Socket Wrench Opening

The present invention relates generally to a rotary tool for driving a hexagonal and/or double hexagonal threaded fastener, and more particularly to a wrench socket opening having driving surfaces which improve the internal stress distributions of the socket.

The present invention relates to improvements in wrench socket designs which redistribute and reduce the internal stresses exerted on the socket during driving and which improve the driving performance of the socket by providing a driving surface at an angle which best matches the fastener face to be driven.

When designing socket wrench openings, to avoid breakage of the wrench and/or deformation of the fastener, it is desirable to minimize the stress exerted on the socket. It is likewise desirable to distribute, as uniformly as possible, the stress exerted on the socket. Stress analysis indicates that three important points of high stress exist when a socket wrench engages the flank or face of a hexagonal or double hexagonal fastener. The first area of stress is where the wrench driving surface meets the fastener face. It is desirable that this surface be as large as possible to more uniformly distribute the stress throughout the socket. It is also important that the drive surface be, as nearly as possible, parallel to the fastener face to minimize peak stress. This is achieved by orienting the drive surface at an angle which takes into account the position of the wrench when it engages the fastener. In this respect, a small clearance exists between the internal socket surface and the fastener to be driven. As this clearance is taken up in turning the wrench to engage the fastener, the wrench is angularly displaced relative to the fastener. Thus, there is a need to choose an angle for the wrench driving surfaces of the socket which best matches that of the fastener when the wrench is in the angularly displaced position.

The second important area of stress concentration is at the outer edge where the driving surface of the socket wrench ceases to contact the fastener, i.e. at the corner of the fastener. Because there is an abrupt contact pressure area at the corner of the fastener which results in an abrupt stress peak, it is desirable that the driving surface not contact the fastener at the corner thereof.

The third area of stress concentration is the portion of the wrench socket adapted to receive the corner of the fastener. In conventional wrench design, this area is a sharp arcuate angle which acts to concentrate the stress exerted on the socket.

The present invention provides a socket wrench opening which maximizes the drive face, avoids contact with the corner of the fastener, and eliminates a sharp angle, i.e. corner, and further provides a wrench socket opening shape which lends itself to efficient, reproducible, and economical manufacture.

In accordance with the present invention there is provided a wrench for turning a fastener nut having a central axis and an even numbered plurality of flat bounding surfaces parallel to the fastener access wherein diametrically opposite pairs of surfaces are parallel to each other and the bounding surfaces intersect in adjacent pair to form fastener corners. The wrench includes a fastener nut socket defined by a central socket axis. The socket includes a plurality of uniformly spaced peripherally and radially disposed protuberances and a plurality of uniformly spaced fastener corner clearance recesses disposed between protuberances. Each protuberance includes side by side, angularly related straight engaging surfaces at substantially 142 degrees outside obtuse angles to each other for registry with the flat surfaces on the fastener nut. Complementary side surfaces diverge outwardly from the engagement surfaces. Each engaging surface has a length substantially equal to 0.0867.times.the minor diameter of the fastener nut to be driven and the side surfaces diverge at least 3 degrees outwardly from the engaging surfaces. Each corner clearance recess is comprised of a first arcuate surface defined about the central axis of the socket and transition surfaces converging from the side surface of the adjacent protuberances outwardly toward the arcuate surface.

More specifically, the engaging surfaces of the socket opening are dimensioned to provide a larger driving surface and are oriented to position these surfaces generally parallel to the flat surfaces of the fasteners during driving engagement. This provides a more uniform distribution of the stress exerted on the socket. Likewise, the side surfaces, which diverge from the driving surfaces, are positioned such that the engaging surfaces of the socket avoid contact with the corner of the fastener. This eliminates any large stress peaks in the engaging surfaces. With respect to the corner recesses of the socket, the arcuate surface and the transition surfaces are dimensioned to provide an approximate rounded area which blends with the other wrenching surfaces. This avoids large stress concentration found in sockets having corner clearance recesses defined by shape arcuate angles.

Importantly, by defining the socket opening with mostly flat surfaces (the exception being the arcuate surface of the recess), it is easier to manufacture the foregoing punches which from the socket opening. In this respect, the disclosed socket design avoids "steps" or imperfections generally found in designs which attempt to include curved surfaces which intersect with each other, in that forging punches must be machined one tooth at a time by cutting tools which produce lines of intersection between each machining pass. This generally results in lines or ridges in designs having mating surfaces which are curved. In other words, designs which appear very smooth when drawn or drafted, are actually very difficult to manufacture. The present invention thus provides a plurality of flat surfaces, which provide a profile which is easier to machine, yet which at the same time avoids sharp corners and stress peaks.

Also important with respect to the present invention is that the claimed socket opening permits longer forging punch life. In this respect, in the practical business of making socket wrench openings, industry standards set certain tolerances which must be met and which effect the manufacture of the sockets. Generally socket openings are tested with gauges which establish the maximum and minimum opening sizes. In the art, it is generally well known that the corners of the forging punches generally wear faster than the flat engaging surfaces of the punch. It has been known to use as large a punch as possible so as to give a reasonable amount of wear on the corners before they become undersized. This results in the across flats dimension being on the large size if the punch is a hexagon design because the across the flats dimension is fixedly linked to the across the corners dimension of the punch. The present invention enables a punch having a reduced across the flat dimension wherein the initial size of the punch can be dimensioned to lie in the midsize of the gauging range. As set forth above, the included angle of the driving surfaces of the wrench are oriented to compensate for the rotation that occurs between the wrench and fastener in the process of engagement. The angle is chosen so as to produce close to parallel engagement between the engaging surface of the socket and the flat portion of the fastener over the range of acceptable fastener sizes. Thus, in addition to providing a socket opening which reduces and distributes more evenly the internal stress exerted on the socket during driving, the present design facilitates reproduction of the socket, as well as forging punch life.

It is an object of the present invention to provide a multi-sided drive for hexagonal and double hexagonal fasteners having drive surfaces which are substantially parallel to the surface flats of the fasteners during driving.

It is another object of the present invention to provide a multi-sided drive as described above which eliminates sharp arcuate angles in the fastener corner clearance recess.

It is another object of the present invention to provide a multi-sided drive as described above which reduces and more uniformly distributes the internal stress that is exerted on the socket during driving.

Another object of the present invention is to provide a multi-sided drive as described above having a shape which lends itself to efficient reproduction and which facilitates longer forging punch life.

These and other objects and advantages will become apparent from the following description of a preferred embodiment of the invention taken together with the accompanying drawings.

The invention may take physical form in certain parts and arrangement of parts, an embodiment of which is described in detail in the specification and illustrated in the accompanying drawings wherein:

FIG. 1 is a perspective view of a socket wrench illustrating the shape of a preferred embodiment of the present invention;

FIG. 2 is an enlarged plan view of the socket shown in FIG. 1;

FIG. 3 is an enlarged view of area 3--3 of FIG. 2 illustrating a typical protuberance and corner recess of the socket shown in FIG. 1;

FIG. 4 is an enlarged view showing the typical surface contact between the engaging face of a socket according to the present invention an the flat portion of a hexagonal or double hexagonal fastener; and

FIG. 5 is an enlarged view of a socket according to the present invention shown in relation to a maximum size standard fastener and socket-opening gauges.

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the present invention and not for purpose of limiting same, FIG. 1 shows a wrench socket for turning a polygonally shaped element such as a conventionally known hexagonal or double hexagonal threaded fastener. For the purpose of illustration, a hexagonal fastener 20 is shown in phantom in FIG. 2. Fastener 20 includes a number of planar faces 22 which are generally parallel and equidistant from a central axis 24. Faces or flanks 22 intersect at dihedral angles to form corners 26. The illustrated fastener 20 is considered as having standard dimensions for any given size and is within the maximum-minimum standard across opposed faces 22--22.

The socket wrench 10 is comprised of a generally cylindrical body 30 which is provided at one end with a substantially square socket 32 (best seen in FIG. 2) for reception of the operating stem of a suitable socket wrench, a motor driven spindle or other actuating member (not shown). The other end of body 30 is provided with a work receiving cavity 34 which is symmetrical about an axis 35, which in FIG. 2 is coincident with axis 24 of fastener 20. Cavity 34 is comprised of an even-numbered plurality of uniformly spaced peripherally and radially disposed protuberances 36 having an equal number of nut corner clearance recesses 38 disposed therebetween. (As used hereinafter, inward or inner shall designate a direction toward the central axis 35 of socket 10, and outward or outer shall designate a direction away from axis 35.)

In the embodiment shown, socket 10 includes twelve (12) protuberances 36 an twelve (12) corner recesses 38. In FIG. 3 an enlarged portion of a socket according to the present invention is shown in relation to axes designated "X" and "Y" which are normal to each other and intersect at the central axis 45 of the socket. Each protuberance 36 includes side by side nut engagement or driving surfaces 40, 42 which diverge outwardly from a point 44. Driving surfaces 40, 42 are disposed at substantially 142.degree. (degrees) outside obtuse angles to each other for registry with the planar faces or flanks 22 of fastener 20. Engagement surfaces 40, 42 have identical predetermined lengths which terminate at edges 46, 48 respectively. Complementary side surfaces 50, 52 diverge outwardly away from surfaces 40, 42 at edges 46, 48. In the embodiment shown, side surfaces 50, 52 diverge away from engagement surfaces 40, 42 respectively at a 5.degree. (degree) angle.

Nut corner clearance recesses 38 are comprised of an arcuate surface 54, and transitional surfaces 56, 58 which diverge from arcuate surface 54 and intersect with complementary side surfaces 50, 52 of adjacent protuberances 36. Arcuate surface 54 is defined by a circle about socket axis 45. Preferably, arcuate surface 54 and transitional surface 56, 58 approximate a circular arc connecting diverging surfaces 40, 42 of adjacent protuberances 32. To minimize stress concentrations at the corners defined by the respective surfaces, it is also preferable that the angle defined between arcuate surface 54 and an adjacent transitional surface 56, 58 by approximately equal to the angle defined between a transitional surface 56, 58 and a diverging surface 50, 52. In this respect, by equalizing these angles, the stress concentrations resulting from such corners are minimized and distributed, to the extent possible, along the entire corner recess 38.

The present invention provides a corner recess design which is easy to manufacture, yet approximates the optimum design of a fully rounded corner. In this respect, a truely rounded corner recess is not actually possible due to manufacturing limitations in creating the forgoing punches used to manufacture the sockets. Cutting machines which cut the forging punch make a number of successive passes along the punch cutting flat surfaces which together approximate a curve. Such cutting machines inevitably leave "steps" between the successive passes. In the present invention, because socket cavity 34 is comprised essentially of flat surfaces, greater dimensional accuracy is provided when manufacturing the forging punches used to form the socket opening 34. As will be appreciated, arcuate surface 54, which is disposed on the periphery of a forging punch, may be machined by a lathe thereby ensuring dimensional accuracy.

The length and orientation of the planar surfaces defining socket cavity 34 is determined by the size of the fastener nut 20 to be turned as well as certain design criteria. In this respect, these planar surfaces are dimensioned to maximize the driving surfaces 40, 42 to avoid contact with the corners 26 of fastener 20; to minimize stress concentrations by avoiding sharp arcuate angles such as at the corner recesses 38; to provide a more parallel engagement between driving surfaces 40, 42 and fastener faces 22. As shown in FIG. 3, the shape of the socket opening 34 may be defined with reference to X-Y coordinates relation to central axis 45. The specific dimensions of the respective surfaces of socket 34 are preferably determined by the following formulas. ##EQU1## In the aforementioned formulas, "MINIMUM FLATS" refers to the industry standard minimum dimension across the flats of a fasteners, and "MEAN FLATS" refers to the standard mean or average dimension across the flats of a typical fastener. The length of engagement surface 40, 42 may be calculated using the above formulas and standard trigonometric functions. The length of such surfaces are substantially equal to 0.867.times.minor diameter of the fastener nut be driven.

As heretofore described, the side-by-side angular related straight surfaces 40, 42 are disposed at substantially 142.degree. (degrees) outside obtuse angles to each other. This 142.degree. (degree) angle (compared to the 150.degree. angle found in the regular double hexagonal opening) provides improved contact between the engagement surfaces 40 and the fastener faces 22. Importantly, the position of engagement surfaces 40 takes into account the position of the wrench at engagement with the fastener during actual driving, which position depends upon the amount of clearance between the wrench and the fastener. More specifically, as the clearance is taken up in timing the wrench to engage the fastener, there is an angular displacement of the wrench relative to the fastener. Thus there is a need to select an angle of engagement surface 40 which best matches that of fastener 20 at that specific position.

FIG. 4 illustrates the position of the respective surfaces of socket 34 and a maximum sized fastener 20. As can be seen, engagement surface 40 approximates the position of planar face 22 of fastener 20. As can also be seen, edge 46 is located away from corner 26 of fastener 20. Thus, the present invention provides improved surface engagement between the socket and the fastener yet avoids contact with the corner 26 of fastener 20.

FIG. 5 illustrates the relative position of socket opening 20 with respect to a maximum sized fastener, a well as to conventional GO and NO GO gauges shown in phantom. As set forth previously, such gauges are used to determine whether a given socket opening is without proper clearance standards. As also mentioned above, forging punches normally wear at the corners thus reducing the overall corner dimension. In this respect, in practice it has been known to use as large a punch as possible so as to give a reasonable amount of wear on the corners before they become undersized and the GO gauge no longer enters the socket opening. This results in a cross flats dimension being on the large size of the punch of a hexagonal design because the across the flats dimension is fixedly linked to the across the corners dimension. As seen in FIG. 5, a portion of the engagement surface 40 of socket 34 falls between the NO GO and GO gauges. In this respect, a forging punch for the disclosed socket opening starts with a closer tolerance in the fastener engaging area of the socket. Thus, as the forging punch begins to wear and the socket opening becomes smaller (the socket corner wears faster than the socket flanks or engaging faces), the increase in the area about the fastener corner enables longer forging punch life without starting with a socket which is oversized in the driving area.

Thus, the present invention provides a socket opening design which increases the driving surface area of the sockets which in turn minimizes and more uniformly distributes the internal therealong. At the same time, a socket according to the present invention avoids contact with the fastener corner which produces high stress concentrations. In addition, the present invention provides a socket design wherein the corner clearance recesses avoid sharp arcuate surfaces by providing a generally rounded corner further reducing stress concentration. Still further, the present invention provides a socket design comprised primarily of planar surfaces which facilitate the design and manufacture of forging punches necessary to fabricate the sockets. As set forth above, the present invention provides a design wherein the angle between adjacent engagement surfaces provides better mating between such engagement surfaces and the flats of the fastener. This also provides less clearance with respect to the socket by positioning a portion of the driving surface between the typical GO and NO GO gauges.

The present invention has been described with respect to a preferred embodiment. Modifications and alterations will occur to others upon the reading and understanding of this specification. It is intended that all such modifications and alterations be included insofar as they come within the scope of the patent as claimed or the equivalence thereof.