Beam type air suspension system with hidden lifting function for low-bed semitrailer

The utility model belongs to the technical field of vehicle suspensions, and particularly relates to a beam-type air suspension system with a hidden lifting function for a low-bed semitrailer, which comprises a support used for being mounted at the bottom of a frame and a main beam used for being mounted on an axle, the front end of the main beam is hinged on the support, a containing cavity is arranged in the support, a backup plate is arranged in the containing cavity, and the backup plate is fixed on the support. The bottom of the backup plate is fixedly connected to the main beam, a lifting air bag is arranged in the containing cavity, and the lifting air bag is clamped between the backup plate and the inner wall of the containing cavity; the rear end of the main beam is provided with the bearing air bag used for being supported at the bottom of the frame, after the lifting air bag is inflated, the backup plate can be pressed, the main beam is promoted to drive the axle to be lifted, at the moment, the fr