XIX. Crawler Motor and Final Drive
(continued)
63
In an overrunning situation (e.g. descending a slope), while the motor overruns fluid from the control valve, the
counterbalance valve senses the pressure drop across the motor and begins to shift back to neutral, thereby
throttling the return flow of the motor. This creates a back pressure that prevents the motor from overspeeding. The
case drain port allows motor case fluid to return to the reservoir.
Final Drive
The final drive gear reducer is a three-stage planetary gearbox that runs in a fluid bath for lubrication. The final
drive hub rides on bearings on the spindle, and contains the gear sets. The input drive from the motor passes
through the motor spindle into the gear sets via a sun gear. The input torque is stepped up through all three gear
sets (rotation speed is stepped down). Drive torque is transmitted to the outer hub of the final drive. As the sprocket
and attached hub turn, the sprocket teeth engage the track chain, moving the machine.
Using the spindle, the final drive assembly is mounted to the undercarriage side frame with bolts. The motor, brakes,
and all hydraulics are contained within the spindle. The gear sets and hub are also attached to the spindle.
FIGURE 69
FINAL DRIVE
Final Drive
Crawler Motor
XL 4200/XL 5200 HYDRAULIC SYSTEM OPERATIONS MANUAL
Form No. 29704
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