Impact wrench having an improved anvil to square driver transition

An anvil adapted to be received within an impact wrench comprises a round body and a square head. The square head is formed at an end of the round body. A tapered ramp extends from the round body to the square head. A radius is formed in the tapered ramp. The radius is defined by a removal of material in the tapered ramp.

FIELD OF THE INVENTION

The present invention relates to an impact wrench and more particularly to an improved anvil in an impact wrench.

BACKGROUND OF THE INVENTION

The traditional design of an anvil for use in an impact wrench includes a round portion that transitions to a square portion. The round portion is received within the impact wrench and acts as a bearing journal. The square portion is received within an impact socket. The transition from the round cross section to the square cross section inherently creates sharp radii within the transition.

These sharp radii may create some inefficiencies in the design. Initially there is minimal clearance between the square portion of the anvil and the impact socket when the pieces are new. However, the impact socket may, over a long period of use, become “damaged”, resulting in a looser fit to the square portion of the anvil. This increased clearance between the square portion interface and the impact socket allows the centerline of the square portion of the anvil and the centerline of the impact socket to become non-parallel. When this occurs, the theoretical line contact between the two that exists axially along the interface of the square portion and the impact socket become points of contact. These points of contact form at the sharp radii in the transition between the round body and the square drive and lead to points of increased stress.

Moreover, as the impact socket becomes “damaged”, the corners of the impact socket tend to “dig” into the sharp radii in the transition. This digging between the impact socket and the square portion can damage the anvil.

Sharp radii also act as stress concentration zones within the anvil. As the stress builds at these points, the anvil may fail at the sharp radii. This then can contribute to an early failure of the anvil.

One solution to the problem of sharp radii in an anvil is to increase the overall strength of the anvil. For example, a thermo cryogenic treatment can be applied to the anvil during manufacturing. However, this added step increases the overall cost of manufacturing the anvil and does not directly address the problems associated with the sharp radii.

Accordingly, there remains a need in the art to provide an improved anvil design that eliminates the stress concentration zones and prolongs the life of the anvil while simultaneously reducing costs associated with its manufacture.

SUMMARY OF THE INVENTION

An anvil adapted to be received within an impact wrench is provided. The anvil comprises a round body and a square head formed at an end of the round body. A tapered ramp extends from the round body to the square head. A radius is formed in the tapered ramp. The radius is defined by a removal of material in the tapered ramp.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 1of the drawings, an exemplary impact wrench8is illustrated to include an improved anvil100that is constructed in accordance with the teachings of the present invention. The impact wrench8also includes a housing12containing an electric motor14whose output is coupled to a gear assembly16. The gear assembly16transfers the output to a cam and carrier18which in turn drives an impactor20. The improved anvil100is mounted within the impactor20. A trigger and handle assembly22mounted to the housing12is used to activate the electric motor14.

With reference now toFIG. 2, a prior art anvil is indicated by reference numeral10. The prior art anvil10includes a round body30and a square drive head32. A transition zone34connects the round body30to the square drive head32, as will be described in greater detail below.

The round body30is generally cylindrical in shape and includes an enlarged base36at one end thereof. The enlarged base36includes two locking wings38extending therefrom and adapted to be received within the impactor20. A base radius40extends around the circumference of the enlarged base36and extends to the round body30thereby connecting the two portions.

The square drive head32includes side faces42and a front face44. A détente pin hole46extends from one of the side faces42through the drive head32. The détente pin hole46is sized to receive a détente pin, not shown. A roll pin hole48extends from another side face42into the square drive head32. The square drive head32is adapted to be inserted into a tool piece, not shown.

The transition zone34includes a tapered ramp52extending from the round body30to the square drive head32. Sharp radii54are formed at the corners of the square drive head32where the faces42meet the tapered ramp52. These sharp radii54form stress concentration zones and are the sources of potential material failure of the anvil10.

With reference now toFIGS. 3 and 4, the improved anvil100will now be described in detail. The improved anvil100includes the round body30of the prior art design. However, the improved anvil100includes an improved square drive head132and an improved transition zone134.

The improved square drive head132includes side faces142and a front face144. A détente pin hole146extends from one of the side faces142through the improved square drive head132. The détente pin hole146is sized to receive a détente pin, not shown. A roll pin hole148extends from the front face144into the improved square drive head132. The roll pin hole148is offset from the longitudinal axis of the anvil100. A cutout149surrounds the roll pin hole148and aids in the removal of the roll pin (not shown) for maintenance purposes. The reorientation of the roll pin hole148to the front face144of the anvil100rather than through the side faces42(as illustrated inFIG. 2) decreases the amount of stress applied to the improved square drive head132, thereby increasing its lifespan. The improved square drive head132is adapted to receive a tool piece, not shown.

With reference now toFIG. 4, and continued reference toFIG. 3, the transition zone134includes a tapered ramp152extending from the round body30to the improved square improved square drive head132. It should be understood that the tapered ramp can be eliminated by making the square head and round body of the same general diameter. The improved anvil100design introduces a removal of material in the transition zone134between the round body30and improved square drive head132of the anvil100, specifically at the tapered ramp152. This removal of material forms a radius154around the circumference at the tapered ramp152. As shown inFIG. 4, the cross-sectional area of the anvil100at the radius154is smaller than the cross-sectional area of the square drive head132.

The radius154eliminates the sharp radii54(FIG. 2) seen on the prior art design and eliminates these stress concentration zones and potential sources of failure in the anvil100. Specifically, the prior art anvil10(FIG. 2) experiences a load of 975 Mpa of stress on the square drive head32through the radii zone54when tested under a work load. The improved anvil100experiences a load of 414 Mpa of stress on the square drive head132through the transition zone134into the round body30when tested under the same work load. Accordingly, the anvil100has an improved lifespan over the prior art design (FIG.2).