Multi-speed transmission for bicycles

A variable sprocket transmission driven by a crank assembly for establishing a plurality of speed ratios, relative to an output member, said transmission comprising:

• a first sprocket coupled to the output member;
• a second sprocket driven by the crank assembly, said second sprocket including a guide plate having a series of guide slots formed therein, a plurality of sprocket segments each retained in one of said guide slots for sliding movement and having an internally threaded bore;
• threaded shafts journally supported from said guide plate and passing through said threaded bore of said sprocket segments, and gear means fixed to each of said threaded shafts such that rotation of said gear means and said threaded shafts in a first direction causes outward radial movement of said sprocket segments and rotation of said gear means and said threaded shafts in a second direction causes inward radial movement of said sprocket segments;
• a drive chain coupling said first sprocket to at least one pair of said sprocket segments;
• an actuator mechanism that is movable from a centered position to either of a first actuated position contacting said gear means for causing rotation of said gear means and said threaded shafts in said first direction or a second actuated position contacting said gear means for causing rotation of said gear means and said threaded shafts in said second direction;
• and
• wherein said shift control means includes an electrically-controlled shift system that is operable in response to a speed signal generated by a speed sensor and which is indicative of the rotary speed of said second sprocket, said speed signal being delivered to an electric control unit having power-operated means interconnected to said actuator mechanism such that when said speed signal exceeds a predetermined threshold value said power-operated means is activated for causing movement of said actuator mechanism to said first actuated position for rotating said gear means and said threaded shafts in said first direction so as to increase said second sprocket diameter and establish a higher speed ratio, and when said speed signal indicates that the speed of said second sprocket is below said threshold value then said power-operated means is activated for causing movement of said actuator means to said second actuated position for rotating said gear means and said threaded shafts in said second direction to decrease said second sprocket diameter and establish a lower speed ratio.

A variable sprocket transmission driven by a crank assembly for establishing a plurality of speed ratios, relative to an output member, said transmission comprising:

• a first sprocket coupled to one of the output member and the crank assembly;
• a second sprocket coupled to the other of the output member and the crank member, said second sprocket including a guide plate and a plurality of chain engaging sprocket segments mounted for independent radial movement with respect to said guide plate;
• a drive chain coupling said first sprocket to at least one pair of said chain engaging sprocket segments;
• and
• means for independently advancing each of said plurality of chain engaging sprocket segments in a radial direction under a substantially no-load condition, said means for independently advancing operatively interconnecting said guide plate and said chain engaging sprocket segments.