Abstract:
A flywheel structure which has a ring made from a composite material of carbon fiber reinforced plastics and a spoke member inserted in the ring. The spoke member is made from the fiber reinforced plastics having a lower modulus of elasticity than that of the ring. A tapered bush is press-fitted into a center portion of the spoke member. Both of the tapered bush and the spoke member are tightly fixed on a shaft by a first spring supported by a holder, and by a second spring urging the holder so as to effectively prevent vibrations due to looseness thereof.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to a composite material flywheel device used for temporarily storing energy. 
     2. Description of the Related Art 
     The use of flywheel devices as apparatus for temporarily storing energy that is dissipated when transportation facilities, such as motor vehicles or railroad cars, are braked as well as nighttime surplus electric power that occurs in electric power systems is currently a subject under study. 
     While a large majority of flywheels of the flywheel devices are metallic ones, composite material flywheels made by molding a glass-fiber reinforced plastic, aramid fiber reinforced plastic or carbon-fiber reinforced plastic are also used to cater to the need for high-speed rotation. 
     A composite material flywheel is described in Japanese Unexamined Patent Publication No. 58-30545, for example, in which the flywheel is of such a construction that an outer part of a rotary shaft mounting portion  2  of a circular disk  1  made of an aluminum alloy thickens toward the outer periphery, a plurality of surfaces that are nearly vertical surfaces of the rotary shaft mounting portion  2  are made to have different inclinations from one another, a ring  4  molded of a high-strength carbon-fiber reinforced plastic is firmly fitted on a cylindrical portion  3  which is formed by the outermost part of the circular disk  1 , and a plurality of radially directed slits  5  are provided in the circular disk  1  and ring  4 , as shown in FIGS. 6 and 7. 
     Also, a flywheel intended for storing energy is described in U.S. Pat. No. 4,569,114, for example, in which the flywheel is of a construction comprising a metallic hub  8  having a plurality of spokes  6  and a ring  7  which are one-piece molded, a glass-fiber reinforced plastic inner ring  9  provided on an outer surface of the metallic hub  8  and a carbon-fiber reinforced plastic outer ring  10  provided on an outer surface of the glass-fiber reinforced plastic inner ring  9 , as shown in FIG.  8 . 
     With the composite material flywheel in which a high-strength carbon-fiber reinforced plastic ring is firmly fitted on a cylindrical portion of a circular disk and a plurality of radially directed slits are provided in the circular disk and a ring, the ring could oscillate in its axial direction due to bending of the circular disk during high-speed rotation, making it difficult to maintain delicate geometric relationship with surrounding equipment. 
     Although the composite material flywheel molded of a high-strength carbon-fiber reinforced plastic allows operation at such a high rotating speed that is not achieved with glass-fiber reinforced flywheels or aramid fiber reinforced flywheels, high degrees of stress and strain occur in the interior of the flywheel and the inside diameters of the metallic circular disk and hub increase due to expansion caused by a centrifugal effect, thus creating a gap between the flywheel and its shaft. This could cause such problems as whirling or other instability-related phenomena. 
     Furthermore, because the ring of the metallic hub is formed of the same metal as the spokes in the aforementioned energy storage flywheel, there arises a problem related to the strength of the ring and there exist limitations in increasing the rotating speed. 
     SUMMARY OF THE INVENTION 
     This invention has been made in the light of the aforementioned problems. Accordingly, it is an object of the invention to provide a composite material flywheel which is applicable to high-speed rotation at 1,300 m/sec or above in terms of tangential speed and can alleviate strain due to residual stress and suppress whirling vibrations. 
     A composite material flywheel according to the invention is constructed by joining a plastic spoke member reinforced with fiber having a modulus of elasticity lower than high-strength carbon fiber to the inside of a high-strength carbon-fiber reinforced plastic ring by press-fitting means. This flywheel is applicable to high-speed rotation at 1300 m/sec or above in terms of tangential speed and can alleviate stress due to initial residual strain. 
     A composite material flywheel device according to the invention has a composite material flywheel in which a plastic spoke member reinforced with fiber having a modulus of elasticity lower than high-strength carbon fiber is joined to the inside of a high-strength carbon-fiber reinforced plastic ring by press-fitting means, a taper bush fitted into a truncated conical shaft hole formed in a central part of the spoke member of the composite material flywheel, and spring means which forces the taper bush toward the spoke member. As the taper bush is forced into the composite material flywheel by way of the spring means, it becomes possible to absorb looseness which occurs when the rotating speed increases and prevent whirling vibrations, and the service life of the flywheel device is increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a composite material flywheel according to the present invention; 
     FIG. 2 is a diagram showing tangential strain at a tangential speed of 1,300 m/sec in relation to permissible tangential strain and radial strain at the tangential speed of 1300 m/sec in relation to permissible radial strain; 
     FIG. 3 is a graph showing energy density at the tangential speed of 1300 m/sec and the permissible strain of high-strength carbon-fiber reinforced plastic; 
     FIG. 4 is a diagram showing a composite material flywheel device according to the invention as it is in a stage prior to installation on a shaft; 
     FIG. 5 is a diagram showing the composite material flywheel device according to the invention as it is in a stage after installation on the shaft; 
     FIG. 6 is a fragmentary front view of a related art composite material flywheel; 
     FIG. 7 is a cross-sectional view of the composite material flywheel of FIG. 6; and 
     FIG. 8 is a partially cutaway perspective view of a related art composite material flywheel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A mode of carrying out this invention is described below with reference to the drawings. 
     FIG. 1 shows a composite material flywheel according to the invention, in which the composite material flywheel  20  has a ring  21  molded to an inside diameter d and outside diameter D and a spoke member  22  integrally joined to the ring  21 . The spoke member  22  includes four arms  23  which are molded together to form a single structure. 
     The aforementioned ring  21  is formed by winding a tape around an unillustrated mandrel in layers, the tape being made by aligning several strands of high-strength carbon-fiber prepreg roving material in parallel, and then joining the layered tape into a single structure by hot pressing means. (Refer to Japanese Patent Application No. 10-205510.) 
     The inside diameter d and outside diameter D of the aforementioned ring  21  are so determined that the ratio of the inside diameter to the outside diameter falls within a range of 0.65 to 0.75. This is for providing the ring  21  with properties to withstand high-speed rotation at a tangential speed of 1300 m/sec. 
     FIG. 2 is a graph showing tangential strain at the tangential speed of 1,300 m/sec in relation to permissible tangential strain and radial strain at the tangential speed of 1300 m/sec in relation to permissible radial strain, in which the vertical axis represents the amount of strain (micro(×10 −6  mm/mm)) and the horizontal axis represents the diameter ratio (d/D). 
     In FIG. 2, a region in which the flywheel  20  can withstand high-speed rotation at the tangential speed of 1300 m/sec is shown by shading with parallel oblique lines. 
     FIG. 3 is a graph showing energy density at the tangential speed of 1300 m/sec and the permissible strain of high-strength carbon-fiber reinforced plastic, in which the vertical axis represents the energy density and the horizontal axis represents the diameter ratio (d/D). 
     In FIG. 3, an area shown by shading with parallel oblique lines is a region in which the energy density determined by the permissible strain becomes a maximum. 
     It is recognized from FIGS. 2 and 3 that the ring  21  can cope with high-speed rotation at the tangential speed of 1300 m/sec by setting the ratio of the inside diameter d to the outside diameter D between 0.65 and 0.75. 
     The aforementioned spoke member  22  is manufactured by machining a plastic plate which has been reinforced by layering equal amounts of high-ductility, high-strength glass fibers or aramid fibers in directions of 0°, 90° and ±45° to provide capabilities to follow up extension and to withstand the centrifugal force of the spoke member  22  itself, wherein the plastic plate is machined such that the directions of the fibers match the directions of the arms  23  of the spoke member  22 . 
     Although the four arms  23  are made by machining operation in such a way that the arms  23  align the 0° and 90° fiber directions in the spoke member  22  shown in FIG. 1, the number of arms  23  may be increased to eight by providing additional arms  23  in the ±45° directions in order to cope with even higher rotation speeds. 
     The composite material flywheel  20  shown in FIG. 1 is produced by joining a high-strength glass-fiber reinforced plastic spoke to a high-strength carbon-fiber reinforced plastic ring whose diameter ratio is between 0.65 and 0.75 by expansion fitting means. 
     More specifically, the composite material flywheel  20  is formed by cooling the spoke member  22  molded from the glass-fiber reinforced plastic to a temperature of −70° C. or less, placing the cooled spoke member  22  inside the ring  21  which has been molded from the high-strength carbon-fiber prepreg, and then returning the cooled spoke member  22  to room temperature to join the spoke member  22  with the ring  21  so that they together form a single structure. With internal stresses produced in the composite material flywheel  20  by the expansion fitting means, it is possible to alleviate the strain of the spoke member  22  caused by the centrifugal force of the composite material flywheel  20 . 
     FIG. 4 shows a composite material flywheel device  30  according to the invention as it is in a stage prior to installation on a shaft, and FIG. 5 shows the composite material flywheel device  30  according to the invention as it is in a stage after installation on the shaft. 
     The aforementioned composite material flywheel device  30  has a composite material flywheel  20  (FIG.  1 ), a truncated conical shaft hole  31  formed in a central part of the spoke member  22  of the composite material flywheel  20 , a taper bush  32  which has an outside diameter corresponding to the truncated conical shaft hole  31  provided in the spoke member  22  and is fitted in the truncated conical shaft hole  31 , a small disc springs  33  which force the taper bush  32  in a direction in which it is fitted into the truncated conical shaft hole  31 , and a holder  35  which is provided with a pit  34  for accommodating the small disc springs  33 . The small disc springs  33  produce an appropriate pushing force in a state they do not rotate so as to force the taper bush  32  toward the spoke member and thereby absorb looseness should any fluctuations occur in rotating conditions. The number of the small disc springs  33  is determined so that they would provide such a level of thrust that is sufficient to leave a pushing force while absorbing the looseness at maximum tangential speed. The holder  35  has a shoulder portion  36  and a sleeve  37  that are provided on a side opposite to the side where the pit  34  is provided. Large disc springs  38  are located on the shoulder portion  36  of the holder  35  and a plate  39  is fitted on the sleeve  37 . The plate  39  pushes the large disc springs  38  located on the shoulder portion  36 . The number of the large disc springs  38  is determined such that they can always push the holder  35  toward the composite material flywheel  20  depending on variations in the thickness of the composite material flywheel  20 . 
     In FIG. 4, the reference numeral  40  designates a shaft having a stepped portion  41  and the reference numeral  42  designates a plate. 
     The shaft  40 , plates  39 ,  42 , bush  32 , springs  34 ,  38 , holder  35 , nuts  44 ,  45  are all made of steel, and due consideration is taken such that an increase in inside diameter at high-speed rotation can be well ignored with the diameter of the shaft  40  set to 90 mm or less and the maximum outside diameter of the taper bush  32  set to 120 mm or less, given the outside diameter 380 mm of the ring  21 . 
     A procedure for installing the composite material flywheel device  30  on the shaft  40  is now described below. 
     First, the plate  42  is mounted on the shaft  40  so that the plate  42  comes in contact with the stepped portion  41  as shown in FIG.  4 . Then, the composite material flywheel  20  is mounted on the shaft  40  with a small-diameter side of the truncated conical shaft hole  31  provided in the spoke member  22  directed forward, and a surface of the composite material flywheel  20  on the small-diameter side of the truncated conical shaft hole  31  is brought into contact with the plate  42 . The plate  42  has a larger diameter than the truncated conical shaft hole  31  and, thus, covers the truncated conical shaft hole  31  and sets the taper bush  32  fitted into the truncated conical shaft hole  31  in position. 
     Next, the holder  35  accommodating the small disc springs  33  in its pit  34  is mounted on the shaft  40  with the side of the small disc springs  33  directed forward, the large disc springs  38  are placed on the shoulder portion  36  of the holder  35 , the plate  39  is mounted on the sleeve  37 , and double nuts  44 ,  45  are screwed on a threaded portion  43  provided on the shaft  40 . 
     When the double nuts  44 ,  45  have been screwed on the threaded portion  43  provided on the shaft  40 , the plate  39  pushes the large disc springs  38  and the holder  35  moves along the shaft  40  up to a position where the holder  35  comes into contact with the composite material flywheel  20  as shown in FIG.  5 . As a result of this movement of the composite material flywheel  20  in the axial direction, the small disc springs  33  accommodated in the pit  34  in the holder  35  push the taper bush  32  so that it is fitted into the truncated conical shaft hole  31  provided in the spoke member  22 . At this point, the installation of the composite material flywheel device  30  onto the shaft  40  is completed. 
     Subsequently, the amount of unbalance is measured at a specified rotating speed and the plate  3 ,  42  or the holder  35  is trimmed to proper thickness to improve balance. 
     Consequently, the composite material flywheel device  30  absorbs its looseness with respect to the shaft  40  by means of the taper bush  32  and eliminates the looseness of the composite material flywheel  20  and increases its out-of-plane stiffness by sandwiching the composite material flywheel  20  between the plate  42  and the holder  35 , making it possible to prevent whirling vibrations. 
     Although one taper bush  32  is fitted into the truncated conical shaft hole  31  provided in the composite material flywheel  20  in the foregoing embodiment, truncated conical shaft holes  31  may be formed on both sides of the composite material flywheel  20  so that two taper bushes  32  can be fitted therein in a case where the composite material flywheel  20  has a large thickness. 
     As thus far described, a plastic spoke member reinforced with fiber having a modulus of elasticity lower than high-strength carbon fiber is joined to the inside of a high-strength carbon-fiber reinforced plastic ring by press-fitting means in a composite material flywheel according to the invention and, as a consequence, it becomes possible to prevent disjuncture of the ring before rotation and alleviate stress due to initial residual strain and the composite material flywheel can be applied to high-speed rotation at the tangential speed of 1300 m/sec or above. 
     Further, a composite material flywheel device according to the invention has a composite material flywheel in which a plastic spoke member reinforced with fiber having a modulus of elasticity lower than high-strength carbon fiber is joined to the inside of a high-strength carbon-fiber reinforced plastic ring by press-fitting means, a taper bush fitted into a truncated conical shaft hole formed in a central part of the spoke member of the composite material flywheel, and spring means which forces the taper bush toward the spoke member, wherein the composite material flywheel device absorbs looseness with respect to a shaft by means of the taper bush and can prevent whirling vibrations. 
     While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that the disclosure is for the purpose of illustration and that various changes modifications may be made without departing from the scope of the invention as set forth in the appended claims