Piston pump for brake system

A piston pump comprising:

• a piston unit configured to reciprocate in a piston housing by driving of a motor cam;
• a sleeve unit disposed to surround at least a part of the piston unit, and having an accommodation space in which brake oil is stored;
• and
• a check valve unit disposed to face the sleeve unit and configured to discharge the brake oil to an outside of the sleeve unit when a pressure of the brake oil stored the accommodation space of the sleeve unit increases,
• wherein the piston unit includes a first piston having a first end in contact with the motor cam and configured to reciprocate, a second piston having a first end press-fitted and coupled to a second end of the first piston and operating in conjunction with reciprocating movement of the first piston to press the brake oil stored in the accommodation space of the sleeve unit, and a spring cap disposed to accommodate an inlet spring therein and coupled to a second end of the second piston,
• wherein the second piston includes:
• a piston head unit having at least a part of which an outer diameter is a first diameter;
• and
• a step unit having at least a part of which an outer diameter is a second diameter greater than the first diameter,
• wherein the spring cap includes:
• a piston coupling unit coupled to at least a part of the piston head unit;
• a cap head unit disposed to accommodate the inlet spring, wherein an inside and an outside of the cap head unit are configured to fluidly communicate with each other;
• a flange unit radially extending from an end-most portion of the spring cap;
• and
• a slope unit extending between the piston coupling unit and the cap head unit and having an inner diameter which decreases in a direction from the piston coupling unit toward the cap head unit, and configured to stop the second piston by contacting an inner circumferential surface of the slope unit with the second piston when the second piston moves to press the brake oil,
• wherein the piston unit includes a first sealing disposed between the flange unit and the step unit in an axial direction,
• wherein the piston coupling unit is disposed between the cap head unit and the flange unit and is coupled to a circumferential surface of the piston head unit, and
• wherein:
• the first piston includes a first coupling unit coupled to at least a part of the second piston;
• the second piston includes a second coupling unit disposed to surround the first coupling unit;
• the first coupling unit and the second coupling unit are press-fitted to each other;
• and
• an outer width of the first coupling unit varies in a radial direction such that at least a portion of the first coupling unit is spaced apart from the second coupling unit when coupled thereto.