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The directive set out the goals in terms of system interoperability, compatibility, reliability and accuracy. The compatibility has to be addressed in case of vehicles with trailer units and the communication shall be based on DSRC standards such that the information is readable by competent authorities. Every 10 minutes the system is requested to deliver the total weight (and optionally the axle weight) with an accuracy of 5% of the GVW. This means that the information shall be available while in standing still condition or in-motion. Thus, the biggest challenge is to make the system independent from axle type (compatibility with others OEM product), suspension system type (leaf spring, air ride, active level control etc.) as well as vehicle and road condition (tire pressure, on-curb parking, asymmetric loads, longitudinal and lateral road grade, parking brake use etc.).
After a review of existing products on the market, new concepts were generated and evaluated in terms of cost estimation, installation and maintenance ease, periodical calibration requirements and need for complementary sensors. The selected concepts relayed on the use of strain gauges and inductive sensors to measure derived physical quantities on the axle housing and on the wheel-ends. In order to optimize the sensor topology, FEM simulations were performed, taking into account variations of the main vertical load as well as different types of solicitations/disturbances deriving from particular vehicle or road conditions. The proof of the concepts took place by the means of quasi-static and dynamic tests performed on a dedicated bench with 10 DoF. Finally, the concepts which have proven to be working on the test bench were optimized and integrated with a demo truck for further testing. Six loading conditions (symmetric and non) were evaluated in various test set-up (parking on curb, tire inflation and deflation cycles, parking brake activation etc. ), both static and in-motion situations.