Methods and apparatus for flexure-based torque sensor in a bicycle

#The present invention relates generally to bicycles.

#In exemplary implementations, this invention helps facilitate motor-assisted pedaling of a bicycle. In this “power pedaling”, an electric motor augments the power provided by a human rider's pedaling. It can feel to the rider as if the rider is pedaling in low gear, but the bike is moving rapidly as if in high gear. The rider can—simply by pedaling—control the power delivered by the bike's motor.

#In a prototype of this invention, a radial flexure is part of a drivetrain that transmits torque from the rider to the back wheel. (The drivetrain includes the bike's pedals, a sprocket, a chain, another sprocket, a freewheel, the flexure and the back wheel's casing.)

#FIG. 1 shows a radial flexure.

#FIG. 2 is a graph that shows motor torque contribution versus wheel velocity.

#FIG. 3 is a diagram showing the flexure, freewheel, back wheel and motor.

#The above Figures illustrate some illustrative implementations of this invention, or provide information that relates to those implementations. However, this invention may be implemented in many other ways. The above Figures do not show all of the details of this invention.

#FIG. 1 shows a radial flexure 101, in an illustrative implementation of this invention. The flexure 101 is disk-shaped, and configured to rotate about an axis of rotation at the center of the flexure. The flexure comprises an outer rim 113, an inner rim 111, and forty “spokes” (e.g., 103, 105) that radiate outward from the axis of rotation. The spokes (e.g., 103, 105) are separated by holes (e.g., 107). Each spoke is shaped roughly like a lop-sided bowtie: it is narrower in its middle (e.g., 125) than at its ends (e.g., 121, 123). Each spoke is lopsided because its outer end (e.g., 123) is wider than the inner end (121). In this context, “outer” means closer to the outer rim 113 and “inner” means closer to the inner rim 111. The spokes are configured to elastically deform when the angular displacement of the pedal is different than the angular displacement of the wheel (in each case measured relative to a reference that is fixed relative to the bike frame). That is, the spokes are configured to elastically deform when θflexure=θpedal−θwheel≠0. In this elastic deformation, the length of the spoke does not change, but the outer end of the spoke tends to rotate about the axis of rotation, relative to the inner end of the spoke. The flexure 101 has a hole 109 at the center of the flexure. Part of the freewheel apparatus is inserted into this hole 109.

#FIG. 2 is a graph that shows motor torque contribution versus wheel velocity, in an illustrative implementation of this invention. FIG. 2 shows the torque contribution of the motor with reference to the wheel velocity given a fixed velocity input provided by the user. This is not the total torque output of the motor, merely the effective torque output to the ground after factoring in the torque provided by the user to maintain the wheel at the fixed velocity input. Also, the graph represents the instantaneous state where the motor meets a specified torque requirement. After this point in time the wheel velocity will increase due to the motor's effective torque contribution being non-zero, which will move the fixed velocity to a new point.