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| Illustration 1 | g00799217 |
725 and 730 machines Diagram of the Transmission/Chassis ECM | |
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| Illustration 2 | g00794557 |
735 machines Diagram of the Transmission/Chassis ECM | |
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| Illustration 3 | g00830644 |
740 machines Diagram of the Transmission/Chassis ECM | |
The transmission/chassis ECM electronically controls the following functions.
- Backup Alarm
- Transmission Shift Points
- Cross Axle Differential Lock
- Interaxle Differential lock
- Secondary Steering
- Neutral Start Function
- Parking Brake
- Hoist System (AXM)
- Ejector System (AZZ)
Not all of the components in the diagram are required during basic machine operation.
Overview
The ECM controls different systems on the machine. The following information is an overview of the systems that are controlled by the ECM.
The ECM controls the transmission shift points. The basic components and corresponding requirements for shifting of the transmission are listed below:
Harness Code - The harness code is from the monitoring system. The strategy for shifting is different on the distinct machine models. The ECM must know the model that the system is on in order to operate correctly. This information is provided to the ECM by the status of the inputs to the monitoring panel. The permanent connections in the machine harness provide this information.
Shift Lever Sensor - The ECM must know the current gear position. The sensor for the shift lever provides a PWM signal. The PWM signal varies with the gear that has been selected.
Transmission Output Speed Sensor (TOS) - The ECM must know the output speed of the transmission. One TOS tells the ECM the speed of the transmission output shaft. The TOS provides this information.
When the operator selects a forward gear the ECM automatically shifts the transmission. The shift is dictated by the transmission output speed. The automatic shift points are stored in the ECM. A shift occurs when the transmission output speed matches the shift point. When the TOS increases to a shift point the ECM activates the proper solenoids in order to change the transmission gear.
Note: The transmission output speed is directly proportional to ground speed and engine speed. This occurs while the transmission is in direct drive. Shift points are based on the calculated engine speed.
The items that follow are exceptions.
- When a shift from a forward gear or a shift from a reverse gear to "NEUTRAL" is made and the machine is moving faster than 8 km/h (5 mph), the ECM will not shift the transmission into neutral until the ground speed is less than 8 km/h (5 mph). This discourages coasting in neutral at high speed, which reduces transmission life. For more information, see the topic in System Operation, "Neutral Coast Function".
- The reverse gear is not engaged until ground speed is less than 4.8 km/h (3 mph). This helps protect the transmission from damaging directional shifts. For additional information, see Systems Operation, "Reverse Shift Inhibit Function".
- The ECM does not downshift when the operator selects a speed that is not appropriate for the current TOS. Automatic upshifting and/or downshifting will continue. The selected gear now becomes the new top gear.
- The ECM shifts the transmission up one gear above the selected gear if the TOS reaches a critical value. This helps protect the engine from overspeed. If the transmission is already in top gear, the lockup clutch is deactivated.
The ECM is designed to regulate the position of the hoist. The ECM energizes the solenoids that are used to control the raising and lowering of the body. This is done with information from both the operator and the machine.
The ECM uses the primary steering pressure status and other inputs from the machine in order to control the secondary steering system.
The ECM controls the interaxle differential locks and the cross axle differential locks. This system is used in order to provide improved traction in some operating conditions.
The ECM controls the parking brake system. This system is used in order to keep the stationary machine from moving.
The ECM controls the neutral start function. This function is used in order to activate the starter. The starter will activate when certain machine conditions have been met.
For the 725 and 730 machines, the ECM controls the retarder. The retarder is used to slow the machine.
The ECM determines if the backup alarm should sound.
The ECM also provides the service technician with enhanced diagnostic capabilities. This is available through the use of onboard memory. Onboard memory stores the possible diagnostic codes for retrieval at the time of service. Service personnel should use the Electronic Technician for troubleshooting.
The following modules communicate with each other through the CAT Data Link: the engine electronic control module, the transmission/chassis ECM and the Caterpillar monitoring system. Communication between the electronic controls allows the sensors of each system to share information.