Self-locking device for blinds and shutters

Improved self-locking device for blinds (21) and shutters of the type that include:

• a drive shaft (1) operateable in both rotational directions,
• a rolling drum (23) for a blind (21) rotating together with the drive shaft (1),
• a first freewheel mechanism (2) in which the drive shaft (1) revolves and whose outer bush (3) is joined to a drive cylinder (4) which has a freeing sector (5),
• a second freewheel mechanism (15) in which a locking shaft (16) revolves and whose outer bush (3) is joined to a transmission pinion (14),
• a cogged wheel (17) joined to the locking shaft (16) that has a number of protuberances (18) on its periphery, suitably spaced so that extensions (19) to slats (20) on the blind (21) fit into them,
• a transmission crown (6) rotating freely on the drive shaft (1) with a locking sector (26) on one of its faces and with a housing to receive the freeing sector (5) on the drive cylinder (4) with a certain clearance,
• a braking mechanism consisting of a brake spring (9) formed by various turns of elastic wire distributed axially on the same diameter with its ends bent radially to form stops (10), the brake spring (9) being firmly housed inside a brake cylinder (7) joined to a casing (11) of the device, the locking sector (26) acting on the stops (10) in a first direction and the freeing sector acting on the stops (10) in a second direction, said second direction being opposite of the first direction, to increase the apparent diameter of the brake spring (9), and the locking sector (26) acting on the stops (10) in the second direction and the freeing sector acting on the stops in the first direction to decrease the apparent diameter of the brake spring,
• a transmission mechanism that joins the transmission crown (6) to the transmission pinion (14),
• characterised in that it comprises:
• a number of teeth (27) on the periphery of the brake cylinder (7),
• multiple articulated ratchets (28) on the transmission crown (6) each equipped with a respective guide (29) which pass through a respective opening (30) in the transmission crown (6) itself, with a respective end (31) of each ratchet (28) being able to be housed in the teeth (27) on the brake cylinder (7),
• wings (32) on the drive cylinder (4) with a respective hole (33) to receive and guide the respective guide (29) on the respective ratchet (28),
• a slot (34) in the freeing sector (5) on the drive cylinder (4) which closely grips one of the stops (10) on the brake spring (9).