Abstract:
Methods for correcting a rotational imbalance of a shaft are disclosed. The methods include determining a rotational imbalance of an unbalanced shaft, determining an imbalance correction and mapping the imbalance correction to predetermined points on the shaft. The imbalance correction can be implemented through the addition of mass to or the subtraction of mass from the shaft.

Description:
FIELD 
     The present disclosure relates to a method for balancing a propshaft assembly. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Various techniques are known for balancing propshaft assemblies, including the welding or adhesive bonding of weights to the propshaft assembly at one or more locations that are identified when the propshaft is rotated about its longitudinal axis. While such processes are suited for their intended purpose, there remains a need in the art for an improved propshaft balancing technique. 
     For example, a significant delay time is needed when balance weights are welded to a metallic tube of a propshaft to permit the weld to cool and solidify. A longer delay is typically required for adhesive curing when adhesive materials are employed to bond a balance weight to a metallic tube of a propshaft assembly. Such delays can be disadvantageous in high volume production as they tend to limit throughput through the equipment that is used to check the rotational balance of a propshaft assembly. Moreover, as the equipment that is used to check the rotational balance of a propshaft assembly can be very expensive, it would be desirable to improve capacity (when increased capacity is desired) without the need for purchasing additional balance checking equipment. Accordingly, an improved method for balancing a propshaft assembly is needed in the art. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, the present disclosure provides a method that includes: providing a thin-walled tube; forming first and second sets of balancing holes radially through the thin-walled tube, wherein the balancing holes of the first set of balancing holes are spaced circumferentially apart from one another in a first predetermined manner and wherein the balancing holes of the second set of balancing hole are spaced circumferentially apart from one another in a second predetermined manner; coupling universal joints to opposite ends of the thin-walled tube after the first and second sets of balancing holes have been formed radially through the thin-walled tube; circumferentially relating at least one rotational imbalance to one of the balancing holes of the first and second sets of balancing holes; determining an imbalance correction to correct for the at least one rotational imbalance, the imbalance correction comprising a set of correction weights and a mapping of the correction weights to the balancing holes of the first and second sets of balancing holes, the mapping of the correction weights matching a specific one of the balance weights to a specific one of the balance holes of the first and second sets of balance holes, wherein each specific one of the correction weights has a mass that is tailored to the specific one of the balance holes; and installing the specific ones of the correction weights according to the mapping to form a balanced shaft assembly. 
     In another form, the present disclosure provides a method that includes: providing a first quantity (n) of thin-walled tubes; forming a second quantity (n+1) of sets of balancing holes in the first quantity (n) of thin-walled tubes, wherein the second quantity (n+1) is one (1) more than the first quantity (n), each set of balancing holes comprising balancing holes that are spaced circumferentially apart from one another in a predetermined manner; coupling universal joints to opposite ends of each of the thin-walled tubes after the sets of balancing holes have been formed radially through the thin-walled tubes to form a shaft assembly, the universal joints coupling each of the thin-walled tubes to one another; circumferentially relating at least one rotational imbalance of the shaft assembly to at least one set of the balancing holes; determining an imbalance correction to correct for the at least one rotational imbalance, the imbalance correction comprising a set of correction weights and a mapping of the correction weights to the balancing holes of the at least one set of balancing holes, the mapping of the correction weights matching a specific one of the balance weights to a specific one of the balance holes of the second quantity (n+1) of sets of balancing holes, wherein each specific one of the correction weights has a mass that is tailored to the specific one of the balance holes; and installing the specific ones of the correction weights according to the mapping to form a balanced shaft assembly. 
     In still another form, the present disclosure provides a method that includes: providing a thin-walled tube; coupling first and second universal joints to opposite ends of the thin-walled tube, the first universal joint having a first yoke portion that is welded to a first end of the thin-walled tube, the second universal joint having a second yoke portion that is welded to a second end of the thin-walled tube, each of the first and second yoke portions having a plurality of discrete added mass sections; circumferentially relating at least one rotational imbalance to the added mass sections of the first and second yoke portions; determining an imbalance correction to correct for the at least one rotational imbalance, the imbalance correction comprising a set of mass reductions and a mapping of the mass reductions to the added mass sections, the mapping of the mass reductions matching a specific one of the mass reductions to a specific one of the added mass sections such that a mass of each specific one of the mass reductions is tailored to the specific one of the added mass sections; and machining the specific ones of the added mass sections to remove material corresponding to the mapping of the mass reductions to the added mass sections to thereby form a balanced shaft assembly. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a partly sectioned side elevation view of a first propshaft assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 2  is a side elevation view of a portion of the first propshaft assembly of  FIG. 1 , illustrating a thin-walled tube in more detail; 
         FIG. 3  is a section view taken along the line  3 - 3  of  FIG. 2 ; 
         FIG. 4  is a section view taken along the line  4 - 4  of  FIG. 2 ; 
         FIG. 5  is a partial lateral section view of the first propshaft assembly taken through the tube illustrating a first manner for coupling a correction weight to the tube; 
         FIG. 6  is a view similar to that of  FIG. 5  but illustrating a second manner for coupling a correction weight to the tube; 
         FIG. 7  is a partly sectioned side elevation view of a second propshaft assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 8  is a section view taken along the line  8 - 8  of a portion of the second propshaft assembly of  FIG. 7 , the view illustrating the construction of a second tube; 
         FIG. 9  is a partly sectioned side elevation view of a third propshaft assembly constructed in accordance with the teachings of the present disclosure; and 
         FIG. 10  is a section view taken along the line  10 - 10  of  FIG. 9 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     With reference to  FIG. 1  of the drawings, a propshaft assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10 . The propshaft assembly  10  comprises a tube  12 , a first universal joint  14 , a second universal joint  16 , and a set of correction weights  18 . The first and second universal joints  14  and  16  can be any type of universal joint, such as a Cardan joint. 
     With reference to  FIGS. 2 and 3 , the tube  12  can be a relatively thin-walled tube that can be formed of a suitable material, such as aluminum or steel. First and second sets of balancing holes  20  and  22 , respectively, can be formed in the tube  12 . The first set of balancing holes  20  can comprise a predetermined first quantity of balancing holes  24 , such as three or four holes, that can be spaced circumferentially about the tube  12  at a first predetermined circumferential spacing (e.g., a first spacing angle A 1 ) and located at a first radial offset  30  from a predetermined radial datum  32  and a first longitudinal offset  34  from a predetermined longitudinal datum  36 . For example, the first spacing angle A 1  can be 120 degrees in a situation where the first quantity of balancing holes  24  is three in number, and can be 90 degrees in a situation where the first quantity of balancing holes  24  is four in number. Those of skill in the art will appreciate, however, that the balancing holes  24  of the first set of balancing holes  20  can be spaced apart from one another in any desired manner and that a spacing angle that is common to all of the balancing holes  24  of the first set of balancing holes  20  need not be employed. 
     With reference to  FIGS. 2 and 4 , the second set of balancing holes  22  can comprise a predetermined second quantity of balancing holes  24 , such as three or four balancing holes  24 , that can be spaced circumferentially about the tube  12  at a second predetermined circumferential spacing (e.g., a second spacing angle A 2 ) and located at a second radial offset  38  from the predetermined radial datum  32  and a second longitudinal offset  40  from the predetermined longitudinal datum  36 . For example, the second spacing angle A 2  can be 120 degrees in a situation where the second quantity of balancing holes  24  is three in number, and can be 90 degrees in a situation where the second quantity of balancing holes  24  is four in number. Those of skill in the art will appreciate, however, that the balancing holes  24  of the second set of balancing holes  22  can be spaced apart from one another in any desired manner and that a spacing angle that is common to all of the balancing holes  24  of the second set of balancing holes  22  need not be employed. Those of skill in the art will further appreciate that the second quantity of balancing holes  24  can be equal to or different from the first quantity of balancing holes  24 . The second predetermined circumferential spacing can be equal to or different from the first predetermined circumferential spacing (e.g., the first spacing angle can be equal to or different from the second spacing angle). The first and second radial offsets  30  and  38  can be equal so that the balancing holes  24  of the first and second sets of balancing holes  20  and  22  can be disposed in lines that are parallel to a longitudinal axis  42  of the tube  12 . In situations where the quantity of balancing holes  24  of the second set of balancing holes  22  is equal to the quantity of balancing holes  24  of the first set of balancing holes  20 , the first and second spacing angles can be equal. The first and second longitudinal offsets  34  and  40  can be different so as to place balancing holes  24  of the first and second sets of balancing holes  20  and  22  at opposite ends of the tube  12 . The balancing holes  24  of the first and second sets of balancing holes  20  and  22  can be deburred on one or both circumferential sides of the tube  12 . 
     Returning to  FIG. 1 , the first universal joint  14  can comprise a first end cap  50 , a first yoke  52 , a second yoke  54 , a first bearing system  56  and a slip coupling  58 . The first end cap  50  can be fixedly coupled to a first end of the tube  12  and configured to close or substantially close the first end of the tube  12 . In the particular example provided, the first end cap  50  is welded to the first end of the tube  12 . The first yoke  52  can comprise a pair of yoke arms that can be fixedly coupled (e.g., integrally formed) with the first end cap  50 . The second yoke  54  can comprise a pair of yoke arms that can be fixedly coupled (e.g., integrally formed) with the slip coupling  58 . The slip coupling  58  can be configured to slidably but non-rotatably engage a power transmitting shaft, such as an output shaft (not shown) of a transmission (not shown). The first bearing system  56  can comprise a cross-trunnion (not specifically shown), a plurality of bearing assemblies (not specifically shown) and a plurality of bearing retainers (not specifically shown). The cross-trunnion is conventional in its configuration and defines four trunnions (not specifically shown) that are circumferentially spaced apart from one another at ninety degree intervals. Each of the bearing assemblies can comprise a bearing cup (not specifically shown), which is configured to be received in a cup aperture (not specifically shown) in an associated one of the yoke arms, and a plurality of bearing elements (not specifically shown) that can be disposed between an inside surface of the bearing cup and a surface of a corresponding one of the trunnions. Prior to coupling the first universal joint  14  to the tube  12 , the first universal joint  14  can be oriented in a desired manner relative to the predetermined radial datum  32  or to one of the balancing holes  24  of the first and second sets of balancing holes  20  and  22 . 
     The second universal joint  16  can comprise a second end cap  60 , a third yoke  62 , a fourth yoke  64 , a second bearing system  66  and a yoke flange  68 . The second end cap  60  can be fixedly coupled to a second end of the tube  12  and configured to close or substantially close the second end of the tube  12 . In the particular example provided, the second end cap  60  is welded to the second end of the tube  12 . The third yoke  62  can comprise a pair of yoke arms that can be fixedly coupled (e.g., integrally formed) with the second end cap  60 . The fourth yoke  64  can comprise a pair of yoke arms that can be fixedly coupled (e.g., integrally formed) with the yoke flange  68 . The yoke flange  68  can be configured to be fixedly but removably coupled to a power transmitting shaft, such as an input pinion (not shown) of an axle assembly (not shown). The second bearing system  66  can comprise a cross-trunnion (not specifically shown), a plurality of bearing assemblies (not specifically shown) and a plurality of bearing retainers (not specifically shown). The cross-trunnion is conventional in its configuration and defines four trunnions (not specifically shown) that are circumferentially spaced apart from one another at ninety degree intervals. Each of the bearing assemblies can comprise a bearing cup (not specifically shown), which is configured to be received in a cup aperture (not specifically shown) in an associated one of the yoke arms, and a plurality of bearing elements (not specifically shown) that can be disposed between an inside surface of the bearing cup and a surface of a corresponding one of the trunnions. Prior to coupling the second universal joint  16  to the tube  12 , the second universal joint  16  can be oriented in a desired manner relative to the predetermined radial datum  32  or to one of the balancing holes  24  of the first and second sets of balancing holes  20  and  22 . 
     With reference to  FIGS. 1 and 2 , the set of correction weights  18  can comprise a plurality of correction weights  70  that are coupled to the tube  12  at locations corresponding to the locations of the balancing holes  24  of the first and second sets of balancing holes  20  and  22 . The mass of each of the correction weights  70  is selected based upon the location of the balancing hole  24  of the first and second sets of balancing holes  20  and  22  and the magnitude and location of the rotational imbalance of the propshaft assembly  10 . More specifically, each of the correction weights  70  is configured to be matched to a specific one of the balancing holes  24  so that the set of correction weights  18  cooperate to form an imbalance correction that at least substantially cancels out a rotational imbalance of the propshaft assembly  10  prior to the installation of the set of correction weights  18  (hereafter referred to as “the unbalanced propshaft assembly”). 
     In this regard, at least one rotational imbalance of the unbalanced propshaft assembly is determined and is circumferentially related to at least one of the balancing holes  24  of the first and second sets of balancing holes  20  and  22 . An imbalance correction is determined to correct for the at least one rotational imbalance. The imbalance correction comprises the set of correction weights  18  and a mapping of the correction weights  70  to the balancing holes  24  of the first and second sets of balancing holes  20  and  22 . The mapping of the correction weights  70  to the balancing holes  24  of the first and second sets of balancing holes  20  and  22  matches a specific one of the correction weights  70  to a specific one of the balancing holes  24  of the first and second sets of balancing holes  20  and  22  so that each of the correction weights  70  has a mass that is tailored to the location on the unbalanced propshaft assembly that corresponds to the specific one of the balancing holes  24 . It will be appreciated that the mapping is configured to provide a location of each of the correction weights  70  in a predetermined manner relative to the predetermined radial datum  32  and the predetermined longitudinal datum  36 . 
     Minimally, each correction weight  70  can comprise a fastener  80  that is configured to be received into the balancing hole  24  and sealingly engaged to the tube  12 . The fasteners  80  can be any type of fastener, and can be secured to the tube  12  via permanent deformation of the fastener  80  as shown in  FIG. 5 , which depicts the fastener  80  as a rivet, or through resilient (elastic) deformation of the fastener  80  as shown in  FIG. 6 , which depicts the fastener  80  as having at least one resilient element  86  that is configured to be pushed through the thin-walled tube  12  such that the resilient element(s)  86  of each fastener is/are engaged to an interior surface  88  of the thin-walled tube  12  to thereby secure the fasteners  80  to the thin-walled tube  12 . Returning to  FIGS. 1 and 2 , the fastener  80  can alternatively be a threaded fastener that is configured to threadably engage the tube  12  and configured to substantially seal a corresponding one of the balancing holes  24 . In the particular example provided, the threaded fasteners comprise self-tapping fasteners that are removably coupled to the tube  12 . 
     Each correction weight  70  may additionally comprise a mass member  90  that can be secured to the tube  12  via the fastener  80 . The mass member  90  can have a mass that is sized or selected based upon the location of its associated balancing hole  24  and the magnitude and location of the rotational imbalance of the propshaft assembly  10 . In situations where the mass member  90  is selected, those of skill in the art will appreciate that the mass member  90  could be selected from a group of mass members  90  having different but predetermined masses (e.g., the group of mass members  90  can comprise a mass member  90  having a mass of 5 grams, a mass member  90  having a mass of 10 grams, a mass member  90  having a mass of 15 grams and a mass member  90  having a mass of 20 grams). 
     Generally speaking, the masses of the correction weights  70  (i.e., the fasteners  80  and the mass members  90 ) is configured to create an imbalance correction that will at least substantially cancel out the rotational imbalance of the unbalanced propshaft assembly. The use of threaded fasteners as the fasteners  80  that secure the mass members  90  to the tube  12  is advantageous in that it permits disassembly of one or more of the correction weights  70  in the event that it is necessary to modify the correction imbalance. Moreover, the use of threaded fasteners permits the propshaft assembly  10  to be rotationally balanced after the tube  12  and the first and second universal joints  14  and  16  have been painted. 
     Accordingly, a method for balancing the unbalanced propshaft assembly can comprise: providing a thin-walled tube  12 ; forming first and second sets of balancing holes  20  and  22  radially through the thin-walled tube  12 , wherein the balancing holes  24  of the first set of balancing holes  20  are spaced circumferentially apart from one another in a first predetermined manner and wherein the balancing holes  24  of the second set of balancing holes  22  are spaced circumferentially apart from one another in a second predetermined manner; coupling first and second universal joints  14  and  16  to opposite ends of the thin-walled tube  12  after the first and second sets of balancing holes  20  and  22  have been formed radially through the thin-walled tube  12 ; circumferentially relating at least one rotational imbalance to one of the balancing holes  24  of the first and second sets of balancing holes  20  and  22 ; determining an imbalance correction to correct for the at least one rotational imbalance, the imbalance correction comprising a set of correction weights  18  and a mapping of the set of correction weights  18  to the balancing holes  24  of the first and second sets of balancing holes  20  and  22 , the mapping of the set of correction weights  18  matching a specific one of the correction weights  70  to a specific one of the balancing holes  24  of the first and second sets of balancing holes  20  and  22 , wherein each specific one of the correction weights  70  has a mass that is tailored to the specific one of the balancing holes  24 ; and installing the specific ones of the correction weights  70  according to the mapping to form a balanced shaft assembly  10 . 
     It will be appreciated that the method of the present disclosure has application to propshaft assemblies having more than one tube, such as the propshaft assembly  10   a  of  FIG. 7 . In this example, the propshaft assembly  10   a  additionally includes a second tube  12   a  and a third universal joint  100 , and both the second universal joint  16   a  and the set of correction weights  18   a  are modified somewhat from the configuration that was discussed above. 
     The second universal joint  16   a  can be configured with a third end cap  102  instead of the yoke flange. The third end cap  102  can be fixedly coupled to the second tube  12   a  so that the second universal joint  16   a  directly couples the tube  12  to the second tube  12   a . The set of correction weights  18   a  can be generally similar to the set of correction weights  18  ( FIG. 1 ) discussed above, except that it can include additional correction weights  70  that are configured for use with the second tube  12   a.    
     With reference to  FIGS. 7 and 8 , the second tube  12   a  can be a relatively thin-walled tube that can be formed of a suitable material, such as aluminum or steel. A third set of balancing holes  110  can be formed in the tube  12   a . The third set of balancing holes  110  can comprise a predetermined third quantity of balancing holes  24 , such as three or four holes, that can be spaced circumferentially about the tube  12  at a third predetermined circumferential spacing (e.g., a third spacing angle) and located at a third radial offset  112  from the predetermined radial datum  32  and a third longitudinal offset  114  from the predetermined longitudinal datum  36 . The third quantity of balancing holes  24  can be equal to or different from the first quantity of balancing holes  24  and/or the second quantity of balancing holes  24 . The third predetermined circumferential spacing can be equal to or different from the first predetermined circumferential spacing (e.g., the first spacing angle A 1  ( FIG. 3 ) can be equal to or different from the third spacing angle A 3 ) and/or the third predetermined circumferential spacing can be equal to or different from the second predetermined circumferential spacing (e.g., the second spacing angle A 2  ( FIG. 4 ) can be equal to or different from the third spacing angle A 3 ). The third radial offset  112  can be equal to the first radial offset  30  ( FIG. 3 ) and the second radial offset  38  ( FIG. 4 ) so that the balancing holes  24  of the first, second and third sets of balancing holes  20 ,  22  and  110  can be disposed in lines that are parallel to a longitudinal axis  42  of the tube  12  in situations where the quantity of balancing holes  24  of the first, second and third sets of balancing holes  20 ,  22  and  110  are equal and the first, second and third spacing angles A 1  ( FIG. 3 ), A 2  ( FIG. 4 ) and A 3 ) are equal. The third longitudinal offset  114  can be configured to place the balancing holes  24  of the third set of balancing holes  110  at an end of the second tube  12   a  that is proximate the third universal joint  100 . The balancing holes  24  of the third set of balancing holes  110  can be deburred on one or both circumferential sides of the second tube  12   a.    
     The third universal joint  100  can be any type of universal joint, such as a Cardan joint. In the particular example provided, the third universal joint  100  is configured in a manner that is similar to that of the second universal joint  16  ( FIG. 1 ). Accordingly, other than merely noting that its (second) end cap  60  is fixedly coupled to the tube  12   a  on an end opposite the end to which the second universal joint  16   a  is coupled, a detailed discussion of the configuration of the third universal joint  100  need not be provided herein. 
     Accordingly, a method for balancing the unbalanced, multi-tube propshaft assembly can comprise: providing a first quantity (n) of thin-walled tubes; forming a second quantity (n+1) of sets of balancing holes in the first quantity (n) of thin-walled tubes, wherein the second quantity (n+1) is one (1) more than the first quantity (n), each set of balancing holes comprising balancing holes that are spaced circumferentially apart from one another in a predetermined manner; coupling universal joints to opposite ends of each of the thin-walled tubes after the sets of balancing holes have been formed radially through the thin-walled tubes to form a shaft assembly, the universal joints coupling each of the thin-walled tubes to one another; circumferentially relating at least one rotational imbalance of the shaft assembly to at least one set of the balancing holes; determining an imbalance correction to correct for the at least one rotational imbalance, the imbalance correction comprising a set of correction weights and a mapping of the correction weights to the balancing holes of the at least one set of balancing holes, the mapping of the correction weights matching a specific one of the balance weights to a specific one of the balance holes of the second quantity (n+1) of sets of balancing holes, wherein each specific one of the correction weights has a mass that is tailored to the specific one of the balance holes; and installing the specific ones of the correction weights according to the mapping to form a balanced shaft assembly. 
     While the above-referenced discussion has focused on the addition of (correction) weights to the tube(s) of a propshaft assembly to create an imbalance correction that reduces or eliminates at least one rotational imbalance, it will be appreciated that the invention, in its broadest aspects, could be configured somewhat differently. With reference to  FIGS. 9 and 10  for example, the unbalanced propshaft assembly could be configured with a plurality of added mass sections  200  (i.e., sections or portions of a tube or universal joint having mass that is included for use in rotationally balancing the propshaft assembly  10   b ). In the particular example provided, the added mass sections  200  are formed on the first and second universal joints  14   b  and  16   b  and the tube  12   b  and the imbalance correction is defined by a plurality of mass reductions  202  that are mapped to the added mass sections  200 . Each of the mass reductions  202  involves a removal of mass from a corresponding one of the added mass sections  200  to create the imbalance correction. Removal of mass may be achieved via machining, such as drilling or milling. 
     Accordingly, a method for balancing the unbalanced, propshaft assembly can comprise: providing a thin-walled tube  12 ; coupling first and second universal joints  14   b  and  16   b  to opposite ends of the thin-walled tube  12 , the first universal joint  14   b  having a first yoke portion that is welded to a first end of the thin-walled tube  12   b , the second universal joint  16   b  having a second yoke portion that is welded to a second end of the thin-walled tube  12   b , each of the first and second yoke portions having a plurality of discrete, circumferentially spaced apart added mass sections  200 ; circumferentially relating at least one rotational imbalance to the added mass sections  200  of the first and second yoke portions; determining an imbalance correction to correct for the at least one rotational imbalance, the imbalance correction comprising a set of mass reductions  202  and a mapping of the mass reductions  202  to the added mass sections  200 , the mapping of the mass reductions  202  matching a specific one of the mass reductions  202  to a specific one of the added mass sections  200  such that a mass of each specific one of the mass reductions  202  is tailored to the specific one of the added mass sections  200 ; and machining the specific ones of the added mass sections  200  to remove material corresponding to the mapping of the mass reductions  202  to the added mass sections  202  to thereby form a balanced shaft assembly  10   b.    
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.