DIRECT DRIVE
Shown is a sectional view of the torque converter lockup clutch valve in DIRECT DRIVE. Supply oil from the transmission charging pump is used to provide lockup clutch oil and has two functions:
1. Supply pressure is reduced to provide pilot pressure.
2. When the solenoid is energized, supply pressure is reduced by the modulation reduction valve to provide lockup clutch pressure.
The lockup solenoid has been energized and directs pump supply pressure to the relay valve. Before moving the selector piston, pilot oil moves a shuttle valve to the right which closes the drain and opens the check valve. Oil then flows to the selector piston. Moving the selector piston blocks the drain passage and the load piston springs are compressed.
• Lockup solenoid energized starts clutch modulation
valve spool down against the force of the inner spring. This initial
movement opens the supply passage (from the transmission charge pump) and permits pressure oil to flow to the clutch. As the clutch fills, pressure oil opens the ball check valve and fills the slug chamber at the top of the reduction valve spool. At the same time, oil flows through the load piston orifice and fills the chamber between the end of the load piston and the selector piston. The load piston orifice provides a pressure drop and time delay in the flow of oil to the load piston chamber. The load piston orifice helps control the rate of modulation. Filling the load piston chamber is made possible when the selector piston covers the drain passage at the decay orifice.
The load piston has now moved completely down against the stop. The modulation cycle is completed and the clutch pressure is at its maximum setting. Because this is a modulation reduction valve, the maximum pressure setting of the clutch is lower than the transmission charge pressure. At the end of the modulation cycle, the pressure in the slug chamber moves the reduction valve a small distance up to restrict the flow of supply oil to the clutch. This is the "metering position" of the
reduction valve spool. In this position, the valve maintains precise control of the clutch pressure.
Primary pressure is adjusted with shims in the load piston. Final lockup clutch pressure is not adjustable. If the primary pressure is correct and final lockup clutch pressure is low, the load piston should be checked to make sure that it moves freely in the selector piston. If the load piston moves freely, the load piston springs should be replaced.
• Lockup clutch at maximum pressure
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The transmission charging pump supplies oil to the transmission
hydraulic control valve and the shift solenoids through the inlet port (1).
Excess transmission charging oil either drops to the bottom of the housing to be scavenged or flows back to the torque converter housing through the outlet hose (2).
The torque converter lockup clutch solenoid (3) is energized by the EPTC II when DIRECT DRIVE (lockup clutch ENGAGED) is required.
Transmission charge pump supply oil flows through the small hose (4) to the lockup clutch control valve. The lockup clutch control valve then engages the lockup clutch.
The transmission charging pressure relief valve is part of the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission charging circuit. Transmission charging pressure can be measured at the tap (5).
1. Transmission
3. Torque converter lockup clutch solenoid
4. Lockup clutch pilot oil hose
5. Transmission charging pressure tap
1. Transmission clutch pressure taps
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3 2
1
Shown is the Individual Clutch Modulation (ICM) transmission hydraulic control valve. Transmission clutch pressures are measured at the pressure taps (1).
The transmission hydraulic control valve contains a priority valve. The priority valve controls the pressure that is directed to the selector pistons in each of the clutch stations. The transmission priority valve pressure has been increased from 1720 kPa (250 psi) to 2585 kPa (375 psi).
Increasing the priority valve pressure also increases the charging pressure available to the lockup clutch valve.
The "D" Station (2) is used to control the dual stage relief valve setting for the clutch supply pressure (shown on next slide).
The transmission lube pressure relief valve (3) limits the maximum pressure in the transmission lube circuit.
2. "D" Station controls dual stage relief valve
• Priority valve pressure increased
3. Transmission lube relief valve
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The transmission control group uses a dual stage relief valve for clutch supply pressure. At high idle in torque converter drive, transmission charging pressure should be 3065 kPa (445 psi) maximum. At low idle in torque converter drive, transmission charging pressure should be
2480 kPa (360 psi) minimum.
Shown is a sectional view of the ICM transmission hydraulic control valve group. The rotary selector spool is in a position that engages two clutches. Pump supply oil from the lockup solenoid flows to the selector piston in station "D." Station "D" reduces the pump supply pressure, and the reduced pressure flows to the lower end of the relief valve. Providing oil pressure to the lower end of the relief valve reduces the clutch supply pressure.
During torque converter lockup (DIRECT DRIVE), clutch supply pressure is reduced to extend the life of the transmission clutch seals.
At high idle in direct drive, clutch supply pressure should be 1620 + 240 - 100 kPa (235 + 35 - 15 psi). The corresponding
transmission charge pressure is reduced to 2205 ± 70 kPa (320 ± 10 psi).
• Dual stage relief valve
1. Transmission lube supply hose
104 3 1
2
Oil flows from the transmission lube section of the torque converter and transmission pump to the transfer gears through a hose (1). Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components.
The transmission lube oil temperature sensor (2) provides an input signal to the VIMS which informs the operator of the temperature of the
transmission lube oil.
The transmission lube pressure relief valve is in the transmission case near the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission lube circuit. Transmission lube oil pressure can be measured at the tap (3).
At HIGH IDLE, the transmission lube pressure should be 110 to 207 kPa (16 to 30 psi). At LOW IDLE, the transmission lube pressure should be 5 to 65 kPa (.5 to 10 psi).
2. Transmission lube oil temperature sensor
3. Transmission lube oil pressure tap
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• Torque converter/
transmission hydraulic system
• Four section pump:
1. Transmission scavenge
2. Torque converter charging
3. Transmission charging
4. Transmission lube
SUCTION
Shown is the torque converter and transmission hydraulic system. A four section torque converter and transmission pump is located at the rear of the torque converter. The four sections (from front to rear) are:
1. Transmission scavenge 2. Torque converter charging 3. Transmission charging 4. Transmission lube
The transmission scavenge pump pulls oil through the magnetic screens located at the bottom of the transmission. The scavenged oil from the transmission is transferred into the torque converter housing through the transmission oil return screen.
The three rear sections of the torque converter and transmission pump pull oil from the torque converter housing sump. Most of the required oil supply is pulled directly from the torque converter and transmission oil cooler return oil. The remaining required oil supply is drawn through a suction screen located in the bottom of the torque converter housing.
charging section transmission pump flows through the torque converter charging filter to the inlet relief valve mounted on the torque converter. The inlet relief valve limits the maximum pressure of the supply oil to the torque converter.
Torque converter charging oil either drops to the bottom of the housing or flows through the torque converter outlet relief valve. The outlet relief valve limits the pressure inside the torque converter.
Most of the oil from the torque converter outlet relief valve flows through the torque converter outlet screen to the torque converter and transmission oil cooler located on the right side of the engine. Oil from the torque converter and transmission oil cooler returns to the torque converter housing.
Oil from the transmission charging section of the torque converter and transmission pump flows through the transmission charging filter. From the filter, transmission charging oil flows in two directions:
- Transmission charging oil flows to the torque converter lockup clutch valve located on top of the torque converter.
- Transmission charging oil also flows to the transmission control valves located on top of the transmission.
Excess transmission charging oil to the transmission control valves either drops to the bottom of the housing to be scavenged or flows back to the torque converter housing.
When the torque converter lockup clutch solenoid is energized, pump supply oil flows to the lockup clutch control valve. The lockup clutch control valve then engages the lockup clutch.
Oil flows from the transmission lube section of the torque converter and transmission pump to the transfer gears. Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components.
• Transmission charging section
• Transmission lube section
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• EPTC II shifts the transmission
A10 A21 A22 A23 A24 A25
TOS
TRANSMISSION
A26 A3 A4 A5
EPTC II
A - 37 PIN CONNECTOR
B - 10 PIN SURE-SEAL CONNECTOR A9
Electronically Programmable Transmission Control (EPTC II) The purpose of the EPTC II is to determine the desired transmission gear and energize solenoids to shift the transmission up or down as required based on information from both the operator and machine.
The EPTC II receives information from various input components such as the shift lever switch, Transmission Output Speed (TOS) sensor,
transmission gear switch and the hoist lever switch.
Based on the input information, the EPTC II determines whether the transmission should upshift, downshift, engage the lockup clutch or limit the transmission gear. These actions are accomplished by sending signals to various output components.
• Shifts controlled by electrical signals
the back-up alarm and others.
The EPTC II also provides the service technician with enhanced
diagnostic capabilities through the use of onboard memory, which stores possible diagnostic codes for retrieval at the time of service.
With the use of a set of service switches, the service technician can access the different modes to gather the stored diagnostic codes or set the
adjustable transmission gear limit functions.
Input and output components on the block diagram are accompanied with a letter and number. The letter A corresponds with the 37 pin connector and the letter B corresponds with the 10 pin Sure-Seal connector that are attached to the transmission control. The numbers next to the letters correspond to the pin numbers in the connector. For example, the shift lever switch is connected to the transmission control through six wires in the 37 pin connector at pin locations 11 through 16.
The Advanced Diesel Engine Management (ADEM II) engine control, the Automatic Retarder Control (ARC), the Vital Information Management System (VIMS) and the EPTC II all communicate with each other through the CAT Data Link. Communication between the electronic controls allows the sensors of each system to be shared. Many additional benefits are provided, such as Controlled Throttle Shifting (CTS). CTS occurs when the EPTC II tells the engine ECM to reduce engine fuel during a shift to lower stress to the power train.
The EPTC II is also used to control the hoist system on the 793C. Several changes have been made to the input and output signals through the EPTC II 37 pin CE connector. The changes are:
1. The bed raise switch has been eliminated and an input signal is no longer transmitted through Pin 7.
2. A Pulse Width Modulation (PWM) type position sensor provides the hoist lever input signal to Pin 28.
3. A raise solenoid output signal has been added to Pin 31. The output is a ground signal to a relay which sends +24 Volts to the raise solenoid.
4. A float solenoid output signal has been added to Pin 32. The output is a ground signal to a relay which sends +24 Volts to the float solenoid.
5. A power down solenoid output signal has been added to Pin 33.
The output is a ground signal to a relay which sends +24 Volts to the power down solenoid.
• Benefits of electronic communication
• EPTC II used to control hoist system
• EPTC II connectors and pin numbers
• Transmission electronic control
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Shown is the Electronic Programmable Transmission Control (EPTC II).
The EPTC II is located to the right of the operator’s seat in the center console. The control contains a diagnostic window with 12 Light Emitting Diodes (LED’s) and a three digit numeric display.
The service switches (arrow) are used to interrogate the EPTC II for stored diagnostic information, event information and to program the transmission top gear limit functions. The switches are labeled with an
"S" for "SET" and a "C" for "CLEAR."
The DIAGNOSTIC MODE of the Electronic Control is changed by DEPRESSING and HOLDING both service switches (SET and CLEAR).
When the desired mode is shown on the display, the switches can be released. By following the instructions in the Service Manual, the serviceman can determine if the transmission electronic control system is operating correctly.
• Service switches (arrow)
• Diagnostic modes changed with service switches
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