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| Illustration 1 | g01250814 |
Basic diagram for the power train system | |
Brief Summary of Operation
- The transmission speed sensor magnetically measures the transmission speed.
- The control for the electronic programmable transmission determines the proper moment for shifting by using the signals from the transmission speed sensor and the shift lever switch. The electronic programmable transmission activates the solenoids in order to make shifts.
- The Cat data link connects the Chassis Electronic Control Module (Chassis ECM) with automatic electronic traction aid and the Monitoring System so the input from the transmission speed sensor can be shared.
- The body raise switch prevents any reverse operation of the transmission during the raise operation of the body. The hoist control position sensor also prevents any reverse operation of the transmission during the lowering operation of the body. The body up sensor will signal the limiting function on the gears. This limits the speed of the machine while the body is up.
- The switch for the parking and secondary brake and the retarder and service brake switch send input signals to the Chassis ECM. When the secondary parking brake switch or the retarder and service brake switch are activated, the anti-hunt timer is deactivated. When the service brake and the retarder switch is activated, the Chassis ECM will allow rapid speed shifts.
- The shift lever switch selects desired speed and direction.
- The Chassis ECM will energize pairs of solenoids on the clutch modulating valves for the transmission. This sequence causes the correct pair of clutches to be engaged for the next desired speed.
- The transmission hydraulic control will individually control the maximum pressure in each clutch. The transmission hydraulic control will individually modulate each clutch in order to control the fill time and the release time.
- When the modulating valve for the torque converter lockup clutch is activated, pressure oil is sent to the torque converter lockup clutch. This oil engages the lockup clutch of the torque converter for direct drive.
- The Chassis ECM uses the Caterpillar Data Link to communicate with the Monitoring System. The Monitoring System informs the operator of the transmission gear that is actually engaged.
General Description
Note: For additional information on the electrical system, refer to Service Manual, " 773F, 775F, and 777F Power Train ECM".
The power train consists of four basic systems. The following systems are the four basic systems:
- Chassis Electronic Control Module (Chassis ECM)
- Torque Converter
- Transfer Gears and Transmission
- Differential and Final Drives
The four basic systems are connected by an electrical connection, a hydraulic connection, a magnetic connection, or a mechanical connection.
The operation of the power train begins at the Chassis Electronic Control Module (Chassis ECM). The Chassis ECM receives the information of the selected operating speed from the shift lever switch in the electrical system. The Chassis ECM uses the information from the switches and the sensors in the electrical system to control the hydraulic system of the torque converter and transmission. This is done by energizing the appropriate solenoids on the modulating valves for the transmission clutches.
These modulating valves for the transmission clutches engage the correct transmission clutches. This mechanically connects the transmission input shaft to the output shaft and to the differential. The transmission will not drive the output shaft unless there is power flow through the torque converter. The power flow can be hydraulic or mechanical.
The torque converter drives the transmission hydraulically, unless the lockup clutch is activated. When the modulating valve for the torque converter lockup clutch is activated, the lockup clutch is hydraulically engaged. The rotating housing of the torque converter is mechanically connected to the output shaft of the torque converter. The drive shaft mechanically connects the torque converter to the transfer gears. The transfer gears are mechanically fastened directly to the transmission.
After the transmission and the torque converter are connected, power is supplied from the engine to the differential through the torque converter, the transfer gears, and the transmission. The rear axles mechanically connect the differential to the final drives. With the rotation of the transmission output shaft, the transmission speed sensor electrically signals the transmission control that the machine has moved.
Neutral Coasting
This function restricts coasting into NEUTRAL from high speeds. This restriction extends the life of the transmission. The transmission speed sensor measures the rotation of the gear teeth on a gear that is fastened to the transmission output shaft. The Chassis ECM uses the input signal from the transmission speed sensor to determine the ground speed. If the measured speed is greater than 8 km/h (5 mph), the transmission will not shift into NEUTRAL.
Note: The operator can bypass the restriction against neutral coasting. However, if the ground speed is greater than 16 km/h (10 mph) and the transmission is in NEUTRAL, the event will be recorded in the Monitoring System.