Abstract
The work presents an approach to instrument the load-sensing bearings for automotive applications for estimation of the loads acting on the wheels. The system comprises fiber-optic sensors based on addressed fiber Bragg structures (AFBS) with two symmetrical phase shifts. A mathematical model for load–deformation relation is presented, and the AFBS interrogation principle is described. The simulation includes (i) modeling of vehicle dynamics in a split-mu braking test, during which the longitudinal wheel loads are obtained, (ii) the subsequent estimation of bearing outer ring deformation using a beam model with simply supported boundary conditions, (iii) the conversion of strain into central frequency shift of AFBS, and (iv) modeling of the beating signal at the photodetector. The simulation results show that the estimation error of the longitudinal wheel force from the strain data acquired from a single measurement point was 5.44% with a root-mean-square error of 113.64 N. A prototype load-sensing bearing was instrumented with a single AFBS sensor and mounted in a front right wheel hub of an experimental vehicle. The experimental setup demonstrated comparable results with the simulation during the braking test. The proposed system with load-sensing bearings is aimed at estimation of the loads acting on the wheels, which serve as input parameters for active safety systems, such as automatic braking, adaptive cruise control, or fully automated driving, in order to enhance their effectiveness and the safety of the vehicle.
Highlights
Various active safety systems such as the antilock braking system (ABS) and electronic stability control (ESC) have been used to increase driving safety for several decades [1,2]. Their efficiency depends on the correctness of tire–road traction parameters that are currently estimated by means of indirect methods [3,4] which do not always provide sufficient accuracy, limiting the capabilities of such systems for vehicle dynamics control
Applying Equation (11) to the simulation and taking into account a typical gauge factor of fiber Bragg gratings (FBGs) equal to 1.2 pm of wavelength shift per microstrain applied to the fiber [40], the central frequency of the addressed fiber Bragg structures (AFBS) is calculated for five cases: without strain, at t = 6.35 s from the beginning of the maneuver for both front left and front right bearings, and at t = 6.8 s for both front left and front right bearings
In order to ensure the uniformity of sensor strain and to eliminate lateral deformation of the sensor, a notch corresponding to the sensor length was made on the outer ring of the bearing
Summary
Various active safety systems such as the antilock braking system (ABS) and electronic stability control (ESC) have been used to increase driving safety for several decades [1,2] Their efficiency depends on the correctness of tire–road traction parameters that are currently estimated by means of indirect methods [3,4] which do not always provide sufficient accuracy, limiting the capabilities of such systems for vehicle dynamics control. Every component of the vehicle transferring the loads from the tire contact patch to the vehicle body can be used to estimate the wheel loads. Wheel force measurements based on load-sensing hub bearings have a number of advantages in comparison with the other approaches. Load-sensing hub bearings are located closer to the contact patch than other suspension components, providing a more precise load estimation. The paper introduces a comprehensive model of the load measurement process and an experimental demonstration of the system operation
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