Introduction
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| Illustration 1 | g01164262 |
Main Pumps (1) Load signal port (travel control valve) (2) Outlet port (pilot pump) (3) Pilot pump (4) Pressure port (right pump) (5) Outlet port (right pump) (6) Right pump (7) Inlet port (8) Pressure port (left pump) (9) Outlet port (left pump) (10) Left pump (11) Drain port (12) Load signal port (travel control valve) (13) Pump housing | |
Hydraulic Pump Group
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| Illustration 2 | g01174904 |
Hydraulic Pump Group (3) Pilot pump (5) Outlet (right pump) (6) Right pump (7) Inlet port (9) Outlet (left pump) (10) Left pump (14) Pilot pump drive gear. (15) Margin pressure adjustment screw (16) Pump control group (17) Input shaft (18) Port plate (19) Actuator piston (20) Piston (21) Barrel (22) Adjustment screw (maximum angle) (23) Outlet passage (24) Housing | |
Illustration 2 shows the major components of the hydraulic pump group: pilot pump (3), right pump (6), left pump (10) and pump control group (16) .
The pump housing contains three pumps: pilot pump (3), right pump (6) and left pump (10). The right pump and the left pump are variable displacement piston pumps. The pilot pump is a gear type pump that is mounted in the pump housing.
Right pump (6) and left pump (10) are a bent axis piston type pump. The bent axis piston type pump describes the angular movement of the piston pump assembly. The output of the pumps changes depending on the angle of barrel (21) .
The flow from right pump (6) and left pump (10) is regulated by pump control group (16). The right pump and the left pump are mechanically connected. The pumps are identical in construction, identical in operation, and identical control systems. Flow from the two pumps is combined in order to operate any functions.
Input shaft (17) of left pump (10) is connected to a flexible coupling. The flexible coupling is bolted to the flywheel of the engine. The input shaft is driven off the flywheel of the engine. The right pump is driven by left pump (10) through a set of gears. The input shaft of pilot pump (3) is connected to the pilot pump drive gear (14). The pilot pump drive gear is meshed to the drive gear of left pump (10) .
Oil from the hydraulic tank flows into inlet port (7) of housing (24). Right pump (6) delivers oil through outlet port (5). Left pump (10) delivers oil through outlet port (9). Pilot pump (3) draws oil from the case of pump housing (13). Pilot pump (3) delivers oil through outlet port (2) .
Right pump (6) and left pump (10) are identical in operation. The left pump is described below. The left pump is similar to the right pump.
Input shaft (17) is driven by the engine. Input shaft (17) turns pistons (20). Therefore, barrel (21) rotates. Barrel (21) is in contact with port plate (18). Barrel (21) rotates on port plate (18). The drive gear of left pump (10) has a plate that retains heads of pistons (20). Therefore, pistons (20) swivel in the sockets.
Oil from the hydraulic tank goes into housing (24) through inlet port (7). The oil goes through the inlet passages in port plate (18). The oil then enters the cylinder passage of barrel (21). The cylinder passage is positioned over the inlet passage. Barrel (21) turns. The openings of the passage in barrel (21) rotate. The openings line up with the position of outlet passage (23) .
The displacement of pistons (20) change depending on the position of barrel (21). The piston draws oil by moving out of barrel (21). Oil is pushed ahead of piston (20) as piston (20) moves through barrel (21). The oil that is pushed ahead of piston (20) goes through passage (7) and then through outlet passage (23) in port plate (18). The oil goes through outlet port (9) to the travel control valve.
Pump Control Group
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| Illustration 3 | g01163738 |
Control Group (right pump) (25) Sleeve. (26) Margin pressure adjustment screw. (27) Torque control piston. (28) Load sensing spool. (29) Horsepower adjustment screw. (30) Horsepower control spool. (A) Signal pressure from left pump. (B) Signal pressure from right pump. (C) Load sensing pressure. (D) Passage to the actuator piston. | |
Illustration 3 shows the major components of the pump control group. The pump control group of the left pump contains the same components.
Note: Power shift pressure is not used on either pump control group.
Torque control piston (27) is a summing valve which combines the forces from signal pressure (A) and signal pressure (B) from the pumps.
Load sensing spool (28) controls the margin pressure. The margin pressure is the difference between the pump system pressure and the work port pressure of the implements. The margin pressure adjustment screw can increase the margin pressure. The margin pressure adjustment screw can decrease the margin pressure.
Horsepower control spool (30) directs signal pressure to the actuator piston or from the actuator piston. The signal pressure on the actuator piston controls the flow rate from the pumps.
Note: The horsepower adjustment screws regulate the hydraulic horsepower output from the pumps.
When the engine drops below 1850 rpm due to the pump load, turn both horsepower adjustment screws equally in the clockwise direction in order to decrease the minimum speed. This will reduce the pilot flow to the spool in the control valve. The horsepower adjustment screws are very sensitive. A 1/4 turn will change the speed by approximately 90 RPM. IQAN can be used in order to monitor the speed of the engine.
Note: If the screws are turned too far into the pump control valve, the mechanism may become jammed.
The spool will shift. The load sensing signal to the pump decreases. The pump will destroke allowing the engine rpm to increase.
Low Pressure Standby
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| Illustration 4 | g01163742 |
Right Pump Control (26) Margin pressure adjustment screw. (27) Torque control piston. (28) Load sensing spool. (29) Horsepower adjustment screw. (30) Horsepower control spool. (A) Signal pressure from left pump. (B) Signal pressure from right pump. (C) Load sensing pressure. (D) Passage to the actuator piston. | |
Low pressure standby occurs when there is no load sensing signal (C) from the implements to right pump (6) and left pump (10) .
When the engine is operating, the oil from right pump (6) flows to the bottom of load sensing spool (28). The oil pressure increases to 2200 kPa (320 psi). Load sensing spool (28) moves upward overcoming the force of the spring. Pump oil flows around load sensing spool (28) through passage (D) to the actuator piston.
The right pump pressure from load sensing spool (28) forces the actuator piston upward. The right pump moves to the minimum displacement. The right pump delivers enough flow in order to maintain the margin pressure.
Upstroking
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| Illustration 5 | g01163743 |
Right Pump Control (26) Margin pressure adjustment screw. (27) Torque control piston. (28) Load sensing spool. (29) Horsepower adjustment screw. (30) Horsepower control spool. (A) Signal pressure from left pump. (B) Signal pressure from right pump. (C) Load sensing pressure. (D) Passage to the actuator piston. | |
Upstroking occurs when right pump (6) increases output because of an increase in flow demand that is caused by a increase in load sensing pressure (C) .
When one of the circuits in the implement control valve is activated, a load sensing signal that is equal to the work port is directed to the top of load sensing spool (28). Load sensing spool (28) moves downward blocking the flow of pump oil to the actuator piston. The oil in the bottom of the actuator piston flows through passage (D) around load sensing spool (28) into the drain passage of the pump housing.
The force of the spring and the pump oil on top of the actuator piston shifts the actuator piston downward. The angle of barrel (21) increases allowing more oil to flow into right pump (6). This causes the pump system pressure to increase.
The pump pressure increases on the bottom of load sensing spool (28). When the pressure reaches margin pressure above load sensing pressure (C), load sensing spool (28) shifts upward. The flow to the actuator piston and from the actuator piston is metered around the center section of load sensing spool (28). The pump flow is constant until load sensing pressure (C) is increased or decreased.
Destroking
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| Illustration 6 | g01163744 |
Right Pump Control (26) Margin pressure adjustment screw. (27) Torque control piston. (28) Load sensing spool. (29) Horsepower adjustment screw. (30) Horsepower control spool. (A) Signal pressure from left pump. (B) Signal pressure from right pump. (C) Load sensing pressure. (D) Passage to the actuator piston. | |
Destroking occurs when right pump (6) is decreasing output because of a decrease in flow demand that is caused by a decrease in load sensing signal pressure (C) .
When the operator deactivates an implement, load sensing pressure (C) from the work port decreases at the top of load sensing spool (28). Load sensing spool (28) is shifted upward by the right pump pressure. The pump oil flows around load sensing spool (28) to the bottom of the actuator piston through passage (D) .
The pressure of the right pump overcomes the force of the spring. The actuator piston shifts upward. The angle of barrel (21) decreases allowing less oil to flow into right pump (6). The decrease in the flow of oil to right pump (6) causes the pump system pressure to decrease.
An orifice inside passage (D) to the actuator piston allows a small portion of the signal pressure to flow to the drain passage. This helps stabilize the movement of the actuator piston.