Rear sprocket for bicycle transmission

A bicycle transmission has among other things a rear hub with a freewheel with an outer freewheel body supporting a plurality of sprockets. A chain is shifted between adjacent pairs of the sprockets by a rear derailleur. Each sprocket includes inner attachment portion and a chain engaging portion having annular root portion and a plurality of teeth. The largest (low gear) sprocket has one or more recesses in the lateral surface that faces towards the center of the bicycle so that the largest (low gear) sprocket overlaps the abutments of the outer freewheel body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a sprocket for a bicycle transmission. More specifically, the present invention relates to a rear sprocket for a bicycle transmission having a large number of rear gears or sprockets.

2. Background Information

Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle transmission.

Over the past several years, bicycle riders have desired an increased number of speeds or gear ratios available in bicycle transmissions. Thus, over the past several years, the bicycle industry has increased the number of sprockets installed on the rear-wheel sprocket assembly of bicycles in order to provide additional different gear ratios. Specifically, road bicycles have seen the number of rear sprockets increase from five (5) to nine (9) to provide additional different gear ratios for the bicycle transmission. Mountain bicycles have also seen the number of rear sprockets increase -similarly. Even more recently, in more recent years, the number of rear sprockets has increased from nine (9) to ten (10) rear sprockets on some bicycles (i.e. road bicycles in particular).

While these ten (10) speed rear sprocket assemblies work well, they suffer from some deficiencies. In particular, ten (10) speed rear sprocket assemblies are typically wider in the axial direction than the previous nine (9) speed rear sprocket assemblies. Accordingly, it can be difficult or even impossible to mount the ten (10) speed rear sprocket assemblies on some rear freewheel assemblies that were originally designed for nine (9) rear sprockets. Additionally, even if the ten (10) speed rear sprocket assemblies can be mounted on rear freewheel assemblies that were originally designed for nine (9) rear sprockets, shifting performance can be adversely affected.

More specifically, in the current the ten (10) speed rear sprocket assemblies, the sprockets and the spacers have typically been constructed to be slightly narrower than the previous nine (9) rear sprockets and spacers, and a narrower chain has been utilized in order to achieve the desired shifting performance with the increased number of rear sprockets. However, even when such modifications are made, the ten (10) speed rear sprocket assembly (cassette) is still typically about 1.0 millimeter wider than a nine (9) speed rear sprocket assembly (cassette). Accordingly, if a ten (10) speed rear sprocket assembly (cassette) is mounted in the current manner, the top sprocket (smallest, outermost sprocket) is located laterally outwardly by about 1.0 millimeter more than the top sprocket of a nine (9) speed sprocket assembly (cassette) mounted on the typical freewheel. In some cases, this arrangement may result in the chain touching the bicycle frame when the chain is located on the rear top sprocket (e.g. if the chain is also located on the front top sprocket or largest outermost front chain ring and/or in certain riding conditions).

In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved rear sprocket for a rear sprocket assembly. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a rear sprocket for a rear bicycle sprocket assembly that includes ten (10) sprockets, which can be mounted on an outer freewheel body in a space normally provided for a nine (9) sprocket assembly.

Another object of the present invention is to provide a rear sprocket for a rear bicycle sprocket assembly that includes ten (10) sprockets, which optimizes shifting performance without adversely affecting strength.

Another object of the present invention is to provide a rear sprocket for a rear bicycle sprocket assembly that includes ten (10) sprockets, which projects axially outwardly only about 0.25 millimeter further than a nine (9) sprocket assembly mounted on the same outer freewheel body.

Another object of the present invention is to provide a rear sprocket for a rear bicycle sprocket assembly, which is relatively simple and inexpensive to manufacture and assemble on the outer freewheel body.

Yet another object of the present invention is to provide an outer freewheel body that facilitates the mounting of a rear bicycle sprocket assembly that includes ten (10) sprockets as described in the previous objects of the present invention.

The foregoing objects can basically be attained by providing a rear sprocket for bicycle transmission that comprises an inner attachment portion, an annular root portion and a plurality of teeth. The inner attachment portion has a first lateral surface facing in a first axial direction, a second lateral surface facing in a second axial direction and an inner peripheral edge extending between the first and second lateral surfaces. The annular root portion is located radially outward of the inner attachment portion with the annular root portion having a first side surface facing in the first axial direction and a second side surface facing the second axial direction such that the second side surface and the second lateral surface lie in a common plane. The teeth extend radially outward from an outer periphery of the root portion. The inner attachment portion has at least one recess formed on the first lateral surface and extending radially outward from the inner peripheral edge.

The foregoing objects can also be basically be attained by providing an outer freewheel body for bicycle transmission that comprises a tubular portion and an abutment surface. The tubular portion has an outer surface with a plurality of sprocket engaging splines extending in an axial direction to define a plurality of sprocket engaging grooves disposed between the splines. The abutment surface is disposed at one end of at least one of the splines and faces in a first direction to limit axial movement of a sprocket. The grooves have bottom surfaces that extend beyond the abutment surface in an opposite axial direction relative to the first direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially toFIGS. 1-4, a bicycle10is illustrated having a rear bicycle hub11with a multi-stage rear sprocket assembly (cassette)12mounted on a freewheel13in accordance with a first embodiment of the present invention. The rear sprocket assembly12includes ten (10) rear sprockets S1-S10that are mounted on the freewheel13with a plurality of spacers U1-U9arranged between the sprockets S1-S10. The sprocket S1is the largest (i.e. has the most teeth), innermost sprocket of the rear sprocket assembly12. The sprocket S10is the smallest (i.e. has the fewest teeth), outermost sprocket. In the illustrated embodiment, the sprockets S1-S10have 23T, 21T, 19T, 17T, 16T, 15T, 14T, 13T, 12T, 11T tooth configurations, respectively. However, it will be apparent to those skilled in the bicycle art from this disclosure that the sprockets S1-S10can have different tooth configurations as needed and/or desired.

The sprocket assembly12and the freewheel13are configured and arranged such that the smallest sprocket S10is located axially only about 0.25 millimeter or less outwardly of the location normally occupied by the smallest sprocket of a conventional nine (9) speed rear sprocket assembly (cassette), when mounted on the freewheel13. In particular, the rear sprocket assembly12of the present invention is about 1.0 millimeter wider than a conventional nine (9) speed rear sprocket assembly as measured axially. However, the largest rear sprocket S1and the freewheel13are configured and arranged such that the rear sprocket assembly12is located about 0.75 millimeter or more closer to a center plane P of the bicycle10than a conventional nine (9) speed rear sprocket assembly when mounted on the freewheel13, as explained below in more detail.

Referring toFIG. 1, the bicycle10basically has a frame14with front and rear wheels15and16rotatably coupled thereto. A front fork17is pivotally coupled to the front of the frame14with the front wheel15rotatably coupled thereto in a conventional manner. A handlebar18is rigidly attached to the front fork17in order to turn the front wheel15to steer the bicycle10. The rear wheel16is rotatably coupled to a rear portion or rear triangle of the frame14via the rear hub11in a conventional manner. A seat19is adjustably coupled to the frame14via a seat post in a conventional manner, and a drive train20is provided on the bicycle10for propelling the bicycle10. The bicycle10is conventional except for selected parts of the drive train20, as discussed below.

The drive train20basically includes the rear multi-stage sprocket assembly12of the present invention, a pair of pedals21, a front multi-stage sprocket assembly22mounted to rotate with the pedals21, and a chain23extending between the rear multi-stage sprocket assembly12and the front multi-stage sprocket assembly22. As mentioned above, the rear sprocket assembly12is preferably coupled to the rear hub11via the freewheel13. The pedals21are coupled to the front multi-stage sprocket assembly22by a conventional crank set to transfer force from the rider to the chain23. The force from the chain23is selectively transferred to the rear wheel16via the rear hub11(e.g. via the rear sprocket assembly12and the freewheel13depending on the direction of rotation) in a conventional manner. The chain23used in the drive train20is designed to be compatible with the rear ten-stage sprocket assembly12. In particular, the chain23is preferably slightly narrower than a chain used with a conventional rear nine-stage sprocket assembly due to the width and spacing of the sprockets S1-S10. Narrower chains such as chain23are well known in the bicycle art. Accordingly, the chain23will not be explained and/or illustrated in detail herein. Similarly, the front sprocket assembly22is configured to be compatible with the relatively narrower chain23. Such front sprocket assemblies22are well known in the bicycle art. Accordingly, the front sprocket assembly22will not be explained and/or illustrated in detail herein.

The drive train20is basically controlled by conventional front and rear shifting units (not shown) that control the lateral positions of front and rear derailleurs27and28in a conventional manner. Thus, when the rider is pedaling, the front and rear sprocket assemblies22and12are rotating to circulate or cycle the chain23due to the movement of the pedals21. The shifting units (not shown) can be actuated by the rider to control the lateral positions of the front and/or rear derailleurs27and/or28. When the chain23is circulated or cycled in the forward (clockwise direction as seen inFIG. 1), the shifting units can be actuated to control the gear ratio of the drive train20by controlling the lateral position of the chain23via the derailleurs27and28in a conventional manner. The derailleurs27and28selectively apply a lateral force inwardly/outwardly to the chain23to cause up/down shifts in a conventional manner. The drive train20is basically conventional, except for the rear multi-stage sprocket assembly12and the freewheel13. Thus, the drive train20will not be discussed and/or illustrated in further detail herein, except as related to the rear multi-stage sprocket assembly12and the freewheel13.

Since the various parts of the bicycle10and most of the parts of the drive train20are well known in the bicycle art, these parts of the bicycle10and the drive train20will not be discussed and/or illustrated in detail herein, except as related to the present invention. However, it will be apparent to those skilled in the bicycle art from this disclosure that various conventional bicycle parts such as brakes, different hub structures, etc., which are not illustrated and/or discussed in detail herein, can be used in conjunction with the present invention as needed and/or desired.

Referring now toFIGS. 2-10, the rear sprocket assembly (cassette)12in accordance with the present invention will now be explained in more detail. As mentioned above, the rear sprocket assembly12includes ten (10) rear sprockets S1-S10that are mounted on the freewheel13with the plurality of spacers U1-U9arranged between the sprockets S1-S10such that the sprockets S1-S10are spaced from each other at predetermined intervals. The sprockets S1-S10and the spacers U1-U9are fixedly mounted on the freewheel13of the rear hub11such that the sprockets S1-S10rotate together about a center hub rotation axis X. The sprockets S1-S10typically rotate together in a forward rotational direction R (e.g., in a clockwise direction as viewed inFIG. 1) when the rider is pedaling in a forward (clockwise) direction to propel the bicycle10in a forward direction as seen inFIG. 1.

In the illustrated embodiment, each of the spacers U1-U9preferably has an axial thickness of about 2.35 millimeters in order to provide the desired spacing for the sprockets S1-S10. Each of the sprockets S1-S10preferably has a substantially uniform maximum axial thickness T of about 1.60 millimeters. Accordingly, the assembled rear sprocket assembly12(i.e. the assembled sprockets S1-S10and spacers U1-U9) preferably has an axial width of about 37.5 millimeters as compared to an axial width of about 36.5 millimeters for a conventional nine (9) speed rear sprocket assembly (not shown) having slightly thicker sprockets and spacers. However, in the illustrated embodiment, the sprocket S1is configured and arranged to be located about 0.75 millimeter or more closer to the center plane P of the bicycle10than a conventional nine (9) speed rear sprocket assembly, as explained below.

Referring mainly toFIGS. 8-10, the sprocket S1basically includes an annular main body portion30, an inner annular attachment portion32and an annular chain engagement or root portion34. Preferably, the main body portion30, the inner attachment portion32and the annular chain engagement portion34are integrally formed together as a one-piece, unitary member from a lightweight, rigid material such as a metallic material (e.g. titanium alloy) with a surface treatment applied thereto in a conventional manner. The inner attachment portion32extends radially inwardly from the main body portion30, while the chain engagement portion34extends radially outwardly from the main body portion30.

The inner attachment portion32includes a first annular lateral surface36, a second lateral surface38, an inner peripheral edge (surface)40, a plurality of primary recesses42and a position recess44. The first lateral surface36faces in a first axial direction (i.e. toward the center plane P). The second annular lateral surface38faces in a second axial direction (i.e. away from the center plane P). The inner peripheral edge40extends between the first and second lateral surfaces36and38. The recesses42and44are arranged and configured such that the sprocket S1will be located axially closer to the center plane P of the bicycle10than a conventional nine (9) speed rear sprocket assembly, as explained below. The first and second lateral surfaces36and38are preferably parallel to each other, and preferably perpendicular to the inner peripheral edge40.

The inner peripheral edge40is preferably a notched surface with a plurality of primary hub engaging projections41aand a positioning hub engaging projection41b. The hub engaging projections41aand41bdefine a plurality of primary hub engaging slots43aand a positioning hub engaging slot43bdisposed between the hub engaging projections41aand41b, as seen inFIG. 9. The hub engaging projections41aand41bextend radially inwardly. The inner peripheral edge40is configured and arranged to non-rotatably mate with a corresponding exterior surface of the freewheel13, explained below. In particular, the positioning hub engaging projection41band the positioning hub engaging slot43bare arranged in a particular orientation relative to the chain engagement portion34. The sprockets S2-S10have similar structures to orient the teeth of the various sprockets relative to each other to optimize shifting in a conventional manner.

The recesses42and44are preferably formed in the first lateral surface36. In the illustrated embodiment with the sprocket S1having a thickness T of about 1.60 millimeter, the recesses42and44preferably have an axial depth D of 0.75 millimeter (preferably between 0.75 and 0.80 millimeter). Thus, in the illustrated embodiment the depth D is preferably about one-half or slightly less than one-half of the thickness T of the sprocket S1. In any case, in the illustrated embodiment with the sprocket S1having a thickness T of about 1.60, the depth D is preferably at least 0.75 millimeter and less than or equal to 1.0 millimeter. Accordingly, with this configuration, the sprocket S10will be located between 0.00 and 0.25 millimeter axially outwardly of the normal position of a top (small) sprocket of a conventional nine (9) speed rear sprocket assembly (preferably 0.25 millimeter).

The primary recesses42are disposed radially outwardly of the primary hub engaging slots43a, while the positioning recess44is disposed radially outwardly of the positioning hub engaging slot43b. The recesses42and44permit the sprocket S1to be mounted on the freewheel13to be axially about 0.75 millimeter closer to the center plane P than a conventional nine (9) speed rear sprocket assembly, as explained in more detail below.

Each of the recesses42and44has a mating configuration to engage the freewheel13, described below. In particular, each of the recesses42and44has a substantially rectangular configuration as viewed axially (FIG. 9) with curved inner and outer radially spaced ends. Each of the primary recesses42includes a contact surface45aand a curved outer radial end surface45bwith axially extending ends45cand45dextending radially inwardly therefrom. The contact surfaces45aare preferably parallel to the first lateral surface36, while the surfaces45b,45cand45dare preferably perpendicular to the contact surfaces45a. The depth D is measured axially between the contact surfaces45aand the first lateral surface36. The positioning recess44has a configuration identical to the primary recesses42, but is slightly smaller.

The main body portion30of the sprocket S1includes a first annular side surface46facing in the first axial direction and a second annular side surface48facing in the second axial direction with a plurality of cutouts50extending between the first and second side surfaces46and48for the purpose of weight reduction. The first side surface46extends radially outwardly from the first lateral surface36of the inner attachment portion32, while the second side surface48extends radially outwardly from the second lateral surface38of the inner attachment portion32. The first and second side surfaces46and48are preferably flat, parallel surfaces with the cutouts50extending therebetween.

The annular chain engagement or root portion34of the sprocket S1includes a plurality of chain engagement teeth52with a plurality of roots54arranged therebetween in a circumferentially spaced, alternating arrangement, as best seen inFIG. 9. A plurality of holes56can optionally be formed in the chain engagement portion34for weight saving. As mentioned above, in the illustrated embodiment, the sprocket S1includes twenty-three chain engagement teeth52.

The sprockets S2-S10and the spacers U1-U9are conventional bicycle parts that are well known in the bicycle art. Accordingly, the sprockets S2-S10and the spacers U1-U9will not be explained and/or illustrated in detail herein, except as related to the present invention. In other words, the sprockets S2-S10are substantially identical to the sprocket S1, except that they are smaller (have fewer teeth), do not include the recesses42and44, and may have other conventional modifications due to their decreased size.

The sprockets S1-S10and the spacers U1-U9are non-rotatably, fixedly attached on an external surface of the freewheel13. In particular, the sprockets S1-S10and the spacers U1-U9are slid onto an external mating surface of the freewheel13in an alternating arrangement, as shown inFIG. 4. After the sprockets S1-S10and the spacers U1-U9are slid onto the freewheel13, a locking ring LR (FIGS. 2 and 3) is attached to the freewheel13in a conventional manner to retain all of the sprockets S1-S10and the spacers U1-U9on the freewheel13. The locking ring LR is a conventional member having an externally threaded tubular portion that threads into an end of the freewheel13and an annular ring-shaped flange extending from one end of the externally threaded tubular portion. With the above arrangement, sprockets with different numbers of teeth can be substituted relatively easily for the sprockets S1-S10, as long as the inner most sprocket has an inner attachment portion like that disclosed herein. Of course, it will be apparent to those skilled in the bicycle art from this disclosure that some or all of the sprockets S1-S10and/or spacers U1-U9can be fixedly attached to each other via a plurality of fasteners (not shown) such as rivets in a conventional manner prior to mounting on the freewheel13as needed and/or desired.

In the illustrated embodiment, the spacers U1-U9are identical, i.e. the spacers U1-U9have the same axial thickness and diameter. However, it will be apparent to those skilled in the bicycle art from this disclosure that the spacers U1-U9can have different configurations as needed and/or desired. Moreover, it will be apparent to those skilled in the bicycle art from this disclosure that various alternative structures can be provided for mounting and spacing the sprockets without departing from the scope of the present invention, as needed and/or desired.

Referring now toFIGS. 2-7, the rear hub11and the freewheel13will now be explained in more detail. The freewheel13basically includes an outer tubular freewheel body60, an inner tubular freewheel body62and a one-way clutch64. The rear hub basically includes a hub axle66and an outer hub body or shell68rotatably mounted on the hub axle66via bearings or the like in a conventional manner. The hub shell68is coupled to the rear bicycle rim via a plurality of spokes in a conventional manner. The inner tubular freewheel body62is freely rotatably mounted on the hub axle66, and non-rotatably connected to the hub shell68. The outer freewheel body60is rotatably mounted relative to the inner freewheel body62with the one-way clutch64disposed therebetween in a conventional manner. Thus, forward rotation R of the rear sprocket assembly12rotates the hub shell68to propel the bicycle, while rearward rotation (in a direction opposite of R) of the rear sprocket assembly12is freely permitted relative to the inner freewheel body62and the hub shell68.

The freewheel13is conventional, except for the outer tubular freewheel body60. Moreover, the outer freewheel body60is conventional except for the external configuration thereof, explained below. Accordingly, the freewheel13will not be explained and/or illustrated in detail herein, except as related to the present invention. Rather, it will be apparent to those skilled in the bicycle art from this disclosure that the freewheel13includes various conventional parts such as bearing assemblies, seals, attachment rings and the like, as best seen inFIG. 6. Moreover, it will be apparent to those skilled in the bicycle art from this disclosure that the freewheel13operates in a conventional manner once the rear sprocket assembly12is mounted thereon and that the locking ring LR is threaded into the free end of the hub body60.

Referring mainly toFIG. 7, the outer tubular freewheel body60basically includes an outer tubular portion70having an outer surface72with a plurality of sprocket engaging splines74extending in the axial direction to define a plurality of axially extending sprocket engaging grooves76between the splines74in an alternating manner. The splines74are configured to mate with the slots43aand43bof the sprocket S1, while the grooves76are configured to mate with the projections41aand41bof the sprocket S1. In other words, one of the splines74is smaller (not shown) than the remaining splines74in order to be received in the positioning slot43b, while one of the grooves76is larger (not shown) than the remaining grooves76in order to receive the positioning projection41bin a conventional manner. Thus, the desired orientation of the sprockets S1-S10relative to each other can be obtained.

Each of the splines74includes a stop section78disposed at one end thereof (i.e. arranged at the inner axial end thereof). The stop sections78extend radially outwardly. Each of the stop sections78includes an axially facing abutment surface80that is configured and arranged to contact the sprocket S1. In particular, the stop sections78and the abutment surfaces80are sized and configured such that the stop sections78are at least partially received in the recesses42and44. Similar to the splines74and the grooves76, one of the stop sections78is smaller (not shown) than the remaining stop sections78in order to be received in the positioning recess44. In other words, the stop sections78are shaped to mate with the recesses42and44of the sprocket S1, with the abutment surfaces80contacting the contact surfaces of the recesses42and44to limit axial movement of the sprocket S1. The abutment surfaces80face in an axial direction away from the center plane P (i.e. a first axial direction).

The grooves76extend axially toward the center plane P beyond the abutment surfaces80in order to accommodate the axially closer position of the sprocket S1to the center plane P. In a particular, each of the grooves76has a bottom surface82that extends axially toward the center plane P (i.e. in a second axial direction opposite the first axial direction) beyond the abutment surfaces80by a distance E that is at least 0.75 millimeter. In the illustrated embodiment, the distance E is about 1.0 millimeter, and then the bottom surfaces82of the grooves76begin to taper outwardly. In any case, the distance E should be at least as large as the depth D of the recesses42and44.

Second Embodiment

Referring now toFIG. 11, a modified bottom sprocket S1′ in accordance with a second embodiment will now be explained. The bottom sprocket S1′ replaces the bottom sprocket S1in the rear sprocket assembly12of the first embodiment on the freewheel13of the rear hub11. Thus, a modified rear sprocket assembly is formed when the modified bottom sprocket S1′ is substituted for the bottom sprocket S1in the rear sprocket assembly12of the first embodiment.

The sprocket S1′ is identical to the sprocket S1of the first embodiment, except the sprocket S1′ includes a single annular recess42′ extending around the inner periphery rather than the multiple recesses42and44of the first embodiment. The recess42′ functions the same as the multiple recesses42and44of the first embodiment. In other words, the single annular recess42′ extending around the inner periphery has the same depth as the multiple recesses42and44of the first embodiment, but simply has a different shape as viewed axially (FIG. 11). The annular shape permits alternate techniques for manufacturing and reduces weight for the sprocket S1′ further. The depth or axial dimension of the single annular recess42′ is the same as the multiple recesses42and44of the first embodiment. Thus, when the modified rear sprocket assembly is mounted on the rear hub11, the single annular recess42′ of the sprocket S1′ will have the same configuration and relationship as shown inFIG. 5.

In view of the similarity between the first and second embodiments, the parts of the second embodiment that are identical to the parts of the first embodiment will be given the same reference numerals as the parts of the first embodiment. Moreover, the descriptions of the parts of the second embodiment that are identical to the parts of the first embodiment may be omitted for the sake of brevity. However, it will be apparent to those skilled in the bicycle art from this disclosure that the descriptions and illustrations of the first embodiment also apply to this second embodiment, except as explained and illustrated herein.

As used herein, the terms “forward, rearward, above, below, lateral and transverse” as well as any other similar directional terms refer to those directions of a bicycle in its normal riding position, to which the rear sprocket assembly12and freewheel13are attached. Accordingly, these terms, as utilized to describe the rear sprocket assembly12and the freewheel13in the claims, should be interpreted relative to the bicycle10in its normal riding position. However, the terms “down shift” and “up shift” as used herein in reference to the rear sprocket assembly12should be interpreted to mean a shift from smaller to larger sprocket and from larger to smaller sprocket, respectively, as shown inFIG. 2.