Rolling resistance modeling for electric vehicle consumption
Due to increasing oil shortage and ever stricter CO2-Emissions regulations vehicle energy consumption simulations are nowadays indispensable for the car industry. Especially the limited range of today’s electric vehicles makes it particularly necessary to
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© Springer Fachmedien Wiesbaden 2015 P.E. Pfeffer (Ed.), 6th International Munich Chassis Symposium 2015, Proceedings, DOI 10.1007/978-3-658-09711-0_49
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Rolling resistance modeling for electric vehicle consumption
1 Introduction Due to increasing oil shortage and ever stricter CO2-Emissions regulations vehicle energy consumption simulations are nowadays indispensable for the car industry. Especially the limited range of today’s electric vehicles makes it particularly necessary to model all energy loss sources as precisely as possible. As the drive train efficiency of electric vehicles is higher than those of conventional vehicles, the percentage of the energy loss caused by driving resistance forces is higher, too. These are composed of the aerodynamic drag, inertial drag, friction in the power train, rolling resistance force and slope resistance. For standard vehicle consumption simulations as presented in [1] the rolling resistance is assumed to be constant, in some cases, if needed it changes as a function of speed. This is most relevant for high velocities from 120 km/h upwards. However, these rolling resistance coefficients correspond to steady state values which were determined according to standards such as the ISO 28580 [2] at one operating point of the tyre. Thus measured at a given pressure, load, ambient temperature and velocity after a warming-up procedure of 30 minutes. At the beginning of the test, the rolling can be roughly 20 % higher than the steady state value and it then drops quickly until it reaches its minimum after 20-30 minutes. This phenomena results in a false calculated energy consumption of the vehicle for a specific cycle. A similar study on the transient rolling resistance was presented in [3] suggesting that the tyre label should take account of this phenomena. This paper deals with the quantification of the rolling resistance variance at driven operation points in the case of compact electric vehicles, such as the electric vehicle Visio.M developed by the “Technische Universität München”, which is equipped with a 115/70R 16 tyre.
2 Contribution of Rolling Resistance to Vehicle Energy Consumption The rolling resistance is defined as the energy consumed by a tyre per unit of distance. The main cause of the energy dissipation is due to the viscoelastic material characteristics of rubber. Viscoelastic materials lose energy in form of heat whenever they are deformed. This energy loss results in a force that opposes the tyre’s direction of movement and therefore the vehicle’s movement. [4]
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Rolling resistance modeling for electric vehicle consumption
2.1 Contribution to Energy Consumption The contributions of each resistance to the driving resistance and hence the total energy consumption is strongly dependent on the operational profile. As presented in [4], figure 1 shows the distribution for a conventional vehicle with a combustion engine, a mass of 1100 kg and a frontal vehicle surface of 0.65 m², an internal friction of 50 N and a maximum engine power of 51 kW. The rolli
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