Quantification of energy losses in suspension dampers and its effects on rolling resistance

The energy consumption of battery electric buses, and electric vehicles in general, depends to a large extent on rolling resistance. Although often aggregated into one, the energy lost due to rolling resistance can be subdivided into losses occurring in or at the tyre and losses occurring in the shock absorbers of the vehicle suspension. In this paper, the energy dissipated by the dampers of a battery electric bus is quantified in an energy consumption context. The analysis is based on a description of the vertical vehicle dynamics using a quarter-car model with a nonlinear dashpot. The model is validated by comparing suspension deflection with a measurement on a known road surface. It is shown that 73% of the energy dissipated in the dampers occurs at road frequencies between 3 and 12 Hz. Model simulations on different simulated ISO 8608 road surfaces reveal that damper losses are in the order of 100 W on smooth roads (classes A and B), yet can reach values of several kW's on rough roads (class D) at 40 km/h. A comparison with rolling resistance coefficients obtained from coast-down tests shows that the damper losses can explain the majority of the rolling resistance difference between road surfaces with a different roughness.