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Abstract: A Study On The Effect Of Hub Motor Mass On Stability And Comfort Of Electric Vehicles

Hub motors have always been considered as propulsion for electric vehicles, but not widely used due to various negative aspects. One of these is the uncertainty of the effect the added wheel mass has on the stability, safety and comfort of the vehicle. In this paper, frequency analysis as well as simulations of the system is done using a simple model that represents the vehicle suspension system and wheels. The results of the hub driven vehicle are compared to that of a standard vehicle. It is shown that the added wheel mass has no effect on the stability of the vehicle and that the frequency response is within the accepted comfort range.

A Study On The Effect Of Hub Motor Mass On Stability And Comfort Of Electric Vehicles – Content

With the introduction of hub motors to the world of electric vehicles, a critical question has arisen: ‘What effect has the added wheel mass of a hub motor on the safety and comfort of a vehicle?’ Moving the propulsion from the vehicle body to the wheels can add up to 50 kg or more, per wheel, to the unsprung mass. Most of the research done on suspension systems has been done for standard vehicles. No real investigations have been done on increased unsprung mass. A few recommendations state that the unsprung mass should not exceed 20% of the sprung mass. Current road vehicles do not exceed this ratio and no real evidence supports this ratio. By increasing the mass of the wheel, the wheel inertia is increased. Increased wheel inertia causes higher acceleration forces during road condition reaction. These forces put relatively high levels of stress on contact and connection points of the wheels. These forces can also cause degradation in ride comfort as experienced by the occupants of the vehicle. The aim of the investigation is to study, through frequency analysis and simulation, the effect of moving mass from the sprung mass to the unsprung mass of a vehicle. The simulation results are compared with that of a standard vehicle to ascertain if it is possible to increase the unsprung mass of a vehicle. The added mass has an effect on the handling of the vehicle as well. It is beyond the scope of the study to investigate this area, as the models and analyses are complex. These will be investigated in a later study to verify the first results as well as simulate vehicle handling. It is the opinion of the author that this study will give enough information to make sufficient conclusions on the effect of increased unsprung mass.