to charge the circuit (29) Spring (30) Spring (31) Valve (32) Chamber (33) Valve | |
A crossover relief and makeup valve is placed in each side of the closed drive loop. The crossover relief valves are designed to remove high-pressure spikes in the drive loops. Some charge oil is lost in the closed drive loop from leakage and flushing. The makeup valves allow charge oil to replenish the low-pressure side of the drive loop.
Oil from the drive loop enters the valve through passage (27). The oil flows into chamber (32). Valve (31) is held closed by spring (30).
The pressure of the oil in chamber (32) acts against valve (31). The force of spring (30) keeps valve (31) closed until oil pressure in the drive loop reaches the relief pressure.
When the force of the pressure of the oil in chamber (32) against valve (31) becomes greater than the force of spring (30), valve (31) opens to the right. The oil in chamber (32) flows around valve (31) to the drain.
When the pressure drops in chamber (32), only the force of spring (29) is acting against valve (33). The high pressure on the left side of valve (33) is greater than the force of spring (29). Valve (33) opens to the right. Oil from the drive loop can now go through passage (28) into the charge circuit.
The valve also acts as a makeup valve for the closed drive loop. When the pressure of the low-pressure side of the closed loop drops below charge pressure, charge oil in passage (28) opens valve (33). Oil from the charge circuit flows into the low-pressure side of the drive loop through passage (27). When the pressure in passage (27) and chamber (32) reaches charge pressure, the force of spring (29) closes valve (33).
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| Illustration 5 | g02443036 |
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Pump control valve (left turn) (4) Feedback lever (5A) Pump control solenoid (5B) Pump control solenoid (7A) Lever arm (7B) Lever arm (8) Pump control spool (34) Feedback pin (35) Spring (36) Passage to the actuator piston (37) Pivot pin (38) Control pin (39) Passage to the actuator piston | |
When the operator moves the steering control lever to RIGHT TURN, left pump control solenoid (5A) is energized by a proportional signal from the machine ECM.
When left pump control solenoid (5A) is energized, pump control spool (8) is shifted to the right. When the spool shifts, charge oil is sent to the actuator piston through passage (39). When left pump control solenoid (5A) shifts pump control spool (8) to the right, control pin (38) forces lever arm (7B) to the right. Spring (35) is placed under a small amount of tension in order to meter oil to the actuator piston.
Charge oil in passage (39) causes the actuator piston to shift to the right. Feedback lever (4) shifts with the actuator piston. Feedback lever (4) and lever arms (7A) and (7B) pivot around pivot pin (37). Feedback pin (34) is in the end of feedback lever (4). As the feedback lever moves with the actuator piston, feedback pin (34) pushes lever arm (7A).
When lever arm (7A) moves, spring (35) is extended. The extended spring pulls lever arm (7B), which causes the lever arm to exert a force on control pin (38). The force on control pin (38) works against the force of pump control solenoid (5A).
Therefore, feedback lever (4) provides resistance to the force of pump control solenoids (5A) and (5B) that shift pump control spool (8). When the actuator piston moves further, the resistance from feedback lever (4) increases. This feedback helps to hold the pump swashplate at the required angle.
When the operator returns the steering control lever to the NEUTRAL position, feedback lever (4), lever arms (7A) and (7B), and spring (35) return pump control spool (8) to the center position.
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| Illustration 6 | g01391654 |
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Actuator piston (3) Actuator piston (6) Notch (40) Springs (41) Notch | |
Oil from the pump control valve flows to either the right end or the left end of actuator piston (3). The oil pressure moves the actuator piston in order to upstroke the pump.
A plate that is pinned to an arm on the swashplate is in notch (6). When the actuator piston moves, the plate moves the arm on the swashplate. The swashplate moves to the angle that corresponds to the position of the actuator piston.
The feedback lever to the pump control valve is in notch (41). The feedback lever works with the pump control valve in order to maintain precise control of the pump displacement.
When the oil is drained from the actuator piston, springs (40) return the piston to the centered position.