Patent Publication Number: US-2023151843-A1

Title: Ballspline shaft with no ball retainer

Description:
TECHNICAL FIELD 
     The invention generally relates to a shaft assembly for transmitting a torque. More specifically, the invention relates to a telescoping shaft assembly for transmitting torque in a driveline system. 
     BACKGROUND 
     A vehicle, such as a car, truck, sport utility vehicle, crossover, mini-van, marine craft, aircraft, all-terrain vehicle, recreational vehicle, or other suitable vehicles, typically include a driveline system for transferring power from an engine or other propulsion system to the wheels. The driveline system generally includes a telescoping shaft assembly capable of transmitting a torque. The telescopic shaft assembly typically includes a tubular outer shaft member and an inner shaft member. The inner shaft member is at least partially disposed within the outer shaft member and moveable relative thereto along a longitudinal axis. The telescopic shaft assembly typically uses rolling elements or bearings between the outer and inner shaft members to reduce friction during repeated telescopic compression and expansion. 
     The rolling elements of the telescopic shaft assembly are typically configured as steel rollers or steel balls. The rolling elements are configured to roll between the outer and inner shaft members during linear, telescopic movement of the telescopic shaft assembly while rotational torque can continued to be transferred between the outer shaft member and the inner shaft member. 
     A telescopic shaft configured to connect two constant-velocity joints is known. This configuration typically includes a bearing retaining cage located between the outer and inner shaft that retains the rolling elements. The bearing retaining cage is typically located between the outer and inner shaft via holding elements. While telescopic shafts with bearing retaining cages are popular, they are not without shortcomings. For example, additional packaging space is typically required to locate the ball retaining cage between the outer and inner shaft. The presence of the ball retaining cage typically also results in a hydraulic-effect that negatively impacts free relative telescopic movement. 
     Accordingly, there is a continuing desire to improve upon the operational framework and efficiency of telescopic shafts in driveline systems to offer longevity of operational life, a reduction of the hydraulic-effect, a reduction in parts, and a reduction of packaging requirements. 
     SUMMARY 
     This section provides a general summary of the disclosure and is not to be interpreted as a complete and comprehensive listing of all of the objects, aspects, features and advantages associated with the present disclosure. 
     This disclosure relates generally to a shaft assembly without a ball retaining cage that improves upon the operational framework of telescopic shafts in driveline systems to offer longevity of operational life, a reduction of the hydraulic-effect, a reduction in parts, and a reduction of packaging requirements. 
     It is one aspect of the present disclosure to provide a shaft assembly for transmitting a torque. The shaft assembly comprises an outer shaft member that extends along an axis and includes an interior surface defining a bore and a plurality of outer grooves at least partially delimiting the bore. An inner shaft member extends along the axis and includes an outer surface defining at least one of a plurality of inner pockets or a plurality of inner grooves aligned with the outer grooves. At least one rolling element is located between the outer grooves and the inner pockets or the outer grooves and the inner grooves. At least one of the outer surface of the inner shaft or the inner surface of the outer shaft is configured to axially retain the at least one rolling element and the shaft assembly does not include a cage. 
     It is another aspect of the present disclosure to provide a method of assembling a shaft assembly for transmitting a torque. The method comprises providing an outer shaft member defining a bore, an inner shaft member, and a sleeve. The method further comprises aligning a first end of the sleeve with the bore and a second end of the sleeve with the inner shaft member. The sleeve includes a tapered section and a straight section. The method further comprises locating a first portion of the inner shaft member in the tapered section and placing a first circumferential array of rolling elements into one of inner pockets or inner grooves defined by an outer surface of the first portion of inner shaft member. The method further comprises placing the first portion and the first circumferential array of rolling elements past the tapered section and into a straight section of the sleeve. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended claims. These and other aspects of the present disclosure are disclosed in the following detailed description of the embodiments, the appended claims, and the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. 
         FIG.  1    is a perspective view of a shaft assembly including an inner shaft member and an outer shaft member, wherein the outer shaft member is illustrated as transparent to show features of the inner shaft member according to the principles of the present disclosure. 
         FIG.  2    is a perspective view of the inner shaft member according to the principles of the present disclosure. 
         FIG.  3    is a perspective view of the outer shaft member according to the principles of the present disclosure. 
         FIG.  4    is a perspective view of another embodiment of a shaft assembly according to the principles of the present disclosure. 
         FIG.  5    is a plan view illustrating sequential steps in a method of assembling the shaft assembly according to the principles of the present disclosure. 
         FIG.  6    is a flow diagram generally illustrating the method of assembling the shaft assembly according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. In general, the subject disclosure is directed to a telescoping shaft assembly for transmitting torque in a driveline system. However, the example embodiments are only provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     Referring to the Figures, wherein like numerals indicate corresponding parts throughout the views, a ballspline shaft with no ball retainer “shaft assembly” and a method of assembly is provided. The shaft assembly and method of assembly that improves upon the operational framework of telescopic shafts in driveline systems to offer longevity of operational life, a reduction of the hydraulic-effect, a reduction in parts, and a reduction in packaging requirements. 
     Referring now to  FIG.  1   , a shaft assembly is shown generally at  10 . The shaft assembly  10  is a rolling-element telescoping shaft assembly  10  capable of connecting to or integrating with a driveline (not shown) and transmitting a torque. Although the shaft assembly  10  may be incorporated into any suitable device, the shaft assembly  10  is particularly suited for use as a telescopic shaft assembly in a driveline system of a vehicle such as an automobile. The shaft assembly  10  includes an outer shaft member  12  and inner shaft member  14  telescopically engaged with the outer shaft member  12 . The outer shaft member  12  extends along a longitudinal axis A and defines an inner surface  16 , which defines an interior bore  18  centered on the axis A. It should be appreciated that a portion of the outer shaft member  12  that defines the bore  18  may be generally tubular. The inner shaft member  14  is located within the bore  18  and moveable telescopically with respect to the outer shaft member  12 . The inner surface  16  may include a ring groove  17  ( FIG.  2   ) for accommodating a snap ring  19  for retaining the inner shaft member  14  within the bore  18 . 
     As best illustrated in  FIG.  2   , the inner surface  16  of the outer shaft member  12  defines at least one (e.g., a plurality of) outer grooves  20  arranged in the inner surface  16 . Each outer groove  20  extends along and may be disposed generally parallel with the axis A. In some embodiments, each outer groove  20  may be circumferentially equidistant relative to the axis A. In some embodiments, each outer groove  20  may be not circumferentially equidistant relative to the axis A. As will be described in greater detail below, each of the outer grooves  20  may be used to transmit torque to the inner shaft member  14  via one or more bearing elements  22  ( FIG.  1   ) located therein. More particularly, a plurality of bearing elements  22  may be located in each of the outer grooves  20 . In some embodiments, each outer groove  20  at least partially houses the same number of bearing elements  22 . The inner surface  16  may further define at least one outer fluid groove  24  for reducing pressure build-up via the hydraulic-effect during operation. In some embodiments, the at least one outer fluid groove  24  includes an outer fluid groove  24  next to one of the outer grooves  20 . In some embodiments, the at least one outer fluid groove  24  extends along the inner surface  16 , parallel to the axis A, an equal or larger length than the outer grooves  20 . In some embodiments, the at least one outer fluid groove  24  has a circumferential width and a radial depth that are less than that of the outer grooves  20 , for example, half the size or less than half the size. The outer fluid grooves  24  may be positioned symmetrically with respect to the axis A. 
     As best illustrated in  FIG.  1    and  FIG.  3   , the inner shaft member  14  is at least partially disposed within or enters the bore  18  of the outer shaft member  12 . The inner shaft member  14  defines an outer surface  26  that extends and is telescopically moveable generally along the longitudinal axis A when the shaft assembly  10  is assembled. The outer surface  26  of the inner shaft member  14  defines at least one (e.g., a plurality of) inner pockets  28  arranged in the outer surface  26 . Each inner pocket  28  may be configured as a partially sphere-shaped depression (e.g., a hemisphere or less). Each inner pocket  28  may be disposed in at least one line of pockets  29  that extends along the axis A and may be disposed generally parallel with the axis A. The at least one line of pockets  29  may include a plurality of lines of pockets  29  and each line of pockets  29  may be circumferentially aligned with one of the outer grooves  20 . In some embodiments, each line of pockets  29  may be circumferentially equidistant. In some embodiments, each line of pockets  29  may be not circumferentially equidistant. An imaginary plane defined by an open end of each outer groove  20  may be positioned at an imaginary plane defined by an open end of an inner pocket  28  in a corresponding line of pockets  29  such that corresponding outer grooves  20  and inner pockets  28  generally mirror each other in circumferential positioning. Together, the corresponding outer grooves  20  and inner pockets  28  form respective bearing openings. 
     In some embodiments, each outer pocket  28  in a line of pockets  29  are spaced axially equidistantly. In some embodiments, the outer surface  26  defines at least one inner fluid groove  30 . In some embodiments, the at least one inner fluid groove  30  includes an inner fluid groove  30  between each of lines of pockets  29 . In some embodiments, the at least one inner fluid groove  30  extends along the outer surface  26 , parallel to the axis A, an equal or larger length than the line of pockets  29 . In some embodiments, the at least one inner fluid groove  30  has a circumferential width and a radial depth that are less than that of the inner pockets  28 , for example, half the size or less than half the size. The inner fluid grooves  30  may be positioned symmetrically with respect to the axis A and generally circumferentially aligned with the outer fluid grooves  24  with respect to the axis A. The inner pockets  28  may have a circumferential width and a radially depth that is generally equal to that of the inner grooves  20 . In some embodiments, the outer grooves  20  extend along the axis A a first distance and the lines of inner pockets  29  extend along the axis A a second distance, wherein the first distance is greater than the second distance. 
     The shaft assembly  10  includes the plurality of rolling elements  22 —e.g., balls or rollers—each of which is rollingly arranged within a corresponding opening between the inner grooves  20  and the outer pockets  28 . The rolling elements  22  rollingly engage the outer shaft member  12  and the inner shaft member  14  during relative axial motion between or telescoping movement of the outer shaft member  12  and the inner shaft member  14  with minimum sliding friction. The rolling elements  22  may be formed of stainless steel. In some embodiments, the rolling elements  22  have a diameter and more than half of the diameter is located within the outer grooves  20  and the inner pockets  28 . For example, because a cage is not needed, 95% or less, 85% or less, or 75% or less of the diameter of rolling elements  22  may be located within the outer grooves  20  and the inner pockets  28 . Moreover, the absence of the ball retaining cage can further permit the shaft assembly  10  to have a smaller outer diameter and a reduction in length as the ball retaining cage typically spaces the rolling elements  22  along the axis A. 
     A number of lines of pockets  29  can correspond to a number of outer grooves  20 , wherein each of the inner pockets  28  in a line of pockets  29  is arranged opposite to a corresponding outer groove  20  to form a pair. The number of pairs may be at least two, at least four, at least six, at least eight, at least ten, or at least twelve. In this case, at least one rolling element  22  is rollingly arranged between each inner pocket  28  and the outer groove  28 . A number of inner pockets  28  in each line of pockets  29  may be equal. For example, the number of inner pockets  28  in each line of pockets  29  may be at least two, at least four, at least six, at least eight, at least ten, or at least twelve. In the illustrated embodiment, the number of inner pockets  28  in each line of pockets  29  may be nine. 
     Referring now to  FIG.  4   , a shaft assembly  110  is shown in the assembled condition in accordance with another embodiment. Unless otherwise stated, the shaft assembly  110  may share all the same features, elements, arrangements, compositions, and methods of assembly as that presented in  FIGS.  1 - 3   . However, the inner pockets  28  are now replaced with an inner groove  128 . More particularly, the shaft assembly  110  includes an outer shaft member  112  and inner shaft member  114  telescopically engaged with the outer shaft member  112 . The outer shaft member  112  includes an inner surface  116  defining a bore  118 . The inner shaft member  114  is located within the bore  118  and moveable telescopically with respect to the outer shaft member  112 . The inner surface  116  of the outer shaft member  112  defines a set of outer grooves  120  and a set of outer fluid grooves (not shown), which may be configured the same as those described in reference to  FIGS.  1 - 3   . The inner surface  116  may further include a ring groove  117  for accommodating a snap ring  119  for retaining the inner shaft member  114  within the bore  118 . 
     The inner shaft member  114  defines an outer surface  126  that extends and is telescopically moveable generally along the longitudinal axis A when the shaft assembly  110  assembled. The outer surface  26  of the inner shaft member  14  defines inner grooves  128  and inner fluid grooves (not shown). The inner grooves  128  may be located in general locations previously described in relation to the line of pockets  29  described in reference to  FIGS.  1 - 3   . Moreover, each inner groove  128  may be configured to retain the same number of rolling elements  122  as the line of pockets  29  previously described. In the illustrated embodiment, each inner groove  128  holds eight rolling elements  122 . Similar to the previous embodiment, the shaft assembly  110  does not utilize a cage for retaining the rolling elements  122 . As illustrated, each inner groove  128  may extend between a first end  134  and a second end  136  and the rolling elements  122  may extend substantially between the first end  134  and the second end  136  and contact one another. The first end  134  and second end  136  may be partially sphere-shaped to abut a spherical surface of the rolling elements  122  and axially retain it therein. In some embodiments, the rolling elements  122  have a diameter and more than half of the diameter is located within the outer grooves  120  and the inner grooves  128 . For example, because a cage is not needed, 95% or less, 85% or less, or 75% or less of the diameter of rolling elements  122  may be located within the outer grooves  120  and the inner grooves  128 . In some embodiments, a diameter of the first end  134  and the second end  136  is slightly larger than the diameter of the rolling elements  122 . 
       FIG.  5    is a plan view illustrating sequential steps in a method  200  of assembling the shaft assembly according to the principles of the present disclosure. With initial reference to the leftmost drawing in  FIG.  5   , a sleeve  238  is located on an end of the outer shaft member  12 ,  112  that defines the bore  18 ,  118 . The sleeve  238  includes an inner surface  240  and defines a straight section  242  located next to the outer shaft member  12 ,  112  and a tapered section  244  spaced from the outer shaft member  12 ,  112  by the straight section  242 . The inner surface  240  of tapered section  244  extends gradually radially outwardly in a direction away from the straight section  242 . A first portion next to a first end  246  of the inner shaft member  14 ,  114  is placed within the tapered section  244  and rolling elements  22 ,  122  are placed in a first circumferential array  248  in the inner pockets  28  or the inner groove  128 . The inner shaft member  14 ,  114  is then is moved deeper into the sleeve  238  such that the first circumferential array  248  is retained against the inner surface  240  of the sleeve  238  and the first portion is located in the straight section  242 . In some embodiments, the inner surface  240  of the straight section  242  may define rolling element retaining grooves  250  extending towards the outer shaft member  12 ,  112 . Next, additional rolling elements  22 ,  122  are placed in a second circumferential array  252  in the inner pockets  28  or the inner groove  128  located on a second portion of the inner shaft member  14 ,  114 . The process continues until each of the inner pockets  28  retain rolling elements  22 ,  122  or the inner groove  128  is filled with rolling elements  22 ,  122  as described above. The snap ring  19 ,  119  is then placed within the ring groove  17 ,  117 . 
       FIG.  6    is a flow diagram generally illustrating the method  200  of assembling the shaft assembly according to the principles of the present disclosure. At  202 , the method  200  includes providing an outer shaft member defining a bore, an inner shaft member, and a sleeve. At  204 , the method continues by aligning a first end of the sleeve with the bore and a second end of the sleeve with the inner shaft member. In some embodiments, the second end of the sleeve defines a tapered section and the first end of the sleeve defines a straight section. At  206 , the method continues by placing a first circumferential array of rolling elements into one of inner pockets or inner grooves defined by an outer surface of a first portion of the inner shaft member. At  208 , the method includes moving the first portion of the inner shaft member further into the sleeve (e.g., into the straight section). In some embodiments, the inner shaft member is moved from the tapered section towards a straight section until the rolling elements are retained between one of inner pockets or inner grooves and an inner surface of the sleeve. At  210 , the method continues by placing additional circumferential arrays (e.g., a second circumferential array) of rolling elements into one of inner pockets or inner grooves defined by another portion of the inner shaft member (e.g., a second portion) and moving the inner shaft member further into the sleeve. Step  210  repeats until all of the inner pockets contain a rolling element or each of the inner grooves are filled to rolling elements. Stated another way, at  210 , the method repeats both steps  206  and  208  until all of the inner pockets contain a rolling element or each of the inner grooves are filled to rolling elements. At  212 , the method continues by placing a snap ring between the outer surface of the inner shaft member and an inner surface of the outer shaft member to retain the inner shaft member in the bore of the outer shaft member. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it is to be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Moreover, any feature, element, or component of any one embodiment can be used in conjunction with any of the other embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description. On the contrary, the disclosure is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation to encompass all such modifications and equivalent structure as is permitted under the law.