Patent Publication Number: US-2007104535-A1

Title: Spline interconnect

Description:
TECHNICAL FIELD  
      This invention relates to a spline member assembly and to an interconnection between an internal spline member and an external spline member.  
     BACKGROUND  
      Conventional spline members are implemented in a variety of applications. For example, an internal spline member and an external spline are known to interconnect shaft members. In some applications, the interconnection transfers torque along a shaft and one shaft may be a propeller driveshaft for a vehicle.  
      With reference to a vehicular application, torque may be transferred along a propeller driveshaft between a transmission and a differential. In an application, a driveshaft may adjust or dynamically compensate for a deviation or the like in a distance between a transmission and an associated differential. Such a deviation in distance may occur, for example, during operation of a vehicle. A known method for accommodating such a change in distance is to telescopically attach or connect an internal spline member to an external spline member. Conventionally, this relationship is known as a slip spline. It is also known to collapsibly connect the shafts. For example, a shaft may be locked and have a collapse threshold that is typically greater than the load of a plungable constant velocity (CV) joint. In an application, a collapse threshold is designed to withstand a pre-defined level of force, and once this threshold is substantially met or exceeded, the shaft is designed to collapse. The collapse threshold may substantially prevent buckling. Conventionally, this relationship is known as a lock spline.  
     SUMMARY  
      The present invention provides a first member for transferring torque to a second member comprising a splined portion having a plurality of splines, at least one of said plurality of splines comprises a pilot spline including a chamfer at an end thereof, wherein a peak width of said pilot spline is different than a general peak width of the remaining splines of said plurality of splines, thereby providing a different contact surface area amount between said first member and said second member.  
      In another embodiment, a shaft assembly comprises an inner member having an external splined portion, and an outer member having an internal splined portion, said inner member in cooperation with said outer member, wherein at least one of said internal splined portion and said external splined portion includes a pilot spline including a chamfer at an end thereof, wherein a peak width of said pilot spline is different than a general peak width of the remaining splines of said plurality of splines, thereby providing a different surface area amount between said first member and said second member.  
      In yet another embodiment, a shaft assembly comprises an inner member in cooperation with an outer member, said inner member and said outer member having a first engaging portion and a second engaging portion, at least one of said inner member and said outer member having means for selectively determining a contact surface area between said first engaging portion and said second engaging portion.  
      The present invention will be more fully understood upon reading the following detailed description in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description:  
       FIG. 1  shows an exploded view of a shaft assembly according to an embodiment of the invention;  
       FIG. 2  shows a cross-sectional view of an inner member having an external spline portion taken along the line  2 - 2  of the shaft assembly of  FIG. 1 ;  
       FIG. 3  shows an enlarged view of a portion of the spline portion of the inner member of  FIG. 2 ;  
       FIG. 4  shows a cross-sectional view of an outer member having an internal spline portion taken along the line  4 - 4  of the shaft assembly of  FIG. 1 ;  
       FIG. 5  shows an enlarged view of a portion of the spline portion of the outer member of  FIG. 4 ;  
       FIG. 6  shows an exploded view of a shaft assembly according to an embodiment of the invention;  
       FIG. 7A  shows a cross-sectional view of the shaft assembly taken along the line  7 - 7  of  FIG. 6 ;  
       FIG. 7B  shows a cross-sectional view of the shaft assembly taken along the line  7 - 7  of  FIG. 6 ;  
       FIG. 8  shows a cross-sectional view of the shaft assembly taken along the line  8 - 8  of  FIG. 7 ;  
       FIG. 9A  shows an enlarged view of a portion of a splined portion; and  
       FIG. 9B  shows an enlarged view of a portion of another splined portion. 
    
    
     DETAILED DESCRIPTION  
      Referring now to the drawings, several exemplary embodiments of the invention are shown in detail. Although the drawings represent some embodiments of the invention, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain the invention. Further, the embodiments set forth herein are not intended to be exhaustive, restrict or otherwise limit the invention to the precise forms and configurations shown in the drawings and disclosed in the following detailed description.  
      Referring now to  FIG. 1 , a shaft assembly  10  is shown according to an embodiment of the invention. In general, shaft assembly  10  includes an inner member  12  having an external splined portion  14 , and an outer member  16  having an internal splined portion  18 . In an embodiment, inner member  12  and outer member  16  may be generally round and/or substantially tubular. In an application, a stub shaft  20  or the like may be fixedly-connected or attached to an end of inner member  12 , and a stub shaft  22  may be fixedly-connected or attached to an end of outer member  16 . Shaft assembly  10 , however, is not limited to the aforementioned fixedly connected or attached stub shafts  20 ,  22 . For example, without limitation, one or both of stub shafts  20 ,  22  may be replaced with a flange, yoke or other connection-related member. In an embodiment, inner member  12  and outer member  16  may be formed from cylindrical tubes and may be manufactured from any suitable material. If desired, inner member  12  and outer member  16  may be made from commercially available materials, such as, without limitation, low carbon alloy steel, lightweight aluminum or the like. In an embodiment, one or both of the shaft ends may not be fixedly connected or attached to inner member  12  and outer member  16 . These and other adjustments to the configuration or possible design modifications will become apparent to one of ordinary skill in the art after considering the present disclosure.  
      In an embodiment, shaft assembly  10  rotates about an axis to transmit torque. External splined portion  14  of inner member  12  includes a plurality of outwardly projecting splines  24  (See e.g.,  FIGS. 2 and 3 ) that are circumferentially formed upon inner member  12 . Similarly, internal splined portion  18  of outer member  16  includes a plurality of inwardly projecting splines  26  (see e.g.,  FIGS. 4 and 5 ) that are circumferentially formed upon outer member  16 .  
      The splines  24 ,  26  may be formed using known processes. Such processes will be known to a person of ordinary skill after consulting this disclosure. For example, without limitation, splines  24 ,  26  can be “cold formed” by the use of the conventional “Grob” process, provided by the Ernst Grob AG Company of Mannedorf, Switzerland. However, the “Grob” process may require a uniform mandrel and a pilot feature to be applied to all teeth. Another process for forming the splines  24 ,  26  is by deforming the splined portions  14 ,  18  radially inwardly. Axially forming the splines  24 ,  26  allow for designs with a varied number of major diameter pilot splines according to the invention to a varied number of spline teeth. Alternatively, portions of splined portions  14 ,  18  can be expanded radially outwardly.  
      The splines  24 ,  26  can also be formed by mechanical crimping, electromagnetic pulse forming, hydroforming, and the like. Electromagnetic pulse forming and hydroforming, for example, can accommodate a varied number of pilot splines according to the invention to a varied number of spline teeth. In addition, a length of the pilot spline can be varied. These and other conventional processes will not be further discussed hereinafter as they are readily known to persons of ordinary skill in the art. As discussed below, in an embodiment the shape and size of the splines  24 ,  26  may additionally be used to determine the magnitude of the collapse force for shaft assembly  10 .  
      Referring to  FIGS. 2 and 3 , an embodiment of an exterior surface of inner member  12  includes projections along splined portion  14  that form outwardly projecting (or external) splines  24 . A valley or depression  27  is provided between adjacent splines  24 . Similarly, with reference to  FIGS. 4 and 5 , an interior surface of outer member  16  includes projections that form inwardly projecting (or internal) splines  26  that substantially correspond (in circumferential spacing, size, and shape) with depressions  27  of external splined portion  14  of inner member  12 . Also, between each inwardly projecting spline, is a valley or depression  29  that substantially corresponds (in circumferential spacing, size, and shape) with splines  24  of inner member  12 . A relationship between external splines  24 , internal splines  26  and the substantially corresponding depressions  27 ,  29  will be discussed in further detail below.  
      The exterior surface of outer member  16  and the interior surface of inner member  12  may additionally include projections and depressions that parallel their opposite surface. For example, without limitation, a depression on an interior surface of inner member  12  may be a projection on the exterior surface of inner member, and vice-versa. Such projections and depressions are sometimes a result of spline forming processes. In another embodiment, at least a portion of one or both exterior surface of outer member  16  and interior surface of inner member  12  may not parallel the opposite surface, and, therefore, the present invention should not be so limited thereby. These and other structural changes will be readily recognizable by one of ordinary skill in the art after consulting the present disclosure without deviating from the intended spirit and scope of the invention.  
      In an embodiment, one or both of internal splined portion  14  and external splined portion  18  has at least a first portion  21  and a second portion  23 . First portion  21  and second portion  23  may be arranged at any position along splined portion  14  and/or  18 . For example, if desired, a splined portion may include be two first portions  21  and/or two second portions  23  as the arrangement thereof may be application specific. In an embodiment, first portion  21  contacts a first surface area amount of the corresponding spline portion and second portion  23  contacts a second surface area amount of the corresponding spline portion. In an embodiment, the first and second surface area amounts may be individually described as a summation of the contacted surface areas along each first and second portion  21 ,  23 , respectively, that occur between splined portion  14  of inner member  12  and splined portion  18  of outer member  16 . In an embodiment, because the contacted surface amounts may at least affect the amount of radial, axial and/or longitudinal friction exerted between inner member  12  and outer member  16 , it may be desirable to structure an interconnection between inner member  12  and outer member  16  to harness or control these and other forces. Thus, by adjusting the total contacted surface area amount (e.g., the first surface area amount plus the second surface area amount) and/or configuring or modifying the arrangement of the first surface area amount with respect to the second surface area amount (i.e., position of first portion  21  and second portion  23 ) the system may be assembled to provide, inter alia, added longitudinal control when compared to a conventional propeller driveshaft. Specifically, among other examples, varying the amount, or degree, of contacted surface area amounts may affect a plunge of inner member  12  and outer member  16 .  
      In an embodiment utilizing a slip spline relationship between inner member  12  and outer member  16 , such that inner member  12  and outer member  16  are telescopically related, contacted surface area amounts may be configured or modified or substantially define or control a plunge relationship between inner member  12  and outer member  16 . For example, adjusting the amount of longitudinal friction exerted along various points along inner member  12  and outer member  16  may influence or urge inner member  12  and outer member  16  to a substantially centered position. In an embodiment, increasing the engagement of inner member  12  and outer member  16  along first portion  21  results in an increased amount of longitudinal friction exerted between inner member  12  and outer member  16  as the first surface area amount is greater than the second surface area amount. Thus, plunge of shaft assembly  10  is becomes increasingly prohibited as inner member  12  and outer member  16  increasingly engage along first portion  21 . Similarly, the longitudinal friction between inner member  12  and outer member  16  may become reduced as second portion  23  becomes increasingly engaged, and increasing engagement with second portion  23  encourages or facilitates a plunging of inner member  12  and outer member  16 . In an embodiment, this feature may be implemented to generally assure a centered shaft assembly. The benefits derived therefrom will be readily recognized by one of ordinary skill in the art.  
      It should be noted that the structural transition between first portion  21  and second portion  23  may be a gradual slope, a step function or transitions therebetween. The advantages of different transitions will become readily apparent, and may be determined by one of ordinary skill after consulting the present disclosure and considering the particularized application. For example, a sloped transition between second portion  23  and first portion  21  may allow a smoother plunge along the transition, wherein a step function transition may prohibit the plunge therebeyond. Moreover, it should be noted, that at different interfaces along shaft assembly  10 , inner member  12  and outer member  16  may engage at both the first portion  21  and the second portion  23 , and a longitudinal friction may be a sum of the individual frictions.  
      In an embodiment enlisting a locked spline relationship between inner member  12  and outer member  16 , such that inner member  12  and outer member  16  are substantially longitudinally fixed unless a collapsing force is exerted thereon, contacted first and second surface area amounts may be configured to adjust or substantially define this collapsing force. In an embodiment, a second portion  23  is arranged at one or both ends of a first portion  21 , wherein inner member  12  and outer member  16  are, generally, fixedly engaged along first portion  21  unless an external force that sufficiently exceeds the collapsing force therebetween is exerted thereon. Collapsing of shaft assembly  10  aids in preventing the buckling of shaft assembly  10 , and absorbs a portion of the external force. Thus, in the event that the collapsing force is met or surpassed by the external force, the first portion  21  and interface between inner member  12  and outer member  16  allow the shaft assembly  10  to substantially collapse. Thus, as second portion  23  becomes engaged due to the collapse, a reduced external force (e.g., below the once satisfied collapse threshold) continues to permit inner member  12  and outer member  16  to collapse and absorb additional external force. Thus, once the collapse of shaft assembly  10  is substantially set in motion, the shaft assembly will generally continue to collapse, in lieu of permitting shaft assembly  10  to buckle.  
      With reference to the Figures, an embodiment of the invention is illustrated and described wherein an external splined portion  14  of an inner member  12  includes first portion  21  and second portion  23 . First portion  21  and second portion  23  of external splined portion  14  are configured to adjust the amount of contacted surface area amounts between external splines  24  and corresponding depressions  29  of outer member  16 . The present invention is not limited by the illustrated embodiments. For example, the internal spline portion  18  of outer member  16  may additionally, or instead, include first portion  21  and second portion  23 . Also, as mentioned above, there may be more than one first portion  21  and/or second portion  23  as the inclusion thereof may be application specific. This and other features will be discussed in further detail hereinbelow.  
      Referring now to  FIGS. 2 and 3 , an embodiment of an external spline  14  of an inner member  12  is shown. External splined portion  14  includes a plurality of outwardly projecting splines  24  with depressions  27  naturally residing therebetween. A floor of depressions  27  defines an inner radius r ext,inner  of inner member  12 , and, similarly, a peak of outwardly projecting splines  24  defines an outer radius r ext,outer  of inner member  12 . The outwardly projecting splines  24  have a height, h, measured from the peak of the projection to the inner diameter of tube  12 . Similarly, the depressions  27  have a depth d. Splines  24  have a general peak width w peak  measured from a first end of the peak of spline  24  to a second end of the peak of spline  24 . In an embodiment, at least outwardly projecting splines  24  contribute to the first and second contact surface area amounts along splined portions  14 ,  18 .  
      Thus, in an embodiment to substantially configure the second surface area amount, one or more pilot splines  30  may be included among the outwardly projecting splines  24 . Each pilot spline  30  has a height, h+Δh, that is greater than the height, h, of the splines  24 . Pilot spline  30  may adjust the second contact surface amount by, for example and without limitation, defining a peak width w peak,pilot  that is different from the general peak width w peak . Further details of pilot spline  30  and uses thereof will be further explained below. It should be noted that although a pilot spline  30  is discussed, one of ordinary skill in the art will recognize that other structures or methods may be used along the different portions. For example, a pilot depression, as opposed to pilot spline  30 , may be used to adjust the second surface area amount. After considering this disclosure, these and other ways will be immediately apparent to one of ordinary skill and the invention should not be so limited thereby.  
      In an embodiment, second surface area amount, or, the longitudinal friction exerted between inner member  12  and outer member  16  along the second portion  23 , may be adjusted by altering the structure of pilot spline  30 . For example, without limitation, reducing or increasing peak width w peak,pilot  of pilot spline may reduce or increase the second surface area amount. In an embodiment, peak width w peak,pilot  of pilot spline  30  is reduced from the general peak width w peak  by including at least one chamfer at an end of pilot spline  30 . Referring to  FIG. 3 , each end of pilot spline  30  includes a chamfer  32 . Chamfer  32  extends at a pre-defined angle θ with respect to its respective end. In an embodiment, chamfer  32  provides exemplary structure to limit the width of the peak of pilot spline  30  w peak,pilot  compared to the general peak width w peak  of splines  24 . One of ordinary skill will readily recognize other alternatives to reduce the length of the peak, and, similarly will recognize benefits realized by the variations of this angle. It should further be noted that the number of pilot splines may be application specific. These and other features of a pilot spline  26  will be discussed in further detail hereinbelow.  
       FIGS. 4 and 5  illustrate an embodiment of an internal spline portion  18  of outer member  16  having inwardly projecting splines  26  with depressions  29  therebetween. The floor of the depressions defines an outer radius r int,outer  and the peak of inwardly projecting splines  26  defines an inner radius r int,inner . Outer radius r ext,outer  of inner member  12  is approximately equal to the inner radius r int,inner  of outer member  16 .  
      Referring to a locked spline relationship, it should be noted that outer diameter r ext,outer  of inner member  12  may be greater than inner radius r int,inner  of outer member  16 . An embodiment of such a relationship, among other possibilities, is illustrated in  FIG. 9A . Thus, as inner member  12  and outer member  16  are combined, it is likely that one or both of inner member  12  and outer member  16  deform to some degree. The force fit and resultant contact between inner member  12  and outer member  16  yields a high first surface area amount, and, thus, a high degree of longitudinal friction is exerted therebetween. This can create a locking effect and a collapse threshold. The collapse threshold is the amount of longitudinal force that effectively meets or exceeds the longitudinal friction. Similarly, it should also be noted that inner radius r ext,inner  of inner member  12  may be smaller than outer radius r int,outer  of outer member  16 , and, in a similar fashion, at least one of inner member  12  and outer member  16  deform to accommodate a size difference.  
      Referring now to a slip spline relationship, it should be noted that outer radius r ext,outer  of inner member  12  may be sized just slightly smaller than inner radius r int,inner  of outer member  16 . An embodiment of such a relationship, among other possibilities, is illustrated in  FIG. 9B . This can create a slip function, such as generally described above. Similarly, it should also be noted that inner radius r ext,inner  of inner member  12  may be smaller than outer radius r int,outer  of outer member  16 . The benefits derived therefrom, and the application specific use therefore will be readily apparent to one of ordinary skill in the art after considering this disclosure. As the pilot feature of the present invention effectively provides structure to control an amount or degree of longitudinal friction between inner member  12  and outer member  16 , the radial clearance between the peak of at least one of splines  24 ,  26  and the floor of depressions  27 ,  29  may be smaller than convention has previously allowed in slip spline assemblies.  
      It should be further noted, that the number of splines  24 ,  26  and depth thereof may application specific to ensure the shaft assembly  10  sufficiently transfers or transmits torque for a particular application. Additionally, the clearance between internally projecting splines  26  and the external spline portion  14  may also be application specific. For example, without limitation, in an embodiment the reduced radial clearance may aid in improving the accuracy of propeller driveshaft balance correction. However, such reductions in radial clearance can sometimes give rise to frictional engagement between component imperfections on interface with minimal clearances, which is addressed by reducing the second contact surface area amount.  
      Referring now to the exemplary embodiments shown in  FIGS. 6 through 9 , inner member  12  is capable of being received within outer member  16  such that the internal splined portion  26  of outer member  16  is adapted to selectively and cooperatively intermesh or engage with the external splined portion  14  of inner member  12 .  
      In an embodiment, pilot splines  30  may be symmetrically disposed circumferentially along the splined portion. However, the present invention may also be utilized in a non-symmetric arrangement, and, therefore, should not be limited to the illustrated embodiment. With reference to  FIGS. 7A-7B , two exemplary embodiments are shown to highlight some of the various possible pilot spline arrangements along second portion  23 .  FIG. 7A  illustrates inner member  12  having a second portion  23  including pilot splines  30  and conventional splines  24  in an alternating configuration.  FIG. 7B  illustrates inner member  12  having a second portion  23  wherein every fourth spline  24  is a pilot spline  30 . It should be noted that the present invention contemplates any arrangement of pilot splines, and, therefore, the present invention should not be limited to the illustrated embodiments. Also, although each outer member  16  and inner member  12  comprise approximately twenty (20) splines  24 ,  26  the number and arrangement thereof may be altered in accordance with the present disclosure.  
       FIG. 8  illustrates an exemplary embodiment of the invention along a segment of first portion  21 . The inner member  12  and the outer member  16  are conventionally interconnected and include conventional splines. In the illustrated embodiments of  FIG. 7  and  FIG. 8 , therefore, the first surface area amount along the first portion  21  of  FIG. 8  is greater than the second surface area amount along the second portion  23  of  FIG. 7 . However, altering the organization or number of first portion  21  and second portion  23  will affect the movement of shafts along the splined portions thereof.  
       FIGS. 9A and 9B  illustrate an exploded view of two exemplary interconnections between inner member  12  and outer member  16  along second portion  21  according to an embodiment of the invention. Specifically,  FIG. 9A  illustrates an embodiment of a lock spline assembly between first member  12  and second member  16  along second portion  23 .  FIG. 9B  illustrates an embodiment of a slip spline assembly between first member  12  and second member  16  along second portion  23 . Each configuration has a second surface area amount that is reduced from a first surface area amount, resulting from the inventive addition of second portion  23  and pilot spline  30 .  
      It should be noted that at least a portion of spline portions  14 ,  18  of one or both of inner member  12  and outer member  16  may be coated with a material having a low coefficient of friction, such as nylon, or the like. The coating can be precision shaved to provide the desired clearance between inner member  12  and outer member  16 .  
      While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.