Travel Control
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| Illustration 1 | g00767193 |
Travel motor (1) Left travel motor (2) Counterbalance valve | |
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| Illustration 2 | g00767200 |
Travel drive (3) Left track (4) Sprocket (5) Final drive | |
The right pump supplies hydraulic oil to the left travel motor through the swivel. The left pump supplies hydraulic oil to the right travel motor through the swivel. When the right pump supplies hydraulic oil to left travel motor (1), the motor rotates and the motor torque is transferred to final drive (5). The final drive reduces the output speed of the travel motor and the final drive increases the output torque of the travel motor. Final drive (5) transfers the increased torque to left track (3) through sprocket (4).
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| Illustration 3 | g00767206 |
Right console (6) Travel speed switch | |
The travel speed can be adjusted by the slight operation of the travel levers/pedals. The travel speed can also be controlled by travel speed control switch (6). This changes the travel speed when the travel levers/pedals are moved to the maximum position. The travel speed control switch can be set at the LOW SPEED position or the HIGH SPEED position. When the travel speed control switch is set at the LOW SPEED position, the tortoise appears on the default message display of the monitor. When the travel speed control switch is set at the HIGH SPEED position, the rabbit appears on the default message display of the monitor. During travel on a flat surface or during gradual downhill travel, the travel speed is set at the HIGH SPEED position in order to realize increased mobility.
When travel speed control switch (6) is set at the HIGH SPEED position, the pressure sensors for pump delivery pressure detect the change in pump load. If the pressure sensors detect a high load, the travel speed is automatically adjusted to LOW SPEED. If the pressure sensors detect a small load, the travel speed is automatically adjusted to HIGH SPEED.
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| Illustration 4 | g00767222 |
Operation of travel (1) Left travel motor (7) Left travel lever/pedal (8) Right travel lever/pedal (9) Idler (10) Forward travel (11) Cab (12) Right travel motor (13) Reverse travel | |
The direction of travel is relative to the position of the lower structure. For normal travel, idler (9) is positioned in front of cab (11) and travel motors (1) and (12) to the rear of the cab. With the machine in the normal position of travel, move the travel levers/pedals (7) and (8) forward. The machine will travel in forward direction (10). This movement is called forward travel. When the travel levers/pedals (7) and (8) are moved toward the operator, the machine travels in reverse direction (13). This direction is called reverse travel.
When cab (11) is rotated by 180 degrees, travel motors (1) and (12) are positioned in front of the cab. The direction of travel and the operation of the travel levers/pedals (7) and (8) are reversed from the normal travel direction.
When the machine is in the normal position of travel and when one of the travel levers/pedals (7) or (8) 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 in order to change the travel direction of the machine in a narrow space. To complete a spot turn operation, move one travel lever/pedal to the rear and move the other travel lever/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 axis of the machine.
Forward Travel
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| Illustration 5 | g00786725 |
(1) Left travel motor (2) Parking brake (4) Swashplate (5) Piston (6) Right travel motor (7) Piston (9) Brake pilot valve (13) Passage (3) Motor rotary group (10) Passage (14) Displacement change valve (11) Passage (8) Spring (12) Counterbalance valve (15) Passage (17) Shock reducing valve (16) Passage (18) Line (19) Line (20) Line (21) Line (22) Swivel (23) Line (24) Line (25) Line (26) Line (27) Line (28) Line (29) Passage (30) Passage (31) Passage (32) Passage (33) Left travel control valve (34) Right travel control valve (35) Passage (36) Passage (37) Passage (38) Pilot control valve (39) Travel speed solenoid valve (40) Pilot manifold (41) Pressure sensor (42) Pressure sensor (43) Left pump (44) Right pump (45) Pilot pump | |
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| Illustration 6 | g00786728 |
Main control valve (33) Left travel control valve (34) Right travel control valve | |
When both of the travel levers/pedals are operated, pilot system oil pressure flows from travel pilot control valve (38) through pilot lines (24) and (25) to left travel control valve (33) and right travel control valve (34). The pilot system oil pressure shifts the spools in both of the travel control valves in an downward direction. The travel control valves allow the oil delivery from right pump (44) and left pump (43) to flow to swivel (22). The swivel transfers the oil delivery from the rotating upper structure to the lines in the lower structure. The oil delivery flows to left travel motor (1) and right travel motor (6) .
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.
When the left travel lever/pedal is moved to the FORWARD TRAVEL position, pilot system oil pressure from travel pilot control valve (38) flows through pilot line (25) to left travel control valve (33). The spool in the left travel control valve shifts in an downward direction. The oil delivery from the right pump in center bypass passage (30) flows through left travel control valve (33), passage (32), line (27), swivel (22) and line (21) to left travel motor (1) .
The oil delivery from the right pump enters left travel motor (1) and flows through counterbalance valve (12) and passage (10) to motor rotary group (3). At the same time, a portion of the oil delivery from the right pump flows through passage (11) and brake pilot valve (9) to parking brake (2). The parking brake is released and the oil delivery from the left pump causes the motor to rotate.
Low Speed
When the travel speed switch is placed in the LOW SPEED MODE position, travel speed solenoid valve (38) and displacement change valve (14) remain deactivated and the displacement change valve blocks oil flow through passage (13) to piston (5). Swashplate (4) is held at the maximum displacement position. Now, more oil is required to turn left travel motor (1) and the motor rotates at a lower speed. The left track travels at a lower speed and the drawbar pull of the left track increases.
Return oil from motor rotary group (3) flows through passage (15), counterbalance valve (12) and line (22) to swivel (23). The oil then goes through line (28) and passage (29) into left travel control valve (33).
The oil flows from left travel control valve (33) through return passage (35) back to the hydraulic tank through return line (37). Right travel motor (6) uses the oil from left pump (43). The description for the right travel circuit is the same description as the left travel circuit.
High Speed
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| Illustration 7 | g00786726 |
(39) Travel speed solenoid valve | |
The explanation for forward travel in the HIGH SPEED MODE position is given relative to left travel motor (1). The description for the right travel circuit is the same description as the left travel circuit.
When the travel speed switch is placed in the HIGH SPEED MODE position, travel speed solenoid valve (39) is energized. Oil from pilot pump (45) flows through travel speed solenoid valve (39), line (26), swivel (22) and line (18) to displacement change valve (14).
The spool in displacement change valve (14) shifts. As the spool shifts, the right pump oil in left travel motor (1) flows through passage (16), displacement change valve (14) and passage (13) to piston (5). The pressure oil from passage (13) pushes piston (5) against swashplate (4) until the swashplate is held at the minimum displacement position. Less oil is now required to turn left travel motor (1). The motor turns at a higher speed.
Automatic Travel Speed Change
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| Illustration 8 | g00786727 |
Pressure sensors (41) Pressure sensor (42) Pressure sensor | |
When the travel speed switch is pressed to the HIGH SPEED MODE position, the travel motor operates with the swashplate at the minimum displacement position. As the load that is placed on the machine increases, the output pressure of the pump increases. As the output pressure reaches a certain level, pressure sensor (41) or pressure sensor (42) sends a signal to the engine and pump electronic control module (ECM). The ECM overrides the signal from the travel speed switch and travel speed solenoid valve (39) is de-energized. The pilot oil drains from displacement change valve (14) back to the hydraulic tank and the spool for the displacement change valve shifts back to the right. As the spool shifts back to the right, supply oil is blocked to piston (5) and oil drains from passage (13) to motor rotary group (3). As the oil drains from passage (13), piston (5) returns to a neutral state and swashplate (4) returns back to the maximum displacement position. When the swashplate returns to the maximum displacement position, the machine travels in SLOW SPEED MODE. When output pressure decreases below a certain value, the ECM re-energizes the travel speed solenoid valve and pilot oil shifts the displacement change valve to the left. The pressure in line (13) pushes piston (5) and the piston moves the swashplate back to the minimum displacement position.