Patent ID: 7520831

Claim:
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.