Permeability of sinter bronze friction material for wet clutches

The characteristics of wet clutches are of great importance for the overall behavior of the drive trains of many modern vehicles. It is considered that the clutch characteristic is affected by the permeability of the friction material. The permeability is considered to influence both the time of engagement and the temperature in the clutch due to the lubricant flow in the permeable material. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of a friction material made of sintered bronze. This friction material is suitable for application such as limited slip differentials or other wet clutches that have to withstand high temperature and high torque transfer. The permeability is also investigated for friction materials with pressed groove patterns. Wet clutch friction material permeability is often accounted for in simulations but the method used to measure the permeability is seldom described. The permeability of the investigated friction material is shown to be so small that it will hardly will affect the temperature in the material due to cooling oil flow inside the material. However, the engagement time can be influenced by the permeability. It is also shown that pressed groove patterns can seal the friction material so that it becomes almost impermeable.