Optimization of ride comfort for vehicles equipped with passive and active hydro-pneumatic suspensions


Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Graduate School of Natural and Applied Sciences, Graduate School of Natural and Applied Sciences, Turkey

Approval Date: 2016

Student: FERHAT SAĞLAM

Supervisor: YAVUZ SAMİM ÜNLÜSOY

Abstract:

The main objective of this study is the optimization of ride comfort performance of vehicles equipped with Hydro-Pneumatic (HP) suspension systems. In order to improve ride comfort performance together with handling behavior as a constraint, active-passive, and unconnected-interconnected HP suspension systems are included in the study. The basic HP suspension model is developed and validated by experiments. Various HP suspension systems of increasing complexity are modeled, and their dynamic characteristics are analyzed and compared with each other. Nonlinear models of the active HP suspension system are derived and nonlinear active suspension controllers are designed in order to improve ride comfort, to control vehicle attitude, and to get safe driving conditions, using a quarter car model with active HP suspension system. Similarly, modeling and active suspension control of the half and full vehicle models with active HP suspension systems are carried out. A nonlinear feedback control method, State Dependent Riccati Equation (SDRE) control, is used for the design of vi the active controllers. Performance of the active suspension systems have been examined by time and frequency domain simulations. Simulation results show that, the active HP suspension systems improve ride comfort and vehicle attitude performance together with vehicle handling characteristics. As the next step of the study, analysis and design of the interconnected HP suspension systems for multi-axle vehicles are performed. Interconnections are enumerated for pitch plane of a three-axle vehicle and then, various interconnection layouts for roll, pitch, and coupled roll and pitch planes of the three axle-vehicles are examined. Stiffness and damping characteristics of different interconnections are obtained and compared with each other. Performances of vehicles with interconnected HP suspension system are evaluated by simulations. Simulation results have shown that, interconnected HP suspension systems improve vehicle handling considerably, together with slightly degraded ride comfort performance, as compared to the unconnected HP suspension systems. A general interconnected suspension design guideline is developed for the systematic parametric design of the HP suspension system for multi-axle vehicles. Finally, suspension system parameters for a three-axle vehicle equipped with unconnected and interconnected HP suspension systems are optimized for ride comfort with handling constraint. Optimization results show that, even though both unconnected and interconnected HP suspension systems improve the ride comfort, interconnected HP suspension system results in additional performance improvement in ride comfort and vehicle handling as compared to the unconnected HP suspension system, due to increased stiffness and damping performance in the roll and pitch planes.