Electric parking brake system

1. 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.

2. The system according to claim 1 , further comprising:

an input gear gearedly connected with the drive gear while being integrally coupled to the sun gear to have the same rotating center as that of the sun gear, the screw member penetrating through the input gear.

3. The system according to claim 1 , wherein:

the nut member includes a power connecting portion penetrating through an input 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 nut portion having a plurality of female threads;

the screw member has a plurality of male threads corresponding to the female threads of the nut portion; and

the pair of parking cables are coupled to an end of the power connecting portion of the nut member and an end of the screw member, respectively.

4. The system according to claim 3 , further comprising:

an input gear gearedly connected with the drive gear while being integrally coupled to the sun gear to have the same rotating center as that of the sun gear, the nut member penetrating through the input gear.

5. The system according to claim 1 , wherein the motor includes a rotary shaft having one end coupled to the drive gear and the other end provided with a release shaft used to manually rotate the drive gear.

6. The system according to claim 1 , wherein at least one load sensor is mounted between the screw-nut unit and at least one of the parking cables, and is used to measure a force being applied to each parking cable by the screw nut unit.

7. The system according to claim 1 , wherein at least one emergency release unit is mounted between the screw-nut unit and at least one of the parking cables, and is used to manually release a connection between the screw-nut unit and the associated parking cable.

8. The system according to claim 1 , further comprising:

at least one planetary reduction gear unit mounted between the plurality of planetary gears and the output carrier,

wherein the planetary reduction gear unit includes a reduction carrier connected to the plurality of planetary gears in a power transmittable manner and adapted to rotate about the same rotating center as that of the sun gear, a reduction sun gear integrally coupled to the center of the reduction carrier, and a plurality of planetary reduction gears gearedly connected with the reduction sun gear and internal gear and adapted to revolve along a periphery of the reduction sun gear, the planetary reduction gears also being connected to the output carrier in a power transmittable manner.

9. The system according to claim 8 , wherein the screw member includes a power connecting portion penetrating through the input gear, reduction carrier, and reduction 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;

the nut member has a plurality of female threads corresponding to the male threads of the bolt portion; and

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.

10. The system according to claim 9 , further comprising:

an input gear gearedly connected with the drive gear while being integrally coupled to the sun gear to have the same rotating center as that of the sun gear, the screw member penetrating through the input gear.

11. The system according to claim 8 , wherein the nut member includes a power connecting portion penetrating through the input gear, reduction carrier, and reduction 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 female threads;

the screw member has a plurality of male threads corresponding to the female threads of the nut portion; and

the pair of parking cables are coupled to an end of the power connecting portion of the nut member and an end of the screw member, respectively.

12. The system according to claim 11 , further comprising:

an input gear gearedly connected with the drive gear while being integrally coupled to the sun gear to have the same rotating center as that of the sun gear, the nut member penetrating through the input gear.

13. The system according to claim 1 , wherein:

the nut member is integrally coupled to the center of the output carrier so as to rotate along with the output carrier;

the screw-member includes a first screw shaft screwed into one end of the nut member in a predetermined first spiral direction, and a second screw shaft penetrating through the sun gear to be screwed into the other end of the nut member in a predetermined second spiral direction opposite to the first spiral direction; and

the pair of parking cables are connected to associated ends of the first and second screw shafts, respectively.

14. The system according to claim 13 , further comprising:

an input gear gearedly connected with the drive gear while being integrally coupled to the sun gear to have the same rotating center as that of the sun gear, the second screw shaft penetrating through the input gear.

15. 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 nut member includes a power connecting portion penetrating through an input 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 nut portion having a plurality of female threads;

wherein the screw member has a plurality of male threads corresponding to the female threads of the nut portion; and

wherein the pair of parking cables are coupled to an end of the power connecting portion of the nut member and an end of the screw member, respectively.

16. The system according to claim 15 , further comprising:

an input gear gearedly connected with the drive gear while being integrally coupled to the sun gear to have the same rotating center as that of the sun gear, the nut member penetrating through the input gear.