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| Illustration 1 | g01165088 |
Schematic for the Power Train/Chassis Electronic Control Module | |
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| Illustration 2 | g01154121 |
Electronic Control Module (Power Train/Chassis) | |
The Power Train/Chassis Electronic Control Module (ECM) is the main component in the power train electrical system. The Power Train/Chassis ECM is located behind the cover at the front of the cab. The Power Train/Chassis ECM has several input signals and output signals. Refer to Illustration 1 for the input components and for the output components.
The Power Train/Chassis ECM receives current through a circuit breaker on the dash panel. This current is used to activate the upshift solenoid, the downshift solenoid, and the lockup clutch solenoid. These solenoids control the option of torque converter drive or the option of direct drive. These solenoids also control the direction and the speed. The Power Train/Chassis ECM also controls the electrical system for the hoist, the retarder, and the parking brake.
The CAT data link is used to share information with other systems such as the Engine Electronic Control Module (ECM), and the Caterpillar Monitoring System. Signals that are sent to the Engine ECM result in reduced engine speed during upshifts and increased engine speed during downshifts.
System Operation
| Operation of the Torque Converter for Transmission Speed | ||
| Transmission Speed | Torque Converter Drive | Direct Drive with an Engaged Lockup Clutch |
| Reverse | X | |
| Neutral | X | |
| First | X | X |
| Second | X | |
| Third | X | |
| Fourth | X | |
Neutral Start Control
The neutral start control ensures that the machine will only start in neutral. The Power Train/Chassis ECM receives a signal from the shift lever position sensor. When the shift lever is in the NEUTRAL position, the signal is grounded and the machine will start. If the shift lever switch is not in the NEUTRAL position, the ground is broken and the machine will not start. This will prevent the machine from being started in a gear.
Note: The parking brake must also be engaged in order for the machine to start.
Neutral (Torque Converter Drive)
When the transmission shift lever is in the NEUTRAL position, the shift lever position sensor is in the NEUTRAL position. With the shift lever position sensor in this position, current flows from the Power Train/Chassis ECM through the shift lever position sensor to machine ground. The Power Train/Chassis ECM then activates the downshift solenoid. When the downshift solenoid activates, hydraulic oil flows to the shift cylinder, this causes the shift cylinder to move. The shift cylinder is connected by linkages to the speed selector spool and the direction selector spool.
The shaft on the transmission gear position sensor is connected to the shift cylinder by linkages and gears. When the transmission gear position sensor is in the NEUTRAL position, current will flow from the Power Train/Chassis ECM through the transmission gear position sensor to ground. This current flow is a signal to the Power Train/Chassis ECM of a completed shift. The downshift solenoid will now be deactivated.
First (Torque Converter or Direct Drive)
When the transmission shift lever is moved to FIRST position, the shift lever position sensor moves to FIRST position. Current then flows from the Power Train/Chassis ECM through the shift lever position sensor to machine ground. This signal informs the Power Train/Chassis ECM that the shift lever position sensor is in FIRST position.
The Power Train/Chassis ECM sends current to the upshift solenoid. When the upshift solenoid activates, hydraulic oil flows to the transmission shift cylinder. This causes the transmission shift cylinder to move the speed selector spool and direction selector spool to the FIRST position.
The shaft on the transmission gear position sensor is connected to the transmission hydraulic control. When the transmission gear position sensor is in the FIRST position, current flows from the Power Train/Chassis ECM through the transmission gear position sensor to ground. This signal informs the Power Train/Chassis ECM that the shift is complete. The machine is now in first gear and the machine is in torque converter drive.
First gear is converter drive at lower ground speeds. First gear is direct drive at higher ground speeds. The transmission speed sensors transmit a signal to the Power Train/Chassis ECM. This signal tells the Power Train/Chassis ECM the ground speed of the machine. When the ground speed reaches approximately 6 km/h (4 mph), the Power Train/Chassis ECM sends current to the lockup clutch solenoid. When the lockup clutch solenoid activates, hydraulic oil flows to the lockup clutch. The machine is in first gear and the machine is in direct drive.
The lockup clutch will stay activated until there is an upshift, a downshift, or a decrease in ground speed. If there is sufficient decrease in ground speed and the machine is still in first gear, the Power Train/Chassis ECM will stop current to the lockup clutch solenoid. The lockup clutch solenoid will deactivate. Hydraulic oil pressure to the lockup clutch will stop and the machine will return to torque converter drive.
Fourth (Direct Drive)
When the transmission shift lever is moved to the FOURTH position, the shift lever position sensor is moved to the FOURTH position. With the shift lever position sensor in this position, current flows from the Power Train/Chassis ECM through the shift lever position sensor to machine ground.
The Power Train/Chassis ECM determines that fourth gear is needed. The shift cylinder moves the transmission gear position sensor as the transmission shifts through the gears. As the transmission hydraulic control moves, the transmission gear position sensor is turned. When the transmission gear position sensor is in the FOURTH position, current flows from the Power Train/Chassis ECM through the transmission gear position sensor to machine ground. The Power Train/Chassis ECM determines that the shift is complete. The machine is now in fourth gear and the machine is in direct drive.
Shifting Procedures
The following sections will explain the operations of automatic upshifts and downshifts. Except for different electrical wires that must be grounded or activated, the shifting sequence is basically identical for all speeds.
Typical Automatic Upshift (Second to Third)
When the transmission shift lever is moved to the THIRD position, the shift lever position sensor is moved to the THIRD position. Current goes from the Power Train/Chassis ECM through the shift lever position sensor to machine ground. This current flow and a signal from the transmission speed sensors will inform the Power Train/Chassis ECM that an upshift is needed. The upshift to THIRD position from SECOND position is automatic when the correct ground speed signal from the transmission speed sensors is sent to the Power Train/Chassis ECM, and the transmission shift lever is in THIRD position or above.
The Power Train/Chassis ECM stops current flow to the lockup clutch solenoid when a shift is necessary. The lockup clutch solenoid deactivates. Hydraulic oil to the lockup clutch stops and the machine is in torque converter drive for a moment. At the same time, the Power Train/Chassis ECM sends a signal to the Engine ECM. The Engine ECM will decrease the engine speed during the upshift.
The Power Train/Chassis ECM sends current through the upshift solenoid to ground. When the upshift solenoid activates, hydraulic oil pressure goes to the shift cylinder which moves the speed selector spool. The movement of the shift cylinder also turns the shaft on the transmission gear position sensor. When the alignment of the transmission gear position sensor changes from SECOND position to THIRD position, current from the Power Train/Chassis ECM will go through the transmission gear position sensor to ground. This new current flow tells the Power Train/Chassis ECM that the transmission is now in third gear.
The Power Train/Chassis ECM deactivates the upshift solenoid when the transmission gear position sensor and the ground speed is in the operating range for third gear. The Power Train/Chassis ECM will then activate the lockup clutch solenoid. The lockup clutch solenoid will send hydraulic oil pressure to the lockup clutch. At the same time, the Power Train/Chassis ECM signals the Engine ECM to increase engine speed. The machine is now in direct drive third gear.
Typical Automatic Downshift (Fourth to Third)
When the transmission shift lever is moved to the THIRD position, the shift lever position sensor turns to the THIRD position. Current goes from the Power Train/Chassis ECM through the shift lever position sensor to machine ground. This current flow and a signal from the transmission speed sensors will inform the Power Train/Chassis ECM that a downshift is needed. The downshift to THIRD position from FOURTH position is automatic when the correct ground speed signal from the transmission speed sensors is sent to the Power Train/Chassis ECM.
The Power Train/Chassis ECM stops current flow to the lockup clutch solenoid when a shift is necessary. The lockup clutch solenoid deactivates. Hydraulic oil to the lockup clutch stops and the machine is in torque converter drive for a moment. At the same time, the Power Train/Chassis ECM sends a signal to the Engine ECM. The Engine ECM will increase the engine speed during the downshift.
The Power Train/Chassis ECM sends current to the downshift solenoid. When the downshift solenoid activates, hydraulic oil flows to the shift cylinder and the speed selector spool moves. The movement of the shift cylinder moves the shaft on the transmission gear position sensor. When the alignment of the transmission gear position sensor changes from FOURTH position to THIRD position, current from the Power Train/Chassis ECM will go through the transmission gear position sensor to ground. This new current flow tells the Power Train/Chassis ECM that the transmission is now in third gear.
The Power Train/Chassis ECM deactivates the downshift solenoid when the transmission gear position sensor and the ground speed is in the operating range for third gear. The Power Train/Chassis ECM will then activate the lockup clutch solenoid. The lockup clutch solenoid will send hydraulic oil pressure to the lockup clutch. The machine is now in direct drive third gear.
Directional Shift Management
Directional shift management reduces torque spikes in the transmission driveline and reduces the energy spikes of the transmission clutch. The transmission driveline is designed to withstand the torque converter stall. The torque converter stall is the maximum amount of torque that is sent to the transmission by the torque converter.
If the engine speed is above 1350 rpm and the operator shifts into the NEUTRAL position, through the NEUTRAL position, or out of the NEUTRAL position, spikes will be generated in the torque converter. The pressure of the spikes could be greater than the levels of the torque converter stall. The Power Train/Chassis ECM stops the pressure spikes by delaying the shift. The Power Train/Chassis ECM then signals the Engine ECM for a reduction of fuel and for a lowering of the engine speed. The Power Train/Chassis ECM then shifts to the requested gear. This reduces the stress on the driveline.
Note: The event will be recorded as an improper shift.
Shift Inhibiting
If the transmission is in any forward speed and the transmission shift lever is moved to the REVERSE position, the transmission will downshift to neutral as the ground speed decreases. When the ground speed decreases to approximately 5 km/h (3 mph), the transmission will make a shift into reverse from neutral.
Neutral Coasting
This function restricts the ability to coast into neutral from high speeds. This restriction extends the transmission life. The transmission speed sensors measure the rotation of the gear teeth on a gear that is fastened to the output shaft of the transmission. The Power Train/Chassis ECM uses this measured speed in order to determine the ground speed. If the measured speed is greater than 5 km/h (3 mph), the transmission will not shift into neutral.
Note: The operator can bypass the restriction against coasting into neutral. However, if the ground speed is greater than 12 km/h (7.5 mph) for more than 2.5 seconds, the event will be recorded in the Power Train/Chassis ECM. The Power Train/Chassis ECM will apply the retarder brakes in order to reduce the ground speed of the machine. Also, the Power Train/Chassis ECM will send a signal to the Engine ECM to increase the engine speed to 1350 rpm. This will increase the flow of lubrication oil to the transmission.