Abstract:
A shaft for a vehicle including a first member having an internal spline and defining an inner cavity, a second member having an external spline, and a boot mounted over the vent and adapted to substantially prevent contaminants from entering the inner cavity through the vent. The external spline of the first member and the internal spline of the second member cooperatively allow an axial sliding movement of the second member into the inner cavity of the first member and substantially prevents rotational movement between the first and second members. One of the first and second members defines a vent communicating with the inner cavity. The first and second members and the boot cooperatively form a substantially airtight enclosure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to a venting system for use in a double-tube “slip-in-tube” shaft.  
           [0002]    U.S. Pat. No. 6,279,221 (“the &#39;221 patent”), issued Aug. 28, 2001, for a double-tube “slip-in-tube” vehicle shaft, is hereby incorporated in full by this reference. A double-tube “slip-in-tube” vehicle shaft includes first and second members each having splined portions. The second member is telescopically positioned within the first member. The splined portion of the first member cooperates with the splined portion of the second member to form the shaft. The cooperating splined portions of the first and second members, however, allow external elements to enter into the double-tube vehicle shaft at the location of the intermeshing splines.  
           [0003]    In order to prevent contaminants from entering the shaft, a boot is mounted to the shaft where the second member slips into the first member. The boot may be attached to the first and second members in a substantially airtight configuration, which prevents contaminating particles from entering the shaft.  
           [0004]    A slip-in-tube shaft contains, depending on diameter and length, approximately 8 to 16 liters of air sealed inside it during assembly. Shaft working temperature varies continuously depending on ambient temperature, driving conditions, momentary torsional load, and depth and frequency of shaft plunging action. These temperature changes affect the internal air pressure inside the shaft tube. In addition, the air column inside the tube experiences compression and decompression by reversing, at various frequencies, plunging motions of the shaft. Those factors cause, at certain frequencies, the air column inside the tube to vibrate and resonate within the shaft, thereby creating shaft noise and boom, which can degrade driveline noise, vibration, and harshness (NVH) performance. In addition, the air inside the tube can create hydraulic lock and resist manual shaft length adjustment for its installation during vehicle final assembly, which can make the installation of the shaft difficult. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is an unassembled perspective view of the prior art, for a slip-in-tube vehicle shaft, as shown in the &#39;221 patent;  
         [0006]    [0006]FIG. 2 is an assembled side view of the shaft shown in FIG. 1;  
         [0007]    [0007]FIG. 3 is a side view of the shaft shown in FIG. 2, taken along view line  3 - 3 ;  
         [0008]    [0008]FIG. 4 is a fragmented perspective view of the portion of the shaft shown in FIG. 3, which illustrates portions of the splines;  
         [0009]    [0009]FIG. 5 is an assembled side view of the shaft shown in FIG. 1 plus the venting system of the present invention; and  
         [0010]    [0010]FIG. 6 is an assembled side view of the shaft shown in FIG. 5, wherein the second member is at the end of a plunging action. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    Referring to the drawings, FIGS.  1 - 4  have been incorporated from the &#39;221 patent for a double-tube “slip-in-tube” vehicle shaft. As shown, a double-tube “slip-in-tube” vehicle shaft  10  includes a generally tubular and hollow first member  16  having a splined portion  18  circumferentially formed upon an interior surface  19 . The shaft  10  further includes a second generally tubular and hollow member  12  having a splined portion  14  circumferentially formed upon an exterior surface  15 . The splined portion  14  of the second member  12  is adapted to selectively and cooperatively intermesh with the splined portion  18  of the first member  16 . The first and second members  16 ,  12  may have various diameters  52 ,  50 . In one non-limiting embodiment, the diameters are approximately one and three-quarter (1.75) inches, respectively, to about five (5.0) inches. Other diameter values may alternatively be utilized.  
         [0012]    The second member  12  is adapted to selectively, movably, and telescopically penetrate the first member  16 . The splined portions  18 ,  14  of the first and second members  16 ,  12  cooperatively intermesh in the usual and known manner. The region of the shaft  10  where this penetration or interaction between the first and second members  16 ,  12  occurs may be referred to as an overlapping region, whereas the region of the shaft where penetration or interaction does not occur may be referred to as a non-overlapping region.  
         [0013]    The first member  16  is coupled, by the use of a conventional flange  20 , to a conventional transmission  21 , while the second member  12  is coupled, by the use of a conventional flange  22 , to a conventional differential  23 . The torque, supplied by the transmission  21  is communicated to the first member  16  and then, by use of the intermeshed splined portions  18 ,  14  of the first and second members  16 ,  12 , is communicated to the second member  12  and to the differential  23 . The cooperating splined portions  18 ,  14  allow the second member  12  to dynamically move along the longitudinal axis  32  of the shaft  10  in response to changes in the distance between the transmission  21  and the differential  23 .  
         [0014]    The first and second members  16 ,  12  may be manufactured from conventional and commercially available lightweight aluminum material. As an example, the first and second members  16 ,  12  are preferably a commercially available “6061-T4” type of aluminum or aluminum alloy material. The splines are preferably “cold formed” upon the surfaces  19 ,  15  by the use of the conventional “Grob” process, which is provided by the Ernst Grob AG company of Mannedorf, Switzerland. Moreover, the splined portions  18 ,  14  of the first and second members  16 ,  12  are preferably hardened or “anodized” in accordance with the commercially available Metalast anodizing process, which is provided by the Metalast International Corporation of Minden, Nev. More particularly, the splined portions  18 ,  14  of the first and second members  16 ,  12 , in one embodiment, are anodized with a layer of “Metalast hardcoat” material having a thickness of about 0.002″.  
         [0015]    The use of such anodized aluminum and cold-formed splined portions  18 ,  14  allows for a relatively lightweight shaft  10  that substantially reduces the amount of vibration and noise which emanates from the operatively formed shaft  10 . The relatively lightweight aluminum construction allows the first and second members  16 ,  12  to be designed with relatively large diameters  52 ,  50 , while minimizing overall weight. The relatively large diameter of the members  16 ,  12  efficiently distributes the applied axial loads over a larger surface area, thereby allowing the shaft  10  to support relatively larger torques at relatively higher speeds than prior shaft assemblies. Further, this relatively light-weight design allows for relatively long splined portions  18 ,  14  which, in one embodiment, may have a substantially identical length  56  approximately equal to at least three times the diameter  52  of the first member  16  (e.g., approximately 13.5 inches). In alternative embodiments, the splined portions  18 ,  14  may have lengths extending approximately half way along the first and second members  16 ,  12 . The anodized aluminum splines also, as is best shown in FIGS. 3 and 4, allow for relatively large splined mating surfaces (or “working areas”). In one embodiment, the working areas have a “tooth thickness”  42  equal to about five to about ten millimeters. The splines allow for distribution of the axial loads imparted upon the spine portions  18 ,  14  and are effective to reduce the overall wear of the splines and the assembly  10 .  
         [0016]    In one embodiment, each end wall  44 ,  46  of each spine cooperatively forms an angle  48  of about forty degrees (40°) to eighty degrees (80°), although other angular configurations may be utilized. Further, while a segment of the splined portion  18  of the first member  16  is shown in FIG. 3, it should be realized that the splined portion  14  of the second member  12  is substantially similar. It should be appreciated that the relatively long length of the splined portions  18 ,  14  reduces the amount of noise and vibrations generated from the shaft  10 .  
         [0017]    A boot  26 , which functions to prevent contaminants from entering the shaft  10 , is mounted to the shaft  10 . Preferably, the boot  26  is a conventional boot that encapsulates at least the overlapping region of the first and second members  16 ,  12 . In order to aptly prevent contaminants from entering the shaft  10 , the boot  26  is preferably mounted to the shaft  10  in a substantially airtight configuration. The boot  26  is preferably fastened at a first end to the first member  16  and at a second end to the second member  12  using conventional fasteners. Alternatively, any suitable method capable of adequately fastening the boot  26  to the shaft  10  may be used. As shown in FIG. 1, the boot  26  is preferably corrugated to allow for relative axial movement between the first and second members  16 ,  12 . Alternatively, any suitable configuration capable of allowing the boot  26  to axially expand and contract without compromising its imperviousness to contaminants may be used. In one embodiment, in addition to being axially expandable, the boot  26  is radially expandable. The boot  26  is preferably constructed of a thermoplastic polymer. However, any suitable material capable of expanding and contracting as air-pressure changes within the boot  26  may be used.  
         [0018]    The prior art shaft  10 , as shown in FIGS.  1 - 4 , contains sealed air inside the hollow shaft members  12 ,  16  with no venting means. As a result, the sealed air inside the hollow shaft members  12 ,  16  of the shaft  10  undergoes extreme changes in pressure during compression and decompression plunging motions of the shaft  10 . To alleviate this problem, the venting system of the present invention minimizes pressure changes within the shaft  10 .  
         [0019]    FIGS.  5 - 6  show the first and second members  16 ,  12  and the boot  26  cooperating to form a substantially airtight enclosure that minimizes pressure changes within the inner cavity of the first member  16 . In a preferred embodiment, the vent  80  is located on the shaft member  16  and under the boot  26 . As shown in FIG. 6, the vent  80  is preferably at a location on the shaft  10  where the first and second members  16 ,  12  do not interact, which is the non-overlapping region of the shaft  10 . This embodiment allows for maximum ventilation between the shaft  10  and the boot  26 , because ventilation occurs throughout the entire plunging and reverse plunging processes. However, any suitable location on the shaft  10  and under the boot  26  may be used. In one embodiment, the vent  80  is located in the first member  16 . However, it should be appreciated that the vent  80  may alternatively be located in the second member  12 . The vent preferably has a diameter of approximately 0.06 inches. However, any suitably sized vent may be used. The vent may be formed in a variety of ways such as through drilling or molding. Any suitable method capable of creating the vent may be used.  
         [0020]    As suggested above, shaft venting takes place through the vent  80 . In operation, when the shaft members  12 ,  16  compress during a plunging motion of the shaft  10 , the high-pressure air inside the members  12 ,  16  vents by passing through the vent  80 . As the high-pressure air passes from the shaft  10  into the boot  26 , the boot  26  expands, thereby reducing the air-pressure within the shaft  10 . As a result, the internal shaft pressure is maintained at an operational level. Similarly, when the shaft members  12 ,  16  decompress during a reverse plunging motion of the shaft  10 , the higher-pressure air of the boot  26  vents by passing through the vent  80  into the shaft  10 . As the high-pressure air passes from the boot  26  into the shaft  10 , the boot  26  contracts, thereby increasing the air pressure within the shaft  10 . Again, the internal shaft pressure is maintained at an operational level. In such a manner, the shaft venting continually equalizes the internal shaft pressure with that of the boot  26 .  
         [0021]    At the same time, external elements, such as, water, dirt, or salt are prevented from contaminating the shaft  10  via the vent  80  due to the structure of the boot  26  encapsulating the vent  80 . In particular, the boot  26  is preferably mounted to the shaft  10  in a substantially airtight configuration. Most external elements are larger than the minimal space between the boot  26  and the shaft  10  and are, therefore, unable to pass into the shaft  10  through the vent  80 . As a result, premature wear or corrosion is avoided.  
         [0022]    It is to be understood that the invention is not to be limited to the exact construction and/or method which has been illustrated and discussed above, but that various changes and/or modifications may be made without departing from the spirit and the scope of the invention.