Mathias R Lidberg

Automated driving and autonomous functions on road vehicles

In recent years, road vehicle automation has become an important and popular topic for research and development in both academic and industrial spheres. New developments have received extensive coverage in the popular press, and it may be said that the topic has captured the public imagination. Indeed, the topic has generated interest across a wide range of academic, industry and governmental communities, well beyond vehicle engineering; these include computer science, transportation, urban planning, legal, social science and psychology. While this follows a similar surge of interest – and subsequent hiatus – of Automated Highway Systems in the 1990s, the current level of interest is substantially greater, and current expectations are high. It is common to frame the new technologies under the banner of ‘self-driving cars’ – robotic systems potentially taking over the entire role of the human driver, a capability that does not fully exist at present. However, this single vision leads one to ignore the existing range of automated systems that are both feasible and useful. Recent developments are underpinned by substantial and long-term trends in ‘computerisation’ of the automobile, with developments in sensors, actuators and control technologies to spur the new developments in both industry and academia. In this paper, we review the evolution of the intelligent vehicle and the supporting technologies with a focus on the progress and key challenges for vehicle system dynamics. A number of relevant themes around driving automation are explored in this article, with special focus on those most relevant to the underlying vehicle system dynamics. One conclusion is that increased precision is needed in sensing and controlling vehicle motions, a trend that can mimic that of the aerospace industry, and similarly benefit from increased use of redundant by-wire actuators.

Implementation of active steering on longer combination vehicles for enhanced lateral performance

A steering-based controller for improving lateral performance of longer combination vehicles (LCVs) is proposed. The controller steers the axles of the towed units to regulate the time span between the driver steering and generation of tyre lateral forces at the towed units and consequently reduces the yaw rate rearward amplification (RWA) and offtracking. The open-loop effectiveness of the controller is evaluated with simulations and its closed loop or driver in the loop effectiveness is verified on a test track with a truck–dolly–semitrailer test vehicle in a series of single- and double-lane change manoeuvres. The developed controller reduces the yaw rate RWA and offtracking considerably without diminishing the manoeuvrability. Furthermore, as a byproduct, it decreases the lateral acceleration RWA moderately. The obtained safety improvements by the proposed controller can promote the use of LCVs in traffic which will result in the reduction of congestion problem as well as environmental and economic benefits.

A generic controller for improving lateral performance of heavy vehicle combinations

A generic controller for improving the lateral performance of heavy vehicle combinations by steering the axles of the towed units is proposed. The lateral performance of nine heavy vehicle combinations, including conventional combinations and existing and prospective longer combinations, are studied with and without the controller. The performance of the passive vehicles clearly indicates a need for improvements, which can be achieved by the proposed controller. The results obtained for controller verification in the frequency and time domains demonstrate that the controller reduces the yaw rate rearward amplification and off-tracking of all studied vehicles significantly, and diminishes trailer swings without reducing manoeuvrability. Furthermore, as a by-product, it moderately reduces the lateral acceleration rearward amplification. The improvements obtained by the proposed controller can promote the use of longer combination vehicles in traffic, which will result in a reduction of congestion, as well as substantial environmental and economic benefits.

On optimal recovery from terminal understeer

This paper addresses the problem of terminal understeer and its mitigation via integrated brake control. The scenario considered is when a vehicle enters a curve at a speed that is too high for the tyre–road friction limits and an optimal combination of braking and cornering forces is required to slow the vehicle down and to negotiate the curve. Here, the driver commands a step steering input, from which a circular arc reference path is inferred. An optimal control problem is formulated with an objective to minimize the maximum off-tracking from the reference path, and two optimal control solutions are obtained. The first is an explicit analytical solution for a friction-limited particle; the second is a numerically derived open-loop brake control sequence for a nonlinear vehicle model. The particle solution is found to be a classical parabolic trajectory associated with a constant acceleration vector of the global mass center. The independent numerical optimization for the vehicle model is found to approximate closely the kinematics of the parabolic path reference strategy obtained for the particle. Using the parabolic path reference strategy, a closed-loop controller is formulated and verified against the solution from numerical optimization. The results are further compared with understeer mitigation by yaw control, and the parabolic path reference controller is found to give significant improvement over yaw control for this scenario.

Path and speed control of a heavy vehicle for collision avoidance manoeuvres

In an emergency situation prior to an imminent accident, first in-vehicle warning systems would intervene and aim to make the driver to take a suitable action. If the risk of accident was not eliminated, then an autonomous collision avoidance manoeuvre can prevent it. In this work, path and speed control are intended to be used to perform such a manoeuvre by using steering and braking actuators respectively. In order to provide actuators with suitable control inputs, first a path is planned for the heavy vehicle to follow during the manoeuvre. Then the path is used to calculate feedforward control inputs whereas a feedback controller assures the path tracking by compensating for errors. As a result, a robust path planning and control algorithm is designed and implemented that can perform autonomous collision avoidance manoeuvres for a heavy vehicle. Promising simulation results support ongoing works on vehicle demonstration and experiments on a real heavy vehicle.

Optimized brake-based control of path lateral deviation for mitigation of secondary collisions

This paper considers brake-based lateral control of a passenger vehicle, for reducing secondary collision risk following an initial impact in a traffic accident. Since secondary collisions are associated with deviations from the original travel path, the control problem is formulated via brake control sequences that minimize lateral path deviation. Optimal sequences are found not to conform to any simple control mode; sometimes all brakes are released, sometimes all wheels are locked, or the brakes may be applied in differential mode. In general, the optimal strategy combines several such actuation modes, and analysis shows it is related to the utilization of instantaneous vehicle force and moment capacity, indicating that a closed-loop control strategy may be developed based on the real-time estimation of tyre force limits during the post-impact event. Yaw motion control is related to response discontinuity and multiple equilibria found in the optimal response – a small change in initial yaw velocity generates large changes in the ensuing vehicle motion and thus in the aimed equilibrium point of the vehicle’s orientation. Overall it is found that braking control strongly influences the post-impact path of the impacted vehicle, and may therefore form the basis of a practical system for avoiding secondary collisions in future traffic accidents.

Predictive yaw and lateral control in long heavy vehicles combinations

We consider the problem of controlling the yaw and lateral dynamics in heavy vehicles, consisting of combinations of a truck and multiple towed units. In such heavy vehicle configurations, undesired yaw rate and lateral acceleration amplifications, causing tail swings and lateral instabilities of the towed units, can be observed at high speed. In this paper, we present a predictive control approach to reduce the Rearward Amplification (RWA) of the yaw rate at the rearmost unit in a truck-dolly-semitrailer combination, while bounding the lateral acceleration in order to prevent the roll-over of the rearmost unit. Simulation results with a nonlinear high fidelity vehicle model are presented in a single lane change maneuver, showing that the proposed approach is able to efficiently reduce the yaw rate RWA and limit the lateral accelerations, compared to the uncontrolled vehicle.

The effectiveness of rear axle steering on the yaw stability and responsiveness of a heavy truck

Rear axle steering (RAS) at low speed is available in heavy trucks to improve their manoeuverability and reduce tyre wear; by extending the functionality of the existing RAS to high speed turning and split-mu braking, considerable safety benefits and enhancement in driver comfort can be gained. In this study, a RAS System was developed and simulated in Matlab–Simulink which showed encouraging results. Furthermore, the developed system was implemented on a Volvo Truck and tested in a series of split-mu braking and ISO double lane change manoeuvers. The obtained results conform to the expectations.

Integrated evasive manoeuvre assist for collision mitigation with oncoming vehicles

ABSTRACT Development and deployment of steering based collision avoidance systems are made difficult due to the complexity of dealing with oncoming vehicles during the evasive manoeuvre. A method to mitigate the collision risk with oncoming vehicles during such manoeuvres is presented in this work. A point mass analysis of such a scenario is first done to determine the importance of speed for mitigating the collision risk with the oncoming vehicle. A characteristic parameter was identified, which correlates well with the need to increase or decrease speed, in order to reduce the collision risk. This finding was then verified in experiments using a Volvo XC90 test vehicle. A closed-loop longitudinal acceleration controller for collision mitigation with oncoming vehicles is then presented. The longitudinal control is combined with yaw stability control using control allocation to form an integrated controller. Simulations in CarMaker using a validated XC90 vehicle model and the proposed controller showed consistent reductions in the collision risk with the oncoming vehicle.

Lateral stability control of a long heavy vehicle combination by active steering of the towed units

A complete vehicle combination controller for enhancing the lateral stability of long heavy vehicle combinations by active steering of the towed units is presented. As a case study, the controller is developed for a truck-dolly-semitrailer combination and is evaluated in a sine with dwell maneuver, using a nonlinear model of this combination. The simulation results show a significant decrease in yaw rate rearward amplification and offtracking of the controlled vehicle.