Design Challenges of an Electric Vehicle And Solutions in Development Matthew Elser, Department of Mechanical Engineering



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Design Challenges of an Electric Vehicle

And Solutions in Development

Matthew Elser, Department of Mechanical Engineering
With the current state of gas shortages, alternatives to internal combustion vehicles are becoming increasingly important. The efficiency of most internal combustion engines is in the range of twenty percenti, as a result of the simple fact that they convert so much potential energy to heat. Electric cars look to be the ideal replacement for the modern petroleum fueled car. As with any new design, there are many obstacles, including maintaining high efficiency, competing with performance that standard cars have after decades of development, and the market. To meet these challenges, electric cars are being developed in increasingly creative ways and must utilize new developments in a wide range of fields.

M
The Kurrent, an NEV http://www.getkurrent.com/gallery/pages/low_profile.html
any electric vehicles are designed to be classified differently by law than the average consumer vehicle so as to have fewer restrictions and requirements. For example the Aptera 1e has three wheels and is thus considered a motorcycle with the ability to travel in HOV lanes. The average driver travels 29 miles per and day spends 55 minute doing soii meaning that low-speed, short range vehicles meet the everyday demand of the usual consumer. There is a classification of vehicle called a “neighborhood vehicle” which may not exceed thirty-five miles per hour or 2500 lbs, and must have four wheelsiii. This classification seems ideal for the near future of electric cars. By meeting the demand for errands and short trips, Neighborhood Electric Vehicles (NEVs) augment the personal transportation system already in place rather than trying to replace it. Consumers can use the NEV for traveling within the immediate area (i.e. for errands or commuting) and their car for longer trips (e.x. vacationing). As cars are at their most efficient at highway speeds and would be replaced at the low speeds at which they are inefficient, NEVs make for a balance between being environmentally friendly and replacing the internal combustion car completely. An example of an NEV for sale today is the Kurrent. Because the average number of travelers for personal automobile trips is 1.6iv, NEVs like the Kurrent save weight and materials by being two person vehicles while still meeting the demand.

Batteries, being such an important part of an electric vehicle, must be carefully chosen for certain specifications. The Lithium-ion battery is a good choice based on its high power-to-weight ratio. There is a risk that lithium based batteries can explode due to the pressure they are under and the amount of energy contained within, but as they all must have restricting circuits the occurrence of such a failure is around three batteries per one million. Other variations of the lithium-ion battery include lithium-polymer (LiPo) and lithium titanate. In LiPo batteries the electrolyte is a polymer, allowing for thinner designs and any shape required. The trade-off is that there is a high internal resistance, commonly combated by using a gel along with the polymer for the electrolyte. Given this drawback, electric vehicles using this technology may do so at a cost to efficiency. Lithium titanate batteries, in development by Altair Technologies, use nanocrystals to increase the surface area of the anode. This, in conjunction with the chemical composition of the anode, provides a lithium ion battery more able to withstand surges of output and input as well as high temperatures. This means that the lithium titanate battery is more durable, has a longer life-span, and can fully charge in about six minutesv.




The Michelin Tweel, an NPT

http://www.gizmag.com/go/3603/picture/7779/


The Non-Pneumatic Tire (NPT) is a recent development currently in the prototype stage. These tries consist of an inner working of compressible spokes surrounded by normal tire tread. The result is a tire that the user will never have to inflate, cannot go flat, and will never experience a blowout. The efficiency and handling of NPTs is comparable to standard radial tiresvi, but at high speeds they experience significant vibrations. As a result they are better suited to lower speed vehicles such as construction equipment and NEVs. Two companies currently developing NPT’s are Resilient Technologies and Michelin. Michelin calls their design the tweel (a combination of tire and wheel), and has displayed prototypes on vehicles from segways and wheelchairs to consumer cars. An environmental advantage of the tweel over radial tires is that the spokes outlast the lifespan of pneumatic tires and can be re-treaded when necessaryvii, using less material.

While the ultimate goal may be to replace all cars with electric vehicles, the infrastructure along with its consumers must be weaned off internal combustion. The first step in doing this is to have NEVs take over where cars are least efficient. To have NEVs succeed in the market, they must perform well by utilizing the most recent developments. Combining these technologies into an NEV would yield an efficient, practical, and advanced vehicle that the market wants and the environment needs.




i Carter, Sarah. “Engine Efficiency, Good or Bad?” 6 June 2005. 23 July 2008.

ii “Daily Passenger Travel.” RITA Bureau of Transportation Statistics. 2002. Research and Innovative Technology Administration (RITA), U.S. Department of Transportation (US DOT). 23 July 2008. < http://www.bts.gov/publications/pocket_guide_to_transportation/2006/html/table_13.html >

iii “Kurrent Facts.” AE American Electric. 2007. American Electric Vehicle Company. 23 July 2008.

iv U.S. Department of Transportation, Federal Highway Administration and Research and Innovative Technology Administration, Bureau of Transportation Statistics, National Household Travel Survey (Washington, DC: 2002).

v Graham-Rowe, Duncan. “Charge a battery in just six minutes.” NewScientist. 7 Mar. 2005. Reed Business Information Ltd. 23 July 2008.

vi Grabianowski, Ed. "How the Tweel Airless Tire Works.” How Stuff Works. 10 May 2007. HowStuffWorks.com. 23 July 2008.

vii   Melanson, Donald. “Michelin's Tweel combination air-less tire and wheel.” Engadget. 5 Jan 2005. Engadget.com. 23 July 2008.

Matthew Elser

 Class of 2011, Department of Mechanical Engineering, Honors Program,

Working under Professor Kenneth Visser








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