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| Illustration 1 | g01822593 |
Engine Compartment (1) Vibratory pump (2) Forward combination valve (3) Reverse solenoid (4) Propel pump (5) Forward solenoid (6) Pressure override relief (POR) valve | |
Propel pump (4) is the first in a series of two pumps which are driven by the engine flywheel. The propel pump is driven by the engine, and vibratory pump (1) is splined to the propel pump. The propel pump is electronically controlled, variable displacement, axial piston pump. The machine ECM controls the pump by directing output signals to forward solenoid (5) and reverse solenoid (3) on the pump.
Note: The forward solenoid and the reverse solenoid are located on the top face of the pump. The K726- BU wire is connected to the reverse solenoid on the propel pump, and the K725- GN wire is connected to the forward solenoid.
The strength and destination of the output signals are determined by the signals that the machine ECM receives from the input devices. For additional information, refer to Systems Operation. The machine ECM provides a variable signal to the propel pump solenoids. Signals from the ECM cause the solenoids to react. Solenoid reactions move the displacement control spool in the pump in order to control the flow of charge oil which acts against either side of the servo cylinder. The position of the servo cylinder controls the position of the swashplate in the pump.
The combination valves on the pump act as makeup and relief valves. The combination valves can be manually opened in order to allow the machine to be towed. In the propel system, the relief section of the valves limits pressure in the high pressure circuit to 45000 ± 2000 kPa (6526 ± 290 psi). The makeup section of the pressure override relief valves allows charge oil to flow into the low pressure circuit in order to replenish the oil lost to loop flushing and internal leakage.
Note: The high pressure relief function of the combination valve is fast acting. The purpose of the high pressure relief valve is to relieve peak pressure in the closed circuit. The high pressure relief valve bypasses all pump flow until the slower acting pressure override relief valve has time in order to respond.
The pump housing contains one pressure override relief (POR) valve (6) and two combination valves. The reverse combination valve (not shown) is located on the bottom side of the pump, and forward combination valve (2) is located on the top side of the pump.
The pressure override relief valve limits the maximum working pressure in the forward circuit and the reverse circuit of the propel system to 42500 ± 2000 kPa (6164 ± 290 psi).
Charge pressure in the vibratory and propel hydraulic systems is controlled by a single charge relief valve that is located on the vibratory pump. The charge relief valve limits the pressure in the charge circuit to 2500 kPa (363 psi). Pressure in the charge system can be measured at the charge pressure tap in the outlet line of the charge filter.
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| Illustration 2 | g01822594 |
Under Propel Pump (7) Swashplate angle sensor | |
Swashplate angle sensor ( 7) is located on the bottom of the propel pump.
Swashplate angle sensor (7) measures the angle of the pump swashplate with respect to the neutral position. This sensor measures swashplate angles between 40 degrees and 40 degrees. This information is monitored by the machine ECM at terminal "J1-36" in order to monitor for uncommanded movement detection (UCMD), a scenario in which the pump is not properly responding to operator control.
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| Illustration 3 | g01822595 |
Pump Cross Section (8) Control orifice (9) Direction control valve (10) Combination valve (11) Rotating group (12) Piston (13) Slipper feet (14) Swashplate (15) Input shaft (16) Servo piston (17) Feedback linkage | |
Engine rotation turns the pump input shaft. The input shaft is splined to the rotating group. The rotating group contains a piston and barrel assembly. The pistons in the group rotate with the barrel assembly. The piston slipper feet allow the pistons to follow the angle of the swashplate. The rotating group only generates flow when the swashplate is not at zero angle.
When the pump control is actuated, the ECM sends a signal to the appropriate pump control solenoid. The pump control solenoid causes the direction control spool to move, and charge oil is metered across the spool. This oil acts against one side of the servo piston, and the other side of the servo piston is open to the pump case drain.
The pressure differential between the two sides of the servo piston causes the piston to move, tilting the swashplate and resulting in piston displacement in the rotating group. As the swashplate moves, a feedback linkage tends to move the direction control spool back to neutral through an internal feedback spring. This action prevents the servo piston from tilting the swashplate too far by blocking the charge oil supply, once the tilt angle is proportional to the input signal for the pump control solenoid.
The slipper pads in the rotating group follow the angle of the swashplate which causes the pistons to move in and out of the barrel assembly as the input shaft rotates. As a piston moves out of the barrel assembly, oil in the low pressure circuit is drawn into the piston chamber. As a piston moves into the barrel assembly, oil is forced out of the piston chamber and into the high pressure circuit.
As the load on the propel 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.
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| Illustration 4 | g01822596 |
Pump Cross Section - Proportional Override and Relief Valve (18) POR valve (19) Forward combination valve (20) Brake solenoid (21) Orifice (22) Relief cartridge (23) Reverse combination valve (24) Large spring (25) Check valve spring (26) Towing valve stud (27) Spindle (28) Shuttle valve (29) Piston (30) Spool | |
The pump is equipped with two combination valves and one pressure override relief valve. The combination valves act as high pressure relief valves, makeup valves, and towing valves. The pressure override relief valve limits the maximum working pressure in the system.
In the high pressure circuit, oil acts against the seat of the high pressure relief section of the combination valve. If an external force causes the pressure in the high pressure circuit to increase above 45000 ± 2000 kPa (6526 ± 290 psi), the oil that is acting against the valve seat compresses the large spring, and oil from the high pressure circuit is directed into the charge circuit.
In the low pressure circuit, low pressure oil acts against one side of the makeup valve poppet in conjunction with the small spring, while charge oil acts on the opposite side of the makeup valve poppet. If the pressure in the low pressure circuit falls below charge pressure, the charge oil that is acting on the lower poppet moves the entire cartridge up allowing charge oil to flow into the low pressure circuit.
Each combination valve is equipped with a towing bypass stud. When the locknut is loosened and the stud is tightened two full turns beyond the first contact with the cartridge assembly, the cartridge assembly is moved against the spindle. The large spring is compressed, and the spindle moves off the poppet. When this action is performed on both combination valves, oil is allowed to freely exchange between the forward and reverse sides of the hydrostatic loop. Manipulation of this stud has no affect on the relief setting of the combination valves.
High pressure oil acts on one end of the shuttle valve in the pressure override relief valve, and low pressure oil acts on the other end. High pressure oil shifts the shuttle valve, which allows high pressure oil to act on the piston. When the pressure in the high pressure circuit is greater than 42500 ± 2000 kPa (6164 ± 290 psi), the pressure unseats the piston and moves the valve spool until the passage from the charge circuit is open to the case drain.
A 1.07 mm (0.042 in) orifice in the system causes the pressure in the high pressure servo piston cavity to decrease. The springs in the servo then move the swashplate to a lesser angle and the flow from the pump decreases causing a pressure drop in the high pressure circuit. Action of the pressure override relief valve maintains the swashplate at an angle which allows the pump to replace any oil that was lost through internal leakage.
The pressure override relief valve is set to a lower pressure than the high pressure relief valves in the combination valves. The lower setting allows the machine to work at high pressures with less heat generation. The pressure override relief valve also reduces the horsepower draw on the engine when the machine is being accelerated.