Derailleur for bicycles

摘要

The invention relates to a rear derailleur cage driven by an electric motor and to a front derailleur cage optionally also driven by an electric motor, with a swivel head, a first and a second parallelogram lever and a chain-guiding mechanism, the four abovementioned components forming a parallelogram via which the chain-guiding mechanism can be displaced parallel in order to transfer the chain from one sprocket to another sprocket arranged parallel thereto. The advantage of the invention consists in that a gearing housing with an internal toothing is integrally formed on the first parallelogram lever, in which housing a driving pinion, which can be driven by an electric motor, engages. The gearing housing is pivoted to and fro by the driving pinion running forwards and backwards, and is guided axially between two inner housing-guiding surfaces in the swivel head via two plane faces which are perpendicular with respect to the axis of rotation of the driving pinion. As a result, the gearing housing is sufficiently well sealed and has the possibility of accommodating a guide for lubricants. Furthermore, a space-saving derailleur cage shape can be achieved by virtue of the arrangement of the electric motor, step-down gear and gearing housing in the swivel head.