Active Suspension Systems for Passenger Cars: Operational Modal Analysis as a Tool for the Performance Assessment Leonardo Soria1,a, Arnaldo delli Carri2,b, Bart Peeters3,c, Jan Anthonis3,d and Herman Van der Auweraer3,e 1Politecnico di Bari, Viale Japigia, 182, 70126 Bari, Italy 2Università degli Studi di Brescia, Via Branze, 38, 25123 Brescia, Italy 3LMS International, Interleuvenlaan 68, B–3001 Leuven, Belgium asoria@poliba.it, barnaldo.dellicarri@unibs.it, cbart.peeters@lmsintl.com, djan.anthonis@lmsintl.com, eherman.vanderauweraer@lmsintl.com ABSTRACT Comfort, road holding and safety of passenger cars are mainly influenced by an appropriate design of suspension systems. Improvements of the dynamic behaviour can be achieved by implementing semi-active or active suspension systems. In these cases, the correct design of a well-performing suspension control strategy is fundamental for obtaining satisfying results. In-Operation Modal Analysis allows the experimental structural identification in real operating conditions: moving from output-only data, leading to modal models linearised around the more interesting working points and, in the case of controlled systems, providing the needed information for the optimal design and verification of the controller performance. All these characters are needed for the experimental assessment of vehicle suspension systems. In the paper, two suspension architectures are considered equipping the same car type. The former is a semi-active commercial system, the latter a novel prototypic active system. For the assessment of suspension performance, two different kind of tests have been considered, proving ground tests on different road profiles and laboratory four poster rig tests. By OMA-processing the signals acquired in the different testing conditions and by comparing the results, it is shown how this tool can be effectively utilised to verify the operation and the performance of those systems, by only carrying out a simple, cost-effective road test. 1 INTRODUCTION Passenger car comfort, road holding, handling and safety are strongly related to an appropriate design of suspensions. In particular, once the sprung body is given, the correct choice of damping values is related to the spring stiffness ones. Improvements of the dynamic behaviour of the whole system can be achieved by implementing semi-active or active suspension systems instead of the simply passive ones, commonly utilised. In these cases, the correct design of a well performing suspension control strategy is of fundamental importance for obtaining satisfying results, and, in the case of active systems, also from energy consumption point of view. The not so high overall efficiency of active systems still remains, indeed, one of their main drawbacks. Operational or Output-only Modal Analysis [1-4] allows the experimental identification of structural dynamics models in the real operating conditions. The strength is that, frequently, (i) only the response data are measureable and not the actual loadings. Hence, the system identification has to be based on output-only data. More over, since all the real systems are to a certain extent non-linear and often also subjected to non-linear constraining conditions, (ii) the modal models obtained under real loadings give a picture of the system, once linearised around the more interesting and representative working points. In the case of control systems, at last, (iii) the identification of the real in-operation behaviour is essential in the areas of the optimal design and verification of the controller performance. All these characters are needed for the experimental assessment of an active suspension system equipping a passenger car. In this paper two Ford S-MAX, two instances of the same type of vehicle, equipped with two different suspension architectures are considered. The former is a commercial vehicle equipped with a sky-hook semi-active suspension system having three different parameter arrangements that the driver is able to select, actually modifying the amount of damping in the system: A normal one which is useful in the most common situations and two other ones corresponding the first to a more comfortable T. Proulx (ed.), Modal Analysis Topics, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series 6, 313 DOI 10.1007/978-1-4419-9299-4_28, © The Society for Experimental Mechanics, Inc. 2011
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