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Service Training

Meeting Guide 757 SERV1757

March 2002

TECHNICAL PRESENTATION

D6R SERIES II

TRACK-TYPE TRACTORS

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31

Torque Divider Group

The D6R Series II Track-type Tractors are equipped with a power shift

transmission and use a torque divider (1) to transfer engine power to the

transmission. The torque dividers on these machines are similar to the

torque dividers on other Caterpillar Track-type Tractors.

The torque divider provides both a hydraulic and a mechanical connection

from the engine to the transmission. The torque converter provides the

hydraulic connection while the planetary gear set provides the mechanical

connection. During operation, the planetary gear set and the torque

converter work together to provide an increase in torque as the load on the

machine increases.

The torque converter outlet relief valve (2) is mounted on the torqueconverter case.

The torque converter outlet pressure tap (3) is located on the back of the

torque converter relief valve.

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Torque divider group:

1. Torque divider

2. Torque converter

outlet relief valve

3. Torque converter

outlet pressure tap

3

2

1

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Priority valve

components:

1. Torque converter

inlet pressure tap

2. Torque converter

inlet relief valve

3. Priority valve group

32

The torque converter inlet pressure tap (1) is located on the side of the

torque converter inlet relief valve (2), which is contained in the priority

valve group (3).

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1

2

3

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33

SUN GEAR

HOUSING

IMPELLER

TURBINE

OUTLET

PASSAGE

OUTPUT SHAFT

STATOR

PLANET CARRIER

PLANET GEARS

ENGINE FLYWHEEL

INLET

PASSAGE

RING GEAR

TORQUE DIVIDER

This illustration shows a typical torque divider. The impeller, rotating

housing, and sun gear (shown in red) are mechanically connected to the

engine flywheel. The turbine and ring gear (blue) are connected and the

planet carrier and output shaft (yellow) are connected.

The sun gear and the impeller always rotate at engine speed. As the

impeller rotates, it directs oil against the turbine blades, causing the

turbine to rotate. Turbine rotation causes the ring gear to rotate. During

NO LOAD conditions, the planet gears (green) and planet carrier rotate asa unit with the planet gears stationary on their shafts.

Torque divider

operation:

- During NO LOAD

condition

components rotate

as unit

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As the operator loads the machine, the output shaft slows down. A

decrease in output shaft speed causes the rpm of the planetary carrier to

decrease. Decreasing the planetary carrier rotation causes the relative

motion between the sun gear and the planet carrier to cause the planet

gears to rotate. Rotating the planet gears decreases the rpm of the ringgear and the turbine. At this point, the torque splits with the torque

converter multiplying the torque hydraulically, and the planetary gear set

multiplying the torque mechanically.

An extremely heavy load can stall the machine. If the machine stalls, the

output shaft and the planetary carrier will not rotate. This condition

causes the ring gear and turbine to slowly rotate in the opposite direction

of engine rotation. Rotating the ring gear and turbine in the opposite

direction provides maximum torque multiplication.

During all load conditions, the torque converter provides 70% of the

output and the planetary gear set provides the remaining 30% of the

output. The size of the planetary gears establishes the torque split

between the hydraulic torque and mechanical torque.

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- During stall, turbine

and ring gear rotate

in opposite

directions

- Torque converter

provides 70% of

output

- Planetary gear set

provides 30% of

output

- Under load, relative

motion slows turbine

rotation

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Component locations:

1. Power train filter

2. SOS tap

3. Power train oil

pump supply

pressure tap

4. Power train oil filter

bypass switch

34

Opening the hinged cover of the compartment on the right fender allows

access to the power train filter (1) for the the D6R Series II. On top of the

power train filter housing are the power train SOS tap (2) and the pump

supply pressure tap (3). The power train filter drain plug is below the

filter housing.

The filter bypass pressure switch (4) opens during cold start-ups and

when the filter is plugged.

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1

4

2

3

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Component locations:

1. Power train oil fill

tube

2. Power train oil

dipstick

35

The power train oil fill tube (1) and dipstick (2) are located at the rear of

the left side engine compartment.

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12

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Power train oil pump:

1. Torque converter

and lube section

2. Transmission and

controls section

3. Transmission and

torque converter

scavenge section

4. Check valve

36

The three section gear-type power train oil pump is located at the right

front of the main case below the floor plate and is driven by a shaft

extending from the rear of the flywheel housing.

The three sections are the torque converter charging section (1), the

transmission charging section (2), and the torque converter and

transmission scavenge section (3).

Under certain conditions, the torque converter charging section and the

transmission charging section combine flow through the check valve (4)

to provide more oil to the transmission and brakes. This will be covered

in more detail later in this presentation.

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1

2 3

4

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3F/3R planetary power

shift transmission

Pressure taps:

1. Transmission main

relief valve

2. Transmission

lubrication

37

Transmission

The three speed FORWARD, three speed REVERSE planetary power

shift transmission transfers power from the engine to the final drives. The

transmission contains three hydraulically controlled speed clutches and

two hydraulically controlled directional clutches. The transmissionshifting function is controlled by the Power Train Electronic Control

System. The Power Train ECM responds to operator shifting requests by

controlling the electrical current to the transmission clutch solenoids. The

solenoid current controls 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. Solenoid valves

control the modulation of the clutch pressure. The Power Train ECM

uses the transmission speed, engine speed, and the power train oiltemperature signals to control smooth engagement of the clutches. Each

transmission clutch in the planetary group has a corresponding solenoid

valve on the transmission hydraulic control group.

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1 2

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The Power Train ECM uses the transmission solenoid valves to directly

modulate the oil pressure to each transmission clutch. The solenoid

valves are proportional. The Power Train ECM modulates the electrical

current to the solenoid valves. Modulating the solenoid valves controls

the power train oil flow to the transmission clutches. Electronic clutchmodulation allows the Power Train ECM to control the time required to

fill a clutch with oil and the rate of the clutch pressure modulation.

The pressure setting for the transmission main relief valve may be

checked using the transmission main relief valve pressure tap (1).

Transmission lubrication pressure may be checked using the transmission

lubrication pressure tap (2). These two pressure taps are located at the

rear of the machine and at the top of the cover for the transmission case.

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38

TEST PORT

FROM

PUMP

BALLVALVE

SPOOL SPRINGORIFICE

SOLENOID PIN

TO

CLUTCH

D6R SERIES II

TRANSMISSION MODULATING VALVE

The transmission clutches are hydraulically engaged and spring released.

The transmission modulating valve solenoid is energized to engage the

clutch.

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, increasing the pressure on the left end of the spool. As the

pressure at the left end of the spool increases, the spool shifts to the right,

blocking the drain passage. Oil is now directed to the clutch. When theclutch fills, pressure begins to increase, engaging the clutch.

As clutch pressure increases, the pressure plus the spring force moves the

spool back to the left. When maximum clutch pressure is reached a

balance is maintained between clutch pressure and the solenoid, holding

the spool in a metering position.

Transmission

modulating valve

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De-energizing the solenoid returns the pin to the left. The pressure on the

left end of the spool forces the ball away from the orifice, which relieves

pressure on the left end of the spool. This, in turn, allows the spool to

shift to the left, due to the spring force plus the clutch oil pressure. Clutch

pressure is then directed to drain, and the clutch is disengaged.

When the transmission is in NEUTRAL, the modulating valve, which

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 the No. 1 or 2 directional

clutch is not engaged, no power is transmitted to the output shaft of the

transmission.

When the transmission is in FIRST SPEED FORWARD, the modulating

valves which control flow to the No. 2 and 5 clutches receive a signal

from the Power Train ECM to allow flow to the clutches and, therefore,

allow the clutches to engage.

NOTE: The transmission modulating valves must be recalibrated

when any of the following procedures are performed:

- Transmission modulating valve and/or solenoid is replaced.

- Transmission is serviced or replaced.

- Power Train ECM is replaced.

For the calibration procedure, refer to the Power Train Electronic

Control System Service Manual (Form SENR8367).

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FIRST FORWARD

NEUTRAL

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39

Transmission clutch

locations:

1. Reverse

2. Forward

3. Third

4. Second

5. First

POWER SHIFT TRANSMISSION

INPUT SHAFT

OUTPUT SHAFT

OUTPUT

SUN GEARS

RING GEARS

INPUT SUN

GEARS

PLANETARY

CARRIER

RING

GEARS

1 2 3 4 5

This illustration shows a sectional view of a typical transmission group.

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 2 are the reverse and forward directional

clutches. Clutches No. 3, 4, and 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.

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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 4

and rotating clutch No. 5. When the No. 2, 3, or 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. 5rotating clutch locks the output components (for FIRST gear) to the

output shaft.

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Priority valve group:

1. Priority valve

2. Torque converter

inlet relief valve

3. Solenoid valve

4. Priority valve

pressure tap

40

Priority Valve

The priority valve group on the D6R Series II contains the priority valve

(1) and the torque converter inlet relief valve (2). A solenoid valve (3)

receives an output signal from the ECM to operate the priority valve at

either high or low pressure. A pressure tap (4) is also installed on the

priority valve to test priority valve pressure.

The priority valve ensures that the steering clutch and brake control valve

receives supply oil along with the transmission control group before

supplying oil to the torque converter circuit. The priority valve only

operates at high pressure during certain conditions to improve efficiency.

The solenoid valve, when DE-ENERGIZED, allows the priority valve to

operate at high pressure or 2930 kPa (425 psi). The solenoid isde-energized for the following conditions: When the oil temperature is

less than 40C (104F), during a speed or directional change, and when

the engine speed is below 1300 rpm.

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4

1

2

3

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The solenoid valve, when ENERGIZED, allows the priority valve to

operate at low pressure or 1100 kPa (160 psi) maximum. The solenoid

valve is energized for the following conditions: When the above

conditions are not fulfilled and when the parking brake is ENGAGED,

regardless of oil temperature or engine speed.

Oil from the torque converter flows through the torque converter outlet

relief valve to the oil cooler. By maintaining oil pressure in the torque

converter, the outlet relief valve ensures efficient power transfer between

the engine and transmission, and also prevents cavitation in the torque

converter.

Oil from the oil cooler lubricates the steering clutches and brakes and the

transmission planetaries before returning to the power train sump. The

implement and winch pump drive gears and bearings receive lubrication

oil from the inlet side of the torque converter.

The torque converter inlet relief valve maintains adequate oil pressure to

the torque converter while the torque converter outlet relief valve prevents

the pressure from becoming too high in the torque converter.

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41

TO TORQUE CONVERTER

SUPPLY

SOLENOID

VALVE

PRIORITY

VALVE

PRIORITY VALVEPRIORITY MODE

The Priority Valve makes sure that oil pressure is first available for

steering, braking, and transmission control, and then for torque converter

operation and lubrication of the steering clutches, brakes, and

transmission. The priority valve has two modes of operation, Priority

Mode and Normal Mode. In Normal Mode, oil flow to the torque

converter, the lubrication system, and controls is separate. In Priority

Mode, priority is given to oil flow for steering, braking, and transmission

control.

This illustration shows the priority valve operating in the Priority Mode.

Oil enters the slug chamber on the left end of the spool, through the small

hole in the center of the valve stem. It then passes through the orifice in

the center of the check valve where it forces the slug against the stop.

Pressure then builds in the slug chamber, moving the valve to the right

against the valve spring, acting like a relief valve. The valve is held in a

metering position so that a pressure of 2965 kPa (430 psi).

Priority Valve:

- Two modes:

- Priority Mode

- Normal Mode

Priority Mode

operation

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During operation in the Priority Mode, the solenoid valve is de-energized,

which results in the valve spool being shifted to the left, as previously

described. The result is a restriction of supply oil to the torque converter

and lube system.

With the spool shifted to the left, supply pressure increases. The increase

in supply pressure causes oil flow to be restricted to the torque converter

and lubrication sections of the power train oil system. This oil combines

with the flow from the transmission and charging pump section through

the check valve (illustration 36, item 4), giving increased flow, or priority,

to steering, braking, and transmission control.

Three conditions will put the system in the Priority Mode: Engine speed

below 1350 rpm, power train oil temperature below 40C (104F), and

during transmission shifts.

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42

TO TORQUE CONVERTER

SUPPLY

SOLENOIDVALVE

PRIORITY

VALVE

PRIORITY VALVENORMAL MODE

This visual shows the priority valve in Normal Mode.

The coil of the solenoid valve is ENERGIZED when in the Normal Mode

of operation, opening up the passage for supply oil to pressurize the

chamber to the left of the slug. Since the left end of the valve spool has a

greater effective area than the right, the valve spool is shifted to the right.

This condition allows more supply oil to be directed to the torque

converter, lube system, and controls.

The increased flow to the torque converter now decreases the upstreamsupply pressure, which allows the check valve to close off. The oil from

the torque converter charging section of the pump is no longer combined

with the oil from the transmission and charging section of the pump, and

the flows from these two sections are once again separate.

Normal Mode

operation

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The priority valve only operates in the Normal Mode when engine speed

is above 1350 rpm, power train oil temperature is above 40C (104F),

and when transmission clutches are engaged.

The pressure tap for testing priority valve pressure is located at the top,

front of the priority valve group (illustration 40, item 4).

The pressure tap for testing the torque converter inlet pressure is located

on the side of the priority valve group (see illustration 32, item 1).

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Pressure tap for

priority valve

Pressure tap for

torque converter inlet

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43

Three section pump:

1. Torque converter

charging section

2. Transmission

charging section

3. Scavenge section

3

4

2

5

1

FROM

CONVERTER

SCAVENGE

PRIORITY

VALVE

TO TORQUE

CONVERTER

FROM OILCOOLER

STEERING AND

BRAKE VALVE

TRANSMISSION

CONTROL

GROUP

POWER TRAIN HYDRAULIC SYSTEMD6R SERIES II WITH FINGER TIP CONTROL

3 2 1

PUMP SECTIONS

1. TORQUE CONVERTER CHARGING SECTION

2. TRANSMISSION CHARGING SECTION

3. TRANSMISSION AND TORQUE CONVERTER

SCAVENGE SECTION

This illustration shows the power train oil system components on the D6R

Series II machines equipped with steering clutches and brakes.

The power train oil system uses a three section gear pump. The scavenge

section (3) returns oil from the torque converter and transmission sumps

to the bevel gear case. The center section (2) sends oil at the same time to

the steering and brake control valve and the transmission control group.

The torque converter charging section (1) directs oil from the case to the

priority valve, the torque converter and, during certain conditions, sends

oil to the steering and brake control valve and the transmission control

group.

NOTE: For more information on the steering and brake controls,

refer to the Technical Instruction Module "Electronically Controlled

Steering and Brake System--D5M/D6M/D6R/D6R Track-type

Tractors" (Form SEGV2628).

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44

Differential steer

power train hydraulic

schematic

3

4

2

5

1

FROM

CONVERTER

SCAVENGE

PRIORITY

VALVE

TO TORQUE

CONVERTER

FROM OILCOOLER

BRAKE

VALVE

TRANSMISSION

CONTROL

GROUP

TO TRANSMISSION

CASE

POWER TRAIN HYDRAULIC SYSTEMD6R SERIES II WITH DIFFERENTIAL STEERING

3 2 1

PUMP SECTIONS

1. TORQUE CONVERTER CHARGING SECTION

2. TRANSMISSION CHARGING SECTION

3. TRANSMISSION AND TORQUE CONVERTER

SCAVENGE SECTION

This illustration shows the power train oil system components on the D6R

Series II machines equipped with differential steering.

The only difference is that the differential steer machine does not have

steering clutches and uses only one proportional solenoid on the brake

valve.