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August 2006

Opinion: The Rocky Road for Hybrid Vehicles

By James E. Gover

If hybrid vehicles are to be adopted widely to gain the benefits of fuel efficiency, more needs to be done in R&D and in educating the new generation of automotive engineers.


Throughout the Clinton Administration the federal government funded the Partnership for a New Generation of Vehicles (PNGV) program for $1.25 billion [http://greenscissors.org/energy/pngv.htm]. The intent of PNGV was to develop by 2004 an automobile that would travel 80 miles on one gallon of gasoline. Although some government-owned laboratories were recipients of PNGV funds, the majority of the funding went to Ford, General Motors and Chrysler. Neither Toyota nor Honda was eligible to receive PNGV funding.

During the PNGV era, General Motors developed and manufactured approximately 1,000 EV1s, an all electric vehicle that could travel 75 to 150 miles on a full electric charge when it used Ovonic's NiMH battery technology [http://en.wikipedia.org/wiki/General_Motors_EV1]. To the dismay of some, this lease-only vehicle has now been recalled by General Motors and is no longer driven. Despite the ambitions of PNGV and the high expectations of the hydrogen economy, the most fuel-efficient vehicles on the road today are hybrid electric vehicles manufactured by Toyota and Honda.

The major problems with today's hybrids include: (1) At today's gas prices, the additional purchase cost of a full hybrid cannot be justified based on gas savings. An entirely new, cost-effective topology must be developed. (2) Because of the high-density packaging and thermal and electrical complexity of hybrid vehicles, the labor costs of repair are outrageous. (3) The lifetime of today's batteries are so sensitive to state of charge that the battery charge is maintained between 60 and 80 percent of full charge by the vehicle control system; therefore, over one-half the battery capacity cannot be used. This results in large batteries that are too expensive, too heavy and too delicate, and imposes limits on vehicle electric power when climbing a grade. (4) Power losses in the battery, electric motor, generator, and power electronics are so high that liquid cooling is necessary with only the battery amenable to air cooling.

Types of Hybrid Vehicles

Hybrid vehicles have three principal topologies: series hybrid, parallel hybrid and series/parallel hybrid. The last of these is the topology used in the Ford Escape and Toyota Prius.

The plug hybrid is a hybrid electric vehicle that can operate as an electric vehicle (EV) for a range of 40-60 miles powered by a home charger, and then be operated as a hybrid electric vehicle. None are currently in production although many hybrid hobbyists are converting existing hybrid electric vehicles to plug hybrid.

Although between one and three decades from major commercialization, fuel cell vehicles are also likely to be hybrids with either an ultracapacitor or battery in addition to the fuel cell to capture regenerative braking energy. The power electronics in a fuel cell vehicle will be similar to that used in today's hybrid vehicles.

Another characterization of a hybrid electric vehicle is the fraction of total vehicle power provided by the electric drive. When this fraction is near 0.1, the vehicle is said to be a mild hybrid; when it approaches 0.5 or more, the vehicle is said to be a full hybrid. Vehicle fuel efficiency is maximum for a full hybrid. The efficiency savings can range between 20 percent for a mild hybrid and 50 percent or more for a full hybrid. The fuel efficiency improvement accrues from regenerative braking, internal combustion engineer (ICE) turn-off at stops, operation of the Atkinson-Miller cycle ICE in its maximum efficiency torque-speed range, and electric power use at start-up and low speeds.

Federal Policies that Promote Hybrids

Federal R&D programs that have private and public payoff are rare and sometimes distorted; otherwise, we would not read again and again the Tang [http://en.wikipedia.org/wiki/Tang_%28drink%29] and Internet [http://www.cnri.reston.va.us/bios/kahn.html] anecdotes as over-generalizations of the payoff from government-sponsored R&D. As the PNGV program illustrates, federal funding for private sector research and development does not always pay off for the public. Furthermore, it can and often does distort the free market by favoring one company over another or by making the funding recipient dependent upon public funding. (For small businesses, this is termed SBIR addiction.) Instead of benefiting the public by making the market more competitive, federal R&D funding can inhibit competition.

On the other hand, federal funding of the National Renewable Energy Laboratory (NREL) to develop the ADVISOR computer program [http://www.nrel.gov/vehiclesandfuels/vsa/vehicle_simulation.html] and make it available to universities at no cost has made it possible for universities around the world to model and study hybrid vehicles [http://darwin.nap.edu/openbook.php?record_id=9873&page=56]. Many of these studies, some done by undergraduates, have been presented at the IEEE Vehicular Technology Society Power and Propulsion Conference and have facilitated a stream of engineering graduates educated and interested in hybrid vehicle development. However, having experienced success, the federal government licensed this software package to a private company and no longer funds NREL to update the software and add new models of hybrid vehicle subsystems.

Another public program that has promoted hybrid electric vehicles has been the tax rebate. This rebate has encouraged early technology adopters to purchase hybrids and helped create a market for manufacturers when manufacturing costs probably exceeded sale price. This program should be continued for at least two more years, but should eventually be discontinued as production scale and improved manufacturing technologies make hybrid vehicles more cost-competitive in the marketplace.

New Federal Programs

  1. The federal government should fund a major computer modeling and packaging software development package at NREL and other federal laboratories with expertise in hybrid vehicle system modeling. This software package should include all of the major components of the hybrid drive train, electrical phenomena and thermal phenomena so that university students can experiment with hybrid packaging and optimization as well as model existing hybrid vehicles, identify design flaws and search for cost reductions. This software development effort should include motors, generators, ICE maps, power converters, power inverters, power split devices, electronic controls, batteries and ultracapacitors and be adaptable to a wide range of design options including regenerative braking.

    In addition, it should include working models of all existing hybrid drive train components currently available in the marketplace and it should include economics, temperature-dependent electrical models, heat transfer, temperature-dependent reliability and thermal cycling models.

    The motivation behind this recommendation is to get as many interdisciplinary university professors and students as practical working on the development of hybrid vehicles; therefore, the lead federal laboratory should maintain and update this software and make it available at no cost to universities and companies. Not only will this effort result in improved technology, it will provide a stream of graduates prepared to work on the development of hybrid vehicles, and it will develop expertise that can easily transition to fuel cell vehicle development should the cost of fuel cells be reduced to a practical level for transportation applications.

  2. The federal government should sponsor R&D at federal laboratories and universities to: (1) reduce the initial and maintenance costs of hybrid vehicles; (2) increase the reliability of all of hybrid drive-train components to a 200,000-mile life; and (3) reduce hybrid vehicle manufacturing costs. However, for this research to be applied and useful, universities must have up-to-date hybrid vehicle laboratories.

    Therefore, to promote future improvements in hybrid vehicle designs, the federal government should set aside $750,000 each for 100 universities to develop hybrid vehicle education, research and development programs complete with up-to-date hybrid vehicle laboratories. A condition for a university to receive this funding is that its students and faculty participate in the hybrid vehicle competition described in the following recommendation.

  3. As a result of the resounding success that the DARPA Grand Challenge competition has had on autonomous vehicles, it is recommended that a similar program be initiated for hybrid electric vehicles. However, the emphasis would not be on software and the ability of a vehicle to traverse a course; instead, teams would be judged based on the ratio of fuel efficiency and hardware costs. The goal of the competition is to inspire applied interdisciplinary research that leads to increased fuel economy and lower hardware costs. Like the Grand Challenge, the competition bar would be raised each year.

To fund these programs, it is recommended that a carbon tax be levied on all liquid fuels. Until this happens, a significant fraction of the American public will remain insensitive to fuel economy, declare global warming a myth and continue to purchase large pick-up trucks and sport utility vehicles lacking hybrid or other technology for energy conservation. To avoid handicapping small businesses that require trucks for business purposes, a fuel tax rebate could be made available to small businesses.



Dr. James E. Gover, IEEE Fellow, is Professor of Electrical Engineering, Kettering University, and a former Congressional Fellow for IEEE-USA. He is presenting the tutorial, Energy Alternatives, at the 2006 IEEE VPPC, held in Windsor, England. The opinions expressed are his own. Comments may be submitted to todaysengineer@ieee.org.

Copyright © 2007 IEEE