Steel Track Machine|
The propulsion control system contains an electrical portion, a hydraulic portion, and a mechanical portion. The electrical portion is made up of electronic control modules (ECMs) and input and output devices. The hydraulic portion consists of two closed circuit hydrostatic drive loops. The mechanical portion is consists of a single speed planetary final drive. Each final drive drives each track.
In each hydrostatic drive loop, the ECMs on the machine control a variable displacement propulsion pump. This pump drives a two-speed propulsion motor. Each motor drives a single speed planetary final drive. The final drives transfer power from the propulsion 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. Oil from the auxiliary pump also shifts the two-speed motors. The ECMs on the machine control the engagement of the parking brake and the shifting of the machine.
The electronic control system monitors the machine and the electronic control system monitors engine operating conditions. The machine contains four control modules. The screed contains one control module. The engine contains one control module. The ECMs on the machine and on the screed communicate through the Cat Data Link. The ECMs on the machine and the engine ECM communicate through controller area network (CAN) lines, and as a backup, through the Cat Data Link.
The control system determines if an output signal should be sent to the pump electronic displacement controls (EDCs). During normal operation, the propulsion system is controlled through closed loop logic. The system prevents the machine from moving under the following conditions:
- The propulsion lever is out of the NEUTRAL position when the machine is started.
- The parking brake switch on either operator station is in the ON position.
- The propulsion lever is in the NEUTRAL position.
- The speed dial is in the minimum position, and the propulsion mode switch is in either the PAVE position or the TRAVEL position.
- The decelerator pedal is fully depressed.
- The parking brake solenoid has a short to battery fault.
- The machine is in a runaway condition or in a rollback condition.
The electronic control system is also programmed with load control logic. The load control logic automatically adjusts the propulsion speed in order to prevent the engine from stalling. At low idle, the electronic control system invokes load control logic when the engine speed falls below 950 rpm. At high idle, the electronic control system invokes load control logic when the engine speed falls below 1950 rpm.
Note: Information in some sections of this document shows a machine with the mobil-trac undercarriage. However, unless otherwise indicated, the information in those areas also apply to machines that have the steel track undercarriage.