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| Illustration 1 | g01228964 |
The propel control system contains an electrical portion, a hydraulic portion, and a mechanical portion. The electrical portion is made up of electronic control modules (ECM's) and input and output devices. The hydraulic portion consists of a closed circuit hydrostatic drive loop. The mechanical portion is consists of a single speed, planetary final drive that drives each track.
In the hydrostatic drive loop, the machine ECM controls a variable displacement propel pump. This pump drives four, two-speed hydraulic motors. Each motor drives a single speed, planetary final drive. The final drives transfer power from the propel motors to the tracks. The planetary final drives have spring-applied, hydraulically released parking brakes. The auxiliary hydraulic pump supplies oil pressure which releases the brakes.
The electronic control system monitors the machine and the engine operating conditions. The machine ECM and the engine ECM communicate through the Cat Data Link. The control system determines if an output signal should be sent to the pump electronic displacement controls (EDC's). The propel system is controlled through open loop logic.
The system prevents the machine from moving under the following conditions:
- The propel lever is out of the NEUTRAL position when the machine is started.
- The parking brake switch is in the ON position.
- The propel lever is in the NEUTRAL position.
The electronic control system is also programmed with load control logic. The electronic control system automatically adjusts the propel speed in order to maintain an optimum engine speed.