Device for guiding the chain of derailleur bicycle gear changers

In a device for guiding the link chain of a bicycle derailleur gear changer on a bicycle having a wheel including a hub, a plurality of sprocket wheels attached to said hub and an endless chain link drive chain having links formed of pairs of articulated fish plates, and a derailleur gear changer for moving the chain between said plurality of sprocket wheels attached to the hub of the bicycle wheel, the improvement comprising external and internal cheek plates rigidly secured to each other in slightly spaced relation to each other with the external cheek plate being spaced further from the bicycle wheel than the internal cheek plate, said cheek plates being pivotally mounted on said derailleur gear changer about an axis extending parallel to the axis of rotation of the sprocket wheels for pivotal movement in planes substantially perpendicular to said axes;

• said plates moving together with the derailleur gear changer transversely with respect to said planes of pivotal movement on a path which covers each of said plurality of sprocket wheels;
• a chain guide pulley and a separate chain tensioning pulley rotatably mounted between said cheek plates in spaced relation to each other adjacent opposite ends of the plates, said chain guide pulley being normally located above the tensioning pulley closer to said sprocket than the tensioning pulley, said link chain passing in contact with the pulleys generally diagonally from said tensioning pulley to said guiding pulley between said cheek plates, said cheek plates, at least in the region thereof adjacent the part of the chain guiding pulley which is normally contacted by the link chain during operation of the bicycle, having extension portions extending radially beyond the periphery of said chain guiding pulley through a distance corresponding to at least the height of a chain link, said radial extensions terminating in edges which are turned over in opposite directions extending away from the guiding pulley;
• the edges of the extensions of the cheek plates having a breadth sufficient to support a segment of chain extending between one of said sprocket wheels and said chain-tensioning pulley;
• said turned over edge of the radial extension of the external cheek plate having, at least in the zone adjacent the chain-guiding pulley, a breadth at least equal to the maximum breadth of the links of the chain.