Abstract:
A method is provided for quickly and inexpensively balancing an article, such a driveshaft tube for use in a vehicular driveshaft assembly, for rotation about an axis. Initially, a balancing structure is provided that includes a chamber that contains a quantity of a first component of a balancing material. The balancing structure is secured to the article. Then, a quantity of a second component of the balancing material is disposed within the chamber so as to initiate solidification of the balancing material. Lastly, before the balancing material solidifies, the article and the balancing structure are rotated so as to cause the balancing material to move within the chamber to a position wherein the combined assembly of the article and the balancing structure are balanced for rotation. The balancing material solidifies in this position, thus permanently balancing the article for rotation.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to drive train systems for transferring rotational power from a source of rotational power to a rotatably driven device. In particular, this invention relates to an improved method for rotatably balancing a driveshaft adapted for use in such a vehicular drive train system for transferring rotational power from an engine/transmission assembly to an axle assembly. 
     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 is 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. 
     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 tube and other components of the driveshaft assembly 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 when rotated during use, therefore, it is commonplace to counteract such imbalances by securing balance weights to selected portions of the driveshaft tube or other components of the driveshaft assembly. The balance weights are sized and positioned to counterbalance the imbalances of the driveshaft assembly such that it is balanced for rotation during use. 
     Traditionally, the balancing process has been performed with the use of a conventional balancing machine. A typical balancing machine includes a pair of fittings that are adapted to support the ends of the driveshaft assembly thereon. The balancing machine further includes a motor for rotating the driveshaft assembly at a predetermined speed. As the driveshaft assembly is rotated, the balancing machine senses vibrations that are caused by imbalances in the structure of the driveshaft assembly. The balancing machine is responsive to such vibrations for determining the size and location of one or more balance weights that, if secured to the driveshaft assembly, will minimize these imbalances. The rotation of the driveshaft assembly is then stopped to allow such balance weights to be secured to the outer surface of the driveshaft tube or other components of the driveshaft assembly in a conventional manner, such as by welding, adhesives, and the like. The driveshaft assembly is again rotated to confirm whether proper balance has been achieved or to determine if additional balance weights are required. A number of such balancing machines of this general structure and method of operation are known in the art. 
     Although such prior art balancing machines have been effective, this balancing process has been found to be relatively slow and inefficient. This is because each driveshaft tube must usually be rotated and measured at least two times, a first time to measure the imbalances and determine the size and location of the balance weights, and a second time to confirm that proper balance has been achieved after the balance weights have been secured thereto. This time consuming process is particularly problematic in the context of balancing vehicular driveshaft tube, which are typically manufactured in relatively large volumes. Additionally, the costs associated with obtaining and maintaining such prior art balancing machines, and to provide the skilled personnel necessary to operate same, are relatively high. Thus, it would be desirable to provide an improved method for quickly and inexpensively balancing an article, such a driveshaft tube for use in a vehicular driveshaft assembly, for rotation about an axis. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved method for quickly and inexpensively balancing an article, such a driveshaft tube for use in a vehicular driveshaft assembly, for rotation about an axis. Initially, a balancing structure is provided that includes a chamber that contains a quantity of a first component of a balancing material. The balancing structure is secured to the article. Then, a quantity of a second component of the balancing material is disposed within the chamber so as to initiate solidification of the balancing material. Lastly, before the balancing material solidifies, the article and the balancing structure are rotated so as to cause the balancing material to move within the chamber to a position wherein the combined assembly of the article and the balancing structure are balanced for rotation. The balancing material solidifies in this position, thus permanently balancing the article for rotation. 
     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 
     FIG. 1 is a side elevational view of a vehicle drive train system having a pair of balance structures in accordance with a first embodiment of this invention secured thereto. 
     FIG. 2 is an enlarged perspective view of a portion of the vehicle drive train system illustrated in FIG. 1 showing a first side of the first embodiment of the balance structure. 
     FIG. 3 is an enlarged exploded perspective view of the portion of the vehicle drive train system illustrated in FIG. 2 showing a second side of the first embodiment of the balance structure. 
     FIG. 4 is an enlarged side elevational view, partially in cross section, of the portion of the vehicle drive train system and the first embodiment of the balance structure illustrated in FIGS. 1,  2 , and  3 . 
     FIG. 5 is a front sectional elevational view of a portion of the vehicle drive train system illustrated in FIG. 1 having a second embodiment of a balance structure in accordance with this invention secured thereto. 
     FIG. 6 is a sectional elevational view of the portion of the vehicle drive train system and the second embodiment of the balance structure taken along the line  6 — 6  of FIG.  5 . 
     FIG. 7 is a front sectional elevational view of a portion of the vehicle drive train system illustrated in FIG. 1 having a third embodiment of a balance structure in accordance with this invention secured thereto. 
     FIG. 8 is a sectional elevational view of the portion of the vehicle drive train system and the third embodiment of the balance structure taken along the line  8 — 8  of FIG.  7 . 
     FIG. 9 is an enlarged sectional elevational view of a portion of the vehicle drive train system illustrated in FIG. 1 having a fourth embodiment of a balance structure in accordance with this invention secured thereto. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 an engine/transmission assembly  11  to a plurality of driven wheels (not shown). The illustrated drive train system  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 system  10  illustrated in FIG. 1 or to vehicle drive train systems in general. On the contrary, as will become apparent below, this invention may be used in any desired environment for the purposes described below. 
     The engine/transmission assembly  11  is conventional in the art and includes an externally splined output shaft (not shown) that is connected to a first slip yoke assembly, indicated generally at  12 . The first slip yoke assembly  12  is conventional in the art and includes an internally splined tubular end portion  13  that slidably engages the externally splined output shaft of the engine/transmission assembly  11 . As a result, the tubular end portion  13  of the first slip yoke assembly  12  is rotatably driven by the output shaft of the engine/transmission assembly  11 , but is free to move axially relative thereto to a limited extent. The first slip yoke assembly  12  further includes a yoke portion  14  that forms one part of a first universal joint assembly, indicated generally at  15 . The first universal joint assembly  15  is also conventional in the art and includes a tube yoke  16  that is connected to the yoke portion  14  by a cross in a known manner. The tube yoke  16  is secured, such as by bonding or welding, to a first end of a first driveshaft section  17  for rotation therewith. The first universal joint assembly  15  thus provides a rotational driving connection between the output shaft of the engine/transmission assembly  11  and the first driveshaft section  17 , while permitting a limited amount of angular misalignment therebetween. Alternatively, the output shaft of the engine/transmission assembly  11  may terminate in a conventional end yoke (not shown) which is directly connected to the cross of the first universal joint assembly  15 . 
     The first driveshaft section  17  can extend through and be supported for rotation by a center bearing assembly, indicated generally at  20 . The center bearing assembly  20  is conventional in the art and includes a rigid frame or bracket  21  that is secured to a support surface, such as a portion of a frame, chassis, or body  22  of the vehicle. The center bearing assembly  20  further includes an annular bearing (not shown) for rotatably supporting the first driveshaft section  17  therein. The first driveshaft section  17  terminates in a second end including an end yoke  23 , which forms one part of a second universal joint assembly, indicated generally at  24 . The second universal joint assembly  24  is also conventional in the art and includes a yoke shaft  25  that is connected to the end yoke  23  by a cross in a known manner. The yoke shaft  25  is, in turn, connected through a second slip yoke assembly, indicated generally at  28 , to a first end of a second driveshaft section  27 . The second universal joint assembly  24  thus provides a rotational driving connection between the first driveshaft section  17  and the second driveshaft section  27 , while permitting a limited amount of angular misalignment therebetween. The structure and operation of the second slip yoke assembly  28  is conventional in the art and forms no part of this invention. 
     The second driveshaft section  27  terminates in a second end having a tube yoke  30  secured thereto. The tube yoke  30  forms one part of a third universal joint assembly  31 . The third universal joint assembly  31  is also conventional in the art and includes a tube yoke  32  that is connected to an input shaft  33  of an axle assembly  34  by a cross in a conventional manner. The third universal joint assembly  31  thus provides a rotational driving connection between the second driveshaft section  27  and the input shaft  33  of the axle assembly  34 , while permitting a limited amount of axial misalignment therebetween. The axle assembly  34  is conventional in the art and is adapted to transmit rotational power from the input shaft  33  to the driven wheels of the vehicle in a known manner. 
     As is well known in the art, most driveshaft tubes, such as the driveshaft sections  17  and  27 , 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, first and second balance structures, indicated generally at  40 , are secured to the outer surfaces of the driveshaft sections  17  and  27 . The first and second balance structures  40  are provided to counterbalance the imbalances of the driveshaft sections  17  and  27  such that the drive train system  10  is balanced for rotation during use. The first and second balance structures  40  are preferably identical in structure, although such is not required. As shown in FIG. 1, the first balance structure  40  is secured to the outer surface of the first driveshaft section  17  a predetermined distance inwardly from the first end thereof (i.e., the left end of the first driveshaft section  17 , when viewing FIG.  1 ), while the second balance structure  40  is secured to the outer surface of the second driveshaft section  27  a predetermined distance inwardly from the second end thereof (i.e., the right end of the second driveshaft section  27 , when viewing FIG.  1 ). Preferably, the balance structures  40  are located relatively close (e.g., within about one inch to about one and one-half inches) to the associated ends of the driveshaft sections  17  and  27  to balance the driveshaft section  17  and  27 . Although the illustrated embodiment shows one balance structure  40  secured to each end of the driveshaft sections  17  and  27 , it will be appreciated that additional balance structures can be secured elsewhere to either or both of the driveshaft sections  17  and  27  counterbalance the amount of imbalances therein. 
     The structure of a first embodiment of one of the balance structures  40  is illustrated in detail in FIGS. 2,  3 , and  4 . As shown therein, the first embodiment of the balance structure  40  includes a mounting bracket including an inner annular bracket portion  42  and one or more outer annular cavity portions  43  positioned adjacent to and radially outwardly from the inner annular bracket portion  42 . In the illustrated embodiment, the mounting bracket of the balance structure  40  is formed from a single piece of metallic material that is pressed or otherwise deformed to the desired shape such that the inner annular bracket portion  42  and the outer annular cavity portion  43  are integrally formed together. However, such is not required, and the mounting bracket of the balance structure  40  may be formed from two or more pieces of material that are joined or otherwise connected together. The mounting bracket of the balance structure  40  may be formed from any desired material or materials. 
     The inner annular bracket portion  42  of the mounting bracket of the balance structure  40  is adapted to be secured to the driveshaft section  27 . In the illustrated embodiment, the inner annular bracket portion  42  of the mounting bracket is press fit onto the outer surface of the driveshaft section  27  in a desired location. The outer annular cavity portion  43  of the balance structure  40  receives and supports a hollow annular chamber  44 . To accomplish this, the outer annular cavity portion  43  of the illustrated balance structure  40  is defined by an annular wall having a generally C-shaped cross-sectional shape, as best illustrated in FIG. 4, so as to form a captive opening, generally indicated at  43   a , within which the hollow annular chamber  44  may be inserted. The captive opening  43   a  resists removal of the hollow annular chamber  44  from the cavity portion  43  of the balance structure  40 . The cavity portion  43  is sized and positioned to support the hollow annular chamber  44  at a predetermined radial distance outwardly from the rotational axis of the driveshaft section  27 . The hollow annular chamber  44  can, for example, be formed from a polymer material that can be cast or molded (e.g., injection molded) to have a desired shape. 
     The hollow annular chamber  44  is closed so as to retain a quantity of a balancing material  45  therein. The hollow annular chamber  44  can be partially or completely filled with the balancing material  45 , as desired. The balancing material  45  contained within the hollow annular chamber  44  may be embodied as any desired material that is capable of balancing the driveshaft section  27  for rotation. For example, the balancing material  45  may be a composite material that includes a first component and a second component. The first component may be a liquid or fluid material having a quantity of relatively heavy balancing media suspended or otherwise retained therein. The balancing media can, for example, be an alloy of several metallic substances. Preferably, the balancing media is a quantity of powdered metal alloy particles that are suspended in the first component of the liquid or fluid material. Thus, the balancing media is free to move easily throughout the first component of the balancing material  45  contained within the hollow annular chamber  44 . The balancing media adds mass to the balance structure  40  so as to counterbalance the imbalance in the driveshaft section  27  in the manner described below. The specific substance and quantity of balancing media used can be based on the particular application and, therefore, can vary from application to application. A variety of balancing media that can be used, as part of the material  45  is available from the Metals Division of the Mallory Alloys Group, located in the United Kingdom. The second component of the balancing material  45  is adapted to be added to the first component so as to react therewith. For example, the second component of the balancing material  45  can be injected through the wall of the hollow annular chamber  44  into the interior thereof. Alternatively, the second component of the balancing material  45  may be disposed within one or more containers (not shown) provided within the hollow annular chamber  45 . The containers can be broken to release the second component into the first component. Regardless of the specific mechanism by which the second component is added to the first component, the second component of the balancing material  45  causes the first component to solidify, thus retaining the balancing media in a position that counterbalances the imbalance of the driveshaft section  27 . 
     During a balancing operation, the balance structure  40  is initially secured to the second driveshaft section  27 . During this initial step, the hollow annular chamber  44  contains only the first component of the balancing material  45 . Thus, the first component of the balancing material  45  and the balancing media suspended therein are free to move throughout the hollow annular chamber  44 . The hollow annular chamber  44  is preferably substantially toroidal in shape to promote the flow of the balancing material  45  circumferentially therein. When the second driveshaft section  27  is ready for balancing, the second component of the balancing material  45  is added to the first component, such as in the manner described above. Immediately thereafter, the second driveshaft section  27  is rotated at a desired speed (e.g., just above resonant frequency of vibration). The centrifugal force created by the rotation of the second driveshaft section  27  causes the balancing media contained within the balancing material  45  to be distributed throughout the hollow annular chamber  44  in such a manner that it will counterbalance any imbalance of the second driveshaft section  27 . While the second driveshaft section  27  rotates a chemical reaction occurs between the first and second components of balancing material  45 . Such chemical reaction causes the balancing material  45  contained within the hollow annular chamber  44  to harden, thereby permanently retaining the balancing media in position to balance the second driveshaft section  27  for rotation. If desired, a lattice or other surface irregularity (e.g., serrations, ribs, or the like), such as indicated generally at  44   a , can be provided on the interior surface of the hollow annular chamber  44 . The lattice  44   a  can be any shape that resists undesirable movement of the balancing material  45  after it has solidified. 
     As an alternative to using a chemical reaction to harden the balancing material  45  as discussed above, the balancing material  45  contained within the hollow annular chamber  44  can be composed of a thermosetting or thermoplastic material, such as an epoxy resin, that may or may not contain a balancing media. The hollow annular chamber  44  can be filled, partially filled, or coated with the thermosetting or thermoplastic material  45 . If a thermosetting balancing material  45  is used, the second driveshaft section  27  is rotated at the desired speed to allow the liquid thermosetting balancing material  45  to be distributed throughout the hollow annular chamber  44  to rotational balance the driveshaft section  27 . Then, the thermosetting balancing material  45  can be activated by an external heating source so as to cause the balancing material  45  to solidify. On the other hand, if a thermoplastic balancing material  45  is used, the second driveshaft section  27  is initially heated by the external heating source to liquefy the thermoplastic balancing material  45 . Then, the second driveshaft section  27  is rotated at the predetermined speed to allow the thermoplastic balancing material  45  to be distributed throughout the hollow annular chamber  44  to rotational balance the driveshaft section  27 . Then, the external heating source is removed, allowing the thermoplastic balancing material  45  to solidify. 
     FIGS. 5 and 6 illustrate a second embodiment of a balance structure, indicated generally at  51 , for rotatably balancing a driveshaft tube, indicated generally at  52 . As shown therein, the balance structure  51  is also adapted to be secured to an outer surface  52   a  of the driveshaft tube  52 , such as by press fitting. The second embodiment of the balance structure  51  includes two or more hollow annular cavities  53  that are provided for supporting respective hollow annular chambers  54  therein. Each of the hollow annular cavities  53  can be provided with an opening, indicated generally at  53   a , through which a corresponding one of the hollow annular chambers  54  may be inserted. Each of the hollow annular chambers  54  is preferably retained in a fixed relationship with the corresponding annular cavity  53  by any conventional retaining structure (not shown). The annular cavities  53  are sized and positioned to support the hollow annular chambers  54  at a predetermined radial distance from the rotational axis of the driveshaft tube  52 . The hollow annular chambers  54  are closed to retain a quantity of a balancing material  55  therein, as discussed above. As also discussed above, a lattice  54   a  or other irregularity (e.g., serrations, ribs, or the like) can be provided on the interior surface of the hollow annular chamber  54  to aid in retaining the balancing media in the desired location. 
     FIGS. 7 and 8 illustrate a third embodiment of a balance structure, indicated generally at  56 , for rotatably balancing a driveshaft tube, indicated generally at  57 . As shown therein, the third embodiment of the balance structure  56  is similar to the second embodiment of the balance structure  51  described above, except that the third embodiment of the balance structure  56  is adapted to be secured to an inner surface  57   a  of the driveshaft tube  57 , such as by press fitting, for example. As described above, the balance structure  56  includes one or more annular cavities  58  that support respective hollow annular chambers  59 . Each of the hollow annular cavities  58  can be provided with an opening, indicated generally at  58   a , through which a corresponding one of the hollow annular chambers  59  may be inserted. Each of the hollow annular chambers  59  is preferably retained in a fixed relationship with the corresponding annular cavity  58  by any conventional retaining structure (not shown). The annular cavities  58  are sized and positioned to support the hollow annular chambers  59  at a predetermined radial distance from the rotational axis of the driveshaft tube  57 . The hollow annular chambers  59  are closed to retain a quantity of a balancing material  60  therein, as discussed above. As also discussed above, a lattice  59   a  or other irregularity (e.g., serrations, ribs, or the like) can be provided on the interior surface of the hollow annular chamber  59  to aid in retaining the balancing media in the desired location. 
     FIG. 9 illustrates a fourth embodiment of a balance structure, indicated generally at  61 , for rotatably balancing a driveshaft tube, indicated generally at  63 . Unlike the balance structures discussed above, the fourth embodiment of the balance structure  61  lacks a mounting bracket and a cavity for retaining an annular chamber. Rather, one or more hollow annular chambers  62  are secured directly to the driveshaft tube  63 . In the illustrated embodiment, the hollow annular chambers  62  are secured to an inner surface  63   a  of the driveshaft tube  63 . However, it will be appreciated that the hollow annular chambers  62  can alternatively be secured to an outer surface  63   b  of the driveshaft tube  63 . The hollow annular chambers  62  are closed to retain a quantity of a balancing material  64  therein. The hollow annular chambers  62  can be formed in the manner described above. If desired, the hollow annular chambers  62  can be enclosed in a rubber material or other resilient material  65 , such as a polymer foam. The resilient material  65  is compressible when the hollow annular chambers  62  are secured to the driveshaft tube  63  to produce an interference fit between the hollow annular chambers  62  and the driveshaft tube  63 . The composition of the resilient material  65  is based on surface friction required between the balance structure  61  and the driveshaft tube  63  to secure the balance structure  61  to the driveshaft tube  63 . 
     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.