Tilman Bünte

Robust automatic steering control for look-down reference systems with front and rear sensors

This paper describes a robust control design for automatic steering of passenger cars. Previous studies showed that reliable automatic driving at highway speed may not be achieved under practical conditions with look-down reference systems which use only one sensor at the front bumper to measure the lateral displacement of the vehicle from the lane reference. An additional lateral displacement sensor is added here at the tail bumper to solve the automatic steering control problem. The control design is performed stepwise: an initial controller is determined using the parameter space approach in an invariance plane; and this controller is then refined to accommodate practical constraints and finally optimized using the multiobjective optimization program. The performance and robustness of the final controller was verified experimentally at California PATH in a series of test runs.

Global Chassis Control Based on Inverse Vehicle Dynamics Models

This work proposes to approach global chassis control (GCC) by means of model inversion-based feedforward with allocation directly on the actuator commands. The available degrees of freedom are used to execute the desired vehicle motion while minimizing the utilization of the tyre’s grip potential. This is done by sampled constrained least-squares optimization of the linearized problem. To compensate for model errors and external disturbances, high-gain feedback is applied by means of an inverse disturbance observer. The presented method is applied in a comparison of eight vehicles with different actuator configurations for steer, drive, brake and load distribution. The approach shows a transparent and effective method to deal with the complex issue of GCC in a unitized way. It gives both a base for controller design and a structured way to compare different configurations. In practice, the transparency supports automatic on-board reconfiguration in the case of actuator hardware failure.

Optimized Force Allocation -A General Approach to Control and to Investigate the Motion of Over-Actuated Vehicles

Abstract A general approach is introduced to allocate the forces acting on the center of gravity to the four wheels of a vehicle by using an inversion of vehicle dynamics and a non-linear optimization. This makes it possible to compare all useful configurations of actively and passively controlled influencing variables of vehicle dynamics (steering angles, brake/drive torques, wheel loads and camber angles), with and without actuator dynamics and to investigate the impact of actuator failures on vehicle dynamics.

How to make steer-by-wire feel like power steering

Abstract In this paper for the design of a Steer-by-Wire (SbW) system a generic controller structure is proposed with bidirectional position feedback. The design goal for SbW here is to match the dynamics of an (electric/hydraulic power) steering system which may notionally be subdivided into a manual and an assistance steering part. For matching the manual steering part a generic linear controller structure and for matching the assistance steering part a nonlinear unilateral controller structure are suggested. The controller design problem is formulated as a system dynamics equivalence problem, either based on a physical or an identified model, and is solved exactly. This result is then adapted according to practical considerations. For robustness and stability analysis of the linear part of the steer-by-wire system passivity theory is applied and performance is evaluated by Bode magnitude plots and a H∞-performance criterion. Nonlinear simulations at various operating conditions (vehicle speed, road/tire contact) with a high fidelity vehicle dynamics model demonstrate the robustness of the whole system.

A NOVEL CONTROL STRUCTURE FOR DYNAMIC INVERSION AND TRACKING TASKS

A new structure for model inversion and tracking control tasks is introduced. It represents a two-degree of freedom controller, which unifies the principle of feedforward exact and high-gain feedback inversion, while preserving advantages of each.

Human machine interface concept for interactive motion control of a highly maneuverable robotic vehicle

A vehicle dynamics human machine interface (HMI) concept for the operation of a highly maneuverable vehicle is presented. This is motivated by the research vehicle ROMO, which is being developed by the German Aerospace Center (DLR) to facilitate research on a wide spectrum of scientific questions dealing with electric and autonomous mobility. With four wheel individual large range steering and electric wheel hub motors, the vehicle dynamics variables of yaw rate, side slip angle and vehicle velocity can be decoupled, thus opening new motion possibilities. The HMI approach includes distinction of various motion operating modes, suitable reference motion parameterization and adequate filtering of the operators inputs, both depending on the operating mode. For rotating on the spot the instantaneous center of rotation may be interactively set by the operator on a touch screen.

Mapping of Nyquist/Popov theta-stability margins into parameter space

Abstract The application of the parameter space method has proven to be useful for robustness analysis of uncertain parametric systems and robust control synthesis for quite a number of applications. However, it has been restricted to linear systems and the consideration of eigenvalue criteria. This paper enhances the application of the parameter space method to include various locus criteria. This allows not only for incorporation of linear criteria (e. g. gain and phase margin) but for nonlinear criteria as well (e.g. Popov- or circle criterion and the dual locus method).

PARADISE-Parametric Robust Analysis and Design Interactive Software Environment: a Matlab-based robust control toolbox

This paper presents a new toolbox for robust control design and analysis. A drawback of physically motivated approaches to robust control has been the amount of extensive calculation required for various methods, e.g. parameter space approach. This new toolbox overcomes these problems and makes parametric robust control methods available in an efficient, easy comprehensible, and flexible manner. The toolbox uses Matlab/Simulink which is a well-know tool to most control engineers.

Robust two degree of freedom vehicle steering controller design

Robust steering control based on a specific two degree of freedom control structure is used here for improving the yaw dynamics of a passenger car. The usage of an auxiliary steering actuation system for imparting the corrective action of the steering controller is assumed. The design study is based on six operating conditions for vehicle speed and the coefficient of friction between the tires and the road representing the boundary of the operating domain of the vehicle. The design is carried out by finding the region in controller parameter plane where Hurwitz stability and a mixed sensitivity frequency domain constraint are simultaneously satisfied. A velocity based gain scheduling type implementation is used. Moreover, the steering controller has a fading effect that leaves the low frequency driving task to the driver, intervening only when necessary. The effectiveness of the final design is demonstrated using linear and nonlinear simulations.

A model predictive control allocation approach to hybrid braking of electric vehicles

With the recent emergence of electric drivetrains, a faster and energy efficient braking actuator the electric motor has become available to complement the operation of the traditional friction brakes. The decision on how to split the braking torque among the friction brake and the electric motor is one of the main issues of such hybrid braking systems. With this challenge in mind, a new model predictive control allocation (MPCA) approach for hybrid braking is proposed. In comparison to state of the art torque blending solutions (daisy chain and dynamic control allocation) the MPCA offers faster transient response, without compromising the energy recuperation efficiency of the actuators. In addition, we also develop a linear wheel slip controller to regulate the braking force during emergency braking maneuvers. The tuning of this wheel slip controller is carried out using robust pole placement techniques, which ensures good operation in spite of uncertainties in the tire-road friction coefficient and the vertical load. Simulation results demonstrate the effectiveness of the proposed method.