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| Illustration 1 | g06194120 |
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Operation of travel (28) Left travel motor (35) Left idler (36) Right travel lever/pedal (37) Left travel lever/pedal | |
The initiation of travel starts at the right travel lever/pedal (36) and left travel lever/pedal (37).
The direction of travel is relative to the position of the lower structure. For normal travel, idler (35) is positioned in front of the cab and travel motors (28) to the rear of the cab. Moving travel levers/pedals (36) and (37) forward will make the machine move forward. This movement is called forward travel. When the travel levers/pedals are moved toward the operator, the machine travels in the reverse direction. This direction is called reverse travel.
When the upper machine swings 180 degrees, the travel motors are positioned in front of the cab. The direction of travel and the operation of the travel levers/pedals 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 is moved forward, the respective track travels forward. The machine turns because the stationary track acts as the pivot point. This type of turn is called a pivot turn.
This machine will spot turn 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.
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| Illustration 2 | g06303620 |
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(27) Travel counterbalance valve
(28) Left travel motor | |
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| Illustration 3 | g06303644 |
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Final drive (31) Final drive (32) Track (33) Sprocket | |
When the travel controls are used, output flow from the pump 1 flows through the swivel to the travel counterbalance valve, and to the right travel motor. Output flow from the pump 2 flows through the swivel to travel counterbalance valve (27), and to left travel motor (28). Pump 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 final drive (31). The final drive increases the torque and the rotational force drives track (32) via sprocket (33).
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| Illustration 4 | g06193754 |
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Right side switch panel (34) Travel speed control switch | |
The travel speed can be adjusted by the amount of rotation of the travel levers/pedals. The travel speed can also be controlled by travel speed control switch (34). 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 indicator light illuminates on the switch. When the travel speed control switch is set at the HIGH SPEED position, the rabbit indicator light illuminates on the switch. The machine defaults to the LOW SPEED position.
When the travel speed control switch is set at the HIGH SPEED position, the pump pressure sensors detect changes in pump load. If the pressure sensors detect a high load, the travel speed is automatically adjusted to low speed to increase the travel motor torque. If the pressure sensors detect a small load, the travel speed is automatically adjusted to high speed.
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| Illustration 5 | g06349972 |
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Hydraulic schematic for forward travel in low speed (1) Return port (2) Travel speed solenoid (3) Left travel backward solenoid (4) Straight travel solenoid (5) Right travel control valve (6) Right travel backward solenoid (7) Parallel feeder passage (8) Center bypass passage (9) Parallel feeder passage (10) Return passage (11) Right travel forward solenoid (12) Pump 2 (13) Pump 1 (14) Pressure port (pump 1) (15) Pump 1 pressure sensor (16) Pump 2 pressure sensor (17) Pressure port (pump 2) (18) Hydraulic tank (19) Left travel forward solenoid (20) Left travel control valve (21) Main control valve (22) Hydraulic lock solenoid (23) Center bypass passage (24) Pilot pressure reducing valve (25) Directional control spool (26) Swivel (27) Directional control spool (28) Left travel motor (29) Right travel motor | |
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| Illustration 6 | g06193784 |
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Main control valve (2) Travel speed solenoid (3) Left travel backward solenoid (4) Straight travel solenoid (5) Right travel control valve (6) Right travel backward solenoid (11) Right travel forward solenoid (19) Left travel forward solenoid (20) Left travel control valve (51) Straight travel control valve | |
Pump 1 (13) and pump 2 (12) supply oil to main control valve (21) through ports (14) and (17). The oil flows to the various valve spools through center bypass passages (8) and (23) for use upon activation. The oil also flows to pilot pressure reducing valve (24). The valve reduces the pressure of the oil for use in the pilot circuit. The pilot oil flows to hydraulic lock solenoid (22). When the hydraulic lock solenoid is energized, pilot oil flows to the control solenoids.
When both travel levers/pedals are moved forward, the machine Electronic Control Module (ECM) receives position data from the pedal sensors. The ECM then proportionally energizes left travel forward solenoid (19) and right travel forward solenoid (11). The shifted solenoid valves allow the flow of pilot oil to travel to left travel valve (20) and right travel valve (5). The pilot oil causes the spools to shift upward against spring pressure. The shifted control valves now allow oil from pump 1 and pump 2 to exit the main control valve and flow to swivel (26). Oil for left travel flows through the swivel at port (A). Oil for right travel flows through the swivel at port (D). The swivel transfers the oil from the rotating upper structure to the lines in the lower structure. The oil then flows to left counterbalance valve (27) and right counterbalance valve (25).
Oil flows through the counterbalance valves and into left travel motor (28) and right travel motor (29). The oil turns the motors which drive the sprockets and tracks to travel forward.
Reverse travel functions similarly when the travel controls are moved rearward toward the operator. Energizing left travel reverse solenoid (3) and right travel reverse solenoid (6) shifts the travel spools downward. Oil would then flow to the motor at ports (B) and (C) to operate the motors in the reverse direction.
More in-depth detail of the operation of the motor and counterbalance valves can be found later in this section.
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| Illustration 7 | g06193795 |
| (2) Travel speed solenoid | |
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| Illustration 8 | g06304336 |
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Left travel motor - low speed (A) Indicator for low speed (B) Indicator for high speed (C) Machine ECM (2) Travel speed solenoid (12) Pump 2 (16) Pump 2 pressure sensor (20) Left travel control valve (21) Main control valve (26) Swivel (27) Directional control spool (28) Left travel motor (34) Travel speed control switch (37) Left travel lever/pedal (39) Swashplate control piston (40) Passage (return oil) (41) Swashplate (42) Motor rotary group (43) Motor brake (44) Passage (supply oil) (45) Displacement change valve (46) Passage (47) Pilot passage (48) Pilot supply | |
When travel speed control switch (34) is set at the LOW SPEED position, indicator (A) illuminates. An electrical signal is sent to machine ECM (C). The machine ECM de-energizes travel speed solenoid valve (2). The spool shifts to the right from spring pressure, blocking pilot supply (48) from flowing into the travel motor.
Oil flows from pump 2 (12) into main control valve (21). The ECM energizes left travel forward solenoid (19) sending pilot oil to left travel control valve (20) causing the valve to shift. The shifted valve allows pump oil to flow to swivel (26) and into travel motor (28). The oil enters the motor at port (B) and shifts directional control valve (27) to the left. Supply oil flows through the control valve into two different paths. In one path oil flows to passage (44), and into motor rotary group (42) for forward travel. With displacement change valve (45) shifted to the left from spring pressure, the oil in swashplate control piston (39) drains to tank through passage (46). The swashplate shifts to maximum displacement. At maximum displacement, the motor rotary group displaces a larger amount of oil flow. Therefore, rotational speed of the left travel motor decreases.
The return oil from the motor rotary group flows through passage (40), directional control valve (27), and swivel (26). The return oil then flows back to main control valve (21) where it flows back to the hydraulic tank.
At the same time, oil flows through directional control valve (27), to motor brake (43). The oil pressure pushes the brake piston back against spring pressure releasing the brake. Once the brake is released and enough pressure is available to turn the motor, the track will start to move. In low speed, the left track moves slowly and better traction is achieved.
The right travel motor functions in the same manner as the left travel motor with the travel speed control in the LOW SPEED position.
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| Illustration 9 | g06304339 |
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Left travel motor - high speed (A) Indicator for low speed (B) Indicator for high speed (C) Machine ECM (2) Travel speed solenoid (12) Pump 2 (16) Pump 2 pressure sensor (20) Left travel control valve (21) Main control valve (26) Swivel (27) Directional control spool (28) Left travel motor (34) Travel speed control switch (37) Left travel lever/pedal (39) Swashplate control piston (40) Passage (return oil) (41) Swashplate (42) Motor rotary group (43) Motor brake (44) Passage (supply oil) (45) Displacement change valve (46) Passage (47) Pilot passage (48) Pilot supply | |
When travel speed control switch (34) is set at the HIGH SPEED position, indicator (B) illuminates. An electrical signal is sent to machine ECM (C). Pressure sensor (16) also sends an electrical signal to the machine ECM. If the travel load is light and pump pressure is below a certain threshold, the machine ECM energizes travel speed solenoid valve (2) for high speed. Energizing the spool causes the spool to shift to the left against spring pressure. Pilot supply (48) flows through the travel speed solenoid to displacement change valve (45) and shifts the valve to the right.
Oil flows from pump 2 (12) into main control valve (21). The ECM energizes left travel forward solenoid (19) sending pilot oil to left travel control valve (20) causing the valve to shift. The shifted valve allows pump oil to flow to swivel (26) and into travel motor (28). The oil enters the motor at port (B) and shifts directional control valve (27) to the left. Supply oil flows through the control valve into two different paths. In one path oil flows to passage (44), and into motor rotary group (42) for forward travel. With displacement change valve (45) shifted to the right from pilot pressure, oil from pump 2 flows into swashplate control piston (39) pushing the piston against spring pressure. The piston shifts the swashplate to minimum displacement. At minimum displacement, the motor rotary group displaces a smaller amount of oil flow. Therefore, rotational speed of left travel motor (28) increases.
The return oil from the motor rotary group flows through passage (40), directional control valve (27), and swivel (26). The return oil then flows back to main control valve (21) where it flows back to the hydraulic tank.
At the same time, oil flows through directional control valve (27) motor brake (43). The oil pressure pushes the brake piston back against spring pressure releasing the brake. Once the brake is released and enough pressure is available to turn the motor, the track will start to move. In high speed, the left track moves faster with less available torque.
The right travel motor functions in the same manner as the left travel motor with the travel speed control in the HIGH SPEED position.
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| Illustration 10 | g06193829 |
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(15) Pump 1 pressure sensor
(16) Pump 2 pressure sensor | |
Pressure sensor (15) monitors the pressure of pump 1 (13). Pressure sensor (16) monitors the pressure of pump 2 (12). Travel motor displacement is low when the travel speed control switch (34) is in the HIGH SPEED position and the travel load is light. As pump load increases, the pressure of the pumps increases. When the pressure of the pumps reaches a certain threshold, the machine ECM de-energizes travel speed solenoid valve (2) effectively switching the travel system to low speed to increase motor torque. The system will operate as previously described in the "Low Speed" section.
When the pump load decreases with the travel speed control switch still in the HIGH SPEED position, the decreased load now causes the machine ECM to energize travel speed solenoid valve (2). The displacement change valves in each motor will be shifted by pilot pressure allowing pump oil to change the swashplates to minimum displacement. The travel speed has now automatically changed back to high speed.
The ability of the machine to change the travel speed automatically provides good performance at times when higher speeds or higher torque are needed.