Analysis of Applied Load Estimation Using Strain for Intelligent Tires

Abstract

From a traffic safety point of view, there is an urgent need for intelligent tires which can optimize braking control by estimating the slip ratio and friction coefficient between road surface and tire. In previous studies, we have proposed an application of strain data for estimating a friction coefficient. However, it only investigated the condition when the vertical or frictional loads changed but the other load remained constant. Since both of the frictional and vertical loads alter the measured strain data, an independent applied load estimation method is needed. This study develops a concurrent method for estimating the frictional and vertical loads applied to the tires from the measured strain data when both loads change. The method decomposes the measured circumferential strain to the frictional and vertical strain components using their symmetrical and anti-symmetrical characteristics. FEM analysis is used for simulating tire deformation under various wheel loads and braking torques and the relationship between the strain distribution at the sensing point and the applied loads are calculated. When the estimated and true applied loads were compared, it was confirmed that the vertical and frictional loads can be estimated independently from the circumferential strain with sufficient accuracy. Using this method, one can represent the slip slope curve during driving, which enables the optimization of vehicle control and implementation of a road condition warning system. 1497in capacitance (10)(11)(12) . The sensor uses a very soft material so that it does not interfere with tire deformation and avoids debonding (11,12) . Another sensor proposed is a self-sensing method that uses the tire structure itself as the sensor (13) . This has the advantage that an attached sensor is not needed and debonding problems are eliminated. An optical method was developed for the concurrent monitoring of in-plane strain and out-of-plane displacement (rolling radius) (14,15) . The optical method enables noncontact measurement of strain distribution. The in-plane strain and out-of-plane displacement are calculated using image processing with an image of the interior surface of a tire that is taken with a single CCD camera fixed on the wheel rim. We have also developed a battery-less wireless communication system (10,16,17) . However, a practical model of strain used for improved tire safety has not yet been presented and is urgently needed.Our previous study (18) investigated the application of strain data for an optimized braking control and road condition warning system. The relationships between strain sensor outputs and tire mechanical parameters, including braking torque, effective radius and contact patch length, are calculated using finite element analysis and an estimating method for the slip ratio and frictional coefficient between road and tire surface were proposed. Here the friction coefficient µ is a key parameter indicating the braking/accelerating efficiency and defined by the normal force (wheel load), F N , div...

OPTYRE – A new technology for tire monitoring: Evidence of contact patch phenomena

“…Using strain signals acquired under dynamic conditions, distances between these points are calculated and result is in line with the measured static footprint of the tire. On this ground it is shown that existing techniques [13,14], which use the distance between the two extrema of the first time derivative of the strain, underestimates the footprint length. This marks a conceptual difference, suggesting the tire segments at the edges of the contact patch have the highest deformation acceleration in respect to the highest deformation speed.…”

“…When the braking torque is applied, shear deformations due to the frictional load (18) arise and give rise to an asymmetrical strain distribution, as stated by Eqs. (13) [13], which predicts the strain induced by the frictional load is antisymmetric in respect to the centre of the footprint.…”

“…The contribution of the frictional force (13) to the vertical load P in the right hand side (RHS) of Eq. (1) is now evaluated, considering an infinitesimal element of the tread, with the sign convention in Fig.…”

“…11 and 13 show the extrema of the first derivative of the strain fall well within the patch edges. It follows methods for the footprint detection, under dynamic conditions, based on the distance between these two points [13,14] underestimate the length of the footprint. The second derivative of the tire strain seems a better candidate for the task, in Fig.…”

Strain Monitoring and Applied Load Estimation for the Development of Intelligent Tires Using a Single Wireless CCD Camera

“…Our previous study (33) proposed a concurrent estimating method for frictional and vertical loads applied to a tire from the tire strain data when both loads were changing. Finite element method (FEM) analysis was used for simulating tire deformation under various wheel loads and braking torques, and the relationship between the strain distribution and the applied loads were investigated.…”