Study on friction in automotive shock absorbers, part 1: Friction simulation using a dynamic friction model in the contact zone of an FEM model

The important change in the transition from partial to high automation is that a vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorber with two friction types: The intended viscous friction dissipates the chassis vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In this article, a simulation approach is introduced to model damper friction based on the most friction-relevant parameters. Since damper friction is highly dependent on geometry, which can vary widely, three-dimensional (3D) structural FEM is used to determine the deformations of the damper parts resulting from mounting and varying operation conditions. In the respective contact zones, a dynamic friction model is applied and parameterized based on the single friction point measurements. Subsequent to the parameterization of the overall friction model with geometry data, operation conditions, material properties and friction model parameters, single friction point simulations are performed, analyzed and validated against single friction point measurements. It is shown that this simulation method allows for friction prediction with high accuracy. Consequently, its application enables a wide range of parameters relevant to damper friction to be investigated with significantly increased development efficiency

Study on friction in automotive shock absorbers, part 2: Validation of friction simulations via novel single friction point test rigs

The most important change in the transition from partial to high automation is that the vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorbers with two friction types. The intended viscous friction dissipates the chassis’ vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In the current article, the simulation approach introduced in part 1 of this study is validated against a single friction point and full damper friction measurements. To achieve that, a friction measurement method with novel test rigs has been developed, which allows for reliable determination of the friction behavior of each single friction point, while appropriately resembling the operating conditions of the real damper. The subsequent presentation of a friction simulation using friction model parameters from different geometry shows the general applicability of the overall friction investigation methodology. Accordingly, the presented simulation and measurement approaches enable the investigation of dynamic friction in automotive shock absorbers with significantly increased development efficiency

Datenbasierte Simulationsumgebung für das Training autonomer, maschineller Regelungssysteme

Nach der Auslegung und Produktion komplexer Systeme, folgen oft umfangreiche Tests zum Nachweis der Produktfähigkeit über die Grenzen der vorausgelegten Randbedingungen hinweg. Solche Tests erfolgen häufig automatisiert unter bestmöglicher Reproduktion der späteren Einsatzbedingungen. Die dabei gemessenen Daten spiegeln das Systemverhalten in Form von Mess-, Berechnungs- und Stellgrößen wieder. Mithilfe dieser Daten soll in der vorliegenden Arbeit ein Vorgehen beschrieben werden, dass sie nutzt und durch den Einsatz neuronaler Netze in eine Black-Box Simulationsumgebung überführt. Diese Simulationsumgebung wird dann dazu verwendet, dass Systemverhalten vorherzusagen, Abweichungen zu erkennen und vor allem autonome Lernalgorithmen auf das System anzuwenden, denn selbst wenn das System fertig entwickelt ist, so bedarf es oft immer noch einer manuellen Parametrisierung der Systemsteuerung

Extending the HSRI tyre model for large inflation pressure changes

The choice of the optimal tyre inflation pressure is always a conflict of aims since the inflation pressure has a significant influence on safety, comfort and environmental behaviour of a vehicle. The development of a dynamic Tyre Pressure Control System (TPCS) can reduce the conflict of minimal rolling resistance and maximal traction. Driven by the requirements for autonomous driving, recently substantial progress was made to predict the road conditions precisely and robust. This premise moves the development of a Tyre Pressure Control System (TPCS) to the focus of research. To study the influence of the tyre inflation pressure on longitudinal tyre characteristics under laboratory conditions, an experimental sensitivity analysis is performed using a multivalent usable Corner Module Test Rig (CMTR) developed by the Automotive Engineering Group at Technische Universität Ilmenau. The test rig is designed to analyse suspension system and tyre characteristics on a roller of the recently installed 4 chassis roller dynamometer. Camber angle, toe angle and wheel load can be adjusted continuously. In addition, it is possible to control the temperature of the test environment between -20°C and +45°C. The results of the experimental study, that covers a wide range of different wheel loads and inflation pressures for three different tyre variations, show a significant influence of the inflation pressure on longitudinal tyre characteristics as slip stiffness or maximum traction force. To simulate the influence of a TCPS on vehicle dynamics with a numerical simulation tool, it is essential to describe the influence of the inflation pressure on tyre characteristics correctly with a tyre simulation model. Consequently, the well-known physically based HSRI tyre model adapted from Dugoff is extended for large inflation pressure changes. The model parameters for the tyre model are determined with a parameter identification method implemented in a developed automatic MATLAB analysis tool. The extended HSRI tyre model shows a good model accuracy to represent the tyre inflation pressure dependent tyre characteristics