Electric parking brake system

1. An electric parking brake system comprising:

a drum ( 1 ) that s rotated along with a vehicle wheel;

first and second brake shoes ( 2 and 3 ) installed in both sides of the drum to apply brake force to the drum;

an operating lever ( 5 ) that supports the two brake shoes and pushes the two brake shoes against an inner surface of the drum when a pivoting lever ( 8 ) is pulled;

a motor ( 110 ) to generate drive power required to drive the pivoting lever;

a cycloid speed reducer ( 120 ) connected to a rotating shaft ( 111 ) of the motor to amplify the drive power;

a spindle member ( 130 ) rotatably connected to the cycloid speed reducer, the spindle member having a male screw portion ( 131 a ); and

a nut member ( 140 ) having a coupling hole at one end thereof in which a female screw portion ( 141 a ) is screwed to the male screw portion of the spindle member in a rectilinear reciprocal manner and the other end of the nut member comes into contact with a lever pin and is provided with an inclined portion,

wherein the nut member is moved in a longitudinal direction of the spindle member and supports an end of the pivoting lever, and

the lever pin rotatably installed to the pivoting lever slides along the inclined portion.

2. The electric parking brake system according to claim 1 , wherein the pivoting lever has a hook ( 8 b ) formed at the end of the pivoting lever, and the lever pin ( 114 ) is rotatably installed to the hook and comes into contact with the nut member.

3. The electric parking brake system according to claim 1 , wherein a support pin ( 143 ) is further provided at an upper end of the inclined portion and stably supports the lever pin.

4. The electric parking brake system according to claim 1 , wherein the cycloid speed reducer includes:

an eccentric rotator ( 121 ) connected to the rotating shaft of the motor to eccentrically transmit rotation;

a cycloid gear ( 123 ), at the center of which the eccentric rotator is installed, the cycloid gear having a plurality of through-holes ( 124 ) radially arranged about the center thereof and being eccentrically rotated by the eccentric rotator;

an internal gear ( 125 ) engaged with an outer circumferential surface of the cycloid gear to perform revolution and rotation of the cycloid gear via rotation of the rotating shaft; and

output eccentric shafts ( 126 ) respectively inserted into the plurality of through-holes to compensate for the eccentric center of the cycloid gear.

5. The electric parking brake system according to claim 4 , wherein the internal gear is fixed to the motor so as not to be rotated.

6. The electric parking brake system according to claim 4 , wherein a bearing ( 122 ) is installed between the cycloid gear and the eccentric rotator.

7. The electric parking brake system according to claim 4 , wherein the spindle member includes:

a spindle shaft ( 131 ) having a predetermined length and provided at an outer circumferential surface thereof with the male screw portion; and

a flange ( 133 ) radially protruding from one end of the spindle shaft, and

wherein the flange is provided with insertion holes ( 134 ) at positions corresponding to the through-holes so that the output eccentric shafts are inserted into the insertion holes.

8. The electric parking brake system according to claim 7 , wherein each of the output eccentric shafts includes:

a circular plate ( 126 a ) taking the form of a cylinder having a large diameter; and

a cylindrical pin ( 126 b ) eccentrically formed at one end of the circular plate and having a smaller diameter than the circular plate, and

wherein the circular plate eccentrically formed relative to the pin is inserted into the through-hole of the cycloid gear, and the pin is fixedly coupled to the insertion hole of the spindle member that is located in front of the pin.

9. The electric parking brake system according to claim 7 , wherein each of the output eccentric shafts takes the form of a cylinder having a predetermined length, one end of which is fixedly coupled to the insertion hole and the other end of which is inserted into the through-hole.

10. The electric parking brake system according to claim 7 , wherein the spindle shaft is provided at the other end thereof with a polygonal connecting shaft ( 132 ), and the polygonal connecting shaft protrudes outward from the male screw portion to allow the spindle shaft to be manually rotated.