Abstract:
A method for balancing an article for rotation includes the initial steps of providing an article having a surface and providing a balance weight including a weight portion having an opening and a rivet portion. The weight portion of the balance weight is disposed against the surface of the article. The rivet portion of the balance weight is inserted within the opening of the weight portion of the balance weight such that a portion of the rivet portion engages the surface of the article. Lastly, the portion of the rivet portion is welded, such as by resistance welding techniques, to the surface of the article.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates in general to a method of balancing an article for rotation. In particular, this invention relates to an improved method for securing a balance weight to an unbalanced article so as to balance the article for rotation.  
         [0002]     Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The front and rear universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.  
         [0003]     Ideally, the driveshaft tube would be formed in the shape of a cylinder that is absolutely round, absolutely straight, and has an absolutely uniform wall thickness. Such a perfectly shaped driveshaft tube would be precisely balanced for rotation and, therefore, would not generate any undesirable noise or vibration during use. In actual practice, however, the driveshaft tubes usually contain variations in roundness, straightness, and wall thickness that result in minor imbalances when rotated at high speeds. To prevent such imbalances from generating undesirable noise or vibration, therefore, it is commonplace to counteract such imbalances by securing balance weights to selected portions of the driveshaft tube. The balance weights are sized and positioned to counterbalance the imbalances of the driveshaft tube such that it is balanced for rotation during use. Balance weights can also be used to counteract any imbalances in the end fittings attached to the driveshaft tube.  
         [0004]     Traditionally, driveshaft tubes and end fittings have been formed from steel or other metallic materials having relatively high melting temperatures. In such driveshaft tubes and end fittings, welding has been commonly used to secure the balance weights thereto. More recently, however, driveshaft tubes and end fittings have been formed from aluminum alloys that are lighter in weight than steel. The aluminum alloys are not well suited for welding the balance weights thereto, particularly in the high volume quantities usually associated with the vehicular manufacturing industry. Thus, it would be desirable to provide an improved method for rotatably balancing an article, such as a driveshaft tube or an end fitting adapted for use in a vehicular drive train assembly for transferring rotational power from an engine/transmission assembly to an axle assembly.  
       SUMMARY OF THE INVENTION  
       [0005]     This invention relates to an improved method for securing a balance weight to an unbalanced article so as to balance the article for rotation. Initially, an article having a surface and a balance weight including a weight portion having an opening and a rivet portion are provided. The weight portion of the balance weight is disposed against the surface of the article. The rivet portion of the balance weight is inserted within the opening of the weight portion of the balance weight such that a portion of the rivet portion engages the surface of the article. Lastly, the portion of the rivet portion is welded, such as by resistance welding techniques, to the surface of the article.  
         [0006]     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a side elevational view of a vehicular drive train system including a driveshaft assembly having a balance weight secured thereto in accordance with the method of this invention.  
         [0008]      FIG. 2  is an enlarged exploded perspective view of a portion of the driveshaft assembly and a first embodiment of the balance weight illustrated in  FIG. 1  shown prior to assembly.  
         [0009]      FIG. 3  is a further enlarged sectional elevational view of a portion of the driveshaft assembly and the first embodiment of the balance weight illustrated in  FIG. 2  shown during assembly.  
         [0010]      FIG. 4  is an enlarged sectional elevational view similar to  FIG. 3  showing a second balance weight being secured to the first balance weight.  
         [0011]      FIG. 5  is an enlarged exploded perspective view of a portion of the driveshaft assembly and a second embodiment of the balance weight illustrated in  FIG. 1  shown prior to assembly.  
         [0012]      FIG. 6  is a further enlarged sectional elevational view of a portion of the driveshaft assembly and the second embodiment of the balance weight illustrated in  FIG. 5  shown during assembly. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Referring now to the drawings, there is illustrated in  FIG. 1   a  drive train system, indicated generally at  10 , for a vehicle that is adapted to transmit rotational power from a source of rotational power, such as an internal combustion or diesel engine (not shown) to a driven device, such as a plurality of driven wheels (not shown). The illustrated drive train assembly  10  is, for the most part, conventional in the art and is intended merely to illustrate one environment in which this invention may be used. Thus, the scope of this invention is not intended to be limited for use with the specific structure for the vehicle drive train assembly  10  illustrated in  FIG. 1  or to vehicle drive train assemblies in general. On the contrary, as will become apparent below, this invention may be used in any desired environment for the purposes described below.  
         [0014]     The illustrated drive train system  10  includes a transmission  11  having an output shaft (not shown) that is connected to an input shaft (not shown) of an axle assembly  12  through a driveshaft assembly  13 . The transmission  11  is rotatably driven by an engine (not shown) that generates rotational power in a conventional manner. The driveshaft assembly  13  includes a cylindrical driveshaft tube  14  having a center portion and a pair of opposed end portions. The output shaft of the transmission  11  and the input shaft of the axle assembly  12  are typically not co-axially aligned. To accommodate this, a pair of universal joints, indicated generally at  15  and  16 , are provided to respectively connect the end portions of the driveshaft tube  14  to the output shaft of the transmission  11  and to the input shaft of the axle assembly  12 . The first universal joint  15  includes a tube yoke  15   a  that is secured to the forward end portion of the driveshaft tube  14  by any conventional means, such as by welding. The first universal joint  15  further includes a cross  15   b  that is connected to the tube yoke  15   a  in a conventional manner. Lastly, the first universal joint  15  includes an end yoke  15   c  that is connected to the output shaft of the transmission  11  and to the cross  15   b . Similarly, the second universal joint  16  includes a tube yoke  16   a  that is secured to the rearward end portion of the driveshaft tube  14  by any conventional means, such as by welding. The second universal joint  16  further includes a cross  16   b  that is connected to the tube yoke  16   a  in a conventional manner. Lastly, the second universal joint  16  includes an end yoke  16   c  that is connected to the cross  16   b  and to the input shaft of the axle assembly  12 . The front and rear universal joints  15  and  16  provide a rotational driving connection from the output shaft of the transmission  11  through the driveshaft tube  14  to the input shaft of the axle assembly  12 , while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.  
         [0015]     As is well known in the art, driveshaft tube  14 , the tube yokes  15   a  and  16   a , and the other components of the drive train system  10  usually contain variations in shape and wall thickness that result in minor imbalances when rotated at high speeds. This invention provides an improved method for balancing any or all of the driveshaft tube  14 , the tube yokes  15   a  and  16   a , and the other components of the drive train system  10  for rotation in order to prevent such rotational imbalances from generating undesirable noise or vibration during use. As will be explained in detail below, such balancing involves the securement of one or more balance weights, indicated generally at  20 , at selected locations on any or all of the driveshaft tube  14 , the tube yokes  15   a  and  16   a , and the other components of the drive train system  10 . In a manner that is well known in the art, the balance weights  20  are sized and positioned to counterbalance the imbalances of the driveshaft tube  14 , the tube yokes  15   a  and  16   a , and the other components of the drive train system  10  such that the drive train system  10  is balanced for rotation during use.  
         [0016]     Referring to  FIGS. 2 and 3 , the structure of a first embodiment of the balance weight  20  shown in  FIG. 1  is illustrated in detail. As shown therein, the first embodiment of the balance weight  20  includes a weight portion, indicated generally at  21 , that is adapted to be secured to the driveshaft tube  14  so as to balance the driveshaft tube  14  for rotation, as described above. The weight portion  21  of the balance weight  20  has an inner surface  21   a  that is adapted to engage an outer surface of the driveshaft tube  14  and an outer surface  21   b  that faces radially outwardly from the driveshaft tube  14 . In the illustrated embodiment, the weight portion  21  is generally flat and rectangular in shape, but is curved such that the inner surface  21   a  of the weight portion  21  defines a radius of curvature that closely conforms with a radius of curvature defined by the outer surface of the driveshaft tube  14 , as best shown in  FIG. 3 . However, the weight portion  21  may be formed having any desired shape. An opening  22  is formed through the weight portion  21 , extending generally radially from the inner surface  21   a  to the outer surface  21   b . In the illustrated embodiment, the opening  22  is generally circular in shape. However, the opening  22  may be formed having any desired shape. In this first embodiment of the weight portion  21 , the opening  22  has a recessed area  22   a  formed thereabout. In the illustrated embodiment, the recessed area  22   a  extends completely about the opening  22  in the nature of a counterbore or a countersink. However, the recessed area  22   a  need not extend completely about the opening  22 . Also, the recessed area  22   a  may be embodied as two or more discrete portions that extend inwardly from the opening  22 .  
         [0017]     The first embodiment of the balance weight  20  also includes a rivet portion, indicated generally at  23 , that is adapted to retain the weight portion  21  of the balance weight  20  on the driveshaft tube  14 . The rivet portion  23  of the balance weight  20  includes an enlarged head  23   a  and a body  23   b  that extends from the head  23   a . In the illustrated embodiment, the head  23   a  of the rivet portion  23  is generally flat and circular in shape, while the body  23   b  of the rivet portion  23  is generally cylindrical in shape. More specifically, the illustrated head  23   a  of the rivet portion  23  is sized and shaped to conform with the size of the recessed area  22   a  of the opening  22  formed through the weight portion  21 , while the illustrated body  23   b  of the rivet portion  23  is sized and shaped to conform with the remainder of the opening  22  formed through the weight portion  21 . Thus, the rivet portion  23  can be inserted through and disposed within the opening  22  formed through the weight portion  21 , as best shown in  FIG. 3 . When so inserted, the head  23   a  of the rivet portion  23  is received within the recessed area  22   a  of the opening  22  such that the outer surface of the head  23   a  is flush (or at least generally flush) with the outer surface  21   b  of the weight portion  21 , as shown in  FIG. 3 . At the same time, the body  23   b  of the rivet portion  23  is received within the remainder of the opening  22 , as also shown in  FIG. 3 . The axial length of the rivet portion  23  can be determined as desired, but is preferably approximately the same as or slightly longer than the radial thickness of the weight portion  21  as measured from the inner surface  21   a  to the outer surface  21   b  thereof. Thus, the inner end of the body  23   b  of the rivet portion  23  is located flush with or extends slightly radially inwardly from the inner surface  21   a  of the weight portion  21  when the head  23   a  of the rivet portion  23  is received within the recessed area  22   a  of the opening  22 .  
         [0018]     The head  23   a  and the body  23   b  of the rivet portion  23  may be formed having any desired shape or shapes. Preferably, the rivet portion  23  defines an outer dimension that is slightly smaller than an inner dimension defined by the opening  22 . Thus, in the illustrated embodiment, the head  23   a  of the rivet portion  23  defines an outer diameter that is slightly smaller than an inner diameter defined by the recessed area  22   a  of the opening  22 , and the body  23   b  of the rivet portion  23  defines an outer diameter that is slightly smaller than an inner diameter defined by the remainder of the opening  22 . By sizing the rivet portion  23  and the opening  22  in this manner, the rivet portion  23  can be easily inserted through and disposed within the opening  22  formed through the weight portion  21  prior to securing the weight portion  21  to the driveshaft tube  14  as described below. However, if desired, the outer dimension defined by the rivet portion  23  can be approximately the same or slightly larger than the inner dimension defined by the opening  22 . By sizing the rivet portion  23  and the opening  22  in this manner, the rivet portion  23  can be press fit within the opening  22  and retained on the weight portion  21  as a pre-assembly prior to securing the weight portion  21  to the driveshaft tube  14 , as described in detail below.  
         [0019]      FIG. 3  illustrates the manner in which the balance weight  20  is secured to the driveshaft tube  14 . As shown therein, the inner surface  21   a  of the weight portion  21  is initially positioned against the outer surface of the driveshaft tube  14  such that the inner end of the body  23   b  of the rivet portion  23  is located flush with or extends slightly inwardly from the inner surface  21   a  of the weight portion  21 , as discussed above. The location at which the balance weight  20  is positioned on the driveshaft tube  14  and the size of the balance weight  20  can be determined by any conventional rotational balancing apparatus, the structures and operations of which are well known in the art. Then, a securement tool  30  is moved into engagement with the outer surface of the head  23   a  of the rivet portion  23 . The securement tool  30  may, for example, be embodied as a conventional resistance welder. Resistance welding is a well known thermal process for joining two or more electrically conductive materials together by passing electrical current through those materials. The heat that results from the electrical resistance to the flow of current through those materials creates the actual weld. The heat that is generated using the resistance welding process is very localized on the driveshaft tube  14 . Although the temperature at the weld joint is high, the short time duration of the resistance welding process (often in the range of from about ten milliseconds to about twenty milliseconds) results in a very little heat being transmitted to the material of the driveshaft tube  14  surrounding the area that is engaged by the inner end of the body  23   b  of the rivet portion  23 .  
         [0020]     In accordance with the method of this invention, the securement tool  30  is initially moved into engagement with the outer surface of the head  23   a  of the rivet portion  23 , thereby causing the inner surface of the body  23   b  of the rivet portion  23  to engage the outer surface of the driveshaft tube  14 . Then, the securement tool  30  is actuated to cause an electrical current to flow through the rivet portion  23  and the driveshaft tube  14 . This flow of electrical current generates a very localized heating in the region of the abutting portions of the inner surface of the body  23   b  of the rivet portion  23  and the outer surface of the driveshaft tube  14 . As a result, the abutting portions of the inner surface of the body  23   b  of the rivet portion  23  and the outer surface of the driveshaft tube  14  are melted and coalesce so as to form a welded region  31 . However, the adjacent regions of the weight portion  21  and the driveshaft tube  14  remain unaffected (or at least substantially unaffected) by this localized generation of heat.  
         [0021]     Thus, in order to perform this resistance welding operation, the rivet portion  23  of the balance weight  20  and the driveshaft tube  14  are formed from electrically conductive materials. Preferably, both the rivet portion  23  of the balance weight  20  and the driveshaft tube  14  are formed from the same material. For example, if the driveshaft tube  14  is formed from an aluminum alloy material, then the rivet portion  23  is preferably formed from the same or similar aluminum alloy material. The weight portion  21  of the balance weight  20  can be formed from any desired material. However, it is desirable that the weight portion  21  of the balance weight  20  be formed from a material that has a relatively large weight density in comparison with the weight density of the material that is used to form the driveshaft tube  14 . This allows the physical size of the weight portion  21  of the balance weight  20  to be minimized, yet still achieve the desired counterbalancing effect. For example, if the driveshaft tube  14  is formed from an aluminum alloy material, then the weight portion  21  of the balance weight  20  is preferably formed from a steel alloy material. The use of a steel alloy weight portion  21  also minimizes or eliminates any melting of the weight portion  21  that might otherwise occur during the resistance welding operation. Thus, it can be seen that the resistance welding operation is effective to secure the rivet portion  23  of the balance weight  20  to the driveshaft tube  14 . The enlarged head  23   a  of the rivet portion  23  mechanically retains the weight portion  21  of the balance weight in the desired position on the driveshaft tube  14 .  
         [0022]     If necessary, one or more additional balance weights (not shown) can be secured to other portions of the driveshaft tube  14  or elsewhere on the drive train system  10  in order to properly balance the drive train system  10  for rotation. Alternatively, as shown in  FIG. 4 , a second balance weight, indicated generally at  20 ′, can be secured to the first balance weight  20 . The second balance weight  20 ′ is similar in structure to the first balance weight  20  described above, and like reference numbers are used to indicate similar structures. The second balance weight  20 ′ can be secured to the head  23   a  of the rivet portion  23  of the first balance weight  20  using the same method described above. As shown in the illustrated embodiment, a second welded region  31 ′ is created to secure the body  23   b ′ of the second balance weight  20 ′ to the outer surface of the head  23   a  of the first balance weight  20 . The securement of the second balance weight  20 ′ can be performed either before, during, or after the securement of the first balance weight  20  to the outer surface of the driveshaft tube  14 .  
         [0023]     Referring to  FIGS. 5 and 6 , the structure of a second embodiment of a balance weight, indicated generally at  40  is illustrated in detail. As shown therein, the second embodiment of the balance weight  40  includes a weight portion, indicated generally at  41 , that is adapted to be secured to the driveshaft tube  14  so as to balance the driveshaft tube  14  for rotation, as described above. The weight portion  41  of the balance weight  40  has an inner surface  41   a  that is adapted to engage an outer surface of the driveshaft tube  14  and an outer surface  41   b  that faces outwardly from the driveshaft tube  14 . In the illustrated embodiment, the weight portion  41  is generally flat and rectangular in shape, but is curved such that the inner surface  41   a  of the weight portion  41  defines a radius of curvature that closely conforms with a radius of curvature defined by the outer surface of the driveshaft tube  14 , as best shown in  FIG. 6 . However, the weight portion  41  may be formed having any desired shape. An opening  42  is formed through the weight portion  41 , extending from the inner surface  41   a  to the outer surface  41   b . In the illustrated embodiment, the opening  42  is generally rectangular in shape. However, the opening  42  may be formed having any desired shape. In this second embodiment of the weight portion  41 , the opening  42  is not provided with a recessed area similar to the recessed area  22   a  described above. However, such a recessed area may be provided if desired.  
         [0024]     The second embodiment of the balance weight  40  also includes a rivet portion, indicated generally at  43 , that is adapted to secure the weight portion  41  of the balance weight  40  to the driveshaft tube  14 . The rivet portion  43  of the balance weight  40  includes an enlarged head  43   a  and a body  43   b  that extends from the head  43   a . In the illustrated embodiment, the head  43   a  of the rivet portion  43  is generally flat and circular in shape, while the body  43   b  of the rivet portion  23  is generally rectilinear in shape. More specifically, the illustrated body  43   b  of the rivet portion  43  is sized and shaped to conform with the remainder of the opening  42  formed through the weight portion  41 . Thus, the rivet portion  43  can be inserted through and disposed within the opening  42  formed through the weight portion  41 , as best shown in  FIG. 6 . When so inserted, the head  43   a  of the rivet portion  43  is not received within the recessed area  42   a  of the opening  42 . but rather abuts the outer surface  41   b  of the weight portion  41 , as shown in  FIG. 6 . At the same time, the body  43   b  of the rivet portion  43  is received within the remainder of the opening  42 , as also shown in  FIG. 6 . The axial length of the rivet portion  43  can be determined as desired, but is preferably approximately the same as or slightly longer than the radial thickness of the weight portion  41  as measured from the inner surface  41   a  to the outer surface  41   b  thereof. Thus, the inner end of the body  43   b  of the rivet portion  43  is located flush with or extends slightly inwardly from the inner surface  41   a  of the weight portion  41 .  
         [0025]     The head  43   a  and the body  43   b  of the rivet portion  43  may be formed having any desired shape or shapes. Preferably, the rivet portion  43  defines an outer dimension that is slightly smaller than an inner dimension defined by the opening  42 . Thus, in the illustrated embodiment, the body  43   b  of the rivet portion  43  defines an outer diameter that is slightly smaller than an inner diameter defined by the remainder of the opening  42 . By sizing the rivet portion  43  and the opening  42  in this manner, the rivet portion  43  can be easily inserted through and disposed within the opening  42  formed through the weight portion  41  prior to securing the weight portion  41  to the driveshaft tube  14  as described below. However, if desired, the outer dimension defined by the rivet portion  43  can be approximately the same or slightly larger than the inner dimension defined by the opening  42 . By sizing the rivet portion  43  and the opening  42  in this manner, the rivet portion  43  can be press fit within the opening  42  and retained on the weight portion  41  as a pre-assembly prior to securing the weight portion  41  to the driveshaft tube  14  as described below. The securement of the second embodiment of the balance weight  40  to the driveshaft tube  14  can be accomplished using the securement tool  30  in the same manner as described above.  
         [0026]     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.