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| Illustration 1 | g01392548 |
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Right Side of Machine (1) Rear upper pump stack (2) Front upper pump stack (3) Rear lower pump stack (4) Front lower pump stack | |
The hydraulic pumps are located on the right side of the machine. The pumps are behind the access door. The machine is equipped with following pump stacks: rear upper (1), front upper (2), rear lower (3) and front lower (4). The following configurations of the pumps are part of the propulsion system:
- Rear lower stack (3) (right propulsion pump and generator pump) (if equipped with a hydraulically driven generator)
- Front lower stack (4) (left propulsion pump and auxiliary pump)
Note: The auxiliary pump supplies oil in order to release the parking brake. The auxiliary pump also supplies oil in order to shift the two speed propulsion motors. For additional information about the auxiliary pump, refer to Specifications, Systems Operation/Testing and Adjusting, KENR5729.
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| Illustration 2 | g01392552 |
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Propulsion Pumps (5) Forward EDC (6) Reverse EDC (7) Charge relief valve (8) Forward multifunction valve (9) Reverse multifunction valve | |
The two propulsion pumps are variable displacement piston type pumps. These pumps provide flow to the closed circuit hydrostatic drive system. Functionally, the right and left pumps are identical.
Each propulsion pump contains an integral gerotor type charge pump. The charge pumps provide makeup oil for the propulsion circuit and for the material feed circuits. The charge pumps also provide the oil which moves the swashplates in the propulsion pumps.
The propulsion pump and the charge pump rotate when the engine is running. The angle of the swashplate in each propulsion pump determines the amount of flow that is generated by the pump. Since the charge pumps are positive displacement pumps, the speed of the engine determines the amount of flow that is generated by the pumps. The charge relief valves limit the pressure in the charge circuits.
Each propulsion pump contains two multifunction valves. One valve is for the forward propulsion circuit, and one valve is for the reverse propulsion circuit. The multifunction valves act as charge system check valves, high pressure relief valves, and system pressure limiters.
The multifunction valves also act as system bypass valves. When the middle locknut on each multifunction valve is loosened by three turns, the propulsion circuit cannot build pressure. The machine can be towed when the bypass function is used and when the parking brakes are manually released.
The machine ECM generates output signals to the forward EDCs and reverse EDCs based on the information received from the input devices. The EDCs control the flow of charge oil which acts against the servo cylinders in the propulsion pumps. The position of the servo cylinder controls the position of the swashplate in the pump. If the propulsion lever is out of the NEUTRAL position when the machine is started, the machine ECM does not allow the propulsion pumps to upstroke. Under these conditions, the machine ECM prevents the machine from moving until the propulsion lever has been returned to the NEUTRAL position, and then moved out of the NEUTRAL position.
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| Illustration 3 | g01392574 |
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Colored Schematic (10) Spool barrel feedback (11) Pump case (12) EDC metering spool (13) Swashplate feedback linkage (14) Pump case (15) Pump case (16) From hydraulic tank (17) Rotating group (18) Case drain (19) Double acting cylinder (20) Propulsion loop return pressure (21) Input shaft (22) Servo motor (23) To material feed system and the track tension manifold (24) Swashplate (25) Servo cylinder (26) Case drain from propulsion motor (27) Servo pressure relief valves (28) Multifunction valves (29) Case drain (30) Charge relief valve (31) Propulsion loop (high pressure) (32) Charge pump (33) Pump electronic displacement control (EDC) (34) Propulsion pump | |
The pump input shaft turns the rotating group and the charge pump when the engine is running. Charge oil flows through internal passages to the charge relief valve, to the multifunction valves, and to the EDC. External lines carry charge oil to the material feed pumps and the track tension manifold.
The forward EDC and reverse EDC are proportional solenoids. The machine ECM uses a pulse width modulated signal to energize the EDC solenoids. Energizing the EDC solenoid causes the plunger to move. The distance that the EDC plunger moves is proportional to the signal coming from the machine ECM.
Note: The coils in the forward EDC and reverse EDC are not designed for 24 volt operation. The signal from the machine ECM provides an average of approximately 12 volts.
When the EDC plunger shifts, charge oil is metered into the end of the displacement control spool. This action creates a pressure differential between the ends of the displacement control spool. The pressure differential causes the spool to move. This sends charge oil to the appropriate servo cylinder. The swashplate in the pump then moves an amount which is proportional to the output signal from the machine ECM.
Metered charge oil from the displacement control spool acts against one side of the servo piston. The opposite side of the servo piston is vented to the case drain. The pressure of the metered charge oil against the servo piston causes the piston to move. This movement tilts the swashplate and this movement causes piston displacement in the rotating group. As the swashplate tilts, the rotation of the pump generates oil flow. Pump supply oil flows through the propulsion motor. The oil which flows through the motor causes the output shaft to rotate.
As the load on the propulsion system increases, increased pressure in the system tends to move the swashplate toward the neutral position. This movement causes the feedback linkage to reposition the direction control spool in order to send additional charge oil into the servo piston. The increased pressure in the servo piston prevents the swashplate from moving back toward the neutral position. The feedback linkage prevents the servo from tilting the swashplate too far.
Pump supply oil acts against the bottom multifunction valve. In the high pressure side of the loop, the multifunction valve acts as a pressure limiter and a pressure relief valve. When the pump supply oil pressure reaches the pressure limiter setting, the pressure limiter opens. At this time, pump supply oil is metered to the end of the servo piston which is open to the case drain. This causes the pump to destroke in order to relieve the excessive load on the propulsion system.
Note: The pressure limiter function is used because no heat is generated as is generated with relief valves.
However, a sequenced pressure relief function limits the momentary pressure surges which normally occur with machine acceleration and steering changes. These pressure surges are purged to the charge circuit. The relief pressure setting is greater than the pressure limiter setting.
When leakage and flushing occur in the propulsion circuit, the pressure in the return circuit becomes lower than charge pressure. In this case, the multifunction valve in the return side of the loop allows charge oil to flow into the low pressure side of the propulsion circuit in order to replenish the oil which was lost.
Note: The nonadjustable servo pressure relief valves prevent excessive servo cylinder pressures. This is done by purging momentary pressure surges to the charge circuit.
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| Illustration 4 | g01361651 |
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Multifunction Valve Cross Section (35) Pressure limiter adjustment (36) Pressure limiter spring (37) Makeup and check valve spring (38) Pressure limiter spool (39) Charge pressure (40) Low pressure loop (41) Bypass locking nut (42) To pump servo (43) Makeup valve (44) Check valve | |
In the low pressure side of the propulsion hydraulic circuit, the multifunction valve acts as a makeup valve.
The spring chamber of the multifunction valve (right side of the valve cartridge) is filled with return oil which comes from the low pressure side of the circuit. Charge oil acts against the effective area of the makeup valve. The cartridge's left spring chamber is filled with charge oil.
Flushing and internal leakage cause pressure in the return side of the closed circuit to decrease. This decrease causes charge pressure to move the makeup valve to the left. The makeup valve contacts the snap ring at the left end of the check valve. When circuit return pressure is low enough, the makeup valve will continue to move left. The makeup valve will eventually unseat the check valve. Charge oil then flows into the circuit return side and the charge oil replenishes the circuit.
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| Illustration 5 | g01361660 |
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Multifunction Valve Cross Section (35) Pressure limiter adjustment (36) Pressure limiter spring (37) Makeup and check valve spring (38) Pressure limiter spool (39) Charge pressure (40) Low pressure loop (41) Bypass locking nut (42) To pump servo (43) Makeup valve (44) Check valve | |
In the high pressure side of the propulsion circuit, the multifunction valve acts as a relief valve. High pressure oil from this circuit does the following:
- Fills the spring chamber (on the right side of the valve cartridge)
- Flows through the cross-drilled holes which are adjacent to the pressure limiter spool
- Flows to the right end of the spool chamber through the clearance between the spool and the housing.
When the pressure in the high side of the circuit becomes great enough, the force that is acting against the right side of the spool will shift the spool to the left. In this situation, oil is directed to the tank side of the pump servo piston. The pump will then destroke.
Note: The pressure limiter can be adjusted when the small locknut is loosened and the limiter adjusting screw is turned.
If a pressure surge occurs, some oil is quickly transferred from the pressure side of the circuit into the charge circuit. At relief pressure, the pressure limiter spool has moved left, which causes a pressure drop in the right spring chamber of the cartridge. This higher pressure acts against the effective area on the right side of the check valve. This higher pressure is sufficient to overcome the combined force from the spring and the decreased pressure on the left. The check valve moves left. This allows some closed circuit oil to enter the charge circuit. As a result, the limiter and relief functions operate in sequence. Main relief pressure is controlled by the pressure limiter setting. Therefore, main relief pressure is not directly adjustable. Main relief pressure will always be approximately