Crank apparatus equipped with labor-saving mechanism and bicycle crank assembly

A crank apparatus, comprising:

• a crank mechanism comprising a crank, an axle-end gear arranged at one end of the crank and a pedal-end gear arranged at another end of the crank;
• a transmission mechanism arranged at an internal of the crank, and comprising a rotating axle, a first gear and a second gear, the rotating axle comprising a first end and a second end, the first gear connected to the first end and engaged with the axle-end gear for transmission, the second gear connected to the second end and engaged with the pedal-end gear for transmission, at least one circular groove formed at the first end and the second end;
• at least one supporting module adapted to sheathe the first end of the rotating axle and at least one supporting module adapted to sheathe the second end of the rotating axle, each one of the supporting modules comprising an outer ring and a plurality of rollers, each one of the rollers received inside a respective one of the circular grooves and clamped between the rotating axle and the outer ring;
• and
• a rotating arm module comprising a first rotating arm and a second rotating arm, one end of the second rotating arm connected to the first rotating arm, another end of the second rotating arm connected to the pedal-end gear;
• wherein the crank comprises an outer housing and an inner housing correspondingly attached to the outer housing, the outer housing comprises an axle-clamping half piece arranged at an internal thereof, the inner housing comprises an another axle-clamping half piece arranged at an internal thereof, the another axle-clamping half piece is arranged corresponding to the axle-clamping half piece to clamp each one of the supporting modules and the rotating axle jointly;
• wherein an upper end of the axle-clamping half piece of the outer housing and an upper end of the another axle-clamping half piece of the inner housing jointly define an upper abutment wall, a lower end of the axle-clamping half piece of the outer housing and a lower end of the another axle-clamping half piece of the inner housing jointly define a lower abutment wall, the supporting module adapted to sheathe the first end of the rotating axle abuts against the upper abutment wall, and the supporting module adapted to sheathe the second end of the rotating axle abuts against the lower abutment wall.