Device for folding seat backrests in vehicles

Described herein is a device (1) for sending down seat backrests (2) in vehicles, the backrests (2) being manually mobile between two operative positions, and the device (1) being provided with: an anchoring plate (10) and a supporting plate (20) hinged to one another and fixed, respectively, to a seat-cushion frame (100) and to the backrest (2); and a blocking plate (30), set between the anchoring plate (10) and the supporting plate (20); the blocking plate (30) being manually mobile against the elastic action of a spring (50) fixed to the anchoring plate (10) and being provided, together with the anchoring plate (10) itself, with respective guide slots (14, 33) engaged by a pin (22) fixed to the supporting plate (20) and mobile between two blocking seats (34a, 34b) made at the opposite ends of the guide slot (33) of the blocking plate (30), in positions staggered with respect to the guide slot (33) of the blocking plate (30) itself.