Abstract:
A bellows for protecting a U-joint in a marine stern drive includes a flexible, hollow body defining an interior space and open at opposite ends, the body formed of a thermoplastic elastomer material to be self-supporting, having a first mating end and a second mating end and being pleated therebetween, a first sealing cuff formed of an elastomeric material, softer than the thermoplastic elastomer material, bonded to the first mating end and, a second sealing cuff formed of an elastomeric material, softer than the thermoplastic elastomer material, bonded to the second mating end.

Description:
BACKGROUND AND SUMMARY 
       [0001]    The present invention relates to inboard/outboard vessel drives and, more particularly, to universal joint bellows for inboard/outboard vessel drives. 
         [0002]    In a stern drive or inboard/outboard drive, the engine is located inboard at or near the transom or stern of the vessel and is connected by a drive shaft which passes through the transom to provide power to the drive unit located outside the transom. Basic components of conventional inboard/outboard boats are shown in U.S. Pat. No. 7,559,814, U.S. Pat. No. 6,468,120, U.S. Pat. No. 6,468,119, and U.S. Pat. No. 6,585,545, all of which are incorporated by reference. To turn the boat to port or starboard, the stern drive unit is mounted to a gimbal ring, a fork, or another device that can be pivoted about a generally vertical axis. To raise the stern drive unit relative to the boat, which may be desirable for various reasons, such as when operating in shallow water, the stern drive unit is ordinarily pivotable relative to the gimbal ring, fork or about a horizontal axis. 
         [0003]    A universal joint is typically provided in the drive shaft to allow the drive unit to be steered and tilted relative to the boat/engine. The universal joint is protected from exposure to water by a flexible rubber bellows. If the bellows is damaged or incorrectly assembled water will damage the bearings in the universal joint and also the support bearing which is mounted in the transom shield directly in front of the u-joint. An example of a stern drive with a bellows is shown in U.S. Pat. No. 4,938,726 to Bland, et al. 
         [0004]    According to the conventional art, the universal joint bellows is made of a chloroprene rubber material with a steel wound wire interior support. The wire support maintains the rubber bellows in a shape defining an interior space to accommodate the universal joint. The rubber bellows also acts as a seal around the shaft opening in the transom shield and also around a shaft opening in the drive housing to keep water away from the drive shaft and the universal joint. 
         [0005]    A problem with the conventional bellows is that movement experienced by the universal joint during normal operation of the drive can damage the bellows, during which, high loads and rubbing from the wound wire support can cause tears. In addition, rubber is quickly degraded by environmental effects such as ultraviolet radiation and ozone. As a result, current practice is to replace the bellows on a regular maintenance schedule, which adds time and cost which could be avoided. 
         [0006]    The invention provides a bellows for a marine drive universal joint that overcomes the deficiencies in the art. 
         [0007]    In non-marine applications, such as the automotive industry, bellows and boots for protecting are formed of thermoplastic elastomers, as described in U.S. Pat. No. 5,295,914 to Milavec. In addition, U.S. Pat. No. 5,236,204 to Hempel discloses a bellows formed of a thermoplastic elastomer and including rubber rings bonded to the outer surface of the end portions to accommodate clamping pressure and avoid cold flow problems with the thermoplastic elastomer. U.S. Pat. No. 4,560,178 to Hempel discloses a sleeve formed of a thermoplastic urethane and having folds in the mating ends to create voids that are filled with a permanent plastic sealing mass. 
         [0008]    None of the above solves fully the problems with the conventional marine drive bellows, in the exposure to water and moisture. 
         [0009]    According to the invention, a bellows body for a marine drive U-joint is formed of a thermoplastic elastomer, for example, a thermoplastic polyester elastomer such as Hytrel® available from E.I. DuPont de Nemours. A thermoplastic elastomer provides better fatigue and environmental resistance than rubber, improving and extending the service life of the bellows. 
         [0010]    In addition, thermoplastic elastomer is a stiffer material, making the bellows body self-supporting and allowing the interior supporting wire to be eliminated. 
         [0011]    According to another aspect of the invention, an elastomer, such as a natural or synthetic rubber, layer is overmolded onto end retaining portions of the bellows body to form sealing cuffs. The sealing cuffs provide engaging surfaces for contacting and sealing against engaging surfaces on the drive unit. Preferably, a rubber layer is molded to and thereby bonded to both an exterior and interior surface of the retaining portions of the bellows body to provide water-tight sealing surfaces. The sealing cuffs are coextensive with the retaining portions of the bellows and may extend beyond the ends of the retaining portions. 
         [0012]    According to the invention, an apparatus for protecting a universal joint in a marine drive, the marine drive of the type including a transom shield, a propulsion unit pivotably connected to the transom shield, and a drive shaft including the universal joint extending from the transom shield to the propulsion unit, includes a flexible, hollow body defining an interior space and open at opposite ends, the body formed of a thermoplastic elastomer material and having a first retaining portion and a second retaining portion at the opposite ends thereof, and, a sealing cuff formed of an elastomeric material bonded to each of the first retaining portion and the second retaining portion. 
         [0013]    According to one aspect of the invention, the sealing cuffs on at least one of the first retaining portion and second retaining portion include a circumferentially extending, radially inwardly projecting bead for engaging a groove on a respective mating surface of the marine propulsion unit. 
         [0014]    According to one embodiment of the invention, a sealing cuff including a circumferentially extending, radially inwardly projecting bead is formed one each of the first retaining portion and the second retaining portion. 
         [0015]    According to an alternative embodiment, a sealing cuff formed on the second retaining portion has a radially outwardly projecting flange and has an axially outwardly facing groove, the flange being engageable between cooperating surfaces of the propulsion unit and a pivot housing. 
         [0016]    According to an aspect of the invention, the elastomeric material for the sealing cuff has a hardness less than the thermoplastic elastomer. 
         [0017]    According to yet another aspect of the invention, the first retaining portion and the second retaining portion of the body are formed with axially extending slots. According to another aspect of the invention, the sealing cuffs formed on the first retaining portion and second retaining portion cover the slots. 
         [0018]    According to one embodiment of the invention, the slots are T-shaped. 
         [0019]    In another aspect of the invention, the body is corrugated between the first retaining portion and the second retaining portion, and may include at least one, and preferably a plurality of pleats between the first retaining portion and the second retaining portion. 
         [0020]    According to an aspect of the invention, the body is self-supporting, requiring no internal supporting device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention will be better understood by reference to the following Detailed Description read in conjunction with the appended drawings, in which: 
           [0022]      FIG. 1  is a section view of an exemplary marine stern or inboard/outboard drive; 
           [0023]      FIG. 2  is a section view of a marine stern drive showing a bellows according to an embodiment of the invention; 
           [0024]      FIG. 3  is a perspective view of a bellows according to the invention; 
           [0025]      FIG. 4  is a section view of the bellows shown in  FIG. 3 ; and, 
           [0026]      FIG. 5  is a section view of a marine stern drive showing a bellows according to an alternative embodiment of the invention; 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    An exemplary stern drive assembly  10  for a marine vessel, for which the protective device according to the invention is useful, is shown in  FIG. 1 . The marine vessel includes a hull  1  having a transom  3  or stern. An engine  5  is installed in the hull  1  adjacent to the stern  3 . A drive shaft (not shown) extends from the engine  5  through the transom  3  to connect with a propulsion unit  16 . 
         [0028]    As known in the art, a stern drive assembly  10  typically includes a transom shield assembly  12 , a gimbal ring  14  and a drive housing  16 . The transom shield assembly  12  is mounted to the stern  3  or transom of a vessel to support the drive assembly  10  and drive shaft (not illustrated) of the engine  5 . The gimbal ring  14  is mounted to the shield assembly  12  for pivotal movement about a vertical axis to allow the drive housing  16  to pivot for steering the vessel. The drive housing  16  is mounted to the gimbal ring  14  for pivotal movement about a horizontal axis  18 . The drive shaft (not illustrated in  FIG. 1 ) extends from the engine  5  through the stern and into the drive housing  16 . The drive shaft is connected to drive the propellers  20  through a vertical transmission shaft and a propeller shaft. To allow pivoting of the gimbal ring  14  relative to the shield assembly  12  and pivoting of the drive housing  16  relative to the gimbal ring, the drive shaft includes a universal joint. 
         [0029]    A bellows (not shown in  FIG. 1 ) covers the drive shaft in the space between the transom shield assembly  12  and the drive housing  16 , where it would otherwise be exposed to water. 
         [0030]    A stern drive as described above may include a pivot housing connecting to a bearing carrier, as described in U.S. Pat. No. 4,938,726 to Bland, et al., the contents of which are incorporated by reference herein. The drive shaft is supported in the drive housing by the bearing carrier. 
         [0031]      FIG. 2  shows a section view of a stern drive as in  FIG. 1  and includes a bellows  30  according to one embodiment of the invention. As mentioned, a drive shaft (not illustrated) connecting the engine to the drive includes a universal joint to accommodate pivoting movement of the drive housing  16  relative to the shield assembly. The bellows  30  covers the drive shaft and universal joint to protect them from exposure to water and must also accommodate pivoting movement of the universal joint. 
         [0032]    The bellows  30  is connected at a first end or first retaining portion  32  to a tube or stem  24  formed on the shield and extending therefrom. The first end  32  mates with the stem  24  by overlapping, fitting over, an end portion of the stem. The bellows  30  may be secured to the stem  24  by a band clamp (not illustrated) or other fastening device. 
         [0033]    The bellows  30  is connected at an opposite second end or second retaining portion  34  to the pivot housing  26  and a portion of the drive housing assembly. In the illustrated embodiment, the second retaining portion  34  of the bellows  30  is secured between the pivot housing  26  and a bearing housing  28 . 
         [0034]    Turning to  FIG. 3 , which shows a perspective view and  FIG. 4 , which shows a section view, the bellows  30  of the invention is formed as a hollow body  36  open at the first end  32  and second end  34 . A portion  36  between the first retaining portion  32  and second retaining portion  34  is formed to allow bending, and may be pleated  38 , with at least one pleat or fold, or, as illustrated and preferred, with a plurality of folds. The body  36  is formed of a thermoplastic elastomer, for example, a thermoplastic polyester elastomer such as Hytrel® available from E.I. DuPont de Nemours. A thermoplastic elastomer provides better resistance to fatigue and weathering than the currently used rubber, improving and extending the service life of the bellows. In addition, thermoplastic elastomer is a stiffer material than rubber, making the bellows self-supporting and allowing the interior supporting wire to be eliminated. 
         [0035]    Thermoplastic elastomer, however, is too hard to provide a sufficient sealing surface with the transom and drive assembly to prevent water ingress. According to the invention, first and second sealing cuffs  40 ,  42 , respectively, are bonded on the first  32  retaining portion and second  34  retaining portions of the bellows body  36 . The sealing cuffs  40 ,  42  are formed of an elastomer, such as natural or synthetic rubber, having a hardness less than that of the thermoplastic elastomer, but also having good resistance to weathering and mechanical stress. For example, a thermoplastic rubber such an engineered thermoplastic vulcanizate 60A01HSL BK001 available from E.I. DuPont de Nemours &amp; Co. has been found to be suitable 
         [0036]    The elastomer provides an ability to stretch and compress so that cuffs  40 ,  42  can conform to the mating surfaces of the drive assembly. The cuffs  40 ,  42  in  FIG. 3  are shown as transparent for the purposes of illustrating features of the first retaining portion  32  and second retaining portion  34  described in more detail below; however, transparency should not be understood as a necessary feature of the material. The first and second cuffs  40 ,  42  may be formed and bonded on the first retaining portion  32  and second retaining portion  34  by an over-molding process, or other convenient method. 
         [0037]    With particular attention to  FIGS. 2 and 4 , the first cuff  40  is bonded or formed on the first retaining portion  32  to provide both an interior surface  44  and an exterior surface  46 . A portion of the cuff  40  extends axially from the first retaining portion  32 . Alternatively, the first cuff  40  may be coextensive with the first retaining portion  32 , as shown in  FIGS. 3 and 4 . According to another alternative, the first cuff  40  is coextensive with the first retaining portion  32  and is formed thereon to provide an interior surface  44  only. The interior surface  44  includes a circumferential bead  48  that projects radially inwardly. As shown in  FIG. 2 , the bead  48  mates with a groove  25  formed in the stem  24  of the shield. The bead  48  and groove  25  cooperate to provide a water seal and help prevent relative movement of the first cuff  40  and stem  24 . 
         [0038]    Returning to  FIGS. 2 and 4 , the second cuff  42  is bonded or formed on the second retaining portion  34  to provide both an interior surface  50  and exterior surface  52 . Alternatively, the second cuff  42  may be coextensive with the second retaining portion  34 , as shown in  FIG. 4 . According to a further alternative, the second cuff  42  may be formed as an exterior surface  52  on the second retaining portion  34 . As seen in  FIG. 4 , the second cuff  42  includes a flange  56  projecting radially outwardly from the exterior surface  52 . The flange  56  is generally T-shaped in cross section to provide a ridge  58  projecting axially inward, that is, toward the first end  32 . As seen in  FIG. 2 , the ridge  58  engages a pocket  60  in the pivot housing  24  defined by a lip  62 . The flange  56  also includes a groove  64  defined by the T-shaped profile and an axially outward facing side of the flange. The groove  64  mates with a nose  29  formed in the bearing housing  28 . The flange  56  is captured between the lip  62  in the pivot housing  24  and the nose  29  in the bearing housing  28 , and may be compressed to form a water-tight seal. The outer surface  52  of the flange  56  is in contact with the pivot housing, further enhancing the seal. 
         [0039]    As may be seen in  FIG. 3 , the first retaining portion  32  and second retaining portion  34  of the bellows both include slots  70  cut from the end axially inward. The slots provide a capacity to expand the first retaining portion  32  and second retaining  34  radially when positioning the first retaining portion  32  over the stem  24  and positioning the second retaining portion  34  inside the pivot housing  26  for good contact. Preferably, the slots are T-shaped as shown in  FIG. 3 , with circumferentially directed slots  72 , shown here with a barbell shape, formed at the axially inward end of the axial slots  70 . Alternatively, the slots  70  may be simple linear cuts in the first retaining portion  32  and second retaining portion  34 . 
         [0040]    A stern drive of another design may omit a pivot housing. This type of stern drive may have a steering fork, rather than a gimbal ring  14  as shown in  FIG. 1 . A steering fork is mounted to the transom shield for pivotable movement about a horizontal axis, and a marine propulsion unit is mounted to the fork for pivoting movement about a vertical axis. The invention applies as well to a stern drive of this configuration. 
         [0041]      FIG. 5  shows a bellows  130  according to an alternative embodiment of the invention for stern drives lacking a pivot housing. The bellows  130  is mounted to and extends between a stem  124  on the shield assembly (not shown) and a bearing housing  128  of the propulsion unit (not shown). A first sealing cuff  140  is bonded to the first retaining portion  132 . The first sealing cuff  140  is formed with layers on the interior side  145  and the exterior side  147  of the first retaining portion  132 . A circumferentially extending, radially inwardly projecting bead  148  formed on the interior of the sealing cuff mates with a circumferentially directed groove  125  formed in a stem  124  formed on the transom shield. 
         [0042]    The second retaining portion  134  includes a second sealing cuff  142  bonded thereto. The second retaining portion  134  engages the bearing housing  128  of the propulsion unit (not shown). The second sealing cuff  142  is formed with layers on the interior surface  150  and exterior surface  152  of the second retaining portion  134 . A circumferentially extending, radially inwardly projecting bead  149  formed on the interior surface  150  engages a circumferential groove  126  formed in bearing housing  128 . 
         [0043]    Both the first retaining cuff  140  and second retaining cuff  142  extend beyond the end of the respective retaining portions  132 ,  134 . The retaining portions  132 ,  134  with their respective sealing cuffs  140 ,  142  may be secured to the stem  124  and bearing housing  128  by band clamps (not illustrated). 
         [0044]    The invention has been described in terms of preferred principles, embodiments, and components; however, those skilled in the art will understand that substitutions may be made for components without departing from the scope of the invention as defined in the appended claims.