Experimental Verification of Evasive Manoeuvre Assist Controller for Collision Mitigation with Oncoming Vehicles

An evasive manoeuvre assist controller to mitigate the risk of collision with oncoming vehicles while performing evasive manoeuvres has previously been formulated and tested in simulation. In this work, a real-time application of this controller is implemented and used in experiments with a Volvo XC90 hybrid test vehicle. For comparison, manoeuvres are also carried out without the controller but with the driver adopting different speed control strategies. Analysis of the results show that the controller can consistently mitigate collision risk with the oncoming vehicle and while driver control of speed can perform better, it is far less robust and is heavily dependant on the driver skill and performance

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. © IMechE 2014

Experimental verification of understeer compensation by four wheel braking

This study is designed to validate a new approach to understeer mitigation chassis control, based on a particlemotion reference: parabolic path reference (PPR). Considering the scenario of excess entry speed into a curve,related to run-off-road crashes, the aim is that automatic braking minimizes lateral deviation from the target pathby using an optimal combination of deceleration, cornering forces and yaw moments. Previous simulationstudies showed that four-wheel braking can achieve this much better than a conventional form of yaw momentcontrol (DYC). The aim of this work is to verify this on a test track with an experimental vehicle, and to compareperformance with DYC and an uncontrolled vehicle. Experiments were performed with a front-wheel-drivepassenger vehicle equipped with an additional four identical brake callipers controlled via an electro-hydraulicbrake (EHB) system, enabling individual brake control. Minimizing the maximum deviation from the intendedcurve radius is the control objective. Feedback to the controller consists of the available steering wheel angle,wheel speeds, yaw rate and lateral acceleration sensors in the vehicle. Additional to these variables, also thevehicle position was logged using a GPS system. It was found that PPR is superior to DYC in reducing themaximum deviation from the intended path, confirming the trends previously found in simulations. Furthermore,the PPR concept is found to be inherently more stable than DYC since more brake force is applied to the outerwheels than the inner wheels throughout the manoeuvre. The experiments involve a first implementation of aPPR control which is not a fully closed-loop control intervention and tuned to a step steer (transition fromstraight to fixed-radius curve. This is the first study to explicitly and systematically evaluate this new approachto understeer mitigation. The approach is fundamentally different from common DYC and suggests the potentialfor a new generation of controllers based on trajectory control via chassis actuators

Safety Margins and Feedback Strategies for AWD Vehicles

The vehicle industry today faces the two-fold challenge of reducing the environmental impact as well as increasing vehicle safety. Electrification of vehicles enables both of these challenges to be addressed by means of improved overall efficiency as well as providing increased possibilities to control the longitudinal forces of each wheel individually.The objectives of this study are to increase the fundamental understanding of the influence of longitudinal forces on vehicle handling and stability. Furthermore, the study shall support the industrial development of electrical driveline systems in particular.The results obtained in this work can be applied for analysis of the performance of current and upcoming driveline and brake systems and as components in the associated active control for these systems. Overall, the present work has expanded the fundamental framework of vehicle modeling, optimization formulations and graphical representations for analysis and optimization of a wide range of driveline system properties and vehicle level characteristics

Development and Vehicle Integration of XWD Driveline Technology

The continuously ongoing development of new driveline hardware, improved vehicle state sensing capabilities and sophisticated vehicle dynamics control algorithms are strong enablers for improvements in both safety and functional performance of road vehicles. The present paper describes one of the latest achievements in this area, namely the development and vehicle integration of a state of the art all-wheel-drive driveline, named XWD or cross-wheel-drive, in the Saab 9-3.This all-wheel-drive driveline concerns an active on demand driven rear-axle, coupled to the front by means of an electronically controlled hydraulic clutch to distribute a variable amount of torque from front to rear. In addition to this front to rear distribution, the system is capable of transferring torque laterally across the rear-axle as well using an electronic Limited Slip Differential. In the next section of this paper, a complete system overview will be provided, detailing each and every component and explain both their mutual and external interfaces. Once having presented all key characteristics, the paper will further expand on how these characteristics determine system behaviour on a vehicle level, i.e. especially on vehicle dynamics properties like traction and handling performance. Furthermore, the paper will present specific development implications related to the integration in the Saab 9-3, i.e. how on one hand the vehicle architecture needs to be changed in order to incorporate the described system, and how on the other hand, the system itself is tailored to excel in this particular vehicle

Design and control of model based steering feel reference in an electric power assisted steering system

Electric Power Assisted Steering (EPAS) system is a current state of the art technology for providing the steering torque support. The interaction of the steering system with the driver is principally governed by the EPAS control method. This paper proposes a control concept for designing the steering feel with a model based approach. The reference steering feel is defined in virtual dynamics for tracking. The layout of the reference model and the control architecture is discussed at first and then the decoupling of EPAS motor dynamics using a feedback control is shown. An example of how a change in steering feel reference (as desired by the driver) creates a change in steering feedback is further exhibited. The ultimate goal is to provide the driver with a tunable steering feel. For this, the verification is performed in simulation environment

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

Collision avoidance at intersections involving a host vehicle turning left across the path of an oncoming vehicle (Left Turn Across Path/Opposite Direction or LTAP/OD) 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 (MHA) 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

Trends in vehicle motion control for automated driving on public roads

In this paper, we describe how vehicle systems and the vehicle motion control are affected by automated driving on public roads. We describe the redundancy needed for a road vehicle to meet certain safety goals. The concept of system safety as well as system solutions to fault tolerant actuation of steering and braking and the associated fault tolerant power supply is described. Notably restriction of the operational domain in case of reduced capability of the driving automation system is discussed. Further we consider path tracking, state estimation of vehicle motion control required for automated driving as well as an example of a minimum risk manoeuver and redundant steering by means of differential braking. The steering by differential braking could offer heterogeneous or dissimilar redundancy that complements the redundancy of described fault tolerant steering systems for driving automation equipped vehicles. Finally, the important topic of verification of driving automation systems is addressed