Modeling and Design of a Cushioning Groove Considering a Slanting Impact

The cushioning groove is a simple means to limit end stop speeds of small devices moving in some fluid, for instance, of spools in switching valves. A shallow groove limited by one or two edges is placed on one or both sides of the moving element. When the groove meets its opposing contact surface the fluid pressed out by the motion causes an increased pressure in the groove which provides the cushioning effect. It overcomes fluid stiction problems which are frequently encountered in squeeze gap type cushioning if the system is under high fluid pressure. The elementary cushioning groove concept assumes that the groove edges are exactly parallel to the contacting surface. In this paper, the performance of the cushioning groove in case of some slanting of the groove edges to the opposing surface is studied by means of a mathematical model. Slanting reduces the cushioning force and causes a resulting torque to the moving system due to an asymmetric pressure. Insufficient cushioning becomes more likely and, in turn, a repelling motion.