Introduction
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| Illustration 1 | g01514452 |
Main Pumps (1) Load signal port (implement control valve) (2) Outlet port (pilot pump) (3) Pilot pump (4) Pressure port (implement pump) (5) Outlet port (implement pump) (6) Implement pump (7) Inlet port (8) Pressure port (travel pump) (9) Outlet port (travel pump) (10) Travel pump (11) Signal port (variable power control) (12) Load signal port (travel control valve) (13) Pump housing | |
Hydraulic Pump Group
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| Illustration 2 | g01515117 |
Hydraulic Pump Group (3) Pilot pump (5) Outlet (implement pump) (6) Implement pump (7) Inlet port (9) Outlet (travel pump) (10) Travel pump (15) Pilot pump drive gear (16) Margin pressure adjustment screw (17) Pump control group (18) Input shaft (19) Port plate (20) Actuator piston (21) Piston (22) Barrel (23) Adjustment screw (maximum angle) (24) Outlet passage (25) Housing | |
Illustration 2 shows the major components of the hydraulic pump group: pilot pump (3), implement pump (6), travel pump (10) and pump control group (16) .
The pump housing contains three pumps: pilot pump (3), implement pump (6) and travel pump (10). The implement pump and the travel pump are variable displacement piston pumps. The pilot pump is a gear pump that is mounted in the pump housing.
Implement pump (6) and travel 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 (22) .
The flow from implement pump (6) and travel pump (10) is regulated by pump control group (17). The implement pump and the travel pump are mechanically connected. The pumps are identical in construction, identical in operation, and identical control systems. Implement pump (6) operates independently from travel pump (10). Flow from the two pumps is not combined in order to operate any functions. The implement pump supplies oil to the implement control valve. The travel pump supplies oil to the travel control valve.
Input shaft (18) of travel 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 implement pump is driven by travel pump (10) through a set of gears. The input shaft of pilot pump (3) is connected to the pilot pump drive gear (15). The pilot pump drive gear is meshed to the drive gear of travel pump (10) .
Oil from the hydraulic tank flows into inlet port (7) of housing (25). Implement pump (6) delivers oil through outlet port (5). Travel 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) .
Implement pump (6) and travel pump (10) are identical in operation. The travel pump is described below. The travel pump is similar to the implement pump.
Input shaft (18) is driven by the engine. Input shaft (18) turns pistons (21). Therefore, barrel (22) rotates. Barrel (22) is in contact with port plate (19). Barrel (22) rotates on port plate (19). The drive gear of travel pump (10) has a plate that retains heads of pistons (21). Therefore, pistons (21) swivel in the sockets.
Oil from the hydraulic tank goes into housing (25) through inlet port (7). The oil goes through the inlet passages in port plate (19). The oil then enters the cylinder passage of barrel (22). The cylinder passage is positioned over the inlet passage. Barrel (22) turns. The openings of the passage in barrel (22) rotate. The openings line up with the position of outlet passage (24) .
The displacement of pistons (21) change depending on the position of barrel (22). The piston draws oil by moving out of barrel (22). Oil is pushed ahead of piston (21) as piston (21) moves through barrel (22). The oil that is pushed ahead of piston (21) goes through passage (7) and then through outlet passage (24) in port plate (19). The oil goes through outlet port (9) to the travel control valve.
Pump Control Group
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| Illustration 3 | g01743038 |
Implement Pump Control (26) Sleeve (27) Margin pressure adjustment screw (28) Torque control piston (29) Load sensing spool (30) Horsepower adjustment screw (31) Horsepower control spool (A) Signal pressure from travel pump (B) Signal pressure from implement pump (C) Load sensing pressure from implement control valve (D) Passage to the actuator piston | |
Illustration 3 shows the major components of the implement pump control. The pump control group of the travel pump contains the same components.
When the pumps are suddenly loaded and the power shift is active, the engine speed should drop below the target of 1725 ± 25 rpm. The engine speed will quickly recover toward the target speed of 1850 ± 25 by destroking the pumps. When the pumps are loaded and the engine does not recover to the target rpm turn screw (30) in a counterclockwise direction. When the pumps are loaded and the engine rpm does not drop to 1725 ± 25 rpm, turn screw (30) in a clockwise direction.
ReferenceFor more information on horsepower, refer to Testing and Adjusting, "Piston Pump (Constant Horsepower Flow Control)".
On machines with the power shift, engine speed should drop to 1725 ± 25 rpm. Engine speed will quickly recover to 1850 ± 25 rpm. IQAN can be used in order to monitor the speed of the engine.
The spool will shift. The load sensing signal to the pump decreases. The pump will destroke allowing the engine rpm to increase.
ReferenceFor more information about the IQAN controller, refer to Systems Operation, RENR8950, "IQAN MDL Control and Monitoring System".
Low Pressure Standby
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| Illustration 4 | g01743079 |
Implement Pump Control (27) Margin pressure adjustment screw (28) Torque control piston (29) Load sensing spool (30) Horsepower adjustment screw (31) Horsepower control spool (A) Signal pressure from travel pump (B) Signal pressure from implement pump (C) Load sensing pressure from implement control valve (D) Passage to the actuator piston | |
Low pressure standby occurs when there is no load sensing signal (C) from the implements to implement pump (6) .
When the engine is running with the functions in the hold position, the oil from implement pump (6) flows to the bottom of load sensing spool (29). The oil pressure increases to 2500 kPa (360 psi). Load sensing spool (29) moves upward overcoming the force of the spring. Pump oil flows around load sensing spool (29) through passage (D) to the actuator piston. Since the pump has spacers for minimum displacement, the standby pressure will be at the differential setting of relief of 4000 ± 200 kPa (580 ± 30 psi).
The implement pump pressure from load sensing spool (29) forces the actuator piston upward. The implement pump moves to the minimum displacement. The implement pump delivers enough flow in order to maintain the margin pressure.
Upstroking
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| Illustration 5 | g01515020 |
Implement Pump Control (27) Margin pressure adjustment screw (28) Torque control piston (29) Load sensing spool (30) Horsepower adjustment screw (31) Horsepower control spool (A) Signal pressure from travel pump (B) Signal pressure from implement pump (C) Load sensing pressure from implement control valve (D) Passage to the actuator piston | |
Upstroking occurs when implement 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 (29). Load sensing spool (29) 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 (29) 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 (22) increases allowing more oil to flow into implement pump (6). This causes the pump system pressure to increase.
The pump pressure increases on the bottom of load sensing spool (29). When the pressure reaches margin pressure above load sensing pressure (C), load sensing spool (29) shifts upward. The flow to the actuator piston and from the actuator piston is metered around the center section of load sensing spool (29). The pump flow is constant until load sensing pressure (C) is increased or decreased.
Destroking
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| Illustration 6 | g01515039 |
Implement Pump Control (27) Margin pressure adjustment screw (28) Torque control piston (29) Load sensing spool (30) Horsepower adjustment screw (31) Horsepower control spool (A) Signal pressure from travel pump (B) Signal pressure from implement pump (C) Load sensing pressure from implement control valve (D) Passage to the actuator piston | |
Destroking occurs when implement 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 (29). Load sensing spool (29) is shifted upward by the implement pump pressure. The pump oil flows around load sensing spool (29) to the bottom of the actuator piston through passage (D) .
The pressure of the implement pump overcomes the force of the spring. The actuator piston shifts upward. The angle of barrel (22) decreases allowing less oil to flow into implement pump (6). The decrease in the flow of oil to implement 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.