Bicycle crank arm parts/assembly and assembly tools

Abstract: A crank axle includes an axle body having first and second ends, a first rotary linkage member (51) disposed at the first end of the axle body for nonrotatably fitting a first crank arm (1) thereto, and a first centring structure (52) disposed at the first end of the axle body in close proximity to the first rotary linkage member (51). 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 (21) having a centring structure (24) for centring the crank axle mounting section to an end of a crank axle (5), and a rotary linkage member (23) for nonrotatably fitting the crank axle mounting section (21) to the end of the crank axle. A special bolt (54) is used to fix the crank arm to the crank axle. The bolt (54) includes a head (541), a threaded section (542) having a diameter greater than or equal to the head, and a flange (55) 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 (59) which extends axially into the threaded section to maximise the tool engaging surface. The crank axle mounting section (21) of the crank arm preferably includes a stop ring or similar structure located so that the flange (55) of the bolt (54) 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.

Description: BACKGROUND OF THE INVENTION The present invention is directed to a bicycle crank axle that offers high mounting precision and fastening strength, and that contributes to lighter weight. 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 centring 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 strength is particularly notable where an aluminium alloy hollow pipe structure has been adopted for the crank axle, or where an aluminium 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 that offers high mounting precision and fastening strength, but also contributes to lighter weight. According to the present invention there is provided a bicycle crank axle comprising: an axle body having first and second ends defining respective first and second end faces; a first rotary linkage member comprising a plurality of first splines disposed at the first end of the axle body for nonrotatably fitting a crank arm thereto; and a second rotary linkage member comprising a plurality of second splines disposed at the second end of the axle body for nonrotatably fitting a crank arm thereto; said first and second rotary linkage members being co-axial with said axle body; the axle body further including: a first smooth-surfaced centring structure disposed at the first end of the axle body in close proximity to the first rotary linkage member; and a second smooth-surfaced centring structure disposed at the second end of the axle body in close proximity to the second rotary linkage member, as is known from FR-A-934 104, the invention being characterised in that: each of said first and second splines includes first and second planar side walls defining troughs between adjacent splines, the planes of the first and second side walls of each one of said first and second splines being parallel to one another; and each of said troughs has an inner end terminating at a radially extending rear wall. Preferably, the first centring structure is disposed adjacent to the first rotary linkage member, and wherein the second centring structure is disposed adjacent to the second rotary linkage member. Preferably, the plurality of first splines are axially straight and have a diameter that does not vary in an axial direction, and wherein the plurality of second splines are axially straight and have a diameter that does not vary in an axial direction. Preferably, the first centring structure is tapered to become progressively smaller towards the first rotary linkage member and the second centring structure is tapered to become progressively smaller towards the second rotary linkage member. Preferably, the plurality of first splines and the first centring structure are tapered to become progressively smaller toward the first end face, and wherein the plurality of second splines and the second centring structure are tapered to become progressively smaller toward the second end face. Preferably, the plurality of first splines consists of eight first splines, and wherein the plurality of second splines consists of eight second splines. Preferably, the first centring structure is contiguous with the first rotary linkage member so that the first rotary linkage member is disposed between the first centring structure and the first end face, and wherein the second centring structure is contiguous with the second rotary linkage member so that the second rotary linkage member is disposed between the second centring structure and the first end face. Preferably, an outer peripheral surface of each of the plurality of first splines forms a continuous and straight surface with an outer peripheral surface of the first centring structure, and wherein an outer peripheral surface of each of the plurality of second splines forms a continuous and straight surface with an outer peripheral surface of the second centring structure. Preferably, the first and second ends of the axle body are provided with internal threads. Preferably, a wall portion of a central section of the axle body has a cross sectional thickness less than a wall portion first and second ends of the axle body. Preferably, the axle body has a constant diameter along its entire length. Preferably, the axle body comprises a hollow pipe which is hollow throughout its entire length. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front view of a particular embodiment of a crank arm for use with a crank axle according to the present invention; Figure 2 is a side view of the crank arm shown in Figure 1; Figure 3 is a longitudinal cross sectional view of the crank arm shown in Figure 1; Figure 4 is a rear view of the crank arm shown in Figure 1; Figures 5A-5C are cross sectional views taken along lines A-A, B-B and C-C, respectively, in Figure 1; Figure 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 Figure 1; Figure 7 is a cross sectional view of right and left side crank arms attached to the crank axle shown in Figure 6; Figure 8 is a cross sectional view illustrating a particular embodiment of a crank arm assembly including the crank axle according to the present invention and including a bolt used to fix the crank arms to the crank axle; Figure 9 is a partial cross sectional view of alternative embodiment of the bolt shown in Figure 8; Figure 10 is an oblique view of the bolt shown in Figure 9; and Figure 11 is a partial cross sectional view of a crank axle according to the present invention mounted to a bicycle frame. DETAILED DESCRIPTION OF THE EMBODIMENTS Figure 1 is a front view of a particular embodiment of a crank arm 1 for use with a crank axle according to the present invention. In this embodiment, the crank arm 1 is fabricated from an aluminium alloy. As shown in Figure 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'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. Figure 2 is a side view of the crank arm shown in Figure 1, and Figure 3 is a longitudinal cross sectional view of the crank arm shown in Figure 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. Figures 5A-5C are cross sectional views taken along lines A-A, B-B and C-C, respectively, in Figure 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. Figure 6 shows the exterior of one embodiment of a crank axle 5 in accordance with the invention. A centring number 52 is formed at each end of the crank axle 5. The centering members 52 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 are provided further towards the end from the centering members 52. The splines 51 have an eight-tooth design. The peripheral surfaces of the splines form a continuous surface with the peripheral surfaces of the centering members 52. The shape of each spline 51 is basically square, with the planes of the sides 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 end surfaces 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 is thinner in the central section than at the two ends, as shown in Fig. 7. In this embodiment, an aluminium 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 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 of the crank axle 5 to afford a linkage having high strength in the direction of rotation. The centering members 52 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 Figure 8, 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 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. Figure 9 is a partial cross sectional view of alternative embodiment of the bolt shown in Figure 8, and Figure 10 is an oblique view of the bolt shown in Figure 9. In the bolt 54 depicted in Figure 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 centre 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. Figure 11 depicts the crank axle 5 which pertains to the present invention installed in the bicycle frame 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 10, a left mounting adapter 101 and a right mounting adapter 102 are threaded between the frame 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. While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the scope of the present invention.

Claims: A bicycle crank axle comprising: an axle body (5) having first and second ends defining respective first and second end faces; a first rotary linkage member (51) comprising a plurality of first splines disposed at the first end of the axle body for nonrotatably fitting a crank arm (1) thereto; and a second rotary linkage member (51) comprising a plurality of second splines disposed at the second end of the axle body for nonrotatably fitting a crank arm (1) thereto; said first and second rotary linkage members (51) being co-axial with said axle body (5); the axle body (5) further including: a first smooth-surfaced centring structure (52) disposed at the first end of the axle body in close proximity to the first rotary linkage member (51) ; and a second smooth-surfaced centring structure (52) disposed at the second end of the axle body in close proximity to the second rotary linkage member (51); characterised in that : each of said first and second splines includes first and second planar side walls defining troughs between adjacent splines, the planes of the first and second side walls of each one of said first and second splines being parallel to one another; and each of said troughs has an inner end terminating at a radially extending rear wall. The crank axle according to Claim 1 wherein the first centring structure (52) is disposed adjacent to the first rotary linkage member (51), and wherein the second centring structure (52) is disposed adjacent to the second rotary linkage member (51). The crank axle according to either preceding Claim, wherein the plurality of first splines are axially straight and have a diameter that does not vary in an axial direction, and wherein the plurality of second splines are axially straight and have a diameter that does not vary in an axial direction. The crank axle according to any of Claims 1 to 3, wherein, the first centring structure 52 is tapered to become progressively smaller towards the first rotary linkage member and the second centring structure 52 is tapered to become progressively smaller towards the second rotary linkage member. The crank axle according to Claim 1 or Claim 2, wherein the plurality of first splines and the first centring structure (52) are tapered to become progressively smaller toward the first end face, and wherein the plurality of second splines and the second centring structure (52) are tapered to become progressively smaller toward the second end face. The crank axle according to any preceding Claim, wherein the plurality of first splines (51) consists of eight first splines, and wherein the plurality of second splines (51) consists of eight second splines. The crank axle according to any preceding Claim, wherein the first centring structure (52) is contiguous with the first rotary linkage member (51) so that the first rotary linkage member (51) is disposed between the first centring structure (52) and the first end face, and wherein the second centring structure (52) is contiguous with the second rotary linkage member (51) so that the second rotary linkage member (51) is disposed between the second centring structure (52) and the first end face. The crank axle according to Claim 7, wherein an outer peripheral surface of each of the plurality of first splines forms a continuous and straight surface with an outer peripheral surface of the first centring structure (52), and wherein an outer peripheral surface of each of the plurality of second splines forms a continuous and straight surface with an outer peripheral surface of the second centring structure (52). The crank axle according to Claim 8, wherein the first and second ends of the axle body (5) are provided with internal threads (53). The crank axle according to Claim 1, wherein a wall portion of a central section of the axle body has a cross sectional thickness less than a wall portion first and second ends of the axle body. The crank axle according to Claim 10, wherein the axle body has a constant diameter along its entire length. The crank axle according to any preceding Claim, wherein the axle body (5) comprises a hollow pipe which is hollow throughout its entire length.

Inventors: YAMANAKA MASAHIRO, YAMANAKA, MASAHIRO
Applicants: SHIMANO KK, SHIMANO INC.
Application year: 1996
Main classification: B62M3
IPC codes: B25B13, B25B27, F16B35, B62M3, F16B37