Patent Publication Number: US-2005143180-A1

Title: Boot for a constant velocity universal joint

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a Continuation of application number 09/303,791 filed on Apr. 30, 1999.  
     TECHNICAL FIELD  
      This invention relates to a boot for a universal joint and more specifically to a rolling diaphragm boot for a constant velocity universal joint.  
     BACKGROUND  
      Constant velocity universal joints are sometimes used in vehicles for coupling the transmission and its corresponding propeller shaft. In four-wheel drive vehicles, constant velocity universal joints are utilized to couple a transfer case to the front and rear propeller shafts extending therefrom to corresponding front and rear drive axles. A constant velocity universal joint used in these applications includes a boot that is crimped into a larger boot-can, which in turn is affixed to an outer race of the constant velocity universal joint. A rolling diaphragm boot is typically used in this application.  
      A rolling diaphragm boot is commonly formed of a rubber or silicone material that is soft enough that a boot of such material is compressible when crimped into the boot-can connector. However, during the operative life of a vehicle, the crimping integrity between the rolling diaphragm of the boot formed of soft material and its mating boot-can connector of a constant velocity universal joint may deteriorate. This may particularly be the case during operation in and exposure of the constant velocity universal joint to temperature extremes.  
      Consequently, the need has developed for an improved design for a constant velocity universal joint which includes an improved rolling diaphragm boot and a mating boot-can having an enhanced crimping integrity, and also having improved properties allowing the boot and the crimping integrity to have improved long-term durability and temperature endurance.  
     SUMMARY OF THE INVENTION  
      The present application discloses a boot adapted for coupling to a boot-can and comprising a cylindrical neck member and an annular member. The annular member includes a longitudinal axis and a crimping lip for being received by the boot-can. The crimping lip has a plurality of radially distributed apertures. The apertures are oriented parallel to the longitudinal axis of the annular member for reducing stiffness of the boot and increasing the compressibility of the crimping lip. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       FIG. 1  is a cross-sectional side view of a constant velocity universal joint and propeller shaft assembly according to the present invention;  
       FIG. 2  is a perspective view of a boot and boot-can assembly according to the present invention;  
       FIG. 3   a  is a side view of the boot and boot-can assembly illustrated in  FIG. 2 ;  
       FIG. 3   b  is a front view of the boot and boot-can assembly illustrated in  FIG. 3   a;    
       FIG. 4   a  is a cross-sectional side view of the boot and boot-can assembly shown in  FIG. 3   a , in an un-crimped state, taken along the line A-A;  
       FIG. 4   b  is an enlarged detail of the encircled portion from  FIG. 4   a , showing the crimping lip of the boot received within the boot can in an un-crimped state;  
       FIG. 5   a  is a cross-sectional side view of the boot and boot-can assembly shown in  FIG. 3   a , in a crimped state, taken along the line A-A;  
       FIG. 5   b  is an enlarged detail of the encircled portion from  FIG. 5   a , showing the crimping lip of the boot received within the boot can in an crimped state;  
       FIG. 6   a  is a perspective view of a first embodiment of a boot according to the present invention;  
       FIG. 6   b  is a front view of the first embodiment of the boot shown in  FIG. 6   a;    
       FIG. 6   c  is a cross sectional view of the first embodiment of the boot, taken along the line  6   c - 6   c  of  FIG. 6   b;    
       FIG. 7   a  is a perspective view of a second embodiment of a boot according to the present invention;  
       FIG. 7   b  is a front view of the second embodiment of the boot shown in  FIG. 7   a ; and  
       FIG. 7   c  is a cross-sectional view of the second embodiment of the boot, taken along the line  7   c - 7   c  of  FIG. 7   b.   
    
    
     DETAILED DESCRIPTION  
      In accordance with the teachings of the present invention,  FIG. 1  of the drawings shows a cross-sectional side view of a constant velocity universal joint and propeller shaft assembly  10  according to the present invention. As shown in  FIG. 1 , assembly  10  includes a propeller shaft  12 , which in the embodiment illustrated includes a propeller shaft housing tube  14  which has a propeller stub shaft  16  aligned and coupled therewith and projecting therefrom. As is known in the art, the propeller shaft  12  is a drive shaft connecting the transmission (not shown) to the driving axle (or front and rear axles in a four-wheel drive vehicle) in order to transmit torque from the transmission to the axle.  
      Further included in assembly  10  is a constant velocity universal joint  18 , which includes an outer race  20  having outer tracks  22 , and an inner race  24  having inner tracks  26 . Constant velocity universal joint  18  is of the ball-and-cage variety. Note that constant velocity joint  18  includes a cage  28  that has a plurality of windows therein, each for holding and carrying a corresponding one of a plurality of ball bearings  30 . Ball bearings  30  are directed by the cage while riding on the outer and inner tracks  22  and  26 , respectively, of joint  18 .  
      Assembly  10  further includes a grease cap  32  therein. Grease cap  32  is mounted to one end of constant velocity universal joint  18  for retaining grease contained within joint  18  for keeping it lubricated and also for keeping any foreign matter and contaminants out of joint  18 . As illustrated in  FIG. 1 , grease cap  32  has an annular flange  33 , which is secured to a first end  19  of outer race  20 . Grease cap  32  may also have a means for venting in order to minimize pressure fluctuations due to expansion and contraction of enclosed air space during operation of the constant velocity universal joint  38 . The means for venting is generally a hole in the center dome of grease cap  32 . Also illustrated is an adaptor member  34  mounted to the first end  19  of outer race  20 . Adaptor member  34  includes a splined bore  36  distal the constant velocity universal joint  18 . Splined bore  36  serves to couple propeller shaft  12  and constant velocity universal joint  18  to another vehicle component, such as a transmission or transfer case (not shown). The transmission or transfer case would therefore include a splined shaft that is received within the splined bore  36  of adaptor member  34 , so that the transmission or transfer case may provide a power transfer to propeller shaft  12 .  
      In keeping with the present invention, also included in assembly  10  is a boot  38  and a boot-can  40 . As shown in the perspective view of  FIG. 2  and the elevational views of  FIGS. 3   a - 3   b ,  4   a - 4   b  and  5   a - 5   b , boot  38  and boot-can  40  may form a subassembly  41 . As illustrated in  FIG. 4   a , boot  38  is an annular member having a longitudinal axis  42 . Boot  38  has a first annular neck member  44  which engages propeller shaft  12  (and more particularly propeller stub shaft  16 ) in order to provide a seal between constant velocity universal joint  18  and propeller shaft  12 , so that (similar to grease cap  32 ) grease is not able to exit joint  18  and foreign matter and contaminants such as water are not able to enter joint  18  and impede its operation. With reference to  FIG. 1 , first annular neck member  44  of boot  38  is attached to propeller stub shaft  16  with a fastener such as an annular clamp  46  in order to maintain the seal therebetween. Such sealing and protection of constant velocity universal joint  18  is desired because, once the inner cavity of joint  18  is partially filled with grease and sealed, it is thus lubricated, and preferably lubricated for life with no required maintenance.  
      Boot  38  is preferably a non-convoluted rolling diaphragm boot. As shown in the cross-section of  FIGS. 1, 4   a  and  5   a , boot  38  transitions from first annular neck member  44  to a stem portion  45 , then transitions from stem portion  45  through an outwardly curved (rolling diaphragm) portion  48 , which then transitions to a second annular end  50 , having a crimping lip  51 . Second annular end  50  has a relatively larger diameter than first annular neck member  44 . Stem portion  45  is substantially frusto-conical in shape and defines a longitudinal opening therethrough for receiving propeller stub shaft  16  therein. As shown in the enlarged views of  FIGS. 4   b  and  5   b , second annular end  50  includes crimping lip  51  having a greater thickness than the other wall portions of boot  38 . The rolling diaphragm shape of boot  38  assists in reducing undue forces from being applied to boot  38  at high angular deflection states.  
      Boot-can  40  provides a means by which boot  38  may be coupled with constant velocity universal joint  18 . Boot-can  40  is a connector which allows the relatively small diameter boot  38  to be mounted to the relatively large diameter outer race  20  of constant velocity universal joint  18  (or the second face  21  thereof). As shown in  FIGS. 1-4   b , boot-can  40  includes an outer end  52  with an annular flange  53  which is mounted to the second face  21  of outer race  20  of constant velocity universal joint  18  (or the end of outer race  20  which is disposed opposite the end  19  mated to grease cap  32 ). Boot-can  40  is preferably formed of a metal.  
      To assist in the mounting of boot-can  40  to outer race  20  universal joint  18 , boot-can  40  has a plurality of holes or openings  55  distributed around its outer end  52 , which correspond with bores (not shown) in outer race  20  of constant velocity universal joint  18 . Accordingly, boot-can  40  may be mechanically fastened to constant velocity universal joint  18 , for example, by using bolts  57  (best shown in  FIG. 1 ) to fasten the mating components boot-can  40  and outer race  20 . The other end  56  of boot-can  40  has a flange  58  that is inwardly turned toward the center of boot-can  40 . In order to assemble subassembly  41 , boot  38  and boot-can  40  are oriented (as shown in  FIGS. 1-2 ,  3   a - 3   b,    4   a - 4   b,    5   a - 5   b ) so that the second annular portion  50  (and more particularly crimping lip  51 ) is received by the inwardly turned flange  58  of boot-can  40  (as shown by the “un-crimped⇄ detail of  FIGS. 4   a - 4   b ). Subsequently, inwardly turned flange  58  is crimped in order to secure crimping lip  51  therein, thereby coupling boot  38  and boot-can  40  as shown by the “crimped” detail of  FIGS. 5   a - 5   b.    
      A preferred embodiment according to the present invention is illustrated in  FIGS. 6   a - 6   c . Shown therein is a boot  38  formed of a thermoplastic elastomer material. Thermoplastic properties provide for a more firm or harder boot than rubber or silicone materials typically utilized in such an application, thus providing additional stability and resistance to environmental contaminants to boot  38 . As shown in the first embodiment of boot  38  shown in  FIGS. 6   a,    6   b  and  6   c,  a plurality of cut-outs  60  are formed in crimping lip  51 . Each cut-out  60  is equally radially distributed from axis  42  along the circumference of the crimping lip  51 . In a more preferred embodiment, each cut-out  60  is spaced apart in a radially distributed pattern around the circumference of crimping lip  51 , as shown in  FIG. 6   b.  Thus, boot  38  having the cut-out  60  design for crimping lip  51  has improved properties, including greater compressibility, because the material reduction in crimping lip  51  (due to cut-outs  60 ) reduces the effective stiffness of the thermoplastic material, thereby allowing the crimping lip  51  to have properties similar to an improved radial spring. Accordingly, the integrity of the crimp seal between crimping lip  51  (of boot  38 ) and flanged edge  58  (of boot-can  40 ) is improved, and according to the objectives of the present invention, the crimp integrity improved over the vehicle&#39;s life, and also has improved performance in cold temperature operation, where thermoplastic is better able to withstand colder temperatures. Thermoplastic material is also sufficiently rigid and substantial to withstand the loss of material in the crimping lip  51  area, due to cut-outs  60 .  
      In the prior art, thermoplastic elastomer (TPE) materials have not been generally considered for rolling diaphragm boots because of their lower compressibility properties. However a boot made of TPE and having the rolling diaphragm form and one of the crimping lip  51  designs according to the present invention has greater compressibility properties due to the material reduction, thereby providing for reduced effective stiffness. In this manner, the integrity of the crimp seal is improved.  
      A second embodiment of a boot  38  according to the present invention is illustrated in  FIG. 7 , and is designated as boot  38 ′. Note that in the second embodiment disclosed herein, many of the similar components from previous embodiments are designated by like reference numerals carrying prime (′) designations, for consistency and ease of reference. As in the first embodiment of  FIGS. 6   a - 6   c , boot  38 ′ is preferably formed of a thermoplastic material. However, instead of cut-outs  60 , an alternative crimping lip  51 ′ design is provided. As shown in  FIGS. 7   a,    7   b  and  7   c,  crimping lip  51 ′ has formed therein a plurality of relatively small apertures  62  which are formed into crimping lip  51 ′. Apertures  62  are particularly shown as holes in this embodiment having a diameter smaller than the thickness of crimping lip  51 ′, as shown in  FIG. 7   b . As in the previous embodiment, the apertures  62  are equally radially distributed from the longitudinal axis  42 ′ along the circumference of the crimping lip  51 ′. More preferably the apertures  62  are spaced apart in a radially distributed pattern around crimping lip  51 ′. As shown in the side elevational cross-sectional view of  FIG. 7   c  (taken along line  7   c - 7   c  of  FIG. 7   b ), each aperture extends partially into crimping lip  51 ′.  
      In one embodiment, the size of cut-outs  60  and apertures  62  are between 35% to 70% of crimping lip  51  thickness. Of course, it is contemplated that cut-outs  60  and apertures  62  may have a size and/or shape as is deemed appropriate and necessary in order to achieve the desired crimping properties according to the objects of the present invention. It is further contemplated that the cut-outs  60  and apertures  62  may be molded or otherwise formed into boots  38 ,  38 ′, respectively.  
      Thus the compressed crimping lip  51  thickness ratio is approximately 50% to 70% of the uncompressed crimping lip  51  thickness. The use of the cut-outs  60  or apertures  62  may reduce standard crimping force required by up to approximately 50%. In this manner, the modified geometry has reduced effective stiffness, allowing for a greater degree of compression of the boot-can  40  to boot  30 . A thermoplastic elastomer rolling diaphragm boot  38 ,  38 ′ of this type further includes a better seal integrity over its operative lifetime, and particularly during cold temperature operation.  
      While the invention has been particularly shown and described in reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.