Abstract:
A sealing component constructed of silicone compound for use in high-temperature, high-speed and high-angle applications is disclosed. The disclosed silicone material may also be reinforced with fibers for added stiffness and stability.

Description:
TECHNICAL FIELD  
       [0001]     The invention is generally directed to driveline sealing components constructed of silicone 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 silicone.  
       BACKGROUND  
       [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 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.  
         [0004]     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 the shaft extending from the inner race of the constant velocity joint. In other words, one open end of the 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.  
         [0005]     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 is to include wax in the boot to smooth the outer surface of the boot. However, undesirable wear still occurs, especially in high temperature applications.  
         [0006]     Another solution to undesirable wear problems for high temperature applications that is known to the present inventor is the use of hydrogenated nitrile butadiene rubber (HNBR) material, as described in co-pending U.S. patent application Ser. No. 10/912,400, incorporated herein by reference in its entirety. HNBR material is useful in applications having a peak temperature of 150° C. peak, or 130° C. continuous. Accordingly, there is a need for a boot that is capable of withstanding higher temperatures (i.e., greater than 150° C. peak temperatures), as well as high-speed, and high-angle applications.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to sealing component for an automotive driveline assembly having a unitary body for use in high-temperature, high-velocity and high-angle applications. In accordance with one aspect of the invention, the sealing assembly is a boot seal for a constant velocity joint. To address undesirable wear conditions of known boots, the boot of the present invention is preferably constructed of silicone. Boots constructed of silicone are capable of withstanding 180° C. peak temperatures and 150° C. constant operating temperatures. For those applications that require increased stiffness in the boot, optional reinforcing fibers may be added to the silicone material. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The accompanying drawings illustrate various embodiments of the present invention and are a part of the specification. The illustrated embodiments are merely examples of the present apparatus and do not limit the scope of the disclosure.  
         [0009]      FIG. 1  is a perspective view of an embodiment of a flexible boot assembly for a constant velocity joint in accordance with the invention;  
         [0010]      FIG. 2  is plan view of the flexible boot assembly of  FIG. 1 .  
         [0011]      FIG. 3  is a cross-sectional view of the flexible boot assembly of  FIGS. 1 and 2 , taken along lines  3 - 3  of  FIG. 2 .  
         [0012]      FIG. 4  is an enlarged view of one end of the flexible boot assembly taken from  FIG. 3 .  
     
    
     DETAILED DESCRIPTION  
       [0013]     Referring to  FIGS. 1-4 , an embodiment of a flexible boot assembly, indicated generally at  10 , for use with a constant velocity joint in accordance with the present invention, 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 the 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-A.  
         [0014]     An outside surface  16  of first end portion  12  includes an annular groove  18  formed therearound. An annular ridge  20  extends around the distal end  22  of first sealing end portion  12 , adjacent to annular groove  18 . Annular ridge  20  defines a first flange surface  24 . In one embodiment, first flange surface  24  is generally planar so as to be generally perpendicular to annular groove  18 . In another embodiment, first flange surface  24  may slope inwardly so as to be angled toward annular groove  18 .  
         [0015]     A second flange  26  is positioned opposite first flange  24 . In one embodiment, second flange  26  is generally planar so as to be generally perpendicular to annular groove  18 . In another embodiment, second flange  26  may slope inwardly toward annular groove  18  from outside surface  16 .  
         [0016]     First end portion  12  also includes an inner contact surface  28 . Inner contact surface  28  may be generally planar as shown in  FIG. 4 . Alternatively, inner contact surface  28  may include a plurality of ridges. In operation, inner contact surface  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 mechanism may be provided around first end portion  12  within groove  18  to secure first end portion  12  to the shaft.  
         [0017]     Second end portion  14  has a generally uniform thickness and 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 an alternative embodiment (not shown) wall portion  34  may be substantially planar. Second end portion  14  includes an outer surface  36  and an inner surface  38  that are connected together at a distal end  40 . In one embodiment, distal end  40  is curved, although it is understood that it may be constructed so as to include a planar surface.  
         [0018]     While in one preferred embodiment outer and inner surfaces  36  and  38  of second end portion  14  are generally planar to provide a large surface engagement area for engaging an outer race (not shown) of a joint, it is understood that outer and inner surfaces  36  may optionally include one or more annular grooves separated by lands.  
         [0019]     In accordance with another aspect of the invention, boot  10  is preferably a unitary construction that is made of a silicone material that is particularly suited for high temperature applications, that is applications that have a 180° C. peak temperature and/or a 150° C. continuous temperature. The inventive compound includes the following components: amorphous silica such as that available from Rhodia Industrial Specialties, Ltd.; a silicone additive that reduces water absorption such as Rhodorsil distributed by Rhodia Industrial Specialties; a release agent, such as polymethlysiloxane; and a peroxide that acts as a curing agent. It is also desirable that the inventive compounds include at least one pigment.  
         [0020]     In some applications, high stiffness and increased strength are needed. To address such needs, in accordance with another aspect of the invention, the above-described silicone material may be reinforced with fibers. More specifically, the silicone material includes a fiber content from about 3-10 pphr and preferably 5 pphr. A suitable fiber includes a phenolic-based fiber such as Novoloid fibers that are 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.  
         [0021]     The fibers may be added to the silicone 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 silicone 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.  
         [0022]     In an alternative embodiment, the mold may be provided with locator pins for fixing the fabric in place as the material flows through the mold. The material is then injection molded into the boot shape and cured.  
         [0023]     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.