Effects on Motorcycle Response Data Using Wheel Force Transducers

Wheel force transducers (WFT) are precise and accurate measurement devices that seamlessly integrate into any vehicle. They can be applied in numerous vehicle applications for both on-road and in laboratory settings. The instrumentation requires replacing an original equipment manufacturer (OEM) wheel with a custom WFT system which is specific to the wheel hub design. An ideal design will minimally impact a vehicle's dynamics, but the vehicle system is inherently modified from the mass of the measurement device. Research and technical documentation have been published which provide conclusions explaining reduction in the unsprung mass reduces dynamic wheel load. However, there doesn’t appear to be clear compensation techniques for how a modified unsprung mass can be related to the original system, thus allowing the WFT signals to be more accurate to the OEM wheel forces. An experimental study was performed on a prototype motorcycle to better understand these differences. An instrumented “impact bump” acting as a force transducer was designed particularly for this testing to assist in characterizing the dynamic responses of a vehicle with variable unsprung mass setups. The motorcycle was equipped with WFTs to measure reaction forces, tri-axial accelerometers for vibration, linear variable differential transducers (LVDTs) for fork and shock travel, and a GPS to reference vehicle speed. The test variables included modifying the unsprung mass of the motorcycle’s front wheel by using OEM wheels, WFT systems, rim masses, hub masses, varying the speed of impact, and changing the motorcycle suspension setup. In this paper, there is consideration to the time domain and frequency domain for these changes in the system dynamic responses. There is discussion of correlation between measurement sensors and the relationship to the mass added from using WFT systems.