Ing. Denis Efremov

Integrated automated safety systems in vehicles significantly reduced the number of car crashes. They help the driver in critical maneuvers when tires lose their grip on the driving surface. For instance, the technology of the anti-lock braking system and its augmentations (electronic stability control and traction control system) has already saved thousands of lives. Nevertheless, we still see room for improvement. This work defines boundaries in the vehicle state-space, excluding unstable vehicle maneuvers. Such boundaries form a so-called driving envelope. The resulting set includes all states where the vehicle’s wheels are not locked, overspun, or skidding. For the definition of the driving envelope, we use the Pacejka tire model and nonlinear single-track model. This paper shows how each tire dynamic property results in vehicle dynamics. Also, it discusses the application of nonlinear and linearized driving envelope boundaries on a single-track model. Then it shows that the linearized driving envelope constraints form a close to control invariant set over the vehicle state-space. Thus, the driving envelope is almost a feasible set, and it could be used in the model predictive control approaches with soft constraints. Protecting the driving envelope, one can preserve each wheel from locking, wheelspin, and skidding.

The steer-by-wire technology opens a possibility to create new advanced driver assistant systems. This work proposes a control structure that keeps the lateral vehicle dynamics in predefined stability boundaries and prevents the dominant sliding motion. We intentionally employed a cascade control law design suited for embedded platforms, often with low computational capacity. The proposed control hierarchical architecture is heavily inspired by aerospace domain solution, the flight envelope protection algorithms, which are still used in modern civil aircraft. The vehicle lateral acceleration is selected as the control system reference signal, commanded by a driver. The controller tracks such reference signal while respecting the driving envelope and vehicle operation safety limits. Several driving experiments were conducted to evaluate the proposed control structure in the statistical sense. The comparison with solution based on model predictive control framework and baseline vehicle without any assistance system is presented. Performed experiments were evaluated based on objective vehicle performance, like lap time and a number of collisions, combined with a human driver’s subjective evaluation. Experiments clearly show the incoherence of results and biased of skilled drivers. The objectively better vehicle performance, faster lap time with fewer collisions, received a lower subjective evaluation from experienced drivers used to current driving style.

Drive-by-wire technology opens a possibility to help the driver to drive a vehicle safely with support made by electronic control units. This paper presents an approach for defining a Driving Envelope that excludes any not welldefined vehicle states both for longitudinal and lateral dynamics. The second contribution is the design of a Model Predictive Controller for envelope protection that prevents critical situations such as the spinning of the vehicle, blocking of a wheel, and loss of the wheel traction. Validation results demonstrating the performance of the approach are obtained from a fixedsimulator with implemented high-fidelity twin-track model.

This paper presents an approach of utilizing Driving Envelope (DE) restrictions to assist the driver in lateral maneuvers. Two fundamental issues are addressed in this work. First, DE protection. Second, how to implement such functionality on a conventional car configuration, where the driver still needs to be a part of the control loop. The proposed functionality is based on a Model Predictive Controller (MPC). Vehicle states are constrained to avoid car critical spin situations (DE protection). The power-assisted steering system is used to guide the driver inside boundaries defined by the DE. The proposed architecture is compared with the standard car, without such an Advanced Driver-Assistance System (ADAS), by means of virtual ride tests performed using a high-fidelity vehicle model.

This paper introduces the idea of the full-time-fullauthority control, known from the flight control field, for the automotive industry. Also, it provides a derivation of a nonlinear single-track vehicle model for an over-actuated car and introduces the vehicle states feasibility set, called here driving envelope, inspired by aircraft flight envelope, providing safe operation zone limits for a vehicle. As an addition, authors show proof based on vehicle dynamic physics, what practical pros can bring the usage of the steered rear axle together with the front axle.