Jochen Rauh

Virtual development of ride and handling characteristics for advanced passenger cars

Summary Advanced requirements for quality and functions, reduced development time, and increasing international competition motivate fundamental changes of the development processes. This puts much attention on the potentials of numerical simulation, i.e. experiments on the virtual product, while experiments on real prototypes will always remain an important part of the development process, for example to fulfill legal requirements, to achieve parameters for the simulation work, and to validate intermediate results and of course the final tuning. One step towards the virtual development of ride and handling characteristics of passenger cars is to achieve accuracy of simulation results which can be compared to what can be achieved with carefully selected experiments. This paper will present the state-of-the-art of current simulation technologies, their already available potentials and some remarks on current limitations. With this type of advanced simulation technologies, engineers are enabled to develop complex mechatronic chassis systems like active suspensions or stability control systems in relatively short periods of time to a high degree of maturity. A second use of these virtual prototypes is for extensive parameter studies or even optimizations, which will also give more insight in the complex nonlinear interactions of the chassis systems. This can even yield to a complete change of development processes from an analytical incremental setup to more target driven work.

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.

Tyre simulation challenges

This paper aims to give an overview on the most challenging tasks of today and tomorrow for tyre simulation success in complete vehicle environments. It gives some comments on the achieved level of maturity in tyre simulation, mentions weak spots and issues in daily work, and suggests some areas worth working on, e.g. open standardised reference implementations of tyre simulation models to improve the cooperation in the vehicle dynamics community of researchers, tyre suppliers, and car manufacturers by far. It also gives insight into the efficient curved regular grid approach to represent digital road profiles for simulation purposes.

Road and track irregularities: measurement, assessment and simulation

Road and track irregularities have an important influence on the dynamic behaviour of vehicles. Knowledge of their characteristics and magnitude is essential for the design of the vehicle but also for comparable homologation and acceptance tests as well as for the planning and management of track maintenance. Irregularities of tracks and roads are regularly measured using various measurement technologies. All have advantages and weaknesses and require several processing steps. Characterisation of irregularities is done in the distance as well as in the wavelength domain. For rail irregularities, various distance domain description methods have been proposed and are in use. Methods have been analysed and compared with regard to their processing steps. Several methods have been analysed using measured irregularity and vehicle response data. Characterisation in the wavelength domain is done in a similar way for track and road irregularities. Here, an important issue is the estimation of the power spectral densities and the approximation by analytical formulas. For rail irregularities, periodic defects also play an important role. The use of irregularities in simulations requires various processing steps if measured irregularities are used, as well as if synthetic data are utilised. This paper gives a quite complete overview of rail irregularities and points out similarities and differences to the road.

Advanced modular modelling of rubber bushings for vehicle simulations

In many applications of numerical vehicle dynamics simulation, the formulation of appropriate mathematical models of rubber bushings is a crucial but difficult task. It can be seen as a balancing act between the demanding mechanical characteristics of the elastomer, the complexity of the associated parameterisation procedure, and the resulting computational expenses. The following article discusses this problem and presents the advanced phenomenological Daimler model for rubber bushings, whose modelling complexity can be easily adapted to problem-specific requirements for a wide variety of simulation tasks. Besides the proper characterisation of the mechanical behaviour, special focus is put on an easy-to-use parameterisation process that allows an efficient implementation of the model in an established workflow process. After a brief description of constitutive mechanical characteristics of rubber bushings, the framework of the modular model structure with different characteristics for stiffness, hysteresis, and damping is explained, followed by a more detailed discussion of each model element and the user-friendly parameterisation process. Finally, two examples of typical chassis bushings under durability load conditions demonstrate the practical applicability and the outstanding performance of the modular and adaptable Daimler model.

Automated simulation of scenarios to guide the development of a crosswind stabilization function

Abstract Mercedes-Benz has recently added a crosswind stabilization function to the Active Body Control (ABC) suspension for the 2009 S-Class. For this purpose the ABC uses the yaw rate, lateral acceleration, steering angle and velocity sensors of the Electronic Stability Program ESP to vary the wheel load distribution via the ABC spring struts, depending on the direction and intensity of the crosswind. This function has to distinguish between vehicle reactions caused by crosswind, by driver interaction, and by road unevenness. The effects of the crosswinds can be compensated in this way, or reduced to a minimum in the case of strong gusts. For developing this function Mercedes Benz used the test case generator TestWeaver to generate thousands of different driving and crosswind scenarios. The scenarios have been executed using a co-simulation of: (i) a dynamic vehicle model (based on the inhouse tool CASCaDE), (ii) a road and crosswind model implemented in C and (iii) a MathWorks/Simulink model of the crosswind stabilization function. This simulation-based approach helped considerably to validate and iteratively improve the safeguarding algorithms of the stabilization function through all design phases.

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.

Assessing the thermo-mechanical TaMeTirE model in offline vehicle simulation and driving simulator tests

This paper presents the experiences using Michelins thermo-mechanical TaMeTirE tyre model for real-time handling applications in the field of advanced passenger car simulation. Passenger car handling simulations were performed using the tyre model in a full-vehicle real-time environment in order to assess TaMeTirEs level of consistency with real on-track handling behaviour. To achieve this goal, a first offline comparison with a state-of-the-art handling tyre model was carried out on three handling manoeuvres. Then, online real-time simulations of steering wheel steps and slaloms in straight line were run on Daimlers driving simulator by skilled and unskilled drivers. Two analytical tyre temperature effects and two inflation pressure effects were carried out in order to feel their impact on the handling behaviour of the vehicle. This paper underlines the realism of the handling simulation results performed with TaMeTirE, and shows the significant impact of a pressure or a temperature effect on the handling behaviour of a car.

Developments in vehicle dynamics and the tire model performance test

Aspects of the vehicle dynamics like handling, ride, comfort, and durability as well as of controlled subsystems are discussed. The increasing importance of simulation to support the development and application process of vehicles with control systems is shown. The role of the tire and the corresponding tire models is highlighted and requirements for the modeling and parameterization of tire models are derived.