Jochen Wiedemann

Sideslip angle estimation based on input-output linearisation with tire-road friction adaptation

An adaptive sideslip angle observer considering tire–road friction adaptation is proposed in this paper. The single-track vehicle model with nonlinear tire characteristics is adopted. The tire parameters can be easily obtained through road test data without using special test rigs. Afterwards, this model is reconstructed and a high-gain observer (HGO) based on input–output linearisation is derived. The observer stability is analysed. Experimental results have confirmed that the HGO has a better computational efficiency with the same accuracy when compared with the extended Kalman filter and the Luenberger observer. Finally, a road friction adaptive algorithm based on vehicle lateral dynamics is proposed and validated through driving simulator data. As long as the tires work in the nonlinear region, the maximal friction coefficient could be estimated. This algorithm has excellent portability and is also suitable for other observers.

The Influence of a Horizontal Pressure Distribution on Aerodynamic Drag in Open and Closed Wind Tunnels

The influence on aerodynamic drag of a non-uniform, streamwise pressure distribution over the wake of an automobile model in both open-jet and closed-jet wind tunnels is considered in this paper. It has long been an unsolved issue in the theory of open-jet interference and is usually not important in closed-wall wind tunnels unless the model is very long. A new, semi-empirical approach is presented that is based on the observation that the drag changes due to a pressure gradient over a wake correlate with the empty-test-section pressure-coefficient difference between the base of the vehicle and the position of wake closure. A method is demonstrated that is able to remove the effect of the pressure gradient and that is not buoyancy related. This method is applied to a range of simplified and detailed automobile shapes at model scale and at full scale in various wind tunnels, as well as to normal flat plates. The paper presents a revision of previous approaches to the estimation of nozzle and collector blockage. Finally, and most importantly, the paper demonstrates that the differences measured between configurations in a wind tunnel with a gradient over the wake will be in error unless a correction is made for the wake distortion induced by the gradient.

Leichtbau bei Elektrofahrzeugen. Wieviel ist er uns (noch) wert

Dem Leichtbau widmen Entwickler bei Fahrzeugneukonstruktionen zunehmend Aufmerksamkeit. Schlieslich hat die Masse einen deutlichen Einfluss auf den Roll- und Beschleunigungswiderstand. Hinzu kommen die bekannten querdynamischen Vorteile leichter Fahrzeuge. Dies erfolgte allerdings vor dem Hintergrund steigender Fahrzeug-Gesamtgewichte. Im Gegensatz zu konventionellen Fahrzeugen ist der Anreiz fur Gewichtsreduzierungen bei elektrifizierten Fahrzeugen allerdings geringer. Dort sind Leichtbau-Masnahmen weniger effizient und verteuern das Produkt. Hier ist die Aerodynamik im Verhaltnis zum Leichtbau schon heute preiswert. Dieser Beitrag beschreibt, warum Leichtbau bei konventionellen und Batteriefahrzeugen unterschiedlich zu bewerten ist.

Nichtlineare Lenkregler für den querdynamischen Grenzbereich (Nonlinear Steering Controllers for the Lateral Dynamics Stability Limit)

Beim Entwurf eines Lenkreglers zur automatischen Spurführung wird das charakteristische Sättigungsverhalten der Seitenkraftkennlinien bei großen Schräglaufwinkeln im Streckenmodell berücksichtigt. Es zeigt sich, dass bei dem aus mathematischer Sicht optimalen modellprädiktiven Regler eine Vielzahl von Reglerparametern auf heuristischem Wege festgelegt werden muss. Daher wird hier, nach dem Prinzip der exakten Linearisierung, ein Rückführgesetz vorgeschlagen, dessen Leistungsfähigkeit dem modellprädiktiven Regler gleichkommt, das dabei aber nur einen Bruchteil der Rechenzeit und lediglich zwei Reglerparameter mit physikalisch anschaulicher Bedeutung benötigt. Die Position des fahrzeugfesten Spurführungs-Referenzpunktes hat erheblichen Einfluss auf das Stabilitätsverhalten im Grenzbereich. Dies kann durch mathematische Stabilitätsanalyse und anhand von Simulationen stabilitätskritischer Fahrmanöver demonstriert werden. Simulationsuntersuchungen mit einem Formelrennfahrzeug und Messfahrten mit einem X-by-wire Versuchsträger im Modellmaßstab, der am Institut für Verbrennungsmotoren und Kraftfahrwesen der Universität Stuttgart (IVK) aufgebaut wurde, belegen die Fähigkeit des hier vorgestellten Regelsystems zur hochpräzisen Spurführung im querdynamischen Grenzbereich. Dabei beträgt die maximale seitliche Abweichung von der Soll-Trajektorie nur wenige Prozent der Fahrzeugbreite. The well known nonlinear shape of the vehicles side force characteristics is considered to design a steering controller for automatic guidance. When applying nonlinear model predictive control, which should be the best possible controller from a mathematical point of view, it turns out that a large number of controller parameters has to be defined using heuristic methods. In this paper, however, exact linearization technique is used to determine a feedback law that matches the performance of the model predictive controller with a much lower amount of computing time and only two controller parameters. The position of the vehicle fixed reference point for automatic guidance significantly affects the stability properties of the control loop, which can be proven by means of mathematical stability analysis and simulation results concerning test maneuvers at the stability limit. The capability of performing precise automatic guidance at the lateral dynamics stability limit is shown by means of a race car simulation model and a 1 : 5 scaled x-by-wire experimental prototype. During these simulations and test runs, the maximum lateral deviation from the desired trajectory was within a few percent of the vehicle width.

Road Load Determination Based on Driving-Torque-Measurement

This paper introduces a driving-torque measurement method for the determination of vehicle road load and its components. To increase the accuracy, the torque measurements are combined with rolling resistance measurements performed with a specially developed trailer. This method is a strictly experimental approach and does not use any mathematical models. The experimental techniques are described as well as the proceedings to compare test stand and road measurements. The results that are shown prove that this method is suitable for the investigation of single road load components. Furthermore, the comparison of different rolling resistance measurement devices shdws the potential of the measurement trailer and the necessity to perform rolling resistance measurements on real road surfaces and not solely on test stands.

Die Fahrzeug-Energieeffizienzkennzahl. Der "Wirkungsgrad" des Fahrzeugs

Der Kraftstoffverbrauch eines Fahrzeugs bestimmt sich durch den Wirkungsgrad des Motors sowie durch fahrzeug seitige innere (Antriebs-) und ausere (Fahr-)Widerstande. Dem Motorwirkungsgrad wurde bislang kein Fahrzeugwirkungsgrad gegenubergestellt. Dieser wird nun von den Autoren des Forschungsinstituts fur Kraftfahrwesen und Fahrzeugmotoren Stuttgart (FKFS) vorgestellt. Das aktuelle Thema der Ruckgewinnung von Bremsenergie wird in die Untersuchung des Fahrzeugwirkungsgrads mit einbezogen.

Further Investigations on Gradient Effects

In automotive wind tunnels with modern road simulation installations boundary layer pre-suction is a widely-used technique for boundary layer control. The consequence of boundary layer pre-suction is an additional pressure gradient in front of the model. In order to investigate the effects of the additional pressure gradient on drag, experiments were conducted with two different models (scale 1:5) in the IVK Model Wind Tunnel. In these experiments the suction velocity of the boundary layer pre-suction served as a parameter to change the static pressure gradient along the test Section and was for this purpose adjusted higher and lower than the standard suction velocity. It is shown that the total drag increment due to boundary layer pre-suction consists of at least two parts: the ground simulation increment and the static pressure gradient increment. The ground simulation increment is due to a decrease in the boundary layer thickness and the resulting modified flow beneath the model. The static pressure gradient increment is due to the unintended additional pressure gradient. Furthermore a method is described to separate both increments and a correction method is proposed to correct the additional gradient effect.

Classification of aerodynamic tyre characteristics

The geometric shape of the tyres can have a large influence on the aerodynamic drag of a passenger car as it has been shown already in different publications. However, so far it is not possible to quantify the aerodynamic characteristics of a tyre without measuring it mounted on a vehicle in a wind tunnel and comparing it to other tyres. For this reason a research project at the Institute for Internal Combustion Engines and Automotive Engineering at the University of Stuttgart (IVK) was launched with the intention of categorising the aerodynamic characteristics of passenger car tyres.

Kann man mit dem Luftwiderstandsbeiwert die Batteriekosten senken

Bei Elektrofahrzeugen wird der Leichtbau als probates Mittel zu Senkung der Batteriekosten propagiert. Der Einfluss der Aerodynamik auf Reichweite und Batteriekosten wird hingegen oft unterschatzt. Dabei fuhrt die Verringerung des Luftwiderstands cw · Ax, wie dieser Beitrag des Forschungsinstituts FKFS zeigt, besonders kosteneffektiv zum gleichen Ziel.

Aerodynamics as troubleshooting of wet fading

The prevention of soiling of glass panes and brakes is an important safety issue. Studies conducted in the thermal wind tunnel of FKFS have shown that brake discs and brake pads at aerodynamically optimized vehicles have greater traction in wet an dirty conditions.