This paper describes an experimental analysis of 2 degree-of-freedom (DOF) quarter-car passive suspension system and hydraulic active suspension system (QC-H-ASS) for ride comfort. The passive suspension system, which models a quartercar suspension, consists of the sprung mass, unsprung mass, a suspension spring and damper and a tyre spring. A hydraulic actuator has been considered as one of the most viable choices for an active suspension system due to its high power-to-weight ratio and low cost. Thus this model is modified to a 2 DOF QC-H-ASS by placing a hydraulic actuator, with its attendant control instrumentation, in between sprung and unsprung masses. The results show considerable improvement in ride comfort over the conventional passive system. The details of the quarter-car model development with the test set-ups for the passive and hydraulic active suspension systems, suspension elements employed, experimental analysis and results are presented.whereas in active suspension, actuator is able to both add and dissipate energy from the system. If a correct control strategy is applied to the actuator system, a better compromise between ride comfort and vehicle stability is possible compared with a passive suspension system (see Figure 2).
Present theories and practicesAutomotive suspension systems have been researched exhaustively by many researchers from all over the continents since long and now have reached to a very high level of sophistication. Sharp and Crolla (1987) have described road surfaces, modelling vehicles and setting up performance criteria to passive, active and semi-active suspension systems. They have elaborated methods of deriving control laws for active systems. Crolla (1996) has reviewed the contributions of vehicle dynamics theory to practical vehicle design. He has nicely highlighted the effect of the suspension on improving the vehicle performance and safety. The practical constraints, which are restricting the commercial development of limited bandwidth active suspension systems, have been mentioned. He has observed that electro-hydraulic technology holds the most commercial promise, but a major breakthrough in electro-hydraulic valve technology will be required, leading to reduce costs if significant further developments are to occur over the next few years. Karnopp (1986) has shown using simple linear two degrees-of-freedom suspension system model that