Multiple sprocket assembly for a bicycle

Abstract: A plurality of sprockets (F 1 to F 14 ) are coaxially mounted together, wherein a spacing between each pair of adjacent sprockets is less than a thickness of at least one of the plurality of sprockets (F 1 to F 14 ). In another embodiment of the invention, a plurality of sprockets (F 1 to F 14 ) are coaxially mounted together, wherein a spacing between each pair of adjacent sprockets is less than or equal to approximately 2.0 millimeters. In yet a further embodiment of the present invention, at least ten sprockets are coaxially mounted together to form a first free side sprocket surface (144) facing laterally outwardly and a second free side sprocket surface (140) facing laterally inwardly. A spacing between the first free side sprocket surface (144) and the second free side sprocket surface (140) is less than or equal to approximately 50 millimeters.

Description: BACKGROUND OF THE INVENTION The present invention is directed to bicycle drive mechanisms and especially, but not exclusively, to a multiple sprocket assembly for a bicycle which includes a large number of freewheel sprockets. Figure 1 is a diagram illustrating a typical bicycle drive mechanism. As shown in Figure 1, crank arms 1 having pedals 3 are rotatably coupled to a bicycle frame 2. A chainwheel assembly C comprising a plurality of sprockets, for example, C1 and C2, are connected to crank arms 1 so that rotating pedals 3 in a circular manner causes sprockets C1 and C2 to rotate together with crank arms 1. A freewheel assembly F comprising a plurality of sprockets F1, F2, etc. are mounted to the rear wheel of the bicycle (not shown), and a chain 4 selectively engages one of the chainwheel sprockets and one of the freewheel sprockets. A front derailleur 5 having a chain guide 6 is provided to switch the chain among the plurality of chainwheel sprocket, and a rear derailleur 7 having a guide pulley 8 and a tension pulley 9 is provided to switch the chain among the plurality of freewheel sprockets. It is desirable to increase the number of sprockets, particularly in the rear freewheel, to provide the bicyclist with a greater choice of gears. However, the amount of lateral space in which to mount the chainwheel and/or freewheel is limited by the design of the bicycle and accepted design standards. Thus, in order to fit more sprockets into the available space, it is usually necessary to decrease the spacing between the adjacent sprockets. On the other hand, the minimum spacing between adjacent sprockets is limited by the width of the chain. Figure 2 is a top view of a segment of the conventional chain 4. A typical chain has pairs of outer links 10A and 10B which alternate with pairs of inner links 11A and 11B, wherein each pair of outer links 10A and 10B is connected to a corresponding pair of inner links 11A and 11B using a press-fit connecting pin 12. More specifically, the ends of each outer link 10A and 10B and the ends of each inner link 11A and 11B have openings for receiving connecting pin 12 therethrough. The corresponding ends of one pair of outer links 10A and 10B are aligned with the ends of an associated pair of inner links 11A and 11B, with the inner links 11A and 11B disposed laterally inwardly of the outer links 10A and 10B, so that the openings in the ends are aligned with each other. The ends of inner links 11A and 11B include flange sections 11C and 11D which abut each other and define the openings of inner links 11A and 11B. A roller 13 is disposed between the pair of inner links 11A and 11B and is rotatably supported by flange sections 11C and 11D. The connecting pin 12 passes through the opening in each link end 10A, 10B , 11A and 11B such that the connecting pin 12 is press fit in the outer link ends 10A and 10B. The lateral width of a typical chain 4 thus equals the top width of two outer links 10A and 10B plus the top width of two inner links 11A and 11B plus the width of the roller 13 (which is approximately equal to the width of the flange sections 11C and 11D). As a result, the number of sprockets in the multiple freewheel assembly is limited accordingly. More specifically, the minimum spacing between adjacent sprockets is equal to the thickness of one inner chain plate plus the thickness of one outer chain plate plus the thickness of the laterally projecting portion of the connecting pin plus a small free area to avoid binding of the chain, the sum of which is approximately equal to 2.8 millimeters. EP 0,561,380 discloses a chain driving mechanism which can be used with a bicycle. SUMMARY OF THE INVENTION According to the present invention, there is provided a sprocket cluster in accordance with Claim 1. A preferred embodiment of the invention provides a bicycle drive mechanism which includes a large number of freewheel sprockets, for example, ten or more and preferably fourteen freewheel sprockets. A very narrow chain may be used with the freewheel sprocket cluster to maximise the number of sprockets which can be mounted together. In one embodiment of the present invention, a plurality of sprockets are coaxially mounted together, wherein a spacing between each pair of adjacent sprockets is less than a thickness of at least one of the plurality of sprockets. In another embodiment of the invention, a plurality of sprockets are coaxially mounted together, wherein a spacing between each pair of adjacent sprockets is less than or equal to approximately 2.0 millimeters. In yet a further embodiment of the present invention, at least ten sprockets are coaxially mounted together to form a first free side sprocket surface facing laterally outwardly and a second free side sprocket surface facing laterally inwardly. A spacing between the first free side sprocket surface and the second free side sprocket surface is less than or equal to approximately 50 millimeters. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram illustrating a typical bicycle chain drive mechanism; Figure 2 is a top view of a typical bicycle chain; Figure 3 is a rear view of a particular embodiment of a sprocket cluster according to the invention attached to a hub; Figure 4 is a side view of a particular embodiment of the sprocket cluster shown in Figure 3; Figure 5 is an exploded view of the sprocket cluster shown in Figure 3; DETAILED DESCRIPTION OF THE EMBODIMENTS SPROCKET CLUSTER Figure 3 is a partial cross sectional rear view of a particular embodiment of a multiple sprocket cluster 100 according to the invention. In this embodiment, sprocket cluster 100 includes at least ten, e.g., fourteen sprockets F 1 through F 14 . Sprocket cluster 100 is part of freewheel assembly F which, in turn, is part of a hub assembly H. Hub assembly H includes flanges 110 and 114, both of which are connected to spokes 116 in a known manner. Spokes 116 connect the hub assembly to a wheel rim (not shown). In this embodiment, freewheel assembly F includes a mounting cylinder 120 having splines 124 on an outer peripheral surface thereof for engaging corresponding splines 126 formed on the inner peripheral surfaces of sprocket cluster 100, and a free end of mounting cylinder 120 includes a threaded portion 128 on an inner peripheral surface thereof which engages a threaded outer peripheral surface 132 of a lock ring 133 to fix sprocket cluster 100 on mounting cylinder 120. In this embodiment, sprocket cluster 100 has a total width of less than or equal to approximately 50 millimeters. More specifically, sprocket cluster 100 has a total width of less than or equal to approximately 47 millimeters, such as 46.42 millimeters, between a free side 140 of sprocket F 1 and a free side 144 of sprocket F 14 . This may be accomplished in part by forming some, if not all, of the sprockets F 1 -F 14 with a thickness less than or equal to approximately 2 millimeters (at least the outer peripheral portions thereof, if not the entire sprocket). In this embodiment, sprockets F 1 -F 14 may have a thickness less than or equal to approximately 1.8 millimeters, such as 1.76 millimeters. Sprocket F 14 may be formed thicker than the other sprockets to accommodate the forces resulting from high speed operation of the bicycle. Furthermore, a spacing between adjacent pairs of sprockets may be, for example, less than the thickness of at least one of the sprockets F 1 -F 14 . Between a larger diameter sprocket and a smaller diameter sprocket, the spacing may be measured between the root circle of the smaller diameter sprocket (e.g., at the area labeled R in Figure 4) and the axially aligned portion of the larger diameter sprocket. The spacing also could refer to the portions of the smaller diameter sprocket above the root circle and the axially overlapping portions of the larger diameter sprocket. In this embodiment, a spacing between each pair of adjacent sprockets (using at least one of the two methods) is less than the thickness of each sprocket F 1 -F 14 , and it may be, for example, 1.66 millimeters. The minimum spacing is limited by the thickness of the outer link of the chain which, in this embodiment, is 0.9 millimeters. Regardless of the measurement method employed, there is at least some free space (e.g., 0.9 millimeters) between the root circle portions R of the smaller diameter sprocket and the axially aligned portion of the larger diameter sprocket. Figure 4 is a side view of sprocket cluster 100. In this embodiment, sprockets F 1 -F 14 are structured and positioned according to the teachings of USP 4,889,521. That is, a center point O 1 between a pair of adjacent teeth on a smaller sprocket and a center point O 2 between a pair of adjacent teeth on the next larger sprocket, positioned on an approximate tangent extending along a chain path when a chain is being shifted from the smaller diameter sprocket to the larger diameter sprocket, is equal to an integer multiple of the chain pitch. Furthermore, chain guide portions 150 are provided at the inside surface of the larger diameter sprocket at a position along the chain path between the center points O 1 and O 2 . Many such structures are provided on the various sprockets F 1 -F 14 . Figure 5 is an exploded view of cluster 100 showing how sprocket cluster 100 comprises three sub-clusters 160, 164 and 168. Sub-cluster 160 includes sprockets F 1 -F 7 ; sub-cluster 164 includes sprockets F 8 -F 9 , and sub-cluster 168 includes sprockets F 10 -F 14 . 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. For example, the size, shape and orientation of the components may be changed as desired. The thickness of each sprocket in sprocket cluster 100 may be nonuniform. The teeth in sprocket cluster 100 may be modified as desired and may include reduced height teeth or omitted teeth. Thus, the scope of the invention should not be limited by the specific structures disclosed. Instead, the true scope of the invention should be determined by the following claims. Of course, although labeling symbols are used in the claims in order to facilitate reference to the figures, the present invention is not intended to be limited to the constructions in the appended figures by such labeling.

Claims: A sprocket cluster (100) for a bicycle comprising: a plurality of sprockets (F 1 -F 14 ) coaxially mounted together in an axially fixed position relative to each other, characterised in that a free space defining a spacing is disposed between a root circle portion (R) of the smaller diameter sprocket (F 2 -F 14 ) of each pair of adjacent sprockets and an axially aligned portion of the larger diameter sprocket (F 1 -F 13 ) of each pair of adjacent sprockets, and wherein said spacing between each pair of adjacent sprockets is less than or equal to a thickness of at least one of the plurality of sprockets (F 1 -F 14 ). The sprocket cluster according to Claim 1 wherein said spacing between each pair of adjacent sprockets is less than or equal to the thickness of each of the plurality of sprockets (F 1 -F 14 ). The sprocket cluster according to Claim 1 or 2 wherein said spacing between each pair of adjacent sprockets is less than or equal to approximately 2.0 millimetres. The sprocket cluster according to any preceding claim wherein said spacing between each pair of adjacent sprockets is less than or equal to approximately 1.8 millimetres. The sprocket cluster according to any preceding claim wherein said plurality of sprockets comprises at least ten sprockets coaxially mounted together and forming a first free side sprocket surface (140) facing laterally outwardly and a second free side sprocket surface (144) facing laterally inwardly, and wherein a spacing between the first free side sprocket surface (140) and the second free side sprocket surface (144) is less than or equal to approximately 50 millimetres. The sprocket cluster according to Claim 5 wherein the spacing between the first free side sprocket surface (140) and the second free side sprocket surface (144) is less than or equal to approximately 47 millimetres.

Inventors: NAKAMURA YASUSHI, NAKAMURA, YASUSHI
Applicants: SHIMANO KK, SHIMANO INC.
Application year: 1997
Main classification: B62M9
IPC codes: B62M9, F16G13