Automatic strap retracting mechanism for wheel restraint devices

An automatic strap retracting mechanism for wheel restraint devices, comprising:

• a shell (1);
• a reel (2) rotatably connected inside the shell (2), the reel (2) capable of winding in and retracting a fastening strap (21);
• a ratchet (3) fixed onto the reel (2), the ratchet (3) having ratchet tooth surfaces;
• a locating surface (31) of the ratchet tooth surfaces, the locating surface (31) capable of preventing the fastening strap (21) from loosening;
• a guiding surface (32) of the ratchet tooth surfaces, the guiding surface (32) capable of preventing the fastening strap (21) from tightening;
• a locking piece (4) hinged to the shell (1);
• a pawl (42) of the locking piece (4), the pawl (42) capable of abutting and locking onto the locating surface (31);
• a locking rod (43) of the locking piece (4), the locking rod (43) fixed to the pawl (42), forming an included angle between the locking rod (43) and the pawl (42);
• and
• a coil spring (5) connected to the reel (2), the coil spring (5) capable of rotating the reel (2) in a strap tightening direction to wind in and retract the fastening strap (21);
• wherein when the pawl (42) detaches from the locating surface (31) and the fastening strap (21) is pulled out, the locking piece (4) is capable of swinging to allow the locking rod (43) to abut on the guiding surface (32).