Gear-shifting apparatus, and bicycle incorporating same Number:7,520,831 from the United States Patent and Trademark Office (PTO) owispatent A gear-shifting apparatus is provided which does not require a position of a chain to be set with high precision, and which reduces a risk of the chain coming off an adjacent sprocket due to a quick gear shifting operation. The gear shifting system includes a derailer for changing the chain from one sprocket to another among a plurality of axially-arranged gear shifting sprockets, and a case for containing the gear shifting sprockets and the chain. The case is provided with a protruding part for preventing the chain from moving axially outwardly at an area too close to the case. The protruding part effectively prevents the chain from coming off from the adjacent sprocket by means of contact of the protruding part with the chain.<H incorporating, apparatus, Gear, shifting, a, 7520831.html, Patent, pto, 7520831

Title: Gear-shifting apparatus, and bicycle incorporating same

Abstract: A gear-shifting apparatus is provided which does not require a position of a chain to be set with high precision, and which reduces a risk of the chain coming off an adjacent sprocket due to a quick gear shifting operation. The gear shifting system includes a derailer for changing the chain from one sprocket to another among a plurality of axially-arranged gear shifting sprockets, and a case for containing the gear shifting sprockets and the chain. The case is provided with a protruding part for preventing the chain from moving axially outwardly at an area too close to the case. The protruding part effectively prevents the chain from coming off from the adjacent sprocket by means of contact of the protruding part with the chain.

Patent Number: 7,520,831 Issued on 04/21/2009 to Kaga, et al.

Inventors: Kaga; Hiroyuki (Saitama, JP), Kimura; Tatsuro (Saitama, JP)
Assignee: Honda Motor Co., Ltd. (Tokyo, JP)

Appl. No.: 11/165,261

Filed: June 23, 2005

Foreign Application Priority Data


Aug 27, 2004 [JP]			2004-249313

Current U.S. Class: 474/144 ; 474/146; 474/78; 474/80; 474/81

Current International Class: B62J 13/00 (20060101); F16D 1/00 (20060101); F16H 57/02 (20060101)

Field of Search: 474/78,80,144,150,81,146,148 280/260,261

References Cited [Referenced By]

U.S. Patent Documents


3477303	November 1969	Brilando
3815439	June 1974	Tarutani
4023424	May 1977	Ryan et al.
4058020	November 1977	Huret et al.
4384864	May 1983	Bonnard
4468979	September 1984	Inagaki et al.
4487424	December 1984	Ellis
4648855	March 1987	Palloch et al.
4683962	August 1987	True
4790554	December 1988	Siegwart, Jr.
5102372	April 1992	Patterson et al.
5312303	May 1994	Hinschlager
5460576	October 1995	Barnett
5718611	February 1998	Schlangen et al.
5873590	February 1999	Abe et al.
6454288	September 2002	Horiuchi
7011323	March 2006	Sayed
7381143	June 2008	Matsumoto et al.
2001/0039222	November 2001	Mukai et al.
2002/0017159	February 2002	Hayabuchi et al.
2004/0009835	January 2004	Heim
2004/3001454	January 2004	Van Der Linde
2004/0022466	February 2004	Deschler
2005/0173889	August 2005	Matsumoto et al.
2005/0176537	August 2005	Matsumoto et al.
2005/0176538	August 2005	Morita
2005/0215367	September 2005	Thomasberg
2006/0046881	March 2006	Matsumoto et al.
2006/0068954	March 2006	Kaga et al.
2006/0068956	March 2006	Matsumoto et al.
2006/0073925	April 2006	Kaga et al.

Foreign Patent Documents


0936134	Aug., 1999	EP
1418120	May., 2004	EP
2004-155280	Jun., 2004	JP

Primary Examiner: Siconolfi; Robert A
Assistant Examiner: Irvin; Thomas W
Attorney, Agent or Firm: Carrier, Blackman & Assoociates, P.C. Blackman; William D. Carrier; Joseph P.

Claims

What is claimed is:

1. In a manually operable bicycle transmission, a gear shifting system which comprises: a main shaft and a drive input sprocket operatively attached to the main shaft for concurrent rotation therewith in a first direction; an output axle; a sprocket cluster comprising a plurality of gear shifting sprockets arranged in an axis direction, said sprocket cluster mounted on the output axle for concurrent rotation therewith; a first chain extending around the sprocket cluster and the drive input sprocket; a changing mechanism for changing the first chain from one gear shifting sprocket to another among the plurality of gear shifting sprockets for the purpose of performing a gear shift; a case in which the drive input sprocket, the plurality of gear shifting sprockets, a major portion of the output axle and the first chain are contained, the case having two spaced-apart side walls, wherein the output axle comprises an end part which extends laterally outwardly from the case; a chain-guiding member disposed inside and operatively attached to the case, said chain-guiding member comprising a guide part having an opening formed therein to receive a portion of the first chain therethrough, and a check part operatively attached to the guide part and having a plurality of grooves formed therein to receive respective sprockets of the sprocket cluster, the chain-guiding member comprising a roller rotatably attached to the guide part adjacent the opening thereof for contacting the first chain; an output sprocket affixed to the end part of the output axle for concurrent rotation therewith, the output sprocket disposed outside of the case; and a second chain including a portion wrapped around the output sprocket, the second chain disposed outside of the case; wherein an adjacent sprocket is the one of the plurality of gear shifting sprockets which is closest to the case in the axis direction, and wherein the case is provided with a restricted part for restricting the first chain's movement in the axis direction, the restricted part being integrally formed as part of the case and fixed in position relative thereto, the restricted part located in a position in which the restricted part, when viewed from the side, overlaps with a wound part of the chain engaging with the adjacent sprocket, wherein the restricted part comprises a protruding part which is molded integrally with the case such that the protruding part protrudes inwardly into the case from one of the side walls towards the wound part of the chain in the axis direction, and wherein when the first chain is engaged with the adjacent sprocket during use of the bicycle, the restricted part prevents the first chain from derailing from the adjacent sprocket by contact of the restricted part with the first chain.

2. The gear shifting system of a bicycle transmission according to claim 1, wherein the case is provided with a reinforcement rib, which extends from the protruding part outwards in a radial direction of the adjacent sprocket such that the reinforcement rib protrudes in the axis direction, and wherein an inner surface in the axis direction of the reinforcement rib is located in almost the same position as the restricted part, such that the inner surface of the reinforcement rib is substantially aligned with an inner surface of the protruding part, and the restricted part restricts the chain from moving in the axis direction by blocking contact of the protruding part of the restricted part with the chain.

3. The gear shifting system of a bicycle transmission according to claim 2, wherein the reinforcement rib is molded integrally with the case.

4. The gear shifting system of a bicycle transmission according to claim 1, wherein the protruding part comprises a first protruding part and a second protruding part, wherein the first protruding part overlaps, when viewed from the side, the portion of the adjacent gear shifting sprocket to which the chain is hooked, and the second protruding part extends from the first protruding part in the direction of forward rotational direction of the gear shifting sprocket beyond the position in which the chain leads out from the gear shifting sprocket so as to prevent a stagnating portion of the chain from moving toward the case.

5. The gear shifting system of a bicycle transmission according to claim 1, wherein the case is provided with a plurality of reinforcement ribs, each of which extend from the protruding part outwards in a radial direction of the adjacent sprocket such that the reinforcement rib protrudes in the axis direction, and wherein the plurality of reinforcement ribs are spaced at intervals in the circumferential direction of the adjacent sprocket.

6. The gear shifting system of a bicycle transmission according to claim 5, wherein each of the plurality of reinforcement ribs comprises an inner rib and an outer rib, the inner rib formed on an inner surface of the case so as to lie on a radially outward portion of the protruding part, the outer rib formed on an outer surface of the case so as to be coincident with the protruding part, wherein the number of inner ribs is the same as the number of outer ribs.

7. The bicycle gear shifting system of claim 1, wherein the sprocket cluster is mounted in the case in a manner such that axial movement of the sprocket cluster in the case is substantially prevented.

8. A bicycle including a gear shifting apparatus, the gear shifting apparatus comprising: a main shaft and a drive input sprocket operatively attached to the main shaft for concurrent rotation therewith in a first direction; an output axle; a sprocket cluster comprising a plurality of gear shifting sprockets arranged in an axis direction, said sprocket cluster mounted on the output axle for concurrent rotation therewith; a first chain extending around the sprocket cluster and the drive input sprocket; a changing mechanism for changing the first chain from one gear shifting sprocket to another among the plurality of gear shifting sprockets for the purpose of performing a gear shift; a case in which the drive input sprocket, the plurality of gear shifting sprockets, a major portion of the output axle and the first chain are contained, with the output axle including an end part which extends laterally outwardly from the case; a chain-guiding member disposed inside and operatively attached to the case, said chain-guiding member comprising a guide part having an opening formed therein to receive a portion of the first chain therethrough, and a check part operatively attached to the guide part and having a plurality of grooves formed therein to receive respective sprockets of the sprocket cluster, the chain-guiding member comprising a roller rotatably attached to the guide part adjacent the opening thereof for contacting the first chain; an output sprocket affixed to the end part of the output axle for concurrent rotation therewith, the output sprocket disposed outside of the case; and a second chain including a portion wrapped around the output sprocket, the second chain disposed outside of the case; wherein an adjacent sprocket is the one of the plurality of gear shifting sprockets which is closest to the case in the axis direction, and wherein the case is provided with a protruding part for restricting the first chain's movement in the axis direction, the protruding part being integrally formed as part of the case, extending inwardly therein, and fixed in position relative thereto, the protruding part located in a position in which the protruding part, when viewed from the side, overlaps with a wound part of the chain engaging with the adjacent sprocket, wherein the protruding part prevents the first chain from derailing from the adjacent sprocket by direct interference of the protruding part with the first chain.

9. The bicycle of claim 8, wherein the sprocket cluster is mounted in the case in a manner such that axial movement of the sprocket cluster in the case is substantially prevented.

10. A transmission apparatus for a bicycle, said transmission apparatus comprising: a hollow case; a chain-guiding member disposed inside and operatively attached to the case, said chain-guiding member comprising a guide part having an opening formed therein to receive a portion of a first chain therethrough, and a check part operatively attached to the guide part and having a plurality of grooves formed therein to receive respective sprockets therein, the chain-guiding member comprising a roller rotatably attached to the guide part adjacent the opening thereof for contacting the first chain; a crankshaft extending through said hollow case and being rotatably supported thereon; a drive input sprocket operatively attached to said crankshaft and concurrently rotatable therewith, said drive input sprocket disposed inside of said case; an output axle having a gear-supporting portion disposed in said hollow case and rotatably supported thereon, said output axle having a central axis and further comprising an outer end portion extending outwardly from said case; a plurality of spaced apart gear-shifting sprockets operatively attached to said output axle and concurrently rotatable therewith, said gear sprockets disposed inside of said case; a first chain extending between said drive input sprocket and a selected one of said gear-shifting sprockets, said first chain disposed entirely within said case; a drive output sprocket operatively attached to the outer end portion of said output axle and being concurrently rotatable therewith, said drive output sprocket disposed outside of said case; a second chain including a portion wrapped around the drive output sprocket, the second chain disposed outside of the case; and a changing mechanism for changing the first chain from one of the plurality of gear-shifting sprockets to a selected other one of the plurality of gear-shifting sprockets in response to a gear-shifting operation; wherein an adjacent sprocket is the one of the plurality of gear shifting sprockets which is closest to the case in the axis direction, and wherein the case is provided with a restricted part for restricting the first chain's movement in the axis direction, the restricted part being integrally formed as part of the case and fixed in position relative thereto, the restricted part located in a position in which the restricted part, when viewed from the side, overlaps with a wound part of the first chain engaging with the adjacent sprocket, wherein the restricted part comprises a protruding part which is molded integrally with the case such that the protruding part protrudes inwardly into the case towards the wound part in the axis direction, and wherein the restricted part prevents the first chain from derailing from the adjacent sprocket by contact of the restricted part with the chain.

11. The transmission apparatus according to claim 10, wherein the case is provided with a reinforcement rib, which extends from the protruding part outwards in a radial direction of the adjacent sprocket such that the reinforcement rib protrudes in the axis direction, wherein an inner surface in the axis direction of the reinforcement rib is located in almost the same position as the restricted part such that the inner surface of the reinforcement rib is substantially aligned with an inner surface of the protruding part, the restricted part restricts the chain from moving in the axis direction by contact of the protruding part of the restricted part with the chain.

12. The transmission apparatus according to claim 10, wherein the protruding part overlaps the wound part when viewed from the side.

13. The transmission apparatus according to claim 10, wherein the protruding part protrudes inwardly towards the wound part in the axis direction, the protruding part comprising a first protruding part and a second protruding part, wherein the first protruding part overlaps, when viewed from the side, the portion of the adjacent gear shifting sprocket to which the chain is hooked, and the second protruding part extends from the first protruding part in the direction of forward rotational direction of the gear shifting sprocket beyond the position in which the chain leads out from the gear shifting sprocket so as to prevent a stagnating portion of the chain from moving toward the case.

14. The transmission apparatus of claim 10, wherein the sprocket cluster is mounted in the case in a manner such that axial movement of the sprocket cluster in the case is substantially prevented.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2004-249313, filed on Aug. 27, 2004. The subject matter of this priority document is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gear-shifting apparatus for a bicycle, and to a bicycle incorporating the apparatus. More particularly, the invention relates to a gear-shifting apparatus of a type using a chain, which shifts the chain from one sprocket to another.

2. Background

One example of a known gear-shifting apparatus for a bicycle is disclosed in Japanese Patent Laid-open Official Gazette No. 2004-155280. This known system includes a drive sprocket connected to a crankshaft through a one-directional clutch, while the drive sprocket is being driven. The known gear-shifting apparatus of this reference also includes a sprocket cluster constituted of a plurality of gear-shifting sprockets, which is connected to an output axle for driving a rear wheel, a chain hooked to the drive sprocket and one of the gear-shifting sprockets, a gear-shifting mechanism, and a case. The gear-shifting mechanism includes a derailer arm for rotatably supporting a guide pulley for guiding the chain to a selected gear-shifting sprocket. When the derailer arm moves along with the guide pulley in the center axis direction of the derailer axle, the chain is shifted from a current gear-shifting sprocket to the selected gear-shifting sprocket among the sprocket cluster. In this way, a gear-shifting operation is done. In addition, the case contains the drive sprocket, the sprocket cluster, the chain and the gear shifting mechanism.

Out of the plurality of gear shifting sprockets, the sprocket which is next to the case in the axis direction is referred to as an adjacent sprocket. If a quick gear shifting operation is performed for the purpose of changing the chain to the adjacent sprocket, the chain moves forcefully in the axis direction along with the guide pulley of the derailer. In such a case, in order to prevent the chain from moving in the axis direction beyond the adjacent sprocket due to inertia and coming off from the adjacent sprocket, a position in the axis direction of the chain or the guide pulley needs to be set with high precision, in response to a gear shifting position based on a gear shifting operation. However, it takes long time to set the position.

The present invention has been made against such a background. An object of the present invention is to provide a gear shifting system which does not require a position of the chain to be set with high precision in response to a gear shifting position, and which prevents the chain form coming off from the adjacent sprocket in conjunction with a quick gear shifting operation. A further object of the present invention is to additionally reduce costs for, and weight of, the gear shifting system provided with a configuration for preventing the chain from coming off the adjacent sprocket. A still further object of the present invention is to additionally improve prevention of chain derailment, and additionally make the case of the gear shifting system highly rigid.

A first aspect of the present invention includes a gear shifting system which comprises a plurality of gear shifting sprockets arranged in an axis direction, and a changing mechanism for changing a chain from one gear shifting sprocket to another among the plurality of gear shifting sprockets for the purpose of performing a gear shifting. The gear shifting system also includes a case in which the plurality of gear shifting sprockets and the chain are contained. In the case of the gear shifting system, a check part is provided for preventing the chain from moving in the axis direction so as to be too close to the case. When viewed from the side, the check part overlaps with a hooked part of the chain engaging with an adjacent sprocket, the adjacent sprocket being the closest sprocket to the case in the axis direction out of the plurality of gear shifting sprockets. The check part prevents the chain from coming off from the adjacent sprocket by means of contact of the check part with the chain.

The check part of the gear shifting system prevents the chain from moving in the axis direction beyond the adjacent sprocket while a gear shifting operation is changing the chain to the adjacent sprocket. Accordingly, the chain will not come off from the adjacent sprocket. For this reason, the position in the axis direction of the chain is not required to be set with high precision, in response to a gear shifting position based on a gear shifting operation.

A second aspect of the present invention includes the invention described above, and further includes the check part being constituted of a protruding part which is molded integrally with the case in a way that the protruding part protrudes towards the hooked part in the axis direction.

In the case of this gear shifting system, since the protruding part constituting the check part is molded integrally with the case, it is not necessary to prepare a specialized member for constituting the protruding part.

A third aspect of the present invention includes the invention described above, and further includes providing the case with a reinforcement rib. The rib extends from the protruding part outwards in a radial direction of the adjacent sprocket, in a way that the reinforcement rib protrudes in the axis direction. A top surface in the axis direction of the reinforcement rib is located in almost the same position as the check part which checks the chain from moving in the axis direction by means of contact of the check part with the chain in the protruding part.

In the case of this gear shifting system, rigidity of the case is further increased by means of the reinforcement rib. In addition, even in a case where a part of the chain extends outwards in the radial direction beyond the protruding part, the part of the chain which extends outwards is prevented from moving in the axis direction beyond the protruding part.

According to the first aspect of the invention, while a gear shifting operation is changing the chain to the adjacent sprocket, the check part prevents the chain from coming off from the adjacent sprocket. For this reason, a position of the chain is not required to be set with high precision in response to the gear shifting position. Accordingly, by means of a simple configuration, the chain is prevented from coming off from the adjacent sprocket due to a quick gear shifting operation.

According to the second aspect of the invention, a specialized member for constituting the protruding part is not required. Accordingly, the number of the parts of, and costs for the gear shifting system are reduced. In addition, the resulting gear shifting system is lighter in weight.

According to the third aspect of the invention, the rigidity of the case of the gear shifting system is increased by means of the reinforcement rib. In addition to the check part, the reinforcement rib prevents the chain from coming off from the adjacent sprocket. Accordingly, the effect of preventing the derailment of the chain is further improved.

Modes for carrying out the present invention are explained below by reference to an embodiment of the present invention shown in the attached drawings. The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent form the detailed description of the embodiment of the invention presented below in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side plan view of a bicycle including an embodiment of the inventive gear-shifting apparatus.

FIG. 2 is an enlarged diagrammatic view of the gear case of the gear-shifting apparatus of FIG. 1 as viewed in the direction of the arrow II in FIG. 4, and a cross section of parts of FIG. 4, which is taken while a second case part of the gear-shifting apparatus of FIG. 1 is removed. In addition, solid lines show an arm which is located in the fastest gear-shifting position. Long dashed double-short dashed lines show an arm which is located in the slowest gear-shifting position.

FIG. 3 is a cross-sectional view of the gear case of the gear-shifting apparatus of FIG. 1 taken along the III-III line in FIG. 2 showing a cross-section of parts of a derailer. In addition, solid lines show the arm Which is located in the fastest gear-shifting position. Long dashed double-short dashed lines show the arm which is located in the slowest gear-shifting position.

FIG. 4 is a cross-sectional view of the gear case of the gear-shifting apparatus of FIG. 1 taken along the IV-IV line in FIG. 2. With regard to the parts of the derailer, FIG. 4 is a cross-sectional view taken along the IVa line in FIG. 2. In addition, solid lines show the arm which is located in the fastest gear-shifting position. Long dashed double-short dashed lines show the arm which is located in the slowest gear-shifting position.

FIG. 5 is a cross-sectional view of the gear case of the gear-shifting apparatus of FIG. 1 taken along the V-V line in FIG. 2.

FIG. 6 is a side view of a main part of a case of the gear-shifting apparatus of FIG. 1, as viewed in the direction of the arrow VI in FIG. 4.

FIG. 7 is a side view of the main part of the case of the gear-shifting apparatus of FIG. 1, as viewed in the direction of the arrow VII in FIG. 4.

FIG. 8 is a cross-sectional view taken in the VIII-VIII line in FIG. 6.

FIG. 9 is an enlarged view of a main part of FIG. 4. In addition, solid lines show the arm which is located in the fastest gear-shifting position. Long dashed double-short dashed lines show the arm which is located in the slowest gear-shifting position.

FIG. 10(A) is a left side view of the arm provided to the derailer of the gear-shifting apparatus of FIG. 1, as viewed in the direction opposite the arrow X in FIG. 9. In addition, solid lines show the arm located in the fastest gear-shifting position. Long dashed double-short dashed lines show the arm located in the slowest gear-shifting position.

FIG. 10(B) is a right side view of the arm provided to the derailer of the gear-shifting apparatus of FIG. 1, as viewed in the direction of the arrow X in FIG. 9. In addition, solid lines show the arm located in the fastest gear-shifting position. Long dashed double-short dashed lines show the arm located in the slowest gear-shifting position.

FIG. 11 is a schematic view of a holder and an arm which are provided to the derailer as viewed in the direction of the arrow XI in FIG. 10(A).

FIG. 12 is a schematic view of the arm which is provided to the derailer as viewed in the direction of the arrow XII in FIG. 10(A).

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, descriptions will be provided for selected illustrative embodiments of the present invention, with reference to FIGS. 1 to 12.

As shown in FIG. 1, a bicycle B is provided with a gear-shifting apparatus T, according to a selected illustrative embodiment of the present invention. The bicycle B includes: a bicycle frame F; a crankshaft 12 operatively mounted to the frame and having a pair of crank arms 12b extending therefrom, with pedals 13 attached to the distal ends of the crank arms. The gear-shifting apparatus T includes an output axle 15 which is driven to rotate by power transmitted thereto after a gear-shifting is performed; and a transmission system, including a drive-power transmitting mechanism.

The bicycle frame F includes a head pipe 1 which rotatably supports the shaft of a front wheel Wf in the lower end thereof, and which supports a front fork 6 mounted with a handlebar 7 at the top of the front fork 6 in a manner such that the front fork 6 can be steered. The bicycle frame F includes a pair of mainframes 2 which are arranged side by side, and which extend obliquely from the head pipe 1 downwards to the rear, down-tubes 3 which obliquely extend from the front ends of the respective two mainframes 2 downwards to the rear, and a pair of under-tubes 4 which are arranged side-by-side, and which connect rear ends respectively of the two main frames 2 to rear ends respectively of the down-tubes 3. The bicycle frame F also includes a saddle frame 5 which extends from each of the main frames 2, and which supports a saddle 8. The two main frames 2 and the two down-tubes 3 are members are initially formed separately from each other, and are later joined together by welding.

It should be noted that positional descriptions of the upper, the lower, the front, the rear, the left and the right in the present specification and claims, respectively, match the upper, the lower, the front, the rear, the left and the right of the bicycle B, considered from the perspective of an operator seated on the saddle 8 and facing forward. In addition, an "axis direction" means a direction in which the axial centerline L3 of rotation of each of gear-shifting sprockets 41-47 extends, and "viewed from the side" means to be viewed in the axis direction.

A pair of swing arms 10 are arranged side by side and are operatively connected to the frame F. The swing arms 10 rotatably support a shaft of the rear wheel Wr at the rear end portions thereof opposite the frame F, as shown. The respective front ends of the swing arms 10 are swingably supported on a pivot axle 9 (see also FIG. 3) provided commonly to rear parts 2a respectively of the two main frames 2 through an axle attached to the respective rear end portions of the pair of swing arms 10. The two swing arms 10 are joined, respectively, to the two main frames 2 through a rear suspension 11. Thereby, the two swing arms 10, along with the attached rear wheel Wr, can swing up and down about the pivot axle 9.

The gear-shifting apparatus T as well as a main shaft 12a of the crankshaft 12 and an output axle 15, both of which are rotatably supported by a case 20 of the gear-shifting apparatus T, are arranged in a space which is located in a lower portion of the bicycle frame F, and which is formed among the rear parts 2a respectively of the two main frames 2 and the two under-tubes 4. In addition, the drive-power transmitting mechanism is arranged on the right side of the bicycle frame F.

As shown in FIG. 2 in addition to FIG. 1, the gear-shifting apparatus T includes a metallic housing or case 20 constituted of a first case part 21 and a second case part 22, which are arranged side by side, and which are joined together with a bolt B1 (see FIG. 5) in two bosses 21a and 22a formed in adjacent peripheral portions thereof. In addition, the case 20 is fixed to each of the two main frames 2 and each of the two under-tubes 4 with bolts B2 (FIG. 1) which are received in a pair of attachment parts (FIG. 2 shows the attachment parts 21b of the first case part 21) formed in the peripheral portions of the case parts 21 and 22, respectively. The first and second case parts 21 and 22, respectively formed of plate materials, are molded through any one of milling out, casting, or pressing.

As shown in FIG. 3 in addition to FIG. 2, the crankshaft 12 is provided as a main shaft 12a which is arranged to penetrate through a lower portion of the case 20 in the left-right direction. As noted above, a pair of crank arms 12b are joined, respectively, to the left and right ends of the main shaft 12a protruding from the case 20. The crankshaft 12 is rotatably supported in the first case part 21 and the second case part 22, respectively, with a pair of bearings 14. In addition, a pedal 13 (see FIG. 13) is rotatably mounted onto the distal end of each of the respective crank arms 12b.

The output axle 15 is arranged in a position forward, and obliquely upward, from the main shaft 12a in a way that a centerline L2 of rotation of the output axle 15 and a centerline of swing of each of the swing arms 10 are in parallel with each other, and in a way that the centerline L2 of rotation of the output axle 15 and the centerline of swing of each of the swing arms 10 are concurrently in parallel with the centerline L1 of rotation of the crankshaft 12. In addition, the centerline L2 of rotation of the output axle 15 and the centerline of swing of each of the swing arms 10 are within a rotation track of the crank arm 12b. The pivot axle 9 is arranged in a position virtually right above the main shaft 12a, such that a centerline L2 of rotation of the output axle 15 and a centerline of swing of each of the swing arms 10 are in parallel with each other, such that the centerline L2 of rotation of the output axle 15 and the centerline of swing of each of the swing arms 10 are concurrently in parallel with the centerline L1 of rotation of the crankshaft 12, and such that the centerline L2 of rotation of the output axle 15 and the centerline of swing of each of the swing arms 10 are within a rotation track of the crank arm 12b. The pivot axle 9, fixed to the main frames 2, is inserted so as to penetrate through-holes respectively of bosses 21c and 22c formed in the first and the second case parts 21 and 22, and supports the first and the second case parts 21 and 22.

As shown in FIG. 4, the output axle 15 contained in the case 20 includes an end part 15a protruding rightwards from the second case part 22. A drive output sprocket 17 for output, which is a drive body for rotational output, is joined to the end part 15a. As shown in FIG. 1 in addition to FIG. 4, a chain 19, which provides a flexible endless power transmission loop for output, is hooked to the drive output sprocket 17 and also to a driven sprocket 18 for output, which is a driven body of rotation for output. In addition, the drive output sprocket 17, the chain 19 and the driven sprocket 18 constitute the drive-power transmitting mechanism for driving the rear wheel Wr which is a drive wheel.

Further descriptions will be provided herein chiefly for the gear-shifting apparatus T, and the structure of the component parts thereof.

As shown in FIGS. 2 to 4, the gear-shifting apparatus T includes the case 20, a speed changing mechanism M1 using a chain, and a gear-shifting mechanism M2 for moving the speed changing mechanism M1 to a desired gear-shifting position, depending on a gear-shifting operation. A derailer 70, which will be described later, is a component of both the speed changing mechanism M1 and the gear-shifting mechanism M2, and is contained in the case 20.

The speed changing mechanism Ml includes: a unidirectional clutch 30; a ball spline 31 which is a sliding mechanism; a drive input sprocket 32; a plurality of gear-shifting sprockets 41 to 47 which are driven sprockets; an endless chain C for gear-shifting and for transmitting a drive force; and a chain-guiding member 50.

The main shaft 12a of the crankshaft 12 is an input axle through which a drive torque is inputted when the rider drives, and rotates, the crankshaft 12. The drive input sprocket 32 is a common sprocket. The drive input sprocket 32 is arranged around the main shaft 12a, and is coaxial therewith. The drive input sprocket 32 is connected to the main shaft 12a through the unidirectional clutch 30 when the drive input sprocket 32 is driven. The unidirectional clutch 30 includes three inner clutch members 30a, three outer clutch members 30b, and three clutch elements 30c. The three inner clutch members 30a are formed as parts of the main shaft 12a. Each of the three outer clutch members 30b has ratchet teeth which are formed in the inner periphery thereof. Each of the three clutch elements 30c is arranged between one of the inner clutch members 30a and corresponding one of the outer clutch members 30b, and includes a claw to engage with the corresponding ratchet teeth of the outer clutch members. The unidirectional clutch 30 transmits to the drive input sprocket 32 only rotations in a direction AO in which the crankshaft 12 makes forward rotations. Hereinafter, reference symbol AO denotes directions in which each of the various axles and the sprockets makes forward rotations when the crankshaft 12 rotates in the forward-rotational direction AO.

Three ball splines 31 are provided between the drive input sprocket 32 and each of the unidirectional clutches 30. Each of the ball splines 31 enables the drive input sprocket 32 to move in a direction A1 in which the centerline L1 of rotation extends (equal to the axis direction) relative to the main shaft 12a, and causes the drive input sprocket 32 to rotate along with the outer clutch member 30b of a corresponding one of the unidirectional clutches 30. Each of the ball splines 31 includes an inner cylinder 31a, an outer cylinder 31b and a plurality of balls 31c. The inner cylinder 31a is joined integrally with the outer clutch member 30b by use of a connecting pin 33, and is rotatably supported by the outer periphery of the main shaft 12a with a bearing 34 located between the inner cylinder 31a and the outer periphery. Outwards in a radial direction of the inner cylinder 31a, the outer cylinder 31b is arranged so as to be coaxial with inner cylinder 31a. Additionally, the outer cylinder 31b is joined integrally with the drive input sprocket 32. The plurality of balls 31c are rollably contained between a pair of containing grooves. The pair of containing grooves are arranged between the inner cylinder 31a and the outer cylinder 31b, and are formed respectively in the inner cylinder 31a and the outer cylinder 31b so as to extend in parallel with the centerline L1 of rotation. Although the above descriptions have mentioned the pair of containing grooves, a plurality of pairs of containing grooves may be provided. In the case of this embodiment, three pairs of containing grooves are provided. For this reason, the outer cylinder 31b and the drive input sprocket 32 rotate integrally with the inner cylinder 31a, with the balls 31c interposed between the outer cylinder 31b and the inner cylinder 31a. On the other hand, the outer cylinder 31b and the drive input sprocket 32 can move in the direction A1 relative to the main shaft 12a and the inner cylinder 31, which can not move in the direction A1.

The output axle 15 is rotatably supported by the case 20 with a pair of bearings 35 therebetween, the pair of bearings 35 being held respectively by the case parts 21 and 22. The output axle 15 has a radial flange 16 formed integrally thereon adjacent a base end thereof, shown on the left in FIG. 4. A sprocket cluster 40 includes a plurality of sprockets which are different from one another in outer diameter and in number of teeth. As shown in FIGS. 4 and 5, the sprocket cluster 40 in mounted on the output axle 15, and is held thereon by a retaining member 48. It will be understood from the drawings that the sprocket cluster is mounted in the case such that axial movement of the sprocket cluster in the case is substantially prevented by the radial flange 16 and by the retaining member 48. As used herein, the outer diameter is the diameter of a circle defined by tooth tips of a sprocket. In the case of this embodiment, the sprocket cluster 40 includes 7 gear-shifting sprockets 41 to 47. The sprocket cluster, thus constituted, is joined with the output axle 15 by use of splines in such a way that the sprocket cluster 40 rotates integrally with the output axle 15, and in such a way that the sprocket cluster 40 is coaxial with the output axle 15. For this reason, a centerline L3 of rotation commonly of the gear-shifting sprockets 41 to 47 matches a centerline L2 of rotation of the output axle 15 in parallel with the centerline L1 of rotation of the crankshaft 12. All of the gear-shifting sprockets 41 to 47 are arranged in their common axis direction, in order from the gear-shifting sprocket 41 for a first speed representing the lowest speed, sequentially to the gear-shifting sprocket 47 for a seventh speed representing the highest speed. In the case of this embodiment, the seven gear-shifting sprockets 41 to 47 are arranged in order leftwards, from a sprocket with the smallest diameter sequentially to a sprocket with the largest diameter.

The chain C is hooked to the drive input sprocket 32 and to a sprocket in operation (hereinafter, referred to simply as a "working sprocket"), which is one of the gear-shifting sprockets 41 to 47. Each of FIGS. 2 to 4 illustrates a state where one of the gear-shifting sprockets 41-47 is selected out of the sprocket cluster 40 by use of the gear-shifting mechanism M2. Accordingly, the output axle 15 is driven, and rotated, by the crankshaft 12, at a ratio which is determined by the drive input sprocket 32 and a working sprocket connected to the drive input sprocket 32 through the chain.

As shown in FIGS. 2 and 5, the chain-guiding member 50 is arranged between the drive input sprocket 32 and the sprocket cluster 40, and in a position in a direction which the chain C driven by the crankshaft 12 forwardly rotating is pulled. The chain-guiding member 50 constitutes a prevention means for preventing a slackened portion of the chain C from getting stuck between the drive input sprocket 32 and the case 20 when a decrease in the tension on the chain causes the slackened portion on the chain C in a position in the direction which the chain C is pulled.

The chain-guiding member 50 includes a guide part 51 and a check part 53. The guide part 51 forms an opening 52 with a width in its axis direction which is slightly larger than a width of the sprocket cluster 40 in its axis direction. The check part 53 prevents a portion of the chain C, which is caused to lead out from one of the gear-shifting sprockets 41 to 47, from moving towards the inside of the orbit of the chain. The guide part 51 guides the chain C which enters the opening 52 from one of the gear-shifting sprockets 41 to 47. The guide part 51 includes an inner guide part 51a, an outer guide part 51b, and side guide parts 51c and 51d. The inner guide part 51a is arranged in a position towards the inside of the orbit of the chain from the opening 52. The outer guide part 51b is arranged in a position toward the outside of the orbit of the chain from the opening 52. The side guide parts 51c and 51d are arranged respectively in positions outside the two sides in the axis direction of the opening 52. In addition, the outer guide part 51b includes a first part 51b1 and a roller 51b2. The first part 51b1 forms the opening 52 in cooperation with the inner guide part 51a, and the side guide parts 51c and 51d. The roller 51b2 is a second part, which is positioned toward the sprocket cluster 40 relative to the first part 51b1, and which guides the chain C to the opening 52. Furthermore, the check part 53 is arranged in a position which makes the check part 53 overlap with each of the gear-shifting sprockets 41 to 47 when the check part 53 is viewed from the side, i.e., from the axial direction. The check part 53 extends from the inner guide part 51a toward each of the gear-shifting sprockets 41 to 47. Sets of teeth respectively of the gear-shifting sprockets 41 to 47 pass respectively of grooves 53b. The grooves 53b have their respective end parts 53a, and the number of the end parts 53a is equal to that of the gear-shifting sprockets 41 to 47.

The inner guide part 51a, the first part 51b1, the check part 53 and the left side guide part 51c are constituted of a first member made of synthetic resin and which is a single member. The right side guide part 51d includes a second member made of synthetic resin. In addition, the first and the second members of the chain-guiding member 50 are joined to the first case part 21 with a pair of bolts B3 (FIGS. 2, 5). This fixes the chain guide member 50 to the case 20. On the other hand, the roller 51b2 is rotatably supported by a supporting axle 54. The left side of the supporting axle 54 is supported by the side guide part 51c and the first case part 21, and the right side of the supporting axle 54 is supported by the side guide part 51d and the second case part 22.

For example, when the bicycle B makes forceful upward and downward motions within a short time due to bumps of the road surface, a portion of the chain C in a direction which the chain C is pulled may jolt up and down, or a portion of the chain C may jolt inward and outward from the orbit of the chain. However, even if such jolts occur on the chain C, the chain guide member configured in the aforementioned manner causes the chain C to come in contact with the inner guide part 51a and the outer guide part 51b while the chain C is passing through the opening 52, thus checking the jolt magnitude of the chain. Accordingly, the chain is inhibited from jolt. This enables the bicycle B to run smoothly.

In addition, the chain C may run in a way that a decrease in the tension on the chain causes a slackened portion on the chain C in a position in the direction which the chain C is pulled. For example, the bicycle B may make an inertial forward motion while the crankshaft 12 is in a state of being in a halt or in a state of making a reverse rotation. In such a case, a torque is transmitted from the rear wheel Wr to the sprocket cluster 40 through the aforementioned drive-power transmitting mechanism and the aforementioned output axle 15. The torque drives the drive input sprocket 32 to rotate in the forward rotational direction A0 through the chain C. In this occasion, a decrease in the tension on the chain generates a slack portion of the chain in a position in the direction which the chain is pulled. Particularly, the bicycle B may continue traveling forward after the crankshaft 12, which has been forwardly rotated, comes to a sudden halt or while the crankshaft 12, which has been forwardly rotated, is caused to rotate in the reverse direction. In such a case, a portion of the chain C may become extremely slack so that the portion of the chain becomes entangled immediately before the drive input sprocket 32. The entangled portion of the chain may get stuck between the drive input sprocket 32 and the case 20.

However, even if a portion of the chain C becomes slack in a position in the direction which the chain is pulled, the chain-guiding member 50 decreases the slack in the chain C. This occurs because the chain-guiding member 50 causes the chain C to come into contact with the inner guide part 51a or the outer guide part 51b, thus checking an amount of the slack in the chain C.

Furthermore, when a portion of the chain is extremely slack in a position in the direction which the chain is pulled, the slackened portion of the chain is checked by the check part 53 of the chain-guiding member 50. This prevents the slackened portion of the chain from getting caught in the gear-shifting sprockets 41 to 47. In addition to that, the slackened portion of the chain is guided along the check part 53 towards the guide part 51. Accordingly, the slackened portion of the chain constitutes a stagnant portion C2 which makes the slackened portion of the chain temporarily stagnate in a position toward the sprocket cluster 40 from the drive input sprocket 32 and the opening 52, the position being between the guide part 51 and the sprocket cluster 40 (FIG. 6 shows a condition where a portion of the chain C stagnates). In this manner, the chain-guiding member 50 prevents the slackened portion of the chain C, which is generated in a position in the direction which the chain C is pulled, from getting stuck between the drive input sprocket 32 and the case 20. Moreover, the inner guide part 51a1 and the roller 51b2 also guide the chain C in a way that the stagnant portion C2 is sequentially drawn in a line and passes through the opening 52. In this respect, the chain guide member 50 is also chain-alignment means for aligning the stagnant portion C2.

Suppose that gear-shifting positions offered by the sprocket cluster 40 are bisected into low and high speed positions. With the portion of the chain C, in a position in a direction which the chain is pulled, the inner guide part 51a contacts a portion of the chain C hooked to one of the gear-shifting sprockets 44 to 47 which is a working sprocket in the high speed positions. The roller 51b2 contacts a portion of the chain C hooked to one of the gear-shifting sprockets 41 to 43 which is a working sprocket in the low speed positions.

As shown in FIGS. 2, 4 and 6 to 9, sprockets 41 and 47 are end sprockets positioned the outermost in the axis direction in the sprocket cluster 40, and concurrently are the most adjacent to the case 20 in the axis direction in the sprocket cluster 40. Of the two gear-shifting sprockets 41 and 47, the gear-shifting sprocket 41 is the closer to the case 20 in the axis direction. For the gear-shifting sprocket 41, the gear-shifting apparatus T is provided with a protruding part 56, using a part of the case 20, which is a check part for preventing the chain C from moving in the axis direction beyond the gear-shifting sprocket 41 while the derailer 70 moving in the axis direction is shifting the chain C to the gear-shifting sprocket 41.

Specifically, the protruding part 56 prevents the chain C from moving in the axis direction beyond the gear-shifting sprocket 41, lest the chain C should come too close to the first case 21 while the chain C is being shifted from one sprocket to another in the sprocket cluster 40. Such a protruding part 56 is provided integrally to the first case 21 which is a part of the case 20, in a position where the protruding part 56 overlaps a portion C1 of the gear-shifting sprocket 41 to which the chain C is hooked when viewed from the side. With regard to the protruding part 56, an inner part 56c, which is positioned inwardly in the axis direction, has an inner surface 56d which is a check surface for checking the chain C from moving too far in the axis direction. Accordingly, the chain C comes into contact with the inner surface 56d when the chain C is about to move in the axis direction beyond the gear-shifting sprocket 41. This prevents the chain C from coming off from the gear-shifting sprocket 41.

The protruding part 56 includes a first part 56a and a second part 56b. The first part 56a overlaps the portion C1 of the gear-shifting sprocket 41 to which the chain C is hooked, when viewed from the side. The second part 56b extends into the first part 56a, and extends longer in the forward rotational direction A0 than the first part 56a near a position of the gear-shifting sprocket 41 from which the chain C is caused to lead out. The second part 56b extends from the first part 56a toward the check part 53 of the chain guide member 50. When the crankshaft 12 does not make a forward rotation, or in an equivalent case, the chain guide member 50 causes the stagnant portion C2 on the chain C. When a gear-shifting operation under such a condition causes a guide pulley 72 to move in the axis direction towards the gear-shifting sprocket 41, the second part 56b prevents the stagnant portion C2 from coming closer in the axis direction to the first case 21 beyond the gear-shifting sprocket 41.

In addition, a reinforcement rib is molded integrally with, and provided to, the first case 21. The reinforcement rib extends in the radial direction of the gear-shifting sprocket 41 from the protruding part 56. The reinforcement rib includes a plurality of inner ribs 57 and a plurality of outer ribs 58. The inner ribs 57 extend outwards in the radial direction from the protruding part 56, and are provided at intervals in the circumferential direction. The outer ribs 58 are provided to the protruding part 56 at intervals in the circumferential direction. The inner ribs 57 are provided so as to protrude in the same axis direction as the protruding part 56 does. As shown in FIG. 8, an inner surface 57a in the axis direction of each of the inner ribs 57 are located in almost the same position as the inner surface 56d of the protruding part 56. Each of the outer ribs 58 is provided in a position at the same angle as a corresponding one of the inner ribs 58 is, with the centerline L3 of rotation defined as the center, when viewed from the side. The number of the outer ribs 58 thus provided is therefore the same as the number of the inner ribs 57.

As shown in FIGS. 1 to 3, the gear-shifting mechanism M2 is provided with a gear-shifting operation mechanism 60 and the derailer 70. The derailer 70 is a changing mechanism for changing the chain C from one sprocket to another within the sprocket cluster 40 in response to a gear-shifting operation through the gear-shifting operation mechanism 60. The chain C is hooked to the drive input sprocket 32, a working sprocket, the guide pulley 72 and a tension pulley 82. The guide pulley 72 and the tension pulley 82 are arranged in a slackened portion of the chain C driven by the forward rotating crankshaft 12.

The gear-shifting operation mechanism 60 is connected to the derailer 70 in the case 20. The gear-shifting operation mechanism 60 is provided with a gear-shifting operation member 61 and an operation cable 62. The gear-shifting operation member 61 includes a gear-shifting lever operated by the rider and the like. The operation cable 62 is an operation force transmitting member for operationally connecting the gear-shifting operation member 61 and the derailer 70 for the purpose of transmitting the operation of the gear-shifting operation member 61 to the derailer 70. The operation cable 62 includes an outer cable 62a and an inner cable 62b. The outer cable 62a is tubular, and is held by the bicycle frame F. The inner cable 62b is inserted inside the outer cable 62a. One end part of the inner cable 62b is connected to the gear-shifting operation member 61, and the other end part of the inner cable 62b is connected to the derailer 70.

As shown in FIGS. 2 to 5 and 9, the derailer 70 is arranged above the main shaft 12a of the crankshaft 12, and is provided with a base part 71, the guide pulley 72, a holder H, a parallelogram link mechanism 73 and a tensioner 74. The base part 71 is fixed to, and is held by, the two case parts 21 and 22, and is provided with a holding part 71a for the outer cable 62a. The base part 71 is shaped like a cylinder. The guide pulley 72 is a guide member for guiding the chain C in such a way that the chain C is hooked to a working sprocket when the chain C is intended to be moved among the gear-shifting sprockets 41 to 47. The holder H rotatably supports the guide pulley 72. The parallelogram link mechanism 72 links the base part 71 and the holder H together, and has a pair of links 73a and 73b. The pair of links 73a and 73b are an operation mechanism for moving the holder H and the guide pulley 72 in the axis direction and in the radial direction of the centerline L3 of rotation in response to a gear-shifting operation through the gear-shifting operation mechanism 60. The tensioner 74 provides a tension force to the chain C.

The holder H includes a first holder part 76 and a second holder part 77 as well as a supporting part 78. The first holder part 76 and the second holder part 77 are arranged respectively in a left part and a right part of the guide pulley 72, which are the two sides of the guide pulley in the