Pump for integrated brake system

1. A pump of an integrated brake system, comprising:

a motor;

a gear unit which converts a rotating force of the motor into linear reciprocating movement;

a piston assembly which is connected to the gear unit and reciprocates based on power conversion of the gear unit;

a piston housing which accommodates the piston assembly; and

a fixed rod fixedly disposed in the piston housing in a longitudinal direction,

wherein the piston assembly comprises a coupling groove formed therein, into which the fixed rod is inserted,

wherein the piston assembly comprises a piston head, a spindle, and a rotation-preventing ring disposed between the piston head and the spindle to prevent rotation of the piston assembly, and

wherein the piston head is configured to reciprocate in a cylinder formed in the piston housing, the spindle has one side inserted into and coupled with an insertion groove formed in one side of the piston head, and a ring member is disposed on an outer circumferential surface of the spindle.

2. The pump of claim 1 , wherein the piston housing comprises a through hole formed in an end thereof to allow the fixed rod to be inserted thereinto and coupled therewith.

3. The pump of claim 2 , further comprising a fixing member which is coupled with a portion of the fixed rod which passes through the through hole and is exposed to fix the fixed rod.

4. The pump of claim 1 , wherein a cross section of the fixed rod is formed in a polygonal shape, and

wherein the coupling groove is formed corresponding to the cross section of the fixed rod.

5. The pump of claim 1 , wherein a hollow is formed in the motor,

wherein the gear unit comprises a nut which is restricted by and coupled with a rotor of the motor and rotates based on rotation of the rotor, and

wherein the piston assembly is disposed in the nut and reciprocates based on rotation of the nut.

6. The pump of claim 5 , wherein the motor is coupled with one side of the piston housing and a through hole is formed in the other side of the piston housing.

7. The pump of claim 5 , further comprising:

a motor housing which accommodates the motor; and

a four-point contact bearing disposed between the motor housing and the rotor.

8. The pump of claim 7 , wherein the motor housing and the piston housing are assembled based on a position of the four-point contact bearing.

9. The pump of claim 5 , wherein:

the spindle is screw-coupled with the nut.

10. The pump of claim 9 , wherein a holding protrusion is formed on an inner circumferential surface of the piston head, and

wherein the spindle is inserted into the insertion groove until the ring member is held by the holding protrusion and then coak-coupled with one side of the piston head to fix the spindle to the piston head.

11. The pump of claim 9 , wherein a holding groove is formed in an inner circumferential surface of the piston head, and

wherein the spindle is inserted into the insertion groove until the ring member is held by the holding groove to fix the spindle to the piston head.

12. The pump of claim 9 , wherein the rotation-preventing ring is disposed in the insertion groove and formed corresponding to the fixed rod, and

wherein the spindle comprises an accommodation groove formed in one side thereof, Which accommodate the rotation-preventing ring.

13. The pump of claim 1 , wherein the rotation-prevention ring has a shape corresponding to the fixed rod so that the fixed rod prevents the rotation of the piston assembly.

14. The pump of claim 1 , further comprising:

a motor housing accommodating the motor; and

a bearing disposed between the motor housing and the piston housing.