Abstract:
A half shaft connects to the mounting bracket of the wheel in a splined connection. The straight external spline of the half shaft is modified to a helical or involute external spline, in which the helix angle adopted is small. The mounting bracket of the wheel can be longitudinally advanced by hand assembly only part way onto the half shaft. The rest of the longitudinal advancement during assembly occurs by tightening the nut to completely eliminate the fit clearance between the external spline and its corresponding mating arrangement. Various road tests of vehicles verify that, when using the present invention, the nut does not loosen during use of the vehicle. The invention enables the locking force of the nut to be reduced, and assembly and maintenance are convenient.

Description:
CROSS-REFERENCE TO RELATED U.S. APPLICATION(S) 
       [0001]    None. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of wheeled land vehicles, and particularly to a type of connecting structure mounting the wheel to its half shaft. 
       BACKGROUND OF THE INVENTION 
       [0003]    In existing wheeled land vehicles, wheels are supported for rotation by a half shaft which rotates about its axis to provide torque to the wheel. For ease of assembly, repair itself, the wheel typically includes a mounting bracket, and the half shaft is connected to the mounting bracket of the wheel has an internal spline which mates with an external spline on the half shaft. While the mating spline may involve a single longitudinally extending ridge in a corresponding recess, more commonly there are numerous longitudinally extending ridges that mate into corresponding recesses. On the half shaft, the spline is located slightly inward from the end of the half shaft, and the end of the half shaft includes a standard male thread similar to a bolt. The mounting bracket of the wheel is then secured to its half shaft by a threaded locking nut rotationally secured onto the male thread of the half shaft. When assembled; the drive force of the half shaft is transmitted to the wheel by the internal spline and the external spline, enabling the wheel work as intended. 
         [0004]    In order to enable assembly, there must be some fit clearance between the external and internal splines. At the same time, during use it is desired to minimize any play between the wheel mounting bracket and its half shaft. Manufacturing tolerance on the two mating splines are accordingly quite tight and precise, increasing cost to the manufacturing process. 
         [0005]    Even with highly accurate manufacturing and tight tolerances, the clearance required for assembly can result in slight movement between the internal spline and the external spline at times of high acceleration or deceleration or when the vehicle is impacted. As a result of this slight back-and-forth movement of the internal spline and the external spline, there are times when the locking nut may slowly loosen. Eventually, the loosened locking nut could lead to unsafe conditions. Ways to prevent loosening of the locking nut are needed, while still permitting ease of initial assembly and repair when needed, and without adding significant cost to the vehicle. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention involves a mounting structure for a wheel of a land vehicle which is mounted on a half shaft. The half shaft has at least one external or internal spline and has a threaded end beyond the spline. The spline has a curvature which differs from a curvature (which can be linear) of the mating arrangement on the wheel mounting bracket, such that longitudinal advancement of the mounting bracket onto the half shaft takes up the clearance between the spline and the mating arrangement and imparts a torsional static binding force between the half shaft and the wheel mounting bracket. A nut threading attaches to the threaded end of the half shaft for securing the wheel mounting bracket to the half shaft. Various road tests of vehicles verify that, when using the present invention, the nut does not loosen during use of the vehicle. The invention enables the locking force of the nut to be reduced, and assembly and maintenance are convenient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an assembled side view, with a portion shown in cross-section, showing the connecting structure provided by the preferred embodiment of the present invention; 
           [0008]      FIG. 2  is an exploded side view, with the mounting bracket and portions of the half shaft and shaft supporting base shown in cross-section, showing the connecting structure provided by the preferred embodiment of the present invention; 
           [0009]      FIG. 3  is a side view of the prior art splined end of the half shaft. 
           [0010]      FIG. 4  is a cross-sectional view of  FIG. 3 , taken along line  4 - 4  through the threaded end of the half shaft and looking endwise at the spline of the prior art, 
           [0011]      FIG. 5  is a side view of the helical splined end of the half shaft of the present invention. 
           [0012]      FIG. 6  is a cross-sectional view of  FIG. 5 , taken along line  6 - 6  through the threaded end of the half shaft and looking endwise at the helical spline of the preferred embodiment of the present invention. 
           [0013]      FIGS. 7A, 7B and 7C  are side views of the assembly sequence showing the connecting structure provided by the preferred embodiment of the present invention. 
       
    
    
       [0014]    In these Figures, reference numerals are as follows:
         1  indicates the half shaft;     2  indicates the shaft supporting base;     3  indicates the mounting bracket of the wheel;     4  indicates the wheel rim;     5  indicates the nut;     6  indicates the split pin;     7  indicates the tire;     11  indicates the helical external spline teeth; and     31  indicates the straight internal spline recesses.       
 
         [0024]    While the above-identified drawing figures set forth a preferred embodiment, other embodiments of the present invention are also contemplated, some of which are noted in the discussion. In all cases, this disclosure presents the illustrated embodiments of the present invention by way of representation and not limitation. Numerous other minor modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    The present invention is directed at the structure for mounting a wheel of a land vehicle such as an automobile or all-terrain vehicle. As shown in  FIG. 1 , the wheel has a rim  4  supporting a tire  7  and mounted from a mounting bracket  3  as well known in the art. A half shaft  1  driving the wheel extends through a supporting base  2 . Rotation of the half shaft  1  drives the wheel to propel the vehicle, although the invention could alternatively be used with undriven half shafts. 
         [0026]    In the preferred embodiment, the mounting bracket  3  of the wheel is identical to prior art mounting brackets. In this particular example, the mounting bracket  3  includes an internal spline arrangement as known in the prior art. For instance, the internal spline of the mounting bracket  3  may consist of  27  tooth recesses  31  that run longitudinally, i.e., each tooth recess runs parallel to the axis defined by the aperture for the half shaft  1 . Moreover, in that  FIGS. 1 and 2  do not provide sufficient detail to show the spline arrangement on the half shaft  1 ,  FIGS. 1 and 2  are equally applicable to the prior art as well as to the present invention. 
         [0027]      FIGS. 3-6  show more detail of the spline arrangement, both of the prior art ( FIGS. 3 and 4 ) and in the present invention ( FIGS. 5 and 6 ). As shown in  FIGS. 3 and 4 , prior art half shafts included the corresponding external spline structure to mate with the internal spline arrangement of the mounting bracket  3 . In this particular example, the half shaft spline arrangement includes 27 teeth  11  running longitudinally, each in a line parallel to the axis defined by the half shaft  1 . The teeth  11  should be of sufficient size to transfer torque, such as having a difference between major and minor diameters in the range of 0.2 to 5 mm. In this particular example, the half shaft spline arrangement has a reference diameter of 27 mm, with a maximum minor diameter of 26 mm and a major diameter of 28 mm with a major diameter tolerance of +0 mm and −0.21 mm. The spline teeth  11  run for a significant interaction length on the half shaft  1 , such as having a spline tooth section which is over 20 mm in length, and more preferably about 38 mm long. 
         [0028]    During assembly of the mounting bracket  3  onto the half shaft  1 , the mounting bracket  3  is positioned so as to align the 27 teeth  11  of the external spline of the half shaft  1  with the 27 recesses  31  of the mounting bracket  3  and then longitudinally advanced onto the half shaft  1 . In order to ensure that the mounting bracket  3  can be advanced longitudinally onto the half shaft  1  during assembly, a designed clearance between the 27 teeth  11  and the 27 recesses  31  is necessary, i.e., each tooth is designed to be slightly smaller, both in diameter from the half shaft axis and in the size of the tooth, relative to its corresponding recess. Further, manufacturing tolerances on both the half shaft  1  and the mounting bracket  3  could lead to greater amounts of clearance. For example, a tooth profile tolerance of 0.02 mm and a tooth lead tolerance of 0.02 mm might be applicable. 
         [0029]    During assembly of the prior art unit, a nut  5  was then threaded onto the threads on the end of the half shaft  1  to hold the mounting bracket  3  onto the half shaft  1 . The mating spline arrangement between the half shaft  1  and the mounting bracket  3  transfers torque, so when the half shaft  1  rotates, the mounting bracket  3  and wheel also rotates. In the prior art best shown in  FIG. 4  and in the preferred embodiment best shown in  FIG. 6 , the pressure angle between the external teeth  11  and the internal teeth  31  is 45°. 
         [0030]    In the preferred embodiment of the present invention shown in  FIGS. 5 and 6 , which is designed for use with the identical mounting bracket  3  of the prior art, the external teeth  11  of the half shaft  1  are accordingly similar to the prior art external teeth in several ways: the teeth  11  have a reference diameter of 27 mm, a maximum minor diameter of 26 mm, a major diameter of 28 mm with a major diameter tolerance of +0 mm and −0.21 mm, a pressure angle of 45°, a tooth profile tolerance of 0.02 mm and a tooth lead tolerance of 0.02 mm. The present invention is equally applicable to other values of each of these parameters. While the preferred embodiment considers teeth  11  on the half shaft  1 , other embodiments use one or more recesses on the half shaft which mate with one or more teeth on the mounting bracket. 
         [0031]    However, unlike the linear external teeth of the prior art, the half shaft spline teeth  11  of the present invention are not linear but instead have a slight helical angle about the axis defined by the half shaft  1 . The amount of the helical angle is chosen to produce a desired spring tightening/binding force between the corresponding spline teeth  11  and recesses  31 , and thus the amount of the helical angle depends significantly on the length of the internal spline teeth  11  on the mounting bracket  3 . The helix angle is also determined somewhat based on the tolerance grade of the internal spline recesses  31  and the external spline teeth  11 . In this preferred example with the spline tooth section  11  being about 38 mm long and with no helix angle on the interior teeth  31  of the mounting bracket  3 , the helical angle should be less than 1°, and more preferably less than 0°20′, such as in the range of 0°15′-0°20′. In the most preferred embodiment, the helical angle of the external spline teeth  11  is 0°18′+−3′. This helical angle of the external spline teeth  11  is difficult to identify in the side view of  FIG. 5 , but can be slightly seen in the end view of  FIG. 6  because the teeth  11  do not exactly line up between the two ends. Compare  FIG. 6  to  FIG. 4 . 
         [0032]    In the preferred embodiment, the helical angle of the external spline teeth  11  is in the right-hand direction, which further helps in maintaining tightness of the mounting bracket  3  to the half shaft  1  after assembly. However, a left hand helical angle could alternatively be used, as the most important aspect for maintaining tightness is the difference between the helical angle of the external spline teeth  11  relative to the helical angle of the spline recesses  31  on the mounting bracket  3 . (In the preferred embodiment, the helical angle of the spline recesses  31  is 0°). 
         [0033]    The assembly method of the present invention is shown in  FIGS. 7A-7C . The half shaft  1  passes through the mounting hole of the shaft supporting base  2  as shown in  FIG. 7A . The mounting bracket  3  of the wheel is placed onto the end of the half shaft  1 . Because the internal recesses  31  and external spline teeth  11  have the same clearance as in the prior art, this initial placement of the mounting bracket  3  is easy just by aligning the external teeth  11  with the internal recesses  31 . However, as the mounting bracket  3  is longitudinally advanced (to the left in  FIG. 7B ), the difference in the helical angle of the external spline teeth  11  relative to the straight internal recesses  31  eats up the initial clearance. Typically, when the recesses  31  are half or two thirds of the way onto the external teeth  11 , the clearance is fully consumed by the helical angle difference, and the teeth begin to bind, preventing further longitudinal advancement by hand. The nut  5  is then tightened and torqued onto the threads of the half shaft  1 , further pushing the mounting bracket  3  to the left and tightening the bind between the external spline teeth  11  and the internal recesses  31  to the position shown in  FIG. 7C . Preferably, the outside end face of the mounting hole of the wheel mounting bracket  3  is a ring, easy to match with the end face of the nut  5 . After the nut  5  has been fully torqued and the assembly is tight, a split pin  6  or similar interference member can be employed such as into a hole on the end of the half shaft  1  to further ensure that no loosening of the nut  5  occurs. 
         [0034]    Workers skilled in the art will appreciate that the helical angle of the spline teeth  11  contributes only slightly to maintaining tightness, and it is the difference in helical angles between the spline teeth  11  and the spline recesses  31  which provides the primary benefit. Essentially the same benefit could be achieved if the spline teeth had a helical angle of 0°0′ and the spline recesses had a helical angle of 0°18′. As another example, essentially the same benefit could be achieved if the spline teeth had a helical angle of 5°18′ and the spline recesses had a helical angle of 5°. In all these examples, the important aspect is that the difference in helical angles causes the spline teeth  11  to take up the clearance with the spline recesses  31  as the mounting bracket  3  is longitudinally advanced on the half shaft  1 , to the point of binding when being held in place by the torqued nut  5 . 
         [0035]    Further, the present application refers to helical angles because, in the preferred embodiments, the helical angle is consistent along the length of the spline teeth  11  and along the length of the spline recesses  31 . Other embodiments include a curvature which changes along the length of the spline teeth  11  and/or spline recesses  31 . For instance, the spline teeth  11  can be linear with a 0° helical angle along the outer 19 mm of its length, and then proceed with a helical angle of 0°36′ along the inner 19 mm of its length, thereby achieving substantially the same result but allowing a greater longitudinal advancement of the mounting bracket onto the half shaft  1  before the initial binding begins. Another embodiment includes a spline tooth helical angle that begins at 0°0′ and gradually increases as it moves inward on the half shaft  1 . The key aspect is the difference in curvature in the longitudinal direction of the teeth  11  relative to their recesses  31 , such that a complete longitudinal advancement of the mounting bracket  3  onto the half shaft  1  first takes up the clearance between the teeth  11  and their recesses  31  and then results in a static torsional stress imparted between the teeth  11  and their recesses  31  to prevent any loosening during use. 
         [0036]    As a result of the curvature/helical angle difference, the present invention appears to have completely solved the prior art problem created by the fit clearance. In various road tests of vehicles testing, the locking nut  5  does a much better job of maintaining its tightness. The present invention thus eliminates the potential safety hazard of the prior art. Additionally, the present invention has been found to enable the locking force of the nut  5  to be reduced, making initial assembly more convenient and making maintenance easier when the locking nut  5  has to be removed. In general, while intentional loosening of the locking nut  5  can be made easier by the present invention, the binding created by the curvature/helical angle disparity may require several blows to the mounting bracket  3  after the locking nut  5  has been removed to overcome the binding and enable the mounting bracket  3  to be pulled longitudinally off the half shaft  1 . 
         [0037]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.