Experimental Parameter Identification of an Energy Harvesting Shock Absorber With Inertia and Friction Nonlinearity

Abstract This work presents an experimental investigation and parameter identification for a full-scale nonlinear energy harvesting shock absorber featuring a pendulum and ball screw-based inerter mechanism. A mathematical model was developed that includes nonlinear friction modeled with a Stribeck formulation. The prototype was tested with sinusoidal displacement input using a hydraulic testing machine. An optimization routine identified friction and damping parameters by minimizing the error between the experimental and the simulated velocity. The validated model was further employed in quarter car model simulations under rough off-road excitation with five distinct driving speeds to evaluate the energy-harvesting performance and mechanical efficiency. Results showed that, due to low power input used for experimental parameter identification, the friction and damping parameters were large and resulted in a friction and damping-dominated system. The average mechanical efficiency was found in simulation to be around 23% for the lowest driving speed, but it was noted that matching the input power in experiments used for the parameter identification with the input power in the real-world scenario would result in more accurate parameter estimations and better simulated efficiency. An increase in the mechanical efficiency of 4 − 9% was also seen for larger driving speed, when the pendulum probability density function was more predominantly bimodal (two peaks), which results in enhanced pendulum motion. Finally, it was shown that the increased inertia nonlinearity, via the pendulum length, could counteract degradation in the mechanical efficiency, while also allowing for simultaneous enhancements in power harvesting, ride comfort, and ride handling.