Characterization of Clearances and its Optimization for Vibration Control of Hydraulic Actuators

A typical linear hydraulic actuator would have clearances between the mating components such as Piston-Cylinder arrangement for achieving the functional requirements. It is observed from the vibration tests that the natural frequencies and the responses vary significantly with the excitation levels in these actuators. With increase in the excitation levels natural frequency of the actuators increases, and the damping ratio reduces significantly indicating a nonlinear behavior of the system. Also due to these clearances, jump phenomena and cubic stiffness nonlinearity are identified on the typical hydraulic actuators. The characterization of the clearances and its impact on the vibratory responses is discussed in this paper. Clearances at two interface locations for a typical hydraulic actuator were identified and a Design of Experiments (DOEs) was formulated with different levels of clearances. Sinusoidal sweep tests with varying input excitations (g) for the critical frequency range were performed and the frequency response is generated to study the presence of nonlinearity. It is observed that the natural frequency was saturated after a certain input excitation level depending on the clearances indicating the saturation of system stiffness. More the clearance, the system stiffness saturates at higher excitation (g) levels and the vibration response reduces while the stiffness saturates. Experimental results show a significant reduction in vibration response with increased clearances however these clearances should be within the tolerance band as specified in seal standard for the appropriate seal performance. A considerable reduction in response is observed by maximizing clearance within the seal standard itself.