Bengt J H Jacobson

Global force potential of over-actuated vehicles

This paper formulates force constraints of over-actuated road vehicles. In particular, focus is put on different vehicle configurations provided with electrical drivelines. It is demonstrated that a number of vehicles possesses non-convex tyre and actuator constraints, which have an impact on the way in which the actuators are to be used. By mapping the actuator forces to a space on a global level, the potential of the vehicle motion is investigated for the vehicles studied. It is concluded that vehicles with individual drive, compared with individual brakes only, have a great potential to yaw motion even under strong lateral acceleration.

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.

Utilization of Actuators to Improve Vehicle Stability at the Limit: From Hydraulic Brakes Toward Electric Propulsion

The capability of over-actuated vehicles to maintain stability during limit handling is studied in this paper. A number of important differently actuated vehicles, equipped with hydraulic brakes toward more advanced chassis solutions, are presented. A virtual evaluation environment has specifically been developed to cover the complex interaction between the driver and the vehicle under control. In order to fully exploit the different actuators setup, and the hard nonconvex constraints they possess, the principle of control allocation by nonlinear optimization is successfully employed. The final evaluation is made by exposing the driver and the over-actuated vehicles to a safety-critical double lane change. Thereby, the differently actuated vehicles are ranked by a quantitative indicator of stability.

Inverse model control including actuator dynamics for active dolly steering in high capacity transport vehicle

This paper describes an advance controller designed using the nonlinear inversion technique of a Modelica® based simulation tool, such as Dymola®, for active dolly steering of a high capacity transport vehicle. Actuator dynamics is included in the inverse model controller. Therefore, it can automatically generate required steering angle request for the dolly axles of the vehicle combination. The resultant controller is transfered as a functional mock-up unit (FMU) to Simulink® environment where the actual simulations are conducted. The controller is simulated against a high-fidelity vehicle model of an A-double combination from Virtual Truck Models (VTM) library - developed by Volvo Group Trucks Technology. Effects of variations of the actual actuator dynamics, with respect to the modeled dynamics in the inverse model controller, on overall vehicle performance are investigated.

Route Adaptation of control strategies for a hybrid city bus

A series hybrid city bus with diesel engine and electric batteries is studied on a specified route. The study uses two different basic control strategies, “On/off” and “Continuous” strategy. These basic strategies are complemented in two ways. First, an “Adviser” strategy which filters the driver commands and gives driver support feedback based on the route data. Second, an “Adapter” strategy, which adapts and the control to the route, using different control depending on the vehicle present position. Simulation results are presented. They show that the adviser and adapter strategies improves both emissions and fuel consumption.

Modular Modelling and Simulation Tool for Evaluation of Powertrain Performance

A modelling and simulation tool for evaluation and comparison of powertrain concepts is described. It is built upon an existing modelling and simulation software package. The tool uses new and powerful modelling techniques for dynamic systems. Object and equation orientation and hierarchically structured libraries are used to provide a powerful yet flexible instrument. The powertrain is studied as part of a total system consisting of vehicle, driver and road. Transient city traffic is focused on. Primary results from simulations are energy consumption and emissions. Simple modelling examples demonstrate the advantages of equation-oriented modelling. New kinds of road and driver models are also included. They make prediction of the outcome of realistically described transportation tasks possible and are useful for evaluating the influence of driver behaviour on energy consumption and emissions. Examples of model implementation and library structure are presented. The ability of the tool is illustrated with simulations which are compared with tests.

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.

Outline of a New Control Concept for Power Shifting of Fixed Step Ratio Automotive Transmissions

Abstract Power shifting transmissions, e.g. automatic transmissions, are traditionally shifted from gear A to B by disengaging a clutch belonging to gear A and engaging a clutch belonging to gear B. This paper tries out the idea of employing a third clutch. In practice, such a third clutch can be one of the clutches which is traditionally used only for other gears. This means that the new concept can be used with only a control software update in an ordinary gearbox. The trade-off between comfort and wear, which is experienced in the traditional control concept, becomes less troublesome. The wear, or the discomfort, can be reduced to roughly half of that corresponding to a traditionally controlled upshift. The work finds the largest potential in using an extra clutch which belongs to a gear higher than the high gear in an upshift. The theoretical study is carried out with a general and simple model, but a simulation example is added using a more detailed model of an existing gearbox.

Driver Model Based Automated Driving of Long Vehicle Combinations in Emulated Highway Traffic

This paper proposes a framework for automated highway driving of an A-double long vehicle combination. The included driving manoeuvres are maintain lane, lane change to right and left, abort lane change to right and left, and emergency brake. A combined longitudinal and lateral driver model is used for the generation of longitudinal acceleration and steering requests. The behaviour of the driver model, both regarding heuristics and safety thresholds, is inspired by human cognition and optical flow theory. Traffic situation predictions of feasible lane changes are calculated using the driver model in combination with prediction models of the subject and surrounding vehicles. The traffic situation predictions are used for the evaluation of constraints related to vehicle dynamics, road boundaries and distance to surrounding objects. When the framework is started, the subject vehicle is initiated in the maintain lane state respecting the road speed limit and the distance to surrounding objects. A lane change manoeuvre is performed on request from the driver when the corresponding traffic situation prediction and control request become feasible. The framework has been implemented in a simulation environment including a high-fidelity vehicle plant model and models of surrounding vehicles. Simulations show that the framework gives anticipated results when initial conditions are varied. Results are shown for maintain lane and lane change manoeuvres at constant longitudinal velocity, varying from 20-80 km/h and lane changes combined with retardation including leading vehicle braking from different initial velocities ranging from 30-80 km/h.