Travel Control
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| Illustration 1 | g02160310 |
(12) Left travel motor (27) Counterbalance valve | |
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| Illustration 2 | g02160312 |
Final Drive (50) Sprocket (51) Final drive (52) Track | |
The output flow from the front pump and the output flow from the rear pump combines and flows through the swivel to the left travel motor and 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. The final drive (51) increases the torque and the rotational force drives track (52) via sprocket (50).
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| Illustration 3 | g02160313 |
Keypad (right console) (53) 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 (53). 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 LOW SPEED MODE or HIGH SPEED MODE. When the travel speed control switch is set at LOW SPEED MODE, the tortoise is illuminated on the keypad. When the travel speed control switch is set at HIGH SPEED MODE, the rabbit is illuminated on the keypad. During travel on a flat surface or during gradual downhill travel, the travel speed is set at the HIGH SPEED MODE position in order to realize increased mobility.
When travel speed control switch (53) is set at the HIGH SPEED MODE position, the pressure sensor for the pump delivery detects the change in pump load. If the pressure sensor detects a high load, the travel speed is automatically adjusted to LOW SPEED MODE. If the pressure sensor detects a small load, the travel speed is automatically adjusted to HIGH SPEED MODE.
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| Illustration 4 | g02160318 |
Operation of travel (1) Right travel motor (12) Left travel motor (61) Forward travel (62) Control lever and pedal (left travel) (63) Idler (64) Control lever and pedal (right travel) (65) Cab (66) Reverse travel | |
The direction of travel is relative to the position of the lower structure. For normal travel, idler (63) is positioned in front of cab (65) and travel motors (1) and (12) to the rear of the cab. With the machine in the normal position of travel, move the travel control levers or pedals (62) and (64) forward. The machine will travel in forward direction (61). This movement is called forward travel. When the travel control levers or pedals (62) and (64) are moved toward the operator, the machine travels in the reverse direction. This direction is called reverse travel.
When cab (65) 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 control levers or pedals (62) and (64) are reversed to the normal travel direction.
When one of the travel control levers or pedals (62) and (64) 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 control lever to the rear and move the other travel control lever 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 | g02160420 |
Hydraulic schematic for forward travel (1) Right travel motor (2) Passage (oil flow to swashplate control piston) (3) Passage (return oil) (4) Displacement change valve (5) Passage (return oil) (6) Shuttle valve (7) Motor rotary group (8) Swashplate (9) Swashplate control piston (10) Passage (supply oil) (11) Line (pilot system oil pressure) (12) Left travel motor (13) Parking brake (14) Displacement change valve (15) Passage (return oil) (16) Shuttle valve (17) Passage (parking brake release pressure) (18) Brake pilot valve (19) Passage (supply oil to brake pilot valve) (20) Motor rotary group (21) Swashplate (22) Swashplate control piston (23) Passage (supply oil) (24) Swivel (25) Return line (26) Supply line (27) Counterbalance valve (28) Line (pilot system oil pressure) (29) Proportional valve for left travel (reverse) (30) Proportional valve for right travel (reverse) (31) Passage (supply oil) (32) Left travel control valve (33) Right travel control valve (34) Passage (supply oil to left travel motor) (35) Passage (supply oil to left travel motor) (36) Passage (return oil) (37) Passage (return oil) (38) Proportional valve for left travel (forward) (39) Proportional valve for right travel (forward) (40) Return line (41) Pilot line (42) Pressure sensor for pump delivery (43) Travel speed solenoid valve (44) Pilot manifold (45) Front pump (46) Rear pump (47) Pilot pump (48) Line (pilot system supply oil) (49) Solenoid valve (hydraulic activation) (50) Passage (supply oil) | |
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| Illustration 6 | g02160611 |
Main control valve (29) Proportional valve for left travel (reverse) (30) Proportional valve for right travel (reverse) (38) Proportional valve for left travel (forward) (39) Proportional valve for right travel (forward) | |
During machine operation, the oil delivery from pilot pump (47) flows through line (48) and pilot manifold (44). The oil then flows through line (41) to the following valves: proportional valve for left travel (forward) (38), proportional valve for right travel (forward) (39), proportional valve for left travel (reverse) (29) and proportional valve for right travel (reverse) (30) .
When both of the travel control levers or pedals are operated, an electrical signal from the control levers or pedals is sent to the machine ECM. The machine ECM sends an electrical signal to the proportional valve for left travel (forward) (38) and to the proportional valve for right travel (forward) (39) .
When proportional valves (38) and (39) are energized, a return passage to the hydraulic tank in each proportional valve begins to open. Pilot system oil pressure that acts on the bottom of the spools in travel control valves (32) and (33) begins to decrease.
Pilot system oil pressure that acts on the top of the spools in travel control valves (32) and (33) moves the spools toward proportional valves (38) and (39). When the spools in travel control valves (32) and (33) shift, the output flow from front pump (45) and rear pump (46) combine and flows through travel control valves (32) and (33). The oil then flows through swivel (24) to right travel motor (1) and left travel motor (12) .
The oil delivery enters left travel motor (12) and flows through counterbalance valve (27) and passage (23) to motor rotary group (20). At the same time, the oil delivery from the pumps flows through passage (19), brake pilot valve (18) and passage (17) to parking brake (13). The parking brake is released and the oil delivery from the pump causes the motor to rotate.
Right travel motor (1) also receives the oil delivery from the pumps. The right travel motor functions in the same manner as the left travel motor.
Low Speed Mode
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| Illustration 7 | g02160645 |
Pilot manifold (43) Travel speed solenoid valve (44) Pilot manifold | |
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| Illustration 8 | g02160780 |
Low Speed Mode (FORWARD) (12) Left travel motor (14) Displacement change valve (15) Passage (return oil) (16) Shuttle valve (20) Motor rotary group (21) Swashplate (22) Swashplate control piston (27) Counterbalance valve (42) Pressure sensor for pump delivery (43) Travel speed solenoid valve (45) Front pump (46) Rear pump (47) Pilot pump (53) Travel speed control switch (A) High speed mode (B) Low speed mode (C) Travel levers/pedals (D) Machine ECM | |
When travel speed control switch (53) is set at the LOW SPEED MODE position, an electrical signal is sent to machine ECM (D). The machine ECM does not energize travel speed solenoid valve (43) and pilot system oil pressure does not flow to displacement change valve (14). When the displacement change valve is not shifted, oil flow from the main pumps and from shuttle valve (16) is blocked at displacement change valve (14). As a result, swashplate control piston (9) moves swashplate (21) to the maximum displacement position. One rotation of motor rotary group (20) 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 (20) flows through passage (15), counterbalance valve (27) and swivel (24). The return oil then flows through line (25), left travel control valve (32), return passage (37) and return line (40) to the hydraulic tank.
Right travel motor (1) also receives the oil delivery from the main pumps. The right travel motor functions in the same manner as the left travel motor in LOW SPEED MODE.
High Speed Mode
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| Illustration 9 | g02160645 |
Pilot manifold (43) Travel speed solenoid valve (44) Pilot manifold | |
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| Illustration 10 | g02160918 |
High Speed Mode (FORWARD) (11) Line (pilot system oil pressure) (12) Left travel motor (14) Displacement change valve (16) Shuttle valve (20) Motor rotary group (21) Swashplate (22) Swashplate control piston (42) Pressure sensor for pump delivery (43) Travel speed solenoid valve (45) Front pump (46) Rear pump (47) Pilot pump (53) Travel speed control switch (A) High speed mode (B) Low speed mode (C) Travel levers/pedals (D) Machine ECM | |
When travel speed control switch (53) is set at the HIGH SPEED MODE position, an electrical signal is sent to machine ECM (D). The pressure sensor for the pump delivery (42) also sends 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 (11) to displacement change valve (14). When the displacement change valve is shifted, oil flow from the main pumps and from shuttle valve (16) flows through the displacement change valve to swashplate control piston (9). Swashplate control piston (9) moves swashplate (21) to the minimum displacement position. One rotation of motor rotary group (20) displaces a smaller amount of oil flow. The rotational speed of the left travel motor increases. The left track moves at a faster speed.
Right travel motor (1) also receives the oil delivery from the pumps. The right travel motor functions in the same manner as the left travel motor in HIGH SPEED MODE.
Automatic Travel Speed Mode
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| Illustration 11 | g02160990 |
Main pump compartment (42) Pressure sensor for pump delivery | |
Pressure sensor (42) monitors the delivery pressure of the front pump. The motor displacement is low when the travel speed control switch is set at the HIGH SPEED MODE position and the travel load is light. When the pump load increases, the delivery pressure of the front pump increases. When the delivery pressure of the front pump 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). Pilot system supply oil is blocked from flowing to displacement change valve (14) by travel speed solenoid valve (43). Oil in piston (9) now flows to the hydraulic tank as return oil. Swashplate (21) moves to the maximum displacement position. One rotation of motor rotary group (20) displaces a larger amount of oil flow. The rotational speed of the left travel motor decreases. The travel speed is automatically changed to LOW SPEED MODE.
When the pump load decreases and the travel speed control switch is set at the HIGH SPEED MODE position, the pressure sensor for pump delivery (42) will now cause the machine ECM to energize travel speed solenoid valve (43). Displacement change valve (14) will be shifted by pilot pressure so that motor rotary group (20) will change to the minimum displacement position. One rotation of the motor rotary group displaces a small amount of oil flow. The travel speed will automatically change to HIGH SPEED MODE.
The right travel motor functions in the same manner as the left travel motor when the travel speed changes automatically.
The ability of the machine to automatically change the travel speed allows good performance at high speed and better traction control.