Abstract:
A tension indicator for use with a fastener that is formed from a stack of conical washers confined in the stack by a cage having a longitudinally extending slot formed therein provides readily discernible visual indication of tension or loss of tension in the fastener joint. The indicator includes a body configured for receipt over the stack of conical washers. The body can include at least one stanchion extending inwardly of the body from the interior surface to define a stanchion end longitudinally spaced from the body end. At least one detent extends inwardly of the body and is longitudinally spaced from the body end. When the stack of conical washers is placed under tension with the uppermost washer in a planar condition, the stanchion lies adjacent the uppermost washer at the interior region. When the stack of conical washers is under a tension insufficient to urge the uppermost washer into the planar condition, the stanchion abuts the uppermost washer at the interior region and the detent is disengaged from the slot in the cage side portion to prevent the cap from securing to the fastener. The body can include an opening for receipt of a gauge for contacting the interior region of the uppermost washer and for determining a height difference between the outer periphery of the uppermost washer and the interior region of the fastener.

Description:
FIELD OF THE INVENTION 
     The present invention pertains to tension loss indicators for a wheel lug nut. More particularly, the present invention pertains to devices for indicating a loss of torque in a lug nut, such as that used for mounting wheels for trucks and utility vehicles. 
     BACKGROUND OF THE INVENTION 
     One type of lug nut is a PACNUT® (PACNUT® is a registered trademark of Illinois Tool Works of Glenview, Ill.). The PACNUT® includes a stack of conical washers assembled on a base washer. The conical and base washers are held in place by a cage and are internally threaded to secure to, for example, a threaded bolt shank. When the PACNUT® is placed in tension, the conical washers are flattened to produce a locking action that results in tension or stretch in the joint. Exemplary of a PACNUT® type of fastener is that fastener disclosed in Mitts, U.S. Pat. No. 6,015,253 and Reynolds, U.S. Pat. No. 4,900,209. 
     These fasteners are used in wheel lug nut applications, typically for trucks and other large utility vehicles. Use of these fasteners facilitates proper tensioning of the wheel to hub joint. Such applications, however, present several critical challenges. For example, it is critical that tension on a stud secured with this type of fastener is carefully monitored for safety reasons. Proper torque on the fastener or tension in the joint provides one indication of safe operating conditions. 
     One known method for measuring the tension on the stud is to measure the torque applied to the fastener such as with a torque wrench. This, however, is a labor intensive undertaking and requires specialized, calibrated tools for measuring the torque. This is particularly the case for large semi-tractor trailers and the like which may include as many as ten fasteners per wheel and more than sixteen wheels for tandem truck arrangements. 
     Also known are caps that include indicating arrows to indicate that the nut has not moved. Such an indicating cap is disclosed in Patti, U.S. Pat. No. 5,120,174. In such a cap, indicia, such as arrows, are oriented in a particular direction (e.g., aligned with one another) to indicate that the nut has not moved and therefore that tension in the joint is acceptable. A change in the arrow orientation generally indicates that the tension has changed and that a failure may have occurred. However, indicating caps require close visual inspection in order to make a determination of whether the arrow orientation has changed from a predetermined setting. In addition, it is possible that the tension in the joint can decrease to an unacceptable or unsafe level without the nut moving. 
     Accordingly, there exists a need for a utility hub lug nut tension or torque loss indicating device that provides ready indication of a change in tension in the joint (or tension on the fastener). Desirably, such a device is self-indicating, and is used without requiring the application of torque to the fastener. Most desirably, such a device is inserted or positioned over the fastener to provide such tension-loss indication quickly and accurately. 
     SUMMARY OF THE INVENTION 
     A tension loss indicator for use with a fastener provides readily discernible visual indication of improper tension in the joint or loss of tension in the joint. The fastener is formed from a stack of conical washers confined in the stack by a cage. The stack defines an uppermost washer having an upper surface and further defines an interior region intermediate an edge thereof and a longitudinal axis of the stack. The cage includes longitudinally extending side portions having a slot formed therein. 
     In one embodiment, the indicator is configured as a cap that cooperates with and is positioned over the fastener. The cap includes a body configured for receipt over the fastener conical washers. The body defines an interior surface. A base flange is contiguous with the body. 
     At least one stanchion, and preferably a plurality of stanchions extend inwardly of the cap from the interior surface. Each stanchion defines an end longitudinally spaced from the base flange. The cap further includes at least one, detent and preferably a plurality of detents, each extending inwardly of the cap from the interior surface. The detents are longitudinally spaced from the base flange. The detents can be circumferentially spaced from the stanchions. 
     When the stack of conical washers is placed under tension with the uppermost washer in a planar condition, the stanchions lie adjacent the uppermost washer at the interior region and the detents engage and secures into the slots in the cage side. This secures the cap to the fastener. Conversely, when the stack of conical washers is under a tension that is insufficient to urge the uppermost washer into the planar condition, the stanchions abut the uppermost washer at the interior region and the detents are disengaged from the slots in the cage. This prevents the cap from securing to the fastener cage and/or dislodges the cap from the fastener. 
     In a current embodiment, the interior surface of the cap body defines a hexagonal cross-sectional shape, defining six contiguous side surfaces. In this hexagonal arrangement, the cap preferably includes three stanchions extending inwardly of the cap from alternating ones of the six contiguous sides, and three detents extending inwardly of cap from alternating others of the six contiguous sides. The cap body is preferably enclosed. The base flange can extend radially outwardly of the body. 
     An alternate embodiment of the tension loss indicator includes a body defining a central nut bore that is configured to snuggly receiving the fastener. A through body eccentric bore is contiguous with and opens into the nut bore. 
     At least one, and preferably a plurality of stops are disposed within the central nut bore. The stops define a baseline plane relative to an outermost periphery of the uppermost washer when the fastener is positioned within the nut bore, in contact with the stops. 
     The indicator includes indicating means, such as a mechanical displacement gauge that is positioned within the eccentric bore for determining a height of the uppermost washer at a location intermediate the outer periphery of the uppermost washer and the longitudinal axis of the stack. The height of uppermost washer (flexed or unflexed) is determined relative to the baseline plane at the outer periphery of the uppermost washer. 
     In a preferred embodiment, the gauge includes a stem portion having a tip, and the eccentric bore is positioned such that the stem tip contacts the fastener immediately adjacent a central stud-receiving opening. In a most preferred embodiment, the fastener stops are formed integral with the body. 
     These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a top perspective view of a tension loss indicator for a PACNUT® type fastener, the indicator embodied in a cap for the fastener, in accordance with e principles of the present invention; 
     FIG. 2 is a top plan sectional view of the cap of FIG. 1, illustrating the stanchions and detents form in the cap wall; 
     FIG. 3 is a cross-sectional view of the cap taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a cross-sectional view of the cap similar to FIG. 2 shown with a portion of the fastener in the cap; 
     FIG. 5 is a cross-sectional view of an exemplary PACNUT® type fastener; 
     FIG. 6 illustrates the exemplary cap being positioned on the fastener of FIG. 5, which fastener is not properly tensioned for use; 
     FIG. 7 further illustrates the fastener of FIGS. 5 and 6 with the cap urged from engagement with the fastener; 
     FIG. 8 illustrates the cap fully engaged with a properly tensioned fastener; 
     FIG. 9 is a perspective view of an alternate embodiment of the indicator embodying the principles of the present invention, this embodiment including indicating means, such as the exemplary mechanical indicator gauge for measuring the amount of flex of the fastener washers, which correlates to tension; 
     FIG. 10 is a cross-sectional view of the body of the indicator of FIG. 9; and 
     FIG. 11 is an illustration of the contact of the mechanical indicator gauge of the FIG. 9 embodiment with the washers of the fastener. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated. 
     Referring now to the figures and in particular to FIG. 1 there is shown an embodiment of a utility lug nut tension indicator  10  embodying the principles of the present invention. The indicator  10  is configured as a cap for receipt over a fastener, such as a PACNUT® brand fastener  12 , as illustrated in FIGS. 5-8. 
     The cap  10  includes a main body portion  14  and a base flange  16 . The main body portion  14  can take any shape that is complementary to the fastener  12  on which it is used. In a typical use, the fastener  12  will include a plurality or stack of conical, hexagonal washers  18   a-e  (referred to collectively as the stack  18 ) and the body  14  of the cap  10  will have a complementary hexagonal inner cross-sectional shape as indicated at  20  in FIG.  2 . As will be recognized by those skilled in the art, although the hexagonal shape is typical and widely accepted in the industry, the fastener  12  can take many shapes and as such, the inner cross-sectional shape  20  of the cap  10  can likewise take many shapes. All such shapes are within the scope and spirit of the present invention. 
     In a typical fastener  12  such as that illustrated in FIG.  5  and the aforementioned patent to Mitts, which is incorporated herein by reference, the conical washers  18   a-e  are secured relative to one another by a cage  22 . The cage  22  is configured having substantially planar side portions  24  that extend longitudinally along the stack of washers  18  and a top portion  26  of the cage  22  that extends from the side portions  24  over a portion of the top surface  28  of the top washer  18   a . Such a cage  22  includes openings or slots  30  extending longitudinally along the side portions  24 . The cage  22  can also include open areas at about one or more of the side/top comer junctures  32  to expose at least a portion (indicated at  34 ) of the top washer  18   a  inward of an outer periphery  36  of the washer  18   a , and between the outer periphery  36  and a longitudinal axis A of the stack  18 . The “exposed” or open interior region  34  of the washer  18   a  coincides with at least a portion of the washer stack  18  that flexes or flattens as it is tensioned onto the bolt shank (not shown). For purposes of the discussion herein, reference to fastener shall be to the above-described conical washer type fastener, such as the exemplary PACNUT® brand fastener. 
     The present cap  10  includes at least one, and preferably a plurality of stanchions  38  extending inwardly from an inner surface  40  of the cap  10 . Referring to the cap illustrated in FIG. 4, in which the cap  10  is formed having a hexagonal inner cross-sectional shape  20  defining a contiguous six-sided inner surface  40   a-f , stanchions  38  extend inwardly from three alternating surfaces  40   a,c,e . The stanchions  38  are configured so that they extend longitudinally along a portion of the surfaces  40   a,c,e  and do not extend into the body of the washer stack  18  when the cap  10  is positioned over the fastener  12 . That is, the stanchions  38  each define an end  42  that is spaced from the base flange  16 . 
     Also on an interior surface  40 , the cap  10  includes at least one and preferably a plurality of inwardly extending detents  44 . In a current embodiment, the cap  10  includes three detents  44  that are disposed on surfaces  40   b,d,f , which are those interior surface between or other than those occupied by a stanchion  38 , (e.g., surfaces adjacent to stanchion-containing surfaces). The detents  44  are formed along the walls  40   b,d,f , also spaced from the base flange  16 . As will be described in more detail below, the distance d 1  between the base flange  16  and the detent  44  is dependent upon the distance d 2  between the base flange  16  and the stanchion end  42 , and the position or length l s  of the slot  30 , as well as its position relative to the height h of the washer stack  18 . 
     In a preferred embodiment, the cap  10  is configured having a closed top  46  to prevent debris such as, dirt, road salt and the like, as well as grease and oil from contacting the fastener  12 . In a current embodiment, the cap  10  is formed from a plastic material and is coated, such as by painting, with a chrome or like finish. Such a finish improves the aesthetics of the cap  10  and is intended to be more visually appealing than the fastener  12  itself or an unfinished cap. 
     Referring now to FIGS. 6 through 8, the cooperation of a cap  10  of the present invention with a typical fastener  12  will be described. FIG. 6 illustrates a fastener  12 , not under tension with a cap  10  positioned partially thereover. As can be seen from this figure, the fastener laminations or washers  18   a-e  are angled upwardly at the interior threaded region  34 . As will be recognized and understood by those skilled in the art, as the fastener  12  is tightened down onto the stud, the laminations or washers  18   a-e  flatten, and become substantially planar. 
     Referring now to FIG. 7, there is shown a cap  10  that is engaged with the fastener  12  of FIG. 6, which fastener  12  has not been properly torqued down onto the stud. The stanchion end  42  contacts the interior region  34  of the top washer  18   a  inwardly of the washer outer periphery  36 . The contact between the stanchion end  42  and washer  18   a  prevents the cap  10  from being fully engaged with the fastener  12 . In this manner, the cap  10  sits loosely on the fastener  12  and can be readily removed therefrom. As will also be appreciated from the figures, the detent  44  does not fully engage the slot  30  in the cage side  24 . This configuration prevents the cap  10  from being “snapped” onto the fastener  12 . 
     Referring now to FIG. 8, a fully torqued fastener  12  is shown in which the washers  18   a-e  flatten as a result of proper tension in the joint. In this arrangement, the interior region  34  of the washers  18   a-e  flatten (i.e., become substantially planar) and thus, do not interfere with downward movement of the stanchion  38  (and thus the cap  10 ). Thus, the top surface  28  of the top washer  18   a  of the fastener  12  is positioned to permit fastening the cap  10  to the fastener  12 . With the cap  10  fully engaged with the fastener  12 , the detent  44  is positioned within the longitudinal slot  30  running along the cage side  24 . Thus, in the condition shown in FIG. 8, where the fastener  12  is properly tensioned on the wheel spindle stud, the cap  10  can fully engage or “snap” onto the fastener  12 . 
     As will be appreciated by those skilled in the art, the stanchion ends  42  are formed at a predetermined longitudinal distance d 3  from the detents  44  that is about equal to the longitudinal distance d 4  between the end of the cage slot  30  and the top of the fastener  12  when it is properly tensioned on the bolt. Thus, if the fastener  12  is not properly tensioned on the bolt, or if the fastener  12  loses tension, the washers  18   a-e  will flex upwardly at the interior region  34  and the longitudinal distance between the interior region  34  and the upper edge of the cage slot  30  will increase. 
     As may occur during operation of the vehicle, it is not unknown for the joint to lose tension due to wearing away of paint or other materials, thus causing the fastener  12  to lose tension in the joint. When this occurs, the fastener  12  will shift from the condition as shown in FIG. 8 to that shown in FIG.  7 . As the washers  18   a-e  of the fastener  12  begin to flex upwardly at the interior region  34 , the upper surface  28  of the uppermost washer  18   a  contacts the bottom end  42  of the stanchion  38 . This results in a force exerted on the stanchion  38  sufficient to dislodge the detent  44  from the slot  30  in the cage side  24 . When this occurs, the cap  10  dislodges from the fastener  12 , thus providing visual indication of a loss of tension in the joint. Thus, if a cap  10  is loose to the touch or missing from the fastener  12  (or from over the fastener  12 ) readily discernable visual indication is provided that the wheel hub tension may be lost or reduced. 
     The present description and drawings have been provided assuming a hexagonal fastener  12  and a hexagonal internal cross-sectional shape  20  of the present cap  10 . As will be recognized by those skilled in the art, although the exemplary hexagonal shape is widely accepted in the industry, a variety of shapes can be used for the fastener  12  and the internal cross-sectional shape  20  of the cap  10  as well. All such shapes are within the spirit and scope of the present invention. 
     Likewise, the present discussion has also provided that stanchions  38  and detents  44  are formed extending inwardly from the inner surface  40  of the cap  10  alternatingly from one another and symmetrically disposed about the cap  10 . However, as will be recognized by those skilled in the art, the stanchions  38  and detents  44  need not be alternatingly configured nor do the stanchions  38  and/or detents  44  need be symmetrical relative to other stanchions  38  and/or detents  44  that are formed in the cap  10 . 
     An alternate embodiment of the indicator  110  is shown in FIGS. 9 through 11. As discussed above, when the fastener  12  is properly tensioned, the washers  18  are planar (i.e., not upwardly flexed), and conversely, when the fastener is not properly tensioned the washers  18  are not planar and flex upwardly. For illustration purposes, the left-hand side of the fastener in FIG. 11 shows the fastener  12  fully loaded or tensioned, and the right-hand side of the fastener shows, in phantom lines, the uppermost washer  18   a  in a less than fully tensioned state, in which the washer  18   a  is flexed upwardly. 
     The indicator  110  includes a body  112  defining a central or nut bore  114  for receiving the fastener  12 . Preferably, the nut bore  114  is configured having a shape that is complementary to that of the fastener  12  for snug fit of the fastener  12  in the bore  114 , and so that the fastener  12  does not rotate relative to the indicator body  112 . The body  112  includes one or more stops  116  that are positioned to accurately longitudinally position the fastener  12  within the body  112 . The stops  116  contact the uppermost washer  18   a  at an outermost periphery  36  to define a first plane P b  relative to that periphery  36 . Because the height h p  of the outermost periphery  36  of the uppermost washer  18   a  remains constant relative to the base  50  of the fastener  12 , regardless of whether the fastener  12  is in tension or not, this height defines a baseline against which the flex of the washers  18  is measured. In this manner, as seen in FIG. 11, regardless of whether the washers  18  are planar or flexed, the stops  116  define a baseline plane at the outer periphery  36  of the uppermost washer  18   a  to measure the flex of the washers  18  at the interior region  34  of the. 
     In a current embodiment, the stops  116  are provided by pins  118  that are inserted into pin bores  120  formed in the body  112 . The pins  118  are inserted into the pin bores  120  and extend into the central nut bore  114 . Thus, when the fastener  12  is positioned in the indicator body  112 , the uppermost washer  18   a  contacts the pins  118  to “stop” or longitudinally position the fastener  12  in the bore  114 . It is anticipated that the stops  116  can be formed in any of a variety of manners, and may be formed integral with the indicator body  112 , as, for example, part of the casting process of the body  112 . These methods for forming the stops will be recognized and appreciated by those skilled in the art and are within the scope and spirit of the present invention. 
     The body  112  further includes a stud bore  122  or like opening contiguous with the nut bore  114  that is configured for receipt of the stud S as it extends upwardly from the fastener  12 . A third opening or gauge bore  124  is formed in the body  112  which opening  124  is eccentrically positioned or off-center relative to the nut bore  114 . The gauge bore  124  extends completely through the body  112  and opens into the nut bore  114 . 
     A depth or displacement gauge  126  is positioned within the gauge bore  124  extending through the indicator body  112  into the nut bore  114 . The gauge  126  is of the type that includes a reciprocating plunger or stem  128 . As the stem  128  reciprocates (i.e., moves up and down), the movement or displacement of the stem  128  is indicated on an indicator  130 , such as the exemplary gauge dial. Those skilled in the art will recognize that other types of gauges can be readily used in lieu of the dial gauge, which other types of gauges are within the scope of the present invention. 
     The gauge  126  is fixedly positioned within the body  112  so that it measures from the baseline plane P b . As positioned in the gauge bore  124 , the tip or touch portion  132  of the gauge  126  contacts the uppermost washer  18   a  immediately adjacent to the central opening  52  in the washer  18   a  (the opening  52  through which the stud S inserts), within the internal region  34  of the washer  18   a.    
     As can be seen by comparing the left and right hand sides of the fastener  12  in FIG. 11, the displacement gauge  126  measures the amount of flex of the uppermost washer  18   a  in that as the washers  18  flex, the uppermost washer  18   a  contacts the gauge tip  132 , moving the gauge stem  128  upwardly, and thus the gauge dial  130  accordingly. In use, the indicator  110  is set or calibrated by positioning the gauge  126  in the gauge bore  124  such that the stem tip  132  rests on the uppermost washer  18   a  when the fastener  12  is properly tensioned. The gauge  126  is then secured in place. This displacement of the stem  132  can be set or calibrated to a “zero” or tensioned value. When the fastener  12  loses tension (as seen on the right-hand side of FIG. 11 in phantom), the stem  128  moves or is urged upwardly, which in turn is shown on the gauge dial  130 . 
     In that the tension on the fastener can be determined empirically, the gauge  126  can be calibrated so that even if the washers  18  begin to flex, but the fastener  12  is still within an acceptable tension or torque value, the gauge dial  130  can show that there is still adequate tension in the joint. 
     From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.