Estimation of the Lateral Force, acting at the Tire Contact Patch of a Vehicle Wheel, using a Hub Bearing Unit instrumented with Strain Gauges and Eddy-current Sensors

Abstract

Load Sensing Bearing (LSB) units are based on the measurement of the elastic deformation of the outer ring of the bearing unit usually using strain gauges which are placed along the circumference of the bearing. The master thesis is aimed at estimating the lateral tire force of a vehicle wheel using the vehicle wheel bearing hub unit which is instrumented to become a LSB and is placed in a BMW E60 lab vehicle. Calibration of the LSB is needed to obtain a strain-force model. In situ calibration is expensive, time consuming and not always possible. Therefore a calibration system, the Bearing Test System (BETSY) has been used. Sensor responses of the LSB are greatly influenced by differences in bearing housing compliance where on one hand the LSB is mounted on the machine and on the other hand in the vehicle. It will be shown how it is possible to use BETSY as calibration system when the LSB is mounted to machine via the actual knuckle and ball joints found in the vehicle. Next, a Multivariate Linear Regression Analysis (MLRA) is used to obtain a strain-force model to estimate the lateral force. However, the strain gauges are subjected to thermal influences of a low frequent nature and can therefore only be used to estimate the ‘high’- frequent lateral force. Besides that, it is not possible with the specific compact wheel hub unit of the BMW E60 lab vehicle to determine, with the strain gauges, whether the vehicle is turning left or right. To overcome these two issues, two Eddy-current sensors measuring the tilting movement of the ABS-ring, which is integrated in the seal of the bearing, are used to determine the direction and to estimate the low frequent content of the lateral force. Calibration and validation experiments are performed to show the accuracy and precision of the lateral force estimation.