Regenerative Shock Absorbers and the Role of the Motion Rectifier

The development of suspension systems has seen substantial improvements in the last years due to the use of variable dampers. Furthermore, the efficiency increase in the subsystems within the automotive chassis has led to the use of regenerative solutions, in which electric machines can be employed as generators to recover part of the energy otherwise dissipated. However, the harvesting capability of regenerative suspensions is often limited by friction and inertial phenomena. The former ones waste mechanical energy into heat, while the latter ones hamper the shock absorption by locking the suspension when subject to dynamic excitation. Besides a suitable design and sizing of components, recent research works highlight the use of the so-called motion rectifier to improve energy recovery by constraining the motion of the electric motor to a single sense of rotation. This strategy can potentially reduce inertial issues related to zero-speed crossing and motion inversion, thus leading to better conversion efficiency. Although results in literature indicate favorable damping characteristics of the shock absorbers equipped with this device, the real advantages introduced by the motion rectifier are yet to be quantified. In this context, the present paper aims to analyze hydraulic regenerative shock absorbers with the particular goal of putting in evidence the benefits and implications introduced by the use of the motion rectifier. Quantitative results from accurate modeling and simulation highlight the capabilities of the device in terms of harvested power, conversion efficiency, comfort and road holding.