Master cylinder for brake system

A master cylinder for brake systems comprising:

• a cylinder body including a first cylinder having a first bore therein and a second cylinder having a second bore therein, the first and second cylinders being joined together by fastening members to allow the first and second bores to communicate with each other;
• first and second pistons installed to move forward and backward in the first and second bores;
• a first hydraulic pressure chamber adapted to be pressed by the first piston arranged in the first bore;
• and
• a second hydraulic pressure chamber adapted to be pressed by the second piston arranged in the second bore,
• wherein each of the first and second bores of the cylinder body comprises a large diameter portion expanded to an inside of the cylinder body to increase a flow rate at an initial stage of braking and a small diameter portion narrowed from the large diameter portion,
• wherein:
• the first hydraulic pressure chamber is divided into a first large hydraulic pressure chamber formed at a position of the large diameter portion of the first bore of the cylinder body and a first small hydraulic pressure chamber formed at a position of the small diameter portion of the first bore of the cylinder body;
• and
• the second hydraulic pressure chamber is divided into a second large hydraulic pressure chamber formed at a position of the large diameter portion of the second bore of the cylinder body and a second small hydraulic pressure chamber formed at a position of the small diameter portion of the second bore of the cylinder body.