Frequency-Domain Mechanism Analysis for the Adverse Effects of the Unsprung Mass of the In-Wheel-Motor EV Through the Suspension Impedance Dynamics

In-wheel motor drive systems can increase vehicle unsprung mass and thereby alter suspension dynamics. This study investigates the frequency-domain mechanisms through which an unsprung mass increment affects ride comfort, suspension working space, and road holding, and proposes a frequency-partitioned active impedance control (FPAIC) strategy. A structural sensitivity operator, M(s), is derived from a linear quarter-car model to quantify the mass-perturbation effect and to identify inertia, damping, and tire stiffness as the principal physical propagation channels. Guided by this mapping, the commanded active force is decomposed into virtual-inertia, virtual-damping, and virtual-stiffness components, which are scheduled according to the estimated dominant excitation frequency. Under swept-frequency simulations with Δmu = 60 kg, the comfort-prioritized LQR benchmark reduces the sprung-mass-acceleration RMS to 93.8% of the baseline but increases the tire-deflection RMS to 144.1%, whereas the road-holding-prioritized H∞ benchmark reduces the tire-deflection RMS to 99.1% at the cost of increasing the sprung-mass-acceleration RMS to 170.9%. The FPAIC yields corresponding RMS values of 98.9%, 85.9%, and 99.4% for sprung-mass acceleration, suspension deflection, and dynamic tire deflection, respectively. Overall, the results demonstrate mechanism-guided coordination across ride comfort, suspension working space, and road holding, while the Δmu = 40 kg case shows that the unchanged FPAIC parameterization retains its mitigation effect without retuning.