Abstract:
A high performance constant velocity universal joint is based on a body which encloses the constant velocity joint components and provides a smooth spherical outer surface. A one-piece semi-rigid plastic boot in the form of a truncated sphere has a smooth internal spherical surface sized to match the outer surface of the body. The plastic of the boot is sufficiently elastic to allow the boot to snap over the body, yet sufficiently resilient to snap the open end closed after the boot is snapped over the body to provide a substantial seal preventing entry of debris under the seal. A retaining ring is positioned on the boot near the truncated end to resist plastic creep which would result in enlarging the opening and allowing debris to enter the seal.

Description:
FIELD OF THE INVENTION 
   This invention relates to constant velocity joints, and more particularly to those capable of being used in adverse environmental conditions. 
   BACKGROUND OF THE INVENTION 
   Constant velocity joints are used in numerous vehicular applications where the rotational velocity oscillation of a conventional cardan joint is unacceptable. For example, in the front suspension of a front wheel drive automobile, there will be two constant velocity joints per axle. They are also used in off-road heavy-duty equipment, in trucks, and in high performance recreation vehicles. 
   When the application is not overly environmentally adverse, constant velocity joints are excellent. However, in environmentally unfriendly applications they are less desirable because of the problems of keeping dirt and debris out of the joint. A better understanding of that will be appreciated upon review of  FIG. 1  which shows a conventional prior art constant velocity joint. 
     FIG. 1  is, as will be apparent to those skilled in the art, a diagram of a constant velocity joint. An input shaft  21  is attached to a housing  22  which is formed to have a plurality of ball races  23 . An inner race member  25  also includes a plurality of ball races, and a plurality of balls  26  connect the two members  25 ,  22  by means of the balls  26  riding in pairs of the associated races. A cage  28  encircles the balls  26  and keeps them in a constant velocity plane as the joint flexes. Typically the inner race  25  is splined at  30  and receives a shaft  32  splined at  31 . By its very nature, the end  40  of the constant velocity joint through which all of the components are assembled is open. A primary seal is provided by boot  35 . It is usually a fairly large and flexible member to accommodate the movement of the joint. Thus it is usually made of relatively flexible rubber and is fixed by a ring  36  to the outside of the housing and by another ring  37  to the outside of the shaft  32 . A bellows area  38  allows for flexing of the boot  35  as the angle of the output shaft  32  changes with respect to the input shaft  21 . 
   In the normal automotive environment a boot of this type can protect the joint for many thousands of miles of operation. However, as has become apparent to some motorists, once the boot tears, debris and moisture can enter the joint because the boot itself is the primary seal. It is not, like in conventional cardan joints, a simple secondary dust shield, but is the primary seal for keeping foreign material out of the workings of the joint mechanism. Thus, when the boot tears, it is not long thereafter, without attention, that the joint will fail. 
   Although it is desirable to use constant velocity joints in more environmentally demanding applications, the inability of the seal to withstand tough environmental conditions is a strong negative factor. In off the road applications, for example, rocks and debris thrown up by the tires, or over which the vehicle can skid is readily available to tear the relatively soft rubber boot. In off the road heavy machinery applications, not only is there a substantial danger of tearing the boot during a relatively short period of operation, but almost a guarantee of enough debris to cause the joint to fail shortly after it has torn. 
   For other recreational applications, such as four wheel drive vehicles, all-terrain vehicles, rock climbers, and the like where the universal joints are flexed to their limits because of the uneven nature of the terrain, the constant velocity joints will also be a benefit. But again, there is also the possibility of likelihood of tearing the rubber boot with almost certain failure of the joint to follow, particularly when running through sand, water, and the like. 
   There are also suggestions in the art to use closer fitting, less flexible covers over constant velocity joints. However, these are typically characterized as complex, often formed of multiple parts, requiring springs or the like to keep them in operation, and having relatively limited flexing capability, well short of the 40 degree flexing capability demanded in some off road applications. 
   BRIEF SUMMARY OF THE INVENTION 
   In view of the foregoing, it is a general object of the present invention to adapt the constant velocity joint to a more hostile environment by providing a more reliable primary seal than has heretofore been provided. 
   It is a further object to make the seal relatively inexpensive, simple to install, and easy to maintain and having a significant flexing capability, on the order of 40 degrees. 
   According to the invention there is provided a high performance constant velocity universal joint which is based on a body which encloses a conventional set of constant velocity components. The body has a smooth spherical outer surface. A one-piece semi-rigid plastic boot is provided in the form a truncated cylinder. The boot has a smooth internal spherical surface sized to match the spherical outer surface of the body. The boot is truncated such that it is larger than a half sphere, and has an opening at the truncated end which is smaller than the inner diameter of the sphere. The plastic of the boot is sufficiently elastic to allow the boot to snap over the body to a conforming position to provide a close sliding fit thereover. The plastic body is sufficiently resilient to snap the open end closed after the boot is snapped over the body to provide a substantial seal preventing entry of debris under the seal formed by the boot. A retaining ring is positioned on the boot near the truncated end to resist plastic creep from enlarging the opening and allowing debris to enter the seal. 
   Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial sectional diagram showing a conventional constant velocity joint with conventional rubber boot; 
       FIG. 2  is a diagram similar to  FIG. 1  but illustrating a constant velocity joint constructed in accordance with the present invention; and 
       FIGS. 3 and 4  are diagrams similar to  FIG. 2  but showing the joint in straight and flexed configuration. 
   

   While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Turning now to the drawings, and particularly to  FIG. 2 , there is shown the components of a constant velocity joint used in practicing the present invention. Like  FIG. 1 , an input shaft  21  is coupled to an output shaft  32  by means of the constant velocity joint. 
   In the  FIG. 2  embodiment an outer housing or body  50  of particular configuration encloses the remaining conventional elements of the constant velocity joint. The body has races  23 , and the joint also includes an inner race  25 , also having races, drive balls  26  and a cage  28 . The inner race  25  has a splined opening to receive the splined end  31  of the output shaft  32 . Thus, the shaft  32  can flex at any angle with respect to the input shaft  21 . The maximum angle which can be accommodated without interference is on the order of 40 degrees. 
   The outer surface  52  of the body  50  is formed as a smooth spherical surface for purposes now to be described. In practicing the invention a semi-rigid plastic boot  60  is provided. The boot has a smooth internal spherical surface  62  which is sized to match the spherical outer surface of the body. By matching the outer surface is meant that when the boot  60  is snapped into place over the body  50 , a sliding fit is provided between the mating spherical surfaces so that one shaft can move angularly with respect to the other while the boot simply slides over the spherical surface of the body to maintain a seal. 
   It can be appreciated from  FIG. 2  that the boot  60  is larger than a half sphere. If the boot  60  were simply a half sphere, it would be truncated at about the phantom line  64  shown dashed in  FIG. 2 . However, it extends beyond that such that where truncated at  65 , the inner diameter of the opening  66  is smaller than the inner diameter of the boot  60 . As a result, the boot  60  itself will simply not fit onto the outside of the spherical body  50  without being forced thereon. Thus, after the joint is assembled, the boot  60  is forced downwardly over the spherical housing  50  which causes the opening  66  to expand sufficiently to fit over the outer diameter of the spherical housing  50 . The boot  60  is sufficiently elastic that the opening  66  momentarily expands to allow the boot  60  to actually pop or snap into place and to assume a rest position in which the surfaces  52 ,  62  of the two spheres  50 ,  60  match as shown in  FIG. 2 . It is locked fairly firmly in this position by the resilience of the plastic material which creates a force which tends to close the opening  66  and thus to maintain the locked and conformed condition between the two elements  50 ,  60 . This sliding fit which is thus provided between the two spherical surfaces  52 ,  62  is adequate to keep the internal workings of the joint clean. To enhance the sealing effect, wiper grooves  70  are provided near the open end  66  which tend to wipe debris off exposed portions of the body  50  as the boot  60  moves over those portions during angular movement of the two shafts  21 ,  32 . 
   We have found that over time plastic creep of the material of the boot tends to relax the gripping action at the opening  66 . To counteract the plastic creep from opening a gap between the end  65  of the boot and the spherical surface  52  of the housing, we position a retaining ring  72  over the plastic boot, near the truncated end. The retaining ring can be, for example, a simple steel ring which is heat treated, then split, then put into the position shown in  FIG. 2 . The original diameter of the ring  72  before heat treatment is smaller than the diameter shown in ring  72 , such that when it is split and forced into place a gap is provided between the ends of the steel ring which causes a continued compressive force around the end of the plastic boot, tending to continually resist the effects of plastic creep. Other forms of mechanical retainer can also be used, but we currently prefer the snap ring because of its simplicity and rugged reliability. 
   The shaft end of the boot is provided with a sliding fit over the outside of shaft  32 . The end portion of the shaft  32  which mates with the boot is a relatively smooth shaft section, and the boot has a cylindrical flange  80  having an inner surface  82  which closely fits over the shaft  32 . A series of grooves  84  are formed on the inside of the cylindrical surface to provide a series of wipers  85  which tend to scrape collected debris from the shaft, upon relative movement, thereby to prevent the introduction of contaminants into the housing via the shaft. 
   Referring briefly to  FIGS. 3 and 4 ,  FIG. 3  is similar to  FIG. 2  and is provided for reference.  FIG. 4  shows the condition when the output shaft  32  is flexed by about 40 degrees with respect to the input shaft  21 . It will be seen that the inside spherical surface  62  of the boot  60  continues to conform to the outer spherical surface  52  of the housing  50  during the entire angular movement of one shaft  32  with respect to the other  21 . The upper portion of the boot  60  covers a greater and greater section of the upper spherical portion  50 , whereas the lower section of the boot  60  slides to very near the tip. It is also noted that the angle of the internal cage  28  has flexed to accommodate the angular motion of the shafts  21 ,  32  and to keep the balls  26  in the constant velocity plane. However, the important thing to note with respect to the present invention is the continued ability of the arrangement to prevent debris from entering. The close fitting nature of the boot  60 , the fact that it is of much harder and less flexible material than flexible boots of the past, and its close fitting nature all contribute to the extreme reliability of the arrangement, even in environmentally adverse conditions. 
   While a variety of materials can be used for molding the plastic boot  60 , at this point we continue to prefer oil-filled nylon. Oil-filled nylon resists moisture absorption, which is a significant characteristic for some applications. Nylon of thicknesses approximately those illustrated in the drawings, on the order of 0.125 inches, can be formed with sufficient elasticity and flexibility to allow the boot  60  to pop over the spherical surface  52  of the housing  50 . The nylon also retains its shape and thus has sufficient resilience to close the gap and closely fit about the spherical surface  52 . The material is subject to plastic creep over time, and this is resisted by the snap ring  72  or other external mechanical restraint. Other forms of plastic, known to those skilled in the art, will also be found suitable for providing these characteristics. 
   All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
   The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
   Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.