Coaxial mid-drive power device of bicycle

A coaxial mid-drive power device of a bicycle, comprising:

• a motor base, wherein a shaft axis is defined on an axis of the motor base;
• a hollow shaft motor disposed in the motor base and having a hollow shaft at a position of the hollow shaft motor corresponding to the shaft axis;
• a reducing structure disposed in the motor base, wherein two opposite sides of the reducing structure respectively have an input end and an output end;
• the input end is engaged with the hollow shaft, and the output end has a sleeve;
• the reducing structure has a shaft hole at a position of the reducing structure corresponding to the shaft axis;
• a sprocket driving assembly having a one-way bearing bracket, wherein the one-way bearing bracket has a first tube section, a second tube section, and a middle section connected between the first tube section and the second tube section;
• an outer diameter of the first tube section is smaller than an inner diameter of the second tube section;
• a first one-way bearing fits around an outer peripheral surface of the first tube section;
• the first one-way bearing fits in an inner peripheral surface of the sleeve;
• an inner peripheral surface of the second tube section fits around a second one-way bearing;
• a rotation direction of the second one-way bearing is opposite to a rotation direction of the first one-way bearing;
• the second tube section is engaged with a sprocket base;
• a crank spindle penetrating through the hollow shaft, the shaft hole, and the one-way bearing bracket along the shaft axis, wherein two ends of the crank spindle respectively penetrate through two sides of the motor base;
• a side of the crank spindle has a wheel portion having a larger diameter than other portions of the crank spindle;
• the wheel portion fits in an inner peripheral surface of the second one-way bearing;
• another side of the crank spindle has a groove, wherein an inner surface of the groove is engaged with a strain gauge;
• and
• a signal transmission assembly having a rotary base fitting around a portion of the crank spindle that has the groove or is in contact with the groove;
• the rotary base has a ring portion, wherein the ring portion is engaged with a circuit board electrically connected to the strain gauge;
• a control circuit board electrically connected to the hollow shaft motor is fixed in the motor base, wherein the circuit board and the control circuit board face each other;
• an elastic sheet assembly is disposed on either the circuit board or the control circuit board, and an annular conductive rail assembly is disposed on a surface of the other one of the circuit board and the control circuit board;
• the elastic sheet assembly elastically abuts against the annular conductive rail assembly in a direction parallel to the shaft axis to be electrically connected to the annular conductive rail assembly.