Mitigating Unsprung Mass in an Electric Vehicle Through Passive and Active Isolation of a Wheel-Integrated Motor

This numerical study examines whether the propulsion mass of a wheel-integrated motor can be isolated from the wheel assembly to reduce the adverse effects of increased unsprung mass. A constant 400 kg vehicle corner is used for three matched configurations. The centralized drive reference has a sprung mass of 370 kg and a wheel mass of 30 kg. Transferring a 40 kg motor to the wheel gives a rigid wheel-mounted motor configuration with a sprung mass of 330 kg and an unsprung mass of 70 kg. In the proposed configuration, the same 40 kg motor becomes an intermediate coordinate between the 330 kg vehicle body and the 30 kg wheel assembly. Rigid motor mounting increases the aggregate bump RMS acceleration, bump peak acceleration, and random-road tire force by 33.1%, 41.1%, and 35.8%, respectively, relative to the centralized drive reference. A 2500-point maximin Latin hypercube search selects a passive isolated motor design with a spring stiffness ratio of 0.869 and local damping of 1774 N s/m. Relative to rigid mounting, this design reduces all six scenario-averaged bump and Class C road measures by 13.3–29.2%. The parameters selected for a 40 kg motor also retain ratios below unity when the motor mass is varied from 20 to 60 kg. Under the selected actuator force limits, the Balanced LQR reduces the mean random-road acceleration by 76.6% and the tire force by 8.3% relative to rigid mounting, but increases suspension travel by 18.2%. The Comfort LQR produces a larger acceleration reduction and larger travel and tire force penalties. All 500 sampled passive and active parameter combinations remained stable within the investigated uncertainty ranges. The contribution is a mass-matched numerical framework that separates the penalty of rigid wheel-mounted motor operation from the recovery obtained by isolating the existing propulsion mass, without adding a separate absorber, and quantifies the further active control tradeoff.