from January 2010 ABT

technical report

Electric Drive Choices for Light, Medium and Heavy-Duty Vehicles to Reduce Their Climate Change Impact in Canada

Abstract

The evolution of electric drive technologies from 1988, at the 9th International Electric Vehicle Symposium (EVS9) in Toronto, to 2007 at EVS23 in Anaheim, is described.

Total hybridization of Canada’s fleet of light, medium and heavy duty vehicles would result in greenhouse reductions savings of 30 Mt of CO2E per year, similar to the savings from a 25% reduction in vehicle weight.

Further savings in greenhouse reductions from plug-in hybrids require a battery cost similar to that needed for electric vehicles. Further development of both ultracapacitors and batteries also are needed, as is work on other parts of the electric drive supply chain.

Introduction

This paper examines the impact of hybridization on the potential to reduce greenhouse gases over the full range of road vehicles in Canada. These greenhouse gas (GHG) emissions are directly related to the fossil fuel used.

The three full-cycle GHG studies referred to at the end of this paper tend to treat all hybrids as being equally efficient. Hybrid architectures vary in efficiency and there are other benefits that can accrue from hybridization. Toyota used a series/parallel drive arrangement and Honda used pre-transmission architecture in their first passenger car hybrids in the U.S. in 1999. The "pre-transmission" hybrid has its electric motor between the engine and the transmission. Both companies had enhanced their vehicles with other technologies. Toyota had realized that the engine needed to be less powerful when boosted by an electric motor and used the Atkinson cycle rather than the more powerful, but less efficient, Otto Cycle. Meanwhile Honda used an all-aluminum-bodied vehicle to bring down vehicle weight and fuel consumption. Honda had a battery with half the voltage and capacity of the Toyota battery and used one, rather than two, electric motors. Honda’s later hybrid Civic also played the engine power reduction card by using a 1.3 liter engine rather than the 1.8 liter engine in the regular vehicle.

Honda’s low-cost "pre-transmission" parallel approach is now the route that Volvo (1) is following for their heavy duty truck. A family of "post-transmission" hybrids, where the motor is after the transmission, is used for medium duty trucks and is intermediate in cost between "pre-transmission" and the series/parallel approach.

Canadian On-Road Greenhouse Gas Emissions

The World Energy Council says that in 2000 movement of goods in medium duty and heavy trucks globally made up 38% of road vehicle energy use and light vehicles made up the remaining 62 %.

Table 2.1 presents the greenhouse gas contribution by vehicles in Canada from data published by the Natural Resources Canada (NRCan). The table defines in more detail some vehicles with high impact and some with negligible impact. Vehicles’ distributions across North America will be similar.

In Canada, medium and heavy trucks produce 34.8% of road vehicle greenhouse gas emissions and light vehicles 62.4%. Note that we can say that in Canada motorcycles, school buses, urban transit and inter-city buses make a negligible contribution as they contribute only 2.9% between them. Overall the split is similar to the World Energy figures mentioned above.

Vehicles used both in and between cities require technologies that can operate on highways and in stop-and-go traffic. This group contributed 54% of the road GHG emissions in 2005 and comprises:

Vehicles used primarily in cities operate in stop and go traffic contributed 16.3% of the road GHG emissions in 2005 and comprise:

Vehicles that operate primarily between cities contributed 26.8% of the road GHG emissions in 2005 and comprise:

The Origin of Electric Drive Vehicles

Electric vehicles and series and parallel hybrids date back more than a century. The early hybrids had the ability for their batteries to be externally charged and were generally "plug-in" hybrid electric vehicles or PHEVs. For example Pieper (4) described a parallel hybrid with the electric motor coaxial with the engine, an approach used by Honda today. The large size of electric motors and the low energy density of batteries could not compete with the internal combustion engine. Wakefield (5) summarizes early hybrid projects around the world, and the first he mentions in Canada is a parallel hybrid built by a team led by the University of Toronto’s F.C. Hooper. This was a PHEV and had a 10kWh lead-acid battery.

Electric Drive from EVS9 1988 to EVS23 2007

When the 9th International Electric Vehicle symposium (EVS9) was held in Toronto in 1988, Victor Wouk (6), reviewed the status of hybrids around the world since 1968. One example was a Lucas-Chloride parallel plug-in hybrid described by Harding et al (7). This had a "pure electric" vehicle range and an onboard charger for the lead acid battery.

At EVS9, Adams and Morgan (8) gave a review of battery activities across Canada and predicted that new developments in advanced magnets and materials would usher in a new age for electric and hybrid vehicles. They reported on three lithium battery initiatives in Canada: two decades later, two of the companies continue as Electrovaya and E-One Moli Energy (Canada) Ltd.

Both these companies were at the 23rd International Electric Vehicle symposium (EVS23) held in Anaheim in 2007. E-One Moli now has mass production cell capability and currently uses a manganese dioxide spinel cathode in the cells which are combined into a battery pack with good thermal packaging and controls by Advanced Lithium Power. Remarkably, the key battery technology, nickel metal-hydride, NiMH, that enabled the arrival of the hybrid, was not mentioned at EVS9 although Ovonic Battery Co. had already been demonstrating cells for two years. By the time EVS23 came around, NiMH was the benchmark against which new lithium batteries, ultra capacitors and their combinations were being set.

The Toronto meeting had sparked an electric motor competition, albeit mostly within the U.S. At EVS9, Colorado-based UQM Technologies showed their first brushless DC motor. At the 2007 meeting Jon Lutz presented UQM’s new 150kW brushless permanent magnet motor/controller system which allows the user to change the negative torque to adjust the regenerative braking. In 1988, MIT student James Worden attended with a UQM equipped solar car. Worden went on to develop an efficient and compact AC motor, and the successor to his company was at EVS23 with production versions of his motor in display vehicles.

On the fuel cell front at EVS9, a hybrid metal-air vehicle was displayed which coupled a low voltage stack to a high voltage battery and drive system. This took advantage of the increasing efficiency of DC-DC inverters (9). The lowering of voltage of the "fuel cell" was to prove to be a step towards improved reliability.

Ballard made an early presentation on their solid polymer fuel cell at EVS9 and was also present at EVS23 in the context of drive systems for future hybrid fuel cell buses. Fuel Cells Canada presented the results on five prototype Ford Focus hybrid fuel cell vehicles with a 260-320km (162-200 mile) driving range. These were part of a 30-vehicle fleet delivered by Ford to evaluation programs. Ballard was the supplier of the fuel cell in a plug-in hybrid displayed at the conference, the prototype Ford Edge. With the latter, the 15.6kWh lithium ion (Li-ion) weighs in at 130kg and takes up 5% of the vehicle weight compared with, say, the 2.8% "battery fraction" in the Toyota Prius.

There were light hybrid cars and also heavier hybrids at EVS23. For example, the first production medium-duty shuttle bus eligible for Federal Transit Administration funding was present. Volvo described a less costly pre-transmission hybrid system for a heavy-duty interurban truck that will be in production in late 2009. Volvo’s presenter said that while there would be only a 10% saving of fuel on the highway, implementation would still give the fleet a positive net present value.

Batteries and Ultracapacitors and On Board Energy Management

In 1988 most development effort in North America was focused on the range limitation of electric vehicles and it is only since the launch of the Toyota Prius in 1997 that the key needs of hybrid batteries have been addressed by the automotive community.

The head of the Ford controls group in 2000, Michael Tamor, (10) pointed out that for a hybrid the battery must be efficient, i.e. the losses during charge and discharge must be minimal. This means that the voltage polarization and impedance losses must be small over the required charge rates. Tamor showed that battery efficiency reduction can result in the vehicle range halving. More recently, in 2007, David Checkel reported detailed results on 1992 plug-in hybrids (11). Checkel’s team had measured the variation of the round-trip efficiency as a function of depth of discharge of the battery. The efficiency can be very poor and as a consequence "conventional hybrid" vehicle producers choose to oscillate their hybrid battery around an optimum state of charge.

Table 5.1 (next column) presents targets that the U.S. Department of Energy posted in 2003 for electric and hybrid vehicle batteries. In this table the high "power density" specification of the hybrid is equivalent to Tamor’s efficiency imperative in that it implies low impedance. Goals for plug-in hybrid batteries were published in 2007 by the U.S. Advanced Battery Consortium. Interestingly the calendar life target had risen to 15 years while a minimum round trip efficiency of 90% is specified. Table 5.1 is used because it better illustrates the enormous gap between pure electric and hybrid vehicle battery needs.

The targets for both the power density and partial state of charge cycles, developed after the arrival of the Toyota Prius, are modest compared with the capability of the ultracapacitor which was already well known as something that might be combined with a battery in a managed energy storage pack. (12)

Iacobelli (13) recently reported a higher round-trip efficiency for ultracapacitors of ~97% vs. ~90% for NiMH in hybrid delivery trucks carrying with certain missions both technologies can yield similar fuel savings, even when the energy capacity of the capacitor was only 10% of the battery.

These observations explain the focus by hybrid vehicle producers on excellence in controls and sensors for on-board energy management. Strategies involve, for example, bypassing battery charging when energy can be directly applied to the wheels.

Toyota cashed in on the ability of a hybrid to use a lower power engine in the selection of the Atkinson cycle for the Prius and Honda that used a smaller engine for the hybrid Civic. This power reduction benefit was applied to fuel cell vehicles which are now generally all hybridized. The lower possible stack voltage made possible by efficient inverters has led to improved reliability. A fuel cell does not have to immediately fire up if there is a battery present and it is a lot easier to manage gas flow over a narrow rather than a wide range. Indeed, the fuel cell in the plug-in Ford Edge peaks at only 35kW.

Choosing Technologies for Their Full Cycle Emissions

We can compare hybrids with regular vehicles as the Ford Escape has the same engine size in a hybrid and non- hybrid option. In NRCan Energuide data combined highway/city driving, the all-wheel drive hybrid saves 28.5% fuel and the two-wheel drive saves 32.9%. The Honda Civic saving is 36.6% but the engine size falls from 1.8 to 1.3L.

Today a post-transmission parallel hybrid medium-duty shuttle bus has been independently tested and shows a 30% fuel saving on the New York City Composite driving cycle. Volvo presented a 10% fuel-saving figure for their Class 8 interurban heavy-duty truck.

We can estimate the greenhouse gas savings from hybridization of the vehicle groups discussed in Table 2.1. Let us apply, from hybridization, a 30% fuel saving to the first group, which has combined urban, and highway use, a 30% saving to the second group, which drives primarily in cities and the 10% saving to the third group, i.e. interurban heavy trucks. These savings are presented in Table 6.2.

The savings from complete hybridization of the three groups would have resulted in a combined saving of 32.8 Mt of CO2E in 2005.

Then we can consider the further benefits of plug-in hybrids or electric vehicles. Two recent U.S. studies, (14) and (15), show that with the present power mix across the United States, plug-in hybrids and hybrids offer similar fossil fuel and greenhouse gas saving. In the first, Samaras and Meisterling (2008) suggest that the situation for plug-in hybrids will improve as cleaner power stations come on line but warn that this is a long-term process and that policy is needed for this to happen. In the second study, Williams (2008) concurs and suggests that a carbon-pricing signal is needed.

This result had been anticipated in Canada with a specific version of the GHGenius model (16) which had been extended to plug-in hybrids and pure electric vehicles (17). With the defaults used, PHEVs do better for GHG reductions than hybrids in Quebec, Manitoba and BC.

For the average power mix in Canada for a personal car, when:

These figures are impacted by distance covered. A Prius covering 100,000 km/year, as is common in a taxi fleet, would reduce GHG emissions to 1/5th the cost of the same personal vehicle covering 20,000km/year. Whatever the further GHG benefits there are from plug-in technology in other vehicle classes, the 3.7 Mt for interurban trucks may not be improved on as these vehicles do not have the usage pattern normally considered for plug-in hybrids.

Savings from Reducing Vehicle Mass

We noted that Honda had used an aluminum structure when it introduced its first hybrid. In their press releases they claimed a 40% weight reduction had been attained. Data was earlier derived (18) for the model year 1999 by combining publicly available "Energuide" data provided to Natural Resources Canada (NRCan) by the automotive manufacturers with curb weight data and adding 300 lbs (136 kg) (a figure given by NRCan as the test weight for their data). Though it covered the light vehicles sold in Canada, it is applicable to the U.S. A vehicle mass decrease from 2000kg to 1200kg (a 40% decrease) was shown to reduce fuel consumption on both the City and Highway driving cycles by 40% with new vehicles.

If the hybrid saving above were applied, the residual emissions of the fleet discussed would be approximately 100 Mt of CO2E. Weight reduction could still be pursued to give similar reductions to those attained from hybridization.

In commercial fleets, there are other factors that determine whether a technology will be implemented. These may include maintenance costs, ability to move in a warehouse with no emissions, vehicle resale value, insurability and drivability. With the fraction of vehicles in commercial fleets likely to rise it behooves us to give them early attention. Perhaps the benefits to fleets, which necessarily filter out those technologies that are uneconomic, will then be more easily implemented in personal vehicles.

Conclusions

The combined savings from complete hybridization of small and large cars, passenger light trucks, freight light trucks, medium trucks and heavy trucks would have been approximately 32.8 Mt of CO2E in 2005.

Savings from vehicle weight reduction of the scale implemented on the first Honda Insight hybrid have the potential to be similar to those from hybridization and area applicable across all vehicle classes.

While some of the heavier vehicles would not be feasible as PHEVs due to their usage, if the remainder of the vehicle fleet were PHEV’s it could potentially triple the cost of reducing CO2E unless the battery costs cited fall.

If its costs fall, the battery vehicle will be as common as the PHEV, given its has a similar cost for CO2E reduction.

Recommendation

Work on batteries and on board energy management needs to continue and grow, but Canada could add work on ultracapacitors, electric motors and power conversion hardware which are pieces of the electric drive supply chain.

Acknowledgments

The author thanks colleagues in the electric vehicle drive community for many stimulating discussions. The data weight reduction analysis of 1999 was assembled by Martin Strange.

References

[1] Fitzpatrick, N., "Electric Drive for Climate Change ’The Art of the Soluble’ Report on the Electric Vehicle Symposium (EVS 23) Advanced Battery Technology, February 2008
www.7ms.com/abt/archive/2008/03/index.html

[2] "2000-Energy for Tomorrow’s World-Acting Now!" Word Energy Council Statement

[3] This table is extracted from public data provided by Natural Resources Canada.

[4] Pieper, H., (1905) U.S. Patent 913,846, filed 1905 issued March 2nd 1909

[5] Wakefield, E.H., "History of the Electric Vehicle, Hybrid Electric Vehicles", SAE, 1998

[6] Wouk, V., "Two Decades of Development and Experience with Hybrids", EVS9, Toronto, 1988

[7] Harding, G.G., Phillips, B.L., Hammond, J.E., "The Lucas Hybrid Electric Car" SAE830113,1983

[8] Adams, W.A., Morgan, J.H., "Canadian Electrochemical Power Sources Research and Development for Traction Applications", EVS 9 Toronto, 1988

[9] Parish D.W., Anderson, W.M., Fitzpatrick, N.P., and O’Callaghan, W.B., "Demonstration of Aluminum-Air Fuel Cells in a Road Vehicle", Future Transportation Technology Conference, Vancouver, BC , SAE891690 August, 1989

[10] "Hybrid Vehicles", September 11th-13th, Seminar, Windsor Ontario, 2000

[11] Checkel, D., "Experience with an early PHEV field trial", PHEV2007, Winnipeg, Manitoba, Nov 1-2, 2007

[12] Halliop, W.J., Stannard, J., Fitzpatrick, N.P., "Low Cost Supercapacitors", Third International Seminar on Double Layer and Similar Energy Storage Devices, Dec. 1993

[13] Iacobelli, R., "Hybrid Electric Delivery Vans and Shuttle Buses Utilizing Ultra-Capacitors" Advanced Capacitor World Summit, San Diego, July 14th-16th, 2008

[14] Samaras, C., Meisterling, K., "Life Cycle Assessment of Greenhouse Gas Emissions from Plug-in Hybrid Vehicles: Implications for Policy", Environ. Sci. Technol., 42 (9), pp 3170—3176, 2008

[15] Williams E., "Plug-in and regular hybrids: A national and regional comparison of costs and CO2 emissions", Nicholas School of the Environment at Duke University, November, 2008

[16] http://www.ghgenius.ca/, A model for lifecycle assessment of transportation fuels.

[17] (S&T) 2 Consultants Inc., "GHG Emissions from Sugar Cane Ethanol, Plug-in Hybrids, Heavy-Duty Hybrids and Materials Review", Report to NRCan, January 30, 2006.

[18] Fitzpatrick, N., "Reducing Greenhouse Gas Emissions with Electricity and Electrochemical Products", Canadian Nuclear Society Symposium on Climate Change and Energy Options", Ottawa, November 17-19, 1999.