Impact Mechanism for an Impact Wrench

• US 20090014193A1
• Filed: 04/13/2005
• Published: 01/15/2009
• Est. Priority Date: 04/13/2005
• Status: Active Grant

• Current Assignee: Cembre S.p.A.
• Original Assignee: Cembre S.p.A.
• Inventors: Barezzani, Gualtiero, Musoni, Gianfranco, Luciani, Gianpaolo
• Granted Patent: US 8,042,621 B2
• Time in Patent Office: Days
• US Class Current: 173/93
• CPC Class Codes: B25B 21/02 with means for imparting impact to screwdriver blade or nut socket
• CPC Class Codes: B25B 21/026 Impact clutches

Abstract

An impact mechanism (12) for an impact wrench comprises an anvil (8) with a middle portion (13), at least one abutment surface (14) radially protruding therefrom, which forms at least one abutment surface (15), a hammer (4) with an impact surface (16) suitable to give rotational pulses to the anvil (8) by the impact surface (16) hitting the abutment surface (15). The anvil (8) comprises a first connection area (17) connecting the abutment portion (14) to the middle portion (13) within the axial extension of the abutment surface (15) and the middle portion (13) and a reinforcement rib (18) axially arranged out of the abutment surfaces (15) that connects the abutment portion (14) to the middle portion (13) of the anvil (8), thereby forming a second connecting area

Claims

1. An impact mechanism (12) for an impact wrench (1), said impact mechanism (12) comprising:

an anvil (8) rotatable about a rotation axis (R) and provided with a middle portion (13), at least one abutment portion (14) radially protruding therefrom, which forms at least one abutment surface (15),

a hammer (4) rotatable about the rotation axis (R) and provided with at least one impact surface (16), wherein the hammer (4) is suitable to give rotational pulses to the anvil (8) by the impact surface (16) hitting the abutment surface (15), wherein the anvil (8) comprises a first connection area (17) connecting the abutment portion (14) to the middle portion (13), said first connection area (17) at least partially extending within the axial extension of the abutment surface (15) and the middle portion (13),

wherein the anvil (8) comprises a reinforcement rib (18) being axially arranged out of the abutment surfaces (15), which connects the abutment portion (14) to the middle portion (13) of the anvil (8), thereby forming a second connection area.

2. The impact mechanism (12) according to claim 1, wherein the anvil (8) comprises two abutment portions (14) that are arranged radially opposite relative to the rotation axis (R).

3. The impact mechanism (12) according to claim 1, wherein the reinforcement rib (18) has a greater circumferential extension, relative to the rotation axis (R), than the angular extension ([alpha]) of the abutment portion (14) or abutment portions (14).

4. The impact mechanism (12) according to claim 1, wherein the reinforcement rib (18) substantially extends to the radially outer end of the abutment portion (14) or abutment portions (14).

5. The impact mechanism (12) according to claim 1, wherein, in the areas remote from the abutment portions (14), the radial extension of the reinforcement rib (18) is lower than its radial extension in the areas near the abutment portions (14).

6. The impact mechanism (12) according to claim 1, wherein the reinforcement rib (18) is substantially flat and plate-like.

7. The impact mechanism (12) according to claim 1, wherein the reinforcement rib (18) lies in a plane perpendicular to the rotation axis (R).

8. The impact mechanism (12) according to claim 1, wherein the reinforcement rib (18) is approximately oval.

9. The impact mechanism (12) according to claim 1, wherein the abutment surfaces (15) are radial relative to the rotation axis (R).

10. The impact mechanism (12) according to claim 1, wherein each abutment portion (14) comprises two impact surfaces (16) opposite to each other, which define the angular extension ([alpha]) of the abutment portion (14), relative to the rotation axis (R), wherein the angular extension α

is 20°

-40°

.

11. The impact mechanism (12) according to claim 10, wherein the abutment portion (14) has a 25°

-35°

angular extension α

.

12. The impact mechanism (12) according to the preceding claim 11, wherein the abutment portion (14) has an angular extension α

of 30°

.

13. The impact mechanism (12) according to claim 1, wherein the reinforcement rib (18) has a lower thickness of the axial extension of the abutment surfaces (15) relative to rotation axis (R).

14. The impact mechanism (12) according to claim 1, wherein the thickness of the reinforcement rib (18) is selected in the range between 0.4 and 0.6 times the axial extension of the abutment surfaces (15) relative to the rotation axis (R).

15. The impact mechanism (12) according to claim 1, wherein the thickness of the reinforcement rib (18) is equal to 0.5 times the axial extension of the abutment surfaces (15) relative to the rotation axis (R).

16. The impact mechanism (12) according to claim 1, wherein the reinforcement rib (18) has a lower thickness of the axial thickness (17) of the first connection area (17) relative to the rotation axis (R).

17. The impact mechanism (12) according to claim 1, wherein the reinforcement rib (18) has a tapered or weight relieved radially outer area (19) near the abutment portion(s) (14).

18. The impact mechanism (12) according to claim 1, wherein the first connection area (17) substantially has the same axial thickness as the axial extension of the abutment surfaces (15).

19. The impact mechanism (12) according to claim 1, wherein the radial distance (D1) between the rotation axis (R) and the abutment surface/s is greater than the radial extension (D2) of said abutment surface(s) (15).

20. The impact mechanism (12) according to claim 1, wherein the ratio (D1/D2 ratio) of the radial distance (D1) between the rotation axis (R) and the abutment surface/s (15) to the radial extension (D2) of said abutment surface(s) (15) is selected in the range between 1.67 and 2.5.

21. The impact mechanism (12) according to claim 20, wherein said ratio (D1/D2 ratio) is about 2.09.

22. The impact mechanism (12) according to claim 1, wherein the hammer (4) comprises two impact relieves (26) that are arranged radially opposite relative to the rotation axis (R).

23. The impact mechanism (12) according to claim 1, wherein the abutment surfaces (16) are radial relative to the rotation axis (R).

24. The impact mechanism (12) according to claim 1, wherein each impact relief (26) comprises two impact surfaces (16) opposite to each other, defining a 20°

-40°

angular extension β

of the impact relief (26) relative to the rotation axis (R).

25. The impact mechanism (12) according to claim 1, wherein the impact relief (26) has 25°

-35°

angular extension β

.

26. The impact mechanism (12) according to claim 1, wherein the impact relief (26) has 30°

angular extension β

.

27. The impact mechanism (12) according to claim 1, wherein the radial distance (D3) between the rotation axis (R) and the abutment surface/s (16) is greater than the radial extension (D4) of said abutment surface(s) (16).

28. The impact mechanism (12) according to claim 1, wherein the ratio (D3/D4 ratio) of the radial distance (D3) between the rotation axis (R) and the abutment surface/s (16) to the radial extension (D4) of said abutment surface(s) (16) is selected in the range between 1.67 and 2.5.

29. The impact mechanism (12) according to claim 28, wherein said ratio (D3/D4 ratio) is about 2.17.

30. The impact mechanism (12) according to claim 1, wherein the hammer (4) comprises a rear portion (22) suitable to provide connection with a reduction mechanism (3) of the impact wrench (1) and a front portion (24) suitable to engage the anvil (8) for the latter to be rotatably driven, wherein said front portion (24) has a greater radial extension or diameter (D5) than the radial extension or diameter (D6) of the rear portion (22).

31. The impact mechanism (12) according to claim 1, wherein the rear portion (22) and the front portion (24) are connected by means of a connecting portion (27) that radially widens towards the front portion (24).

32. The impact mechanism (12) according to claim 1, wherein the connecting portion (27) has an overall substantially tubular shape, either of a truncated cone or bell-like shape, the wall thickness thereof increasing towards the front portion (24).

33. The impact mechanism (12) according to claim 31, wherein the maximum radial wall thickness of the connecting portion (27) is substantially equal to the radial extension (D4) of the impact relieves (26).

34. The impact mechanism (12) according to claim 31, wherein the front portion (24) comprises a base plate (25), the impact relieves (26) protruding therefrom in the axial direction, wherein said base plate (25) connects diametrically opposing areas of the front portion (24) thereby stiffening this front portion (24) in a plane perpendicular to the rotation axis (R).

35. The impact mechanism (12) according to claim 34, wherein the base plate (25) has the shape of an annular disc.

36. The impact mechanism (12) according to claim 34, wherein the axial thickness of the base plate (25) is lower than the radial wall thickness of the connecting portion (27) at the base plate (25).

37. The impact mechanism (12) according to claim 34, wherein the axial thickness of the base plate (25) is lower than or equal to the axial extension of the impact surfaces (16).

38. The impact mechanism (12) according to claim 1, wherein the hammer (4) comprises a strain relief groove (28) extending at the impact relief/relieves (26).

39. An impact wrench (1) comprising an impact mechanism (12) according to claim 1.