Patent Publication Number: US-2021190132-A1

Title: Tubular body used for power transmission shaft and 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/JP2019/010061, filed on Mar. 12, 2019 and therefore also claims the priority benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2019-033922, filed on Feb. 27, 2019, the entire contents of each of PCT application No. PCT/JP2019/010061 and Japanese Patent Application No. 2019-033922 is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a tubular body used in a power transmission shaft and to a power transmission shaft. 
     BACKGROUND ART 
     A power transmission shaft (propeller shaft) mounted in a vehicle extends in a front-rear direction of the vehicle and transmits power, generated in a motor and subjected to speed reduction in a transmission, to a final drive gear. As such a power transmission shaft, there is a shaft made of a fiber reinforced plastic. 
     As a tubular power transmission shaft made of a fiber reinforced plastic, there is a shaft which includes a main body portion, a connection portion having a larger diameter than the main body portion, and an inclined portion formed between the main body portion and the connection portion and in which a shaft portion of a universal joint is fitted into the connection portion (see, for example, Patent Literature 1). 
     In the aforementioned power transmission shaft, when a vehicle is hit from the front side and impact load exceeding a predetermined value is inputted into the power transmission shaft, the shaft portion slides relative to the connection portion and comes into contact with an inner surface of the inclined portion and the inclined portion thereby fails. This causes an engine and a transmission mounted in a front portion of a vehicle body to quickly retreat and the front portion of the vehicle body absorbs impact energy. 
     Moreover, as another configuration of the power transmission shaft, there is a configuration in which a peripheral wall portion of a connection portion is formed of multiple layers and, when impact load exceeding a predetermined value is inputted into the power transmission shaft, an inner layer portion of the connection portion peels off together with a shaft portion and the shaft portion retreats 
     (see, for example, Patent Literature 2). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Publication No. H09-175202 
     Patent Literature 2: Japanese Patent Application Publication No. H07-208445 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the configuration in which the shaft portion slides relative to the connection portion only when the impact load exceeding the predetermined value is inputted out of the aforementioned conventional power transmission shafts, joining force between the connection portion and the shaft portion needs to be accurately set. To this end, the dimensions of the connection portion and the shaft portion need to be accurately molded and the diameter of the connection portion increases. This causes a problem of increases in manufacturing cost and weight. 
     Moreover, in the configuration in which the inner peripheral portion of the connection portion peels off together with the shaft portion in impact out of the aforementioned conventional power transmission shafts, the peripheral wall portion of the connection portion is formed of multiple layers and this causes a problem of an increase in manufacturing cost. 
     An object of the present invention is to solve the aforementioned problems and provide a power transmission shaft that can achieve low cost and weight reduction, and that surely fail when predetermined load is inputted in a direction of an axis. 
     Solution to Problem 
     A first aspect of the present invention for solving the aforementioned problems is a tubular body used in a power transmission shaft that transmits power by rotating and that is made of a fiber reinforced plastic. The tubular body includes a tubular main body portion that is centered at an axis and a connection portion which is continuous with an end portion of the main body portion and to which a coupling member is joined. A rupture portion that fails when load inputted in an axial direction exceeds a predetermined value is formed in the main body portion and a linear rupture portion is formed on the outer peripheral surface of the weak portion. 
     A second aspect of the present invention for solving the aforementioned problems is a power transmission shaft. The power transmission shaft includes a tubular body used in the power transmission shaft and the coupling member joined to the connection portion. 
     Advantageous Effects of Invention 
     In the power transmission shaft including the tubular body used in the power transmission shaft of the present invention, when load is inputted in the axial direction and exceeds a predetermined value, the weak portion fails and the main body portion is partially crushed. 
     In this configuration, joining force between the connection portion and the coupling member does not have to be accurately set and the molding of the connection portion is facilitated. Moreover, the linear rupture portion is easily processed on the outer peripheral surface of the weak portion. Furthermore, the weak portion can be formed without increasing the size of the main body portion or providing other members in the main body portion. 
     Accordingly, the power transmission shaft of the present invention can achieve cost reduction and weight reduction. Moreover, in the power transmission shaft of the present invention, a load value at which the weak portion fails can be set by adjusting the shape of the linear rupture portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view illustrating a power transmission shaft of a first embodiment. 
         FIG. 2  is a side view illustrating a weak portion of the power transmission shaft in the first embodiment. 
         FIG. 3  is a side view illustrating a state where the weak portion is failed in the power transmission shaft of the first embodiment. 
         FIG. 4  is a side view illustrating a weak portion in a power transmission shaft of a second embodiment. 
         FIG. 5  is a side view illustrating a weak portion in a power transmission shaft of a third embodiment. 
         FIG. 6  is a side view illustrating a power transmission shaft of a fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, a tubular body and a power transmission shaft in each of embodiments are described with reference to the drawings. Note that, in each embodiment, description is given of an example in which the power transmission shaft of the present invention is applied to a propeller shaft mounted in a FF (front-engine, front-drive)-based four-wheel drive vehicle. Moreover, technical elements common among the embodiments are denoted by the same reference numerals and description thereof is omitted. 
     First Embodiment 
     As illustrated in  FIG. 1 , a power transmission shaft  1  of a first embodiment includes a substantially-cylindrical tubular body  2  (pipe) that extends in a front-rear direction of the vehicle. Moreover, the power transmission shaft  1  includes a stub yoke  3  of a Cardan joint joined to a front end of the tubular body  2  and a stub shaft  4  (“coupling member” in the scope of claims) of a constant-velocity joint joined to a rear end of the tubular body  2 . 
     The power transmission shaft  1  is coupled to a transmission, mounted in a front portion of a vehicle body, via the stub yoke  3  and is also coupled to a final drive gear, mounted in a rear portion of a vehicle body, via the stub shaft  4 . 
     When power (torque) is transmitted from the transmission to the power transmission shaft  1 , the power transmission shaft  1  rotates about an axis O 1  and the power is transmitted to the final drive gear. 
     The tubular body  2  is made of a carbon fiber reinforced plastic (CFRP). Note that reinforcement fibers used in the fiber reinforced plastic of the present invention are not limited to carbon fibers and may be glass fibers or aramid fibers. 
     A method of manufacturing the tubular body  2  is such that a continuous carbon fiber is wound around a not-illustrated mandrel to form a molded body and then a pre-preg (sheet obtained by impregnating carbon fibers with a resin) is wound around an outer periphery of the molded body. Accordingly, the power transmission shaft  1  is manufactured by incorporating two crafting methods of the filament winding method and the sheet winding method. 
     In this case, the molded body manufactured by the filament winding method has high mechanical strength (particularly, torsional strength) because the continuity of the fiber (carbon fiber) is maintained. 
     Meanwhile, in the sheet winding method, the carbon fibers can be arranged to extend in an axial direction of the mandrel. Thus, the molded body with high elasticity in the axis O 1  direction can be manufactured. 
     Specifically, in the aforementioned manufacturing method, a fiber layer made of a fiber wound about the axis O 1  and a fiber layer made of fibers extending in the axis O 1  direction are stacked one on top of the other in the tubular body  2  and the tubular body  2  with high mechanical strength and high elasticity in the axis O 1  direction can be manufactured. 
     Note that a PAN (polyacrylonitrile) based fiber is preferable as the fiber aligned in a circumferential direction and pitch fibers are preferable as the fibers aligned in the axis O 1  direction. 
     The method of manufacturing the tubular body  2  of the present invention is not limited to the manufacturing method described above. As a method of manufacturing the tubular body  2 , it is possible to employ a method in which a pre-preg is wound around a mandrel to form a molded body and a continuous carbon fiber is wound around an outer periphery of the molded body. Alternatively, one type of manufacturing method (filament winding method or sheet winding method) may be used as the manufacturing method of the tubular body  2 . 
     The tubular body  2  includes a tubular main body portion  10  having the axis O 1  as a center axis, a first connection portion  20  arranged in front of the main body portion  10 , and a second connection portion  30  arranged behind the main body portion  10 . Moreover, in the power transmission shaft  1 , a weak portion  50  is formed in the main body portion  10 . 
     When the main body portion  10  is cut along a plane whose normal is the axis O 1 , a cross-sectional shape of an outer peripheral surface  15  of the main body portion  10  is a circular shape. 
     Moreover, the main body portion  10  decreases in outer diameter while extending from a center portion toward both end portions and the outer diameter in the center portion is larger than the outer diameters in both end portions. 
     Specifically, when the main body portion  10  is cut along the axis O 1 , the cross-sectional shape of the outer peripheral surface  15  of the main body portion  10  is an arc shape that forms gentle curves and protrudes outward. Thus, the outer shape of the main body portion  10  is a barrel shape having a center portion bulging outward in a radial direction. 
     Although the cross-sectional shape of the outer peripheral surface  15  of the main body portion  10  in the case where the main body portion  10  is cut along the axis O 1  is the arc shape in the tubular body  2  of the first embodiment, the cross-sectional shape of the outer peripheral surface  15  of the main body portion  10  may be formed to be a step shape in the present invention. 
     Alternatively, the cross-sectional shape of the outer peripheral surface  15  of the main body portion  10  in the case where the main body portion  10  is cut along the axis O 1  may be linearly inclined to come closer toward the center while extending from the center portion toward both end portions. 
     A shaft portion (not illustrated) of the stub yoke  3  is fitted into the first connection portion  20 . An inner peripheral surface of the first connection portion  20  has a polygonal shape following a polygonal outer peripheral surface of the shaft portion of the stub yoke  3 . The tubular body  2  and the stub yoke  3  are thus configured not to rotate relative to each other. 
     A shaft portion  5  of the stub shaft  4  is fitted into the second connection portion  30 . An inner peripheral surface of the second connection portion  30  has a polygonal shape following a polygonal outer peripheral surface of the shaft portion  5  of the stub shaft  4 . The tubular body  2  and the stub shaft  4  are thus configured not to rotate relative to each other. 
     A cylindrical inclined portion  40  is formed between the main body portion  10  and the second connection portion  30 . The inclined portion  40  gradually decreases in outer diameter while extending from the main body portion  10  toward the second connection portion  30  and has a truncated cone shape. 
     The inclined portion  40  gradually decreases in wall thickness while extending from an end portion (rear end portion, one end portion) on the second connection portion  30  side (rear side) toward an end portion (front end portion, other end portion) on the main body portion  10  side (front side). Accordingly, the wall thickness is smallest in the front end portion of the inclined portion  40  and the front end portion of the inclined portion  40  forms the weak portion. The weak portion is a portion in which the shear strength of the inclined portion  40  is lowest. 
     Although the wall thickness varies over the entire inclined portion  40  in the tubular body  2 , the wall thickness may vary in a partial section of the inclined portion  40 . 
     Alternatively, the weak portion may be provided in the rear end portion of the inclined portion  40  by causing the inclined portion  40  to gradually decrease in wall thickness while extending from the end portion (front end portion, other end portion) on the main body portion  10  side (front side) toward the end portion (rear end portion, one end portion) on the second connection portion  30  side (rear side). 
     As illustrated in  FIG. 2 , the weak portion  50  is formed in a rear portion  12  of a main body portion  10 . 
     Linear rupture portions  51  obtained by cutting into an outer peripheral surface  15  of the main body portion  10  are formed in the weak portion  50  of the first embodiment. The rupture portions  51  are cut lines linearly extending in the axis O 1  direction (front-rear direction) of the main body portion  10 . 
     Moreover, the linear rupture portions  51  do not penetrate a peripheral wall portion of the main body portion  10  and are configured such that water and dust do not enter the main body portion  10  from the rupture portions  51 . 
     Multiple rupture portions  51  are formed at intervals in a circumferential direction of the outer peripheral surface  15  in the weak portion  50  of the first embodiment. 
     Forming multiple rupture portions  51  in the main body portion  10  as described above forms the weak portion  50  with lower strength than other portions of the main body portion  10 . 
     Note that the number of rupture portions  51  is not limited to a certain number in the present invention and, for example, only one rupture portion  51  may be formed on the outer peripheral surface  15  of the weak portion  50 . 
     Moreover, the length and width of the linear rupture portions  51  are not limited to certain length and width. Furthermore, the linear rupture portions  51  may be curved or bent with respect to the axis O 1  direction. Moreover, multiple rupture portions  51  may be arranged in the axis O 1  direction. 
     In the power transmission shaft  1  including the tubular body  2  of the first embodiment as described above, when the vehicle is hit from the front side and impact load inputted into the power transmission shaft  1  in the axis O 1  direction exceeds a predetermined value, the rupture portions  51  are cut open in the circumferential direction and fail as illustrated in  FIG. 3 . The weak portion  50  (rear portion  12 ) of the main body portion  10  thereby bulges in the radial direction and is crushed. The failure of the power transmission shaft  1  in vehicle impact thus allows the engine and the transmission mounted in the front portion of the vehicle body to quickly retreat and the front portion of the vehicle body absorbs impact energy. 
     As described above, in the tubular body  2  and the power transmission shaft  1  of the first embodiment, as illustrated in  FIG. 2 , joining force between the second connection portion  30  and the stub shaft  3  does not have to be accurately set and the molding of the second connection portion  30  is facilitated. Moreover, the linear rupture portions  51  are easily processed on the outer peripheral surface  15  of the weak portion  50 . Furthermore, the weak portion  50  can be formed without increasing the size of the main body portion  10  or providing other members in the main body portion  10 . 
     Accordingly, the tubular body  2  and the power transmission shaft  1  of the first embodiment can achieve cost reduction and weight reduction. Moreover, in the tubular body  2  and the power transmission shaft  1  of the first embodiment, a load value at which the weak portion  50  fails can be set by adjusting the shape of the linear rupture portions  51 . 
     Moreover, in the tubular body  2  and the power transmission shaft  1 , since the center portion of the main body portion  10  where the bending stress tends to concentrate is formed to have a large outer diameter as illustrated in  FIG. 1 , the center portion has predetermined bending strength. 
     Furthermore, since the tubular body  2  and the power transmission shaft  1  are made of the fiber reinforced plastic, a degree of freedom in design is high and the cost can be further reduced. 
     Second Embodiment 
     Next, a power transmission shaft  101  including a tubular body  102  according to a second embodiment of the present invention is described. 
     As illustrated in  FIG. 4 , the power transmission shaft  101  of the second embodiment includes the tubular body  102 , the stub yoke  3  (see  FIG. 1 ) joined to a front end of the tubular body  102 , and the stub shaft  4  joined to a rear end of the tubular body  102 . 
     The tubular body  102  of the second embodiment includes a main body portion  10 , the first connection portion  20  (see  FIG. 1 ) arranged in front of the main body portion  10 , and the second connection portion  30  arranged behind the main body portion  10 . Moreover, a weak portion  150  is formed in the main body portion  10 . 
     Linear rupture portions  151  formed in the weak portion  150  of the second embodiment are grooves obtained by recessing the outer peripheral surface  15  of the main body portion  10 . The rupture portions  151  linearly extend in the axis O 1  direction (front-rear direction) of the main body portion  10 . 
     When the rupture portions  151  of the second embodiment are cut along a plane whose normal is the axis O 1 , the cross-sectional shape of the rupture portions  151  is a quadrilateral shape. However, in the present invention, the cross-sectional shape of the rupture portions  151  is not limited to a certain shape and may be formed to be, for example, a semi-circular shape or a triangular shape. 
     In the weak portion  150  of the second embodiment, multiple rupture portions  151  are formed at intervals in the circumferential direction of the outer peripheral surface  15 . 
     Note that the number, length, width, shape, and arrangement of the rupture portions  151  in the second embodiment are not limited to certain number, length, width, shape, and arrangement as in the power transmission shaft  1  (see  FIG. 2 ) of the first embodiment. 
     In the power transmission shaft  101  using the tubular body  102  of the second embodiment as described above, when the vehicle is hit from the front side and impact load inputted in the axis O 1  direction exceeds a predetermined value, the rupture portions  151  open in the circumferential direction and fail and the weak portion  150  of the main body portion  10  is crushed. The failure of the power transmission shaft  101  in vehicle impact thus allows the engine and the transmission mounted in the front portion of the vehicle body to quickly retreat and the front portion of the vehicle body absorbs impact energy. 
     As described above, in the tubular body  102  and the power transmission shaft  101  of the second embodiment, the molding of the second connection portion  30  and the main body portion  10  is facilitated as in the power transmission shaft  1  (see  FIG. 2 ) of the first embodiment and, in addition, the linear rupture portions  151  are formed on the outer peripheral surface  15  of the weak portion  150 . Accordingly, the tubular body  102  and the power transmission shaft  101  of the second embodiment can achieve cost reduction and weight reduction. Moreover, in the tubular body  102  and the power transmission shaft  101  of the second embodiment, a load value at which the weak portion  150  fails can be set by adjusting the shape of the linear rupture portions  151 . 
     Third Embodiment 
     Next, a power transmission shaft  201  including a tubular body  202  according to a third embodiment of the present invention is described. 
     As illustrated in  FIG. 5 , the power transmission shaft  201  of the third embodiment includes the tubular body  202 , the stub yoke  3  (see  FIG. 1 ) joined to a front end of the tubular body  202 , and the stub shaft  4  joined to a rear end of the tubular body  202 . 
     The tubular body  202  of the third embodiment includes a main body portion  10 , the first connection portion  20  (see  FIG. 1 ) arranged in front of the main body portion  10 , and the second connection portion  30  arranged behind the main body portion  10 . Moreover, a weak portion  250  is formed in the main body portion  10 . 
     A linear rupture portion  251  formed in the weak portion  250  of the third embodiment is a cut line formed in a helical shape in the circumferential direction of the main body portion  10 . The rupture portion  251  of the third embodiment is helically curved with the axis O 1  being the center axis. Although the rupture portion  251  of the third embodiment is one continuous helical line, in the present invention, the rupture portion  251  may be formed of broken lines arranged at certain intervals. Moreover, the rupture portion  251  may be formed of a helical groove. 
     In the power transmission shaft  201  including the tubular body  202  of the third embodiment as described above, when the vehicle is hit from the front side and impact load inputted in the axis O 1  direction exceeds a predetermined value, the rupture portion  251  is cut open and fails and the weak portion  250  of the main body portion  10  is crushed. The failure of the power transmission shaft  201  in vehicle impact thus allows the engine and the transmission mounted in the front portion of the vehicle body to quickly retreat and the front portion of the vehicle body absorbs impact energy. 
     As described above, in the tubular body  202  and the power transmission shaft  201  of the third embodiment, the molding of the second connection portion  30  and the main body portion  10  is facilitated as in the power transmission shaft  1  (see  FIG. 2 ) of the first embodiment and, in addition, the linear rupture portion  251  is formed on the outer peripheral surface  15  of the weak portion  250 . Accordingly, the tubular body  202  and the power transmission shaft  201  of the third embodiment can achieve cost reduction and weight reduction. 
     Moreover, in the tubular body  202  and the power transmission shaft  201  of the third embodiment, a load value at which the weak portion  250  fails can be set by adjusting the shape of the weak portion  250 . Note that the turning direction of the helical rupture portion  251  is not limited to a certain direction. 
     Fourth Embodiment 
     Next, a power transmission shaft  301  including a tubular body  302  according to a fourth embodiment of the present invention is described. 
     As illustrated in  FIG. 6 , the power transmission shaft  301  of the fourth embodiment includes the tubular body  302 , the stub yoke  3  (see  FIG. 1 ) joined to a front end of the tubular body  302 , and the stub shaft  4  joined to a rear end of the tubular body  302 . 
     The tubular body  302  of the third embodiment includes the main body portion  310 , the first connection portion  20  arranged in front of the main body portion  310 , and a second connection portion  30  arranged behind the main body portion  310 . Moreover, a weak portion  350  is formed in the main body portion  310 . 
     The main body portion  310  of the fourth embodiment has a uniform outer diameter from a front end portion to a rear end portion. Specifically, the outer shape of the main body portion  310  in the fourth embodiment is a straight cylindrical body. 
     Although the main body portion  310  of the fourth embodiment has a uniform outer diameter from the front end portion to the rear end portion, in the present invention, the main body portion  310  may be formed to decrease in outer diameter while extending from a center portion to one end portion and have a uniform outer diameter from the center portion to the other end portion. 
     Linear rupture portions  351  formed in the weak portion  350  of the fourth embodiment are cut lines formed by cutting into an outer peripheral surface  315  of a rear portion  312  of the main body portion  310 . In the fourth embodiment, multiple rupture portions  351  are formed at intervals in a circumferential direction of the outer peripheral surface  315  of the weak portion  350 . 
     Note that the number, length, width, shape, and arrangement of the rupture portions  351  in the fourth embodiment are not limited to certain number, length, width, shape, and arrangement as in the power transmission shaft  1  (see  FIG. 2 ) of the first embodiment. 
     In the power transmission shaft  301  including the tubular body  302  of the fourth embodiment as described above, when the vehicle is hit from the front side and impact load inputted in the axis O 1  direction exceeds a predetermined value, the rupture portions  351  open in the circumferential direction and fail and the weak portion  350  of the main body portion  310  is crushed. The failure of the power transmission shaft  301  in vehicle impact thus allows the engine and the transmission mounted in the front portion of the vehicle body to quickly retreat and the front portion of the vehicle body absorbs impact energy. 
     As described above, in the tubular body  302  and the power transmission shaft  301  of the fourth embodiment, the molding of the second connection portion  30  and the main body portion  310  is facilitated as in the power transmission shaft  1  (see  FIG. 2 ) of the first embodiment and, in addition, the linear rupture portions  351  are formed on the outer peripheral surface  315  of the weak portion  350 . Accordingly, the tubular body  302  and the power transmission shaft  301  of the fourth embodiment can achieve cost reduction and weight reduction. Moreover, in the tubular body  302  and the power transmission shaft  301  of the fourth embodiment, a load value at which the weak portion  350  fails can be set by adjusting the shape of the linear rupture portions  351 . 
     Although the embodiments are described above, the present invention is not limited to the examples described in the embodiments. 
     For example, although the weak portion is formed in the rear portion of the main body portion in the power transmission shafts of the embodiments, the weak portion may be formed in a front portion or an intermediate portion of the main body portion.