Lee Alexander

IMpRH server: an RH mapping server available on the Web.

SUMMARY The INRA-Minnesota Porcine Radiation Hybrid (IMpRH) Server provides both a mapping tool (IMpRH mapping tool) and a database (IMpRH database) of officially submitted results. The mapping tool permits the mapping of a new marker relatively to markers previously mapped on the IMpRH panel. The IMpRH database is the official database for submission of new results and queries. The database not only permits the sharing of public data but also semi-private and private data.

Friction estimation on highway vehicles using longitudinal measurements

This paper develops a real-time tire-road friction coefficient measurement system that can reliably distinguish between different road surface friction levels and quickly detect abrupt changes in friction coefficient. The measurement system relies on the use of differential GPS and utilizes a nonlinear longitudinal tire force model. Compared to previously published results in literature, the advantage of the system developed in this paper is that it is applicable during both vehicle acceleration and braking and works reliably for a wide range of slip ratios, including high slip conditions. The system can be utilized on front/rear-wheel drive as well as all-wheel drive vehicles. Extensive results are presented from experimental results conducted on various surfaces with a winter maintenance vehicle called the SAFEPLOW. The experimental results show that the system performs reliably and quickly in estimating friction coefficient on different road surfaces during various vehicle maneuvers. The developed friction measurement system has many applications in vehicle safety systems such as ABS, skid control and collision avoidance systems and is also useful for winter maintenance vehicles in which knowledge of the friction coefficient can be used to determine the amount and type of deicing chemicals to be applied to a winter roadway.

Estimation of Tire-Road Friction Coefficient Using a Novel Wireless Piezoelectric Tire Sensor

A tire-road friction coefficient estimation approach is proposed which makes use of the uncoupled lateral deflection profile of the tire carcass measured from inside the tire through the entire contact patch. The unique design of the developed wireless piezoelectric sensor enables the decoupling of the lateral carcass deformations from the radial and tangential deformations. The estimation of the tire-road friction coefficient depends on the estimation of slip angle, lateral tire force, aligning moment, and the use of a brush model. The tire slip angle is estimated as the slope of the lateral deflection curve at the leading edge of the contact patch. The portion of the deflection profile measured in the contact patch is assumed to be a superposition of three types of lateral carcass deformations, namely, shift, yaw, and bend. The force and moment acting on the tire are obtained by using the coefficients of a parabolic function which approximates the deflection profile inside the contact patch and whose terms represent each type of deformation. The estimated force, moment, and slip angle variables are then plugged into the brush model to estimate the tire-road friction coefficient. A specially constructed tire test rig is used to experimentally evaluate the performance of the developed estimation approach and the tire sensor. Experimental results show that the developed sensor can provide good estimation of both slip angle and tire-road friction coefficient.

Dynamics of Narrow Tilting Vehicles

Narrow commuter vehicles can address many congestion, parking and pollution issues associated with urban transportation. In making narrow vehicles safe, comfortable and acceptable to the public, active tilt control systems are likely to play a crucial role. This paper concentrates on developing a dynamic model for narrow vehicles that can be used for the design and evaluation of active tilt control systems. The model has four degrees of freedom including lateral and tilt dynamics. The influence of gyroscopic forces due to rotating wheels and the influence of front wheel trail are included but secondary coupling effects are ignored so as to keep the model tractable. The model is used in this paper to understand the influence of vehicle tilt on the steering angle required for cornering, the desired tilt angle for any specified cornering maneuver and the influence of gyroscopic moments on transient tilting/cornering maneuvers. A study of the model equations also provides insight into how narrow vehicles can be designed so as to be self-stabilizing.

A fundamental investigation of tilt control systems for narrow commuter vehicles

One way of addressing traffic congestion is by efficiently utilizing the existing highway infrastructure. Narrow tilting vehicles that need a reduced width lane can be part of the solution if they can be designed to be safe, stable, and easy to operate. In this paper, a control system that stabilizes the tilt mode of such a vehicle without affecting the handling of the vehicle is proposed. This control system is a combination of two different types of control schemes known as steering tilt control (STC) and direct tilt control (DTC) systems. First, different existing variations of both STC and DTC systems are considered and their shortcomings analysed. Modified control schemes are then suggested to overcome the deficiencies. Then a new method of integrating these two control schemes that guarantees smooth switchover between the controllers as a function of vehicle velocity is proposed. The performance of the proposed STC, DTC, and integrated systems is evaluated by carrying out simulations for different operating conditions and some experimental work. The design of a second-generation narrow tilting vehicle on which the developed control system has been implemented is presented.

Road bank angle considerations in modeling and tilt stability controller design for narrow commuter vehicles

Narrow tilting vehicles that occupy a half width lane can play a big role in addressing traffic congestion problems by effectively doubling the capacity of existing highway lanes. In designing the tilt stability control system of such a vehicle consideration of the road bank angle is crucial since it plays a big role in minimizing the torque requirement of the tilt actuation system. In this paper the dynamic model of a tilting vehicle that takes into account the road bank angle is first developed. Then the design of a direct tilt control scheme that stabilizes the tilt mode of such a vehicle is outlined. Since the controller designed makes use of current road bank angle data, a method is outlined on how to determine the road bank angle from accelerometer readings. Finally simulation results are presented and discussion of the results is given

Differential GPS based control of a heavy vehicle

A control system, developed at the University of Minnesota to facilitate research into preventing run-off-the-road accidents, is described, and experimental results are presented. This system controls the steering, throttle and brakes of a class-8 truck tractor using differential GPS as the sole position sensor. Using this system, the truck was able to automatically maintain proper position in its lane at speeds of up to 80 kph on straight roads and to negotiate curves with a radius of 85 m at slower speeds. These limits were due to the test track constraints and not to the methodology. One potential application is then described. This application attempts to sense the driver falling asleep, and then actively intervenes by pulling the truck over to the side of the road and bringing it to a safe stop.

A novel wireless piezoelectric tire sensor for the estimation of slip angle

This paper introduces a simple approach for the analysis of tire deformation and proposes a new piezoelectric tire sensor for physically meaningful measurements of tire deformations. Tire deformation measurements in the contact patch can be used for the estimation of slip angle, tire forces, slip ratio and tire–road friction coefficient. The specific case of a wireless tire deformation sensor for the estimation of slip angle is taken up in this paper. A sensor in which lateral sidewall deformation can be decoupled from radial deformation is designed. The slope of the lateral deflection curve in the contact patch is used to calculate slip angle. A specially constructed tire test rig is used to experimentally evaluate the performance of the developed sensor. Results show that the developed sensor can accurately estimate slip angles up to values of 5°.

GPS-Based Real-Time Identification of Tire-Road Friction Coefficient

Vehicle control systems such as collision avoidance, adaptive cruise control and automated lane-keeping systems as well as ABS and stability control systems can benefit significantly from being made “road-adaptive”. The estimation of tire-road friction coefficient at the wheels allows the control algorithm in such systems to adapt to external driving conditions. This paper develops a new tire-road friction coefficient estimation algorithm based on measurements related to the lateral dynamics of the vehicle. A lateral tire force model parameterized as a function of slip angle, friction coefficient, normal force and cornering stiffness is used. A real-time parameter identification algorithm that utilizes measurements from a differential GPS system and a gyroscope is used to identify the tire-road friction coefficient and cornering stiffness parameters of the tire. The advantage of the developed algorithm is that it does not require large longitudinal slip in order to provide reliable friction estimates. Simulation studies indicate that a parameter convergence rate of one second can be obtained. Experiments conducted on both dry and slippery road indicate that the algorithm can work very effectively in identifying a slippery road. Two other new approaches to real-time tire road friction identification system are also discussed in the paper.Copyright

Development and Experimental Evaluation of a Tilt Stability Control System for Narrow Commuter Vehicles

This paper concentrates on development and experimental investigation of a compound control system designed for tilt stability of a narrow commuter vehicle. The control system is a combination of three different types of control schemes: Steering Tilt Control (STC) system, Direct Tilt Control (DTC) system and Tilt Brake system. These schemes utilize different types of actuators and offer complementary advantages over different ranges of operating speeds. The design of the control system is discussed. Then the combined STC-DTC system is first validated by running standard vehicle maneuver experiments such as turns and lane changes. The performance of the Tilt Brake algorithm is then verified for different low speed maneuvers. The feasibility of a stand alone DTC system is also experimentally investigated. Finally different experimental results are presented to demonstrate the effect of desired tilt angle definition on the handling of a narrow tilting vehicle.