BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a joint structure for power transmitting member and a method for producing the joint structure for power transmitting member. More particularly, the present invention relates to a joint structure for propeller shaft for vehicle and method for producing the joint structure for propeller shaft for vehicle.  
           [0003]    2. Description of the Related Art  
           [0004]    It is known that there is a great demand for weight reduction in many fields, especially automobiles, from the viewpoint of fuel economy, environmental protection, etc. As a means for achieving this, use of propeller shafts formed of FRP (fiber-reinforced plastics) is being considered, and some of such propeller shafts have already been put into practical use. Such a propeller shaft has a tube that is made of FRP, and a metal joint that is joined to the end of the tube.  
           [0005]    One example of a power transmitting member is the propeller shaft for a vehicle. The propeller shaft for a vehicle is disclosed in, for example, Japan Patent Publication (koukai) No. 2001-65538 (incorporated herein by reference). According to that publication, as shown in FIG. 11 of the pre-grant application, the propeller shaft includes an FRP tube  1  and universal joints  2 ,  3  which are joined to both ends  1   a ,  1   b  of the tube  1 . A transmission torque generated from an engine (not shown) is transmitted to the following elements in order: a transmission (not shown), the universal joint  2 , the tube  1 , the universal joint  3 , a differential gear (not shown), and a rear wheel (not shown).  
           [0006]    The tube  1  comprises a main layer Ic and sub layers  4 ,  4 . The main layer Ic has reinforcing fibers helically wound extending over the length thereof. The sub layers  4 ,  4  are formed at the ends of the main layer Ic so as to be integral with and internal to the main layer  1   c  and including hooped reinforcing fibers. The universal joints  2 ,  3  comprise input axis yokes  5 ,  5  and output axis yokes  6 ,  6 . Each of the input axis yoke and the output axis yoke are joined together at yoke portions  7 ,  7 . The output axis yokes have fitting portions  8 ,  8 . Each of the fitting portions  8 ,  8  is joined to the ends  1   a ,  1   b  of the tube  1  by press fitting.  
           [0007]    As shown in FIGS. 9 and 10 of the pre-grant application, the fitting portion  8  has a sealing portion  8   a , a flange portion  9 , and ajoint portion  10 . The sealing portion  8   a  has a uniform outer diameter. The flange portion  9  is integrally molded with the fitting portion  8 . When a load that is bigger than the prescribed value in an axial direction to the axis of the propeller shaft, is applied to the propeller shaft, the flange portion  9  causes the main layer  1   c  and the sub layer  4  to be separated from each other. This enables an energy absorbing effect to be realized due to the crashable body structure. The joint portion  10  has a serration surface. When the fitting portion  8  is joined to the end of the tube  1  by press fitting, a fastening structure between the tube  1  and the fitting portion  8  is obtained by engaging of the serration surface of the joint portion  10 .  
           [0008]    Next, a way to join each of the ends  1   a ,  1   b  and the fitting portions  8 ,  8  as shown in FIG. 11 will be described. As shown in FIGS. 9 and 10, first, a liquid packing compound  11  is applied to an edge of the joint portion  10 , so as to surround the joint portion  10 . Then, the tube  1  is forced into the joint portion  10  of the fitting portion  8  with press fitting until an end surface of the tube  1  almost strikes the flange portion  9 . Thereby, the fastening structure between the tube  1  and the fitting portion  8  is obtained with press fitting. In addition, clearances between an inside of the tube  1  and an outer surface of the fitting portion  8 , and between the end surface of the tube  1  and the flange portion  9  are filled with the liquid packing compound  11 . In effect, the clearances are sealed by the liquid packing compound  11 .  
           [0009]    When the fitting portion  8  is joined to the end of the tube  1 , the liquid packing compound  11  is spread between the inside of the tube  1  and the outer surface of the fitting portion  8 . The liquid packing compound  11  is extended into the flange portion  9 . However, in this structure for the power transmitting member, the sealing portion  8   a  has a uniform outer diameter, and the tube  1  has a uniform inner diameter, i.e., a clearance between the outer surface of the sealing portion  8   a  and the inside of the tube  1  has a uniform width in an axial direction of the axis of the tube  1 . Therefore, a pressure force, which acts between the inside of the tube  1  and the outer surface of the fitting portion  8 , is averaged around the edge of the inside of the tube  1 . As a result, it is hard to fill to a corner  12 , which defined between the flange portion  9  and the sealing portion  8   a , entirely with the liquid packing compound  11 .  
           [0010]    Therefore, a failed portion C, in which the liquid packing compound does not adequately fill, may appear. In this case, airtightness between the tube  1  and fitting portion  8  by the liquid packing compound can not be retained. The airtightness degrades with the passage of time. As a result, the tube  1  and the fitting portion  8  may be separated from each other by exfoliation, i.e., the performance of the seal between the tube  1  and the fitting portion  8  may degrade.  
         SUMMARY OF THE INVENTION  
         [0011]    According to an embodiment of the present invention an improved joint structure for a power transmitting member is provided. The joint structure includes a fiber rein forced plastic tube, a joint comprising a joint portion for joining to an end portion of the tube, and a sealing portion formed on an end of the tube side of the joint portion, wherein the joint portion and the sealing portion are disposed in an interior of the tube, a liquid packing compound for sealing between the tube and the joint, wherein the liquid packing compound fills at least an area between the sealing portion and the tube wherein the sealing portion has a tapered surface, whose diameter increases toward the end of the tube.  
           [0012]    In another embodiment, the joint structure may include a fiber rein forced plastic tube, a joint comprising a joint portion for joining to an end portion of the tube, and a sealing portion formed on an end of the tube side of the joint portion, wherein the joint portion and the sealing portion are disposed in an interior of the tube, an adhesive for sealing and joining between the tube and the joint, wherein the adhesive fills at least an area between the sealing portion and the tune, wherein the sealing portion has a tapered surface whose diameter increases toward the end of the tube.  
           [0013]    According to another aspect of the present invention, a method for producing a joint structure for a power transmitting member is provided. The method includes providing a fiber rein forced plastic tube and a joint comprising a joint portion for joining to an end portion of the tube and a sealing portion formed on the same axis of the joint portion, wherein the sealing portion has a tapered surface whose diameter increases from the joint portion side, applying an amount of a liquid packing compound for sealing at least between the tube and the sealing portion, inserting the joint from the joint portion side into the tube until at least the sealing portion is inserted in the tube, whereby the joint and the tube are joined by press fitting.  
           [0014]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    These and other features, aspects and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.  
         [0016]    [0016]FIG. 1 is an enlarged sectional view of a joint structure for a power transmitting member before the joining of a tube  20  and a fitting portion  23  according to a first embodiment of the present invention;  
         [0017]    [0017]FIG. 2 is an enlarged sectional view of a joint structure for a power transmitting member after the joining of the tube  20  and the fitting portion  23  according to the first embodiment of the present invention;  
         [0018]    [0018]FIG. 3 is an enlarged sectional view of the joint structure for a power transmitting member before the joining of the tube  20  and the fitting portion  23  according to a second embodiment of the present invention;  
         [0019]    [0019]FIG. 4 is an enlarged sectional view of the joint structure for a power transmitting member after the joining of the tube  20  and the fitting portion  23  according to the second embodiment of the present invention;  
         [0020]    [0020]FIG. 5 is an enlarged sectional view of the joint structure for a power transmitting member before the joining of the tube  20  and the fitting portion  23  according to a third embodiment of the present invention;  
         [0021]    [0021]FIG. 6 is an enlarged sectional view of the joint structure for a power transmitting member after the joining of the tube  20  and the fitting portion  23  according to a third embodiment of the present invention;  
         [0022]    [0022]FIG. 7 is an enlarged sectional view of the joint structure for a power transmitting member before the joining of the tube  20  and the fitting portion  23  according to a fourth embodiment of the present invention;  
         [0023]    [0023]FIG. 8 is an enlarged sectional view of the joint structure for a power transmitting member after the joining of the tube  20  and the fitting portion  23  according to the fourth embodiment of the present invention;  
         [0024]    [0024]FIG. 9 is an enlarged sectional view of the joint structure for a power transmitting member before the joining of the tube  1  and the fitting portion  8  according to the related art;  
         [0025]    [0025]FIG. 10 is an enlarged sectional view of the joint structure for power transmitting member after the joining of the tube  1  and the fitting portion  8  according to the related art; and  
         [0026]    [0026]FIG. 11 is a sectional view of the propeller shaft for vehicle according to the related art. 
     
    
     DETAILED DESCRIPTION  
       [0027]    A joint structure for a power transmitting member according to preferred embodiments will now be described with reference to the drawings. FIGS. 1 and 2 show a first embodiment of the present invention. In this first embodiment, the joint structure is applied for a transmitting member of the propeller shaft of the vehicle. As shown in FIG. 1, the joint structure comprises a tube  20  made of carbon fiber-reinforced plastic (CFRP) and an output axis yoke  21  having a yoke portion  22  and a fitting portion  23 . The yoke portion  22  is joined to an input axis yoke (not shown). The fitting portion  23  has a tube shape, and that is joined to the end of the tube  20  by press fitting.  
         [0028]    The tube  20  has a main layer  20   b  and a sub layer  24 . The main layer  20   b  has a uniform inner diameter. The tube  20  is formed by helically winding a bundle of carbon fibers impregnated with an epoxy resin. The sub layer  24  is provided at least at an inner end portion of the main layer  20   b . The sub layer  24  is formed by circumferentially winding a bundle of carbon fibers impregnated with the epoxy resin.  
         [0029]    The fitting portion  23  has a joint portion  26  and a flange portion  27  on an outer surface of the fitting portion  23 . The joint portion  26  has a serration surface. When the fitting portion  23  is joined to the end of the tube  20  by press fitting, a fastening structure between the tube  20  and the fitting portion  23  is obtained by engaging of the serration surface of the joint portion  26 . The flange portion  27  is integrally molded with the fitting portion  23 . When a load that is bigger than the prescribed value in an axial direction to the axis of the propeller shaft, is applied to the propeller shaft the flange portion  27  causes the main layer  20   b  and the sub layer  24  to be separated from each other. In this way, the propeller shaft of the vehicle can be provided which is capable of absorbing the load upon collision of the vehicle.  
         [0030]    The fitting portion  23  has a sealing portion  25   a  formed between an end portion  26   a  of the joint portion  26  and the flange portion  27 . The sealing portion  25   a  has a tapered surface whose diameter increases from the end portion  26   a  to the corner  27   a . The tapered surface is formed at an angle 0 of about 10 degrees from the axis of the tube  20 . The diameter of the sealing portion  25   a  is largest at the corner  27   a . The largest diameter of the sealing portion  25   a  is almost the same as the inner diameter of the tube  20 , (i.e., the inner diameter of the sub layer  24 ).  
         [0031]    The liquid packing compound  28  is filled between the inside of an end portion  20   a  of the sub layer  24  and the outer surface  25  of the fitting portion  23 .  
         [0032]    According to this embodiment, as shown in FIG. 1, first, the liquid packing compound  28  is applied in a loop around the end portion  26   a . Then, the tube  20  is pushed into the output axis yoke  21  with press fitting between the end portion  20   a  of the sub layer  24  and the serration surface of the joint portion  26 .  
         [0033]    The end surface  24   a  of the sub layer  24  of the tube  20  spreads the liquid packing compound  28 . As a result, the sealing portion  25   a  is covered by the liquid packing compound  28 .  
         [0034]    As shown in FIG. 2, the tube  20  is forced into the output axis yoke  21  until the end surface  24   a  almost strikes the flange portion  27 . In this position, the end surface  24   a  of the sub layer  24  presses the liquid packing compound  28  against the flange portion  27 . Furthermore, the end surface  24   a  strongly presses the liquid packing compound  28  into the corner  27   a . Therefore, the liquid packing compound  28  completely fills the entire corner  27   a , and an airtightness between the tube  20  and the fitting portion  23  by the liquid packing compound  28  is obtained.  
         [0035]    As a result, degradation of the seal performance between the tube  20  and the fitting portion  23  is controlled. This certainly lends long term stability to the airtightness. Specially, as this joint structure is applied for a vehicle (i.e., the tube  20  is the propeller shaft), the entry of the rainwater is prevented.  
         [0036]    Therefore, the joint portion  26  is protected from rust.  
         [0037]    In addition, the liquid packing compound  28  is applied to the entire sealing portion  25   a  along its tapered surface since the tapered surface is continuously smoothly formed.  
         [0038]    [0038]FIGS. 3 and 4 show a second embodiment of the present invention. In this second embodiment, an annular groove  30  is formed by the end portion  26   a  of the joint portion  26 . The liquid packing compound  28  is held on the annular groove  30  before the joining of the tube  20  and the fitting portion  23 . The annular groove  30  is formed in a loop around the fitting portion  23 . The depth and the width of the annular groove  30  is set according to an amount of the liquid packing compound  28 , which is held on the annular groove  30 . The depth of the annular groove  30  is formed deeper than the outer surface  25  and is formed to a prescribed width.  
         [0039]    In this embodiment, the same or similar references used to denote elements in the joint structure of the first embodiment (i.e., the tapered surface of the sealing portion  25   a  etc.) are applied to the corresponding elements used in the second embodiment except the annular groove  30 .  
         [0040]    Therefore, in this embodiment, it is easy to find out a position in which the liquid packing compound  28  is applied by virtue of the annular groove  30  formed on the fitting portion  23 . In addition, an area for sealing is expanded inside of the annular groove  30 . This certainly lends long term stability to the seal performance between the tube  20  and the fitting portion  23 .  
         [0041]    [0041]FIGS. 5 and 6 show a third embodiment of the present invention. In this case, as shown in FIG. 5, the liquid packing compound  28  is applied inside of the end portion  20   a  of the sub layer  24  and on the end surface  24   a  of the sub layer  24  other than the fitting portion  23 . In this case, as shown in FIG. 6, when the tube  20  is joined into the fitting portion  23 , the liquid packing compound  28  fills not only on the sealing portion  25   a  and flange portion  27 , but also between the sub layer  24  and the joint portion  26 . Therefore, the area for sealing is further expanded and the seal performance is further improved.  
         [0042]    [0042]FIGS. 7 and 8 show a fourth embodiment of the present invention. In this case, as shown in FIG. 7, the liquid packing compound  28  has a string shape. The liquid packing compound  28  is wound around the sealing portion  25   a  from the end portion  26   a  to the corner  27   a . Adjacent hoops of the liquid packing compound  28  are wound to be close together. FIG. 8 shows the transmitting member after the joining of the tube  20  and the fitting portion  23 .  
         [0043]    According to the fourth embodiment, the liquid packing compound  28  can be easily applied on the sealing portion  25   a . This improves the workability of the applying liquid packing compound  28 . In addition, the amount of the liquid packing compound  28 , which is applied on the sealing portion  25   a , can be optimized by choosing the thickness or the number of the hoops of the liquid packing compound  28 . This reduces the cost of the materials.  
         [0044]    While the present invention is described on the basis of certain preferred embodiment, it is not limited thereto, but is defined by the appended claims as interpreted in accordance with applicable law. For example, according to the previously described preferred embodiments of the present invention, although the tapered surface of the sealing portion  25   a  is formed at an angle of about 10 degrees from the axis of the tube  20 , the angle of the tapered surface can be adjusted according to the specifications covering the tube  20  or the fitting portion  23 . Also, although the tube  20  is made of carbon fibers and the epoxy resin, the tube  20  may be made of glass fibers or polyaramid fibers as fibers and unsaturated polyester resin, phenol resin, vinyl ester resin, polyimide resin, polyamide resin, polycarbonate resin or polyether imide resin as the resin. Also, although the tapered surface of the sealing portion  25   a  is continuously smoothly formed, the pared surface may be formed by a staircase pattern. Also, although the liquid packing compound  28  is filled for sealing between the tube  20  and the sealing portion  25   a , an adhesive may be filled for sealing between the tube  20  and the sealing portion  25   a . In this case, the joint between the tube  20  and the sealing portion  25   a  becomes stronger. Also, although the joint portion  26  has a serration surface, the joint portion  26  may have no serration surface. In this case, the reinforcing fibers of the tube  20  are not scratched by the serration surface of the joint portion  26 . When the joint portion  26  has no serration surface, the adhesive is preferable to liquid packing compound  28  for sealing between the tube  20  and the fitting portion  23 . Also, although the tube  20  is circular in cross section, the tube  20  may have a square cross section or another cross section shape. Also, when the joint portion  23  is joined to the end portion of the tube  20  by press fitting, although in the preferred embodiment, the tube  20  is pushed into the output axis yoke  21 , press fitting of the tube  20  and the joint portion  23  maybe accomplished in a number of ways, including where the output axis  21  is pushed into the tube  20 , and where the tube  20  and the joint portion  23  arc pushed together.  
         [0045]    This application relates to and incorporates herein by reference in its entirety Japanese Patent application No. 2001-273320, filed on Sep. 10, 2001, from which priority is claimed.
A joint structure for a power transmitting member comprising a fiber rein forced plastic tube, a joint comprising a joint portion for joining to an end portion of the tube, and a sealing portion formed on an end of the tube side of the joint portion, wherein the joint portion and the sealing portion are disposed in an interior of the tube, a liquid packing compound for sealing between the tube and the joint, wherein the liquid packing compound fills at least an area between the sealing portion and the tube, wherein the sealing portion has a tapered surface, whose diameter increases toward the end of the tube. Thereby, when the joint portion is joined to the end of the tube, a clearance between the tube and the joint portion is entirely filled with the liquid packing compound.