Torque limiting fastener
An adjustable torque limiting fastener has a shank extending along an axis from a proximal end to a distal end. The fastener has a head at the proximal end of the shank. A torque limiter is integrated between the head and the shank. The torque limiter is operable to rotatably decouple the head from the shank when a torque applied to the head exceed a maximum torque. The maximum torque is set by a spring plunger integrated to the head for friction engagement with the proximal end of the shank.
1 . A fastener comprising:
a shank extending along an axis from a proximal end to a distal end, the shank having a threaded portion at the distal end;
a head defining a cavity coaxial with the axis, and a plunger hole transversal to the cavity, the proximal end of the shank extending into the cavity, wherein the cavity has an open end on a side of the head opposite to the shank, and wherein the open end of the cavity is closed by a cap mounted to the head;
a wheel fixed to the proximal end of the shank inside the cavity of the head, the wheel axially retained captive inside the cavity by the cap;
a torque limiter between the head and the wheel, the torque limiter operable to rotatably decouple the head from the wheel when a torque applied to the head exceed a torque limit, the torque limiter comprising:
a spring-loaded plunger mounted in the plunger hole, the spring-loaded plunger including a plunger and a compression spring pressing the plunger in engagement with a detent provided on the wheel; and
an adjustment screw threadably engaged with a threaded portion of the plunger hole, the adjustment screw adjustable in the plunger hole to adjust a compression of the compression spring.
2 . The fastener of claim 1 , wherein the compression spring is held in compression between the adjustment screw and the plunger, the adjustment screw operable to vary a force exerted by the compression spring on the plunger.
3 . The fastener of claim 1 , wherein the detent includes a circumferential array of depressions defined in an outer surface of the wheel, the plunger engageable in the depressions to clamp the head to the shank.
4 . The fastener of claim 3 , wherein the circumferential array of depressions are formed in a circumferential peripheral surface of the wheel about the axis.
5 . The fastener of claim 4 , further comprising a bushing fitted over the proximal end of the shank inside the cavity of the head, the bushing axially adjacent to the wheel.
6 . The fastener of claim 1 , wherein the cap is at least partly transparent over the spring-loaded plunger, and wherein a visual scale including graduated markings is provided on the cap along a length of the spring-loaded plunger to correlate an insertion depth of the adjustment screw to the torque limit to be applied on the head to overcome a coupling force exerted by the spring-loaded plunger on the wheel.
7 . The fastener of claim 1 , wherein the wheel is axially trapped between the cap and an inner annular arresting shoulder formed in the cavity.
8 . The fastener of claim 1 , wherein the plunger includes a ball or a rounded tip projecting partly out from the plunger hole into the cavity for engagement with the detent.
9 . A fastener comprising:
a shank extending along an axis from a proximal end to a distal end;
a head at the proximal end of the shank; and
a wheel secured to the proximal end of the shank inside a cavity defined in the head;
a bushing fitted over the proximal end of the shank inside the cavity of the head, the bushing axially adjacent to the wheel; and
a torque limiter between the head and the wheel on the shank, the torque limiter operable to rotatably decouple the head from the shank when a torque applied to the head exceed a maximum torque, the maximum torque set by a spring plunger integrated to the head for friction engagement with the wheel at the proximal end of the shank.
10 . The fastener of claim 9 , wherein the spring plunger comprises a compression spring disposed in a plunger hole defined in the head of the fastener, a plunger pressed by the compression spring against the proximal end of the shank, and an adjustment screw threadably engaged with mating threads defined in the plunger hole, the adjustment screw operatively connected to the compression spring to adjust a compression level of the compression spring.
11 . The fastener of claim 10 , wherein the plunger hole intersects the cavity, the plunger partially projecting out from the plunger hole into the cavity for friction engagement against the wheel secured to the proximal end of the shank.
12 . The fastener of claim 11 , wherein the compression spring urges the plunger in friction contact against a circumferential surface of the wheel.
13 . The fastener of claim 12 , wherein the circumferential surface has a plurality of circumferentially distributed detents, the plunger engageable with the detents.
14 . An adjustable torque limiting bolt comprising:
a shank extending along an axis from a proximal end to a distal end, the shank having a threaded portion at the distal end;
a head defining a cavity, the proximal end of the shank extending into the cavity; and
a torque limiter integrated to the head for rotatably decoupling the head from the shank when a torque applied to the head exceed a pre-set torque, the torque limiter including one or more ball detents, a first one of the one or more ball detents including a spring urging a ball in engagement with a detent provided at the proximal end of the shank inside the cavity of the head, the spring operatively connected to an adjustment screw threadably engaged with the head, the adjustment screw operable to adjust the pre-set torque by varying a compression of the spring; and
wherein the first one of the one or more ball detents comprises a visual scale, the visual scale correlating the pre-set torque to an insertion depth of the spring.
15 . The adjustable torque limiting bolt of claim 14 , wherein the one or more ball detents comprise an array of ball detents circumferentially distributed about the shank inside the head, each ball detents of the array of ball detents being individually adjustable.
16 . The adjustable torque limiting bolt of claim 14 , wherein the cavity is closed by a cap mounted to the head, the visual scale including graduations provided on the cap.
17 . The adjustable torque limiting bolt of claim 14 , wherein the proximal end of the shank comprises a wheel, the one or more ball detents frictionally engaged with a circumferentially extending peripheral surface of the wheel, the wheel retained axially captive within the cavity.