Manfred Plöchl

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.

Recent advances in tyre models and testing procedures

Owing to the advances in the simulation techniques of vehicle development and design, the modelling of the tyre is of special importance. Thereby, not only the reliability of quantitative results but also the extension to higher frequency ranges and the possibility to account for local road surface structures smaller than the tyre patch is becoming a necessity. A description of some tyre models and the required features for these last two aspects are presented. Reliable modelling of tyre characteristics based on measurements and efficient application with multi-body system (MBS) programs for vehicle dynamics simulation are checked with the ‘Tyre Model Performance Test (TMPT)’. With the TMPT handling and high frequency behaviour of tyre models are tested with a virtual test rig implemented in three different MBS software programs. Also, the validation of measurements is combined with specific capability tests to show the range of application of the tyre models. After an outline of the test conditions, the participating tyre models are introduced. A selection of results offers the possibility to compare the tyre models, the tyre model—MBS software combinations and simulation results with measurements. It becomes obvious that a thorough check of the tyre model and the interaction with the MBS software is essential to be aware of the range of application of simulations and the quality of the results.

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.

Tyre model performance test: first experiences and results

The tyre model performance test (TMPT) provides information about the efficiency and problems of the simulation sequence from tyre measurements (tyre modelling and parametrization) to multibody-system (MBS) software integration. Based on test rig tyre measurements with respect to vehicle-handling behaviour and higher-frequency-range tests (running over a cleat; vibration modes), tyre models have to be provided in a way that they can be connected with the standard Tyre interface (STI) or a modified tyre interface to at least one of the three MBS programs ADAMS, DADS and SIMPACK. The test conditions and the simulation test rig were defined in advance by an international group of experts. Four tyre model providers participated for the handling (low-frequency) manoeuvres and four for the low- and higher-frequency-ranges. Since a planned feedback from the MBS simulation results (they were done by the MBS-program providers) to the tyre model providers was not completely finished, the results shown are preliminary only. For the steady-state behaviour, all tyre models show good agreement with measurements for lateral and longitudinal tyre forces while, for the self-aligning torque, larger differences appear. For ‘crossing of a cleat’, all high-frequency-range models show good agreement with measurements as well but, for some tests (e.g. sinusoidal sweeps), qualitative differences even between MBS programs for the same tyre model can be noticed. This indicates that the application of tyre models within MBS programs requires some preliminary testing and maybe additional checks before using them for vehicle dynamics analysis.

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.

Transient heating of a rotating elastic–plastic shrink fit

The stress distribution in a rotating shrink fit with solid shaft subject to a temperature cycle is investigated. It is presumed that both components are in a state of generalized plane strain and exhibit the same elastic-perfectly plastic material behavior. Applying Trescas yield condition and the flow rule associated with it, the problem is accessible to a quasi-analytical treatment. It is found that the interface pressure and therefore the transferable moment show a permanent reduction due to plastic deformation as well as a temporary reduction due to the thermal expansion of the hub; these effects may lead to a failure of the device.

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.

STABILITY CONTROL OF A PASSENGER CAR BY COMBINED ADDITIONAL STEERING AND UNILATERAL BRAKING

SUMMARY To investigate the combined control of the side slip angle and yaw velocity of a vehicle in critical driving situations a complex vehicle model (developed in ADAMS) with ABS and adequate tyre characteristics are used. The control loop includes an observer to estimate the side slip angle of the vehicle and a ‘sliding mode controller’ based on a simplified 2-wheel and 4-wheel vehicle model respectively. The output of the controller is one of the three combinations containing two of the possible actuator actions: additional steering at the front, at the rear and in combination with unilateral braking, an additional yaw moment. This yaw moment has to be transformed via corresponding longitudinal slip values into braking moments. Simulation results for a severe steering step input and braking during cornering very well illustrate the advantages of all three investigated control strategies. Only for heavy braking during cornering (for more than 0.7g longitudinal deceleration on a dry surface) the combination unilateral braking with additional steering of the front wheels is less favourable as a result of the control limitations due to the dominant ABS.

Simulation model of an aircraft landing gear considering elastic properties of the shock absorber

Abstract For the investigation of elastic bending of the landing gear shock absorber of an aircraft under dynamic loads upon landing and subsequent braking during roll out, an MBS-based model of the landing gear is introduced. To separate effects of the elastic bending of the main landing gear the fuselage is considered rigid. After performing a flare with subsequent landing, the aircraft is stopped by means of an antiskid system. For comparison, an analytical-numerical study of a finite-element model of the main landing gear shock strut components is done for simple static and dynamic loads considering Bernoullis hypothesis. Simulation of a rough-landing manoeuvre reveals that vibrations due to the elastic properties of the shock absorber not only increase loads on the components but significantly affect the braking process as well.

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.