2590 Track Feller Buncher Machine Systems Caterpillar


Piston Pump (Main Hydraulic)

Usage:

2590 P6B

Introduction




Illustration 1g01227087

Main Pumps

(1) Load signal port (implement and 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) Signal Port (variable power control)

(12) Load signal port (implement and travel control valve)

(13) Pump housing

Hydraulic Pump Group




Illustration 2g01762153

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




Illustration 3g01762139

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.

The horsepower adjustment screws should be adjusted so that the engine speed drops to 1725 ± 25 rpm due to pump load and the engine speed quickly recovers to 1850 ± 25 rpm.

Low Pressure Standby




Illustration 4g01762138

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 and the joystick is in the NEUTRAL, the oil from right pump (6) flows to the bottom of load sensing spool (28). The oil pressure increases to 2500 ± 100 kPa (360 ± 15 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.

Since the pump has spacers for minimum displacement, the standby pressure will be at the relief setting of the differential valve of 4000 ± 200 kPa (580 ± 30 psi).

The right pump pressure from load sensing spool (28) forces the actuator piston upward. The right pump moves to the minimum displacement.

Upstroking




Illustration 5g01762140

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




Illustration 6g01762137

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.

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