Patent Publication Number: US-2021180645-A1

Title: Method for manufacturing tube body used in power transmission shaft

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a PCT Bypass Continuation application of and claims the priority benefit under 35 U.S.C. § 120 to PCT application No. PCT/JP2019/010049, filed on Mar. 12, 2019 and therefore also claims the priority benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2019-033777 filed on Feb. 27, 2019, the disclosures of all of which (both the PCT application No. PCT/JP2019/010049 and Japanese Patent Application No. 2019-033777) are hereby incorporated in their entireties by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a method for manufacturing a tube body used in a power transmission shaft. 
     BACKGROUND OF THE INVENTION 
     A power transmission shaft (propeller shaft) mounted in a vehicle includes a tube body extending in a front-rear direction of the vehicle, and transmits the power generated by an engine and decelerated by a transmission to a final reduction gear by means of the tube body. A tube body used in such a power transmission shaft includes one made of fiber-reinforced plastic. A method for manufacturing a tube body, made of fiber-reinforced plastic and used in a power transmission shaft, for example, includes winding a continuous fiber impregnated with a thermosetting resin around a mandrel in multiple layers to form a cylindrical molded body. Then, the molded body is heated to cure the resin to form a cylindrical tube body. Subsequently, the mandrel is withdrawn from an opening at an end of the cured tube body, to complete the manufacturing process (see Japanese Patent Application Publication No. H03-265738). 
     SUMMARY OF THE INVENTION 
     Problems to be Solved 
     Incidentally, with respect to the shape of the tube body, it has been studied in recent years to make the tube body into a so-called barrel shape in which the central portion bulges outward in the radial direction more than both ends. However, when a mandrel in a barrel shape is used to form a tube body of the above shape, the central part of the mandrel bulges outward to inhibit the mandrel from being removed out of the tube body through the opening of the tube body. Therefore, a new manufacturing method that can manufacture a tube body without using any core material (mandrel) is desired 
     The present invention has been made to solve these problems and is intended to provide a method for manufacturing a tube body used in a power transmission shaft, without using any core material. 
     Solution to Problems 
     A first aspect of the present invention, for solving the aforementioned problems, provides a method for manufacturing a tube body made of fiber-reinforced plastic and used in a power transmission shaft, including: a generating step of disposing an uncured fiber-reinforced resin on a cavity surface of a mold and generating a resin body in a cylindrical shape; and a curing step of supplying a fluid inside the resin body and curing the resin of the resin body. 
     In addition, a second aspect of the present invention, for solving the aforementioned problems, provides a method for manufacturing a tube body made of fiber-reinforced plastic and used in a power transmission shaft, including: a preparing step of disposing a cylindrical bulging body having a fiber wound therearound in a mold; a bulging step of supplying a fluid into the bulging body to bulge the bulging body; a supplying step of supplying uncured resin within the mold; and a curing step of curing the uncured resin. 
     Advantageous Effects of the Invention 
     According to the present invention, a tube body having a shape to follow the mold is manufactured. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a power transmission shaft; 
         FIG. 2  is a cross-sectional view of a main body of a tube body used in the power transmission shaft, taken along an axial direction; 
         FIG. 3  is a flowchart of manufacturing a tube body according to a first embodiment; 
         FIG. 4  illustrates a preparing step of manufacturing the tube body according to the first embodiment; 
         FIG. 5  illustrates a generating step of manufacturing the tube body according to the first embodiment; 
         FIG. 6  illustrates a curing step of manufacturing the tube body according to the first embodiment; 
         FIG. 7  illustrates a removing step of manufacturing the tube body according to the first embodiment; 
         FIG. 8  illustrates a curing step of manufacturing a tube body according to a second embodiment; 
         FIG. 9  illustrates a generating step of manufacturing a tube body according to a third embodiment; 
         FIG. 10  is a flowchart of manufacturing a tube body according to a fourth embodiment; 
         FIG. 11  illustrates a preparing step of manufacturing a tube body according to the fourth embodiment; and 
         FIG. 12  illustrates a supplying step of manufacturing the tube body according to the fourth embodiment. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     Next, a method for manufacturing a tube body used in a power transmission shaft will be described in embodiments with reference to the drawings. Technical elements common to the embodiments are denoted by common reference numerals and descriptions thereof are omitted. First, a power transmission shaft to be manufactured by the manufacturing methods is described. 
     &lt;Power Transmission Shaft&gt; 
     As shown in  FIG. 1 , a power transmission shaft  101  is a propeller shaft mounted on a front-engine front-drive (FF) based four-wheel drive vehicle. The power transmission shaft  101  includes a tube body  102  in a substantially cylindrical shape extending in a front-rear direction of a vehicle, a stub yoke  103  of a cross shaft joint joined to a front end of the tube body  102 , and a stub shaft  104  of a constant velocity joint joined to a rear end of the tube body  102 . The stub yoke  103  is a coupling member to couple a transmission mounted at a front of a vehicle body with the tube body  102 . The stub shaft  104  is a coupling member to couple a final reduction gear mounted at a rear of the vehicle body with the tube body  102 . When power (torque) is transmitted from the transmission, the power transmission shaft  101  rotates about an axis O 1  and transmits the power to the final reduction gear. 
     The tube body  102  is formed of carbon fiber reinforced plastic (CFRP). A fiber layer formed of fibers circumferentially extending about the axis O 1  and a fiber layer formed of fibers extending along the axis O 1  are stacked inside the tube body  102 . This allows the tube body  102  to have high mechanical strength and high elasticity along the axis O 1 . In addition, a PAN (Polyacrylonitrile) fiber is preferred as a fiber oriented in the circumferential direction, and pitch fibers are preferred as fibers oriented along the axis O 1 . Note that the fibers used in the fiber-reinforced plastic are not limited to carbon fibers in the present invention, and may be glass fibers or aramid fibers. The tube body  102  includes a main body  110  to make up the majority of the tube body  102 , a first connection portion  120  disposed at a front of the main body  110 , a second connection portion  130  disposed at a rear of the main body  110 , and an inclined portion  140  located between the main body  110  and the second connection portion  130 . 
     Note that a shape of the tube body  102  is exaggeratedly depicted in  FIG. 2  and subsequent figures for the purpose of illustrating a shape of the tube body  102 . As shown in  FIG. 2 , the first connection portion  120  continues to a front end portion  111  of the main body  110 , and the inclined portion  140  continues to a rear end portion  112  of the body  110 . 
     When the main body  110  is sectioned in a plane normal to the axis O 1 , an outer periphery  114  and an inner periphery  115  of the main body  110  each have a cross section in a circular shape. An outer diameter of the main body  110  decreases from a central portion  113  toward both ends (the front end  111  as one end, and the rear end  112  as the other end), and an outer diameter R 1  of the central portion  113  is larger than outer diameters R 2  of both ends (the front and rear ends  111 ,  112 ). Note that an inner diameter of the main body  110  also decreases from the central portion  113  of the main body  110  toward both ends (the front and rear ends  111 ,  112 ). 
     When the main body  110  is sectioned along the axis O 1 , the outer periphery  114  and inner periphery  115  of the main body  110  each have a cross section gently curved and the central portion  113  protrudes outward in an arc. Accordingly, the outer shape of the main body  110  has a barrel shape, with the central portion  113  bulging radially outward. With respect to the cross-sectional shapes, a plate thickness of the main body  110  decreases from both ends (the front and rear ends  111 ,  112 ) toward the central portion  113 , and a plate thickness T 1  of the central portion  113  is smaller than a plate thickness T 2  of both ends (the front and rear ends  111 ,  112 ). 
     As shown in  FIG. 1 , a shaft portion  103   a  of the stub yoke  103  is fitted into the first connection portion  120 . The outer periphery of the shaft portion  103   a  is formed in a polygonal shape. The first connection portion  120  has an inner periphery thereof formed in a polygonal shape, to follow the outer periphery of the shaft portion  103   a . This configuration prevents the stub yoke  103  and the tube body  102  from rotating relative to each other. A shaft portion  104   a  of the stub shaft  104  is fitted into the second connection portion  130 . The second connection portion  130  has an inner periphery thereof formed in a polygonal shape, to follow the outer periphery of the shaft portion  104   a . This configuration prevents the stub shaft  104   a  and the tube body  2  from rotating relative to each other. 
     An outer diameter of the inclined portion  140  gradually decreases from the main body  110  toward the first connection portion  120 , to have a conical trapezoidal shape. A plate thickness of the inclined portion  140  gradually decreases from an end thereof closer to the second connection portion  130  (rear side) toward an end thereof closer to the main body  110  (front side). This causes the inclined portion  140  to have the smallest plate thickness at a front end thereof as a weak portion. Based on above configuration, if a vehicle is collided from up ahead to have a collision load inputted to the power transmission shaft  101 , a shear force acts on the inclined portion  140 , which is inclined with respect to the axis O 1 . If the shear force acting on the inclined portion  140  exceeds a predetermined value, damaged is the front end (weak portion) of the inclined portion  140 . This allows the engine and transmission mounted on the front of the vehicle body to be quickly moved rearward, in the event of a vehicle collision, to absorb the collision energy by the front of the vehicle body. 
     According to the above-described tube body  102 , the central portion  113  of the main body  110 , where bending stress is likely concentrated, has the outer diameter R 1  increased to have a predetermined bending rigidity. In contrast, both ends of the main body  110  (the front and rear ends  111 ,  112 ), where bending stresses are less likely concentrated, have the outer diameter R 2  decreased so as to be reduced in weight. In addition, the central portion  113  of the main body  110  has the small plate thickness T 1  to have a reduced weight. Then, the tube body  102  has the main body  110  reduced in weight while maintaining a predetermined bending rigidity at the central portion  113 , to improve the primary bending resonance point of the tube body  102 . 
     First Embodiment 
     As shown in  FIG. 3 , a manufacturing method of a first embodiment includes a preparing step (step S 1 ) of disposing an uncured fiber-reinforced resin in a mold  1 , a generating step (step S 2 ) of generating a resin body  15  in a cylindrical shape with the mold  1  closed, a curing step (step S 3 ) of heating the resin body  15  so as to be cured, and a removing step (step S 4 ) of removing the tube body  102  used in the power transmission shaft  101  from the mold  1 . 
     &lt;Preparing Step&gt; 
     As shown in  FIG. 4 , the preparing step (step S 1 ) of the first embodiment involves disposing a plurality of prepregs on a cavity surface  4  to dispose fiber-reinforced resin in the mold  1 . 
     The mold  1  has an upper mold  2  (not shown in  FIG. 4 , and then see  FIG. 5  and subsequent figures) and a lower mold  3 . The cavity surface  4  is formed in a lower surface of the upper mold  2  and an upper surface  3   a  of the lower mold  3  to form an outer shape of the tube body  102 . The cavity surface  4  of the first embodiment is elongated in one direction. The cavity surface  4  has, in order from one end in a longitudinal direction thereof toward the other end, a first-connection-portion mold area  5 , a main-body mold area  6 , an inclined-portion mold area  7 , and a second-connection-portion mold area  8 . The first-connection-portion mold area  5  is an area to form an outer shape of the first connection portion  120  of the tube body  102 . The main-body mold area  6  is an area to form an outer shape of the main body  110 . The inclined-portion mold area  7  is an area to form an outer shape of the inclined portion  140 . The second-connection-portion mold area  8  is an area to form an outer shape of the second connection part  130 . 
     The lower surface of the upper mold  2  and the upper surface  3   a  of the lower mold  3  have two communicating holes  9  to communicate the inside of the mold  1  with outside when the mold is tightened. One of the communicating holes  9  is disposed on “one end” side of the first-connection-portion mold area  5 , and another is disposed on “the other end” side of the second-connection-portion mold area  8 . 
     A thermosetting resin is used as the resin of the prepreg. Additionally, the thermosetting resin is used in an uncured state. Note that a semi-cured resin may also be used, even with a wording of “an uncured state.” That is, the resin even when cured to some extent can be deformed into a shape along the cavity surface  4  of the mold  1 , to allow for being used in a semi-cured state. The prepreg may not be of a size to cover all over the cavity surface  4  alone. In other words, a plurality of prepregs of a size to cover only a part of the cavity surface  4  may be joined together to cover all over the cavity surface  4 . Regarding the prepreg, the number of sheets to be disposed is adjusted so as to achieve a predetermined thickness after curing. For example, the prepreg disposed on the main-body mold area  6  is disposed so that the number of layers decreases from both ends in the longitudinal direction toward the central portion, to cause the central portion to have a smaller thickness than both ends. In addition, a mold release agent is applied on the cavity surface  4  in the preparing step, before the prepreg is disposed thereon. Then, according to this step, resin portions  10  in a semi-cylindrical shape are formed on the respective cavity surfaces  4  of the upper mold  2  and lower mold  3 , as shown in  FIG. 4 . 
     &lt;Generating Step&gt; 
     As shown in  FIG. 5 , the generating step (step S 2 ) of the first embodiment disposes supply pipes  11  of a heating device to be described below in the communicating holes  9  of the lower mold  3 . Then, a bulging body  12  of the heating device is held to tips of the supply pipes  11  of the heating device, and is positioned above the resin portion  10  in the lower mold  3 . Then, the upper mold  2  is superimposed on the lower mold  3 , and the mold  1  is closed and fastened to prevent the upper mold  2  from being loosened from the lower mold  3 . According to this step, circumferential ends of the resin portion  10  disposed on the cavity surface  4  of the lower mold  3  come into contact with circumferential ends of the resin portion  10  disposed on the cavity surface  4  of the upper mold  2 , to generate the resin body  15  in a cylindrical shape. In addition, the bulging body  12  is disposed in the center of the resin body  15 . 
     &lt;Curing Step&gt; 
     As shown in  FIG. 6 , the curing step (step S 3 ) of the first embodiment is a step of supplying high-temperature fluid from a heating device via the supply pipe  11  into the bulging body  12  to cure the resin of the resin body  15 . The bulging body  12  is an elastic member in a cylindrical shape and bulges in proportion to an amount of fluid flowing thereinto. The elastic member is made of a material having heat resistance to high-temperature fluid, such as silicone rubber, fluoro rubber, or acrylic rubber. Note that the bulging body  12  is sealed at both ends thereof to prevent the fluid supplied through the supply pipe  11  from being leaked. The heating device is a device to generate and supply high-temperature fluid. The fluid supplied in the first embodiment is a liquid. The temperature of the liquid is set to a temperature at which the resin body  15  is cured (e.g., 130° to 180°). The liquid is supplied to the extent that the bulging body  12  bulges to cause an outer periphery of the bulging body  12  to contact an inner periphery of the resin body  15 . According to this step, the bulged bulging body  12  contacts the resin body  15 , to transmit the temperature of the liquid via the bulging body  12  to the resin body  15 , as shown in  FIG. 6 . As a result, the resin of the resin body  15  is cured to have the power transmission shaft  101 . 
     &lt;Removing Step&gt; 
     The removing step (step S 4 ) of the first embodiment moves the upper mold  2  to open the mold  1 . In addition, the heating device is driven to recover the liquid supplied into the bulging body  12 . This causes the bulging body  12  to have the pressure therein reduced to restore an original shape thereof in a cylindrical shape. Next, the supply pipes  11  are removed from the bulging body  12 , and the bulging body  12  restored to a cylindrical shape is also removed from the tube body  102  as shown in  FIG. 7 . As a result, there is nothing to hold the power transmission shaft  101  to allow the tube body  102  to be removed from the lower mold  3 . 
     As described above, according to the first embodiment, the tube body  102  in a so-called barrel shape is manufactured without using any core material. 
     Second Embodiment 
     As shown in  FIG. 8 , a method of a second embodiment for manufacturing a tube body  202  used in a power transmission shaft  201  includes a preparing step (step S 1 ) of disposing a fiber reinforced resin in a mold  21 , a generating step (step S 2 ) of closing the mold  21  and generating a resin body  35  in a cylindrical shape, a curing step (step S 3 ) of heating the resin so as to be cured, and a removing step (step S 4 ) of removing the power transmission shaft  201  from the mold  21  (see  FIG. 3 ). Hereinbelow, a description is given, focusing on differences from the first embodiment. 
     The preparing step (step S 1 ) of the second embodiment forms resin portions  30  in a semi-cylindrical shape, by a hand lay-up technique, on cavity surfaces  24  of an upper mold  22  and a lower mold  23 . In other words, fibers are disposed on the cavity surfaces  24  of the mold  21  and an uncured resin (thermosetting resin) is applied to the cavity surfaces  24  to form fiber-reinforced resin (resin portion  30 ) on the cavity surfaces  24 . This hand lay-up technique allows for fine-tuning a thickness of the resin portion  30  formed on the cavity surface  24 . 
     The cavity surface  24  of the mold  21  is formed with the first-connection-portion mold area  5 , a main-body mold area  26 , the inclined-portion mold area  7 , and the second-connection-portion mold area  8 . Here, the main-body mold area  26  includes a first surface  26   a  formed to have a constant diameter from the central portion toward the first-connection-portion mold area  5 , and a second surface  26   b  formed to have a diameter gradually decreasing from the central portion toward the inclined-portion mold area  7 . According to the mold  21 , the shape of the main body  210  of the tube body  202  is in a shape having a constant diameter from a central portion  213  to a front end  211  and a diameter decreasing from the central portion  213  toward a rear end  212 . 
     In the curing step (step S 3 ) of the second embodiment, the heating device supplies a high-temperature gas via the supply pipe  11 . According to the step, the high-temperature gas is supplied into the resin body  35  to cure the resin of the resin body  35 . Additionally, in the curing step (step S 3 ), the mold  21  is heated by a heater, not shown, or the like. This allows for heating the resin body  35  from the cavity surface  24  of the mold  21 , to shorten a time of heating the resin body  35 . 
     According to the second embodiment, the tube body  202  made of fiber-reinforced plastic is manufactured without using any core material. 
     Third Embodiment 
     As shown in  FIG. 9 , a manufacturing method of a third embodiment includes a preparing step (step S 1 ) of disposing fiber-reinforced resin in a mold  41 , a generating step (step S 2 ) of closing the mold  41  and generating a resin body  55 , a curing step (step S 3 ) of heating the resin so as to be cured, and a removing step (step S 4 ) of removing a tube body  302  from the mold  41  (see  FIG. 3 ). Hereinbelow, a description is given, focusing on differences from the first embodiment. 
     In the preparing step (step S 1 ) of the third embodiment, a cavity surface  44  of the mold  41  is provided with the first-connection-portion mold area  5 , a main-body mold area  46 , the inclined-portion mold area  7 , and the second-connection-portion mold area  8 . The main-body mold area  46  has a constant diameter from one end (first-connection-portion mold area  5 ) to the other end (inclined-portion mold area  7 ). The mold  41  allows for manufacturing the tube body  302  having a main body  310  in a cylindrical shape formed with a constant diameter. 
     A bulging body  52  of the third embodiment has annular members  53  wound around on an outer periphery thereof, at ends in a longitudinal direction thereof. The annular member  53  is formed of an elastic material such as silicone rubber, fluoro rubber, and acrylic rubber. This causes the bulging body  52 , when bulged, to be less bulged at the ends than at the center portion. Accordingly, the resin of the resin body  55  on the first-connection-portion molding area  5  and the second-connection-portion molding area  8  is prevented from being pressed more than necessary by the bulging body  52  to flow to other molding areas. 
     Fourth Embodiment 
     As shown in  FIG. 10 , a manufacturing method of a fourth embodiment includes a preparing step (step S 11 ) of disposing a bulging body  72  having a fiber  71  wound therearound in a mold  61 , a bulging step (step S 12 ) of supplying fluid into the bulging body  72  and bulging the bulging body  72 , a supplying step (step S 13 ) of supplying uncured resin into the mold  61 , a curing step (step S 14 ) of curing the uncured resin, and a removing step (step S 15 ) of removing the tube body  102  from the mold  61 . 
     &lt;Preparing Step&gt; 
     The preparing step (step S 11 ) prepares the mold  61 . As shown in  FIG. 11 , the mold  61  has an upper mold  62  and a lower mold  63 . Cavity surfaces  64  of the upper mold  62  and lower mold  63  each have, in order from one end in the longitudinal direction thereof toward the other end, a first-connection-portion mold area  65 , a main-body mold area  66 , an inclined-portion mold area  67 , and a second-connection-portion mold area  68 , as with the mold  1  described in the first embodiment. The mold  61  is also formed with communicating holes  9  penetrated by the supply pipes  11  and a spool  69  to supply resin into the mold  61 . 
     The bulging body  72  is of the same structure as the bulging body  12  described in the first embodiment. The fiber  71  is used to reinforce strength of the tube body  102 , and may be a carbon fiber, a glass fiber, or an aramid fiber. Note that a technique of winding the fiber  71  and orientation of the fiber  71  are not particularly limited. The bulging body  72  is arranged so as to be held to the tips of the supply pipes  11  having penetrated the communicating holes  9 . Accordingly, the bulging body  72  is fixed in the mold  61  so as to be separated from the cavity surfaces  64 . 
     &lt;Bulging Step&gt; 
     In the bulging step (step S 12 ), a fluid is supplied from a heating device via the supply pipe  11  into the bulging body  72 . The fluid is supplied to the extent that the bulging body  72  bulges to have an outer periphery of the bulging body  72  contacting the cavity surfaces  64  (see  FIG. 12 ). Note that windings of the fiber  71  wound around the bulging body  72  define gaps therebetween, and the gaps are enlarged in the bulging step. Thus, the gaps define a flow channel through which the resin flows in the supplying step to follow. In addition, the temperature of the fluid is set to one at which the resin is not cured in the supplying step. 
     &lt;Supplying Step&gt; 
     In the supplying step (step S 13 ), the uncured resin is supplied into the mold  61  through the spool  69 . Accordingly, the resin flows through the gaps between the windings of the fiber  71 , to form a resin body  75  in a cylindrical shape between the outer periphery of the bulging body  72  and the cavity surfaces  64 , as shown in  FIG. 12 . 
     &lt;Curing Step&gt; 
     In the curing step (step S 14 ), the fluid in the bulging body  72  is discharged through one of the two supply pipes  11  while the high temperature fluid is supplied into the bulging body  72  through the other supply pipe  11 . Here, the temperature of the fluid to be supplied is set to one at which the resin can be cured (e.g., 130° to) 180°. According to the step, the resin body  75  is cured to form the tube body  102  made of fiber-reinforced resin. 
     &lt;Removing Step&gt; 
     The removing step (step S 15 ) recovers the liquid in the bulging body  72 . This causes the bulging body  72  to have the pressure therein decreased and to be restored to the original shape of a cylinder. Next, the mold  61  is opened and the bulging body  72  is removed from the tube body  102 , to finish the tube body  102 . 
     As described above, according to the fourth embodiment, the tube body  102  in a so-called barrel shape is manufactured without using any core material. 
     Hereinabove, the embodiments have been described, but the present invention is not limited thereto. For example, connection-portion mold areas (the first-connection-portion mold area  5  and second-connection-portion mold area  8 ) of the cavity surface of the mold, which form connection portions (the first and second connection portions  120 ,  130 ) to connect with the stub yoke  103  or stub shaft  104 , may have a cross section in a polygonal shape. This causes the first and second connection portions  120 ,  130  to have a cross section formed in a polygonal shape. Accordingly, time and effort required to separately form the first and second connection portions  120 ,  130  into polygonal shapes are eliminated. 
     In addition, the annular member  53  is used as an example of restricting the bulging amount of the bulging body, but alternatively a thickness of the bulging body itself may be changed to restrict the bulging amount. 
     Further, regarding the tube body of the present invention, the cross section of the main body  110 , taken along the axis O 1 , is not limited to have an arc shape. For example, the cross section of the main body  110 , taken along the axis O 1 , may have a stepped shape. That is, the main-body mold area  6  of the cavity surface of the mold may have a cross section, taken along the longitudinal direction, in a stepped shape. 
     Furthermore, the tube bodies manufactured by the manufacturing methods of the present invention are not limited to those described above. For example, a plate thickness of the inclined portion may gradually decrease from an end closer to the main body (front side) toward an end closer to the second connection portion (rear side). Accordingly, the inclined portion has the smallest plate thickness at a rear end thereof as a weak portion. Alternatively, a recess may circumferentially be formed in an outer or inner periphery of the inclined portion so as to have a plate thickness of the recess partly changed to form a weak portion. 
     LEGEND FOR REFERENCE NUMERALS 
     
         
         
           
               1 ,  21 ,  41 ,  61  mold;  4 ,  24 ,  44 ,  64  cavity surface;  6 ,  26 ,  46 ,  66  main-body mold area;  10 ,  30  resin portion;  11  supply pipe;  12 ,  52 ,  72  bulging body;  15 ,  35 ,  55 ,  75  resin body; and  101 ,  201 ,  301  power transmission shaft.