Patent Publication Number: US-2021180644-A1

Title: Tube 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/JP2019/010029, filed on Mar. 12, 2019 and therefore also claims the priority benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2019-033434 filed on Feb. 27, 2019, the disclosures of all of which (both the PCT application No. PCT/JP2019/010029 and Japanese Patent Application No. 2019-033434) are hereby incorporated in their entireties by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a tube for a power transmission shaft and a power transmission shaft. 
     BACKGROUND OF THE INVENTION 
     A power transmission shaft (propeller shaft) mounted in a vehicle includes a tube 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. A tube for such a power transmission shaft includes one made of fiber-reinforced plastic. A tube made of fiber-reinforced plastic disclosed in Japanese Patent Application Publication No. H03-265738, for example, is in a cylindrical shape, to have a constant outer diameter end-to-end in a longitudinal direction of the tube, so that a middle portion of the tube has the same outer diameter as an end portion of the tube. 
     SUMMARY OF THE INVENTION 
     Problems to be Solved 
     Incidentally, the tube made of fiber-reinforced plastic has improved bending rigidity in order to improve the primary bending resonance point. For this reason, the outer diameter of the tube has been increased to have the tube increased in weight. 
     The present invention has been made to solve these problems and is intended to provide a tube for a power transmission shaft and a power transmission shaft, which are reduced in weight. 
     Solution to Problems 
     A tube for a power transmission shaft according to a first aspect of the present invention, for solving the aforementioned problems, is made of fiber-reinforced plastic, rotated to transmit power, and includes a main body in a shape of cylinder about an axis, wherein the main body has an outer diameter thereof gradually decreasing from a central portion thereof toward both ends thereof, and has a thickness thereof gradually decreasing from said both ends toward the central portion. 
     A tube for a power transmission shaft according to a second aspect of the present invention, for solving the aforementioned problems, is made of fiber-reinforced plastic, rotated to transmit power, and includes a main body in a shape of cylinder about an axis, wherein the main body has an outer diameter thereof formed to have the same diameter from one end thereof to a central portion thereof and gradually decreasing from the central portion toward the other end thereof, and has a thickness thereof gradually decreasing from said the other end toward the central portion and uniformly formed from the central portion to said one end. 
     Advantageous Effects of the Invention 
     According to the present invention, the central portion of the main body, where bending stresses are likely concentrated, has a larger outer diameter to secure predetermined bending rigidity. In contrast, both ends (or the other end) of the main body, where bending stresses are less likely concentrated, have a smaller outer diameter to have a reduced weight. In addition, the central portion of the main body is reduced in thickness to have a reduced weight. Accordingly, the entire main body is reduced in weight. Additionally, an amount of material required for manufacturing is reduced to have a reduced cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a tube for a power transmission shaft of a first embodiment; 
         FIG. 2  is a cross-sectional view of a main body of the tube of the first embodiment, taken along an axial direction thereof; 
         FIG. 3  is a cross-sectional view of an inclined portion and a second connection portion of the tube of the first embodiment, taken along the axial direction; 
         FIG. 4  is a cross-sectional view of a main body of a tube of a second embodiment, taken along an axial direction thereof; 
         FIG. 5  is a cross-sectional view of a main body of a tube of a third embodiment, taken along an axial direction thereof; and 
         FIG. 6  is a cross-sectional view of a main body of a tube of a fourth embodiment, taken along an axial direction thereof. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     Next, power transmission shafts having tubes of respective embodiments are described with reference to the drawings. Note that the embodiments each describe a case where the power transmission shaft of the present invention is applied to a propeller shaft installed in a front-engine, front-drive (FF) based four-wheel drive vehicle. Technical elements common to the embodiments are denoted by common reference numerals and duplicate descriptions are avoided. 
     First Embodiment 
     As shown in  FIG. 1 , a power transmission shaft  1  includes a tube  2  in a substantially cylindrical shape extending in a front-rear direction of a vehicle, a stub yoke  3  of a cardan joint joined to a front end of the tube  2 , and a stub shaft  4  of a constant velocity joint joined to a rear end of the tube  2 . The stub yoke  3  is a coupling member to couple a transmission mounted at a front of a vehicle body with the tube  2 . The stub shaft  4  is a coupling member to couple a final reduction gear mounted at a rear of the vehicle body with the tube  2 . When power (torque) is transmitted from the transmission, the power transmission shaft  1  rotates about an axis O 1  and transmits the power to the final reduction gear. 
     The tube  2  is formed of carbon fiber reinforced plastic (CFRP). 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. 
     A method of manufacturing the tube  2  includes wrapping a continuous carbon fiber around a mandrel, which is not shown, to form a first molded body, and then wrapping a prepreg (a sheet of carbon fibers impregnated with a resin) around a periphery of the first molded body. Therefore, the tube  2  is manufactured using two techniques, a filament winding technique and a sheet winding technique. Here, the first molded body produced by the filament winding technique has high mechanical strength (especially torsional strength) because the continuity of a fiber (carbon fiber) is maintained. In contrast, the sheet winding technique allows the carbon fibers to be arranged so as to extend in an axial direction of the mandrel, to produce a second molded body with high elasticity along the axis O 1 . In other words, according to the above-described manufacturing method, a fiber layer formed of fibers wound about the axis O 1  and a fiber layer formed of fibers extending along the axis O 1  are stacked inside the tube  2 , to allow for manufacturing the tube  2  having high mechanical strength and high elasticity along the axis O 1 . Note that 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 . 
     The present invention is not limited to the above-mentioned manufacturing method. The tube  2  of the present invention may be manufactured by wrapping a prepreg around a mandrel to form a first molded body, and then wrapping a continuous carbon fiber around a periphery of the first molded body. Alternatively, the power transmission shaft of the present invention may be manufactured by a single manufacturing technique (filament winding technique or sheet winding technique). 
     The tube  2  includes a main body  10  to make up the majority of the tube  2 , a first connection portion  20  disposed at a front of the main body  10 , a second connection portion  30  disposed at a rear of the main body  10 , and an inclined portion  40  located between the main body  10  and the second connection portion  30 . 
       FIG. 2  shows only the main body  10  of the tube  2 , with exaggeration on features of the main body  10  for the purpose of illustrating the shape of the main body  10 . As shown in  FIG. 2 , the first connection portion  20  continues to a front end  11  of the main body  10 , and the inclined portion  40  continues to a rear end  12  of the main body  10 . 
     When the main body  10  is sectioned in a plane normal to the axis O 1 , an outer periphery  14  and an inner periphery  15  of the main body  10  each have a cross section in a circular shape. The outer diameter of the main body  10  decreases from a central portion  13  toward both ends (the front and rear ends  11 ,  12 ), and an outer diameter R 1  of the central portion  13  is larger than outer diameters R 2  of said both ends (the front and rear ends  11 ,  12 ). Similarly, an inner diameter of the main body  10  also decreases from the central portion  13  of the main body  10  toward both ends (the front and rear ends  11 ,  12 ). 
     When the main body  10  is sectioned along the axis O 1 , the outer periphery  14  and inner periphery  15  of the main body  10  each have a cross section gently curved and protruding outward in an arc. Accordingly, the outer shape of the main body  10  has a barrel shape, with the central portion  13  bulging radially outward. With respect to the cross-sectional shapes, the curvature of the inner periphery  15  is greater than that of the outer periphery  14 . In other words, a plate thickness of the main body  10  decreases from both ends (the front and rear ends  11 ,  12 ) toward the central portion  13 , and a plate thickness T 1  of the central portion  13  is smaller than a plate thickness T 2  of said both ends (the front and rear ends  11 ,  12 ). 
     As shown in  FIG. 1 , a shaft portion  3   a  of the stub yoke  3  is fitted into the first connection portion  20 . The outer periphery of the shaft portion  3   a  is formed in a polygonal shape. The first connection portion  20  has an inner periphery thereof formed in a polygonal shape, to follow the outer periphery of the shaft portion  3   a . This configuration prevents the stub yoke  3  and the tube  2  from rotating relative to each other. 
     As shown in  FIG. 3 , a shaft portion  5  of the stub shaft  4  is fitted into the second connection portion  30 . The shaft portion  5  of the stub shaft  4  has an outer periphery  6  thereof formed in a polygonal shape. The second connection portion  30  has an inner periphery  31  thereof formed in a polygonal shape, to follow the outer periphery  6  of the shaft portion  5  of the stub shaft  4 . This configuration prevents the tube  2  and the stub shaft  4  from rotating relative to each other. In addition, the outer diameter of the second connection portion  30  is smaller than that of the rear end  12  of the main body  10 . Note that reduction of the second connection portion  30  in diameter leads to reduction in torsional strength. Therefore, the plate thickness of the second connection portion  30  of the present embodiment is formed larger than that of the rear end  12  of the main body  10 , to have a predetermined torsional strength. 
     The inclined portion  40  is a cylindrical portion formed between the main body  10  and the second connection portion  30 . The inclined portion  40  has the outer diameter thereof gradually decreasing from the main body  10  toward the first connection portion  20 , to have a conical trapezoidal shape. The inclined portion  40  has the plate thickness thereof gradually decreasing from an end thereof closer to the second connection portion  30  (rear side) towards an end thereof closer to the main body  10  (front side). This causes the inclined portion  40  to have the smallest plate thickness at a front end  41  thereof as a vulnerable portion. 
     According to the above-described tube  2  for the power transmission shaft  1 , the central portion  13  of the main body  10 , where bending stress is likely concentrated, has the outer diameter R 1  increased to have predetermined bending rigidity. In contrast, both ends of the main body  10  (the front and rear ends  11 ,  12 ), where bending stresses are less likely concentrated, have the outer diameter R 2  decreased so as to be reduced in weight. Then, the main body  10  is reduced in weight while maintaining predetermined bending rigidity at the central portion  13 , to improve the primary bending resonance point of the main body  10 . 
     In addition, as the bending stress to act on the main body  10  of the tube  2  varies (decreases) from the central portion  13  toward both ends (the front and rear ends  11 ,  12 ), in an arc (in a curve), the outer shape of the tube  2  of the present embodiment is formed in an arc shape so as to be reduced in size in proportion to a rate of change. Thus, the main body  10  is reduced in weight, while having predetermined bending rigidity not only at the central portion  13  and both ends (the front and rear ends  11 ,  12 ), but also at intermediate portions between the central portion  13  and both ends. In short, the main body  10  of the tube  2  is reduced in weight to an extreme degree, while having the predetermined bending rigidity required for the respective portions, to greatly improve the primary bending resonance point of the main body  10 . 
     Further, the main body  10  of the tube  2  has the plate thickness thereof increasing from the central portion  13  toward both ends (the front and rear ends  11 ,  12 ) in proportion to the rate of change in outer diameter (rate of reduction in diameter), in order to accommodate torsional stress. This ensures a predetermined strength corresponding to the torsional stresses acting uniformly on every portion of the main body  10 . In short, the main body  10  of the tube  2  has strength corresponding to the predetermined bending and torsional stresses. 
     Still further, both ends of the tube  2  (the first and second connection portions  20 ,  30 ) need to be reduced in size and have the strength so as to be coupled with metal parts (the stub yoke  3  and stub shaft  4 ). According to the tube  2  of the present embodiment, although the central portion  13  has a large diameter, the first connection portion  20  and the second connection portion  30  are reduced in diameter and increased in plate thickness, to satisfy the requirements of being reduced in size and ensuring strength. 
     Still further, the central portion  13  is reduced in thickness and both ends (the front and rear ends  11 ,  12 ) are reduced in diameter, to have an amount of material required for manufacturing the tube  2  reduced. Then, costs may be reduced. Additionally, the tube  2  is formed of fiber-reinforced plastic, to have a high degree of freedom in design, and then costs may further be reduced. 
     Still further, according to the tube  2  as described above, if a vehicle is collided from up ahead to have a collision load inputted to the tube  2 , a shear force acts on the inclined portion  40 , which is inclined with respect to the axis O 1 . If the shear force acting on the inclined portion  40  exceeds a predetermined value, damaged is the front end (vulnerable portion)  41  which is the most vulnerable in the inclined portion  40 . 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. 
     Second Embodiment 
     Next, a power transmission shaft  101  of a second embodiment is described with reference to  FIG. 4 . Note that  FIG. 4  shows it, with exaggeration on features of a main body  110 . The power transmission shaft  101  of the second embodiment includes a tube  102 , the stub yoke  3  (see  FIG. 1 ) to be joined to a front end of the tube  102 , and the stub shaft  4  (see  FIG. 1 ) to be joined to a rear end of the tube  102 . As shown in  FIG. 4 , the tube  102  includes the main body  110 , the first connection portion  20  disposed in front of the main body  110 , the second connection portion  30  disposed behind the main body  110  (not shown in  FIG. 4 ), and an inclined portion  140  located between the main body  110  and the second connection portion  30 . 
     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. The outer diameter of the main body  110  decreases from a central portion  113  toward both ends (a front end  111  and a rear end  112 ), and an outer diameter R 3  of the central portion  113  is larger than an outer diameter R 4  of said both ends (the front and rear ends  111 ,  112 ). Similarly, 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 in a stepped shape. A plate thickness of the main body  110  decreases from both ends (the front and rear ends  111 ,  112 ) toward the central portion  113 . Thus, a plate thickness T 3  of the central portion  113  is smaller than a plate thickness T 4  of both ends (the front and rear ends  111 ,  112 ). 
     Although not particularly shown, the plate thickness of the inclined portion  140  gradually decreases from an end thereof closer to the main body  110  (front side) toward an end thereof closer to the second connection portion  30  (rear side). This causes the inclined portion  140  to have the smallest plate thickness at the rear end thereof, making the rear end of the inclined portion  140  as a vulnerable portion. Accordingly, if the vehicle is collided from up ahead and a shear force acting on the inclined portion  140  exceeds a predetermined value, damaged is the rear end (the vulnerable portion) which is the most vulnerable in the inclined portion  140 . 
     According to the tube  102  for the power transmission shaft  101  of the second embodiment, the main body  110  is reduced in weight and the primary bending resonance point of the main body  110  is improved, as with the tube  2  of the first embodiment. In addition, both ends (the front and rear ends  111 ,  112 ) are reduced in diameter and the central portion  113  is reduced in thickness, to have an amount of material required for manufacturing reduced, and then costs may be reduced. 
     Third Embodiment 
     Next, a power transmission shaft  201  of a third embodiment is described with reference to  FIG. 5 . Note that  FIG. 5  shows it, with exaggeration on features of a main body  210 . The power transmission shaft  201  of the third embodiment includes a tube  202 , the stub yoke  3  (see  FIG. 1 ) to be joined to a front end of the tube  202 , and the stub shaft  4  (see  FIG. 1 ) to be joined to a rear end of the tube  202 . As shown in  FIG. 5 , the tube  202  includes the main body  210 , the first connection portion  20  disposed in front of the main body  210 , the second connection portion  30  (not shown in  FIG. 5 ) disposed behind the main body  210 , and the inclined portion  40  located between the main body  210  and the second connection portion  30 . 
     When the main body  210  is sectioned in a plane normal to the axis O 1 , an outer periphery  214  and an inner periphery  215  of the main body  210  each have a cross section in a circular shape. The outer diameter of the main body  210  decreases from a central portion  213  toward both ends (a front end  211  and a rear end  212 ), and an outer diameter R 5  of the central portion  213  is larger than an outer diameter R 6  of said both ends (the front end  211  and rear end  212 ). Similarly, an inner diameter of the main body  210  also decreases from the central portion  213  toward both ends (the front and rear ends  211 ,  212 ). 
     When the main body  210  is sectioned along the axis O 1 , the outer periphery  214  of the main body  210  has a cross section in an arc and the inner periphery  215  has a cross section in a stepped shape. A plate thickness of the main body  210  decreases from both ends (the front and rear ends  211 ,  212 ) toward the central portion  13 , and thus a plate thickness T 5  of the central portion  213  is smaller than a plate thickness T 6  of said both ends (the front end  211  and rear end  212 ). 
     According to the tube  202  for the power transmission shaft  201  of the third embodiment, the main body  210  is reduced in weight and the primary bending resonance point of the main body  210  is improved, as with the tube  2  of the first embodiment. In addition, both ends (the front and rear ends  211 ,  212 ) are reduced in diameter and the central portion  213  is reduced in thickness, to have an amount of material required for manufacturing reduced, and then costs may be reduced. Further, the tube  202  is formed of fiber-reinforced plastic, to have a high degree of freedom in design, and then costs may be reduced. 
     Fourth Embodiment 
     A power transmission shaft  301  of a fourth embodiment includes a tube  302 , the stub yoke  3  (see  FIG. 1 ) to be joined to a front end of the tube  302 , and the stub shaft  4  (see  FIG. 1 ) to be joined to a rear end of the tube  302 . As shown in  FIG. 6 , the tube  302  includes a main body  310 , the first connection portion  20  disposed in front of the main body  310 , the second connection portion  30  disposed behind the main body  310  (not shown in  FIG. 6 ), and then inclined portion  40  located between the main body  310  and the second connection portion  30 . 
     When the main body  310  is sectioned in a plane normal to the axis O 1 , an outer periphery  314  and an inner periphery  315  of the main body  310  each have a cross section in a circular shape. The outer diameter of the main body  310  is identically formed from a front end  311  to a central portion  313 , and decreases from the central portion  313  toward a rear end  312 . Thus, an outer diameter R 7  of the front end  311  and central portion  313  is larger than an outer diameter R 8  of the rear end  312 . Similarly, the inner diameter of the main body  310  is identically formed from the front end  311  to center portion  313  of the main body  310 , and decreases from the center portion  313  toward the rear end  312 . 
     When the main body  310  is sectioned along the axis O 1 , the outer periphery  314  and inner periphery  315  of the main body  310  each have a cross section in a shape of a straight line from the front end  311  to the central portion  313 , and a cross section in a shape of a gentle curve in an arc from the central portion  313  to the rear end  312 . In addition, the plate thickness of the main body  310  decreases from the rear end  312  toward the central portion  313  and is uniformly formed from the central portion  313  to the front end  311 . Thus, a plate thickness T 7  of the front end  311  and central portion  313  is smaller than a plate thickness T 8  of the rear end  312 . 
     According to the tube  302  for the power transmission shaft  301  of the fourth embodiment, the central portion  313  of the main body  310  is formed to have the large outer diameter R 7  to ensure predetermined bending rigidity. The rear end  312  of the main body  310  is formed to have the small outer diameter R 8  to reduce weight. In addition, the central portion  313  of the main body  310  has the small plate thickness T 7  to reduce weight. Thus, the main body  310  is reduced in weight while maintaining predetermined bending rigidity of the central portion  313 , to improve the primary bending resonance point of the main body  310 . Further, the rear end  312  is reduced in diameter and the central portion  313  is reduced in thickness, to have an amount of material required for manufacturing reduced, and then costs may be reduced. Furthermore, the tube  302  is formed of fiber-reinforced plastic, to have a high degree of freedom in design, and then costs may be reduced. 
     Hereinabove, the embodiments have been described, but the present invention is not limited to those described in the embodiments. For example, the tube of each embodiment is provided with connection portions (the first and second connection portions  20 ,  30 ) for coupling with the stub yoke  3  and the like, but the present invention may provide a tube having only a main body. In other words, a tube of the present invention may be composed of only a main body to have the stub yoke  3  and the like respectively fitted into both ends of the main body. 
     The inclined portion  40  of each embodiment gradually decreases in plate thickness to have an easily-damaged vulnerable portion at an end, but may have the plate thickness uniformly formed and have a recess provided in the outer or inner periphery as a vulnerable portion. 
     LEGEND FOR REFERENCE NUMERALS 
     
         
         
           
               1 ,  101 ,  201 ,  301 : power transmission shaft;  2 ,  102 ,  202 ,  302 : tube;  10 ,  110 ,  210 ,  310 : main body;  11 ,  111 ,  211 ,  311 : front end;  12 ,  112 ,  212 ,  312 : rear end;  13 ,  113 ,  213 ,  313 : central portion;  20 : first connection portion;  30 : second connection portion;  40 : inclined portion; and O 1 : axis.