Abstract:
A sealing component constructed of hydrogenated nitrile butadiene rubber (“HNBR”) compound for use in high temperature, high speed and high angle applications is disclosed. The disclosed HNBR material may also be reinforced with fibers for added stiffness and stability.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present inventions relates to driveline sealing components constructed of rubber material and more particularly to a boot assembly for a constant velocity joint that is capable of withstanding high temperature, high speed, and high angle applications that is constructed of hydrogenated nitrile butadiene rubber.  
         [0002]     Driveline sealing components are frequently used for covering the chamber of a joint that is filled with a lubricating agent. The sealing components prevent lubricating agents from leaving the joint chamber while preventing dirt and other contaminants from entering the joint chamber.  
         [0003]     One application that utilizes sealing components is constant velocity joints. A constant velocity joint is used to transmit the rotating power from one joint member to the other joint member so as to rotate at a constant velocity while allowing the above two joint members to freely deflect the axial center lines thereof from each other within a predetermined angle range. When the constant velocity joint is used in a driveline system of a vehicle, the joint portion of the constant velocity joint is typically covered with a boot. The boot is flexible and generally has a deformable shape such as bellows. A typical boot includes a first relatively large end that is secured to an outer race of the constant velocity joint and a second relatively small end that is secured to a shaft extending from an inner race of the constant velocity joint. In other words, one open end of the dust boot is positioned on the outer periphery of one joint member while the other open end is positioned on the outer periphery of the other joint member.  
         [0004]     In the boot of this type, adjacent folds locally come in contact with one another when the constant velocity joint rotates at a high velocity with a large joint angle. As a result, wear occurs in the boot, reducing the sealing effectiveness of the boot, and shortening the effective life of the boot. One known solution to overcome the wear problems of the boot, is to include wax in the boot to smooth the outer surface of the dust boot. However, undesirable wear still occurs, especially in high temperature applications. Accordingly, there is a need for a boot that is capable of withstanding high temperature, high speed, and high angle applications.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention relates to sealing components for an automotive driveline assembly having a unitary body for use in high temperature, high velocity and high angle applications. In accordance with an aspect of the present invention, the sealing assembly is a boot seal for a constant velocity joint as specified in claim  1 . To address the undesirable wear conditions of known boots, the boot of the present invention is preferably constructed of hydrogenated nitrile butadiene rubber (“HNBR”). Boots constructed of HNBR have been found to be capable of withstanding 150° C. peak temperatures and 130° C. constant operating temperatures. Further, adding reinforcing fibers to the HNBR material may increase stiffness in the boot. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The accompanying drawings illustrate various embodiments of the present apparatus and method and are a part of the specification. The illustrated embodiments are merely examples of the present apparatus and method and do not limit the scope of the disclosure.  
         [0007]      FIG. 1  is a perspective view of an embodiment of a flexible boot assembly for a constant velocity joint in accordance with the invention;  
         [0008]      FIG. 2  is plan view of the flexible boot assembly of  FIG. 1 .  
         [0009]      FIG. 3  is a cross-sectional view of the flexible boot assembly of  FIG. 1 , taken along lines  3 - 3  of  FIG. 2 .  
         [0010]      FIG. 4  is an enlarged view of one end of the flexible boot assembly taken from  FIG. 3 .  
         [0011]      FIG. 5  is an enlarged view of another end of the flexible boot assembly taken from  FIG. 3 .  
         [0012]      FIG. 6  is an enlarged view of an optional design of the second end of the flexible boot assembly. 
     
    
     DETAILED DESCRIPTION  
       [0013]     Referring to  FIGS. 1-6 , an embodiment of a flexible boot assembly, indicated generally at  10 , for use with a constant velocity joint, is shown. Boot assembly  10  includes a first sealing end portion  12 , and a second sealing end portion  14 . First sealing end portion  12  has a first outer diameter d that is less than an outer diameter D of second sealing end portion  14 . Both first and second sealing end portions  12 ,  14  are positioned around a common axis A.  
         [0014]     An outside surface  16  of first end portion  12  includes an annular groove  18  formed therearound. An annular ridge  20  extends around a distal end  22  of first sealing end portion  12 , adjacent to annular groove  18 . Annular ridge  20  defines an inwardly sloping first flange  24 . A second flange  26  is positioned opposite first flange  24 . Second flange  26  also slopes inwardly toward annular groove  18  from the outside surface  16 .  
         [0015]     First end portion  12  also includes an inner contact surface  28 . Inner contact surface  28  may be generally planar as shown in  FIG. 5 . Alternatively, inner contact surface  28 ′ may include a plurality of ridges  30  as shown in  FIG. 6 . In operation, inner contact surface  28  or  28 ′ of first end portion  12  frictionally engages the outside surface of a shaft (not shown). A metal band clamp (not shown) or other retaining structure may be provided to secure first end portion  12  to the shaft. The inwardly extending flanges  24  and  26  serve to direct the clamp to the center of annular groove  18 .  
         [0016]     Second end portion  14  is connected to first end portion  12  by a main body portion  32  and a wall portion  34 . In one embodiment, wall portion  34  is curved. In another embodiment (not shown) wall portion  34  may be substantially planar. Second end portion  14  includes an outer surface  36  and an inner surface  38 . As best shown in  FIG. 4 , outer surface  36  may include a plurality of ribs  40  defined by a series of grooves  42  separated by lands  44 . Alternatively, outer surface  36  may include an annular groove (not shown) similar to annular groove  18  provided on first end portion  12 . Inner surface  38  may also be provided by at least one groove  46  that is flanked by lands  48 . Groove  46  and lands  48  provide an engagement surface  50  for engaging an outer race (not shown) of the constant velocity joint.  
         [0017]     In accordance with another aspect of the invention, boot  10  is preferably a unitary construction that is made of a hydrogenated nitrile butadiene rubber compound (“HNBR”) that is particularly suited for high temperature applications, such as applications that have a 150° C. peak temperature and/or a 130° C. continuous temperature. The inventive compound includes the following components: a hydrogenated nitrile elastomer such as Zetpol® available from Zeon Chemical Products, Inc.; magnesium oxide such as Maglite D from C.P. Hall Company; a plasticizer that improves oil and heat resistance such as TP-95 distributed by Rohm and Haas; a release agent, such as stearic acid; at least one antioxidant that acts as a thermal stabilizer such as Naugard® 445 distributed by Uniroyal Chemical Company, Inc. or Rhenogan ZMMBI-50 distributed by Rhein-Chemie Rheinau GmbH; a peroxide such as Vulcup 40KE distributed by Hercules Inc.; and filler material such as carbon black. In a preferred embodiment, the HNBR material includes two different antioxidants.  
         [0018]     In some applications, high stiffness and increased strength is needed. To address such needs, in accordance with another aspect of the invention, the above-described HNBR material may be reinforced with fibers. More specifically, the HNBR material includes a fiber content from about 3-10 part per hundred rubber by weight pphr and preferably 5 pphr. A suitable fiber includes a phenolic based fiber such as Kynol® KF02BT that is distributed by American Kynol, Inc. The preferred fibers are approximately 15 μm in diameter, have an average length of 0.2 mm and have approximately 30-50% elongation.  
         [0019]     The fibers may be added to the HNBR material in a number of different methods. To insure that the fibers are sufficiently dispersed in the resulting boot, one method includes injection molding a first layer of the HNBR material into the shape of boot  10 . The first layer is then cured. Next, the fibers are placed over the first layer. Alternatively, an adhesive is applied to the fibers before being placed over the first layer. A second, or top, layer is then compression molded to final form boot  10 . The second layer is then cured.  
         [0020]     In an alternative embodiment, the mold may be provided with locator pins for fixing the fibers in place as the material flows through the mold. The material is then injection molded into the boot shape and cured.  
         [0021]     It is to be understood that the above description is intended to be illustrative and not limiting. Many embodiments will be apparent to those skilled in the art upon reading the above description. The scope of the invention should be determined, however, not with reference to the above description, but with reference to the appended claims with full scope of equivalents to which such claims are entitled.