Travel Control
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| Illustration 1 | g00830226 |
(1) Left travel motor (52) Motor head (travel) | |
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| Illustration 2 | g00830230 |
Final drive (53) Track (54) Sprocket (55) Final drive | |
The output flow from the right pump flows through the swivel to the right travel motor. The output flow from the left pump flows through the swivel to the left 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. The final drive (55) increases the torque and the rotational force drives track (53) via sprocket (54).
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| Illustration 3 | g00699127 |
Keypad (right console) (56) Travel speed control 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 (56). 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 (56) 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 | g00830236 |
Operation of travel (1) Left travel motor (15) Right travel motor (57) Forward travel (58) Left travel lever/pedal (59) Idler (60) Right travel lever/pedal (61) Cab (62) Reverse travel | |
The direction of travel is relative to the position of the lower structure. For normal travel, idler (59) is positioned in front of cab (61) and travel motors (1) and (15) to the rear of the cab. With the machine in the normal position of travel, move the travel levers/pedals (58) and (60) forward. The machine will travel in forward direction (57). This movement is called forward travel. When the travel levers/pedals (58) and (60) are moved toward the operator, the machine travels in reverse direction (62). This direction is called reverse travel.
When cab (61) is rotated by 180 degrees, travel motors (1) and (15) are positioned in front of the cab. The direction of travel and the operation of the travel levers/pedals (58) and (60) 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 (58) or (60) 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 | g00886850 |
Hydraulic schematic for FORWARD TRAVEL (1) Left travel motor (2) Swashplate (3) Motor rotary group (4) Passage (5) Swashplate control piston (6) Passage (return oil) (7) Passage (return oil) (8) Swashplate (9) Swashplate control piston (10) Passage (supply oil) (11) Passage (parking brake) (12) Passage (parking brake) (13) Passage (14) Passage (15) Right travel motor (16) Passage (17) Pilot line (18) Displacement change valve (19) Passage (20) Displacement change valve (21) Passage (22) Passage (23) Counterbalance valve (24) Passage (25) Brake pilot valve (26) Pilot line (27) Pilot line (28) Line (supply oil) (29) Line (return oil) (30) Line (supply oil) (31) Line (return oil) (32) Swivel (33) Line (supply oil) (34) Line (return oil) (35) Passage (supply oil) (36) Passage (return oil) (37) Return passage (38) Passage (39) Left travel control valve (40) Center bypass passage (41) Right travel control valve (42) Travel pilot control valve (43) Pressure sensor for left pump delivery (44) Left pump (45) Right pump (46) Pilot line (forward left travel) (47) Pilot line (forward right travel) (48) Return line (49) Pressure sensor for right pump delivery (50) Pilot pump (51) Pilot valve (straight travel) (52) Pilot line (forward left travel) (53) Pilot line (forward right travel) (54) Travel speed solenoid valve (55) Resolver valve (56) Pilot line (forward straight travel) | |
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| Illustration 6 | g00938955 |
Main control valve (39) Left travel control valve (41) Right travel control valve | |
When both of the travel levers/pedals are operated, pilot system oil pressure flows from travel pilot control valve (42) through pilot lines (52) and (53) to resolver valve (55). Oil pressure shifts the ball valves. This allows oil to flow through pilot lines (46) and (47) to left travel control valve (39) and right travel control valve (41). The pilot system oil pressure shifts the spools in both of the travel control valves in an upward direction. The travel control valves allow the oil delivery from the right pump and the left pump to flow to swivel (32). 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 (15) .
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 (42) flows through pilot line (46) to left travel control valve (39). The spool in the left travel control valve shifts in an upward direction. The oil delivery from the left pump in center bypass passage (40) flows through passage (38), left travel control valve (39), passage (35), line (33), swivel (32) and line (28) to left travel motor (1) .
The oil delivery from the left pump enters left travel motor (1) and flows through passage (13) to motor rotary group (3). At the same time, a portion of the oil delivery from the left pump flows through passage (24) to brake pilot valve (25) and passage (21) to counterbalance valve (23). When the oil pressure is greater than the spring pressure in brake pilot valve (25), the oil shifts the spool in the brake pilot valve to the left. When the spool is shifted oil flows to passage (11) in order to release the parking brake. The oil pressure also shifts the spool in counterbalance valve (23) to the right in order to open a passage for the return oil. The parking brake is released and the oil delivery from the left pump causes the motor to rotate.
Straight Travel Pilot Valve
When the straight travel pedal is operated, pilot system oil pressure flows from travel pilot control valve (51) through pilot line (56) to resolver valve (55). Oil pressure shifts the ball valves. This allows oil to flow through pilot lines (46) and (47) to left travel control valve (39) and right travel control valve (41). The pilot system oil pressure shifts the spools in both of the travel control valves in an upward direction. The travel control valves allow the oil delivery from the right pump and the left pump to flow to swivel (32). 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 (15) .
LOW SPEED
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| Illustration 7 | g00811674 |
Left travel motor (LOW SPEED) (1) Left travel motor (2) Swashplate (3) Motor rotary group (4) Passage (5) Swashplate control piston (6) Passage (return oil) (13) Passage (18) Displacement change valve (23) Counterbalance valve (27) Pilot line (43) Pressure sensor (left pump) (44) Left pump (50) Pilot pump (51) Travel speed solenoid valve (56) Travel speed control switch (58) Left travel lever/pedal (A) Indicator for HIGH SPEED (B) Indicator for LOW SPEED (C) Engine and pump controller | |
When travel speed control switch (56) is set at the LOW SPEED position, an electrical signal is sent to engine and pump controller (C). The engine and pump controller does not energize travel speed solenoid valve (51) and pilot system oil pressure flows through pilot line (27) to displacement change valve (18). The spool in the displacement change valve shifts downward. A portion of the oil flow from the left pump in passage (13) flows through displacement change valve (18) and passage (4) to swashplate control piston (5). As a result, swashplate control piston (5) moves swashplate (2) to the maximum displacement position. At the same time, the oil that acts on swashplate control piston (5) flows into the case drain of the travel motor. One rotation of motor rotary group (3) displaces a larger amount of oil flow. The rotational speed of the left travel motor decreases. The left track moves slowly and better traction is achieved.
The return oil from motor rotary group (3) flows through passage (6), counterbalance valve (23), line (29) and swivel (32). The return oil then flows through line (34), left travel control valve (39), return passage (37) and return line (48) to the hydraulic tank.
Right travel motor (15) receives the oil delivery from the right 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 | g00773193 |
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| Illustration 9 | g00811675 |
Left travel motor (HIGH SPEED) (1) Left travel motor (2) Swashplate (3) Motor rotary group (5) Swashplate control piston (6) Passage (return oil) (13) Passage (18) Displacement change valve (19) Passage (23) Counterbalance valve (27) Pilot line (43) Pressure sensor (left pump) (44) Left pump (50) Pilot pump (51) Travel speed solenoid valve (56) Travel speed control switch (58) Left travel lever/pedal (A) Indicator for HIGH SPEED (B) Indicator for LOW SPEED (C) Engine and pump controller | |
When travel speed control switch (56) is set at the HIGH SPEED position, an electrical signal is sent to engine and pump controller (C). Pressure sensors (43) and (49) also send an electrical signal to the engine and pump controller. If the travel load is light and when the pump delivery pressure is below a certain pressure, the engine and pump controller energizes travel speed solenoid valve (51). Pilot system oil pressure is blocked from travel speed solenoid valve (51). The spool in the displacement change valve shifts. A portion of the oil delivery from the left pump flows through the displacement change valve to swashplate control piston (5). Swashplate control piston (5) moves swashplate (2) to the minimum displacement position. At the same time, the oil that acts on swashplate control piston (5) flows into the case drain of the travel motor. One rotation of motor rotary group (3) 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 (3) flows through passage (6), counterbalance valve (23), line (29) and swivel (32). The return oil then flows through line (34), left travel control valve (39), return passage (37) and return line (48) to the hydraulic tank.
Right travel motor (15) receives the oil delivery from the right 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 | g00938979 |
Main pump compartment (43) Pressure sensor for left pump delivery (49) Pressure sensor for right pump delivery | |
Pressure sensor (49) monitors the delivery pressure of the right pump. Pressure sensor (43) monitors the delivery pressure of the left 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 engine and pump controller. The engine and pump controller de-energizes travel speed solenoid valve (51). Spring pressure shifts travel speed solenoid valve (51). This allows the flow of pilot oil to displacement change valves (18) and (20). The oil in swashplate control pistons (5) and (9) now flows into the case drain of the travel motors. Swashplates (2) and (8) 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 (43) and (49) will now cause the engine and pump controller to energize travel speed solenoid valve (51). The displacement change valves will be shifted by spring 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 automatically change the travel speed allows good performance at high speed and better traction control.