The damping ratio of chassis suspension is a key parameter for damping matching of in-wheel motor vehicles (IWMVs).
Because the motor is attached to the driving wheel, the initial design method of the damping ratio for traditional cars
is not entirely suitable for IWMVs. This paper proposes an innovative initial design method of the damping ratio for
IWMVs. Firstly, a traveling vibration model of occupant-vehicle-road (OVR) for IWMVs is established. The model involves
the occupant, cushion, suspension, in-wheel motor, road, and running speed. Secondly, on the basis of the model, using a
special form of infinite integral, a mathematical expression of the occupant root-mean-square (RMS) acceleration is
derived. Thirdly, based on the RMS optimization criterion for ride comfort, an 8 order polynomial equation about the
suspension optimal damping ratio is deduced. Subsequently, through factors analysis, the change principles of the
optimal damping ratio versus vehicle parameters are unveiled. Finally, the reliability of the optimal damping ratio is
validated by test using a commercially available IWMV. The relative deviation of the calculated optimal damping ratio
and the tested damping ratio is 5.4%. The results show that the proposed optimal damping ratio can be used in the
preliminary design phase for IWMVs.