Dieter Ammon

Vehicle dynamics analysis tasks and related tyre simulation challenges

During the past 20 years, enormous progress has been made in chassis engineering and driveability. Todays vehicles are significantly safer and at the same time more comfortable than their predecessors. Among the reasons are the variety of electronic control systems on offer today, but also the fact that engineers have succeeded in making suspension and chassis design and tuning more precisely and significantly by using modern analysis and simulation methods. This allows product maturity to be assured and intensified, despite wider model ranges and shorter development times. In this context, the significance of modelling and simulation of the tyre behaviour becomes increasingly important. As the link between the vehicle and the road, the tyre ultimately determines the driving properties that can be realized, any latent safety reserves that can be activated, and the vehicle vibration comfort, at least in as far as road-surface-induced excitations are concerned.

System dynamics of electrified vehicles: some facts, thoughts, and challenges

Mainly motivated by ecological aspects and the resulting worldwide regulations, electrified vehicles are getting increasing attention from researchers, car manufacturers, and consumers. While most discussions are focusing on the hybrid or completely electric propulsion technologies, this contribution will focus on the aspects of system dynamics related to electrified vehicles. Most of the aspects discussed here are also interesting for vehicles with conventional combustion engines, which will be dominating the mobility market for many years to come. Here, after discussing some basic principles of energy consumption and recuperation potentials, chassis systems are discussed with respect to energy efficiency and fitness for electrified vehicles. Further on, some system implementations are presented to show promising or already successful solutions to the arising challenges.

Problems in road surface modelling

SUMMARY The properties of real roads along the lateral axis cannot not be adequately explained with the classic model of the isotropic road. With a realistic assumption of spatial invariance (homogeneity), a more general surface model has been formulated and compared with the experimental data. A good match of measurements and “theory” has been achieved. A simple parametric approximation is developed for the coherence function on the basis of the extended unevenness model. In addition to the undulation exponent of the road surface and the track width, the curve is characterized by three other key figures. The adaptation to the experimental data results in comparatively small yet justifiable parameter intervals. Due to the further development of filter methods for the synthesis of random irregularities, a model family is now available which facilitates a satisfactory balance between model accuracy and numerical complexity for most applications. The main difficulties would appear to lie in the formulation o...

Approximation and generation of Gaussian and non-Gaussian stationary processes

Abstract Combining a linear dynamical filter system and a nonlinear transform makes it possible to adapt the power density spectrum of an artificial stationary process as well as its probability distribution function to given quantities. A linear and a nonlinear approximate method for Gaussian processes are presented. An extension of the linear system by a static polynomial transform yields a non-Gaussian process. Varying the polynomial coefficients its distribution can be adapted. Using the analytical input-output relation of the power spectra, a suitable target spectrum for the linear filter can be evaluated. The entire adaptation concept is derived and principally discussed.

High Performance System Dynamics Simulation of the Entire System Tire-Suspension-Steering-Vehicle

SUMMARY A problem-specific multi-body-system approach, the dynamic suspension models, was developed to obtain an almost complete description of the nonlinear dynamic properties of modern suspensions. The concept includes the spatial elasticities and damping effects of the bushings, forces and moments of inertia of the links, and related friction and clearance effects. In combination with the sophisticated physical tire simulation model BRIT [4] and comparable models for the hydraulics of the power steering system, we obtain an effective simulation tool for the analysis of the entire suspension system dynamics as well as for the entire vehicle system dynamics. This approach enables steady-state vibration phenomena as well as transient response problems of the suspension system such as shimmy, steering roughness, or excitations due to misbalanced wheels to be investigated efficiently and with respect to realistic excitation conditions. The results are compared with driving test data.

Simulation of the Perceptible Feed-Forward and Feed-Back Properties of Hydraulic Power-Steering Systems on the Vehicle's Handling Behavior Using Simple Physical Models

Today, often complex component-oriented simulation models are used to study the influences of hydraulic power-steering systems on the vehicle’s handling properties. In these simulation models, we have a detailed description of the vehicle suspension components (links, joints, springs, etc.) extended by complex component simulation models of tires, bushings, and of course also by power-steering models. These power-steering models contain a detailed physical description of the complex mechanical and hydraulics properties of the system, like friction in seals, aspects of hydraulic power supply, etc. On the other hand, there is a need for simple model approaches used for basic assessments and system development. These simple models should represent all the essential properties of the vehicle’s handling behavior, without the need for the large-scale parameter setup and compute-time requirements of the more complex models. For many applications in handling, we use the class of single-track two-wheel bicycle-type vehicle models. With some nonlinear extensions, these models can represent the complete operating conditions of the vehicle. The parameterization of these models can be achieved online while driving or offline by analysis and identification, on the basis of some standard test maneuvers. In these models, all properties of steering, suspension and tire are condensed to the cornering stiffness or side-force map, a separation e.g. of the steering system influence does not take place. This article shows how modeling of a hydraulic power-steering system can be done to represent the essential feed-forward and feed-back properties, and how this model can be integrated to the complete vehicle’s description. This new model approach gives a better insight into the four-pole properties of steering systems and introduces a separation between the steering system and the suspension even in simple model classes.

Advanced Road Vehicles: Control Technologies, Driver Assistance

Advanced road vehicles require sophisticated tools for the ride and handling analysis during the design phase. The corresponding model based development process is described, and driving performance measures are introduced. Active suspensions, active steering and the overall vehicle dynamics management are considered. Driver assistance systems are presented and discussed.

Ermittlung der Reibwerte von Gummistollen zur genauen Parametrierung von Reifenmodellen

Alle Fuhrungs-, Antriebs- und Bremskrafte von Strasenfahrzeugen werden uber eine etwa postkartengrose Kontaktflache, den sogenannten Latsch, vom Reifen auf die Fahrbahn ubertragen. Die Kraftubertragung beruht auf Haft- und Gleitreibungsvorgangen zwischen Reifengummi und Fahrbahnoberflache. Die Daimler-Chrysler AG und das Institut fur Maschinenkonstruktionslehre und Kraftfahrzeugbau der Unversitat Karlsruhe wollen mit diesem Bericht die Kraftschlussvorgange im Reifenlatsch detailliert analysieren und schlieslich zur Klarung beitragen, inwieweit die Kraftubertragung zwischen Reifen und Fahrbahn weiter erhoht werden kann

CO2-reducing chassis and vehicle dynamic systems

Besides primary measures to reduce CO2 emissions at the combustion engine, it is also possible to decrease the climate-relevant gases with the chassis. Daimler developed efficient chassis systems which support recuperation and use systems like the active suspension Active Body Control and the foresight system Pre-Scan.

Determination of the friction coefficients of rubber ribs: For the exact parameterisation of tyre models

All guidance, drive and braking forces of road vehicles are transmitted from the tyre to the road surface via an area of contact that has approximately the size of a postcard, the so-called contact area. The transmission of forces is based on adhesion and sliding friction processes between the tyre rubber and the road surface. Daimler-Chrysler and the Institut fur Maschinenkonstruktionslehre und Kraftfahrzeugbau of Karlsruhe University want to analyse the processes in the tyre contact area in this article in detail and, finally, contribute to clarify to what extent the transmission of forces between tyre and road surface can be increased.