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| Illustration 1 | g00635070 |
Components of the Propel Pump (1) Inlet port and outlet port (2) Valve plate (3) Barrel assembly (4) Servo piston (5) Piston (6) Electrical displacement control (EDC) (7) Shaft (8) Housing (9) Swashplate (10) Spring (11) Inlet port and outlet port (12) Charge pump | |
When the engine is running, shaft (7), barrel assembly (3) and charge pump (12) are rotating. There are nine pistons (5) in the barrel assembly. Valve plate (2) and swashplate (9) are fastened to housing (8). The valve plate and the swashplate do not rotate. Spring (10) keeps a force on barrel assembly (3) in order to make a high pressure seal between the barrel assembly and valve plate (2). When barrel assembly (3) is rotating, each piston (5) follows the angle of the swashplate.
If the swashplate angle is at zero, the pistons do not move in and out of the barrel assembly and there is no oil flow. Charge oil from charge pump (12) maintains oil pressure in the propel pump. The charge oil performs the following functions for the propel pump: keeping the barrel assembly full of oil, lubricating the pump components and making up for the normal loss of oil due to internal leakage.
The position of swashplate (9) is controlled by electrical displacement control (EDC) (6) and servo piston (4). The pressure control pilot valve receives an electrical signal from the propel electronic control module. The propel electronic control module receives information from the following controls: propel control, travel/pave/maneuver speed control, speed sensor and brake pedal sensors. The propel electronic control module sends a signal to the pressure control pilot valve of the EDC in order to cause a servo valve that is inside the EDC to move. The servo valve routes charge oil in order to activate servo piston (4). The servo piston controls the amount of the swashplate angle.
Oil flows from the pump to the propel motor and back to the pump through inlet ports and outlet ports (1) and (11). The position of swashplate (11) determines the direction of the flow. The high pressure line is also determined by the swashplate between the two loop lines.
Electrical Displacement Control (EDC)
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| Illustration 2 | g00635638 |
Electrical Displacement Control (EDC) (1) Pressure control pilot valve (2) Port to servo piston (3) Port to servo piston (4) Metering spool (5) Control linkage (6) Swashplate feedback (7) Port from the charge pump (8) Drain | |
The electrical displacement control (EDC) is a two-stage electrohydraulic control. The EDC uses mechanical swashplate feedback (6) and the oil from port (7) in order to set up a closed loop swashplate control circuit. The propel electronic control module (ECM) receives information from the following controls: propel control, travel/pave/maneuver speed control, speed sensor and brake pedal sensors. The ECM sends a signal to pressure control pilot valve (1) of the EDC.
The current from the ECM meters the charge oil pressure in the pressure control pilot valve to metering spool (4) in order to shift the pressure control pilot valve. When the metering spool shifts, the spool opens ports (2) and (3) to the servo piston. One port allows charge oil to pass from the EDC to one side of the servo piston. The other port allows charge oil to pass from the other side of the servo piston back to the EDC. The oil then returns to the hydraulic tank. Oil that is acting upon the servo piston causes the piston to shift. This rotates the swashplate.
One end of control linkage (5) is attached to metering spool (4) and the other end is attached to the swashplate. The control linkage provides mechanical feedback between the swashplate and metering spool (4). As the swashplate rotates, control linkage (5) moves with the swashplate. As control linkage (5) moves with the swashplate, the control linkage provides an opposing force. The pressure from the pressure control pilot valve balances the swashplate at an angle that is proportional to the input current from the ECM input to the EDC.
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| Illustration 3 | g00635639 |
Pressure Control Pilot Valve (9) Pole piece (10) Centering springs (11) Armature (12) Pole piece (13) Magnet (14) Magnet (15) Pivot point (16) Flapper (17) Nozzle (18) Nozzle (19) Oil supply port (20) Orifice (21) Orifice (22) Control port (23) Oil return port (24) Control port | |
PCP valve (1) is the first stage of the electrical displacement control (EDC). Each side of the armature contains two coils. The machine uses the PCP coils inside the EDC to control the forward track speed and the reverse track speed. One PCP coil controls the forward drive speed. The second PCP coil controls the reverse speed.
The hydraulic portion of the PCP valve is an open loop circuit. The PCP electrical section receives a direct current input when the section is in the torque motor stage. The torque motor stage of the PCP valve consists of armature (11) that is mounted on pivot point (15) and suspended in a magnetic field air gap. Magnets (13) and (14) are permanent magnets of parallel polarity that are constructed in order to form a magnetic bridge.
When the EDC is at null, the armature is centered in the air gap. The equal magnetic forces of the opposing magnets and centering springs (10) keep the armature in the centered position. While the armature is centered, flapper (16) is centered between nozzles (17) and (18). Orifices (20) and (21) are upstream from the nozzles. A control port is located between the orifice and the nozzle.
In the null position, charge oil enters oil supply port (19) and passes through the two orifices. When the flapper is centered between the two nozzles, there is no pressure difference. Therefore, an equal amount of the oil flows through the nozzles and past the flapper. The oil then flows out of oil return port (23) .
As current is increased in one direction, the end of the armature becomes polarized north or south. The armature then moves toward the opposing magnetic field. The amount of movement is dependent upon the amount of amperage of control current that is introduced to pole pieces (9) and (12) .
As current is applied in order to cause the armature to move toward magnet (14), a torque shift occurs at pivot point (15). The torque shift causes the flapper to move closer to nozzle (17). As the flapper moves closer to the nozzle, the pressure rises between nozzle (17) and orifice (21). This pressure increases in order to cause the oil to flow through control port (22) to one side of the swashplate servo piston.
Due to initial input from the control current, the flapper closes off the nozzle that is sending all the oil through the control port. This causes the pump to go to full stroke. As the oil pressure rises in the passageway that is between the nozzle and the orifice, the oil pressure moves the flapper back to the null position. When the torque outputs of the torque motor stage and the pressure feedback are equal, the pilot control system is equalized. When the pilot control system is equalized, the flapper is in the position in order to maintain the desired speed setting. The control oil pressure in passage (22) is now proportional to the control current plus the control oil pressure in passage (24) .
The ECM regulates the output flow of the propel pumps by controlling the current that is in the EDC coils. The ECM monitors the speed of each propel motor. The ECM then compares the speed to the desired track speed. The position of the following operator controls determine the desired track speed: propel control, travel/pave/maneuver speed control, brake pedal sensors, speed sensor and position of the steering wheel. The pulse width modulated sensor that is mounted on the bottom of the steering column shaft determines the steering column position.
When the machine is making a right turn, the amperage of the EDC drive coil of the right side pump is less than the EDC drive coil of the left side pump. This temporary change in the amperage of the EDC drive coil causes the swashplate angle of the right side drive pump to decrease and the swashplate angle of the left side drive pump to increase. The speed of the right track will be slower and the speed of left track will be faster. This causes the machine to turn to the right.
When the machine is making a left turn, the amperage of the EDC drive coil of the left side pump is less than the EDC drive coil of the right side pump. This temporary change in the amperage of the EDC drive coil causes the swashplate angle of the left side drive pump to decrease and the swashplate angle of the right side drive pump to increase. The speed of the left track will be slower and the speed of right track will be faster. This causes the machine to turn to the left.
Multifunction Valve
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| Illustration 4 | g00635087 |
Multifunction Valve (1) Adjustment screw with locknut (2) Pressure limiter section (3) Main relief valve section (4) Charge check valve section (5) Pressure limiter valve poppet (6) Bypass actuator nut | |
Each propel pump has two multifunction valves. One multifunction valve is for the forward drive loop circuit and the other multifunction valve is for the reverse drive loop circuit. Each multifunction valve performs the following functions in the circuit: high pressure relief valve, system loop bypass, charge system check valve and system pressure limiter.
High Pressure Relief
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| Illustration 5 | g00635088 |
(2) Pressure limiter section (7) Makeup valve | |
The function for the high pressure relief of the multifunction valve operates in the high pressure side of the main drive loop circuit. This function protects the circuit from high pressure spikes. When the system pressure reaches the high pressure setting, makeup valve (7) is forced off the seat. This action directs high pressure oil instantly to the low pressure side of the drive loop circuit as the arrows in the graphic above indicate. This condition may occur if the machine encounters a large external force.
System Loop Bypass
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| Illustration 6 | g00635089 |
(1) Adjustment screw with locknut (6) Bypass actuator nut (7) Makeup valve (8) Spring for the pressure limiter | |
Bypass actuator nut (6) is used when conditions such as towing the machine require flow but no pressure in the propel system. Loosen bypass actuator nut (6) by three turns. When you loosen the bypass actuator nut, the force of spring (8) for the pressure limiter is removed. When the bypass valve is open, very low oil pressure lifts the plunger of the makeup valve (7) off the seat. Oil flows from the high pressure loop circuit to the low pressure loop circuit as the arrows in the graphic above indicate. This procedure must be performed on both the propel pumps in order for the machine to be towed.
Adjustment screw (1) is part of the bypass actuator nut (6). When the bypass actuator nut is moved, the adjustment screw moves the same number of turns. Therefore, the main relief valve setting does not change. After the machine has been towed, tighten the bypass actuator nut (6) by three turns and torque the nut to the proper specification. No adjustment is needed to the main relief valve setting if the system loop bypass has been used.
Charge System Check Valve
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| Illustration 7 | g00635093 |
(7) Makeup valve (9) Charge system check valve (10) Spring for the makeup check valve | |
The function for the charge system check valve of the multifunction valve operates in the low pressure side of the main drive loop circuit.
The right side of the makeup valve (7) and the seat for the charge system check valve is open to the charge oil circuit. As leakage occurs in the closed loop circuit, charge oil pressure and the low pressure side of the closed loop circuit vary. Charge pressure overcomes the force of spring (10) for the makeup check valve and the oil pressure of the low side of the closed loop. The pressure moves makeup valve (7) to the left. The makeup valve comes into contact with a snap ring on charge system check valve (9). As the makeup valve continues to move to the left, the makeup valve lifts charge system check valve (11) off the seat. When charge system check valve (11) is off the seat, charge oil flows across the seat in order to replenish the closed loop circuit as the arrows in the graphic above indicate.
High pressure oil that is from the propel pump enters the multifunction valve through the openings. The oil acts on the inlet side of the high pressure spool and the oil acts on the opposite end of the charge system check valve. As loop pressure increases, charge oil pressure is overcome. This causes the check valve to reseat. When the check valve reseats, the flow between the loop circuit and the charge circuit is stopped.
System Pressure Limiter
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| Illustration 8 | g00650837 |
System pressure is limited to approximately 2345 kPa (340 psi) below the main relief valve setting by pressure limiter section (2) of the multifunction valve. When the system pressure reaches the pressure limiter setting, the pressure limiter routes oil to the servo valve. This causes the propel pump to destroke. The destroking of the pump reduces the pump output pressure. Adjustments to the system pressure are made with adjustment screw (1) .
Charge Relief Valve
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| Illustration 9 | g00635055 |
Each propel pump has a charge relief valve (7). The charge oil enters the propel pump through the charge oil supply lines. The charge relief valves are located in the pump housings. When the charge relief valve opens, excess oil is directed back to the hydraulic tank through the case drain line. The charge relief valve is adjustable in order to maintain a constant system pressure.