Abstract
We estimated the mechanism of brake behavior by focusing on the difference of piston retraction between phenolic pistons and steel pistons. The factors that affected piston retraction were studied by quantitatively evaluating the piston movement and fluid pressure of phenolic and steel pistons side by side. The difference of brake behavior between phenolic piston and steel piston is due to the difference of piston retract amount from applying pressure to depressurization. And we clarified that difference of retract amount between phenolic piston and steel piston is affected by surface friction coefficient. From this, we thought that pedal feeling can be made equivalent by making surface friction coefficient of phenolic piston equal to that of steel piston. In addition, retract amount of phenolic piston and steel piston tend to decrease as pressure increase. We estimated that the more pressure increase, the more only seal rubber’s return amount increase until retraction start. As a result, we revealed seal rubber’s elastic force is not used for piston retraction in high pressure. As shown above, we clarified mechanism of braking behavior by checking factors involved in piston retraction.