Johannes Edelmann

Driver models in automobile dynamics application

Understanding the driver of an automobile has been attractive to researchers from many different disciplines for more than half a century. On the basis of their acquirements, models of the (human) driver have been developed to better understand, analyse and improve the combined couple of driver and automobile. Due to distinctive demands on the models in accordance with different kinds of applications, a variety of driver models is available. An overview of driver models is given with respect to their application and different methodical modelling approaches. The emphasis is put on the interest of engineers, who generally focus on the automobile (like design and optimization of vehicle components and the overall vehicle dynamics behaviour) by applying their approved (mathematical) methods. Nonetheless, a brief look beyond is added to better complete the view on the involved task of driving and driver modelling for automobile dynamics application.

A passenger car driver model for higher lateral accelerations

Due to increasing demands for time and cost efficient vehicle and driver assistant systems development, numerical simulation of closed-loop manoeuvres becomes increasingly important. Thus, the driver has to be considered in the modelling. On the basis of a two-layer approach to model a drivers steering behaviour, the field of application is extended to higher lateral accelerations in this study. An analytical method to determine the driver parameters is presented, which is based on the two-wheel vehicle model. The simulation results are determined using a full vehicle model including all essential nonlinearities. Standard manoeuvres in the nonlinear range of vehicle handling behaviour are performed. A cornering manoeuvre is chosen to show the characteristics of the proposed driver model.

Handling characteristics and stability of the steady-state powerslide motion of an automobile

Powerslide of an automobile may be defined as a steady-state cornering motion at a large side slip angle of the vehicle, considerably large traction forces and a large negative steering angle of the handwheel. In this case the front wheels direct towards the outside of the turn. As this extrem driving condition, which can be seen e.g. in Rallye sports, is hardly addressed in literature so far, this paper investigates the respective handling characteristics. Therefore, a nonlinear four-wheel vehicle model is applied including nonlinear tyre characteristics, the load transfer between inner and outer wheels and the influence of the traction forces on the lateral tyre forces. A basic stability analysis reveals the unstable nature of the steady-state powerslide motion of a certain test vehicle. To approve the numerical findings, measurements have been performed with a sports utility vehicle with rear-wheel drive at various speeds on a wet circular test track.

On the wobble mode of a bicycle

Wheel shimmy and wobble are well-known dynamic phenomena at automobiles, aeroplanes and motorcycles. In particular, wobble at the motorcycle is an (unstable) eigenmode with oscillations of the wheel about the steering axis, and it is no surprise that unstable bicycle wobble is perceived unpleasant or may be dangerous, if not controlled by the rider in time. Basic research on wobble at motorcycles within the last decades has revealed a better understanding of the sudden onset of wobble, and the complex relations between parameters affecting wobble have been identified. These fundamental findings have been transferred to bicycles. As mass distribution and inertial properties, rider influence and lateral compliances of tyre and frame differ at bicycle and motorcycle, models to represent wobble at motorcycles have to prove themselves, when applied to bicycles. For that purpose numerical results are compared with measurements from test runs, and parametric influences on the stability of the wobble mode at bicycles have been evolved. All numerical analysis and measurements are based on a specific test bicycle equipped with steering angle sensor, wheel-speed sensor, global positioning system (GPS) 3-axis accelerometer, and 3-axis angular velocity gyroscopic sensor.

Wobble of a racing bicycle with a rider hands on and hands off the handlebar

So far fundamental papers on the understanding of the wobble mode at motorcycles have been published, but in contrast, little research has been published on the wobble mode at bicycles. Wobble denotes a characteristic unstable oscillatory mode dominated by oscillations of the front wheel about the steering axis. The wobble mode of a trekking bicycle at low speeds has already been analysed, where no influence of the riders hands on the steering system is taken into account. The wobble mode of a racing bicycle at higher speeds has not been addressed in more detail so far. The paper points out the difference between a trekking bicycle and a racing bicycle in particular with respect to the wobble mode. Different geometry, mass and stiffness properties of both types of bicycles and different characteristic positions of the rider are considered. As the wobble at racing bicycles often occurs at high speeds, when riding down a grade with hands on a dropped handlebar, a passive rider model, that takes into account the movement of the riders arms, is presented.

Basics of Vehicle Dynamics, Vehicle Models

For the understanding and knowledge of the dynamic behaviour of passenger cars it is essential to use simple mechanical models as a first step. With such kind of models overall characteristic properties of the vehicle motion can be investigated. For cornering, a planar two-wheel model helps to explain understeer–oversteer, stability and steering response, and influences of an additional rear wheel steering. Another planar model is introduced for investigating straight ahead acceleration and braking. To study ride comfort, a third planar model is introduced. Consequently, in these basic models, lateral, vertical and longitudinal dynamics are separated. To gain insight into e.g. tyre–road contact or coupled car body heave, pitch and roll motion, a 3D-model needs to be introduced, taking into account nonlinearities. Especially the nonlinear approximation of the tyre forces allows an evaluation of the four tyre–road contact conditions separately—shown by a simulation of a braking during cornering manoeuvre. A near reality vehicle model (NRVM) comprises a detailed 3D description of the vehicle and its parts, e.g. the tyres and suspensions for analysing ride properties on an arbitrary road surface. The vehicle model itself is a composition of its components, described by detailed sub-models. For the simulation of the vehicle motion, a multi-body-system (MBS)-software is necessary. The shown fundamental structure of the equations of motion allows to connect system parts by kinematic restrictions as well, using closed loop formulations. A NRVM also offers the possibility for approving a theoretical layout of control systems, generally by using one of the simple vehicle models as observer and/or part of the system. An example demonstrates the possibility of additional steering and/or yaw moment control by differential braking.

Vehicle side-slip angle estimation on a banked and low-friction road

The effective application of integrated vehicle dynamics control and automatic driving require consistent vehicle state variables and parameters. Considering lateral vehicle dynamics, the yaw rate and (estimated) vehicle side-slip angle are the minimum set of state variables that can give insight into the handling characteristics of a vehicle. Various methods of vehicle side-slip angle (lateral velocity) estimation have been tested in virtual and real world applications, in particular on a horizontal dry road. Vehicle side-slip angle, however, is not only affected by the (steering) commands of the driver, and possibly by a vehicle dynamics controller, but can also arise from a banked road or result from a low-friction surface, changing tyre–road contact. The combined effects require a comprehensive estimation approach, which is less often touched upon in the literature. Based on earlier findings on important aspects of observability, the paper addresses a modular vehicle side-slip angle estimation approach that is particularly focused upon practical aspects of modelling and design. Estimation of the combined vehicle side-slip angle, road bank angle and maximum tyre–road friction coefficient has been broadly tested with a vehicle equipped with an electronic stability control (ESC) and electric power-assisted steering (EPS) sensor configuration, for various road conditions, driving situations and vehicle/tyre setups.

Simulation-based identification of excitation spectra for a dynamic suspension test rig

The objective characterization of modern vehicles on roads and test rigs regarding ride comfort delivers a key factor for an efficient vehicle development process. To completely understand the vibration phenomena of a vehicle, detailed information about the subsystem suspension in the relevant frequency range is required.

Advanced Vehicle Control : Proceedings of the 13th International Symposium on Advanced Vehicle Control (AVEC'16), September 13-16, 2016, Munich, Germany

This paper considers a novel approach to active rollover prevention, incorporating online estimation of the driver’s intended path. The problem is formulated as one of minimizing lateral deviation from the intended path subject to friction and rollover limits. A recently published control allocation and moderation method is developed to be applicable to the rollover problem in such a way that speed is optimally reduced. Furthermore, a new Time-To-Rollover (TTR) metric, based on driving intention prediction, is incorporated into the system concept. Finally, mediation provides a general approach to designing a cooperative system, coordinating between the human driver and the onboard autonomous safety system to reduce the sensitivity of vehicle response to any sudden or emergency driver actions.This work evaluates the intrinsic contribution of the yaw rate reference to the overall handling performance of an electric vehicle with torque vectoring control in terms of minimum-time manoeuvring. A range of yaw rate references are compared through optimal control simulations incorporating closed-loop controller dynamics. Results show yaw rate reference has a significant effect on manoeuvre time.

Advanced Vehicle Control AVEC’16: Proceedings of the 13th International Symposium on Advanced Vehicle Control (AVEC’ 16), Munich, Germany, 13–16 September 2016

This paper considers a novel approach to active rollover prevention, incorporating online estimation of the driver’s intended path. The problem is formulated as one of minimizing lateral deviation from the intended path subject to friction and rollover limits. A recently published control allocation and moderation method is developed to be applicable to the rollover problem in such a way that speed is optimally reduced. Furthermore, a new Time-To-Rollover (TTR) metric, based on driving intention prediction, is incorporated into the system concept. Finally, mediation provides a general approach to designing a cooperative system, coordinating between the human driver and the onboard autonomous safety system to reduce the sensitivity of vehicle response to any sudden or emergency driver actions.This work evaluates the intrinsic contribution of the yaw rate reference to the overall handling performance of an electric vehicle with torque vectoring control in terms of minimum-time manoeuvring. A range of yaw rate references are compared through optimal control simulations incorporating closed-loop controller dynamics. Results show yaw rate reference has a significant effect on manoeuvre time.