Straight travel (tracking) can be maintained even during swing or implement operation.
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| Illustration 1 | g06616750 |
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Main control valve (1) Straight travel solenoid | |
The main control valve is equipped with a straight travel control valve that maintains straight travel even during swing or implement operation. The straight travel control valve is especially useful for pipelayer control, placement of timbers or any other material handling application.
When the machine travels without swing motor or implement use, the only demand for oil is from the travel motors. Pump 1 propels the right travel motor and pump 2 propels the left travel motor. Because both travel circuits are separate, the machine continues to travel straight, unless a difference in travel resistance occurs between the right and left tracks.
Pump 1 and pump 2 are used for the travel motors, but the pumps also supply oil for swing and implement usage. During travel, if an implement is used or a swing occurs the oil supply to each travel motor will differ. This action 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 straight travel system ensures the straight travel of the machine when other circuits are operated during travel.
The straight travel control valve is activated by the machine Electronic Control Module (ECM). The ECM uses input data from the sensors to determine when to activate the valve.
The following actions occur when the straight travel control valve is activated.
- Pump 2 provides the flow for both travel motors.
- Pump 1 provides most of the flow for the swing motor and the implements.
- Residual flow from pump 2 is mixed into the same circuit as pump 1 to aid the implements.
Forward Travel - Straight Travel Control Deactivated
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| Illustration 2 | g06313174 |
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Straight travel control valve (NEUTRAL position) (1) Straight travel solenoid (2) Right travel reverse solenoid (3) Right travel forward solenoid (4) Right travel control valve (5) Main relief valve (6) Straight travel control valve (7) Parallel feeder passage (8) Return passage (9) Parallel feeder passage (10) Left travel control valve (11) Pump 1 (12) Pump 2 (13) Left travel reverse solenoid (14) Left travel forward solenoid | |
When only the travel levers/pedals are activated, straight travel solenoid (1) is not energized. Pilot oil flow is blocked at the straight travel solenoid so the control valve remains stationary in the neutral position. The oil from pump 1 (11) and pump 2 (12) flows in the following manner.
- Pump 1 oil enters the main control valve at port "P1" and splits into different directions. In one direction the oil flows to main relief valve (5). In the other direction the oil flows to parallel feeder passage (7) where the oil flows to the boom, bucket, and stick 2 control valves for use. The oil also flows into straight travel control valve (6) to two ports at right travel control valve (4). One of the passages is blocked, but oil flows through the open passage to the right travel motor for forward travel.
- Pump 2 oil enters the main control valve directly at port "P2". The oil flows up to main relief valve (5). The oil also flows to straight travel control valve (6). The oil flows through the valve and down to parallel feeder passage (9). The parallel feeder supplies oil to the swing, boom 2, auxiliary, and stick 1 control valves for use. Oil also flows to two ports at left travel control valve (10). One of the passages is blocked, but oil flows through the open passage to the left travel motor for forward travel.
Forward Travel - Straight Travel Control Activated
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| Illustration 3 | g06313234 |
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Straight travel control valve (activated position) (1) Straight travel solenoid (2) Right travel reverse solenoid (3) Right travel forward solenoid (4) Right travel control valve (5) Main relief valve (6) Straight travel control valve (7) Parallel feeder passage (8) Return passage (9) Parallel feeder passage (10) Left travel control valve (11) Pump 1 (12) Pump 2 (13) Left travel reverse solenoid (14) Left travel forward solenoid | |
When the travel levers/pedals are activated at the same time as either one of the joysticks, the machine ECM energizes straight travel solenoid (1). The pilot oil flows through the straight travel solenoid to straight travel control valve (6). The pilot oil enters the spring chamber and pushes the control valve spool upward. The change in position of the spool changes pump oil flow in the following manner.
- Flow from pump 2 (12) is now blocked from flowing into parallel feeder passage (9) by the shifted straight travel control valve. Instead, pump 2 supply oil is directed to right travel control valve (4) by the straight travel control valve. Oil flows through the right travel control valve to the right travel motor. Pump 2 always has a path to supply oil to left travel control valve (10) and oil flows through the control valve to the left travel motor. Both travel motors are now supplied by pump 2 and create equal flow and thus equal speed at each motor. When pressure from pump 2 exceeds pressure in the pump 1 circuit, residual oil flow from pump 2 will flow into the pump 1 circuit through the orifice and check valve in the straight travel control valve. This provides supplemental oil to the implements.
- With straight travel control valve (6) shifted, oil from pump 1 now flows into parallel feeder passage (9). The oil in passage (9) supplies oil to the swing motor and the implements.