US Patent 7574775 Snap hinge for supporting a closure element

A snap hinge for supporting a closure element, which comprises a first articulated quadrilateral and a second articulated quadrilateral, which share a first lever and a second lever, which have as their base element respectively a plate for coupling to a fixed element and a plate for fixing to a closure element, an elastic element acting between a point of the first lever and a point of the second lever, and an auxiliary elastic element, arranged in series to the elastic element and has one end articulated to the first lever and the opposite end articulated to an abutment element rigidly associated with the coupling plate.