Hydraulic Schematic for Forward Travel
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| Illustration 1 | g01622081 |
(1) Left travel motor (2) Parking brake assembly (3) Rotary group (4) Piston (5) Displacement change valve (6) Passage (7) Check valve (8) Counterbalance valve (9) Line (10) Line (11) Passage (12) Swivel (13) Brake pilot valve (14) Passage (15) Passage (16) Line (17) Right travel motor (18) Parking brake assembly (19) Rotary group (20) Cam plate (21) Piston (22) Passage (23) Displacement change valve (24) Passage (25) Pilot control valve (left travel and right travel) (26) Line (27) Line (28) Line (29) Line (30) Line (31) Passage (32) Passage (33) Passage (34) Center bypass passage (35) Right travel control valve (36) Left travel control valve (37) Return passage (38) Return line (39) Travel speed solenoid valve (40) Drive pump (41) Idler pump (42) Pilot pump (43) Line (44) Line (45) Pressure sensor | |
Travel Control
Introduction
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| Illustration 2 | g01124798 |
Travel motor (1) Left travel motor (46) Brake valve | |
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| Illustration 3 | g01124809 |
Travel drive (47) Left track (48) Sprocket (49) Left travel drive | |
Left travel motor (1) and right travel motor (17) are supplied oil through swivel (12) from idler pump (41) and drive pump (40). When left travel motor (1) is operated by idler pump oil, the motor torque is transferred to left travel drive (49). Left travel drive (49) reduces the speed of left travel motor (1). Left travel drive (49) increases the torque of left travel motor (1). The increased torque turns left track (47). Left track (47) is connected to left travel drive (49) through sprocket (48).
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| Illustration 4 | g01124816 |
Keypad (right console) (50) Travel speed control switch | |
Travel speed control switch (50) provides a selection of HIGH or LOW travel speed. During partial movements of the travel control lever, the travel speed varies with the travel distance of the lever. When the switch is placed in the TORTOISE position, the machine travels at the LOW speed mode. When the switch is placed in the RABBIT position, the machine travels at the Automatic Travel Speed mode. Select the automatic travel speed mode for increased mobility when the machine is on a flat surface or a sloped surface.
When travel speed control switch (50) is in the HIGH position, pressure sensor (45) automatically changes the travel speed. The travel speed depends on the load on the machine. The machine travels at LOW speed when a larger load is present. The machine travels at HIGH speed under a smaller load.
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| Illustration 5 | g01622166 |
Operation of travel (1) Left travel motor (17) Right travel motor (51) Forward direction (52) Left travel pedal (53) Idler (54) Right travel pedal (55) Cab (56) Reverse direction | |
The direction of travel is relative to the position of the lower structure. For normal travel, idler (53) is positioned in front of cab (55) and travel motors (1) and (17) to the rear of the cab. With the machine in the normal position of travel, move the travel pedals (52) and (54) forward. The machine will travel in forward direction (51). This movement is called forward travel. When travel pedals (52) and (54) are moved toward the operator, the machine travels in reverse direction (56). This direction is called reverse travel.
When cab (55) is turned to the opposite direction, travel motors (1) and (17) will be positioned in front of the cab. The direction of travel and the operation of travel pedals (52) and (54) are reverse when the machine is in the normal travel direction.
A pivot turn is made when the travelling direction of the machine is changed. When one of the travel pedals (52) or (54) is moved forward, the respective track travels forward. The machine turns because the stationary track acts as the pivot point. This is called a pivot turn.
This machine will spot turn when the travelling direction of the machine is changed in a narrow place. To complete a spot turn operation, move one travel pedal to the rear and the other travel pedal forward at the same time. One track will travel to the rear and the other track will travel forward. The machine will spot turn around the center of the machine.
Forward Travel Operation
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| Illustration 6 | g01622152 |
Main control valve compartment (35) Right travel control valve (36) Left travel control valve | |
When the travel pedals are operated, pilot oil from pilot control valve (25) shifts the stem in travel control valves (36) and (35). Travel control valves (35) and (36) allow oil flow from idler pump (41) and drive pump (40) to flow to swivel (12). The swivel transfers oil from the rotating upper structure to the lines in the lower structure. The oil flows to left travel motor (1) and right travel motor (17) .
Note: The right and left travel controls function in the same manner. The explanation for the left travel control will be used to explain both the right and left travel controls.
Pilot oil from control valve (25) flows through line (29) and into left travel control valve (36). The pilot oil shifts the stem of left travel control valve (36). Idler pump oil in passage (34) flows through passage (33) to passage (32). The pump oil in passage (32) flows through line (28), swivel (12), line (10), and counterbalance valve (8). Pilot oil enters motor rotary group (3) through passage (15) from the counterbalance valve.
Part of the idler pump oil flows through passage (11), brake pilot valve (13), and passage (14) to parking brake assembly (2). Parking brake assembly (2) releases. The left travel motor rotates in the forward direction.
Low Speed
When travel speed control switch (50) is placed in the LOW position, displacement change valve (5) remains deactivated. Oil flow from passage (15) through check valve (7) to piston (4) is blocked. This causes the cam plate to turn increasing the angle of the cam plate. The cam plate remains in the maximum angle position. More oil is required to turn travel motor (1) to the left. This causes the motor to rotate at a slower speed. The left track travels at a lower speed. The slower speed increases the drawbar pull.
Return oil from motor rotary group (3) flows through passage (6), counterbalance valve (8), and line (9) to swivel (12). Oil flows through line (27), passage (31) and left travel control valve (36) to return passage (37). The oil flows back to the hydraulic tank through return line (38) .
Oil from the drive pump turns right travel motor (17) .
High Speed
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| Illustration 7 | g01140595 |
Pilot oil manifold compartment (39) Travel speed solenoid valve | |
The right and left travel motors function in the same manner. The explanation for the right travel motor will be used to explain forward travel in high speed mode.
When travel speed control switch (50) is placed in the HIGH speed position, travel speed solenoid valve (39) is energized. When the pump delivery pressure does not increase to a certain pressure, automatic travel speed solenoid valve (39) remains open. Oil from pilot pump (42) flows through line (43), travel speed solenoid valve (39), line (26), swivel (12), and line (16) to displacement change valve (23). The spool in displacement change valve (23) shifts. When the spool shifts, the drive pump oil in right travel motor (17) flows to displacement change valve (23), and passage (22) to piston (21) .
The pressure oil in passage (22) pushes piston (21), which decreases the angle of cam plate (20). The pressure oil holds cam plate (20) in the minimum angle position. Less oil is required to turn right travel motor (17). Therefore, the motor turns at a higher speed.
Automatic Travel Speed
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| Illustration 8 | g01622142 |
Pump compartment (45) Pressure sensor | |
The right and left travel motors function in the same manner. The explanation for the right travel motor will be used to explain the automatic travel speed. Place the travel speed control switch in the HIGH speed position.
Drive pump (40) and idler pump (41) have pressure sensors in order to monitor pump output pressure. Oil pressure holds cam plate (20) in the minimum angle position. The angle of plate (20) increases as the load on the machine increases. The output pressure of the pump increases as the load on the machine increases.
When the output pressure increases to a high level, a signal from pressure sensor (45) de-energizes travel speed solenoid valve (39) and pilot oil is not supplied to displacement change valve (23). Displacement change valve (23) shifts to the off position. The angle of the cam plate in the travel motor increases. The machine travels at LOW speed.
When the circuit pressure in line (44) decreases to a certain range because of decreased pump output pressure, automatic travel speed solenoid valve (39) is energized. Displacement change valve (23) receives pilot oil from line (16). The angle of the cam plate decreases. The machine travels at HIGH speed.
Automatic travel speed solenoid valve (39) allows the machine to adjust speeds. The machine will travel at HIGH speed under a small load. The machine will travel at LOW speed under a large load. This ensures that the machine has high mobility and a high drawbar pull.