Abstract: An automatic door closing device for use in a sliding type door, which includes a driving section having a spiral spring disposed in a casket to urge the sliding door toward closing direction and a buffer mechanism having a cylinder and a piston for moderating closing speed of the door. The inner end of the spring is secured to a stationary shaft on which the piston is coaxially mounted. The casket containing the spring and fixing the outer end thereof and the cylinder containing the piston through an anti-rotating mechanism are integrally formed as a housing, into which lubricating oil is filled.

Abstract: A door operator mechanism includes a spring biased piston 5 having a non-return valve 6 in its end face slidably disposed in a hydraulic cylinder 3 and coupled to a door lever arm through a pinion shaft 11, a pinion gear 9, and a tooth rack 7 on the piston. If the door is opened beyond a normal angle a rod member 16 disposed within the spring 4 engages and compresses a resilient member 15 disposed between one end of the cylinder and the spring. The resilient member has a higher coefficient of resiliency than the spring and thus is not initially compressed thereby, and its restraining force increases sharply at high compression ratios, to thereby increasingly resist door overtravel.