Methodology for comparing the functional performance of energy harvesting shock absorbers

Abstract

The energy balance of internal combustion engines used in vehicles today shows that between 50 and 80% of the fuel energy is lost. This waste of energy has fostered a growing interest in energy harvesting systems in the automobile sector. This energy can be recovered, for example, from the cooling and exhaust systems, the brakes or the suspension system. With regard to suspension system harvesters, usually called Energy Harvesting Shock Absorbers (EHSAs), many solutions, based on different technologies, have been proposed so far in the literature available. Unfortunately, to date there is no commonly-accepted approach that allows the designers to select the best technology to replace a conventional damper with another component, i.e. an EHSA, which harvests energy but at the same time offers the same contribution to comfort and handling as the conventional damper. This paper presents a general methodology which can be used to compare present or future EHSA solutions. It studies the technology behind direct drive and electromechanical shock absorbers, and an electromechanical representation is proposed for each of them. Besides, for comparison purposes, a common equivalent mechanical representation for each EHSA is suggested. Some experimental results, using track-recorded data to estimate an urban road profile and also the ISO 8608 standard class C roughness index, are included, which demonstrate the ability of the methodology to compare effectively different EHSAs which harvest energy but at the same time have the damping characteristics of a conventional shock absorber.