Theoretical and experimental investigations for noise reduction of clearance joints in vertical vibrations

Simple revolving clearance pin and bush joint is standard and is widely used in machines and mechanisms. Clearance is necessary for rotational mobility of the joint parts, but it may lead to contact loss, which produces noise. To avoid the contact loss, it is necessary to ensure equality between the accelerations of the driver and the driven parts of the joint. In the case of a driver pin inside a bush as a free-driven part of the clearance joint, the acceleration of the bush in the vertical direction is limited to gravity. Therefore, if the exciting pin vibrates with downward acceleration more than the gravity, the contact loss will occur. As a solution, the acceleration of the free part was increased by a symmetric set of springs and a wire. To predict the contact condition, a set of dynamic equilibrium equations was developed and used to obtain the minimum spring stiffness and preload. Simulation and experimental results verified the concept of the contact loss and proved the effectiveness of using proper spring on noise reduction. Theoretical results show that with a sufficient spring preload, it is possible to use an arbitrary stiffness down to a limit even at relatively large accelerations. According to the acoustic tests, the noise picks were attenuated considerably, and the noise level was reduced to the background noise level after using proper springs.