Derong Yang

Quasi-Linear Optimal Path Controller Applied to Post Impact Vehicle Dynamics

This paper investigates brake-based path control of a passenger vehicle, aimed at reducing secondary collision risk, following an initial impact in a traffic accident. This risk may be reduced if lateral deviations from the preimpact path can be minimized, at least on straight roads. Numerical optimization has previously shown that coupled control of lateral forces and yaw moments can be applied to effectively minimize such path deviations. In this paper, a quasi-linear optimal controller (QLOC) is proposed to achieve this control target. QLOC uses nonlinear optimal control theory to provide a semiexplicit approximation for optimal post impact (PI) path control. The controller design method is novel, combining linear costate dynamics with nonlinear constraints due to tire friction limits. A fully closed-loop form of the controller is presented; it is applicable to multiple-event accidents occurring on straight roads, including adaptive estimation of the time instant at maximum deviation. The controller achieves performance that is very similar to that of open-loop numerical optimization. Assuming that the vehicle remains on the road surface after the impact and that the brake actuators remain operational, it is verified that the path controller is effective over a wide range of PI kinematic conditions. It is expected that the QLOC controller will prove useful in other cases where chassis systems directly control the vehicle path, e.g., in crash-imminent avoidance maneuvers.

Closed-loop Controller for Post Impact Vehicle Dynamics Using Individual Wheel Braking and Front Axle Steering

This paper presents a vehicle path controller for reducing the maximum lateral deviation (Ymax) after an initial impact in a traffic accident. In previous research, a Quasi-Linear Optimal Controller (QLOC) was proposed and applied to a simple vehicle model with individually controlled brake actuators. QLOC uses non-linear optimal control theory to provide a semiexplicit approximation for optimal post-impact path control, and in principle can be applied to an arbitrary number of actuators. The current work extends and further validates the control method by analysing the effects of adding an active front axle steering actuator at different post-impact kinematics, as well as increasing the fidelity of the vehicle model in the closed-loop controlled system. The controller performance is compared with the results from openloop numerical optimisation which uses the same vehicle model. The inherent robustness properties of the QLOC algorithm are demonstrated by its direct application to an independent high-fidelity multi-body vehicle model. Towards real-time implementation, the algorithm is further simplified so that the computational efficiency is enhanced, whereas the performance is shown not to be degraded.

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.

A nonlinear post impact path controller based on optimised brake sequences

This paper investigates brake-based path control of a passenger vehicle, aimed at reducing secondary collision risk following an initial impact in a traffic accident. Previous results from numerical optimisation showed that, at varying severity levels of post-impact states, there exist three identifiable components within the optimal control strategy so as to reduce the lateral deviation. The paper presents a path controller, based on nonlinear optimal control theory, that incorporates the three components. It is shown that friction adaptation may be implemented in a very efficient manner; the controller deals with different levels of road friction by scaling the dynamic variables from a fixed reference level. The approach provides an algorithm for adapting switching thresholds between the different components of the controller. In this study it is verified that the controller can deal with a wide range of kinematic conditions, and compares favorably with previous results of open-loop trajectory optimisation.

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.

Optimal motion control for collision avoidance at Left Turn Across Path/Opposite Direction intersection scenarios using electric propulsion

ABSTRACT Collision avoidance at intersections involving a host vehicle turning left across the path of an oncoming vehicle (Left Turn Across Path/Opposite Direction) have been studied in the past, but mostly using simplified interventions and rarely considering the possibility of crossing the intersection ahead of a bullet vehicle. Such a scenario where the driver preference is to avoid a collision by crossing the intersection ahead of a bullet vehicle is considered in this work. The optimal vehicle motion for collision avoidance in this scenario is determined analytically using a particle model within an optimal control framework. The optimal manoeuvres are then verified through numerical optimisations using a two-track vehicle model, where it was seen that the wheel forces followed the analytical global force angle result independently of the other wheels. A Modified Hamiltonian Algorithm controller for collision avoidance that uses the analytical optimal control solution is then implemented and tested in CarMaker simulations using a validated Volvo XC90 vehicle model. Simulation results showed that collision risk can be significantly reduced in this scenario using the proposed controller, and that more benefit can be expected in scenarios that require larger speed changes.

Towards Evaluation of Post Impact Braking Function in Driving Simulator

This paper presents a method to evaluate the vehicle Post Impact Braking function in driving simulator environment. This function is designed to apply automatic braking after an initial impact on the vehicle body. Four representative impact scenarios and three typical driving styles are investigated, assuming Anti-lock Brake System (ABS) is either functioned or malfunctioned. The performance of PIB is quantified by comparing certain post impact states when the function is enabled and disabled. The results show that PIB helps the drivers to lower the risk and severity of secondary collisions with respect to reduced displacements and road leaving speed, while it leads to higher risk for possible side collisions due to increased yaw angle, these influences seem to be more considerable when no ABS is available. Passive drivers are found to gain more benefits than Alert-Skilled drivers that it indicates full-braking can degrade the vehicle steer ability and thus the lateral and yaw responses to some extent.