Design of an Efficient, Low Weight Battery Electric Vehicle Based on a VW Lupo 3L
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© EVS-25 Shenzhen, China, Nov. 5-9, 2010 The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition Design of an efficient, low weight battery electric vehicle based on a VW Lupo 3L I.J.M. Besselink1, P.F. van Oorschot1, E. Meinders1, and H. Nijmeijer1 1Faculty of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands E-mail: [email protected] Abstract—A battery electric vehicle is being developed at the Eindhoven University of Technology, which will be used in future research projects regarding electric mobility. Energy storage in batteries is still at least 25 times heavier and has 10 times the volume in comparison to fossil fuel. This leads to an increase of the vehicle weight, especially when trying to maximise the range. A set of specifications is derived, taking into consideration the mobility requirements of people living in the Netherlands and the capabilities of electric vehicles. The VW Lupo 3L 1.2 TDI has been selected as the vehicle to be converted into a battery electric vehicle, since it has many favourable characteristics such as a very low mass and good aerodynamics. The design choices considering the power train and component selection are discussed in detail. Finally the battery electric Lupo is compared to the original Lupo 3L considering energy usage, costs per km and CO2 emissions. With respect to these aspects the advantages of electric propulsion are relatively small, as the donor vehicle is already very fuel efficient. Copyright Form of EVS25. Keywords—battery electric vehicle, power train, vehicle performance project is to develop and demonstrate environmentally 1. Introduction friendly alternatives for personal transport. On the Dutch Battery electric passenger cars have a very long history, national car exhibition (AutoRAI) in 2007 the vehicle, but they have failed to gain any significant market share, a known as the c,mm,n 1.0, was presented [3]. Mock-ups of short period at the beginning of the 20th century aside. At the exterior, interior and hydrogen powered power train the beginning of the 1970’s with the oil crisis and were on display, as created by the students of the three increasing worries about air pollution the electric car technical universities of the Netherlands. Inspired by the gained interest again. At the Eindhoven University of work of for example Ulf Bossel [4], a critical review of the Technology a project was executed in which a VW Golf well-to-wheel efficiency of a hydrogen powered vehicle was converted to a battery electric vehicle, figure 1 gives was made and it is concluded that a battery electric vehicle an impression. Though interesting research was done with is the most efficient way to get energy from renewable this vehicle, in particular regarding the possible efficiency sources to the wheels. increase using various gearbox configurations, it was also At the AutoRAI 2009 the electric c,mm,n 2.0 was clear that the converted vehicle was no match for the presented and an action plan was offered to the Dutch internal combustion engine (ICE) cars of those days [1]. government to speed up the introduction of the electric vehicles in the Netherlands [5]. The next step in the development of the c,mm,n is to create a running prototype. As building an entirely new vehicle from scratch will prove to be quite difficult and costly, the choice was made start with converting an existing vehicle. This paper is organised as follows. In section 2 a comparison is made between carrying the propulsion energy in batteries and fossil fuel. Existing battery electric vehicles are analysed and some rules of thumb are developed. In section 3 the design objectives are discussed. The aim is to develop a car with four seats, Figure 1: The TU/e battery electric VW Golf 1 as developed in which could be attractive to a large audience and to the years 1980 to 1983. minimise the impact of the inherent limitations of a battery Actually it turns out that throughout the 20th century that electric vehicle. the electric car always has kept the promise of being the Section 4 discusses the selection of the donor vehicle “car of tomorrow” but failed to deliver for various (not and the various power train components. The various only technical) reasons, as described by Mom [2]. With design choices are substantiated. Emphasis is put on the advent of mobile phones, laptop computers and achieving a low curb weight, energy efficiency, practical cordless power tools in the 1990’s battery technology usability and good performance characteristics. In section developed rapidly. These new technologies also found 5 calculations are made to compare some characteristics of their way into road vehicles, with the Tesla Roadster the battery electric vehicle with those of the donor ICE probably being the most exciting example. vehicle. In particular energy usage, CO2 emissions and In 2005 the Eindhoven University got involved in the costs per km are analysed. Some concluding remarks are “car of the future” project, as initiated by the Netherlands given in section 6. Society for Nature and Environment. The aim of this © EVS-25 Shenzhen, China, Nov. 5-9, 2010 The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition 2. BEV characteristics 0.8 now accounting for efficiency losses, (1) now gives an equivalent flow of 1.5 litres of petrol per hour. At a regular In a battery electric vehicle (BEV) all energy to propel fuel station the petrol flow is around 40 litres per minute. the vehicle is carried in batteries, which has major So for a petrol car the energy transfer is 1600 times faster consequences for the vehicle design and performance. compared to charging a BEV on a regular European power Table 1 gives an impression of the different possibilities socket. Even when considering state-of-the-art level 3 DC for energy storage and it is clear that the energy density of fast charging (50 kW), it is still a factor 120 slower. fossil fuels is orders of magnitude greater than that of the battery technologies available today. For the batteries a Table 1: Comparison of different energy carriers. utilization factor has to be taken into account, as it is good energy carrier and powertrain characteristics practice to limit the depth of discharge to 80% of the kWh/kg kWh/L efficiency utilisation nominal battery capacity in order to achieve an acceptable petrol 12.10 9.12 18% 100% diesel 11.80 9.97 22% 100% life. The efficiency of the all electric drive train is much battery (lead-acid) 0.030 0.06 80% 80% better than that of a petrol or diesel internal combustion battery (NiMH) 0.060 0.15 80% 80% engine (ICE), about a factor of four. Nevertheless the battery (LiFePO4) 0.100 0.15 80% 80% overall picture is that carrying energy in the form of battery (LiPo/LiCo) 0.135 0.25 80% 80% batteries is 25 to over 100 times heavier than petrol, with respect to the volume factors ranging from 10 to 40 apply. 10 kWh at the wheels relative to petrol An overview of different battery electric vehicles has energy mass volume mass volume been created using data from a multitude of sources on the kWh kg L - - internet. When comparing the BEV to the ICE equivalent, petrol 55.6 4.6 6.1 1.00 1.00 carrying the energy in batteries results in a heavier vehicle diesel 45.5 3.9 4.6 0.84 0.75 as is clearly shown in figure 2. For the battery electric battery (lead-acid) 12.5 520.8 260.4 113 43 vehicles at least 15% up to over 35% of the vehicle mass battery (NiMH) 12.5 260.4 104.2 57 17 consists of batteries. Certainly for the higher percentages battery (LiFePO4) 12.5 156.3 104.2 34 17 the sheer volume and vehicle load carrying capacity may battery (LiPo/LiCo) 12.5 115.7 62.5 25 10 become somewhat problematic. Typically between 15% to 25% battery to vehicle mass it appears to be feasible to battery mass/capacity construct a family car with four seats and sufficient VW Golf I luggage space. Figure 2 also makes clear that vehicle weight without the batteries is very similar to that of the VW Golf I EV (TU/e, 1983) 450 kg/15 kWh ICE equivalent. An electric motor can be much lighter VW Golf III than the equivalent ICE with a similar power rating, as VW Golf III Citystromer (1992) 512 kg/15.4 kWh will be discussed. But apparently this weight advantage is GM EV‐1 lead acid (1996) 533 kg/16.5 kWh lost in other systems of the electric power train and/or GM EV‐1 NiMH (1999) 481 kg/26.4 kWh chassis reinforcements to carry the batteries. Peugeot 106 Despite the significant mass and volume of the batteries, Peugeot 106 Electrique (1996) 264 kg/12 kWh the amount of energy which is carried in the vehicle is still Toy ota RAV 4 small compared to an ICE vehicle resulting in a limited Toy ota RAV 4 EV (1998) 450 kg/28 kWh range. The results presented in table 1 can be used to Nissan R'nessa develop some rule of thumb: in order to get the same energy at the wheels the required energy from the battery Nissan Altra EV (1998) 365 kg/32.4 kWh in kWh is about twice the required amount of petrol Think City A306 (2007) 245 kg/28 kWh expressed in litres.