shaft CHRYSLER CARAVAN 2002 Workshop Manual

BI-DIRECTIONAL
OVERRUNNING CLUTCH
DESCRIPTION
The bi-directional overrunning clutch (BOC) (Fig.
28) works as a mechanical disconnect between the
front and rear axles, preventing torque from being
transferred from the rear axle to the front. The BOC
is a simply an overrunning clutch which works in
both clockwise and counter-clockwise rotations. This
means that when the output (the rear axle) is rotat-
ing faster in one direction than the input (front axle),
there is no torque transmission. But when the input
speed is equal to the output speed, the unit becomes
locked. The BOC provides significant benefits regard-
ing braking stability, handling, and driveline durabil-
ity. Disconnecting the front and the rear driveline
during braking helps to maintain the braking stabil-
ity of an AWD vehicle. In an ABS/braking event, the
locking of the rear wheels must be avoided for stabil-
ity reasons. Therefore brake systems are designed to
lock the front wheels first. Any torque transfer from
the rear axle to the front axle disturbs the ABS/brak-
ing system and causes potential instabilities on aslippery surface. The BOC de-couples the rear driv-
eline as soon the rear wheels begin to spin faster
than the front wheels (front wheels locked) in order
to provide increased braking stability. Furthermore
the BOC also reduces the likelihood of throttle off
over-steer during cornering. In a throttle off maneu-
ver, the BOC once again de-couples the rear driveline
forcing all the engine brake torque to the front
wheels. This eliminates the chance of lateral slip on
the rear axle and increases it on the front. The vehi-
cle will therefore tend to understeer, a situation
which is considered easier to manage in most circum-
stances. During this maneuver, and during the ABS
braking event, the BOC does not transmit torque
through to the rear wheels. The rear driveline mod-
ule, with the BOC, will perform the same as a front
wheel drive vehicle during these events. The gear
ratio offset between the front and rear differentials
force the BOC into the overrunning mode most of the
time. This allows BOC to significantly reduce the
rolling resistance of the vehicle, which improves fuel
consumption, allows the downsizing of the driveline
components, and prevents the PTU and propshaft
joints from overheating.
3 - 36 REAR DRIVELINE MODULERS
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Fig. 28 Bi-directional Overrunning Clutch and Viscous Coupler
1 - POWERFLOW - BOC OVERUNNING 6 - VISCOUS COUPLER
2 - POWERFLOW - BOC LOCKED 7 - BOC ROLLER CAGE
3 - BOC GROUND TAB 8 - BOC INPUT SHAFT
4 - FRICTION BRAKE SHOES 9 - INPUT FLANGE
5 - BOC ROLLERS
RSREAR DRIVELINE MODULE3-37
BI-DIRECTIONAL OVERRUNNING CLUTCH (Continued)
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OPERATION
In order to achieve all-wheel drive operation in
reverse, the overrunning clutch locking functional direc-
tion must be reversible. The bi-directional overrunning
clutch (BOC) changes the operational mode direction
depending on the propeller shaft direction. The propel-
ler shaft rotates in the clockwise (when viewed from the
front) direction when the vehicle is moving forward,
which indexes the BOC to the forward overrunning
position. When the vehicle is in reverse, the propeller
shaft will rotate counter-clockwise and index the BOC
to the reverse overrunning position.
The BOC acts as a mechanical stator. It is active
(transmitting torque), or it is not active and in over-
running mode (not transmitting torque). This ªall or
nothingº approach to torque transfer would cause a
sudden application of all available power to the rear
wheels, which is not desirable. Therefore it is run in
series with a viscous coupler to smooth, dampen, and
limit the transmission of torque to the rear axle and
to prevent a step style torque input to the rear axle.
STEADY STATE, LOW TO MODERATE SPEED, NO
FRONT WHEEL SLIP, FORWARD DIRECTION
During normal driving conditions, (no wheel slip), the
inner shaft (front axle) and outer race (viscous coupler)
are running at different speeds due to the different gear
ratios between the front and rear differentials. In this
condition, the outer race is always spinning faster (over-
driving between 5-32 rpm) than the inner shaft. When
the BOC (Fig. 29) is running under these conditions, at
low vehicle speeds the drag shoes and the cage keep the
rollers up on the left side (forward side) of the inner
shaft flats. This is what is known as ªoverrunning
mode.º Notice that when the clutch is in overrunning
mode, the rollers are spinning clockwise and with the
outer race, thus no torque is being transferred.
NOTE: Low speed, forward and reverse operation is
identical, just in opposite directions. (Fig. 29) shows
forward direction in reverse the rollers are on the other
side of the flats due to a reversal of the cage force.
TRANSIENT CONDITION (BOC LOCKED), FRONT
WHEEL SLIP, FORWARD DIRECTION
When the front wheels lose traction and begin to
slip, the propeller shaft and rear axle pinion speed
difference decreases to zero. At this point the input
shaft (cam) becomes the driving member of the BOC
(Fig. 30), compressing the rollers against the outer
race. This locks the input shaft with the outer race
and transmits torque to the housing of the viscous
coupler, that in turn transmits torque to the rear
axle pinion. It should also be noted that when the
device is locked, the inner shaft and the outer raceare rotating at the same speed. The rollers are
pinched at this point and will stay locked until a
torque reversal (no front wheel slip) occurs. When
locked, the viscous coupler slips during the torque
transfer and the amount of torque transferred is
dependent on the coupling characteristic and the
amount of front wheel slip.
Fig. 29 BOC Operation at Low Speeds With No
Front Wheel Slip
1 - CAGE
2 - ROLLER
3 - INPUT SHAFT
Fig. 30 BOC Operation with Front Wheel Slip
3 - 38 REAR DRIVELINE MODULERS
BI-DIRECTIONAL OVERRUNNING CLUTCH (Continued)
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STEADY STATE, HIGH SPEED, NO WHEEL SLIP
The roller cage positions the rollers on the input shaft
flats during low and high speed overrunning and during
initial BOC lockup. The roller cage is rotating at input
shaft (propeller shaft) speed at all times. At low speeds,
the friction shoes (Fig. 31) are pressed against the fric-
tion ground via the garter spring (Fig. 32), creating a
drag force on the roller cage. The drag force positions
the cage, which in turn positions the rollers to one side
of the flat. The direction of this drag force (position of
the roller) is dependent on the input (propeller shaft)
rotational direction. Since the rollers are always in con-
tact with the outer race, due to centrifugal forces, the
rollers want to follow the outer race due to drag. During
overrunning operation, the outer race is rotating faster
than the input; causing the rollers to want to traverse
the flat from one side to the other. During low speeds,
the brake shoes counteract this effect. To avoid exces-
sive wear, the ground shoes are designed to lift off from
the friction ground due to centrifugal forces at higher
rotational speeds.
To keep the rollers in the overrunning position and
avoid undesired9high speed lockup9, a high speed
latch (Fig. 33) positions the cage before the ground
shoes lift off. A further explanation of the high speed
effects follows as well. Utilizing only the friction
shoes approach means that at high speed the
required ground shoe drag torque would cause exces-
sive brake shoe wear or the roller will begin tomigrate to the opposite side of the flat due to the
drag force of the outer race. This would result in sys-
tem lock-up. (Fig. 34) shows the BOC as it crosses
the speed where the brake shoe force is overcome by
the roller drag on the outer race. Notice that the
roller is locking up on the opposite side of the flat
and the cage supplies no force on the rollers.
Fig. 31 Front View of BOC
1 - GARTER SPRING
2 - FRICTION BRAKE SHOES
3 - FRICTION GROUND CONNECTED TO GROUND TAB
4 - INPUT SHAFT
Fig. 32 Location of the Grounding Element
1 - DIFFERENTIAL HOUSING
2 - GROUND TAB
3 - GARTER SPRING
Fig. 33 BOC High Speed Latch (Not Engaged)
1 - TOOTH (TWO PLACES)
2 - GARTER SPRING
3 - TABS AT BOTH ENDS FIT INTO SLOTS IN CAGE
4 - TWO PART DESIGN
RSREAR DRIVELINE MODULE3-39
BI-DIRECTIONAL OVERRUNNING CLUTCH (Continued)
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This lock-up is not desired, and requires the use of
another mechanism to prevent the lock-up. The
device that prevents undesired high-speed lock-up is
called a9high speed latch9.
Similar to the friction shoes, the two-piece high-
speed latch will separate from each other at high
rotational speeds due to centrifugal effects. (Fig. 35)
shows the high speed latch engaged. The gap9x9
increases with speed, eventually locking into one of
the slots in the BOC shaft. When the high-speed
latch is activated (propeller shaft speed reaches X
amount), the cage is partially fixed, and cannot lock
on the wrong side of the flat as shown (Fig. 34). The
high speed latch is a one way device and does not
prevent high-speed lockup in the reverse direction. At
high speeds, the BOC provides the same function as
low speeds, transferring torque to the viscous coupler
only when front wheel slip overcomes the axle ratio
offset.
Fig. 34 BOC Operation During High Speed Lock-up Without High Speed Latch
Fig. 35 High Speed Latch Engaged
1 - CAGE FORCE EXERTED BY ROLLERS AT HIGH SPEED
3 - 40 REAR DRIVELINE MODULERS
BI-DIRECTIONAL OVERRUNNING CLUTCH (Continued)
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At high speed, the rollers are forced outward to the
outer race because of centrifugal force. At high
speeds, the friction shoes can no longer prevent lock-
up. When the teeth on the high-speed latch engage
into the input shaft, it keeps the rollers centered
above the flats because the tabs on the latch are
locked into the cage. (Fig. 36) shows the roller config-
uration with the High-Speed Latch engaged.
On the BOC shaft, the high speed latch teeth lock
up in the grooved areas, shown in (Fig. 37), when the
turning speed reaches the critical value. (Fig. 37)
also shows the outer race/viscous coupler. Notice the
surface (outer race) the rollers mate against when
transferring torque.
DIFFERENTIAL ASSEMBLY
DESCRIPTION
The differential gear system divides the torque
between the axle shafts. It allows the axle shafts to
rotate at different speeds when turning corners.
Each differential side gear is splined to an axle
shaft. The pinion gears are mounted on a pinion
mate shaft and are free to rotate on the shaft. The
pinion gear is fitted in a bore in the differential case
and is positioned at a right angle to the axle shafts.
OPERATION
In operation, power flow occurs as follows:
²The pinion gear rotates the ring gear²The ring gear (bolted to the differential case)
rotates the case
²The differential pinion gears (mounted on the
pinion mate shaft in the case) rotate the side gears
²The side gears (splined to the axle shafts) rotate
the shafts
During straight-ahead driving, the differential pin-
ion gears do not rotate on the pinion mate shaft. This
occurs because input torque applied to the gears is
divided and distributed equally between the two side
gears. As a result, the pinion gears revolve with the
pinion mate shaft but do not rotate around it (Fig.
38).
Fig. 36 BOC Operation at High Speed with High
Speed Latch
Fig. 37 BOC Input Shaft
1 - GROOVED AREA (2 LOCATIONS)
2 - ROLLER MATING SURFACE
Fig. 38 Differential OperationÐStraight Ahead
Driving
1 - IN STRAIGHT AHEAD DRIVING EACH WHEEL ROTATES AT
100% OF CASE SPEED
2 - PINION GEAR
3 - SIDE GEAR
4 - PINION GEARS ROTATE WITH CASE
RSREAR DRIVELINE MODULE3-41
BI-DIRECTIONAL OVERRUNNING CLUTCH (Continued)
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When turning corners, the outside wheel must
travel a greater distance than the inside wheel to
complete a turn. The difference must be compensated
for to prevent the tires from scuffing and skidding
through turns. To accomplish this, the differential
allows the axle shafts to turn at unequal speeds (Fig.
39). In this instance, the input torque applied to the
pinion gears is not divided equally. The pinion gears
now rotate around the pinion mate shaft in opposite
directions. This allows the side gear and axle shaft
attached to the outside wheel to rotate at a faster
speed.
FLUID - DIFFERENTIAL
ASSEMBLY
STANDARD PROCEDURE - DIFFERENTIAL
ASSEMBLY FLUID DRAIN AND FILL
The drain plug (Fig. 40) for the differential assem-
bly is located in the bottom of the differential assem-
bly case, toward the rear of the unit.
The fill plug (Fig. 41) for the differential assembly
is located on the rear of the assembly case.
The correct fill level is to the bottom of the fill plug
hole. Be sure the vehicle is on a level surface, or is
hoisted in a level manner, in order to obtain the cor-
rect fill level.
(1) Raise the vehicle on a hoist.
(2) Position a drain pan under the differential
drain plug (Fig. 40).
(3) Remove the drain plug and allow the fluid to
drain into the pan.
(4) Install the drain plug and torque to 35 N´m (26
ft. lbs.).
(5) Re-position the drain pan under the differential
fill plug.
(6) Remove the differential fill plug (Fig. 41).
Fig. 39 Differential OperationÐOn Turns
1 - PINION GEARS ROTATE ON PINION SHAFT
Fig. 40 Differential Drain Plug
1 - DIFFERENTIAL DRAIN PLUG
Fig. 41 Differential Fill Plug
1 - DIFFERENTIAL FILL PLUG
3 - 42 REAR DRIVELINE MODULERS
DIFFERENTIAL ASSEMBLY (Continued)
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Fig. 46 Bi-directional Overrunning Clutch (BOC) and Viscous Coupler Powerflow
1 - POWERFLOW - BOC OVERUNNING 6 - VISCOUS COUPLER
2 - POWERFLOW - BOC LOCKED 7 - BOC ROLLER CAGE
3 - BOC GROUND TAB 8 - BOC INPUT SHAFT
4 - FRICTION BRAKE SHOES 9 - INPUT FLANGE
5 - BOC ROLLERS
RSREAR DRIVELINE MODULE3-45
VISCOUS COUPLER (Continued)
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TORQUE ARM
REMOVAL
(1) Raise vehicle on hoist.
(2) Remove rear driveline module assembly. (Refer
to 3 - DIFFERENTIAL & DRIVELINE/REAR DRIV-
ELINE MODULE - REMOVAL)
(3) Remove six torque arm-to-differential assembly
bolts (Fig. 47). Remove torque arm.
INSTALLATION
(1) Install six torque arm-to-differential assembly
bolts (Fig. 47) and torque to 60 N´m (44 ft. lbs.).
(2) Install rear driveline module assembly. (Refer
to 3 - DIFFERENTIAL & DRIVELINE/REAR DRIV-
ELINE MODULE - INSTALLATION)
(3) Lower vehicle.
INPUT FLANGE SEAL
REMOVAL
(1) Raise vehicle on hoist.
(2) Remove propeller shaft. (Refer to 3 - DIFFER-
ENTIAL & DRIVELINE/PROPELLER SHAFT -
REMOVAL)
(3) Using tool 6958, remove input flange nut and
washer (Fig. 48).
(4) Remove input flange (Fig. 49).
Fig. 47 Torque Arm Fasteners
1 - TORQUE ARM ASSEMBLY
2 - BOLT (SIX)
Fig. 48 Input Flange Nut
1 - INPUT FLANGE
2 - TOOL 6958
Fig. 49 Input Flange
1 - INPUT FLANGE/SHIELD
3 - 46 REAR DRIVELINE MODULERS
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(5) Using suitable screwdriver, remove input
flange seal from overrunning clutch housing (Fig.
50).
INSTALLATION
(1) Using tool 8802, install input flange seal to
overrunning clutch case (Fig. 51).(2) Install input flange (Fig. 52).
(3) Install flange nut and washer. Using tool 6958,
torque flange nut to 135 N´m (100 ft. lbs.) (Fig. 53).
(4) Install propeller shaft. (Refer to 3 - DIFFER-
ENTIAL & DRIVELINE/PROPELLER SHAFT -
INSTALLATION)
(5) Lower vehicle.
Fig. 50 Input Flange Seal Removal
1 - INPUT FLANGE SEAL
2 - SCREWDRIVER
Fig. 51 Input Flange Seal Installation
1 - TOOL 8802
2 - HAMMER
Fig. 52 Input Flange
1 - INPUT FLANGE/SHIELD
Fig. 53 Input Flange Nut
1 - INPUT FLANGE
2 - TOOL 6958
RSREAR DRIVELINE MODULE3-47
INPUT FLANGE SEAL (Continued)
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