Abstract:
A shock absorber for mounting between a first frame member and a second frame member of a bicycle includes a first member adapted to couple to the first frame member and a second member adapted to couple to the second frame member, wherein the first member and the second member rotate relative to each other. The first member includes a first member protrusion extending inwardly from an inner surface thereof and forming a first border surface at a junction of the first member protrusion and the inner surface. Similarly, the second member includes a second protrusion extending outwardly from an outer surface thereof and forming a second border surface at a junction of the second member protrusion and the outer surface. The first member protrusion faces the second member protrusion in a circumferential direction. An elastic member is disposed between the first member protrusion and the second member protrusion and contacts at least one of the first border surface and the second border surface.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to bicycle components and, more particularly, to a bicycle shock absorber wherein the elastic shock absorber elements are efficiently placed within the shock absorber. 
     Cycling grows in popularity not only as a transportation means but, to a greater extent, as a mode of recreation. In addition, cycling is a popular competitive sport for professionals and amateurs. It is known that mountain and road bicycles are currently provided with front or rear suspensions to absorb shocks transmitted to the rider both on and off the road. Numerous structures, ranging from simple to complex, are used for such suspensions. For example, Japanese Unexamined Patent Application 9-290790 teaches an inexpensive bicycle suspension with a simple structure. This suspension comprises a cylindrical external member with a plurality of projections extending inwardly and an internal member mounted inside the external member and having a plurality of projections extending radially outwardly, wherein the plurality of projections extending from the external member radially face the plurality of projections extending from the internal member. Elastic members are mounted between the external member and the internal member and are compressionally deformed by the relative rotation of the two members. Side plates are integrally attached to both ends of the internal member. The external and internal members may be integrally linked to respective front and rear frame members of the bicycle, wherein the rear frame member is fixed to the side plates. The elastic members, which are interposed between the internal member and the external member, generate reaction force when compressed by the relative rotation of the two members. 
     In the conventional bicycle suspension described above, the elastic members are merely interposed in the space between the internal member and the external member, and hence sometimes slip and change their configuration in the space between the two members when compressed only slightly. A change in the configuration of the elastic members alters the state of the system during compression and results in a varying, unstable shock absorption performance. In view of this, it was suggested to place the elastic members in compact fashion in the space between the two members in order to prevent changes in configuration. However, compact placement of the elastic members makes it more difficult for the elastic members being compressed to expand, markedly increases the reaction force of the two members per unit angle of rotation, and it fails to ensure adequate shock absorption. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a bicycle shock absorber which provides stable shock absorption characteristics. In one embodiment of the present invention, a shock absorber for mounting between a first frame member and a second frame member of a bicycle includes a first member adapted to couple to the first frame member and a second member adapted to couple to the second frame member, wherein the first member and the second member rotate relative to each other. The first member includes a first member protrusion extending inwardly from an inner surface thereof and forming a first border surface at a junction of the first member protrusion and the inner surface. Similarly, the second member includes a second protrusion extending outwardly from an outer surface thereof and forming a second border surface at a junction of the second member protrusion and the outer surface. The first member protrusion faces the second member protrusion in a circumferential direction. An elastic member is disposed between the first member protrusion and the second member protrusion and contacts at least one of the first border surface and the second border surface. If desired, a first space may be defined on a first side surface of the first member protrusion facing the second member protrusion in the circumferential direction, and a second space may be defined on a second side surface of the first member protrusion, wherein the first elastic member is disposed in the first space. A second elastic member may be disposed in the second space. 
     In another embodiment of the present invention, a shock absorber for mounting between a first frame member and a second frame member of a bicycle includes a first member adapted to couple to the first frame member and a second member adapted to couple to the second frame member, wherein the first member and the second member rotate relative to each other. The first member includes a first member protrusion extending inwardly from an inner surface thereof, and the second member includes a second protrusion extending outwardly from an outer surface thereof. The first member protrusion faces the second member protrusion in a circumferential direction. An elastic member is disposed between the first member protrusion and the second member protrusion, wherein a side surface of the first elastic member contacts a facing side surface of at least one of the first member protrusion and the second member protrusion along substantially an entire length of the at least one of the first member protrusion and the second member protrusion. Additionally, the side surface of the first elastic member has a same shape as the facing side surface of the at least one of the first member protrusion and the second member protrusion when the first elastic member is in an uncompressed state. 
     In yet another embodiment of the present invention, a shock absorber for mounting between a first frame member and a second frame member of a bicycle includes a first member adapted to couple to the first frame member, wherein the first member includes at least one first member protrusion extending inwardly from an inner surface thereof; and a second member adapted to couple to the second frame member, wherein the second member includes at least one second member protrusion extending outwardly from an outer surface thereof. The first member and the second member rotate relative to each other. At least one of the first member protrusion and the second member protrusion has a first space defined on a first side surface thereof and a second space defined on an opposite second side surface thereof. The first space has a first circumferential area, and the second space has a second circumferential area. The first circumferential area is greater than the second circumferential area, and an elastic member is disposed in the first space. 
     In yet another embodiment of the present invention, a shock absorber for mounting between a first frame member and a second frame member of a bicycle includes a first member adapted to couple to the first frame member, wherein the first member includes at least one first member protrusion extending inwardly from an inner surface thereof; and a second member adapted to couple to the second frame member, wherein the second member includes at least one second member protrusion extending outwardly from an outer surface thereof. The first member and the second member rotate relative to each other. At least one of the first member protrusion and the second member protrusion has a first space defined on a first side surface thereof and a second space defined on an opposite second side surface thereof. The first space has a first circumferential width, and the second space has a second circumferential width measured at a same radial distance as the first circumferential width. The first circumferential width is greater than the second circumferential width, and a first elastic member is disposed in the first space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a bicycle that includes a particular embodiment of a shock absorber according to the present invention; 
     FIG. 2 is a more detailed view of the pedal drive area of the bicycle shown in FIG. 1; 
     FIG. 3 is a top view of the driving parts of the bicycle shown in FIG. 1; 
     FIG. 4 is an exploded view of a particular embodiment of a shock absorber according to the present invention; 
     FIG. 5 is a cross-sectional view of the assembled bicycle shock absorber shown in FIG. 5; 
     FIG. 6 is a view taken along line VI—VI in FIG. 5 showing the bicycle shock absorber in a rest state; 
     FIG. 7 is a cross-sectional view of the bicycle shock absorber in a shock absorbing state; 
     FIG. 8 is a graph illustrating the shock absorbing characteristics of the shock absorber shown in FIGS. 6 and 7; and 
     FIG. 9 is a fragmentary cross-sectional view of another embodiment of a shock absorber according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In FIGS. 1 and 2, the bicycle  10  in which an embodiment of the present invention is employed is a BMX-type bicycle provided with a frame  12  and a suspension assembly  14 . The frame  12  primarily has a main frame member (an example of a first frame member)  16  and a rear frame member (an example of a second frame member)  18  elastically linked to the main frame member  16  via the suspension assembly  14 . 
     The bicycle  10  further comprises a rear wheel  19 , which is mounted on the rear part of the frame  12  while allowed to rotate about a rear hub  19   a ; a front wheel  20 , which is linked to the front part of the frame  12  while allowed to rotate about a front hub  20   a ; and a drive part  22  for propelling the bicycle. As shown in FIG. 3, the drive part  22  has the same structure as in the past; that is, it comprises a bottom bracket  23  (FIG. 3) having a bottom bracket axle  23   a , a right crank  24  equipped with a front sprocket  25  and nonrotatably mounted on the right end of the bottom bracket axle  23   a , a left crank  26  nonrotatably mounted on the left end of the bottom bracket axle  23   a , a rear sprocket  29  mounted on the rear hub  19   a , and a drive chain  28  passed over the two sprockets  25  and  29 . A pedal  27  is mounted on the tip of either crank  24  and  26 . 
     The main frame member  16  is composed of a plurality of rigid tubular members welded together. Specifically, the main frame member  16  has a seat tube  30 , a head tube  32 , an upper tube  33  for linking the two tubes  30  and  32 , and a down tube  34 . The main frame member  16  should preferably be manufactured using a rigid material such as a high-strength steel, chromium-molybdenum steel, aluminum alloy, titanium alloy, or other metal material; or a carbon composite or other such fiber-reinforced resin material. A seat post  38 , with a saddle  37  mounted in the distal end thereof, is fixed to the seat tube  30  such that the vertical position thereof can be adjusted. A front fork  40  is rotatably mounted in the head tube  32 . The front wheel  20  is rotatably mounted in the lower end of the front fork  40 , and a steering handle assembly  42  is mounted on the upper end thereof such that the vertical position thereof can be adjusted. 
     A pair of brackets  50  for mounting the suspension assembly  14  are fixedly welded to the linkage portion of the down tube  34  and the seat tube  30 . As shown in FIGS. 2 and 3, the brackets  50  have a first fixing part  50   a , which is fixedly welded to the down tube  34 ; a second fixing part  50   b , which is fixedly welded to the seat tube  30  diagonally underneath the first fixing part  50   a ; and a link  50   c , which is bent into a quarter-circle segment and which links the two fixing parts  50   a  and  50   b . Such brackets  50  allow the main frame member  16  to be reinforced by mounting the suspension assembly  14  and linking the down tube  34  and the seat tube  30 . In addition, the main frame member  16  can be reinforced by linking the two tubes  34  and  30  with the aid of the suspension assembly  14  when the suspension assembly  14  is mounted separately on the tubes  34  and  30  without the use of the link  50   c.    
     The suspension assembly  14  is mounted between the two brackets  50  and is fixed with bolts  56 . Each of the brackets  50  is provided with two bolt holes (not shown) for receiving the bolts  56  therethrough. The dismounting of the suspension assembly  14  or the rear frame member  18  is thus facilitated by the detachable mounting of the suspension assembly  14  on the main frame member  16  with the bolts  56 . 
     The rear frame member  18  has a pair of substantially identical arm members  60 , as shown in FIG.  4 . Each arm member  60  has a circular suspension-mounting part  62  at the base end and a hub-mounting part  64  at the distal end. The suspension-mounting part  62  is fixed in the internal member (see below) of the suspension assembly  14 . The rear hub  19   a  is mounted between the two hub-mounting parts  64 , and a hub axle  19   b  is fixed in the hub-mounting parts  64 . 
     The suspension-mounting parts  62  have central holes  70  for accommodating the bottom bracket  23 , and five bolt holes  72  for mounting bolts  74  are provided around each central hole  70 . The bolts  74  are used to fix the suspension-mounting parts  62  to the internal member of the suspension assembly  14 . The hub-mounting parts  64  are provided with slits  76  that extend in the longitudinal direction of the arm members  60 , and the hub axle  19   b  of the rear hub  19   a  is fixed in these slits  76  by a known method. 
     As shown in FIGS. 4-6, the suspension assembly  14  comprises an external member (first member)  80  fixed to the main frame member  16 ; an internal member (second member)  82  disposed around the inside of the external member  80  and fixed to the rear frame member  18 ; first and second elastic members  83  and  84 , which are expanded and contracted by the relative rotation of the external member  80  and internal member  82 ; and a link mechanism  86  for concentrically positioning the external member  80  and internal member  82  and linking the two members  80  and  82  in a relatively rotatable and axially immovable fashion. 
     The external member  80  is a substantially cylindrical member that is made of metal and that has in its interior a circular opening  90  centered around a central axis extending to the right and left of the bicycle  10 . Aluminum alloys, titanium alloys, chromium-molybdenum steel, high-strength steel, stainless-steel alloys, and the like are preferred as the metals for use in these. The internal member  82  can be accommodated together with the bottom bracket  23  and the two elastic members  83  and  84  in the opening  90 . The opening  90  is formed such that its central axis coincides with the central axis of the bottom bracket  23  (axial center of the bottom bracket axle  23 ), and it is provided with five first protrusions  92  extending radially inward from a circumferentially extending inner surface  93 . As shown in FIG. 6, circularly beveled first retaining parts  92   a  are provided along the border between the circumferentially extending inner surface  93  of the external member  80  and the radially extending side surfaces  92   c  of the first protrusions  92 . The angular portions  83   a  around the outside of the first elastic members  83  are kept in contact by these first retaining parts  92   a . The radially extending side surfaces  92   c  of the first protrusions  92  also have portions  92   d  that extend in a circumferential direction over and face the circumferentially extending inner surface  93 . 
     Two mounting parts  94  extending radially outward are provided around the outside of the external member  80 . The distal ends of each mounting part  94  are provided with screw holes  96  extending to a prescribed depth from both ends. These screw holes  96  are formed at positions that face the bolt holes of the brackets  50 , and the suspension assembly  14  is mounted on the main frame member  16  by screwing the bolts  56  passing through the bolt holes of the brackets  50  into these screw holes  96 . The base end of each mounting part  94  is provided with notches  97  cut out at both ends, and circular surfaces  98  are formed on the outer circumferential surfaces at the two ends of the external member  80 . 
     The internal member  82  is a substantially cylindrical member made of metal and provided with a through hole  104  for the internal mounting of the bottom bracket  23  by a mounting technique based on the use of known screws. Aluminum alloys, titanium alloys, chromium-molybdenum steel, high-strength steel, stainless-steel alloys, and the like are preferred as the metals for use in these. Five second protrusions  102  extending radially outward are formed on the circumferentially extending outer surface  81  of the internal member  82 . The second protrusions  102  are disposed alternately with the first protrusions  92 . As a result, it is possible to form two types of substantially rectangular spaces whose volume is varied by the relative rotation of the external member  80  and internal member  82  between the first protrusions  92  and the second protrusions  102 . Of these, the first elastic members  83  are mounted in the wider spaces, and the second elastic members  84  are mounted in the narrower spaces. Circularly beveled second retaining parts  102   a  are provided along the border between the circumferentially extending outer surface  81  of the internal member  82  and radially extending side surfaces  102   c  of the second protrusions  102 . The angular portions  83   b  around the inside of the first elastic members  83  are kept in contact with these second retaining parts  102   a . The radially extending side surfaces  102   c  of the second protrusions  102  have portions  102   d  and  102   e  that extend in a circumferential direction over and face the circumferentially extending outer surface  81 . 
     The other radially extending side surfaces  92   b  of the first protrusions  92  and the other radially extending side surfaces  102   b  of the second protrusions  102  face each other in a substantially parallel fashion in a state in which the two elastic members  83  and  84  are mounted. Screw holes  106  for screwing in the bolts  74  are formed on the tip side of the second protrusions  102 . The rear frame member  18  is fixed to the suspension assembly  14  and elastically linked to the main frame member  16  by screwing the bolts  74  into these screw holes  106  through the bolt holes  72  of the arm members  60 . 
     In this embodiment, the first elastic members  83  are members manufactured from bar-shaped elastic bodies and provided with a deformed rectangular shape in cross section. Urethane rubber, nitrile rubber, polyethylene elastomer, or the like can be used for such elastic bodies. In the first elastic members  83 , the angular portions  83   a  on the outer circumferential side in contact with the first protrusions  92  are rounded in the form of acute angles, as are the angular portions  83   b  on the inner circumferential side in contact with the second protrusions  102 . The first elastic members  83  are mounted while pressure is applied to one of the spaces formed by the first protrusions  92  and second protrusions  102 , and both ends thereof are brought into contact with a second bushing  112 . The angular portions  83   a  are held by the first retaining parts  92   a  around the outside in areas of contact with the first protrusions  92 , whereas the angular portions  83   b  are held by the second retaining parts  102   a , which are disposed along the inner circumference diagonally from the first retaining parts  92   a , in areas of contact with the second protrusions  102 . The first elastic members  83  are thus held by the corresponding diagonally arranged retaining parts  92   a  and  102   a , thus making it more difficult for the first elastic members  83  to slip in a manner other than that involving expansion in the thickness direction (direction that intersects the direction of contraction) as a result of a contraction occurring when the first elastic members  83  are compressed and deformed. The shock absorption performance can therefore be stabilized. 
     The first elastic members  83  are mounted in a secured state in one of the spaces while gaps  108   a  are formed near the inner circumferential surface of the external member  80 . These gaps gradually become narrower in the clockwise direction away from the area of contact with the second protrusions  102 . With such mounting, gaps  108   b  are also formed near the outer circumferential surface of the internal member  82 . These gaps gradually become narrower in the counterclockwise direction away from the area of contact with the first protrusions  92 . Because the first elastic members  83  are disposed such that the gradually narrowing gaps  108   a  and  108   b  are formed, the first elastic members  83 , when gradually sandwiched and contracted between the protrusions  92   a  and  102   a , can swell in the direction that intersects the contraction direction, making it possible to increase the amount of rotation for the members  80  and  82  and to ensure adequate shock absorption. 
     When the internal member  82  performs relative rotation, and the first elastic members  83  first contract and then expand into the gaps  108   a  and  108   b , the first elastic members  83  gradually adhere to the inner circumferential surface of the external member  80  and to the outer circumferential surface of the internal member  82 , lowering the amount of slippage in the area where adhesion-induced friction occurs, reducing the likelihood that the first elastic members  83  will be worn down, and making it possible to inhibit wear-induced variations in the shock absorption performance. 
     In this embodiment, the second elastic members  84  are made of substantially plate-shaped elastic bodies mounted for the purpose of applying pressure to the first elastic members and inhibiting the collision noise resulting from contact between the two protrusions  92  and  102 . Urethane rubber, nitrile rubber, polyethylene elastomer, and the like are preferred for use in such elastic bodies. The other radially extending side surfaces  92   b  of the first protrusions  92  and the other radially extending side surfaces  102   b  of the second protrusions  102  face each other in a substantially parallel fashion in a state in which pressure is exerted by the second elastic members  84  on the first elastic members  83 . Consequently, the gaps between the other radially extending side surfaces  92   b  of the first protrusions  92  and the other radially extending side surfaces  102   b  of the second protrusions  102  remain unchanged, and the pressure applied to the first elastic members  83  is less likely to vary when the second elastic members  84  slip in the radial direction. Here, applying pressure to the first elastic members  83  suppresses the movement of the suspension assembly  14  under the weight of the rider when the latter mounts the bicycle. 
     The link mechanism  86  has a first bushing  110  made of a synthetic resin and fixed to the external member  80 , and a second bushing  112  made of metal, disposed around the outside of the first bushing  110 , and fixed to the internal member  82 . Polyacetal resins, nylon, Teflon (registered trade name), and other synthetic resins are preferred for use as the synthetic resins for the first bushing  110 . Iron-based metals, copper, brass-based alloys, and other metals are preferred for use as the metals for the second bushing  112 . The first bushing  110  is a flanged annular member having a first cylindrical part  114  in contact with the circular surfaces  98  of the external member  80  and a first annular part  116  folded away from the first cylindrical part  114  and kept in contact with the end face of the external member  80 . The first bushing  110  is fixed by being fitted over the circular surfaces  98  of the external member  80 . 
     The second bushing  112  is a flanged annular member having a second cylindrical part  118  in contact with the first cylindrical part  114  of the first bushing  110  and a second annular part  120  folded away from the second cylindrical part  118  and kept in contact with the first annular part  116  of the first bushing  110 . Five bolt holes  122  are formed in the second annular part  120  at positions facing the five bolt holes  72 . The second bushing  112  is fixed by the bolts  74  to the internal member  82  together with the rear frame member  18 . 
     The shock-absorbing operation of the suspension assembly  14  will now be described. 
     When a shock or load acts on the rear wheel  19 , the rear frame member  18  rotates clockwise together with the internal member  82  about the bottom bracket axle  23   a  in FIG.  1 . Such rotation about the bottom bracket axle  23   a  prevents the drive chain  28  from being stretched, loosened, or otherwise adversely affected in the manner encountered when rotation is induced in other areas. Pedaling loss and the like can therefore be suppressed. During the application of a shock or load to the bicycle, the first elastic members  83  are deformed by being compressed between the two protrusions  92  and  102 , absorbing this shock or load. At this time, the gaps  108   a  and  108   b  between the first elastic members  83  and the external member  80  (and internal member  82 ) gradually become narrower, and if such compression continues until the gaps disappear (as shown in FIG.  7 ), the entire contact surface restricts the movement of the first elastic members  83 , completing the stroke. 
     Releasing the shock or load causes the first elastic members  83  to be expanded by elastic restoring force and returns the internal member  82  to its initial position. The corresponding relation between the load and the stroke of the internal member  82  is depicted in FIG.  8 . Here, gaps  108   a  and  108   b  are formed between the first elastic members  83  and the external member  80  (and internal member  82 ), making it possible to obtain a large stroke in relation to the load (as shown by the bold line in FIG. 8) and widening the shock-absorbing range. The stroke decreases in relation to the load (as shown by the thin line in FIG. 8) in the absence of the gaps  108   a  or  108   b.    
     Radial movement of the first elastic members  83  during compression is inhibited because the first elastic members  83  are held at two locations in the diagonal direction of bite during compression. Consequently, the shock absorption characteristics depicted in FIG. 8 always vary in a uniform manner, yielding a stable shock absorption performance. Furthermore, radial slippage of the external member  80  and the internal member  82  is inhibited because the two members  80  and  82  are linked by the link mechanism  86  in a relatively rotatable and axially immovable fashion. Consequently, contact between the members  80  and  82  during impact can be prevented, and the two members  80  and  82  are less likely to be damaged when a shock is applied. 
     While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. For example, the size, shape, location or orientation of the various components may be changed as desired. The functions of one element may be performed by two, and vice versa. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). 
     Although the external and internal members had cylindrical shapes in the described embodiments, the shape of these two members is not limited to a cylindrical shape and includes rectangular columnar shapes and the like. Furthermore, although the first elastic members in the above embodiments were configured from bar-shaped members provided with a deformed rectangular shape in cross section, the shape of the first elastic members is not limited to the aforementioned shape alone. As shown, for example, in FIG. 9, it is also possible provide a first elastic member  83   d  with a longitudinal cross section that is trapezoid in shape, to form along the two ends  83   e  of the first elastic member  83   d  gaps that become wider in the direction radially outward, and to allow the first elastic member  83   d  to gradually adhere to the annular parts of second bushings  112 . In this case, the expansion space for the first elastic member  83   d  can be further expanded, the shock absorption capabilities improved, friction-induced slippage additionally reduced, and wear-induced variations in the shock absorption performance further inhibited. 
     Although the arm members in the above embodiments were configured such that the hub axle of the rear wheel was chain-driven and supported at both ends, it is also possible for the rear wheel to be shaft-driven by a bevel-gear shaft, and the hub axle of the rear wheel to be supported on one side. Furthermore, although the external member in the described embodiments were fixed to the main frame member, and the internal member was fixed to the rear frame member, the manner in which the internal and external members are fixed to the frame is not limited to the above and may include arrangements in which the rear frame member is fixed to the external member, and the main frame member to the internal member. 
     Although the above embodiments involved mounting second elastic members  84  and applying pressure to the first elastic members  83 , it is also possible to dispense with the mounting of the second elastic members  84 . When the second elastic members  84  are mounted, it is also possible to mount elastic bodies that are sufficiently soft to prevent pressure from being applied to the first elastic members  83 . Such second elastic members  84 , while incapable of applying pressure, can still prevent noise from being generated by the impact between the protrusions  92  and  102 , and make it possible to absorb shocks during a return to the original state. 
     Thus, the scope of the invention should not be limited by the specific structures disclosed or the apparent initial focus on a particular structure or feature.