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. 44) are
pressed against the friction ground via the garter
spring (Fig. 45), 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 direc-
tion of this drag force (position of the roller) is depen-
dent
on
the
input
(propeller
shaft)
rotational
direction. Since the rollers are always in contact 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 excessive 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 undesired
9high speed lockup9, a high speed
latch (Fig. 46) 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 to
migrate 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. 47) 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. 44 Front View of BOC
1 - GARTER SPRING
2 - FRICTION BRAKE SHOES
3 - FRICTION GROUND CONNECTED TO GROUND TAB
4 - INPUT SHAFT
Fig. 45 Location of the Grounding Element
1 - DIFFERENTIAL HOUSING
2 - GROUND TAB
3 - GARTER SPRING
Fig. 46 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
CS
REAR DRIVELINE MODULE
3 - 45
BI-DIRECTIONAL OVERRUNNING CLUTCH (Continued)