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

This work presents an experimental investigation and parameter identification for a full-scale nonlinear energy harvesting shock absorber (EHSA) 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 experimental and 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 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. 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 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 mechanical efficiency of 4-9% was also seen for larger driving speed, when the pendulum probability density function (PDF) was more predominantly bimodal (two peaks), which results in enhanced pendulum motion. Finally, it was shown that increased inertia nonlinearity, via the pendulum length, could counteract degradation in mechanical efficiency, while also allowing for simultaneous enhancements in power harvesting, ride comfort, and ride handling.