Fig. 3: Share of resistance factors for different driving cycles of a passenger car example Share of resistance factors for different driving cycles
City (ECE) Aerodynamic resistance
90km/ h const.
120km/ h const.
Source: [VW AG 2002]
The share of resistance factors for a passenger car in three different driving cycles is illustrated in Fig. 3. In the city driving cycle aerodynamic resistance is very low (12%) because of the low speed, but acceleration and rolling resistance are high. With a steady speed of 120 km/ h (e. g. on highways) the share of aerodynamic resistance is about 75 %, energy consumption is thus mainly due to the weight independent aerody- namic resistance. For high speed trains running at 250 - 300 km/ h the share of aerody- namic resistance can be even higher, according to [HAIGERMOSER 2000] around 85 %. “However, air resistance has also a considerable influence on the energy con- sumption of slower trains, in particular on freight trains. Freight trains have usually not a very good or optimised aerodynamic design” [ANDERSSEN 2000].
For energy savings we distinguish specific energy savings per 100 km and an abso- lute weight reduction by 100 kg and relative energy savings in % by a relative weight reduction by 10 %. Relative energy savings would be 0 % for a weightless vehicle which faces only aerodynamic resistance and 10 % for a vehicle which faces only weight de- pendent resistance factors and no aerodynamic resistance at all. The absolute and relative values can not be directly compared.
In contrast to combustion engines, for electric engines energetic recovery systems are already in use. In principle, the kinetic and potential energy can be fed back, with ex- ception of losses due to electrical systems and running resistance, but in practice the regeneration of energy is limited ([ANDERSSEN 2000]). An average of 20 % and up to 25 % ([EHINGER et al. 2000], [SCHWANHÄUSSER et al. 1990]) or even 27 % ([ALBERT et al. 1997]) of the energy which is lost can be recovered and used for the next acceleration or ascending period. The energetic recovery systems are already used in rail vehicles and are often already reflected in the data used for this study.