Patent Publication Number: US-2011052316-A1

Title: Spline Shaft Assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a spline shaft, more particularly to a spline shaft assembly capable of transmitting torque. 
     2. Description of the Related Art 
     Referring to  FIGS. 1 and 2 , a conventional spline shaft assembly  1  comprises a rotatable shaft  11  extending along an axial direction (X), and a transmission member  12  configured as a spur gear. The rotatable shaft  11  has an outer surface and a plurality of keys  111  formed in the outer surface of the rotatable shaft  11 . The transmission member  12  is formed with a through hole  121  and has an inner surface defining the through hole  121 , and a plurality of axially extending grooves  122  formed in the inner surface of the transmission member  12 . The rotatable shaft  11  extends through the through hole  121 . The keys  111  of the rotatable shaft  11  engage respectively the grooves  122  of the transmission member  12  such that the rotatable shaft  11  and the transmission member  12  are co-rotatable. 
     The grooves  122  of the conventional spline shaft assembly  1  may be formed by a cutting piece  2  that rotates about a transverse axis (Y) perpendicular to the axial direction (X) to thereby grind or mill the inner surface of the transmission member  12 . However, if the through hole  121  is too narrow to allow extension of a driving device that drives the cutting piece  2  to rotate, the grooves  122  can be formed only by broaching. 
     When it is desired to form the grooves  122 , a broach of a broaching machine (not shown) is extended through the through hole  121  to broach the inner surface of the transmission member  12 . However, the broaching machine is expensive, and the cutting amount thereof per unit time is relatively small (approximately 0.02 mm). Furthermore, the rectangular groove-defining walls of the grooves  12  deform easily after a heat-treatment is applied. As such, the rotatable shaft  11  must be machined to engage fittingly the grooves  12 , which results in a troublesome manufacturing process for the conventional spline shaft assembly  1 . Once the rotatable shaft  11  and the grooves  12  of the transmission member  12  do not engage fittingly, unwanted noise and vibration will be generated to thereby reduce the operating efficiency of the conventional spline shaft assembly  1 . 
     Referring to  FIG. 3 , a conventional ball-bearing type spline shaft  3  comprises a rotatable shaft  31 , a transmission member  32 , a retaining member  33  co-rotatable with the transmission member  32 , and a plurality of balls  34 . The rotatable shaft  31  has a plurality of axially extending grooves  311  formed in an outer surface thereof. The transmission member  32  has a plurality of axially extending grooves  321  formed in an inner surface thereof. The grooves  311 ,  321  receive the balls  34  therein. Since the balls  34  are in point contact with the transmission member  32  and the rotatable shaft  31 , the retaining member  33  is required to maintain the balls  34  within the grooves  311 ,  321 . The retaining member  33  has a plurality of through holes  331  arranged along the axial direction (X) for receiving the balls  34 , respectively. The configuration of the ball-bearing spline shaft  3  is complicated and the installation of the ball-bearing spline shaft  3  is cumbersome. 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the present invention is to provide a spline shaft assembly capable of alleviating the above drawbacks of the prior art. 
     Accordingly, a spline shaft assembly of the present invention comprises a rotatable shaft extending along an axial direction, and having an outer surface, and a plurality of first grooves formed in the outer surface. Each of the first grooves is defined by a semi-circular groove-defining wall. A transmission module is formed with a through hole and has an inner surface defining the through hole, and a plurality of axially extending second grooves formed in the inner surface of the transmission module. Each of the second grooves is defined by a semi-circular groove-defining wall. The rotatable shaft extends through the through hole. A spline key set has a plurality of cylindrical keys extending along the axial direction and disposed between and engaging the first grooves of the rotatable shaft and the second grooves of the transmission module, and at least two positioning members connected to the transmission module and associated with the cylindrical keys such that the transmission module and the cylindrical keys are co-rotatable. 
     The spline shaft assembly of the present invention is easier to construct compared to the conventional spline shaft assemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a perspective view of a conventional spline shaft assembly; 
         FIG. 2  is a schematic view of a transmission member of the spline shaft assembly of  FIG. 1 ; 
         FIG. 3  is a partly cutaway perspective view of another conventional spline shaft assembly; 
         FIG. 4  is an exploded perspective view of a first preferred embodiment of a spline shaft assembly of the present invention; 
         FIG. 5  is a partly cutaway perspective view of the first preferred embodiment of the present invention; 
         FIG. 6  is a partly cutaway perspective view of a second preferred embodiment of a spline shaft assembly according to the present invention; 
         FIG. 7  is a partly cutaway perspective view illustrating a modified transmission member of the second preferred embodiment; and 
         FIG. 8  is a partly cutaway perspective view of a third preferred embodiment of a spline shaft assembly according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
     As shown in  FIGS. 4 and 5 , a first preferred embodiment of a spline shaft assembly according to the present invention comprises a rotatable shaft  4 , a transmission module  5 , and a spline key set  6 . 
     The rotatable shaft  4  extends along an axial direction (X), and has an outer surface  41 , and a plurality of first grooves  42  formed in the outer surface  41 . Each of the first grooves  42  is defined by a semi-circular groove-defining wall  420 . 
     The transmission module  5  has a transmission member  51  configured as a spur gear in this embodiment. The transmission member  51  is formed with a through hole  50 , and has an inner surface  511  defining the through hole  50 , and a plurality of axially extending second grooves  512  formed in the inner surface  511 . Each of the second grooves  512  is defined by a semi-circular groove-defining wall  5120 . The rotatable shaft  4  extends through the through hole  50 . The transmission member  51  has an annular groove  513  formed in the inner surface  511  and disposed at one end of the transmission member  51 , and an internally threaded portion  514  formed at the other end of the transmission member  51 . 
     The spline key set  6  has a plurality of cylindrical keys  61  and two positioning members configured respectively as a C-ring  62  and an externally threaded fastener  63 . The keys  61  of the spline key set  6  extend along the axial direction (X), and are disposed between and engage the first grooves  42  of the rotatable shaft  4  and the second grooves  512  of the transmission member  51 . The positioning members are connected to the transmission member  51  and are associated with the cylindrical keys  61  such that the transmission member  51  and the cylindrical keys  61  are co-rotatable. The transmission member  51  and the rotatable shaft  4  are interconnected co-rotatably through the cylindrical keys  61  and the positioning members (i.e., the C-ring  62  and the fastener  63 ). Through engagement between the keys  61  and the first and second grooves  42 ,  512 , the rotatable shaft  4  and the transmission member  51  can slide relative to each other along the axial direction (X). 
     The C-ring  62  engages the annular groove  513  and abuts against one end of each of the cylindrical keys  61 . The fastener  63  engages the internally threaded portion  514  of the transmission member  51  and abuts against the other end of each of the cylindrical keys  61 . 
     It should be noted that a grinder (not shown) is employed as a manufacturing tool in this embodiment. A spindle (not shown) of the grinder extends through the through hole  50  and rotates about an axis parallel to the axial direction (X) to thereby grind the inner surface  511  of the transmission member  51  to form one of the second grooves  512  at a time. 
     As shown in  FIG. 6 , a second preferred embodiment of the spline shaft assembly according to the present invention has a structure similar to that of the first embodiment. The main difference between this embodiment and the first embodiment resides in the following. The transmission module  5  has a transmission member  53  and a shaft sleeve  52  surrounded by the transmission member  53  and formed with the through hole  50 . The transmission member  53  is connected co-rotatably to the shaft sleeve  52  by a plurality of screws  54  (only one is shown). The transmission member  53  is configured as a spur gear. The shaft sleeve  52  has an inner surface  521 , a plurality of axially extending second grooves  522  formed in the inner surface  521 , an annular groove  523  formed in the inner surface  521  and disposed at one end of the shaft sleeve  52 , and an internally threaded portion  524  formed at the other end of the shaft sleeve  52 . Each of the second grooves  522  is defined by a semi-circular groove-defining wall. The rotatable shaft  4  extends through the through hole  50 . 
     The positioning members are configured respectively as a C-ring  62  and an externally threaded fastener  63 . The C-ring  62  engages the annular groove  523  and abuts against one end of each of the cylindrical keys  61 . The fastener  63  engages the internally threaded portion  524  of the shaft sleeve  52  and abuts against the other end of each of the cylindrical keys  61 , such that the transmission member  53  and the cylindrical keys  61  are co-rotatable. The second preferred embodiment has the same advantages as those of the first preferred embodiment. As shown in  FIG. 7 , a modified transmission member  53  is configured as a belt pulley. 
     Referring to  FIG. 8 , a third preferred embodiment of the spline shaft assembly according to the present invention has a structure similar to that of the second embodiment. The main difference between the third embodiment and the second embodiment resides in the following. The transmission member  53  includes a plurality of angularly equidistant camshafts connected fixedly to and extending radially and outwardly from the shaft sleeve  52 . The spline key set  6  has a plurality of the positioning members each configured as a radially extending screw  64 . The screws  64  (only one is shown) of the spline key set  6  extend through the shaft sleeve  52  and are threaded respectively to the keys  61 , such that the keys  61 , the shaft sleeve  52  and the transmission member  53  are co-rotatable. The annular groove  523  (shown in  FIG. 6 ) of the shaft sleeve  52  and the internally threaded portion  524  (shown in  FIG. 6 ) of the shaft sleeve  52  are omitted in this embodiment. The third preferred embodiment has the same advantages as those of the second preferred embodiment. 
     To sum up, the advantages of the spline shaft assembly according to the present invention are as follows. The second grooves  512 ,  522  are formed by a grinding process that simplifies the manufacturing process and decreases the manufacturing costs of the spline shaft assembly. Therefore, the spline shaft assembly of the present invention is easier to construct compared the conventional spline shaft assemblies. 
     While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.