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| Illustration 1 | g01094459 |
The traction control valve (1) (if equipped) is mounted to the bottom of the propel pump. The engine compartment provides access to this component.
The traction control valve prevents the tires from spinning during machine operation. The valve contains a relief valve and the solenoid for traction control (2). The solenoid is controlled by the traction control switch. The solenoid is energized when the switch is closed.
Forward Direction without Wheel Spin
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| Illustration 2 | g01094493 |
When the machine is traveling in the forward direction, pump supply oil enters the traction control valve through the P port. The traction control valve directs oil to the flushing spool, to the two relief valves, and to the spool for traction control. The spool creates a restriction to the flow, and pump supply pressure increases.
Pump supply pressure acts to open both relief valves. At each relief valve, the combined force from a spring and the pressure in the passage between the orifice and the solenoid for traction control act to close the relief valves. When the solenoid for traction control is de-energized, the force which acts to open each relief valve quickly becomes greater than the force which acts to close the relief valves. Under these conditions, the relief valves open, and oil flows to the right and left propel motors.
The downstream pressure in the right and left motor lines remains equal as long as the underfoot conditions at the right and the left wheels remain equal. In this case, the traction control valve directs fifty percent of the pump supply oil to each propel motor.
Forward Direction with Left Wheel Spin
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| Illustration 3 | g01094494 |
When underfoot conditions are not equal, the wheels on the side of the machine which encounters the least resistance start to spin. the above schematic illustrates the situation when the left side of the machine encounters the least resistance. Since resistance to flow in the left motor circuit is low, the pressure in that circuit drops.
In this case, the pressure which acts to open each relief valve remains constant, and both valves remain fully open. Under these conditions, most of the pump output or all of the pump output follows the path of least resistance. This path is through the left motor circuit. Since the left wheels are spinning, the machine will not move.
Forward Direction with Traction Control
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| Illustration 4 | g01095918 |
When the operator engages the traction control switch, the solenoid for traction control is energized. When this solenoid is energized, the spool for traction control blocks the return line. This action causes the pressure between the orifice and the solenoid for traction control to quickly equalize with pump supply pressure. In this case, both relief valves close. All pump supply flow is forced through the spool.
When the pressure in the right motor line becomes greater than the pressure in the left motor line, the spool moves. This movement restricts pump supply flow into the left motor circuit. The spool allows supply oil to flow into the right motor circuit. In this situation, the left wheels stop spinning, and power is sent through the right wheels.
Reverse
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| Illustration 5 | g01094504 |
During normal operation in reverse, the traction control valve functions as a combiner valve and the traction control valve continues to maintain the fifty percent split of flow between the propel motors on the right and left side of the machine. The return oil from each motor must flow through the orifices in the corresponding side of the spool. The orifices create back pressure at the outlets of the motors, which results in a slight braking effect on the motors. Because the orifices in both spools are of equal size, the resistance to flow through the motors is also equal.