Patent ID: 8475466

Claim:
A torque-limiting fastener driver, which comprises: a) a housing comprising a proximal housing section having a drive end at which a drive interface is disposed, and a distal housing section connected to the proximal housing section by a housing coupling, wherein the distal housing section has a shaft port into which a driver output shaft is detachably insertable to extend along a rotation axis of the fastener driver; b) a torque-limiting assembly disposed within the housing, the torque-limiting assembly comprising: i) a cam bearing assembly comprising at least two ball bearings held in a departured relationship to each other by a ball cage, and ii) an outer cam race in which the ball bearings are received, wherein the outer cam race has an inner race surface provided with a plurality of repeating asymmetric cam lobes, each asymmetric cam lobe comprising a cam high point spaced from a bottom ball detent portion intermediate opposed ramp portions of a lesser and a greater pitch, and iii) an inner race comprising a dome-shaped outer surface aligned symmetrically along the rotation axis, iv) wherein the outer cam race contacts each ball bearing received in a lobe at a radial vector (Vr) that is aligned substantially along a radius perpendicular to the rotation axis of the fastener driver, and the outer surface of the inner race contacts each ball bearing at a non-radial vector off-set by an angle from the radial vector; and c) a bearing load assembly providing a bias force (F) against the torque-limiting assembly, wherein the bias force is adjustable to selectively set a maximum amount of torque that is transmittable via the drive interface to the driver output shaft that is detachably insertable into the shaft port at the distal section of the housing, d) wherein in a rest position of the driver, the ball bearings reside in the bottom ball detent portion of a first cam lobe of the outer cam race and in contact with the inner race, and e) wherein with the driver output shaft received in the shaft port at the distal housing section, the drive end of the proximal housing section is manipulatable to impart a torque force that causes the inner race to rotate about the rotation axis as the ball bearings contacting the outer cam race at the radial vector move up the lesser pitch ramp of one of the plurality of asymmetric cam lobes while contacting the outer surface of the inner race at the non-radial vector to thereby axially displace the inner race in a first direction along the rotation axis until the ball bearings crest at the cam high point and fall along the greater pitch ramp into the bottom ball detent portion of a next one of the plurality of asymmetric cam lobes with the inner race then moving in a second, opposite direction along the rotation axis back to the rest position.