Master cylinder for brake system

1. A master cylinder for a brake system, comprising: a cylinder body in which a bore is formed;

at least one piston provided to be movable forward and backward in the bore; a hydraulic chamber pressurized by the at least one piston; an oil port connected to a reservoir and configured to supply oil to the hydraulic chamber of the cylinder body; and

a sealing member installed in the cylinder body and configured to block a flow of oil between the oil port and the hydraulic chamber according to a movement of the at least one piston,

wherein the at least one piston includes a piston groove having an inclined surface in contact with the sealing member and a plurality of piston holes formed along an outer circumferential surface of the piston groove configured to communicate the oil port with the hydraulic chamber, and

wherein the oil port has an expanded path, of which a diameter in an axial direction of

the at least one piston increases as the expanded path approaches the plurality of piston holes

so as to increase a flow rate introduced into the plurality of piston holes

wherein the expanded path is formed by concavely recessing an end portion of an inner surface of the oil port in the axial direction of the at least one piston.

2. The master cylinder of claim 1 , wherein:

the plurality of piston holes are formed in a portion in which the piston groove is formed.

3. The master cylinder of claim 1 , wherein the plurality of piston holes are formed in a polygonal shape or a polygonal shape with rounded corners, an area of the polygonal shape or polygonal shape with rounded corners is greater than an area of a circular shape having a diameter equal in length to a width of the polygonal shape.

4. The master cylinder of claim 1 , wherein the expanded path includes an inclined portion with respect to the axial direction of the at least one piston, which connects a vicinity of an end portion of an accommodation groove in which the sealing member is accommodated and an inner surface of the oil port.

5. The master cylinder of claim 1 , wherein:

the sealing member includes an outer wing in contact with the cylinder body and an inner wing in contact with an outer circumferential surface of the at least one piston; and

the inner wing is provided to be pressed against the inclined surface in a stand-by state before the piston operates.

6. The master cylinder of claim 1 , wherein:

the inclined surface of the piston groove includes a front inclined portion provided in a forward direction of the at least one piston and a rear inclined portion provided in a backward direction of the at least one piston; and

a slope of the front inclined portion is greater than a slope of the rear inclined portion.

7. The master cylinder of claim 6 , wherein the plurality of piston holes are provided in the rear inclined portion.

8. The master cylinder of claim 1 , wherein the plurality of piston holes communicate with the oil port in a lost travel section of the at least one piston and is provided to be partially sealed by the sealing member in the lost travel section.

9. The master cylinder of claim 8 , wherein:

the sealing member is disposed in a front part of the plurality of piston holes; and

a rear part of the plurality of piston holes communicate with the oil port in the lost travel section.