Pilot Pressure Proportional Control (PPC) [PDF]

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Pilot pressure Proportional Control (PPC) Section 2.5

Section 2.5

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Pilot-pressure Proportional Control (PPC) Pressure Reducing Valve (PRV) The PRV is to reduce the discharge pressure supplied from the front pump down to pilot pressure to be used by solenoid valves and PPC valves. Pump pressure vary from:

40 - 380 kg/cm2.

PPC pressure is to be an even

33 kg/cm2

Merge-Divider Valve Drain

Pump Pressure 1

Back Pressure Valve Lower spools of Control Valve & 2stage Relief Valve

Solenoid valves block, LS. & PC Solenoid Valves

Section 2.5

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Pressure Reducing Valve

When PPC Pressure is Low The PRV receives the oil from PP1 discharge. Oil passes through the PRV spool through to the PR port. The spool has two cavities connected by an orifice. One cavity is on the oil supply side, the other relies on the oil through the orifice. Providing the oil pressure is not above the set spring tension on the relief valve. the oil pressure on both sides will be equal and the spool will remain open.

Section 2.5

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Pressure Reducing Valve When PPC Pressure is High If the oil pressure goes above the set spring tension on the relief valve the valve opens. The oil in the spool cavity will drain back to tank. As a result, a pressure difference is created between the to sides of the orifice. Spool moves to the right closing off the supply of oil to the PR port. Until the oil passes through the orifice to equalise on both sides of the spool the oil will be restricted, maintaining the PPC pressure. Section 2.5

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Pressure Reducing Valve

Abnormally High If the pressure in the PRV becomes abnormally high, a ball (16) is pushed against a spring to open. Draining the excess pressure back to tank. This valve is designed to protect the PPC valves and solenoids.

Section 2.5

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Pressure Reducing Valve (Summary)  Large size poppet: To keep hydraulic oil, giving priority to that of reduced pressure.  Constant pressure pick-up valve: To pick up constant pressure (33kg/cm2) under fluctuating condition of hydraulic pressure and pump delivery.  Relief valve: To prevent constant pressure circuit from rising over 55kg/cm2.

Section M2-B1-054 2.5

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Pilot-pressure Proportional Control (PPC) PPC Accumulator. An accumulator is installed before the PPC valves, it has been designed to take out any small fluctuations in pressure, this adds to a smooth operation of the work equipment. If the machine stops unexpectedly the stored pilot pressure will allow the work equipment to be lowered to the ground to bring the machine to a safe position.

Nitrogen Gas

PP

Section 2.5

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Pilot-pressure Proportional Control (PPC) Safety Lock Valve Safety lock lever is designed to isolate the pilot pressure to the PPC valves when moving out of the operators cabin. This stops any involuntary movement of work equipment when dismounting. Lever in the Up Position: In work mode, as pilot pressure is supplied to the PPC valves. However it is difficult for the operator to climb out of the cabin because the lever is obstructing the exit. Lever Down: The work equipment is not going to move as the pilot pressure is isolated from the PPC valves. Exit route out of the cabin is clear.

Section 2.5

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Pilot-pressure Proportional Control (PPC)

PPC Valve: Neutral The oil from the PRV enters port P and is blocked by the spools. Ports P1 & P2 are connected to drain port through Fine Control Hole X. Fine Control Hole X

Section 2.5

The control valve spool is held in the neutral position by the spool return springs.

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Pilot-pressure Proportional Control (PPC) PPC Valve: Operated

Metering Spring

When the operator moves the lever, the poppet puts pressure on the metering spring. The metering spring pushes spool down until the Fine Control Hole X is opened to the pressurized oil in port P. As a result, the pressurized oil flows into port P1 to the control valve spool. As the spool is pushed to the RIGHT, (opening the spool), the spool return spring on the RIGHT is becoming tighter. This will increasing the pressure in port P1. When the pressure in P1 equals the Metering Spring pressure the spool will push back up until the Fine Control Hole X is closed off by the housing between port P and port T. Therefore the pressure the operator puts on the control lever is proportional to the pressure in port P1.

Section 2.5

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Pilot-pressure Proportional Control (PPC)

Section 2.5

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Pilot-pressure Proportional Control (PPC) Travel Signal/Steering Function While Turning Right RH lever are is operated , therefore we have 2 signals going to the travel pressure switches

Steering signal valve

Section 2.5

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Pilot-pressure Proportional Control (PPC) Travel Signal/Steering Function While Traveling Straight Both levers are operated in the same direction, therefore we have a signal only going to the travel pressure switch with no steering function.

Section 2.5

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Pilot-pressure Proportional Control (PPC) Travel Signal/Steering Function When Steered or Pivot Turned During steering operation or pivot steer, the shuttle valves ensure a higher pressure signal goes to one side of the steering signal valve which in turn sends a signal to the steering pressure switch to the controller which then activates the travel junction valve

Section 2.5

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Pilot-pressure Proportional Control (PPC) Solenoid Valves Solenoid valves are an electric over hydraulic control valve used to activate small hydraulic actuators. The Solenoid Valves are either ON or OFF, unlike the EPC Solenoids that are proportional to the current flow. This solenoid bank activates: 1. PPC Lock. 2. Travel junction. 3. Merge/divide valve. 4. Travel speed. 5. Swing brake. 6. 2 stage relief.

Section 2.5

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Pilot-pressure Proportional Control (PPC)

When Solenoid is Turned OFF. There is no signal current to the solenoid. The spool spring is pushing the spool to the left. Closing the oil supply to the actuator port. Tank port is open to the actuator port allowing any pressure to return to tank.

Section 2.5

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Pilot-pressure Proportional Control (PPC)

When Solenoid is Turned ON. There is a signal current to the solenoid. The force of the solenoid pushes the spool to the RIGHT against the spool spring. Closing the Tank port. Opening the PP to the actuator port and energizing the actuator.

Section 2.5

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Pilot-pressure Proportional Control (PPC) PPC Oil Pressure Switch. There is a block of switches connected to each actuator PPC lines. Each time an actuator is activated, the pressure switch transmits a signal to the controller.

Section 2.5

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PPC Valve (Summary)  PPC valve changes hydraulic pressure in accordance with moving distance of PPC valve lever.  Control valve spool determines its opening area for oil flow (or oil volume) by its traveling distance in accordance with the pressure generated by PPC valve.

Section 2.5

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Pilot-pressure Proportional Control (PPC)

End of Pilot pressure Proportional Control (PPC)

Section 2.5

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