New sensors and estimation systems for the measurement of tire-road friction coefficient and tire slip variables

This thesis introduces two new measurement systems developed for the estimation of tire-road friction coefficient and tire slip variables on highway vehicles.The first part of the thesis focuses on the development and experimental evaluation of a friction estimation system based on a novel adaptive feedforward vibration cancellation algorithm. The friction estimation utilizes a small instrumented wheel on the vehicle. Unlike other systems previously documented in the literature, the developed system can provide a continuous measurement of the friction coefficient under all vehicle maneuvers, even when the longitudinal and lateral accelerations are both zero.A key challenge in the development of the estimation system is the need to remove the influence of vibrations and the influence of vehicle maneuvers from the measured signal of a force sensor. An adaptive feedforward algorithm based on the use of accelerometer signals as reference inputs is developed. The parameters of the feedforward model are estimated by the adaptive algorithm and serve to determine the friction coefficient. The influence of vibrations and vehicle maneuvers is also removed.Detailed experimental results are presented on a skid pad wherein the road surface changes from dry asphalt to ice. Results are presented at different speeds and with and without lateral and longitudinal maneuvers. Excellent performance is obtained in estimation of the friction coefficient. The performance of the adaptive feedforward algorithm is shown to be significantly superior to that of a simple cross-correlation based algorithm for friction estimation.An alternative algorithm without using an accelerometer, namely the quadratic mean square vibration cancellation algorithm, is also developed and evaluated to eliminate the excessive vibrations. This algorithm does not perform as well as the adaptive feedforward accelerometer based algorithm.The continuously estimated tire-road friction coefficient signal and a predefined threshold enable the design of a closed-loop controller for the applicator of a snowplow which automatically applies deicing material whenever an icy spot on the road is detected. The time delays of the applicator actuator on the snowplow and of the friction estimation algorithm are both determined experimentally and the system is shown to work reliably at speeds up to 25 mph. The closed-loop system is able to cover any detected slippery surface with the deicing chemical right from the beginning of the road surface transition point from dry to icy. It is also shown with a simple experiment that the system can operate along with a GPS receiver in order to map the friction coefficient of a designated snowplow route.The second part of the thesis introduces a simple approach for the analysis of tire deformations and proposes a new wireless piezoelectric tire sensor for the measurements of tire deformations. The tire deformation profile inside the contact patch can be used for the estimation of tire slip variables, tire forces and tire road friction coefficient.A wireless piezoelectric tire sensor for the specific case of slip angle and tire-road friction coefficient estimation is developed in this work. A sensor which decouples the lateral sidewall deformation from the radial and tangential sidewall deformations is designed. The slope of the lateral deflection profile at the leading edge of the contact patch is used to estimate the slip angles. A second order polynomial is used to model the lateral deflection profile of the sidewall. The parameters of this function are employed to estimate the lateral force and the conventional brush model is employed to estimate the tire road friction coefficient.A specially constructed tire test rig is used to evaluate the performance of the developed tire sensor. Results show that the sensor can accurately estimate slip angles up to 5.0 degrees. The sensor is also tested on different surfaces and results obtained for the estimation of friction coefficient are promising.