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| Illustration 1 | g03717370 |
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Main pump components (1) Soft stop for destroke (2) Barrel (3) Stop screw for maximum angle (4) Shaft (5) Plug (6) Swashplate (7) Drain plug (8) Stop screw for minimum angle (9) Electronic pump control solenoid (10) Electronic pump control adjustment screw (11) Spline of shaft and barrel (12) Rotary group piston (13) Adjustment screw for power-shift spool (14) Main pump control valve (15) Actuator piston (16) Maximum angle piston (17) Input from tank (18) Pressurized flow to main control valve (19) Minimum angle piston (20) Plug (control pressure) | |
Illustration 1 shows the internal components of the main pump. The main pump is a variable displacement piston pump with a swashplate that is directly mounted to the engine flywheel housing. The pump is driven by a flexible coupling. The pump is self-priming.
Mounted beneath the main pump is main pump control valve (14). The main pump control valve consists of two spools. One, the power-shift spool, which senses power shift pressure from the main pump PRV in order to regulate hydraulic horsepower output. The other is the electronic pump control solenoid spool.
Three control pressures are used by the machine ECM and used in order to regulate pump flow. These pressures are: load sensing signal pressure, pump supply pressure and pilot pressures.
The pump generates flow when shaft (4) splines with barrel (11). The spline causes pistons (12) in the rotary group to rotate while riding on the inclined surface of swashplate (6). Maximum angle stop screw (3) determines the maximum pump flow. Minimum angle stop screw (8) only keeps the pump flow from going over center during minimum operating angle actuation. The minimum pump flow is fixed by the length of the destroke rod and the position of the opening to the passage inside maximum angle piston (16).
When maximum angle piston (16) is moved to the left, swashplate (6) approaches the minimum displacement angle. As swashplate (6) approaches the minimum displacement angle the destroke pressure begins to purge through the passage into the pump case. Progressively bleeding off the destroke pressure softly stops swashplate (6) before the swashplate contacts minimum angle stop screw (8).
Minimum angle stop screw (8) is used to determine the minimum swash plate angle and flow
The output flow is proportional to the rpm and to the swashplate angle. The pump control determines the amount of pump flow by regulating the oil pressure that is supplied to maximum angle piston (16).
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| Illustration 2 | g03717700 |
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Right side view (21) Main pump control (14) Main pump | |
The nearest pump to the engine is main pump (15). Main pump (15) supplies flow to all of the implement and travel circuits.
Main pump regulation is electronically controlled. The pump regulator contains two spools:
- Displacement spool
- Power shift spool
Electronic pump regulation utilizes input from Adaptive Flow Control (AFC) and Electronic Load Sensing (ELS) to control pump output.
The AFC receives operator input from the joysticks via pressure sensors in the pilot lines on the boom, stick, bucket, and blade/stabilizer valve sections. The signals are an input to the AFC algorithm, which results in an estimated flow based on detected input signals.
The ELS system calculates actual margin pressure, which is determined from the pressure sensor readings of the main pump and pilot pressure sensor signal. Actual margin pressure is compared to nominal margin pressure, which results in flow to match nominal margin pressure.
For information on main pump regulation, refer to Systems Operation, "Pump Control (Main Hydraulic)".