Overrunning bi-directional clutches are known, see for example U.S. Pat. Nos. 6,409,001; 7,004,875; and 7,037,200. Such clutches are mounted between two coaxial shafts and are used to transfer power between the two shafts. The clutch is fixed to a first shaft and selectively engages the second shaft so as to transfer power between the two shafts. Typically, the first shaft is the power input shaft and typically, the first shaft is the inner shaft. The output shaft or second shaft can be a geared wheel.
Overrunning bi-directional clutches comprise a fixed ring, a slipper ring, cylindrical rollers which are housed between the two rings and may have an actuator. The fixed ring and the slipper ring are coaxial cylindrical rings with opposing faces. Each of the opposing faces has concave bearing surfaces which define pockets. Each pocket houses a roller.
The slipper ring has an axial groove or slit that extends both radially and axially through the ring. The slit allows the slipper ring to move radially under force and the memory inherent in the material from which the slipper ring is made allows the ring to return to a rest position once the force is withdrawn. The fixed ring is mounted onto the first shaft while the slipper ring is spaced in close proximity to the second shafts such that when the slipper ring moves radially, it engages the second shaft, thereby transferring power between the two shafts. Once the force is removed from the slipper ring, it returns to its rest position and no longer engages the second shaft.
The actuator is used to maintain the clutch in the freewheel mode and to move the clutch to the lock mode. Typically, the actuator has a radially moveable pin which is mounted to the fixed ring and retractable from the slipper ring. When the actuator pin engages both rings the two rings are coupled and the clutch is in the freewheel mode. In the freewheel mode, the opposing concave bearing surfaces are aligned with each other and the rollers rest in the bottom of each of the opposing concave surfaces. When the actuator pin is withdrawn from the slipper ring, the two rings move relative to one another and the rollers move out of the bottom of the opposing concave surfaces and rise up along diagonally opposing surfaces of the pocket so as to force the slipper ring to move radially and to engage the second shaft, thereby transferring power between the two shafts locking the clutch and placing the clutch in lock mode.
One of the limitations of overrunning bi-direction clutches is the amount of torque that can be transferred between the two shafts. Conventionally, in order to increase the amount of torque that the clutch can handle, the diameter of the rings is increased. The problem with increasing the diameter of the ring is that the volume needed for handling such clutches also increases. In certain applications, increase of diameter of the ring is not an option.
Another problem associated with overrunning bi-directional clutches is the vitality of the spring used to effect the lock mode of the clutch. The actuator has a spring which withdraws the actuator pin from the slipper ring to uncouple the two rings and effect the lock mode. The actuator also has a cam to move the actuator pin back into engagement of the slipper ring so as to couple the two rings and effect the freewheel mode. The spring can become worn and does not provide for direct control of the movement to lock mode.