Externally adjustable clutch

1. An adjustable clutch assembly comprising:

a base portion;

a clutch housing cap;

a first rotary member having a first torque transfer surface;

said first rotary member configured to rotate about a clutch axis and to rotationally couple to a first shaft;

a second rotary member having a second torque transfer surface opposing said first torque transfer surface of said first rotary member at a slip joint;

said second rotary member configured to rotate about said clutch axis and to rotationally couple to a second shaft;

a spring element disposed axially between said clutch housing cap and said first rotary member and configured to bias said opposed first and second torque transfer surfaces axially towards each other;

a gear drive comprising a wheel configured to rotate about said clutch axis and a shaft in engagement with said wheel and configured to rotate about an adjustment axis to thereby selectively rotate said wheel about said clutch axis;

said wheel in engagement with said clutch housing cap;

said shaft having a first portion to which an adjustment torque may be applied;

a locking element constraining rotational movement of said clutch housing cap relative to said base portion; and

said gear drive, said base portion, said locking element and said clutch housing cap configured such that selective rotation of said wheel about said clutch axis causes axial movement of said clutch housing cap along said clutch axis relative to said base portion or said second rotary member;

whereby said bias of said spring may be adjusted by rotation of said shaft.

2. The assembly set forth in claim 1 , wherein said first rotary member is a driving member and said second rotary member is a driven member.

3. The assembly set forth in claim 1 , wherein said first torque transfer surface comprises a friction liner layer.

4. The assembly set forth in claim 1 , wherein said spring element comprises a cylindrical compression spring oriented about said clutch axis.

5. The assembly set forth in claim 4 , wherein said clutch housing cap comprises a spring seat axially retaining a first end of said spring and further comprising a spring cup receiving a second end of said spring.

6. The assembly set forth in claim 5 , and further comprising a bearing disposed axially between said spring cup and said first rotary member and disposed radially between said first rotary member and said clutch housing cap.

7. The assembly set forth in claim 6 , and further comprising a cylindrical bushing disposed radially between said bearing and said clutch housing cap.

8. The assembly set forth in claim 1 , wherein said wheel comprises an outer cylindrical surface having outwardly extending circumferentially spaced teeth and said shaft comprises an outer cylindrical surface having a threaded portion, and wherein said engagement of said wheel with said shaft comprises said threaded portion of said shaft rotationally engaging said teeth of said wheel.

9. The assembly set forth in claim 1 , wherein said first portion of said shaft comprises a recess configured to receive a torqueing tool.

10. The assembly set forth in claim 1 , wherein said clutch housing cap comprises an outer cylindrical surface having a threaded portion and said wheel comprises an inner cylindrical surface having a threaded portion, and wherein said engagement of said wheel with said clutch housing cap comprises said threaded portion of said inner cylindrical surface of said wheel rotationally engaging said threaded portion of said outer cylindrical surface of said clutch housing cap.

11. The assembly set forth in claim 1 , wherein said locking element comprises an annular locking plate fixed to said base portion and engaging an outer surface of said clutch housing cap.

12. The assembly set forth in claim 11 , wherein said annular locking plate comprises multiple protrusions extending radially inwards towards said clutch axis and said outer surface of said clutch housing cap comprises multiple axially extending grooves, wherein said protrusions may slide axially relative to said clutch axis in said grooves and are constrained from rotational movement about said clutch axis by said grooves, whereby said clutch housing cap is axially movable relative to said base portion and rotationally constrained relative to said base portion.

13. The assembly set forth in claim 11 , wherein said annular locking plate is fixed to said base portion via a plurality of shaft elements.

14. The assembly set forth in claim 11 , wherein said wheel is rotationally supported by a plurality of bearings and said bearings are supported between said annular locking plate and said base portion on said respective shaft elements.

15. The assembly set forth in claim 14 , wherein said shaft elements comprise turn studs and further comprising multiple spring elements disposed between said annular locking plate and said respective bearings on said respective turn studs and configured to bias said locking plate away from said base portion.

16. The assembly set forth in claim 1 , and further comprising a hoist housing fixed to said base portion and a second bearing disposed radially between said second rotary member and said hoist housing.

17. The assembly set forth in claim 16 , wherein said second rotary member comprises an outer journal for receiving said second bearing.

18. The assembly set forth in claim 1 , wherein:

said first rotary member and said spring element are disposed between said base portion and said clutch housing cap;

said clutch housing cap has an inner surface and said first rotary member has a surface opposing said inner surface of said clutch housing cap;

said spring element acts between said inner surface of said clutch housing cap and said surface of said first rotary member opposing said inner surface of said clutch housing cap; and

wherein said clutch housing cap and said first rotary member are configured such that axial movement of said clutch housing cap relative to said first rotary member adjusts said bias of said spring element.

19. The assembly set forth in claim 18 , wherein said gear drive is disposed outside of said clutch housing cap.