The invention discloses an automatic closing door closer which comprises a door closer body, an automatic closing device and an auxiliary closing device. The automatic closing device is connected with an output shaft on one side of the main body and comprises a mechanical
locking mechanism composed of an angle
cam, a sliding block and a supporting spring and a triggering mechanism composed of a swing connecting rod, an unlocking connecting rod and an electric driving mechanism with a gear motor, the output shaft is stably locked in a normally-open state, electric unlocking is achieved when fire signals are triggered, and the automatic closing device can automatically close the output shaft. And the door leaf is automatically closed by the door closer main body. The auxiliary closing device is connected with an output shaft on the other side of the main body and comprises a
cam shaft with a concave part and a trigger assisting
assembly composed of a roller, a
piston and a pressure spring, and when the door leaf is closed to the angle smaller than the set angle, the roller falls into the concave part of the
cam, and the pre-tightened spring elastic force is released to generate auxiliary torque. According to the fireproof door, the functions of normally-open locking and releasing and door closing
tail section assisting are integrated, and the automatic closing reliability and the final leakproofness of the fireproof door in a fire disaster are remarkably improved.