Device for automatically adjusting the clearance of a parking brake

A method for adjusting clearance between first and second shoes of a drum brake, the method comprising:

• providing a device for automatically adjusting clearance of a drum brake, comprising
• an extendable strut assembly comprising a toothed ring, said extendable strut assembly being arranged between a first shoe and a second shoe that cooperate with a braking surface of a drum, said first and second shoes being moved by an actuating device that biases the first and second shoes from a resting position, in which the first and second shoes are distanced from said braking surface at least by a predetermined minimum operating clearance, to a braking position, in which the first and second shoes abut against said braking surface, wherein said extendable strut assembly is subjected to a compression action applied by said first and second shoes, and wherein rotation of said toothed ring is blocked thereby preventing an extension of said extendable strut assembly when said compression action is higher than a predetermined threshold;
• said device further comprising:
• a first lever assembly associated with said extendable strut assembly and comprising a ratchet mechanism at an end thereof operatively in contact with said toothed ring,
• a second lever assembly hinged to said first shoe and comprising a coupling portion at a second lever assembly first end, wherein said coupling portion is biased in rotation by said first and second shoes when said first and second shoes are biased by said actuating device, and
• a connecting member connected to said first lever assembly and comprising a connecting seat configured to connect said second lever assembly,
• wherein said coupling portion is coupled to said connecting seat with a predetermined functional clearance so that when said first and second shoes move by action of said actuating device from said resting position approaching said braking surface by said predetermined minimum operating clearance, said coupling portion slides in said connecting seat with an idle stroke equal to said predetermined functional clearance without transmitting motion to said connecting member and to said first lever assembly and wherein said second lever assembly is configured to transmit motion at least to said connecting member after said coupling portion has covered said idle stroke equal to said predetermined functional clearance;
• applying a compression action of less than the predetermined threshold force to the extendable strut assembly by rotating the first and second shoes;
• rotating the second lever assembly by sliding said coupling portion in the connecting seat with an idle stroke equal to said predetermined functional clearance without transmitting motion to said connecting member and to said first lever assembly;
• alternatively,
• if the compression action remains below the predetermined threshold force, rotating the second lever assembly thereby transmitting a motion integral to the connecting member and to the first lever assembly and engaging the ratchet mechanism in the toothed ring and rotating the toothed ring thereby extending the extendable strut assembly;
• or
• if the compression action exceeds the predetermined threshold force, turning the second lever assembly without transmission of motion to said first lever assembly, thereby avoiding biasing said toothed ring.