Straight Travel Operation
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| Illustration 1 | g01622365 |
Main control valve compartment (1) Right travel control valve (2) Straight travel control valve (3) Left travel control valve | |
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| Illustration 2 | g01622373 |
Hydraulic schematic (right travel and left travel) (1) Right travel control valve (2) Straight travel control valve (3) Left travel control valve (4) Main control valves (5) Line (6) Line (7) Drive pump (8) Idler pump | |
Straight travel control valve (2) maintains straight travel even though there is a swing operation or implement operation during travel.
Straight travel control valve (2) also improves the control of operations such as pipe laying or placement of timbers. When the machine travels without swing operation or implement operation, oil from drive pump (7) flows through right travel control valve (1) to the right travel motor. Oil from idler pump (8) flows through straight travel control valve (2) and left travel control valve (3) to the left travel motor. Because both travel circuits are separated, the machine continues to travel straight, unless a difference in travel resistance occurs between the right and left tracks.
The straight travel system ensures the straight travel of the machine when other circuits are operated during travel. The drive pump and the idler pump supply oil to the travel motors. The drive pump and the idler pump also supply oil for a swing or implement operation. During travel, if an implement operation or a swing operation occurs the oil supply to each travel motor will differ. This would cause the right travel motor and the left travel motor to rotate at different speeds. The different speeds will cause the machine to turn.
The following actions occur when pilot oil pressure activates straight travel control valve (2) .
- Drive pump (7) supplies oil to the left travel circuit and to the right travel circuit in order to drive both motors in parallel.
- The swing circuit and implement circuits get oil from the idler pump. When the machine is travelling, the swing circuit and implement circuits do not require a large amount of flow. The swing circuit and implement circuits are operated at speeds that are low enough for stable machine operation. The remainder of the oil is shared by the right travel circuit and the left travel circuit.
Travel And Implement Operation
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| Illustration 3 | g01622396 |
Hydraulic schematic (1) Main control valves (2) Stick I control valve (3) Swing control valve (4) Left travel control valve (5) Passage (6) Right travel control valve (7) Bucket control valve (8) Boom I control valve (9) Passage (10) Pilot Passage (11) Pilot Passage (12) Passage (13) Passage (14) Center bypass passage (15) Straight travel control valve (16) Passage (17) Passage (18) Passage (19) Passage (20) Drain line (21) Center bypass passage (22) Parallel feeder passage (23) Pilot passage (24) Passage (25) Passage (26) Pilot passage (27) Parallel feeder passage (28) Pilot passage (29) Line (30) Drive pump (31) Idler pump (32) Pilot pump (33) Pilot oil manifold (34) Line | |
If the boom is operated and the machine is travelling, pilot oil from the travel pilot control valve flows through passage (26) to right travel control valve (6). Pilot oil also flows through pilot passage (23) to left travel control valve (4). Pilot oil from the boom pilot control valves flows to control valve (8) through pilot passage (28). When control valve (8) is operated, passage (12) is blocked. When passage (12) is blocked the pilot oil pressure increases in pilot passages (10) and (11). The increased pilot pressure activates straight travel control valve (15) .
Control valve (2), swing control valve (3), control valve (8) and bucket control valve (7) are connected in series by passage (5). When any of these control valves are operated, the connection between passage (5) and passage (9), (13) or (19) is blocked. The pilot oil pressure in passages (10) and (11) increases enough to activate straight travel control valve (15) .
If all of the control levers for control valve (2), swing control valve (3), control valve (8) and bucket control valve (7) are in the NEUTRAL position, pilot passage (10) is open to the hydraulic tank. The oil pressure in pilot passages (10) and (11) decreases. Straight travel control valve (15) does not activate.
When straight travel control valve (15) is activated, oil from the drive pump and the idler pump flows in the following manner so that the machine can travel straight.
- Oil from drive pump (30) flows through line (29) to passage (16) in main control valve (1). Drive pump oil in passage (16) separates into two flow paths. One path flows through center bypass passage (21) to right travel control valve (6). The other path flows through passage (25), straight travel control valve (15) and center bypass passage (14) to left travel control valve (4). The right and left travel motors now receive an equal amount of drive pump oil.
- Oil from idler pump (31) flows through line (34) to passage (17) in main control valve (1). Idler pump oil in passage (17) separates into two flow paths. One path flows through parallel feeder passage (22) to swing control valve (3) and control valve (2). The other path flows through passage (24) and straight travel control valve (15) to parallel feeder passage (27). From parallel feeder passage (27), the oil flow separates into two paths. One path flows to bucket control valve (7). The other path flows to control valve (8) .
Portions of the idler pump oil in passage (24) flows through the check valve and the orifice in straight travel control valve (15). This oil from the check valve and straight travel control valve (15) combines with the drive pump oil in center bypass passage (14). This combined flow helps power the right travel motor and the left travel motor.
Straight Travel Control Valve
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| Illustration 4 | g01467467 |
Straight travel control valve (NEUTRAL position) (1) Parallel feeder passage (2) Center bypass passage (3) Center bypass passage (4) Parallel feeder passage (5) Pilot passage (6) Piston chamber (7) Spring (8) Passage (9) Line (10) Line (11) Passage (12) Stem (13) Straight travel control valve (14) Drive pump (15) Idler pump | |
When only the travel control is activated, pilot pressure in pilot passage (5) is low. The oil pressure in piston chamber (6) also remains low. Stem (12) is shifted all the way to the right by the force of spring (7). Oil from the drive pump and the idler pump flows in the following manner.
- Oil from drive pump (14) flows through line (10) to passage (11) in the straight travel control valve. The drive pump oil separates into two flow paths. One path flows through center bypass passage (3) and into the right travel control valve. The other path flows through parallel feeder passage (4) and into the attachment control valve, the bucket control valve, the boom I control valve and the stick II control valve.
- Oil from idler pump (15) flows through line (9) to passage (8) in the straight travel control valve. The idler pump oil separates into two flow paths. One path flows through parallel feeder passage (1) and into the swing control valve, the stick I control valve and the boom II control valve. The other path flows through center bypass passage (2) and into the left travel control valve.
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| Illustration 5 | g01469825 |
Straight travel control valve (activated position) (1) Parallel feeder passage (2) Center bypass passage (3) Center bypass passage (4) Parallel feeder passage (5) Pilot passage (6) Piston chamber (7) Spring (8) Passage (9) Line (10) Line (11) Passage (12) Stem (13) Straight travel control valve (14) Drive pump (15) Idler pump (16) Check valve (17) Passage (18) Passage (19) Orifice | |
When the travel control is activated with either the implement control or the swing control, pilot pressure in pilot passage (5) increases. The oil pressure in piston chamber (6) also increases. Stem (12) is shifted all the way to the left against the force of spring (7). Oil from the drive pump and the idler pump flows in the following manner.
- Oil from drive pump (14) flows through line (10) to passage (11) in the straight travel control valve. The drive pump oil separates into two flow paths. One path flows through center bypass passage (2) and into the left travel control valve. The other path flows through center bypass passage (3) and into the right travel control valve.
- Oil from idler pump (15) flows through line (9) to passage (8) in the straight travel control valve. The idler pump oil separates into two paths. One path flows through parallel feeder passage (1) and into the swing control valve, the stick I control valve and the boom II control valve. The other path flows through passage (17) and into parallel feeder passage (4). Oil flows from parallel feeder passage (4) into the attachment control valve, the bucket control valve and the boom I control valve. Part of the idler pump oil in passage (17) flows through orifice (19), check valve (16) and passage (18) to center bypass passage (2). The idler pump oil combines in center bypass passage (2) with the drive pump oil. This helps power the right travel motor and the left travel motor.