Electric vehicle
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| 2.8 EVs for the Future The future of EVs, of course, remains to be written. However, the need for vehicles that minimise damage to the environment is urgent. Much of the technology to produce such vehicles has been developed and the cost, currently high in many cases, is likely to drop with increasing demand, which will allow quantity production. This has certainly proved true already in the case of the lithium ion battery. The following chapters describe the key technologies that are the basis of EVs now and in the future batteries and other energy stores (Chapter 3), fuel cells (Chapter hydrogen supply (Chapter 6) and electric motors (Chapter 7). Once the basic concepts are understood, their incorporation into vehicles can be addressed. Avery important aspect of this is vehicle performance modelling, and so Chapter 8 is devoted to this topic. The subsequent chapters address the important topics of the design of safe and stable vehicles, and of the comfort facilities that are essential in a modern car. Finally, the environmental impact of EVs needs to be honestly addressed – to what extent do they really reduce the environmental damage done by our love of personal mobility? The prospect of cities and towns using zero-emission vehicles is areal one, as is the use of vehicles that use electrical technology to reduce fuel consumption. It is up to engineers, scientists and designers to make this a reality. Further Reading The following two books have good summaries of the history of electric vehicles: Wakefield, EH. (1994) History of the Electric Automobile, The Society of Automobile Engineers, Warrendale, PA. Westbrook, M.H. (2001) The Electric Car , The Institution of Electrical Engineers, London. 3 Batteries, Flywheels and Supercapacitors 3.1 Introduction We have seen in the previous chapter that there are many different types and sizes of EVs. However, in nearly all road vehicles the battery is a key component. In the classical EV the battery is the only energy store, and the component with the highest cost, weight and volume. In hybrid vehicles the battery, which must continually accept and give out electrical energy, is also a key component of the highest importance. Some fuel cell (FC) vehicles have been made which have batteries that are no larger than those normally fitted to IC engine cars, but it is probably that most early FC-powered vehicles will have quite large batteries and work in hybrid FC/battery mode. In short, a good understanding of battery technology and performance is vital to anyone involved with electric road vehicles. What is an electric battery A battery consists of two or more electric cells connected together. The cells convert chemical energy to electrical energy. The cells consist of positive and negative electrodes in an electrolyte. It is the chemical reaction between the electrodes and the electrolyte which generates DC electricity. In the case of secondary or rechargeable batteries the chemical reaction can be reversed by reversing the current and the battery returned to a charged state. The lead acid battery is the traditional rechargeable type, but there are others which are becoming popular in modern EVs. The first EV using rechargeable batteries preceded the invention of the rechargeable lead acid battery by a quarter of a century, and there area very large number of materials and electrolytes that can be combined to form a battery. However, only a relatively small number of combinations have been developed as commercial rechargeable electric batteries suitable for use in vehicles. At present these include lead acid, nickel iron, nickel cadmium, nickel metal hydride (NiMH), lithium polymer and lithium iron, sodium sulfur and sodium metal chloride. There are also more recent developments of batteries that can be mechanically refuelled, the main ones being aluminium–air and zinc–air. Despite all the different possibilities tried, and Electric Vehicle Technology Explained, Second Edition. James Larminie and John Lowry. © 2012 John Wiley & Sons, Ltd. Published 2012 by John Wiley & Sons, Ltd. 30 Electric Vehicle Technology Explained, Second Edition about 150 years of development, a suitable battery has only recently been developed which allows mass production of EVs. From the EV designer’s point of view the battery can be treated as a black box that has a range of performance criteria. These criteria will include specific energy, energy density, specific power, typical voltages, amphour efficiency, energy efficiency, commercial availability, cost, operating temperatures, self-discharge rates, number of life cycles and recharge rates – terms which will be explained in the following section. The designer also needs to understand how energy availability varies with ambient temperature, charge and discharge rates, battery geometry, optimum temperature, charging methods, cooling needs and likely future developments. However, at least a basic understanding of the battery chemistry is very important, otherwise the performance and maintenance requirements of the different types, and most of the disappointments connected with battery use, such as their limited life, self-discharge, reduced efficiency at higher currents, and so on, cannot be understood. This basic knowledge is also needed in regard to likely hazards in an accident and the overall impact of the use of battery chemicals on the environment. Recycling of used batteries is also becoming increasingly important. The main parameters that specify the behaviour and performance of a battery are given in the following section. In the later sections the chemistry and performance of the most important battery types are outlined, and finally the very important topic of battery performance modelling is outlined. Download 3.49 Mb. Share with your friends:
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