The torque divider is also equipped with a freewheel stator. The stator is splined to a cam which rotates around the stationary carrier in only one direction. Machined into the cam are tapered openings, each of which contain a roller and a spring. Spring force holds the roller against the taper and the carrier. This restricts the cam from turning.
When the machine is under a load, and the impeller and turbine are rotating at different speeds, the stator is held stationary by the rollers being wedged in the taper of the openings by spring force. This mechanical connection keeps the stator stationary and allows oil flow to be directed back to the impeller, multiplying the torque.
During all load conditions, the torque converter provides 70% of the output, and the planetary gear set provides the remaining 30% of the output.
When the machine speed increases with no load, the speed of the turbine and impeller increases.
During this condition the stator does not need to redirect oil back to the impeller. The stator begins to turn in the same direction as the impeller and the turbine. This moves the rollers from the tapered openings against spring pressure. The mechanical connection between the cam and the stationary carrier is broken. The stator, turning freely with the turbine and impeller, will reduce the turbulence of the oil in the torque converter. The lack of turbulence in the torque converter permits the engine to work easier, reducing fuel consumption and minimizing heat build-up in the power train oil system.
When the machine is in a downhill situation and engine overspeed occurs, the Power Train ECM will automatically apply the service brakes, up to 8% of brake capacity, in an effort to slow the machine. If this strategy does not slow the engine enough, Advisor will warn the operator to change the mode of operation (down shift or apply the service brakes) to further slow the machine.
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The illustration above shows the dual purpose housing which contains the torque converter inlet relief valve manifold and the lube distribution manifold. This dual purpose housing is located at the left front of the main case.
The torque converter inlet relief valve is a check valve (not visible above) that is pressed into a port on the front of the main case (see illustration 69). Torque converter oil enters the manifold from the back side, through a hard tube inside the main case. The torque converter oil exits the manifold (after the torque converter inlet relief valve) through the lower port (2). The torque converter oil is then directed to the torque converter inlet port, at the rear of the torque divider housing.
The lube distribution manifold inlet (1) is the upper port on the dual purpose manifold body. Oil from the power train oil cooler is directed to the lube distribution manifold through the hose (3) connected to the upper port. The lube oil is then distributed to the brakes, the transmission, and the bevel gears through hard steel tubes inside the main case.
The uppermost hose (4) is the connection between the main case sump and the power train oil high-speed oil change coupling, located in the left side engine compartment.
2
3 1
4
69
The torque converter inlet relief valve protects the components in the torque converter by limiting the maximum oil pressure to the torque converter. The torque converter inlet relief valve protects the torque converter when the engine is started and the oil is cold.
Oil from the torque converter charge section of the power train oil pump is directed to the priority valve. From the priority valve, the torque converter oil is then directed to a passage at the front of the main case through a hard steel tube inside the case.
The dual purpose manifold is installed on the front of the main case and directs the torque converter oil to the torque converter inlet relief valve through an internal passage in the manifold. The manifold also directs the torque converter oil to the torque converter through a hose connected to the front of the manifold.
Torque converter oil pressure acts against the top of the poppet in the inlet relief valve. When the pressure acting against the top of the poppet overcomes the force of the spring, the poppet opens (down) and dumps the excess oil back into the main case, limiting the pressure in the torque converter circuit.
The torque converter inlet relief valve is not adjustable.
To Main Sump
Torque Converter Inlet Relief Valve
Front of Main Case Bottom of
Main Case From Priority Valve
70
The torque converter outlet relief valve (1) is installed at the right rear of the torque divider housing.
Torque converter oil exiting the torque converter enters the torque converter outlet relief valve from the back side of the valve body (1). The oil then exits the outlet relief valve and is directed to the power train oil cooler through the upper steel tube (2). After the oil passes through the oil cooler, it returns through the lower steel tube (3), where it is directed to the lube distribution manifold.
The torque converter oil temperature sensor (4) is installed in the torque converter outlet relief valve. It senses the temperature of the oil exiting the torque converter and provides a signal to the Power Train ECM. Cat Advisor monitors this temperature data from the Power Train ECM and uses it to operate the torque converter oil temperature gauge (analog), at the upper right of the instrument cluster.
The small hose (5) directs torque converter outlet relief pressure to the bank of three remote power train pressure taps.
The status of the torque converter oil temperature sensor may be viewed through the Advisor panel (Power Train System Status screens and Performance 1 screen) or through Cat ET.
1
2
3 4
5
71
The torque converter outlet relief valve maintains a constant minimum pressure inside the torque converter.
Oil from the torque converter enters the torque converter outlet relief valve through the inlet passage. The pressure of the oil acts against the top of the spool. When the pressure of the torque converter oil becomes greater than the force of the spring, the spool shifts down. Torque converter oil then flows through the holes around the circumference of the spool to the outlet passage. The outlet passage directs the hot torque converter oil to the power train oil cooler.
The torque converter outlet relief valve may be adjusted by adding or removing shims between the spring and the spool.
Inlet Passage from Torque Converter Spool
Spring Shim
Outlet Passage to Power Train
Oil Cooler
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The power train oil cooler (1) is an oil-to-water type oil cooler. It is located at the right rear of the engine compartment.
Oil from the torque converter outlet relief valve enters the cooler at the cooler inlet (2). The hot oil is cooled as it flows through tubes that are surrounded by engine coolant. The cooled oil then exits the power train oil cooler through the cooler outlet (3), where it is directed to the lube distribution manifold.
Engine coolant flows from the water pump (4) to the engine oil cooler (5). After cooling the engine oil, the coolant then flows into the bottom of the power train oil cooler. The coolant flows up through the power train oil cooler, then exits the cooler and enters the engine block through a port (not visible) behind the power train oil cooler.
1 2
3
4
5
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Power Shift Transmission
The planetary power shift transmission is capable of three speeds in FORWARD and three speeds in REVERSE. Power is transferred from the engine and the torque divider to the transmission through the input shaft (1). Power is transferred from the transmission to the transfer and bevel gears through the output shaft (2). The transfer and bevel gears transfer power to the final drives.
The transmission contains three hydraulically controlled speed clutches and two hydraulically controlled directional clutches located in the planetary group (3). The transmission shifting function is controlled by the Power Train Electronic Control System. The The Power Train Electronic Control System consists of all the inputs to and outputs from the Power Train ECM, including the Power Train ECM. The Power Train ECM responds to shifting requests by
controlling the electrical current to the solenoids of the transmission modulating valves (4). The transmission modulating valves control the hydraulic circuits that engage the transmission clutches.
The Power Train ECM selects the transmission clutches to be engaged and the clutch pressure is modulated electronically. Transmission modulating valves control the flow of oil to and from the clutches. The Power Train ECM uses the transmission speed, the engine speed, and the power train oil temperature signals to control smooth engagement of the clutches.
2
3
6 7
Each transmission clutch in the planetary group (3) has a corresponding solenoid controlled transmission modulating valve located on the transmission hydraulic control manifold (5).
The Power Train ECM uses the transmission modulating valves to directly control the oil
pressure to each transmission clutch. The modulating valves operate proportionally. The Power Train ECM sends an electrical current to the modulating valve solenoid. Electronic clutch modulation by the Power Train ECM controls the time required to fill a clutch with oil.
Although clutch engagement pressure calibrations no longer need to be performed with the
"common top pressure" power train strategy, clutch fill time calibrations are still required. The automated clutch fill time calibration procedure can be performed using Cat Advisor or by using Cat ET. This calibration routine "teaches" the Power Train ECM the length of time required for each clutch modulating valve to attain its clutch engagement pressure. The ECM applies current to the solenoid until the transmission output speed sensors detect a slight movement of the output shaft. When the output shaft begins to move, the ECM has "learned" and stored in memory the time required to pressurize the clutch to its engagement pressure.
Transmission output speed and direction are sensed by the two transmission output speed sensors (6). The speed/direction pick-up wheel (7) is splined to the transmission output shaft.
As the speed/direction pick-up wheel moves past the sensors, the wheel induces a current (signal) into each sensor. The difference in the timing between the signals of the two sensors determines the output shaft speed. Output shaft rotational direction is determined by sensing which sensor provides a signal first, then second. The signals from the sensors are monitored by the Power Train ECM. These signals are used by the Power Train Electronic Control System to modify the timing of clutch engagements.
The status of all five transmission modulating valve solenoids may be viewed through the Advisor panel (Power Train System Status screens) or through Cat ET.
NOTE: With the "common top pressure" strategy, clutch No. 1 (reverse direction), clutch No. 2 (forward direction), clutch No. 3 (speed 3), and clutch No. 4 (speed 2) operate at main relief pressure. Main relief pressure is approximately 2551 kPa (370 psi), at low idle (700 engine rpm) and with the transmission in NEUTRAL. At high idle, these same clutch pressures should be approximately 2758 kPa (400 psi), with the transmission in NEUTRAL. The Power Train ECM sends approximately 1.0 amp of current to these four transmission modulating valve solenoids to attain the clutch engagement pressure.
Clutch No. 5 (speed 1) operates at a reduced pressure, which is approximately 2206 kPa (320 psi). The Power Train ECM regulates the pressure to the No. 5 clutch by sending a reduced current (approximately 0.7 - 0.8 amps) to the No. 5 transmission modulating valve solenoid.
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The transmission clutches are hydraulically engaged and spring released. The transmission modulating valve solenoids are energized to send transmission charge oil to the clutches, as shown in the illustration above. As current is applied to the solenoid, the pin extends to the right and moves the ball closer to the orifice. The ball begins to restrict the amount of oil to drain through the orifice. This restriction causes the pressure to increase at the left end of the valve spool. As the pressure at the left end of the valve spool increases, the spool shifts to the right, closing off the passage from the clutch to the drain. At the same time, the movement of the valve spool to the right opens the passage from the pump supply to the clutch. This causes the clutch pressure to increase.
De-energizing the solenoid decreases the force of the pin against the ball. This decreased force allows the pressure at the left end of the valve spool to unseat the ball, de-pressurizing the chamber at the left end of the spool. With no pressure at the left end of the spool, the valve spool shifts to the left due to the spring force plus the supply oil pressure. This condition reduces the pressure to the clutch by closing off the supply passage to the clutch and opening up the drain passage. When the pressure to the clutch falls below the clutch engagement pressure, the clutches will be released by spring force.
Ball
Valve
Spool Spring Orifice
Solenoid Pin
To Clutch
Supply Oil from Pump
When the transmission is in NEUTRAL, the transmission modulating valve that controls engagement of the No. 3 clutch allows flow to the clutch. The other modulating valves stop flow to the clutches, thereby allowing the clutches to be released by spring force. Since neither the No. 1 nor the No. 2 directional clutches are engaged, no power is transmitted to the output shaft of the transmission.
When the transmission is in FIRST SPEED FORWARD, the modulating valves that control flow to the No. 2 and the No. 5 clutches receive a signal from the Power Train ECM. This signal energizes the solenoid which sends flow to engage the clutches.
NOTE: Clutch Engagement Pressure Calibrations are no longer necessary due to the common top pressure strategy. However, transmission Clutch Fill Time Calibrations must be performed when any of the following repair procedures have been performed:
-Transmission modulating valve and/or solenoid is replaced.
-Transmission is serviced or replaced.
-Power Train ECM is replaced.
Transmission Clutch Fill Time Calibrations may be performed using Cat Advisor or by using Cat ET.
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The transmission main relief valve is located in the transmission hydraulic control manifold.
The manifold is on top of the transmission planetary group. The transmission main relief valve maintains the "common top pressure" from the transmission charging section of the power train oil pump. This oil is used to operate the brakes and the transmission clutches.
Oil to the main relief valve is supplied by the transmission charging section of the power train oil pump, when the priority valve is in the Normal Mode. If the priority valve is in the Priority Mode, the oil supply to the transmission main relief valve is a mixture of transmission charge oil and torque converter charge oil.
Oil from the power train oil pump flows through the transmission charge oil filter and flows to the electronic brake control valve and the transmission modulating valves. The transmission main relief valve is downstream from the electronic brake control valve and the transmission modulating valves. The excess oil that flows over the main relief valve combines with the oil from the lube distribution manifold and is is used to lubricate the transmission planetary group.
The transmission main relief pressure should be set to approximately 2550 kPa (370 psi), at Low Idle engine speed (700 rpm).
To PT Lube Circuit Locknut
Screw Chamber
To Transmission Hydraulic Control
From Trans. Charging Section of PTO Pump
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This visual shows a sectional view of a typical transmission group like that used in the D8T Track-type Tractor. The planetary group has two directional and three speed clutches which are numbered in sequence (1 through 5) from the rear of the transmission to the front. Clutches No. 1 and No. 2 are the reverse and forward directional clutches. Clutches No. 3, No. 4, and No. 5 are the third, second and first speed clutches. The No. 5 clutch is a rotating clutch.
In this sectional view of the transmission, the input shaft and input sun gears are shown in red.
The output shaft and output sun gears are blue. The ring gears are shown in green. The planetary carrier is brown. The planet gears and shafts are shown in orange. The clutch discs, clutch plates, pistons, springs and bearings are shown in yellow. The stationary clutch housings are shown in gray.
The input sun gears are splined to the input shaft and drive the directional gear trains. The output shaft is driven by output sun gears No. 3 and No. 4 and rotating clutch No. 5. When the No. 2, No. 3, or No. 4 clutches are engaged, their respective ring gears are held stationary. The No. 1 planetary carrier is held when the No. 1 clutch is engaged. When engaged, the No. 5 rotating clutch locks the output components (for FIRST gear) to the output shaft.
Input Shaft
Output Shaft Output
Sun Gears Ring Gears
Input Sun Gears
Planetary Carrier
Ring Gears
2 3 4 5