Vibration Damping using Regenerative Suspensions for More Ecient Vehicles

Vehicle vibration problem has been always an important area of research due to its negative effect on passenger comfort and vehicle safety. This problem can be solved partially by designing a good suspension system capable of maintaining an acceptable level of comfort and ensuring the vehicle safety on irregular roads. However, the conventional vehicle suspension dissipates the mechanical vibration energy in the form of heat which would waste a considerable amount of energy. Regenerative shock absorber can capture the previously dissipated vibration energy and convert it to usable electrical energy for charging a battery or powering on-board electronic devices. Moreover, it can achieve both the better ride comfort and improved road handling performance at the same time when certain control is applied. To achieve this objective, the oscillatory motion of the suspension system is employed to drive power generator. However, the frequent bidirectional oscillation of the generator can cause a large impact force. This further leads to deteriorated energy harvesting performance, moving parts fatigue, and even system failure. In addition, the bidirectional oscillating motion will produce an irregular AC voltage. In order to charge batteries or power vehicle electronics, the voltage needs to be commutated with an electrical rectifier, in which the forward voltage of diodes unavoidably reduces the circuit’s efficiency. As such, this thesis presents a study of an Electro-Hydrostatic Shock Absorber (EHSA) which can integrate the vibration damping and energy generation. The presented device consists of a modified twin-tube shock absorber with two check valves working as a hydraulic rectifier by which the bidirectional motion across the damper is converted to an asymmetric unidirectional rotation to drive the generator. The device has an advantage of having less number of check valves than the other counterpart devices which in turn would increase the overall efficiency of the system. Following the system description, mathematical and numerical models have been developed to examine the response behavior of the regenerative shock absorber. Unlike the mathematical model in which some of the system dynamics were neglected, the numerical model took into consideration all the linear and non-linear elements of the presented device. For this purpose, Matlab's Simscape Toolbox has been used as an environment for multi-domain physical system. The study is about the analysis of the performance of the electro-hydrostatic shock absorbers for automotive applications. The objective is to evaluate the fuel saving allowed by such solution. The study is performed by numerical analysis at different level of accuracy in two different configurations: with motion rectifier and without motion rectifier. The study evidences that both solutions have a promising potential of energy recuperation with a slight advantage of that with motion rectifier. The results have shown that the developed regenerative shock absorber is capable of capturing a maximum of 24W average power with a maximum conversion efficiency of 42\% if the vehicle is going over a C-class road and when the load resistance is tuned to 2.6 Ohm. In case of using the device without motion rectifier, the average power is reduced to 22W with conversion efficiency of 38%. The carbon emissions that can be reduced by a car having this shock absorber can reach to 2.1 Gram of CO2 /km.