Patent ID: 7779968

Claim:
An electric parking brake system comprising a pair of parking cables each connected to a brake that is used to stop rotation of an associated wheel of a vehicle and adapted to operate the brake, and a motor to generate a driving force required to selectively operate the parking cables, further comprising: a drive gear adapted to be rotated by the motor; a planetary gear unit including a sun gear connected to the drive gear in a power transmittable manner, a plurality of planetary gears gearedly connected with the sun gear so as to revolve along a periphery of the sun gear, an internal gear formed along a revolving path of the planetary gears so as to be gearedly connected with the planetary gears, and an output carrier connected to the planetary gears in a power transmittable manner and adapted to rotate about the same rotating center as that of the sun gear; and a screw-nut unit including a screw member and a nut member screwed to the screw member to perform a relative linear movement therebetween, the screw-nut unit being connected to the output carrier in a power transmittable manner, wherein the parking cables are connected to opposite ends of the screw-nut unit, respectively, and are adapted to be operated by the relative linear movement of the screw member and nut member during rotation of the output carrier; wherein the screw member includes a power connecting portion penetrating through the sun gear to be coupled to the output carrier while being movably inserted through a non-circular center hole perforated through a rotating center of the output carrier, the power connecting portion having a non-circular cross section corresponding to the center hole, and a bolt portion having a plurality of male threads; wherein the nut member has a plurality of female threads corresponding to the male threads of the bolt portion; and wherein the pair of parking cables are coupled to an end of the power connecting portion of the screw member and an end of the nut member, respectively.