Effects of friction and gas modelling on vehicle dynamics simulation

Abstract

Validated simulation models have become ever more important in the current technological and economic environment, where simulation is an integral part of the design process. In the field of vehicle dynamics, it is no different, where vehicle manufacturers and researchers are relying more heavily on simulation than ever before. In the competitive field of research and development, the phrase as accurate as possible, as complex as is necessary rings true for vehicle models. Due to the as complex as necessary approach, many complex phenomena such as suspension kinematics and suspension friction remain un-modelled, as the assumption is made that the effects are negligible. The seemingly negligible effects negatively affect the validity of simulation models, especially when deviating from the specific manoeuvre for which the model was originally created. In this study, focussed on a vehicle with a hydropneumatic suspension system, the effect of gas modelling methodology, friction, and friction modelling strategy on the validity the suspension unit characteristics, and a full non-linear vehicle dynamics model is presented. The approach to gas modelling included three permutations of the ideal gas formulation, namely isothermal, adiabatic, and a heat transfer dependent thermal time-constant approach. The effects of friction were accounted for using a rudimentary lookup table approach, a LuGre, and a Modified LuGre friction model, while using the case where friction is neglected as reference. The results showed that the gas modelling approach, and the effects of friction, each have a significant effect on model accuracy and validity when compared to physical test results. The improvement is witnessed on both the single suspension unit characteristic as well as on the full non-linear simulation model. This effectively proves that seemingly negligible effects may have a significant effect on model validity.

Gevalideerde simulasie modelle word al hoe meer belangrik in die huidige tegnologiese en ekonomiese omgewing, waar simulasie as n integrale deel van die ontwerp prosess is. In die voertuig-dinamika veld is dit ook die geval, waar vervaardigers en navorsers meer op simulase staatmaak as ooit tevore. In die navorsings en ontwikkelings veld met sy strawwe kompetisie, word die frase so akkuraat moontlik, so kompleks as nodig dikwels ter harte geneem met die ontwikkeling van voertuig modelle. Die so kompleks as nodig benadering het die gevolg dat baie verskynsels soos suspensie kinematika en wrywing nie in ag geneem word nie, aangesien daar aanvaar word dat die effekte weglaatbaar klein is. Hierdie oënskynlikke weglaatbare effekte, het n negatiewe impak op die akkuraatheid en geldigheid van die model waneer daar afgewyk word van maneuvers waarvoor die model oorspronklik ontwikkel is. In hierdie studie, waar gefokus word op n voertuig met n hidro-pneumatiese suspensie stelsel, word die effek van gas modelering, wrywing, en wrywings modelering strategie op die geldigheid van die suspensie eenheid karakterestieke, asook die vol nie-linieêre voertuig model voorgelê. Die benadering tot gas modelering sluit drie permutasies van die ideale gas wet in, naamlik isotermies, adiabaties, en die hitte-oordrag afhanklikke termiese tyd-konstante formulering. Die effekte van wrywing is op drie maniere in ag geneem, naamklik n opsoek matriks, n LuGre, en n Aangepaste LuGre wrywings model, terwyl die geval waar wrywing weggelaat is gebruik word as verwysing. Die resultate wys dat die gas modelerings strategie, asook die effek van wrywing elkeen n waarneembare effek op die model akkuraatheid en geldigheid het waneer dit vergelyk word met fisiese toets resultate. n Verbetering is gesien in die enkel suspensie eenheid karakterestiek sowel as die vol nie-linieêre simulasie model. Dit bewys effektief dat sekere verskynsels, alhoewel dit klein is in vergelyking met ander effekte, n groot impak op model geldigheid en akkuraatheid kan hê.