Vehicle brake systems

A vehicle brake system comprising:

• a caliper body including a cylinder;
• a piston part that is movably disposed on the cylinder and disposed to face a brake pad;
• a nut screw part that is disposed inside the piston part, rotates by receiving rotational force from an actuator, and including an outer ball rail that forms a circulation path of ball members on an inner circumferential surface;
• and
• a bolt screw part including a bolt body coupled with the nut screw part and receiving the rotational force from the nut screw part and a bolt head provided separately from the bolt body, coupled with the bolt body, and disposed to face the piston part, wherein an inner ball rail is provided on an outer circumferential surface of the bolt body to face the outer ball rail and forms a circulation path of the ball members,
• wherein the nut screw part includes a first return hole unit through which the ball members enter and exit, a return passage communicating with the first return hole unit, and a second return hole unit communicating with the return passage and through which the ball members enter and exit.

A vehicle brake system comprising:

• a caliper body including a cylinder;
• a piston part that is movably disposed on the cylinder and disposed to face a brake pad;
• a nut screw part that is disposed inside the piston part and rotates by receiving rotational force from an actuator;
• and
• a bolt screw part including a bolt body that is coupled with the nut screw part to receive the rotational force from the nut screw part, and a bolt head that is separately provided from the bolt body to be coupled with the bolt body and disposed to face the piston part, wherein when the bolt body is moved toward the piston part by a set distance, movement toward the piston part is blocked by the nut screw part.