Steffen Müller

A new model to compute the desired steering torque for steer-by-wire vehicles and driving simulators

This paper deals with the control of the hand wheel actuator in steer-by-wire (SbW) vehicles and driving simulators (DSs). A novel model for the computation of the desired steering torque is presented. The introduced steering torque computation does not only aim to generate a realistic steering feel, which means that the driver should not miss the basic steering functionality of a modern conventional steering system such as an electric power steering (EPS) or hydraulic power steering (HPS), and this in every driving situation. In addition, the modular structure of the steering torque computation combined with suitably selected tuning parameters has the objective to offer a high degree of customisability of the steering feel and thus to provide each driver with his preferred steering feel in a very intuitive manner. The task and the tuning of each module are firstly described. Then, the steering torque computation is parameterised such that the steering feel of a series EPS system is reproduced. For this purpose, experiments are conducted in a hardware-in-the-loop environment where a test EPS is mounted on a steering test bench coupled with a vehicle simulator and parameter identification techniques are applied. Subsequently, how appropriate the steering torque computation mimics the test EPS system is objectively evaluated with respect to criteria concerning the steering torque level and gradient, the feedback behaviour and the steering return ability. Finally, the intuitive tuning of the modular steering torque computation is demonstrated for deriving a sportier steering feel configuration.

A discrete-continuous track-model for wheelsets rolling over short wavelength sinusoidal rail irregularities

SUMMARY A semi-analytical method for the analysis of the high frequency vibrations of wheelset and railway track is presented. In a first step a harmonically oscillating load is moving over a discretely supported rail. In a second step a wheelset, rolling over vertical sinusoidal irregularities, is considered. It will be shown that in both cases of excitation the problem can be treated completely analytically. The only numerical step is the solution of an eigenvalue problem. This procedure can also be applied for the treatment of lateral vibrations. The method is used to investigate the influence of frequency and velocity of the moving load and the moving wheelset respectively on the vertical direct receptance of the rail. Finally it will be investigated whether such a complicated analysis is necessary for technical problems such as the calculation of corrugation growth rates.

Lateral trajectory tracking control for autonomous vehicles

In this contribution a structure for high level lateral vehicle tracking control is presented. It is based on the two degrees of freedom structure that allows to separately define the command response and disturbance attenuation. The application of the disturbance observer guarantees robust compensation of the disturbances. An advantage of the presented structure is its robustness against variable vehicle parameters. Only a considerably reduced model is necessary which significantly simplifies the application process. Moreover the presented approach is characterized by its extensibility and its modularity.

Driver steering model for closed-loop steering function analysis

In this paper, a two level preview driver steering control model for the use in numerical vehicle dynamics simulation is introduced. The proposed model is composed of cascaded control loops: The outer loop is the path following layer based on potential field framework. The inner loop tries to capture the drivers physical behaviour. The proposed driver model allows easy implementation of different driving situations to simulate a wide range of different driver types, moods and vehicle types. The expediency of the proposed driver model is shown with the help of developed driver steering assist (DSA) function integrated with a conventional series production (Electric Power steering System with rack assist servo unit) system. With the help of the DSA assist function, the driver is prevented from over saturating the front tyre forces and loss of stability and controllability during cornering. The simulation results show different driver reactions caused by the change in the parameters or properties of the proposed driver model if the DSA assist function is activated. Thus, the proposed driver model is useful for the advanced driver steering and vehicle stability assist function evaluation in the early stage of vehicle dynamics handling and stability evaluation.

Model-based Rack Force Estimation for Electric Power Steering

Abstract In modern cars, hydraulic power steering (HPS) is continuously substituted by the electric power steering (EPS), active front steering (AFS) or steer-by-wire (SbW). In general, the main task of the EPS/HPS is the support of the driver in controlling the lateral position of the car and compensating the tyre aligning torques. These torques result in a steering rack force, which reliable long-term measurement induces disadvantages e.g. high sensor costs. Since the knowledge of the steering rack force is useful to improve various automotive control applications, the estimation of the steering rack force with real-time capable algorithms is in the focus of this research. First, a non-linear dynamic 4-mass model is given and validated by a prototype EPS. Second, an algorithm for steering rack force estimation is introduced using a non-linear friction compensation module and a linear disturbance observer. Finally, the estimation algorithm is analysed by means of validated numerical EPS model, a steering test bench and a real prototype car. The results state the excellent performance of the estimation algorithm, even under real operation conditions.

Comparison of Semi-Analytical Methods of Analysing Periodic Structures under a Moving Load

SUMMARY We compare two well known semi-analytical methods to analyse infinite periodic structures. The one method uses a generalized Fourier approach for the infinite periodic structure, the other uses Floquets theorem and takes only one section into account. The calculations for a discretely supported, undamped rail show that both methods produce similar results. The application to related problems is discussed.

Evidence-based security configurations for cloud datastores

Cloud systems offer a diversity of security mechanisms with potentially complex configuration options. So far, security engineering has focused on achievable security levels, but not on the costs associated with a specific security mechanism and its configuration. Through a series of experiments with a variety of cloud datastores conducted over the last years, we gained substantial knowledge on how one desired quality like security can have a significant impact on other system qualities like performance. In this paper, we report on select findings related to security-performance trade-offs for three prominent cloud datastores, focusing on data in transit encryption, and propose a simple, structured approach for making trade-off decisions based on factual evidence gained through experimentation. Our approach allows to rationally reason about security trade-offs.

A PID and state space approach for the position control of an electric power steering

The steering system is one of the primary controls for a vehicle. With the increase in driver assistance the demands of this subsystem have drastically increased. This has brought along much greater control intelligence. As with some assistance functions, autonomous driving requests a front steer angle for the vehicle to conduct a manoeuvre. The front steer angle is realized through the position control of the electric power steering (EPS). Thus far, the control of EPS systems in literature has focused heavily on generating a desired driver hand torque as is shown in works by Mehrabi et al. (2011), Fankem et al. (2014) and Dannohl et al. (2011). The absence of a driver in the loop yields new challenges for control of an EPS. For instance, autonomous driving means that the steering wheel is free moving without the hands of the driver to control it. The resonance frequency caused by the free motion dynamics has an adverse effect on the position control. Moreover, both internal and external disturbances which are normally compensated by the driver have to be regulated by the EPS controller. Work by von Groll et al. (2006) shows that the most of the relevant frequencies for driver’s inputs are below 4Hz. This is the frequency range where the controller should perform well in order to achieve all the relevant manoeuvres. Additionally, the steering wheel should move in a smooth and non-erratic way.

Kollisionsfreie Längs- und Quertrajektorienplanung unter Berücksichtigung fahrzeugspezifischer Potenziale

Zusammenfassung In diesem Beitrag wird ein Planungsansatz für teil- und hochautomatisierte Fahrfunktionen vorgestellt. Die Planungsaufgabe wird dabei von zwei Teilsystemen durchgeführt. Eine semi-globale Grobplanung gibt den Zielbereich vor, während eine lokale Trajektorienplanung den Verlauf der Trajektorie plant. Der vorgestellte Ansatz generiert Trajektorien, die Kollisionsfreiheit mit umliegenden Objekten gewährleisten. Gleichzeitig werden fahrdynamische Randbedingungen (wie ein begrenzter Reibwert) oder Aktuatorbegrenzungen berücksichtigt, sodass die geplante Trajektorie von der unterlagerten Regelung umsetzbar ist. Eine große Herausforderung in diesem Bereich stellt die Umsetzung auf Seriensteuergeräten dar, die in ihrer Rechenkapazität begrenzt sind.

Top-down development of controllers for highly automated driving using solution spaces

The complexity of highly automated driving functions and the large number of testing scenarios require the application of virtual design and testing methods. A common method to develop robust controllers is based on Γ-, Β and/or Θ- stability which need highly simplified vehicle models. Most of such models are linear and neglect relevant vehicle dynamics phenomena. Thus, it cannot be guaranteed that the closed-loop system including these simplified models covers all significant effects. This paper adopts a design method that computes solution spaces for controller parameters of arbitrary black box systems and models with no restrictions regarding linearity. This way the modelling represents the real system and disturbances more accurately. Parameter space approach and solution space approach are applied to a simple linear physical model of a steering system. Then, a more detailed model demonstrates the capabilities of the design method based on solution spaces. Requirements on the closed-loop system ex-pressed as boundaries of the stability regions are derived to ensure that the vehicle stays within a defined safety corridor next to the target trajectory. Additionally, a solution space for feasible controller parameters is specified. These requirements take nonlinear effects into account, thus increasing the validity of virtual testing. The effectiveness of this approach is demonstrated by designing the lateral controller of a highly automated vehicle.