Development Of An Equipment For Measuring The Damping Of A Rotary Viscous Damper

The commonly used method to dampen the oscillation of the crankshaft system is toinstall a Torsional Vibration Damper (TVD) at one end of the shaft. As an importantapplication, the viscous damper has several advantages, such as its small size, simple structureand strong damping. But the damping, which is the most important performance index of aviscous damper, is affected by many factors so the computing value must be repeatedlycorrected based on experiments. Therefore, it is necessary to develop an equipment formeasuring the damping of a rotary viscous damper for product design and quality assurance.An equivalent mechanical model for a viscous damper is advanced in this paper. Thebasic principle of the equipment to measure the damping of a rotary viscous damper isillustrated, so that two methods to obtain the damping by resonance experiments can be got.When measuring the damping of one particular viscous damper, the resonance experimentsonly need to be conducted within a specific frequency range, which can be calculated inadvance.The equipment for measuring the damping of a rotary viscous damper is established. Anexcitation system that produces sinusoidal torque excitation by unbalanced inertial force ofeccentric blocks in the planet gears of a planet-sun-gear system is designed and manufactured.A driven system is developed to rotate the viscous damper at different speeds to simulate itsreal working conditions. A rotary encoder is used to get both the resonance frequency of theequipment, and the peak value of Frequency Response Function (FRF) of the flange (thetorsional angle versus the excitation torque) through signal analysis processing.The amplitude and frequency of the excitation torque are obtained by theoreticaldeduction. The theoretical methods for estimating the inertia parameters of the equivalentmechanical model of the equipment and the torsional stiffness of the vibration shaft system,using3D modeling or Finite Element Method (FEM) software, are proposed. However, thetorsional stiffness of the vibration shaft system and the damping generated by the lubricating oil in the excitation system are finally identified by experiments owing to the inaccuracy andcomplexity of theoretical calculation.The errors of the equipment for measuring the damping of a viscous damper are dividedinto two categories. The first category is determined by the precision of the experimentalsetup, while the other one is caused by the calculation methods for estimating the damping.With reference to the first one, the influence of installation angle errors of the eccentric blockson the excitation torque and the generated force at the bearing in the radial direction is mainlydiscussed. Besides, some solutions to mitigate the impact of the installation angle errors aregiven. Then two methods to compute the damping of a viscous damper are compared and theone using the resonance frequency of the equipment is chosen because of its better stability.Two samples are prepared to verify the validity of the theoretical calculation for therange of measurement frequency. The experimental procedure is drawn up to carry out themeasurement for the damping of two viscous dampers. The tested results show that thedamping grows up with the increase of the rotary speed, and tends to be stable when a certainspeed (1000rpm) is reached.