QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL Qual. Reliab. Engng. Int. 2001; 17: 71–84 SIMULATED EXPERIMENTAL DESIGN USED TO DEFINE THE CHARACTERISTIC CURVES OF CAR SHOCK-ABSORBERS G. ARCIDIACONO 1∗ , R. CAPITANI 1 AND M. VIANELLO 2 1 DMTI, University of Florence, via S. Marta, 3-50139 Florence, Italy 2 DT Fiat Auto, Affidabilit` a Prodotto-Corso Settembrini, 40-10135 Torino, Italy SUMMARY This paper introduces a special ‘quality’ parameter on automotive perspective, i.e. the quality index in order to measure the customer satisfaction with car manoeuvrability. In particular, it describes how the characteristic setting curves of a car shock-absorber can be optimized using subjective customer assessment of three categories of perception: handling, steering quality and ride-comfort. These, called manoeuvrability indices, were used to represent the assessment of customer satisfaction with car manoeuvrability. The characteristic curves for each shock-absorber setting were defined using parameters which uniquely determined their shape. Subsequent analysis was carried out using simulated experimental design which adopts a numeric model of vehicle simulation thereby enabling experimental costs to be reduced. This analysis made it possible to ascertain which setting parameter values provided the best compromise among the three categories of required performance. A codified method of optimization was then developed. This method, which includes the three categories of perception, will be extended to all new projects. Copyright  2001 John Wiley & Sons, Ltd. KEY WORDS: manoeuvrability index; simulated experimental design; DACE; car shock-absorber 1. INTRODUCTION The study of vehicle dynamics plays an important role in car design and development: dynamic behaviour is the determining factor in driver assessment of the comfort, directional response and handling aspects of vehicle manoeuvrability. The function of vehicles is to transport people and goods from one place to another with as little disturbance as possible. Disturbance levels are assessed using the ride comfort parameter (0–100 Hz) which refers to vibration comfort and not noise comfort (100 Hz– 20 KHz); ride comfort is associated with the low- frequency car-body movements perceptible to the human body. Directional response during manoeuvres such as cornering and turning refers to objective properties of a vehicle while it is changing direction and, at the same time, sustaining lateral acceleration. For example, cornering ability may be quantified by the level of lateral acceleration that can be sustained in a stable condition; directional response may be quantified by the time required for lateral acceleration to develop ∗ Correspondence to: G. Arcidiacono, DMTI, University of Florence, via S. Marta, 3-50139 Florence, Italy. Email: g.arcidiacono@dmti.unifi.it following a steering input. Handling, on the other hand, includes not only these objective properties but also the vehicle qualities that feed back to the driver affecting the ease of the driving task or his ability to maintain control. The comfort, directional response and handling as- pects have an evident impact on customer perceptions, i.e. on the sensations perceived while driving and they form part of customer expectations. This means the design engineer has to take subjective customer expectations into consideration when studying vehicle dynamics. In order to undertake customer-oriented project design, Fiat Auto has prepared a procedure which correlates objective physical vehicle behaviour with the sensations perceived by the driver of that vehicle. All aspects of physical performance can be expressed in terms of sensations perceived by the customer and these can be quantified by grades as- signed by the customers themselves, provided ade- quate physical parameters are used; these parameters are weighted using surveys carried out on a represen- tative sample of potential customers. The three types of vehicle behaviour cited above can be associated with the following three categories of customer perception: • Handling: car performance during cornering; Received 24 January 2000 Copyright  2001 John Wiley & Sons, Ltd. Revised 22 September 2000