The aim of this thesis is to explore and improve the accuracyofweight estimation in vehicles with air suspension. The main focushasbeen to understand the hysteresis and characteristics ofdifferentsuspension types used in Scania NCG trucks. The thesis hasled toinsights into the attributes affecting hysteresis and theaccuracy ofweight estimation. As a proof of concept a softwareimplementationhas been developed from the knowledge derived troughout the thesisto account for hysteresis. The result of this work hasproven it tobe possible to increase the accuracy and reduce the errorto lessthan half compared to today's method.

The aim of this study is to investigate the use of multi-body vehicle simulation models to predict the suspension forces acting on the chassis of the vehicle, in order to perform durability analyses. Traditionally, durability of vehicles is evaluated with proving ground tests. This implies that a physical prototype of the vehicle is required before its durability can be evaluated. If we were able to evaluate the durability of the vehicle without any physical part or a full prototype of the vehicle available, great cost and time savings may be gained. These possible gains have lead to the use of computer aided engineering (CAE) tools. These tools have supplemented the proving ground durability test by using historical measured data and/or predicted data from vehicle simulation models, as input to the durability analyses i.e. Finite Element Analyses (FEA). The usefulness of the historical test data is limited and many of the vehicle simulation models that are used to predict the input data, have not been validated. In this study a validated mathematical model of a 40 ton flat bed tri-axle semi-trailer, able to predict the suspension forces, is created. The validation of the full vehicle model includes correlations for displacements, velocities, accelerations and forces of various vehicle parameters. A validated mathematical model of the air springs, that includes mass transfer and flow effects for use in full vehicle dynamic simulations, is also developed. The results obtained indicate that the air spring model, integrated into the full vehicle model, is able to give relative accurate predictions of displacements, velocities, accelerations and forces of various vehicle parameters, over a discrete road event and over a rough road. / Dissertation (MEng)--University of Pretoria, 2009. / Mechanical and Aeronautical Engineering / Unrestricted

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In this paper, we present a new compact hydraulic linear actuator. The concept is developed to change the rolling piston diameter of an active air spring during usage. By doing so, the air spring can actively apply pressure and tension forces. The actuator is designed for small movements at high forces. It is insensitive to side forces, which are introduced by the bellows rolling on the rolling piston of the air spring. A diaphragm sealing is used to minimize friction. Hence a precise adjustment of small displacements at high dynamics is possible and the system is completely leakage-free. We describe the design and development of this actuator and show first measurement results from preliminary tests to show its functionality.

Mountain biking is a sport where riders bike on trails, varying in slope and difficulty. Mountain bikes are generally equipped with suspension on the front wheel and often also on the rear. Some types of rear shocks use pressurized air for a spring action instead of the traditional metal coil. Air is sealed inside the shock’s air can by means of X-ring seals, providing a spring force on the wheel. It is of great importance that the sealing system performs as intended so the air spring does not quickly lose pressure during use. An experimental plan is conducted in an attempt to estimate the effects of seal dimension, lubrication and surface roughness on air leakage for more robust shocks. Accelerated tests were performed in a dynamometer, believed to repeatedly cause significant wear on the shock’s air seal within 24 hours. Nineteen tests were carried out, for a duration up to 72 hours, with variations to test parameters such as stroke length and frequency. The expected failure modes did not occur in any of them. Eleven tests showed no signs of failure while the other eight failed due to unexpected components breaking or wearing out. The shock’s main seal was found to wear out faster than the air seal, causing leakage within the air spring, between its positive and negative air chambers. This unforeseen failure needs further examination with tests conducted on more shock types. / Mountainbike är en sport där utövare åker på stigar med varierande lutning och svårighet. Terrängcyklar är generellt utrustade med stötdämpare eller fjädrar på framhjulet och ofta också på bakhjulet. Vissa terrängcyklar har stötdämpare bak som använder trycksatt luft för att dämpa istället för att använda traditionella stålfjädrar. Luften är sluten inuti stötdämparen med hjälp av X-rings tätningar, vilket ger en fjäderkraft på hjulet. Det är viktigt att tätningen fungerar så att luftfjädern inte snabbt tappar trycket när den används. En experimentplan skapades i ett försök att uppskatta effekten av tätningsdimension, smörjning och ytjämnhet på luftläckage för mer robusta stötdämpare. Accelererade tester gjordes i en dynamometer, som troddes kunna skapa signifikant slitage på en stötdämpares tätning inom 24 timmar upprepade gånger. 19 test gjordes med en körtid på upp till 72 timmar med variation av testparametrar som slaglängd och frekvens. De förväntade felkällorna uppstod inte i något av testerna. 11 tester visade inga tecken på fel medan 8 tester misslyckades på grund av att oväntade komponenter slets ut eller gick sönder. Stötdämparens huvudtätning visade sig slitas fortare än lufttätningen, vilket resulterade i läckage inuti luftfjädern mellan dess positiva och negativa kammare. Detta oförutsedda fel behöver vidare undersökning med tester på fler olika typer av stötdämpare.

På Scania RTCC önskas högre kontroll och precision på dess luftbälgar vid simulering i AdamsCar. Därför har uppdrag tagits fram för att modellera luftbälgar från dragbilens hytt ochhjulupphängning. Till arbetet ingick test av tre luftbälgar som genomgick belastningsmätning i rigg. Modellens struktur togs fram av tre delar som empirisk areamodell Ae, teoretisk tryckmodell P’och empirisk volymmodell VK. Empirisk modell av effektiva arean Ae togs från mätningarna så samband mellan tryck ochkraft kan användas. För att undvika reglerteknisk modellering försummas hysteresen såmodellen blir reversibel. Rapporten kombinerade två av litteraturens tryckmodeller till en egen så samband fåsmellan tryckets förändring P’, luftmassans förändring m’ och volymens relativa förändringVK. Tryckmodellen har med avsikt inte gjorts beroende av volymen eller temperaturen dåmätning av dessa storheter saknas. Temperaturens inverkan på bälgen förenklas tillhastighetskonstanten n som är 1 för mycket långsam körning och 1,4 för normal körning. För att undvika bälgens volym modelleras den relativa volymförändringen VK från trycketsteori samt de empiriska mätningarna. Här idealiseras förändringen på samma sätt som förarean Ae till att vara reversibel genom att ta bort hysteresen. Modellens sammansatta ekvation ger ett lagom enkelt samband för kraftens förändring hos bälgen:Kraftmodellen har förenklingar som ger kända och okända fel. Utan hysteres fås 1,5 % fel viddynamisk körning och antagandet av konstant volym vid förändrad massa ger okända fel. Trotsdet rekomenderas att modellen avänds och utvecklas vidare så felen och osäkerheten minskas. / Scania RTCC requires greater control and precision on its air bellows when simulated in Adams Car. Therefore, assignments have been developed to model air bellows from the trailer's cab andwheel suspension. The work included tests of three air bellows that underwent load deformation. The structure of the model was developed by three parts as empirical area model Ae, theoreticalpressure model P' and empirical volume model VK. Empirical model of the effective area Ae was shaped by measurements so that pressureto-force relationship can be used. To avoid control engineering modeling, the hysteresisis neglected so the model becomes reversible. The report combined two of the literature's pressure models to a new model betweenchange in pressure P', change in air mass m' and change in relative volume VK. Themodel is intentionally independent of the volume or temperature where measurement ofthese have not been taken. The effect of the temperature on the bellows is simplified tothe speed constant n which is 1 for slow driving and 1,4 for normal driving. To avoid the volume of the air bellows, the relative change in volume VK is modeledfrom the pressure model and the empirical measurements. VK is simplified in the manneras for the area Ae by removing the hysteresis and making it reversible. Put together, the model provides a fairly easy theory of the force's change in the air bellows from the equation underneath. The force model has simplifications that give known and unknown errors. Without hysteresis,deviations of 1,5% are obtained during dynamic driving, and the assumption of constant volumeat changed mass gives unknown errors. It is the reports recommendation that the model beimplemented and further developed so that the errors and uncertainties are reduced.

This diploma thesis studies the use of air springs for race car, precisely Formula Student race car. Research part of the thesis deals with choosing suitable air spring for given application. In practical part, there is computation of parameters for appropriate setting of air spring, so it will comply with the rules of Formula Student. There is also simulation of air spring functionality in real use.

In this paper, we present a new compact hydraulic linear actuator. The concept is developed to change the rolling piston diameter of an active air spring during usage. By doing so, the air spring can actively apply pressure and tension forces. The actuator is designed for small movements at high forces. It is insensitive to side forces, which are introduced by the bellows rolling on the rolling piston of the air spring. A diaphragm sealing is used to minimize friction. Hence a precise adjustment of small displacements at high dynamics is possible and the system is completely leakage-free. We describe the design and development of this actuator and show first measurement results from preliminary tests to show its functionality.

With regard to autonomous driving the demands on comfort are increasing. This makes it attractive to use active suspension systems. The system developed at TU Darmstadt is able to increase driving comfort up to 28 % while maintaining driving safety compared to a passive suspension system. This paper investigates the influence of available energy and power of the active system. The investigation is based on a simulation of a quarter car model and an uneven country road. This paper shows that the more energy the active system has at its disposition, the greater is the range between a comfortable and a sporty chassis. Furthermore the driving comfort can be increased by 28 % with constant driving safety. The average power required for this is 15 W and the maximum power is 300 W.