L. Alvarez

Adaptive emergency braking control with underestimation of friction coefficient

In this paper, a control scheme for emergency braking maneuvers in automated highway systems and a new online identification scheme to determine the tire-road friction characteristics of the vehicle are presented. The proposed controller determines the required pressure in the master cylinder of the braking system to achieve maximum deceleration during braking, based on the estimation of the tire-road friction characteristics and the overall braking system gain, for the given set of parameter estimates. With persistence of excitation, the identified static map between the tire longitudinal slip and the tire-road friction coefficient is guaranteed to converge to the actual map. When there is no persistence of excitation, and under a proper choice of initial conditions and adaptation gains, the proposed scheme underestimates the maximum coefficient of friction and its corresponding slip, and allows a conservative calculation of the safety critical inter-vehicle spacing.

Emergency vehicle maneuvers and control laws for automated highway systems

In this report control laws and maneuvers for high priority emergency vehicle transit on automated highways are presented. The work presented is specifically designed for use with the Partners for Automated Transit and Highways (PATH) hierarchical control architecture. The types of control laws that are needed for the different hierarchical layers are examined, and specific maneuvers for the coordination and link layers are presented. Simulations using SmartCAP (a mesoscopic traffic simulator) and SmartAHS (a microscopic traffic simulator) demonstrate the maneuvers functionality.

Semi-active control of civil structures using magnetorheological dampers

Two semiactive control schemes for protecting structures against earthquakes using magnetorheological dampers as control devices are presented. The design of the schemes is based on the LuGres dynamic friction model adapted to describe the behavior of dampers. Seismic attenuation with respect to the case of noncontrolled structures is demonstrated. Numerical simulation of a scaled structure under seismic excitation show very good performance.

A dynamic tire/road friction model for 3D vehicle control and simulation

A tire/road friction model based on the LuGre dry friction model and on tire dynamics is presented. The dynamics of the longitudinal and lateral forces, and the self-aligning torque are described by a set of first order differential equations. This model is suitable for 3D vehicle traction/braking simulation and control. A comparison of the forces and torque produced by this dynamic model with the well known magic formula is presented.

Emergency braking control with an observer-based dynamic tire/road friction model and wheel angular velocity information

A control scheme for emergency braking of vehicles is designed. The scheme utilizes a LuGre dynamic friction model to estimate the tire/road friction. The control system output is the pressure to the braking system, and is calculated using only the wheel angular speed information. The controller utilizes estimated state feedback control to achieve near maximum deceleration. The state observer gain is calculated by using linear matrix inequality (LMI) techniques. This system has two advantages when compared with an antilock braking system (ABS), it generates less chattering during braking and produces a source of a priori information regarding safe spacing.

Adaptive emergency braking control in automated highway systems

A control scheme is designed for emergency braking of vehicles in automated highway systems (AHS). The scheme is based on the estimation of both the tire/road friction and the braking system gain. The control system output is the pressure in the braking system calculated in such a way that a maximum deceleration level is achieved at all times during braking. This system is designed to work combined with an anti-lock braking systems providing two advantages, less chattering during braking and a source of a priori information regarding safe spacing.

Tire friction modeling under wet road conditions

This paper reviews the physics of tire/road contact under wet conditions. A technique to include road moisture in physical tire models is proposed. Stationary friction base tire models are used to illustrate these developments.

A fault management system for longitudinal vehicle control in AHS

The design of a fault management system (FMS) for longitudinal control in automated highway systems (AHS) is presented. A hierarchical AHS architecture with vehicles organized in platoons is considered. The FMS is based on a fault identification module that presents a set of residuals to the FMS. The system handles up to twelve single different faults in the actuators, sensors and communication devices. Strategies to handle faults are divided into two groups. In the first group, redundancy of the fault detection schemes is exploited to substitute faulty information; normal mode operation of the AHS is still feasible if some critical parameters are adjusted. The second group contains faults whose occurrence requires specific degraded mode maneuvers to be executed. The FMS was implemented using SHIFT, a hybrid system simulation language. The simulation results obtained in SmartAHS, a micro-simulator for AHS based on SHIFT, are presented.

Observer based emergency braking control in automated highway systems

Emergency braking maneuver control in automated highway systems (AHS) is addressed. Based on the on-line estimation of the longitudinal velocity of the vehicle and the tire/road friction characteristics, a pressure in the master cylinder of the braking system that attempts to achieve maximum deceleration during braking is calculated. Based on the estimated characteristics a braking strategy is applied. The designed system provides information for safe vehicle spacing and traffic flow control.

Meso-microscale traffic simulation of an AHS control architecture

A recently developed meso-microscale traffic simulator allows a stationary region of microsimulation to be defined within a larger, mesosimulated automated highway system (AHS). This simulator permits analysis of traffic behavior in situations where both microscopic (vehicle-level) and mesoscopic (aggregate flow) effects are important, while avoiding the prohibitive computational cost of microsimulating a large-scale AHS. This paper describes the software structure of the meso-micro simulator, which implements the PATH AHS control architecture. Simulation results indicate that the meso-micro simulator generates consistent traffic flows across both meso, and microsimulated regions.