Device for adjusting the clearance of a drum brake

A device for adjusting the clearance of a drum brake arranged between a first shoe and a second shoe which cooperate with a braking surface of a drum, said first shoe and said second shoe are moved by an actuation device which stresses them from a resting position, in which said first shoe and said second shoe are away from said braking surface at least by a minimum operating clearance, to a braking position, in which said first shoe and said second shoe abut against said braking surface, wherein:

• said clearance adjustment device comprises an extensible strut assembly arranged between said first shoe and said second shoe, which creates a reaction action on said first shoe and said second shoe when stressed by a braking action applied by the actuation device;
• said extensible strut assembly comprising:
• a piston rotationally constrained to said first shoe;
• a support rotationally constrained to said second shoe and slidingly connected to said piston making the extensible strut assembly extensible to adjust the distance of said first and second shoe;
• a toothed ring rotational with respect to said piston and abutting against said support, by rotating said toothed ring applies an action on said piston and on said support thus extending said extensible strut assembly and moving away said first shoe and said second shoe;
• and wherein said clearance adjustment device further comprises:
• a lever assembly having a first lever end arranged in contact with said second shoe and biased in rotation by said second shoe when said second shoe is stressed by said actuation device;
• said lever assembly rotating about a lever pin;
• and wherein said clearance adjustment device further comprises:
• a sliding guide rotationally connected to said lever assembly, the sliding guide comprising at least one sliding guide portion inserted in the extensible strut assembly directly or indirectly in contact between the support and the toothed ring making a coupling of said sliding guide and said extensible strut assembly;
• said sliding guide sliding with respect to said extensible strut assembly during the rotation of said lever assembly;
• and wherein
• said sliding guide comprises a ratchet mechanism which acts on said toothed ring so as to turn said toothed ring when said sliding guide slides with respect to said extensible strut assembly and when it exceeds a predetermined idle stroke thereof of said ratchet mechanism with respect to said toothed ring;
• and wherein
• said coupling of said sliding guide and said extensible strut assembly makes the sliding of said sliding guide possible when the reaction action, equal and contrary to the braking action, is lower than a predetermined threshold, thus allowing the ratchet mechanism to run said idle stroke and possibly actuate said toothed ring extending said extensible strut assembly;
• and wherein
• said coupling of said sliding guide and said extensible strut assembly prevents the sliding of said sliding guide when the reaction action, equal and contrary to the braking action, is higher than a predetermined threshold, thus preventing the ratchet mechanism, when said threshold is reached, from actuating said toothed ring and preventing the extension of said extensible strut assembly.