Bicycle hub transmission with a power control mechanism for a shift assist mechanism

A hub transmission for a bicycle comprising:

• a hub axle;
• a driver rotatably supported to the hub axle;
• a hub shell rotatably supported to the hub axle;
• a power transmitting mechanism disposed between the driver and the hub shell for communicating rotational power from the driver to the hub shell through a plurality of power transmission paths;
• a shift mechanism for selecting the plurality of power transmission paths;
• a shift assist mechanism for communicating rotational power from the driver to the shift mechanism;
• and
• a power control mechanism disposed between the driver and the shift assist mechanism and coupling rotational power from the driver to the shift assist mechanism for communicating rotational power from the driver to the shift mechanism to prevent locking between the driver and the shift mechanism when the shift assist mechanism engages the driver to communicate rotational power from the driver to the shift mechanism and the shift mechanism provides excessive resistance to the shift assist mechanism;
• wherein the power control mechanism is structured so that a magnitude of rotational power output from the power control mechanism varies by a non-constant coefficient relative to a magnitude of rotational power input to the power control mechanism as the driver rotates;
• wherein the power control mechanism comprises:
• an assist cam including a plurality of ratchet teeth;
• an engaging member comprising a first pawl supported by the assist cam;
• a first pawl biasing member that biases the first pawl toward the inner peripheral surface of the driver;
• a plurality of first rotational power communicating elements comprising at least one first projection for communicating rotational power from the driver to the shift mechanism when the plurality of first rotational power communicating elements are engaged by the engaging member;
• a plurality of second rotational power communicating elements comprising at least one first recess for communicating no rotational power from the driver to the shift mechanism when the plurality of second rotational power communicating elements are engaged by the engaging member;
• wherein the shift mechanism comprises:
• an actuator member rotatably supported by the hub axle;
• and
• a shift control sleeve rotatably supported by the hub axle, wherein the shift control sleeve is operatively coupled to the actuator member for rotating in response to the rotation of the actuator member;
• and
• wherein the shift assist mechanism comprises:
• a first shift member coupled for rotation with the actuator member;
• a second shift member coupled for rotation with the shift control sleeve;
• a biasing device that biases the first shift member and the second shift member towards each other so that the first shift member rotates together with the second shift member until the shift control sleeve significantly resists rotation of the actuator member whereupon the first shift member rotates relative to the second shift member;
• a second pawl coupled to one of the first shift member and the second shift member for movement between an engaged position wherein the second pawl engages the ratchet teeth of the assist cam and a disengaged position wherein the second pawl is disengaged from the ratchet teeth;
• a second pawl biasing member that biases the second pawl toward the engaged position;
• and
• a pawl control member coupled to the other one of the first shift member and the second shift member for maintaining the second pawl in the disengaged position when the first shift member rotates together with the second shift member and for allowing the second pawl to move to the engaged position when the first shift member rotates relative to the second shift member.