Almost-decoupling active control of in-wheel motors-driving 5DOF vehicle via complementary acceleration-difference feedback force control strategy

By incorporating the vertical–pitch dynamic coupling, the primary mechanism underlying motion sickness mitigating, we propose an almost-decoupling active control framework for a five-degree-of-freedom (5DOF) semi-vehicle powered by in-wheel motors (IWMs) grounded in frequency response analysis. A novel complementary acceleration-difference feedback (CAF) force control strategy is theoretically derived to suppress pitching angular acceleration and achieve almost-decoupling between vertical and pitch motions. The CAF force control law synthesizes suspension force from spatially differentiated vertical acceleration measurements acquired at the chassis–front and chassis–rear suspension interfaces. Root-mean-squared (RMS) values and frequency responses of key performance metrics, including vehicle-body acceleration, pitch angular acceleration, and related dynamic quantities are evaluated for the IWM-equipped 5-DOF semi-vehicle model subjected to stochastic road excitation conforming to ISO 8608 Class C. Results demonstrate that, across the speed range of 5–50 m/s, the proposed CAF force control strategy reduces the RMS pitch angular acceleration by up to 47.8% and attenuates its dominant frequency-domain peak amplitude by up to 41.1% at 20 m/s. The novelty of the proposed CAF force control strategy lies in its practical realizability and underlying almost-decoupling framework, not in the mathematical form of the control law. By applying only the acceleration difference between two suspension connection points, easily measured with two low-cost, off-the-shelf accelerometers, it provides a practical and cost-effective solution for real-world active suspensions. The present framework offers flexibility and compatibility for integrating diverse advanced control strategies—integration of which is central to our ongoing research.