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 1 ) are pressed against the friction ground via the garter spring (Fig 2 ), 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 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.

Fig 1: Front View Of BOC

Courtesy of DAIMLERCHRYSLER CORP.

To keep the rollers in the overrunning position and avoid undesired "high speed lockup", a high speed latch (Fig 3 ) 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 excessive 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 system lock-up. (Fig 4 ) 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 2: Identifying Location Of Grounding Element

Courtesy of DAIMLERCHRYSLER CORP.