Operation
The regulators for the right pump and the left pump are identical in construction and operation. The following description is given for the left pump regulator.
The main pump regulators are controlled in the following manner.
Power Shift System - The pump regulators are controlled by the electronic control system. The engine and pump controller continually monitors the engine speed and the load on the engine. The engine and pump controller sends an electrical signal to the proportional reducing valve for power shift pressure. The proportional reducing valve assists in controlling the output flow of the pumps by changing the hydraulic signal pressure (power shift pressure) that flows to the pump regulators.
Cross sensing control - The pump regulators are controlled by cross sensing control. In order to maintain the engine horsepower to the pumps at a constant rate, the pump regulators receive average delivery pressure of the right pump and the left pump through the cross sensing control. This is called constant horsepower control.
Negative Flow Control - When the joysticks and/or the travel levers/pedals are in the NEUTRAL position or when the joysticks and/or the travel levers/pedals are partially moved from the NEUTRAL position, the pump regulators receive negative flow control pressure from the main control valve. The main pumps are controlled by negative flow control pressure at this time.
Reference: For more information concerning the power shift system, refer to Systems Operation, "Pilot Hydraulic System".
Reference: For more information concerning the negative flow control operation at the main control valve, refer to Systems Operation, "Negative Flow Control".
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| Illustration 1 | g00687567 |
P-Q characteristic curve (A) Pressure/flow point (destroke point) (B) P-Q characteristic curve | |
The output characteristics of each pump depends on the following pressures.
- Pump output circuit pressure
- Power shift pressure
- Negative flow control pressure
The flow rate of each pump is represented on P-Q characteristic curve (B) from pressure/flow point (A). Each point on the P-Q characteristic curve represents the flow rate and pressure when pump output horsepower is maintained at a constant rate.
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| Illustration 2 | g01147545 |
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| Illustration 3 | g01147546 |
Pump compartment (1) Proportional reducing valve (power shift pressure) (44) Line (negative flow control pressure to right pump regulator) (67) Line (pilot oil flow to proportional reducing valve) (68) Line (negative flow control pressure to left pump regulator) (69) Line (power shift pressure from proportional reducing valve to left pump regulator) | |
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| Illustration 4 | g00819903 |
Main pumps (6) Port (negative flow control pressure to the right pump) (17) Port (negative flow control pressure to the left pump) | |
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| Illustration 5 | g00747104 |
Left pump regulator (20) Swashplate (26) Pin (31) Passage (32) Passage (33) Passage (average delivery pressure of the right pump and the left pump) (34) Guide (35) Slide plate (36) Control linkage (38) Passage (power shift pressure) (39) Spring (40) Spring (41) Spool (42) Pilot piston (43) Control piston (44) Passage (NFC) (46) Passage (47) Piston (48) Piston chamber (49) Passage (50) Passage (51) Sleeve (52) Shoulder (54) Pin (56) Left body (65) Piston chamber (66) Passage (P2) Left pump delivery pressure | |
Left pump delivery pressure (P2) flows through passage (66) and passage (32) into the left chamber around spool (41). Spool (41) meters the oil flow through passage (49) to passage (46), passage (31) and piston chamber (48) in order to control the movement of piston (47) .
The cross sensing control delivers the average delivery pressure of the right pump and the left pump (PM) through passage (33). Under total horsepower control, the average delivery pressure of the right pump and the left pump (PM) from passage (33) acts on shoulder (52) of pilot piston (42) .
Power shift pressure (PS) that flows through passage (38) acts on the right end of pilot piston (42). The average delivery pressure of the right pump and the left pump (PM) combines with the power shift pressure (PS) in order to control the movement of pilot piston (42) and spool (41) .
During negative flow control, negative flow control pressure (PN) from line (44) enters piston chamber (65). The right end of control piston (43) is pressurized. Control piston (43) acts on spool (41) in order to control the output flow of the pump.
The position and the movement of piston (47) determines the position and the movement of swashplate (20) and sleeve (51). Pin (26) connects one end of control linkage (36) to piston (47). The other end of control linkage (36) is connected to left body (56) by pin (54). When piston (47) shifts, control linkage (36) rotates on the axis of pin (54). The movement of the control linkage causes slide plate (35) to move sleeve (51). The movement of sleeve (51) and spool (41) cause passages (49) and (50) to open, and/or the movement of sleeve (51) and spool (41) cause passages (49) and (50) to close. As piston (47) shifts to the right, swashplate (20) moves toward the minimum angle position.
STANDBY Position
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| Illustration 6 | g00747107 |
Main pump regulator in the STANDBY position (20) Swashplate (31) Passage (32) Passage (33) Passage (average delivery pressure of the right pump and the left pump) (36) Control linkage (38) Passage (power shift pressure) (39) Spring (40) Spring (41) Spool (42) Pilot piston (43) Control piston (44) Passage (NFC) (46) Passage (47) Piston (48) Piston chamber (49) Passage (50) Passage (51) Sleeve (52) Shoulder (53) Piston chamber (55) Passage (57) Stopper (64) Spring (65) Piston chamber (P2) Left pump delivery pressure | |
Illustration 6 shows the left pump regulator in the STANDBY position. All of the joysticks and the travel levers/pedals are in the NEUTRAL position. The main pump regulators are controlled by the negative flow control pressure (PN) in piston chamber (65) .
The engine and pump controller controls the power shift pressure (PS) to a level that is dependent on engine speed. When the main pump regulator is in the STANDBY position, decreased power shift pressure flows through passage (38). The decreased power shift pressure acts on the end of pilot piston (42) .
The cross sensing control delivers the average delivery pressure of the right pump and the left pump (PM) through passage (33). The average delivery pressure of the right pump and the left pump (PM) acts on shoulder (52) in the center of pilot piston (42). Since the main pump regulators are in the STANDBY position, pressure (PM) in passage (33) is low pressure standby pressure.
When all of the joysticks and the travel levers/pedals are in the NEUTRAL position, all of the control valves for the implements, swing and travel are in the NEUTRAL position. The oil flow rate through the center bypass passage in the main control valve is maximum. The oil flow through the center bypass passage is restricted at the negative flow control orifice. High negative flow control pressure (PN) flows from the main control valve through line (44) and port (17) to piston chamber (65) of the left pump regulator. When the negative flow control pressure is maximum, the output flow of the pump is maintained at a minimum (STANDBY).
Negative flow control pressure (PN) enters the left pump regulator at port (17). The negative flow control pressure (PN) flows to piston chamber (65). When the negative flow control pressure (PN) increases, control piston (43) is pushed to the left against the force of spring (64). As the negative flow control pressure increases further, control piston (43) pushes pilot piston (42) and spool (41) to the left. The movement of the control piston, the pilot piston and the spool will stop when the force of the negative flow control pressure becomes equal to the force of springs (39), (40) and (64). Left pump delivery pressure (P2) is now blocked at passage (49) .
The negative flow control pressure in piston chamber (48) flows through passage (31), passage (50), past spool (41) and through passage (55) to the case drain of the pump.
The left pump delivery pressure (P2) in piston chamber (53) pushes piston (47) to the right. Piston (47) moves to the right until the piston contacts stopper (57). Control linkage (36) causes swashplate (20) to rotate toward the minimum angle position. As a result, the output flow of the pump decreases.
UPSTROKE Position
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| Illustration 7 | g00747108 |
Main pump regulator in the UPSTROKE position (20) Swashplate (31) Passage (32) Passage (33) Passage (average delivery pressure of the right pump and the left pump) (34) Guide (36) Control linkage (38) Passage (power shift pressure) (39) Spring (40) Spring (41) Spool (42) Pilot piston (43) Control piston (44) Passage (NFC) (46) Passage (47) Piston (48) Piston chamber (49) Passage (50) Passage (51) Sleeve (52) Shoulder (64) Spring (65) Piston chamber (P2) Left pump delivery pressure | |
Three conditions that can cause an increase in flow from the main pumps are listed below.
- A decrease in the system pressure or a decrease in cross sensing (PM)
- A decrease in power shift pressure
- A decrease in negative flow control pressure
Illustration 7 shows the main pump regulator in the UPSTROKE position due to an decrease in negative flow control pressure.
When the joysticks and/or travel levers/pedals are slowly moved from the NEUTRAL position, the oil flow rate through the center bypass passage in the main control valve decreases proportionally by the amount of movement of the individual spools in the main control valve. The negative flow control pressure decreases proportionally to the length of spool movement. Therefore, the negative flow control pressure (PN) that flows to piston chamber (65) decreases proportionally with the amount of movement of the joysticks and/or travel levers/pedals. Control piston (43) moves to the right against the force of springs (39), (40) and (64). The angle of swashplate (20) gradually increases and the output flow of the pump gradually increases. Since pump delivery flow is proportional to the amount of movement of the joysticks and/or travel levers/pedals, fine operation of the implements can be performed. During fine operation of the implements, the output flow rate of the pump is controlled by the negative flow control pressure.
The average delivery pressure of the right pump and the left pump (PM) from passage (33) acts on shoulder (52) of pilot piston (42). Power shift pressure (PS) from passage (38) acts on the right end of pilot piston (42). The combined force of pressure (PM) and pressure (PS) attempt to force pilot piston (42) and spool (41) to the left against the force of springs (39) and (40). The combined force of pressure (PM) and pressure (PS) is less than the force of springs (39) and (40). Springs (39) and (40) push guide (34) to the right. The position of spool (41) in sleeve (51) closes passage (50) so that the flow of left pump delivery pressure (P2) to case drain is blocked. Left pump delivery pressure (P2) now flows through passages (32), (49), (46) and (31) to piston chamber (48). Now left pump delivery pressure (P2) acts on both ends of piston (47). Since the surface area on the right end of the piston is greater than the surface area on the left end of the piston, piston (47) is positioned fully to the left. As a result, control linkage (36) positions swashplate (20) at the maximum angle position. At the UPSTROKE position, the pump delivers the maximum output flow.
DESTROKE Position
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| Illustration 8 | g00747110 |
Main pump regulator in the DESTROKE position (20) Swashplate (31) Passage (32) Passage (33) Passage (average delivery pressure of the right pump and the left pump) (34) Guide (35) Slide plate (36) Control linkage (38) Passage (power shift pressure) (39) Spring (40) Spring (41) Spool (42) Pilot piston (43) Control piston (44) Passage (NFC) (46) Passage (47) Piston (48) Piston chamber (49) Passage (50) Passage (51) Sleeve (52) Shoulder (53) Piston chamber (55) Passage (65) Piston chamber (P2) Left pump delivery pressure | |
Three conditions that can cause a decrease in flow from the main pumps are listed below.
- An increase in system pressure or the cross sensing (PM) .
- An increase in power shift pressure
- An increase in negative flow control pressure
Illustration 8 shows the main pump regulator in the DESTROKE position due to an increase in system pressure.
The negative flow control pressure in piston chamber (65) is low. Control piston (43) is shifted to the right.
The average delivery pressure of the right pump and the left pump (PM) in passage (33) increases. The increased pressure (PM) acts on shoulder (52) of pilot piston (42). Pilot piston (42) forces spool (41) to the left. Spool (41) compresses springs (39) and (40). Passages (50) and (49) close and the flow of left pump delivery pressure (P2) from passage (32) to piston chamber (48) is blocked.
As the average delivery pressure of the right pump and the left pump (PM) in passage (33) increases further, pilot piston (42) and spool (41) shift farther to the left. Passage (50) opens. The oil from piston chamber (48) now flows through passages (31), (46), (50) and (55) to the case drain of the pump. Since the pressure in piston chamber (48) is now lower than the pressure in piston chamber (53), piston (47) shifts to the right. As a result, control linkage (36) moves swashplate (20) toward the minimum angle position.
Piston (47) is connected to sleeve (51) by control linkage (36). As piston (47) shifts, the movement of the control linkage causes slide plate (35) to move sleeve (51) to the left. Sleeve (51) closes passages (49) and (50). The spool, the sleeve and the swashplate stop in a position that maintains the engine horsepower to the pumps at a constant rate.