Torque limiting device for air impact tool

Abstract

An air impact tool has an air motor driving a rotary impact mechanism which has a drive shaft which is coupled to a coaxial load shaft through a torque-limiting clutch mechanism which includes a rigid torque member coupled to one of the shafts and having a peripheral drive surface with drive surface portions, and a yieldable torque member coupled to the other shaft. A plurality of flexible and resilient arms on the yieldable torque member are equiangularly spaced apart around the axis of rotation parallel thereto and are cantilevered from a support yoke, the distal ends of the arms being respectively engaged with the drive surface portions of the torque receiving member. A retaining cylinder encircles the arms and holds them against the drive surface, the retaining cylinder being threadedly engaged with an adjusting member which is rotatable but axially fixed to effect axial movement of the retaining cylinder to vary the retaining force on the torque transmitting arms. Embodiments showing internally and externally threaded retaining cylinders, and planar and concave drive surface portions are disclosed.

I claim: 
     
       1. A torque limiting mechanism comprising: two coaxial shafts having an axis of rotation, a rigid torque member coupled to one of said shafts and having a peripheral drive surface including a plurality of drive surface portions, a plurality of flexible and resilient torque members coupled to the other of said shafts for engagement with said peripheral drive surface, threaded cylindrical retaining means encircling said resilient torque members and disposed in engagement therewith for holding said resilient torque members in engagement with said peripheral drive surface with a predetermined force for preventing rotation of said resilient torque members and said rigid torque member relative to each other about said axis at torques below a predetermined torque, said retaining means having a sloping engagement portion shaped and dimensioned substantially to make point contact with each of said resilient torque members longitudinally thereof, said resilient torque members being yieldable at said predetermined torque and above to accommodate relative rotation between said resilient torque members and said rigid torque member, an adjusting member encircling said resilient torque members and disposed in threaded engagement with said cylindrical retaining means, and means coupled to said adjusting member for accommodating rotation thereof about said axis while preventing axial movement thereof, thereby to effect axial movement of said cylindrical retaining means relative to said resilient torque members for varying said predetermined force to vary the torque at which said resilient torque members will yield.   
     
     
       2. The mechanism of claim 1, wherein said retaining means is internally threaded. 
     
     
       3. The mechanism of claim 2, wherein said adjusting member is manually rotatable about said axis. 
     
     
       4. The mechanism of claim 3, and further comprising manually operable means removably mounted on said adjusting member for facilitating manual rotation thereof. 
     
     
       5. The mechanism of claim 1, and further comprising anti-rotation means coupled to said retaining means for preventing rotation thereof. 
     
     
       6. The mechanism of claim 5, wherein said anti-rotation means includes a housing encompassing said retaining means and having an opening therein, and a set screw extending through said opening and engageable with said retaining means. 
     
     
       7. The mechanism of claim 6, wherein said retaining means has an elongated axial groove therein, said set screw being fixed to said housing and disposable in said groove for guiding axial movement of said retaining means while preventing rotation thereof. 
     
     
       8. The mechanism of claim 1, wherein said retaining means is externally threaded. 
     
     
       9. The mechanism of claim 8, and further comprising gear mechanism coupled to said adjusting member for effecting rotation thereof. 
     
     
       10. The mechanism of claim 1, wherein said peripheral drive surface has a transverse cross section which defines a regular polygon. 
     
     
       11. The mechanism of claim 1, wherein said drive surface portions are concave. 
     
     
       12. The mechanism of claim 1, and further comprising support means coaxial with said shafts and unitary with said resilient torque members for supporting said resilient torque members in cantilever fashion. 
     
     
       13. The mechanism of claim 12, wherein each of said resilient torque members is generally trapezoidal in transverse cross section. 
     
     
       14. The mechanism of claim 12, wherein said resilient torque members are removably mounted on said support means. 
     
     
       15. A power tool for applying torque to a load comprising: motive means for generating torque, two coaxial shafts respectively adapted for coupling to the load and said motive means and having an axis of rotation, and torque-limiting clutch mechanism interconnecting said shafts, said clutch mechanism including a rigid torque member coupled to one of said shafts and having a peripheral drive surface including a plurality of drive surface portions, a plurality of flexible and resilient torque members coupled to the other of said shafts and disposed for engagement with said peripheral surface, threaded cylindrical retaining means encircling said resilient torque members and disposed in engagement therewith for holding said resilient torque members in engagement with said peripheral drive surface with a predetermined force for preventing rotation of said resilient torque members and said rigid torque member relative to each other about said axis at torques below a predetermined torque, said retaining means having a sloping engagement portion shaped and dimensioned substantially to make point contact with each of said resilient torque members longitudinally thereof, said resilient torque members being yieldable at said predetermined torque and above to accommodate relative rotation between said resilient torque members and said rigid torque member, an adjusting member encircling said resilient torque members and disposed in threaded engagement with said cylindrical retaining means, and means coupled to said adjusting member for accommodating rotation thereof about said axis while preventing axial movement thereof, thereby to effect axial movement of said cylindrical retaining means relative to said resilient torque members for varying said predetermined force to vary the torque at which said resilient torque members will yield.   
     
     
       16. The power tool of claim 15, wherein said tool is an impact tool. 
     
     
       17. The power tool of claim 15, wherein said retaining means is internally threaded. 
     
     
       18. The power tool of claim 15, wherein said retaining means is externally threaded. 
     
     
       19. The power tool of claim 15, and further comprising anti-rotation means coupled to said retaining means for preventing rotation thereof. 
     
     
       20. The power tool of claim 15, wherein said peripheral drive surface has a transverse cross section which defines a regular polygon. .Iadd. 
     
     
       21.  A torque limiting mechanism comprising: first and second rotatable torque structures,   the first torque structure including a rigid torque member having a peripheral drive surface including a plurality of drive surface portions,   the second torque structure having an axis of rotation and including a plurality of flexible and resilient torque members spaced radially from the axis and engageable with said peripheral drive surface;   a retainer disposed entirely radially outwardly of the entirety of said resilient torque members and disposed in engagement therewith for holding said resilient torque members in engagement with said peripheral drive surface with a predetermined force for preventing rotation of said resilient torque members and said rigid torque member relative to each other at torques below a predetermined torque,   said resilient torque members being yieldable at said predetermined torque and above to accommodate relative rotation between said resilient torque members and said rigid torque member; and   rotatable adjusting structure disposed entirely radially outboard of the entirety of said resilient torque members and threadedly engaged with said retainer for cooperation therewith to effect axial movement of said retainer relative to said resilient torque members for varying the predetermined force to vary the torque at which said resilient torque members will yield. .Iaddend.