Actuator of electronic brake system

1. An actuator of an electronic brake system comprising:

a drive unit generating a power and including a motor having a stator and a rotor;

a piston unit operated by the drive unit and including a piston reciprocating in a bore chamber provided in a piston housing to contain a fluid;

a power transmission unit having one end coupled to the rotor and the other end coupled to the piston to convert a rotational motion of the rotor into a linear motion of the piston;

a sensing magnet coupled to the power transmission unit to rotate along the motor; and

a motor position sensor disposed coaxially with and spaced apart from the sensing magnet to sense a position of the motor based on the rotation of the sensing magnet,

wherein the power transmission unit includes a spindle coupled to the rotor to rotate together with the rotor, the spindle including a magnet holder provided to extend into the bore chamber, and the sensing magnet is provided at an end of the magnet holder and located in the bore chamber containing the fluid.

2. The actuator of an electronic brake system according to claim 1 ,

wherein the power transmission unit further includes a nut screwed to the spindle, and

the nut is provided integrally with the piston.

3. The actuator of an electronic brake system according to claim 1 ,

wherein the bore chamber is provided to pass through the piston housing, and

one end of the bore chamber is coupled to and sealed by the drive unit, and the other end of the bore chamber is sealed by a bore cap.

4. The actuator of an electronic brake system according to claim 1 ,

wherein the rotor includes a hollow cylinder therein, and

the power transmission unit is provided in the hollow cylinder and a space forming the bore chamber.

5. The actuator of an electronic brake system according to claim 1 ,

wherein the piston includes a rotation preventing member, and

the rotation preventing member includes a rotation preventing ring provided at an end of the piston, at least one rail protrusion provided to protrude from the rotation preventing ring, and at least one rail groove provided along a longitudinal direction on an inner wall of the bore chamber so that the at least one rail protrusion is slidably moved therein.

6. The actuator of an electronic brake system according to claim 1 ,

further comprising a bore cap for sealing an end of the bore chamber,

wherein the bore cap includes a cap body provided in a disk shape, and a cap cylinder provided to extend from the cap body to the drive unit, and

the cap cylinder accommodates the magnet holder therein.

7. The actuator of an electronic brake system according to claim 1 ,

wherein the bore chamber is divided into a first chamber and a second chamber by the piston, and

the piston generates a hydraulic pressure in the first chamber when the piston moves in one direction and generates a hydraulic pressure in the second chamber when the piston moves in the other direction.

8. The actuator of the electronic brake system according to claim 1 , wherein the sensing magnet is positioned between the motor and a cap body sealing the fluid of the bore chamber.

9. The actuator of the electronic brake system according to claim 1 , wherein the piston housing comprises: one end portion of the piston housing connected with the drive unit including the motor, and an opposite end portion of the piston housing where the sensing magnet is positioned inside the bore chamber containing the fluid.

10. The actuator of an electronic brake system according to claim 1 , wherein the motor position sensor is provided on an electronic control unit.

11. The actuator of an electronic brake system according to claim 1 , wherein the motor position sensor is provided on an electronic control unit, and the piston unit is positioned between the drive unit and the electronic control unit.