Design of a Disc-on-disc-type CNC Tribometer Targeted at Dry Clutch Friction Plate Wear Characterization

The paper presents design of a disc-on-disc-type CNC (Computer Numerical Control) tribometer aimed at experimental characterization of friction and wear behaviors of automotive dry clutches. The torque or normal force, slip speed, friction interface temperature, and closing time are accurately controlled during tests by employing rotational- and vertical-axis servodrives and a water-cooling system built in both axes. A compact two-axial piezoelectric torque and force sensor is built in between the vertical-axis spindle and the pressure plate, in order to provide direct measurements of friction torque and normal force. The slip speed is sensed by using an encoder placed at the rotating table that carries the friction plate. The disc temperature is controlled by means of imposing a delay between two consecutive clutch closing cycles, variable cooling pump speed, and a valve that can bypass the coolant flow around the pressure plate. The torque control system is realized in a cascade structure including inner normal force and vertical axis speed controllers. The closing time is controlled by means of “electrical inertia” implemented through rotational-axis servomotor torque control. The tribometer performances are demonstrated through a study of dry clutch friction plate wear rate characterization.