Efstathios Velenis

Dynamic friction models for road/tire longitudinal interaction

Summary In this paper we derive a new dynamic friction force model for the longitudinal road/tire interaction for wheeled ground vehicles. The model is based on a dynamic friction model developed previously for contact-point friction problems, called the LuGre model. By assuming a contact patch between the tire and the ground we develop a partial differential equation for the distribution of the friction force along the patch. An ordinary differential equation (the lumped model) for the friction force is developed, based on the patch boundary conditions and the normal force distribution along the contact patch. This lumped model is derived to approximate closely the distributed friction model. Contrary to common static friction/slip maps, it is shown that this new dynamic friction model is able to capture accurately the transient behaviour of the friction force observed during transitions between braking and acceleration. A velocity-dependent, steady-state expression of the friction force versus the slip coefficient is also developed that allows easy tuning of the model parameters by comparison with steady-state experimental data. Experimental results validate the accuracy of the new tire friction model in predicting the friction force during transient vehicle motion. It is expected that this new model will be very helpful for tire friction modeling as well as for anti-lock braking (ABS) and traction control design.

Dynamic Tire Friction Models for Combined Longitudinal and Lateral Vehicle Motion

An extension to the LuGre dynamic friction model from longitudinal to longitudinal/lateral motion is developed in this paper. Application of this model to a tyre yields a pair of partial differential equations that model the tyre-road contact forces and aligning moment. A comparison of the steady-state behaviour of the dynamic model with existing static tyre friction models is presented. This comparison allows one to determine realistic values of the parameters for the new dynamic model. Via the introduction of a set of mean states we reduce the partial differential equations to a lumped model governed by a set of three ordinary differential equations. Such a lumped form describes the aggregate effect of the friction forces and moments and it can be useful for control design and online estimation. A method to incorporate wheel rim rotation is also proposed. The proposed model is evaluated by comparing both its steady-state as well as its dynamic characteristics via numerical simulations. The results of the simulations corroborate steady-state and dynamic/transient tyre characteristics found in the literature.

Energy Management in Plug-in Hybrid Electric Vehicles: Recent Progress and a Connected Vehicles Perspective

Plug-in hybrid electric vehicles (PHEVs) offer an immediate solution for emissions reduction and fuel displacement within the current infrastructure. Targeting PHEV powertrain optimization, a plethora of energy management strategies (EMSs) have been proposed. Although these algorithms present various levels of complexity and accuracy, they find a limitation in terms of availability of future trip information, which generally prevents exploitation of the full PHEV potential in real-life cycles. This paper presents a comprehensive analysis of EMS evolution toward blended mode (BM) and optimal control, providing a thorough survey of the latest progress in optimization-based algorithms. This is performed in the context of connected vehicles and highlights certain contributions that intelligent transportation systems (ITSs), traffic information, and cloud computing can provide to enhance PHEV energy management. The study is culminated with an analysis of future trends in terms of optimization algorithm development, optimization criteria, PHEV integration in the smart grid, and vehicles as part of the fleet.

Minimum Time vs Maximum Exit Velocity Path Optimization During Cornering

Numerical optimization has been used as an extension of vehicle dynamics simulation in order to repro- duce trajectories and driving techniques used by expert race drivers and investigate the effects of several vehicle param- eters in the stability limit operation of the vehicle. In this work we investigate how different race-driving techniques may be reproduced by considering different optimization cost functions. We introduce a bicycle model with suspension dynamics and study the role of the longitudinal load transfer in limit vehicle operation, i.e., when the tires operate at the adhesion limit. Finally we demonstrate that for certain vehicle configurations the optimal trajectory may include large slip angles (drifting), which matches the techniques used by rally-race drivers. I. INTRODUCTION

Optimality Properties and Driver Input Parameterization for Trail-braking Cornering

In this work we present an analysis of rally-racing driving techniques using numerical optimization. We provide empirical guidelines for executing a Trail- Braking (TB) maneuver, one of the common cornering techniques used in rally-racing. These guidelines are verified via experimental data collected from TB maneuvers performed by an expert rally driver. We show that a TB maneuver can be generated as a special case of the minimum-time cornering problem subject to specific boundary conditions. We propose simple parameterizations of the drivers steering, throttle and braking commands that lead to an alternative formulation of the optimization problem with a reduced search space. We show that the proposed parametrization of the drivers commands can reproduce TB maneuvers along a variety of corner geometries, requiring only a small number of parameters.

Optimal velocity profile generation for given acceleration limits: theoretical analysis

A semi-analytical method is proposed to generate minimum-time optimal velocity profiles for a vehicle with given acceleration limits driving along a specified path. The method is formally proven to provide optimal results using optimal control theory. In addition, several undesirable cases, where loss of controllability occurs, and which have been neglected in the literature, are dealt with in this work.

Steady-state cornering equilibria and stabilisation for a vehicle during extreme operating conditions

In this work we study steady-state cornering conditions for a single-track vehicle model, without imposing restrictive conditions on the tyre slip. Inspired by recent progress in the understanding of advanced driving techniques, we design a sliding-mode control scheme stabilising steady-state cornering conditions, using only longitudinal control inputs, i.e., accelerating/braking torques applied at the front and/or rear wheels. The effectiveness of the control scheme is demonstrated in a variety of simulation scenarios, motivated by competitive race driving. Results are presented using both the baseline model, and an increased-fidelity model taking into account suspension dynamics.

Minimum time cornering: the effect of road surface and car transmission layout

This paper investigates the minimum time/limit handling car manoeuvring through nonlinear optimal control techniques. The resulting ‘optimal driver’ controls the car at its physical limits. The focus is on cornering: different road surfaces (dry and wet paved road, dirt and gravel off-road) and transmission layouts (rear-wheel-drive, front-wheel-drive and all-wheel-drive) are considered. Low-drift paved circuit-like manoeuvres and aggressive/high-drift even counter-steering rally like manoeuvres are found depending on terrain/layout combinations. The results shed a light on the optimality of limit handling techniques.

Designing a low-cost spacecraft simulator

The greatest difficulty in implementing spacecraft control laws is that ground-based experiments must take place in a 1g environment, whereas the actual spacecraft will operate under 0g conditions. This article describes a spacecraft simulator facility used to educate undergraduates in spacecraft attitude dynamics and control.

Optimal Velocity Profile Generation for Given Acceleration Limits; The Half-Car Model Case

A method to generate on-line optimal acceler- ation/deceleration and attitude profiles for a half-car model in high-speed cornering is presented. The methodology is an extension of (1) where a point-mass model of the vehicle was used. The acceleration envelope of the vehicle (GG- diagram) from the locus of the front and rear tire forces is used for selecting the optimal control inputs. A stable implementation of the algorithm for a path of increasing radius is also presented.