Mechanism of Negative Pressure Generation in the Sliding Process of Paper-based Wet Frictional Material

It has been reported that negative pressure value was detected on the sliding surface of paper-based porous frictional material which is used in the automatic transmission. In this study, the effects of sliding velocity, contact pressure and surface geometry including diameter of measurement hole, surface roughness of frictional material, and porosity on the pressure detected by the hydraulic system were investigated, and mechanism of the negative pressure generation was discussed. It is considered that the pressures produced by various origins are summated into the resultant value indicating negative in the conventional oil film pressure measurement system.