A disassembly-free test rig-based method for determining the unsprung masses of a passenger car based on a non-linear dynamic model of the stationary tire

The vehicle unsprung mass plays a key role for simulating driving dynamics and ride comfort. Conventional methods for determining the unsprung mass involve dismantling the vehicle axles. This paper presents a disassembly-free method for determining the unsprung masses of a passenger car. For the method, quasi-static and dynamic measurements of one passenger car on a full vehicle test rig and of one tire on a single-axis hydropulser test rig are conducted. Non-linear dynamic mathematical models of the axle and tires are developed, parameterized, and validated. To determine the unsprung masses, the vehicle body is rigidly connected to the full vehicle test rig. The wheels of an axle are dynamically excited with the test rig platforms at the wheel contact patches. The excitation signal corresponds to a vertical in-phase displacement excitation with frequency sweep signals in a frequency range of 5–20 Hz and a constant amplitude of 3 mm in order to excite the natural frequencies of the unsprung masses. The measurements are conducted with a total of four different variations of the unsprung masses. The unsprung masses are obtained by simulative optimization on the dynamic measurements of the full vehicle test rig. The developed tire model can be used for the simulation of similar test rig measurements. The method is performed and validated for a MacPherson axle and is able to determine the unsprung mass of the axle with an accuracy of 99.6%.