The EPTC II receives current through a fuse on the fuse block. This current is used to activate the solenoids. These solenoids control the option of converter drive or the option of direct drive. These solenoids also control the direction and the speed.
The Caterpillar Data Link is used to share information with other systems such as the Engine Electronic Control Module (Engine ECM) and the Vital Information Management System (VIMS). 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 | |
| Fifth | X | |
| Sixth | X | |
Neutral Start Control
The neutral start control ensures that the machine will start only in NEUTRAL. The EPTC II receives a signal from the shift lever switch. When the shift lever is in NEUTRAL, the signal is grounded and the machine will start. If the shift lever switch is not in NEUTRAL, 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 ON in order for the machine to start.
Neutral (Torque Converter Drive)
This machine has two neutral positions on the rotary actuator. Position NEUTRAL-1 on the rotary actuator has a detent position on the rotary selector spool. Position NEUTRAL-1 is NEUTRAL on the operator console. Position NEUTRAL-2 on the rotary actuator also has a detent position on the rotary selector spool.
Position NEUTRAL-2 on the rotary actuator does not have a position on the operator console. The operator does not have control over NEUTRAL-2. The rotary actuator and the rotary selector spool automatically go through NEUTRAL-2 on all shifts to NEUTRAL and from NEUTRAL.
When the transmission control is in NEUTRAL position, the rotor for the shift lever switch is in NEUTRAL-1 position. With the shift lever switch in this position, current flows from the EPTC II through the shift lever switch to machine ground. The EPTC II then activates the downshift solenoid. When the downshift solenoid activates, hydraulic oil pressure goes to the rotary actuator. This causes the rotary selector spool to turn.
The rotor on the transmission gear switch is connected to the rotary selector spool by a flexible coupling. When the rotor on the transmission gear switch is in the NEUTRAL-1 position current will flow from the EPTC II through the transmission gear switch to ground. This current flow is a signal to the EPTC II of a completed shift. Normally, the downshift solenoid would be deactivated. However, the EPTC II keeps the downshift solenoid activated in the NEUTRAL-1 position. This holds the rotary selector spool in NEUTRAL position.
First (Torque Converter Drive or Direct Drive)
When the transmission control is moved to FIRST position, the rotor for the transmission control moves to FIRST position. Current then flows from the EPTC II through the shift lever switch to machine ground. This signal informs the EPTC II that the shift lever switch is in FIRST position.
The rotor on the transmission gear switch is connected to the rotary selector spool by a flexible coupling. When the rotor on the transmission gear switch is in the FIRST position, current flows from the EPTC II through the transmission gear switch to ground. This signal informs the EPTC II 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 sensor transmits a signal to the EPTC II. This signal tells the EPTC II the ground speed of the machine. When the ground speed reaches approximately 6 km/h (4 mph), EPTC II sends current to the lockup clutch solenoid. When the lockup clutch solenoid activates, hydraulic oil pressure goes 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 a sufficient decrease in ground speed and the machine is still in FIRST, the EPTC II 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 control is moved to the FOURTH position, the rotor for the shift lever switch is moved to the FOURTH position. With the shift lever switch in this position, current flows from the EPTC II through the shift lever switch to machine ground.
EPTC II determines that FOURTH gear is needed. The rotary selector spool turns the rotor on the transmission gear switch as the transmission shifts through the gears. As the rotary selector spool turns, the rotor on the transmission gear switch is turned by a flexible coupling. When the rotor on the transmission gear switch is in the FOURTH position, current flows from the EPTC II through the transmission gear switch to machine ground. EPTC II 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 control is put in THIRD speed position, the rotor for the shift lever switch is turned to the THIRD speed position. Current goes from the EPTC II through the shift lever switch to machine ground. This current flow and a signal from the transmission speed sensor will inform the EPTC II that an upshift is needed. The upshift to THIRD speed position from SECOND speed position is automatic when the correct ground speed signal from the transmission speed sensor is sent to the EPTC II, and the transmission control is in THIRD speed position or above THIRD speed position.
The EPTC II 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, EPTC II sends a signal to the Engine ECM. The Engine ECM will decrease the engine speed during the upshift.
EPTC II sends current through the upshift solenoid to ground. When the upshift solenoid activates, hydraulic oil pressure goes to the rotary actuator which turns the rotary selector spool. The rotary selector spool turns the rotor on the transmission gear switch. When the alignment of the rotor on the transmission gear switch changes from SECOND speed position to THIRD speed position, current from the EPTC II will go through the transmission gear switch to ground. This new current flow tells EPTC II that the transmission is now in THIRD speed position.
EPTC II deactivates the upshift solenoid when the transmission gear switch and the ground speed is in the operating range for THIRD speed. EPTC II will then activate the lockup clutch solenoid. The lockup clutch solenoid will send hydraulic oil pressure to the lockup clutch. At the same time, EPTC II signals the Engine ECM to increase engine speed. The machine is now in direct drive THIRD speed.
Special Upshifts
The transmission switch will go through position NEUTRAL-2 when an upshift is performed from the NEUTRAL-1 position. This provides a delay that is needed by the hydraulics. The operator has no control over this occurrence.
During an upshift from NEUTRAL to REVERSE or from NEUTRAL to FIRST, no signal is sent to the lockup clutch solenoid. Both speeds are torque converter drive and the lockup clutch is not used.
An upshift from FIRST to SECOND is a typical automatic upshift.
Typical Automatic Downshift (FOURTH to THIRD)
When the transmission control is put in THIRD speed position, the rotor for the shift lever switch turns to the THIRD speed position. Current goes from the EPTC II through the shift lever switch to machine ground. This current flow and a signal from the transmission speed sensor will inform EPTC II that a downshift is needed. The downshift to THIRD speed position from FOURTH speed position is automatic when the correct ground speed signal from the transmission speed sensor is sent to the EPTC II.
The EPTC II 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 EPTC II sends a signal to the Engine ECM. The Engine ECM will increase the engine speed during the downshift.
The EPTC II sends current to the downshift solenoid. When the downshift solenoid activates, hydraulic oil pressure goes to the rotary actuator and the rotary selector spool turns. The rotary selector spool turns the rotor on the transmission gear switch. When the alignment of the rotor on the transmission gear switch changes from FOURTH speed position to THIRD speed position, current from the EPTC II will go through the transmission gear switch to ground. This new current flow tells EPTC II that the transmission is now in THIRD speed position.
The EPTC II deactivates the downshift solenoid when the transmission gear switch and the ground speed is in the operating range for THIRD speed. EPTC II 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 speed.
Special Downshifts
The transmission switch will go through position NEUTRAL-2 when a downshift is performed to the NEUTRAL-1 position. This provides a delay that is needed by the hydraulics. When a downshift from REVERSE to NEUTRAL occurs the delay is timed and slightly longer. The operator has no control over this occurrence.
During a downshift from REVERSE to NEUTRAL or from FIRST to NEUTRAL, no signal is sent to the lockup clutch solenoid. Both speeds are torque converter drive and the lockup clutch is not used.
A downshift from SECOND to FIRST is a typical automatic downshift.
Directional Shift Management
Directional shift management reduces torque spikes in the transmission driveline. Directional shift management 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 is greater than the levels of the torque converter stall. The EPTC II stops the pressure spikes by delaying the shift. The EPTC II then signals the Engine ECM for a reduction of fuel and for a lowering of the engine speed. The EPTC II then shifts to the requested gear. This reduces the stress on the driveline. This also prevents wear on the transmission and premature failures of the final drive or of the differential.
The event will be recorded as a improper shift.
Shift Inhibiting
If the transmission is in any forward speed and the transmission control is moved to REVERSE, 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 the NEUTRAL position.
Neutral Coasting
This function restricts the ability to coast into NEUTRAL from high speeds. This restriction extends the transmission life. The transmission speed sensor measures the rotation of the gear teeth on a gear that is fastened to the output shaft of the transmission. The EPTC II uses this measured speed in order to determine the ground speed. If the measured speed is greater than 5 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 mph and the transmission is in NEUTRAL, the event will be recorded in the EPTC II. Also, the Engine ECM will increase the engine speed to 1300 rpm. This will increase the flow of lubrication oil to the transmission.