Abstract: A chainless transmission mechanism includes a reinforcing shell capped on a front casing and locked by a lock nut to reinforce the structural strength of the front casing, a locating rod inserted into an inside locating groove of a fourth bevel gear and a second locating groove of a rear-wheel axle to prohibit rotation of the fourth bevel gear relative to the rear-wheel axle, and screw rods respectively threaded into respective screw holes on the fourth bevel gear and engaged into a first locating groove of the rear-wheel axle to prohibit axial displacement of the fourth bevel gear relative to the rear-wheel axle.

Abstract: A chainless transmission mechanism for a bicycle, including a casing mounted in a bottom bracket to hold a bottom bracket bearing axle, permitting the bottom bracket bearing axle to be driven by pedals to turn a rear-wheel hub through a transmission shaft and two transmission gear sets, wherein the bottom bracket has a first end, a second end, and a notch at the second end thereof; the casing is a cylindrical shell inserted through the bottom bracket, having a first end secured to the bottom bracket outside the first end of the bottom bracket by a clamp, a second end disposed outside the second end of the bottom bracket, and a hollow projecting block raised from its second end and forced into engagement with the notch at the second end of the bottom bracket.

Abstract: A wheel hub and transmission gear arrangement of a chainless transmission mechanism for a bicycle, including a wheel hub having an axle block with an outside annular groove and intersected locating grooves, a transmission gear having an annular base mounted on the axle block, the annular base having a plurality of inward projecting blocks respectively forced into engagement with the locating grooves of the axle block and an inside annular groove, and a split binding ring mounted within the outside annular groove of the axle block and the inside annular groove of the transmission gear to firmly secure the axle block and the transmission gear together.