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Vehicle Dynamics and Control At The Limits of Handling

Towards Automated Vehicle Control Beyond the Stability Limits: Drifting Along a General Path

Professional drivers in drifting competitions demonstrate accurate control over a car's position and sideslip while operating in an unstable region of state-space. Could similar approaches help autonomous cars contend with excursions past the stable handling limits, thereby improving overall safety outcomes? As a first step towards answering that question, this paper presents a novel controller framework for automated drifting along a path. The controller is derived for the general case, without reference to a nearby equilibrium point.

A Sequential Two-Step Algorithm for Fast Generation of Vehicle Racing Trajectories

The problem of maneuvering a vehicle through a race course in minimum time requires computation of both longitudinal (brake and throttle) and lateral (steering wheel) control inputs. Unfortunately, solving the resulting nonlinear optimal control problem is typically computationally expensive and infeasible for real-time trajectory planning. This paper presents an iterative algorithm that divides the path generation task into two sequential subproblems that are significantly easier to solve.

A Synthetic Input Approach to Slip Angle Based Steering Control for Autonomous Vehicles

A new method is presented for low-level steering control of autonomous vehicles. By tracking tire slip angle instead of steering angle, the new controller makes possible a more direct use of force-based high-level control schemes since uncertain, noisy measurements of the vehicle states do not have to be used to convert a desired tire slip angle to a commanded steer angle. Experimental data from a full-size vehicle show that this approach offers some advantages when combined with a force-based path tracking controller.

From the Racetrack to the Road: Real-time Trajectory Replanning for Autonomous Driving

In emergency situations, autonomous vehicles will be forced to operate at their friction limits in order to avoid collisions. In these scenarios, coordinating the planning of the vehicle's path and speed gives the vehicle the best chance of avoiding an obstacle. Fast reaction time is also important in an emergency, but approaches to the trajectory planning problem based on nonlinear optimization are computationally expensive.

Vehicle control synthesis using phase portraits of planar dynamics

Phase portraits provide control system designers strong graphical insight into nonlinear system dynamics. These plots readily display vehicle stability properties and map equilibrium point locations and movement to changing parameters and system inputs. This paper extends the usage of phase portraits in vehicle dynamics to control synthesis by illustrating the relationship between the boundaries of stable vehicle operation and the state derivative isoclines in the yaw rate–sideslip phase plane.

Learning From Professional Race Car Drivers to Make Automated Vehicles Safer

Autonomous vehicles have the potential to eliminate the vast number of motor-vehicle accidents that occur each year. However, as the burgeoning technology becomes more publicly available, self-driving cars will continue to encounter emergency situations. To maximize the vehicle's ability to navigate these situations safely, autonomous driving technology needs to be able to use all of the vehicle's performance capability.

Tire Modeling to Enable Model Predictive Control of Automated Vehicles From Standstill to the Limits of Handling

Model predictive control (MPC) frameworks have been effective in collision avoidance, stabilization, and path tracking for automated vehicles in real-time. These MPC formulations use a variety of vehicle models that capture specific aspects of vehicle handling, focusing either on low-speed scenarios or highly dynamic maneuvers. However, these models individually are unable to handle all operating regions with the same performance. This work introduces a novel linearization of a brush tire model that is affine, timevarying, and effective at any speed.

Speed Control for Robust Path-Tracking for Automated Vehicles at the Tire-Road Friction Limit

At the limit of tire-road friction, steering becomes an ineffective control input for tracking a desired path. In challenging automated driving scenarios, conventional lateral control through steering could therefore lead to road departures or hinder successful evasive maneuvers. Conservative path planning might prevent the occurrence of uncontrollable path-tracking dynamics; however, not using the full tire-force potential can also impede a successful emergency maneuver.

A Controller for Automated Drifting Along Complex Trajectories

The ability to operate beyond the stable handling limits is important for the overall safety and robustness of autonomous vehicles. To that end, this paper describes a controller framework for automated drifting along a complex trajectory. The controller is derived for a generic path, without assuming operation near an equilibrium point. This results in a physically insightful control law: the rotation rate of the vehicle’s velocity vector is used to track the path, while yaw acceleration is used to stabilize sideslip.


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