High-efficiency constant-toque output single-cylinder engine

The invention relates to a high-efficiency constant-toque output single-cylinder engine, which comprises a casing, a cylinder, a piston, a crank link mechanism and a valve mechanism. The bottom end of the piston is connected with a power output mechanism. The power output mechanism comprises a rack, a gear, a backstop and a power output shaft, wherein one end of the rack is connected with the bottom end of the piston, the other end of the rack is connected with the link rod of the crank link mechanism, the gear is sheathed on the outer ring of the backstop, the rack is engaged with the gear and the inner ring of the backstop is connected with the power output shaft. The reciprocating movement of the piston is transferred to the gear through the rack connected on the piston and the power is output by the backstop installed on the inner ring of the gear through the power output shaft. Thereby, the invention has the advantages that the movement 'dead point' of the output power of the crank link mechanism of the