Travel Control
Introduction
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| Illustration 1 | g02176679 |
Travel motor (8) Counterbalance valve (14) Left travel motor | |
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| Illustration 2 | g02173869 |
Final drive (47) Sprocket (48) Left track (49) Left final drive | |
The output flow from the idler pump flows through the swivel to the left travel motor. The output flow from the drive pump flows through the swivel to the right travel motor. The pump delivery flow causes rotation of the travel motors. The torque of the travel motors is transmitted to the final drives. The rotational speed of the travel motors is reduced by gear reduction in the final drive. Final drive (49) increases the torque and the rotational force drives track (48) via sprocket (47) .
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| Illustration 3 | g02638036 |
Soft switch panel (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 speed position, the pump pressure sensors 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 | g02173260 |
Operation of travel (14) Left travel motor (18) Right travel motor (51) Left travel pedal (52) Right travel pedal (53) Reverse direction (54) Cab (55) Idler (56) Forward direction | |
The direction of travel is relative to the position of the lower structure. For normal travel, idler (55) is positioned in front of cab (54) and travel motors (14) and (18) to the rear of the cab. With the machine in the normal position of travel, move the travel pedals (51) and (52) forward. The machine will travel in forward direction (56) . This movement is called forward travel. When travel pedals (51) and (52) are moved toward the operator, the machine travels in reverse direction (53) . This direction is called reverse travel.
When cab (54) is turned to the opposite direction, travel motors (14) and (18) will be positioned in front of the cab. The direction of travel and the operation of travel pedals (51) and (52) are reverse when the machine is in the normal travel direction.
A pivot turn is made when the traveling direction of the machine is changed. When one of the travel pedals (51) or (52) is moved forward, the respective track travels forward. The machine turns because the stationary track acts as the pivot point. This action is called a pivot turn.
This machine will spot turn when the traveling 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 5 | g03561656 |
Hydraulic schematic for FORWARD TRAVEL (1) Parking brake assembly (2) Rotary group (3) Swashplate (4) Swashplate control piston (5) Displacement change valve (6) Passage (return oil) (7) Check valve (8) Counterbalance valve (9) Line (return oil) (10) Line (supply oil) (11) Passage (12) Brake pilot valve (13) Swivel (14) Left travel motor (15) Passage (supply oil) (16) Line (pilot system oil pressure) (17) Passage (18) Right travel motor (19) Parking brake assembly (20) Rotary group (21) Swashplate (22) Swashplate control piston (23) Passage (24) Displacement change valve (25) Passage (26) Line (pilot system oil pressure) (27) Pilot travel control valve (28) Drain line (29) Line (pilot system oil pressure) (30) Line (pilot system oil pressure) (31) Line (supply oil) (32) Line (return oil) (33) Return passage (34) Passage (35) Center bypass passage (36) Right travel control valve (37) Main control valve (38) Straight travel control valve (39) Left travel control valve (40) Pressure sensor (idler pump) (41) Pressure sensor (drive pump) (42) Line (supply oil) (43) Travel speed solenoid valve (44) Pilot pump (45) Drive pump (46) Idler pump | |
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| Illustration 6 | g02173267 |
Main control valve compartment (36) Right travel control valve (38) Straight travel control valve (39) Left travel control valve | |
When the travel pedals are operated, pilot oil from pilot control valve (27) shifts the stem in travel control valves (36) and (39) . Travel control valves (36) and (39) allow oil flow from idler pump (46) and drive pump (45) to flow to swivel (13) . The swivel transfers oil from the rotating upper structure to the lines in the lower structure. The oil flows to left travel motor (14) and right travel motor (18) .
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 (27) flows through line (29) and into left travel control valve (39) . The pilot oil shifts the stem of left travel control valve (39) . Idler pump oil in passage (35) flows through passage (34) , line (31) , swivel (13) , line (10) , and counterbalance valve (8) . Pump oil enters motor rotary group (2) through passage (15) from the counterbalance valve.
Part of the idler pump oil flows through passage (11) , brake pilot valve (12) , and passage (17) to parking brake assembly (1) . Parking brake assembly (1) releases. The left travel motor rotates in the forward direction.
For more information concerning the travel parking brake, refer to Systems Operation, "Travel Parking Brake".
Low Speed
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| Illustration 7 | g03583243 |
Left travel motor (LOW SPEED) (2) Motor rotary group (3) Swashplate (4) Swashplate control piston (5) Displacement change valve (6) Passage (return oil) (8) Counterbalance valve (14) Left travel motor (15) Passage (supply oil) (26) Pilot line (37) Main control valve (40) Pressure sensor (idler pump) (43) Travel speed solenoid valve (44) Pilot pump (46) Idler pump (50) Travel speed control switch (51) Left travel lever/pedal (A) Indicator for HIGH SPEED (B) Indicator for LOW SPEED (C) Machine ECM | |
When travel speed control switch (50) is set at the LOW SPEED position, an electrical signal is sent to machine ECM (C) . The machine ECM does not energize travel speed solenoid valve (43) and pilot system oil pressure does not flow through pilot line (26) to displacement change valve (5) . The spool in the displacement change valve does not shift. Oil flows from the idler pump in passage (15) to the motor rotary group (2) . Since displacement change valve (5) is not shifted, oil is restricted from swashplate control piston (4) . The swashplate remains in the maximum displacement position. One rotation of motor rotary group (2) displaces a larger amount of oil flow. The rotational speed of the left travel motor decreases. The left track moves slowly and increases the drawbar pull.
The return oil from motor rotary group (2) flows through passage (6) , counterbalance valve (8) , line (9) and swivel (13) . The return oil then flows through line (32) , left travel control valve (39) and return passage (33) to the hydraulic tank.
Right travel motor (18) receives the oil delivery from the drive pump. The right travel motor functions in the same manner as the left travel motor in the LOW SPEED position.
High Speed
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| Illustration 8 | g02173277 |
Pilot oil manifold compartment (43) Travel speed solenoid valve | |
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| Illustration 9 | g03583244 |
Left travel motor (HIGH SPEED) (2) Motor rotary group (3) Swashplate (4) Swashplate control piston (5) Displacement change valve (6) Passage (return oil) (8) Counterbalance valve (14) Left travel motor (15) Passage (supply oil) (26) Pilot line (37) Main control valve (40) Pressure sensor (idler pump) (43) Travel speed solenoid valve (44) Pilot pump (46) Idler pump (50) Travel speed control switch (51) Left travel lever/pedal (A) Indicator for HIGH SPEED (B) Indicator for LOW SPEED (C) Machine ECM | |
When travel speed control switch (50) is set at the HIGH SPEED position, an electrical signal is sent to machine ECM (C) . Pressure sensors (40) and (41) also send an electrical signal to the machine ECM. If the travel load is light and when the pump delivery pressure is below a certain pressure, the machine ECM energizes travel speed solenoid valve (43) . Pilot system oil pressure flows through travel speed solenoid valve (43) and line (26) to displacement change valve (5) . The spool in the displacement change valve (5) shifts. A portion of the oil delivery from the idler pump flows through the displacement change valve to swashplate control piston (4) . Swashplate control piston (4) moves swashplate (3) to the minimum displacement position. One rotation of motor rotary group (2) displaces a smaller amount of oil flow. The rotational speed of the left travel motor increases. The left track moves at a faster speed.
The return oil from motor rotary group (2) flows through passage (6) , counterbalance valve (8) , line (9) and swivel (13) . The return oil then flows through line (32) , left travel control valve (39) and return passage (33) to the hydraulic tank.
Right travel motor (18) receives the oil delivery from the drive pump. The right travel motor functions in the same manner as the left travel motor in HIGH SPEED position.
Automatic Travel Speed Change
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| Illustration 10 | g03583246 |
Pump compartment (40) Pressure sensor (idler pump) (41) Pressure sensor (drive pump) | |
Pressure sensor (41) monitors the delivery pressure of the drive pump. Pressure sensor (40) monitors the delivery pressure of the idler pump. The motor displacement is low when the travel speed control switch is set at the HIGH SPEED position and the travel load is light. As the pump load increases, the delivery pressure of the pumps increases. When the delivery pressure of the pumps reaches a certain pressure, the pressure sensor sends an electrical signal to the machine ECM. The machine ECM de-energizes travel speed solenoid valve (43) . Travel speed solenoid valve (43) blocks the flow of pilot system supply oil to displacement change valves (5) and (24) . The oil in swashplate control pistons (4) and (22) now flows into the case drain of the travel motors. Swashplates (3) and (21) move to the maximum displacement position. One rotation of the motor rotary groups in the travel motors displaces a larger amount of oil flow. The rotational speed of the travel motors decreases. The travel speed is automatically changed to LOW SPEED.
When the pump load decreases and the travel speed control switch is set at the HIGH SPEED position, pressure sensors (40) and (41) will now cause the machine ECM to energize travel speed solenoid valve (43) . Displacement change valves (5) and (24) will be shifted by pilot pressure so that the motor rotary groups will change to the minimum displacement position. One rotation of the motor rotary groups displaces a small amount of oil flow. The travel speed will automatically change to HIGH SPEED.
The ability of the machine to change the travel speed automatically ensures that the machine has high mobility and a high drawbar pull.