Abstract:
A crank axle includes an axle body having first and second ends, a first rotary linkage member disposed at the first end of the axle body for nonrotatably fitting a first crank arm thereto, and a first centering structure disposed at the first end of the axle body in close proximity to the first rotary linkage member. The rotary linkage member may be formed as a plurality of splines, and the same structure may be formed at the second end.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of application Ser. No. 08/890,744, filed Jul. 11, 1997, now U.S. Pat. No. 6,276,885 which is a division of application Ser. No. 08/687,203, Jul. 25, 1996 now U.S. Pat. No. 5,845,543. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to a bicycle crank axle, a crank arm, and a crank set that offer high mounting precision and fastening strength, and that contribute to lighter weight. It also relates to a bolt and assembly tools used for assembling these components. 
     In conventional mounting mechanisms for the crank arms and crank axle in a bicycle, both ends of the crank axle are shaped into essentially square columns, a square hole is made in each crank arm, and the two are fitted together to fasten the crank arm onto the axle. The precision of centering afforded by the conventional mechanism for fitting together the crank arms and the crank axle is inadequate, and the strength of the linkage in the direction of rotation is inadequate as well. The problem of inadequate linkage strength is particularly notable where an aluminum alloy hollow pipe structure has been adopted for the crank axle, or where an aluminum alloy hollow structure has been adopted for the crank arms in order to reduce weight. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a bicycle crank axle, a crank arm, and a crank set that offer high mounting precision and fastening strength, but also contribute to lighter weight. Novel bolt and assembly tools used are for installing and removing these components so that assembly and disassembly may be accomplished very easily. 
     In one embodiment of the present invention, a crank axle includes an axle body having first and second ends, a first rotary linkage member disposed at the first end of the axle body for nonrotatably fitting a first crank arm thereto, and a first centering structure disposed at the first end of the axle body in close proximity to the first rotary linkage member. If desired, the rotary linkage member may be formed as a plurality of splines, and the same structure may be formed at the second end. A crank arm for fitting to the crank axle includes a crank axle mounting section having a centering structure for centering the crank axle mounting section to an end of a crank axle, and a rotary linkage member for nonrotatably fitting the crank axle mounting section to the end of the crank axle. If desired, the rotary linkage member for the crank arm may comprise splines that mesh with splines on the end of the crank axle. Such a structure provides secure linking of the crank arm to the crank axle without adding excessive weight. 
     To facilitate removal of the crank arm, a special bolt is used to fix the crank arm to the crank axle. The bolt includes a head, a threaded section having a diameter greater than or equal to the head, and a flange disposed between the head and the threaded section. The flange preferably has a diameter greater than the diameter of the threaded section, and the head defines a multiple-sided tool-engaging hole which extends axially into the threaded section to maximize the tool engaging surface. The crank axle mounting section of the crank arm preferably includes a stop ring or similar structure located so that the flange of the bolt is disposed between the stop ring and the first end of the axle body. As a result, the bolt flange presses the crank arm apart from the crank axle when the bolt is loosened. 
     Special tools may be provided to allow easy installation and removal of the components. For example, a tool that can be used for both fixing the axle to the bicycle and fixing a chainwheel to the crank arm includes a tool-mount member shaped to be held and turned by a tool, wherein the tool-mount member defines an opening for receiving a portion of the axle body therethrough. An operating member having a plurality of splines formed on an inside surface thereof is coupled to the tool-mount member. The splines may engage corresponding splines on a mounting adapter for the crank axle or corresponding splines on a nut used to fix a chainwheel to the crank arm. In the latter case, an auxiliary tool may be provided to ensure stable operation of the tool. The auxiliary tool may include a grip section disposed in close proximity to a first end thereof, wherein the grip section has a diameter greater than or equal to a diameter of an end of the crank axle. A support section may be disposed adjacent to the grip section and sized to fit within the opening in the tool-mount member. A second end of the auxiliary tool has a threaded inner peripheral surface which can engage with the bolt used to mount the crank arm to the axle. In this case the bolt serves to temporarily fix the main and auxiliary tool to the crank arm so that the main tool can reliably tighten the chainring fixing nut. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a particular embodiment of a crank arm according to the present invention; 
     FIG. 2 is a side view of the crank arm shown in FIG. 1; 
     FIG. 3 is a longitudinal cross sectional view of the crank arm shown in FIG. 1; 
     FIG. 4 is a rear view of the crank arm shown in FIG. 1; 
     FIGS. 5A-5C are cross sectional views taken along lines  5 A— 5 A,  5 B— 5 B and  5 C— 5 C, respectively, in FIG. 1; 
     FIG. 6 is an oblique view of a particular embodiment of a crank axle according to the present invention for use with the crank arm shown in FIG. 1; 
     FIG. 7 is a cross sectional view of right and left side crank arms attached to the crank axle shown in FIG. 6; 
     FIG. 8 is a cross sectional view illustrating a particular embodiment of a crank arm assembly according to the present invention including a bolt used to fix the crank arms to the crank axle; 
     FIG. 9 is a partial cross sectional view of alternative embodiment of the bolt shown in FIG. 8; 
     FIG. 10 is an oblique view of the bolt shown in FIG. 9; 
     FIG. 11 is a partial cross sectional view of a crank axle according to the present invention mounted to a bicycle frame; 
     FIG. 12 is a cross sectional view illustrating a main tool and an auxiliary tool according to the present invention used to fix chainwheels to the crank arm shown in FIG. 3; 
     FIG. 13 is an oblique view of the main tool shown in FIG. 12; 
     FIG. 14 is an end view of the tool shown in FIG. 13; and 
     FIG. 15 is a partial cross sectional view of the auxiliary tool shown in FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIG. 1 is a front view of a particular embodiment of a crank arm  1  according to the present invention. In this embodiment, the crank arm  1  is fabricated from an aluminum alloy. As shown in FIG. 1, the crank arm end on the pedal mounting side  4  is narrow, and the crank arm end on the crank axle mounting side  2  is wide. Varying the width of the crank arm  1  depending on the position in this way ensures that the stress bearing on crank arm is essentially constant at any point. A chamfered section  11  is formed at the front sides of the crank arm  1 . The size of the chamfer is greater in proximity to the crank arm end on the crank axle mounting side  2  and becomes continuously smaller towards the crank arm end on the pedal mounting side  4 . The front surface of the crank arm  1  can be inscribed with the manufacturer&#39;s logo, a trademark indicating the product name, or the like using laser marking or other means. 
     A crank axle mounting hole  21  for mounting the crank arm  1  onto the crank axle  5  is formed on the crank axle mounting side  2  of the crank arm  1 . The crank arm  1  is mounted onto the crank axle  5  using this crank axle mounting hole  21  as illustrated in FIG. 6. A pedal mounting hole  41  is formed at the crank arm end on the pedal mounting side  4  of the crank arm  1 . The pedal (not shown) is mounted in this pedal mounting hole  41 . 
     FIG. 2 is a side view of the crank arm shown in FIG. 1, and FIG. 3 is a longitudinal cross sectional view of the crank arm shown in FIG.  1 . As shown in those figures, a groove  31  that extends in the lengthwise direction is formed on the back surface of the central section  3  of the crank arm. The shape of the groove  31  is such that in proximity to the two ends of the groove  31 , the depth of the groove becomes progressively smaller towards each end, with the groove depth reaching a minimum at each end. Thus, the bottom surface of the groove may be termed a “ship hull shape”. The bottom surface of the groove  31  in its central section is essentially parallel to the front surface of the central section  3  of the crank arm. 
     A stepped section  32  is formed at the open side of the groove  31 . A cap member  33  is inserted into this stepped section  32 , and the cap member  33  is affixed at its perimeter to the body of the crank arm  1  by inert gas welding using argon gas. The front surface of the body of the crank arm  1  and the surface of the cap member  33  are flush. The pad produced in welding should be removed by machining or other means in order to make the surface flush. 
     A crank axle mounting hole  21  is formed on the crank axle mounting side  2 . The inside wall of the crank axle mounting hole  21  has a flange  22  that projects inward, and female splines  23  which are contiguous with the back surface of this flange  22 . The section of the crank axle mounting hole  21  located closer to the back surface than the splines  23  constitutes the centering member  24 . The centering member  24  can be straight, with an inside diameter that does not vary in the axial direction, but more commonly has a tapered shape whose inside diameter flares out towards the back. The taper angle is 2 to 3°. Male splines  25  for locking the chainring  6  in place are formed on the outer periphery of the basal portion of the protruding section located on the back surface of the crank arm end of the crank axle mounting side  2 . A thread  26  for affixing the chainring  6  is formed on the outer periphery of the protruding section on the back surface. 
     FIG. 4 shows the crank arm  1  viewed from the back. As shown in FIG. 4, the splines  23  and  25  each comprise eight teeth. Too few teeth results in inadequate linkage strength on the part of the rotary linkage member. Providing too many teeth requires complex machining and entails higher costs, and increases the probability of errors in distribution and positioning in the direction of rotation. 
     FIGS. 5A-5C are cross sectional views taken along lines  5 A— 5 A,  5 B— 5 B and  5 C— 5 C, respectively, in FIG.  1 . As shown in those figures, the groove  31  constitutes the majority of the cross section interior in the central section  3  of the crank arm in order to decrease the weight. 
     FIG. 6 shows the exterior of the crank axle  5 . Centering members  52 A, 52 B are formed at each end of the crank axle  5 . The centering members  52 A, 52 B can be straight, with a diameter that does not vary, but they usually have a tapered shape which narrows at the ends. The taper angle is 2 to 3°. Male splines  51 A, 51 B are provided further towards the end from the centering members  52 A, 52 B. The splines  51 A, 51 B have an eight-tooth design. The peripheral surfaces of the splines form continuous unstepped radially outer transition surfaces  555 A and  555 B with the peripheral surfaces of the centering members  52 A, 52 B. The shape of each splines  51 A, 51 B is basically square, or rectangular when viewed perpendicular to the axle axis (X) as shown in FIG. 8, with the planes of the radially straight sides  51 AX, 51 AY,  51 BX,  51 BY being essentially parallel. The linking force in the direction of rotation is borne by planes which are essentially orthogonal to the direction of force, so chatter is largely eliminated. The innermost ends of splines  51 A,  51 B terminate at rear walls  51 AZ,  51 BZ that are essentially straight radially and essentially perpendicular to axle axis (X). Also, the bottom of splines  51 A,  51 B terminate at bottom floors  51 AW,  51 BW that are essentially straight axially and essentially parallel to axle axis (X) for forming right angle corners  51 AK,  51 BK (FIG. 8) with rear walls  51 AZ,  51 BZ. 
     The end faces  49 A, 49 B of the crank axle  5  are provided with internal threads  53  for affixing the crank arms  1 . The crank axle  5  is a hollow pipe whose wall portion  501  is thinner in the central section  502  than wall portions  503 A,  503 B of the centering members  52 A,  52   b , as shown in FIG.  7 . In this embodiment, an aluminum alloy is used as the material for the crank axle  5 . This, together with the fact that the axle is hollow, contributes to reduced weight. 
     FIG. 7 depicts the crank axle  5 , the crank arms  1 , 100 , and the chainring  6  in assembled form. The chainring  6  is mounted onto the crank arm  1  on one side, locked in place by the splines  25 , and fixed with a nut  61 . The crank arm  1  to which the chainring  6  has been affixed is mounted onto one end of the crank axle  5  and affixed by a bolt  54 . The crank arm  100  without a chainring attached is affixed to the other end of the crank axle  5 . The centering members  24  of the crank arms  1 , 100  fit tightly with the centering members  52 A, 52 B of the crank axle  5  so that the components are centered with high precision. The female splines  23  of the crank arms  1 , 100  mesh with the male splines  51 A, 51 B of the crank axle  5  to afford a linkage having high strength in the direction of rotation. 
     The centering members  52 A, 52 B of the aforementioned crank axle  5  and the centering members  24  of the crank arms  1 , 100  have tapered junctions, so the two tapered surfaces fit together tightly. It is therefore necessary to use a removal tool in order to remove the crank arm  1 , 100  from the crank axle  5 . However, the alternative embodiment depicted in FIG. 8 is designed so that a bolt  54  that fastens the crank axle  5  and the crank arm  1  (or  100 ) can be used to release the components. 
     As shown in FIG. 12, an integrated flange  55  is formed on the head of the bolt  54 . When fastening the crank axle  5  and the crank arm  1  together, a washer  56  is inserted and the bolt  54  is tightened. A stop ring  58  is inserted into and retained by a groove  57  located on the inside surface of the crank axle mounting hole  21 . To remove the crank arm  1  from the crank axle, a hexagonal Allen key is inserted into the hexagonal hole  59  in the crank arm fixing bolt  54  and turned in the reverse direction. The flange  55  of the bolt  54  then pushes the side surface of the stop ring  58 . The flange  55  thus forces the crank arm  1  in the axial direction, so the tight-fitting tapered junctions of the centering members  52 A, 52 B of the crank axle  5  and the centering members  24  of the crank arms  1  can be easily released. Thus, the need for a special tool such as an extractor is obviated. 
     FIG. 9 is a partial cross sectional view of alternative embodiment of the bolt shown in FIG. 8, and FIG. 10 is an oblique view of the bolt shown in FIG.  9 . In the bolt  54  depicted in FIG. 8, the diameter of the thread section and the diameter of the head are about the same, but in the bolt  54  depicted in FIG. 9 and 10, the diameter of the thread section  542  is greater than the diameter of the head  541 , and the diameter of the flange  55  is greater than the diameter of the thread section  542 . The provision of a thread section  542  with a large diameter ensures sufficient strength on the part of the thread section even when the component is fabricated from a light alloy such as an aluminum alloy, and affords adequate tightening force on the part of the bolt  54 . 
     A hexagonal hole  59  formed in the center of the end of the head  541  extends in the direction of the bolt axis. The hexagonal hole  59  extends almost to the distal end of the bolt  54 , such that its bottom surface is located in proximity to the end surface. A longer hexagonal hole  59  provides a greater area of contact between the tightening tool (an Allen key) and the hexagonal hole  59  so that adequate tightening can be achieved even with a light alloy bolt. The length of the hexagonal hole  59  can be chosen in accordance with the tightening force required, but it is necessary for the length to be at least such that the bottom surface of the hexagonal hole  59  extends to the inside surface of the thread section  542 . The diameter of the thread section  542  is rather thick, so the hexagonal hole  59  can extend into its interior; it has adequate strength even when the hexagonal hole  59  is extended into its interior. When fabricated from an aluminum alloy, the bolt  54  has both light weight and adequate strength. 
     FIG. 11 depicts the crank axle  5  which pertains to the present invention installed in the bicycle frame bottom bracket  10 . The crank axle  5  pertaining to this embodiment is provided with a retainer member  50  which protrudes from the center of its outside surface for retaining the bearings. To install the crank axle  5  in the frame bottom bracket  10 , a left mounting adapter  101  and a right mounting adapter  102  are threaded between the frame bottom bracket  10  and the crank axle  5  so that the bearings are retained by the retainer members  50 . The outsides of the ends of the left mounting adapter  101  and a right mounting adapter  102  are provided with male splines. These male splines mesh with the female splines of the assembly tool  7  so that each adapter can be screwed in. 
     The design of an assembly tool  7  is shown in FIG.  13 . The end facing the viewer is provided with an essentially regular hexagonal wrench mount member  71 . A wrench or other tool is fitted over the wrench mount member  71 , and the entire assembly tool  7  is rotated around its axis. A middle section  72  is located adjacent to the wrench mount member  71 . The peripheral surface of the middle section  72  is cylindrical, and is cut away at opposing faces to produce flat surfaces. Tools such as wrenches of different sizes can be fitted over the flat sections of the middle section  72 . The other end of the assembly tool  7  has a large-diameter section  73 . 
     FIG. 14 shows the assembly tool  7  viewed from the large-diameter section  73  side. The inside of the large-diameter section  73  takes the form of an open cavity. As shown in FIG. 14, female splines  74  are located in the interior. These female splines  74  mesh with the male splines of the left mounting adapter  101  and the right mounting adapter  102 . A through-hole  75  which extends in the axial direction is located in the center of the assembly tool  7 . The diameter of the through-hole  75  is such that the end of the crank axle  5  will pass through it. When the left and right mounting adapters are screwed in, the ends of the crank axle  5  are passed through the through-holes  75  so that the crank axle  5  serves as a guide for rotation of the assembly tool  7 , thus facilitating the assembly operation. 
     FIG. 12 shows the crank arm  1  with the chainring  6  attached. As illustrated in FIG. 12, the chainring  6  is mounted onto the crank arm end on the crank axle mounting side  2  of the crank arm  1  and fixed by a nut  61 . The peripheral surface of the nut  61  is provided with male splines having the same pitch as the male splines of the left mounting adapter  101  and the right mounting adapter  102 , as shown in FIG.  11 . Thus, the nut  61  can be tightened using the same assembly tool  7  as that shown in FIG.  11 . 
     An auxiliary assembly tool  8  is also used in the tightening operation in order to prevent the assembly tool  7  from coming off during tightening. The design of the auxiliary assembly tool  8  is shown in FIG.  15 . One end of the approximately cylindrical auxiliary assembly tool  8  is provided with a grip section  81  whose outside surface has been knurled to prevent slippage. The diameter of the grip section  81  is greater than the diameter of the through-hole  75  of the assembly tool  7 , and it is designed to retained the assembly tool  7 . A inside surface support section  82  is formed next to the grip section  81 . The diameter of the inside surface support section  82  is about the same as the diameter of the end of the crank axle  5 . Thus, the inside surface of the through-hole  75  in the assembly tool  7  can be rotatably supported by the inside surface support section  82 . The other end of the auxiliary assembly tool  8  is provided with a threaded section  83  into which the bolt  54  can be screwed from the end. The length of the auxiliary assembly tool  8  has been designed such that when the auxiliary assembly tool  8  has been fixed to the crank arm  1  by the bolt  54 , there is a slight gap (about 0.5 mm) between the grip section  81  and the assembly tool  7 . Thus, the assembly tool  7  is rotatably supported by the auxiliary assembly tool  8  in such a way that it will not come off from the nut  61 . Thus, a wrench or other tool can be fitted onto the wrench mount member  71  and the nut  61  can be tightened to fix the chainring  6  to the crank arm  1  while the assembly tool  7  is supported by the auxiliary assembly tool  8 . Since the assembly tool  7  is prevented from coming off from the nut  61 , the operation may be conducted easily and efficiently. 
     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, in the embodiment shown in FIG. 8, a stop ring  58  was provided in crank arm  1 . However, an integrated member which corresponds in function to the stop ring  58  may be formed on the crank arm  1  instead of the stop ring  58 , or some other component may be welded on. Thus, the scope of the invention should not be limited by the specific structures disclosed. Instead, the true scope of the invention should be determined by the following claims. Of course, although labeling symbols are used in the claims in order to facilitate reference to the figures, the present invention is not intended to be limited to the constructions in the appended figures by such labeling.