Parking brake apparatus

A parking brake apparatus comprising:

• a bolt screw rotated by a driving force transmitted from an actuator;
• one or more pistons disposed at one side or both sides of the bolt screw;
• one or more screw nuts accommodated in the piston, screwed to an end of the bolt screw, and moved along with the rotation of the bolt screw;
• one or more elastic members disposed around the screw nut within the piston, and elastically deformed, in response to a displacement of the screw nut while the screw nut is moved by a set distance, to press the piston toward a shoe;
• and
• a load transfer unit disposed in the piston, and configured to transmit, to the piston, a displacement of the screw nut when the screw nut moves more than the set distance, thereby pressing the piston toward the shoe,
• wherein:
• the load transfer unit comprises a laminated elastic member disposed around the screw nut within the piston and disposed in series with the elastic member;
• the piston comprises:
• a piston body having a receiving space in which the screw nut, the elastic member and the laminated elastic member are accommodated;
• and
• a rotation restraining groove recessed axially from an end of the receiving space, a polygonal end of the screw nut being slidably installed in the rotation restraining groove;
• and
• the receiving space comprises:
• a reduced diameter portion having a first diameter and formed to be continuous with the rotation restraining groove, a portion of the elastic member being accommodated in the reduced diameter portion;
• and
• an enlarged diameter portion having a second diameter larger than the first diameter and formed to be continuous with the reduced diameter portion, the laminated elastic member having a width larger than the first diameter and the other portion of the elastic member protruding by the set distance from the reduced diameter portion being accommodated in the enlarged diameter portion.