Methodology and Application on Load Monitoring Using Strain-Gauged Bolts in Brake Calipers

As technology evolves, the number of sensors and available data on vehicles grow exponentially. In this context, it is essential to use sensors for monitoring key components, increasing safety and reliability, and gathering data useful for mechanical dimensioning and control systems. This paper presents an application of strain-gauged bolts on brake calipers fixation of two electric vehicles. With this approach it was possible to evaluate the loads applied to the brake pads fixation zone and correlate them with braking behavior, therefore gaining insights on braking conditions and system state for an improved braking function control. The goal of the study is analyzing the strengths and limitations of the method and proposing developments to deploy it in real applications. This is particularly important and novel for electric vehicles, where powertrains can create positive/negative torques and generate complex interactions with braking system. Strain-gauges are a long-known technology applied in many fields, and its usage in bolts and screws is well established. However, within automotive field, it could represent cutting edge technology for load sensing and monitoring. The application shows promising results and proves a valid option for monitoring safety components due to its low cost, small dimensions, and reliability. The presented case study takes place in a straight-line test track, where three braking maneuvers were performed: low-pressure braking, mid-pressure braking, and emergence braking. The effects of ABS intervention and wet disk conditions were investigated from an experimental point of view. The paper describes the method used for the strain-gauge application in the bolts, calibration in a dynamometer traction and compression test, installation in the vehicle, and data analysis and post-processing. Results present consistent readings in the higher-pressure conditions, while for the low-pressure cases, the challenges related to load sensing sensitivity are more evident, with a clear tradeoff between system stiffness and measure sensitivity. Finally, evolutions of the system and further investigations on this promising technology applied to the automotive field are presented.