6
Hybrid Power Trains

INTRODUCTION

Hybrid vehicles achieve reduced fuel consumption by incorporating in the drive train, in addition to an internal combustion (IC) engine, both an energy storage device and a means of converting the stored energy into mechanical motion. Some hybrids are also able to convert mechanical motion into stored energy. In its most general sense, the storage device can be a battery, flywheel, compressible fluid, elastomer, or ultra capacitor. The means of converting energy between storage and mechanical motion is through the use of one or more motors/generators (e.g., electric, pneumatic, hydraulic). In motor mode, these devices convert stored energy into mechanical motion to propel the vehicle, and in generator mode, these devices convert vehicle motion into stored energy by providing part of the vehicle braking function (regeneration). Similarly, a fuel cell vehicle is also a hybrid in which the internal combustion engine is replaced by the fuel cell, but this system will likely need supplemental energy storage to meet peak power demands and to allow the fuel cell to be sized for the average power requirement.

In this chapter, hybrid vehicle designs employing an internal combustion engine and battery-energy storage are considered. Battery electric and fuel cell vehicles (BEVs and FCVs) are also briefly discussed as other alternative power trains.

Hybrid electric vehicles incorporate a battery, an electric motor, and an internal combustion engine in the drive train. In its most effective implementation this configuration permits the IC engine to shut down when the vehicle is decelerating and is stopped, permits braking energy to be recovered, and permits the IC engine to be downsized and operated at more efficient operating points. It should be emphasized that the benefits of hybrids are highly dependent on the drive cycle used to measure fuel consumption. For example, a design featuring only idle-stop operation, which shuts off the internal combustion engine when the vehicle is stopped, will demonstrate a large improvement on the city cycle portion of the Federal Test Procedure (FTP), where stop-start behaviors are simulated, but virtually no improvement on the highway cycle.

In addition to the introduction of an electric motor, hybrid designs may include the functions of idle-stop and regenerative braking, and the IC engine is frequently downsized from that in its equivalent conventional vehicle. As shown in Table 6.A.1 in the annex at the end of this chapter, for a hybrid vehicle, these operational and physical changes alone or in combination can result in an increase in fuel economy (mpg) of between 11 and 100 percent or a decrease in fuel consumption (gallons per 100 miles driven) of between 10 and 50 percent, depending on the vehicle class, as is discussed below in this chapter. Hybrid vehicles are the fastest-growing segment of the light-duty vehicle market, although they still make up less than 3 percent of the new car market in the United States.

HYBRID POWER TRAIN SYSTEMS

As stated above, hybrid vehicles are defined as having an internal combustion engine and one or more electric machines that in some combination can provide tractive force to propel the vehicle. An exception to this definition is the simple idle-stop design, which provides no electrically derived tractive force. Depending on the architectural configuration of the motors, generators, and engine, hybrid designs fall into three classes—parallel, series, and mixed series/parallel. The third design is commonly known as power split architecture. Schematics of these architectures are shown in Figures 6.1, 6.2, and 6.3. Within each class there are variations of implementation. Broadly defined, the series hybrid uses the internal combustion engine for the sole purpose of driving a generator to charge the battery and/or powering an electric drive motor. The electric motor provides all the tractive force. Energy flows from the IC engine through the generator and battery to the motor. In the parallel and mixed series/parallel designs, the IC engine not only charges the battery but also is mechanically connected to the wheels and, along with the electric motor, provides tractive power.



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6 Hybrid Power Trains INTRODUCTION stop-start behaviors are simulated, but virtually no improve- ment on the highway cycle. Hybrid vehicles achieve reduced fuel consumption by In addition to the introduction of an electric motor, hybrid incorporating in the drive train, in addition to an internal designs may include the functions of idle-stop and regen- combustion (IC) engine, both an energy storage device and a erative braking, and the IC engine is frequently downsized means of converting the stored energy into mechanical motion. from that in its equivalent conventional vehicle. As shown Some hybrids are also able to convert mechanical motion into in Table 6.A.1 in the annex at the end of this chapter, for a stored energy. In its most general sense, the storage device hybrid vehicle, these operational and physical changes alone can be a battery, flywheel, compressible fluid, elastomer, or in combination can result in an increase in fuel economy or ultra capacitor. The means of converting energy between (mpg) of between 11 and 100 percent or a decrease in fuel storage and mechanical motion is through the use of one or consumption (gallons per 100 miles driven) of between 10 more motors/generators (e.g., electric, pneumatic, hydraulic). and 50 percent, depending on the vehicle class, as is dis- In motor mode, these devices convert stored energy into me- cussed below in this chapter. Hybrid vehicles are the fastest- chanical motion to propel the vehicle, and in generator mode, growing segment of the light-duty vehicle market, although these devices convert vehicle motion into stored energy by they still make up less than 3 percent of the new car market providing part of the vehicle braking function (regeneration). in the United States. Similarly, a fuel cell vehicle is also a hybrid in which the in- ternal combustion engine is replaced by the fuel cell, but this HYBRID POWER TRAIN SYSTEMS system will likely need supplemental energy storage to meet peak power demands and to allow the fuel cell to be sized for As stated above, hybrid vehicles are defined as having the average power requirement. an internal combustion engine and one or more electric ma- In this chapter, hybrid vehicle designs employing an chines that in some combination can provide tractive force internal combustion engine and battery-energy storage are to propel the vehicle. An exception to this definition is the considered. Battery electric and fuel cell vehicles (BEVs simple idle-stop design, which provides no electrically de- and FCVs) are also briefly discussed as other alternative rived tractive force. Depending on the architectural configu- power trains. ration of the motors, generators, and engine, hybrid designs Hybrid electric vehicles incorporate a battery, an elec- fall into three classes—parallel, series, and mixed series/ tric motor, and an internal combustion engine in the drive parallel. The third design is commonly known as power split train. In its most effective implementation this configura- architecture. Schematics of these architectures are shown in tion permits the IC engine to shut down when the vehicle Figures 6.1, 6.2, and 6.3. Within each class there are varia- is decelerating and is stopped, permits braking energy to tions of implementation. Broadly defined, the series hybrid be recovered, and permits the IC engine to be downsized uses the internal combustion engine for the sole purpose of and operated at more efficient operating points. It should be driving a generator to charge the battery and/or powering emphasized that the benefits of hybrids are highly dependent an electric drive motor. The electric motor provides all the on the drive cycle used to measure fuel consumption. For tractive force. Energy flows from the IC engine through the example, a design featuring only idle-stop operation, which generator and battery to the motor. In the parallel and mixed shuts off the internal combustion engine when the vehicle is series/parallel designs, the IC engine not only charges the stopped, will demonstrate a large improvement on the city battery but also is mechanically connected to the wheels cycle portion of the Federal Test Procedure (FTP), where and, along with the electric motor, provides tractive power. 84

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85 HYBRID POWER TRAINS Hybrid vehicles are further differentiated by the relative Parallel sizes of the IC engine, battery, and motor. Some of the more common variants of these broad classes are described in Wheels the following paragraphs. In all cases an economically and Motor/ Engine Transmission functionally significant component of the system is the power Generator electronic subsystem necessary to control the electrical part Differential of the drive train. The hybridization of diesel (compression ignition; CI) vehicles is expected to have somewhat lower efficiency ben- Electronics Wheels efits than hybridization of gasoline vehicles, in part because conventional CI vehicles already exhibit lower fuel consump- Battery tion than comparable gasoline vehicles. Further, CI vehicles Electrical link also have very low fuel consumption at idle, making the Mechanical link benefits of idle-stop less attractive. Conventional CI power trains are more expensive than their gasoline counterparts FIGURE 6.1 Schematic of parallel hybrid power train configuration. (see Tables 5.4, 5.5, and 5.6), which, when added to the cost of hybridization, makes a CI hybrid power train very expensive for the additional fuel consumption reductions Figure 6-1 new.eps provided over and above just moving to a hybrid or CI power redrawn, vector train alone. As a result, it is unlikely that original equipment manufacturers (OEMs) will offer a wide array of CI hybrids. The most likely levels of CI hybridization will be idle-stop and, perhaps, some mild hybrids. Idle-stop will not provide much fuel consumption reduction on the city driving portion of the FTP test cycle, upon which the judgments in this report are based. However, OEMs may still offer such technologies since they provide in-use fuel consumption reductions. In Europe, a number of new diesel hybrid vehicles have been announced for production in 2010 or 2011, especially for larger and heavier vehicles (e.g., Land Rover). There are numerous hybrid vehicles now in production, and the committee believes it is more representative to quote actual data rather than analyze the effectiveness of each FIGURE 6.2 Schematic of series hybrid power train configuration. design to estimate fuel consumption benefits. This is prefer- Figure 6-2.eps able to having the committee and its consultants estimate bitmap, consists of slices fuel consumption benefits through simulations. It is assumed that the production vehicles are designed to meet customer expectations, including acceleration, passenger space, and adequate trunk space. The average fuel consumption of pro- duction hybrid HEVs was determined from fuel economy data supplied by Oak Ridge National Laboratory and in- cluded as Table 6.A.1 in the annex at the end of this chapter. Belt-Driven Alternator/Starter In the belt-driven alternator/starter (BAS) design, some- times known as a micro or mild hybrid, the starter and generator of a conventional vehicle are replaced by a single belt- or chain-driven larger machine, capable of both starting FIGURE 6.3 Schematic of power-split hybrid power train configuration. the engine and generating electric power. In some BAS de- signs, in addition to the new belt-driven starter generator, the original geared-to-flywheel starter is retained for cold starts. Fuel consumption is reduced by turning off and decoupling the engine at idle and during deceleration. In some designs, particularly those that have replaced the belt with a chain for

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86 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES increased torque transmission, both electric vehicle launch architectural approaches to achieving a full hybrid, the three and some degree of braking energy regeneration are possible. in current production being the integrated starter/generator This mode of operation is known as idle-stop, and while (ISG) or integrated motor assist (IMA), the power split, and not technically qualifying as a hybrid since the motor/ the two-mode. These are all parallel or power split designs. generator provides no or little tractive power, it is included The HEV may also provide a limited electric-only range if in this chapter for completeness. Idle-stop designs reduce the battery capacity and motor size are sufficient. fuel consumption by up to 6 percent in urban driving with SI The ratio of electric to mechanical power provided for engines (Ricardo, Inc., 2008). For SI engines having variable propulsion of an HEV varies with driving conditions and valve timing to reduce inlet throttling loss the benefit may the state of charge of the battery. This operational feature is be less than 6 percent. For CI engines, the benefit of idle- accomplished with sophisticated computer controls. Com - stop drops to about 1 percent because CI engines are more mercially available HEVs such as the Toyota Prius, Honda efficient at idle due to their lack of inlet throttling. Civic, Nissan Altima, or Ford Escape can support a limited The BAS design is not quite as simple as it first appears. all-electric range at limited speeds. In these vehicles the Maintaining hydraulic pressure in the automatic transmission battery is operated in a charge-sustaining (CS) mode; that is necessary for smooth and rapid restart, and safety issues is, the state of charge (SOC) of the battery is allowed to related to unexpected restart must be considered. The com- vary over a very narrow range, typically 15 to 20 percent, pany ZF has designed a transmission that provides a means to ensure long battery life. The IC engine operates over a of maintaining hydraulic pressure using a “hydraulic impulse narrow speed/load range to improve efficiency, and regen- storage device” that appears to address the transmission eration is employed to recover braking energy. According problem (Transmission Technology International, 2008), to Toyota, as shown in Figure 6.4, the contributions of stop- which is also addressed in existing designs by an electrically start, regenerative braking, and engine modifications to fuel driven hydraulic pump. consumption improvements are approximately 5, 10, and 30 percent, respectively. Full Hybrid ISG/IMA Hybrid The full hybrid (HEV) has sufficient electrical energy storage and a powerful enough electric motor to provide In the ISG/IMA design, the starter and generator are significant electrical assist to the IC engine during accel- replaced by a larger electrical machine connecting the en- eration and regeneration during braking. There are several gine and transmission. These vehicles generally use a larger Figure 6-4.eps FIGURE 6.4 Individual technology contributions to fuel consumption in hybrid electric vehicles. SOURCE: Fushiki and Wimmer (2007). Reprinted with permission. bitmap

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87 HYBRID POWER TRAINS Series Hybrid battery and a higher voltage (e.g., 140 V) than the BAS. Additionally, the motor/generator and battery are power- The series HEV is configured with the engine driving ful enough to provide electrical launch from a stop and the a generator providing electric power to charge the bat- ability to support some degree of electric-only travel. In its tery. The wheels are driven by an electric motor powered simplest form the ISG is mechanically fixed to the IC engine from the battery. The only function of the IC engine is to crankshaft, but in some designs a second clutch isolates the charge the battery while driving. Because there is no me- engine and the electrical machine to enable larger regen- chanical connection between the IC engine and the wheels, eration of braking energy (Dan Hancock, General Motors, the motor and the battery must be sized for the vehicle’s personal communication, November 30, 2007). When incor- full torque and power requirements. The advantages of this porating an effective regenerative braking system, the ISG configuration are that a smaller engine can be used since it hybrid achieves a fuel consumption reduction of 34 percent is not required to provide the power needed for accelera- in the combined driving cycle, as demonstrated by the Honda tion, and the engine can be optimized with respect to fuel Civic. A part of the improved fuel consumption comes from consumption. At present the only OEM planning a series vehicle modifications, including the use of a smaller, more hybrid is GM, which is proposing it as a plug-in hybrid efficient SI engine. electric vehicle (PHEV). Power-Split Hybrid Plug-In Hybrid The power-split hybrid design, typified by the Toyota The principal difference between the previously described Prius, the Ford Escape, and the Nissan Altima, incorporates HEV variants and the PHEV is that the latter is fitted with a differential gear set that connects together the IC engine, a larger battery that can be charged from the electric utility an electrical generator, and the drive shaft. The drive shaft grid (“plugged in”) and that operates in a charge-depleting is also connected to an electric motor. This mechanical con- mode; that is, the state of charge of the battery is allowed figuration incorporating the addition of a generator provides to vary over a much larger range, 50 percent being typically the flexibility of several operational modes. In particular the proposed. The significant fuel consumption benefit is ob- wheels can be driven by both the IC engine and the electric tained during urban driving when the vehicle can be driven motor, with the motor’s power coming from the generator, on electric power only. Once the all-electric range has been not the battery. The car is thus driven in both series and achieved and the battery discharged to its lowest allow- parallel modes simultaneously, which is not a possible mode able state of charge, the vehicle is operated in the charge- for the ISG design. This operational mode allows the IC sustaining mode and differs little from the HEV. A small engine operation to be optimized for maximum reduction in industry has developed around the conversion of the Prius fuel consumption. The vehicles that use this power split de- power-split HEVs to PHEVs by supplementing the battery sign show a range of fuel consumption reduction from 10 to and modifying the control electronics. 50 percent. The low end of this range is the Toyota Lexus, the PHEVs require a much larger battery than other hybrids design of which is optimized for performance, not low fuel (4 to 24 kWh)1 depending on the desired electric-only consumption. In Chapter 9, where the committee estimates range. There has been much activity related to PHEVs since fuel consumption benefits for vehicle classes, the Lexus is the committee inaugurated its work in 2007. The General not used in the range of benefits for the power split design. Motors Volt mentioned above is planned for introduction in This gives the fuel consumption benefits from the power split 2010 provided that a suitable battery is developed (Tate et design a range of 24 to 50 percent. al., 2009). The Volt currently is expected to be launched late General Motors (GM) is working with BMW and Chrysler in 2010 as a 2011 model. Toyota has also announced plans on a different split hybrid architecture that uses the so-called for a plug-in hybrid for 2011, although it will be built on a two-mode system (Grewe et al., 2007). This also splits the Prius platform using its power split architecture (Fushiki power flow from the engine but uses more clutches and gears and Wimmer, 2007). In addition to the Volt and the Prius, to match the load to the drive and minimize electrical losses. the Volkswagen Golf PHEV is expected in 2010 and Ford’s The claim is that by using multiple gears the drive is more Escape SUV PHEV is due out to the general public in 2012. efficient in real-world driving situations and reduces fuel A PHEV in China went on sale to the public in China early consumption when towing a trailer or driving at high speed. in 2010. Toyota is using a similar approach with one or two gears in While the micro and ISG hybrids offer some improve- its latest hybrid systems. The fuel consumption reduction ment in fuel consumption for a relatively modest cost, it is for the two-mode power split design, characterized by the Chevrolet Tahoe and Saturn Vue, ranges from 25 to 29 per- 1 The cent. However, the committee thinks that other implementa- Energy Independence and Security Act of 2007 defines a plug-in hybrid as a light-, medium-, or heavy-duty vehicle that draws motive power tions of the two-mode system could provide a maximum fuel from a battery with a capacity of at least 4 kilowatt-hours and can be re- consumption benefit of about 45 percent. charged from an external source of electricity.

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88 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES the power-split HEV and PHEV architectures that promise the Tesla S, with a range of 160, 230, or 300 miles, depending on optional battery size.4 Nissan has also announced produc- a significant improvement. The PHEV also offers the long- term potential for displacing fossil fuels with other primary tion of its Leaf EV, a five-passenger car with a range of 100 miles.5 This vehicle has a Li-ion battery with a total storage energy sources such as nuclear or renewable sources of electricity, depending on the fuel source of the electric grid capacity of 24 kWh. from which the PHEV draws electricity. Within the horizon of this study, the most likely future for large numbers of battery electric vehicles in the United States is in the limited-range, small-vehicle market. Range Battery Electric Vehicles extended electric vehicles (hybrids and PHEVs) are more The prospect for widespread introduction of full- likely to satisfy the electricity-fueled full-performance— performance all-electric vehicles depends on significant market, from both cost and technological considerations, advancements of the battery technologies discussed above, over the next 15 years. and the commercial viability of these vehicles depends on a battery cost breakthrough. Advances in electric motors, BATTERY TECHNOLOGY power electronics, and batteries for automotive applications, which have resulted from the development and production In spite of the significant progress that battery technology of hybrid vehicles, have renewed interest in the development has experienced in the last 20 years, the battery is still the of battery electric vehicles. However, the cost, low energy most challenging technology in the design of hybrid vehicles. density, and required charging time of batteries will continue Figure 6.5 illustrates the dramatic difference between the en- to constrain the introduction of BEVs. The high low-speed ergy densities of today’s commercial batteries and gasoline, torque performance of electric motors gives the BEV a diesel fuel, ethanol, compressed natural gas, and hydrogen. potential acceleration advantage over conventional internal At the time of this report, all production hybrid vehicles used combustion engine-powered vehicles, and this can be an at- batteries employing nickel-metal-hydride (NiMH) chemis- tractive feature for some customers try. It is anticipated that the NiMH battery will be replaced A review of zero-emission vehicle technology com- by Li-ion batteries in the near future. The acceptability of missioned by the California Air Resources Board (CARB) today’s hybrid vehicles has been shown to be strongly de- concluded that commercialization (tens of thousands of pendent on the price of gasoline, as evidenced by the rapid vehicles) of full-performance battery electric vehicles would growth of hybrid sales in 2008, when gasoline prices were not occur before 2015 and that mass production (hundreds high, and the fact that hybrid sales dropped dramatically in of thousands of vehicles) would not occur before 2030 early 2009 when prices returned to lower values. The key to (Kalhammer et al., 2007). These projections were based on improving the competitive position of hybrid vehicles of the the continued development of lithium-ion (Li-ion) battery HEV and PHEV types is the commercial development of technology leading to reduced cost, higher energy densi- batteries with parameters that are substantially better than ties, and reduced charging times, all of which allow greater those of today’s batteries, leading to reduced cost and size. range. They pointed to a possible role for a limited range, The required parametric improvements are as follows: city electric vehicle (CEV), which could meet the require- ments of a majority of household trips. However, recent BEV • Higher cycle life at increased SOC variation, introductions suggest that progress in the technology and • Higher energy density, acceptance of Li-ion batteries may be more rapid than the • Higher power density, and CARB study concluded. • Lower cost. Early commercial application of Li-ion battery technology to vehicles includes the Tesla Roadster, a high-performance Figure 6.6 shows the desirable characteristics of batteries sports car. This vehicle, of which about 1,000 have been suitable for the HEV, the PHEV, and the all-electric (EV or sold, has a fuel consumption of 0.74 gal/100 miles (energy BEV) vehicles. The HEV uses electric propulsion primarily equivalent basis, EPA combined city/highway).2 The manu- as an assist to the IC engine, thus requiring a battery with facturer claims a range of 244 miles (also EPA combined a high power capability but relatively little energy capacity, city/highway) and a useful battery life of more than 100,000 i.e., a high power to energy (P/E) ratio. To preserve battery miles.3 The base price of $128,000 indicates the continuing life and maintain the capacity to recover charge through problem of battery cost when used in near full-performance regenerative braking, the battery is cycled over a relatively vehicles. Tesla has announced that it will produce and sell, small state of charge. This mode of operation is known as at about half the price of the Roadster, a five-passenger BEV, charge sustaining (CS). The PHEV is expected to provide 2 C alifornia Air Resources Board (2009), available at http://www. 4 See http://news.cnet.com/tesla-motors-ceo-model-s-is-cheaper-than- driveclean.ca.gov. 3 Tesla Motors (2009), available at http://www.teslamotors.com/display_ it-looks/. 5 See http://www.nissanusa.com/leaf-electric-car/tour.jsp#/details. data/teslaroadster_specsheet.pdf; IEEE Vehicular Technology, March 2010.

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89 HYBRID POWER TRAINS FIGURE 6.5 Volumetric and gravimetric energy densities of different energy storage mechanisms. SOURCE: Fushiki and Wimmer (2007). Reprinted with permission. Figure 6-5.eps bitmap FIGURE 6.6 Energy capacity, state-of-charge variation, and relative power density to energy density ratios for batteries applicable to full- hybrid (HEV), plug-in hybrid (PHEV), and all-electric (EV) vehicles. The units of P/E are kW/kWh. SOURCE: Amine (2007). some degree of electric-only range. Its battery must therefore HEV battery, but because of the higher energy requirement, contain sufficient energy to provide this range. The battery the P/E ratio is smaller. The BEV requires an even higher en- may be allowed to expend all of its stored energy to achieve ergy capacity battery than the PHEV, the value depending on this range goal, in which case the battery is said to be oper- the desired driving range. Since the BEV has no IC engine, ated in the charge-depleting (CD) mode. The power require- its battery cannot be charged during driving, and therefore it ment of this battery is not much different from that of the cannot operate in a CS mode. In all cases the SOC variation

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90 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES is limited to a specified range by the vehicle manufacturer to shown in Table 6.1. The column heads denote the com - preserve battery cycle life. Figure 6.6 shows typical ranges mon abbreviation for the different chemistries: NCA for the HEV, PHEV, and BEV. Thus the usable energy is less (nickel-cobalt-aluminum), LFP (lithium-iron-phosphate), than the battery rated (or “nameplate”) capacity. MS (manganese-spinel), MNS (manganese-nickel-spinel), Despite substantial improvements in the packaging and a nd MN (manganese-nickel). The first entry gives the performance of lead-acid batteries, their energy and power detailed composition of the anode and cathode materials, densities are still considerably inferior to those of NiMH. with the positive (cathode) material shown first. The second And while other chemistries, like Li-air, have theoretically entry gives the gravimetric energy density of the chemistry better performance than Li-ion, their development is not at a in milliampere-hours/gram (mAh/g), the third entry shows stage where one could envision them in practical automotive the open-circuit terminal voltage when the cell is 50 per- applications within the timeline of this study. Therefore the cent depleted (50 percent state of charge), and the fourth committee considers only NiMH and Li-ion as chemistries entry gives the area specific impedance (ASI) as measured of interest here. during a 10-second pulse at the 5C rate, which is indica - tive of the battery’s ability to provide power necessary for acceleration. The relative safety of the different chemistries NiMH Batteries is given in the fifth entry. The safety of using Li-ion bat - The highest-performance battery currently available in teries has received considerable attention since the 2006 commercially significant quantities for HEVs and PHEVs recall of Li-ion batteries used in laptops. In some of the uses NiMH chemistry. Despite significant improvements in chemistries, particularly those using a cobalt (Co)-based lifetime and packaging, these batteries are still expensive, cathode, failure can occur due to overheating or separator heavy, and in application are restricted to a SOC range of failure. This problem is well known, and safety is a char- about 20 percent to preserve battery cycle life. Because acterizing parameter common to all the Li systems. Some of their relatively poor charge/discharge efficiency, special manufacturers believe they can solve the safety problem c onsideration must be given to their thermal manage - through careful monitoring and charge control. Relative ment. The NiMH chemistry also exhibits a high rate of cost among the different Li chemistries is shown in the self-discharge. seventh entry, although at this time the absolute cost of all The most technically advanced NiMH battery used in the is considerably higher than the cost for NiMH. The last Toyota Prius has a weight of 45 kg and an energy capacity of entry in Table 6.1 indicates the state of the technology. Pilot 1.31 kWh. This results in a usable energy of approximately scale indicates that cells are currently being manufactured 0.262 kWh when applied with a SOC variation of 20 percent. in sufficient quantities for testing in vehicle fleets of limited size. Development means that the chemistry is well con - trolled, but the production of practical cells is anticipated Li-Ion Batteries and under development. Research indicates just that—the The most promising battery technologies are those chemistry is still a subject of research, and the production employing various Li-ion chemistries. Characteristics of of cells using the chemistry has not been demonstrated to the more common lithium-based cell compositions are an extent sufficient to anticipate their use. TABLE 6.1 Comparative Characteristics and Maturity of Lithium-Ion Battery Chemistries Battery System NCA-Graphite LFP-Graphite MS-TiO MNS-TiO MN-Graphite Electrodes Positive LiNi0.8Co 0.15Al 0.05O2 LiFePO4 LiMn2O4 LiMn1.5Ni0.5O4 Li1.2Mn0.6Ni0.2O2 Negative Graphite Graphite Li4Ti5O12 Li4Ti5O12 Graphite Capacity, mAh/g Positive 155 162 100 130 275 Negative 290 290 170 170 290 Voltage, 50% 3.6 3.35 2.52 3.14 3.9 state of charge ASI for 10-s, 25 25 9.2 100 25 Safety Fair Good Excellent Excellent Excellent Life potential Good Good Excellent Unknown Unknown Cost Moderate Moderate Low Moderate Moderate Status Pilot scale Pilot scale Develop. Research Research NOTE: NCA, Ni-Co-Al; LFP, Li-Fe-PO4; MS-TiO, Mn(Spinel)-Ti-O; MNS-TiO, Mn-Ni(Spinel)-Ti-O; MN-Graphite, Mn-Ni-Graphite.

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91 HYBRID POWER TRAINS POWER ELECTRONICS The relative gravimetric energy densities of Li-ion, NiMH, and Pb-acid are approximately 4, 2, and 1, respectively. An The term power electronics refers to the semiconductor additional advantage of the Li systems is their high cell poten- switches and their associated circuitry that are used to tial, approximately 3 times that of NiMH. This means that 66 control the power supplied to the electrical machines or percent fewer Li-ion cells are required to achieve a given bat- to charge the battery in an HEV or PHEV. For purposes of tery voltage. The ecologically benign materials in the Li-ion driving electric motors these circuits function as an inverter, systems are also an advantage. A disadvantage of Li-ion cells changing the battery direct voltage into an alternating volt - is that the requirement for cleanliness in the manufacturing age of controlled amplitude and frequency. For charging environment is considerably more severe than for NiMH the propulsion battery they function as a controlled recti - cells (Zempachi Ogumi, Kyoto University, personal commu- fier, changing the ac voltage of the machine to the dc value nication, December 8, 2008). This increases manufacturing required by the battery. The direction of power flow is either costs. Another critical issue is how the performance of Li-ion into or out of the battery, depending on vehicle mode of batteries is impacted by low and high temperatures (Amine, operation. Plug-in hybrids also require power electronic 2007; Reilly, 2007; Andermann, 2007). circuits to convert the ac main voltage to a precise dc voltage The first three columns in Table 6.1—NCA-Graphite, to charge the propulsion battery. LFP-Graphite, and MS-TiO—represent the most promising Power electronic circuits known as dc/dc converters Li-ion systems currently under development. The NCA- change the propulsion battery dc voltage to the dc voltage ap- graphite chemistry is used by JCS/SAFT in its VL41M propriate to charging the accessory battery (i.e., the standard module that has undergone dynamometer testing in a Toyota 12 V battery retained to power vehicle accessories). A dc/dc Prius at Argonne National Laboratories (ANL) (Rousseau converter may also be used to increase system efficiency et al., 2007). The lithium-iron phosphate (LFP) system is by stepping up the propulsion battery voltage before it is currently receiving a great deal of attention because of its supplied to the inverter. The latest Toyota Prius uses such stability, potentially lower material costs, and its application a design. in power tools. Its development is being aggressively pursued Both inverter and dc/dc converter technologies are well by A123 and Enerdel. The manganese-spinel-lithium-titanate developed for industrial and other applications. The special system (MS-TiO) is the safest of any being studied because problems for hybrid vehicles are cost, cooling, and pack- of the mechanical stability of the spinel structure, but its cell aging. Although the ambient environment for automotive voltage is considerably lower than those of the NCA and electronics is much harsher than that in industrial or com- LFP systems. However, it has the highest charge/discharge mercial applications, the cost in the automotive application is efficiency, and it is predicted to be the lowest-cost system. required to be lower. Figure 6.7 illustrates the improvement To put in perspective the merits of the Li-ion battery rela- over a 10-year period in the volumetric power density of the tive to NiMH, consider the requirements for a 20-mile all- motor drive inverter for Toyota’s hybrid product line. The electric range PHEV. According to an ANL study (Nelson et significant improvement after 2005 is due in large measure al., 2007), which assumed a 100 to 10 percent SOC range, the to the increased switching frequency made possible by the required battery capacity for its assumed vehicle is 6.7 kWh. higher-speed motor and higher voltage introduced in 2005. For an MS-TiO battery the calculated weight is 100 kg. If These changes reduce the physical size of magnetic com- an NiMH battery were used, with a SOC range of 20 to 80 ponents and improve the utilization of silicon devices. Both percent and a gravimetric energy density one-half that of these consequences result in improved packaging density. the MS-TiO system, the committee estimates that it would require a capacity of 10.35 kWh and weigh 300 kg. ROTATING ELECTRICAL MACHINES AND The needs of HEVs and PHEVs are quite distinct, as CONTROLLERS shown in Figure 6.6. HEVs need high power density and long cycle life over a very small excursion of the SOC. For With the possible exception of microhybrids, all vehicles example the Prius battery has a nominal rating of 1.3 kWh use permanent magnet alternating current motors. Since the but it uses only 260 Wh in +/-10 percent excursions around battery capacity is the key limitation for hybrid vehicles, 50 percent SOC. On the other hand, the larger energy re- electrical machine efficiency is of paramount importance. quirement of the PHEV argues for a battery with a higher Most systems employ “buried magnet” rotating machine energy rating and the capability of deeper cycling. The Volt, configurations with expensive rare-earth high-strength mag- the PHEV being developed by GM, uses a 16-kWh battery nets. GM and Honda are using flat wire for the armature to meet its advertised all-electric range of 40 miles. This winding to increase efficiency. Although rectangular conduc- is a substantial challenge to achieve at acceptable weight, tors are common for large machines, their use in relatively volume, and cost. The Li-ion chemistry comes closest to small machines shows the extent to which manufacturers are meeting it, given the present state of battery development. It going to get better efficiency. Rotating machine technologies should be noted that the Volt is designed to use only 8 kWh and designs are well developed, and the automotive applica- by operating from 80 percent to 30 percent SOC.

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92 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES FIGURE 6.7 Evolution of hybrid drive inverter volumetric power density. SOURCE: Fushiki and Wimmer (2007). Figure used with permis - sion of Toyota. Figure 6-7.eps low-resolution bitmap tion challenge is to lower their manufacturing cost. Because achieved by increasing the speed of the electric motor in its rotating machines are such a mature component, the cost of hybrid vehicles. their manufacture in high volumes is driven principally by Computers have been used to control emissions and op- the cost of materials. Thus their cost is relatively unrespon- timize efficiency of conventional power trains. In addition sive to technology developments. Major improvements in to engine control, controllers in hybrid vehicles monitor the volumetric power density can be achieved by increasing the state of charge of the battery and determine power flows to and speed of the motor. This volumetric improvement results in from the battery and engine. The control task is more complex materials reduction but generally also in increased losses. for the PHEV where there is a greater opportunity to optimize High-speed motors also require a gear set to match the me- the tradeoff between electric and IC engine use with respect chanical speed required of the drive train. While the design to fuel consumption. One suggested approach is to have the of the motor/inverter system is an optimization problem, controller predetermine the propulsion profile from expected no technology breakthroughs that would radically improve route data provided by the driver or an off-board wirelessly the state of the art are foreseen. Figure 6.8 illustrates the connected server. Vehicle computers are powerful enough to improvement in volumetric power density that Toyota has handle these tasks, and no technical problems are expected. FIGURE 6.8 Evolution of the volumetric power density of electric motors used in Toyota’s hybrid vehicles. SOURCE: Fushiki and Wimmer (2007). Figure used with permission of Toyota. Figure 6-8.eps low-resolution bitmap

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93 HYBRID POWER TRAINS COST ESTIMATES justification for using an RPE of 1.33 for hybrids is that the factory cost estimates it developed already include engineer- The objective in determining costs of new technologies is ing costs and other part costs, including labor and overhead, understanding their factory cost. The factory cost is the direct for integrating the technology. Using a cost multiplier of 1.5 cost to the OEM of replacing existing production technology would double count these costs. A by technology B. It is determined as follows: As an example of the process, Table 6.2 shows an esti- mated breakdown of the factory cost of a “mature” Prius—a 1. Take the price (B) that a supplier charges the OEM for Prius-type drive that has benefited from the learning curve technology B; and has an annual production volume in excess of 100,000 2. Add the engineering cost (C) to the OEM of integrating units. The additional components and their estimated OEM technology B into a vehicle; costs from the supplier are listed. The committee also lists 3. Add the cost (D) of any parts that the OEM makes the cost decrement of items, such as the automatic transmis - in-house to implement the technology (labor cost plus sion, that will be removed from the baseline vehicle, a Toyota factory overhead, plus amortization of required new Corolla in this case. The net cost increase for the mature Prius investment); and is then calculated as $3,385. 4. Subtract the cost ( A ) of technology A similarly Next the committee projects costs for 5-year increments calculated. to 2025, as shown in Table 6.3. Percentage cost reductions The factory cost is then B + C + D – A. The cost estimates have been validated by soliciting TABLE 6.2 Factory Cost Estimation Process Applied to a feedback from a number of U.S. and Japanese OEMs and Mature Prius-type Hybrid Vehicle in U.S. Dollars suppliers. The costs presented here are a consensus that the numbers are “about right.” The costs of hybrid technologies Factory Cost vary depending on the degree of hybridization, from a low (B + C + D - A) 20 kW cost in the case of the BAS design, to a very high cost for a Motor/generator/gears 1,100 series PHEV. It should be noted that the factory cost defini- Control electronics + dc/dc (1.2 kW) 1,100 tion used here includes engineering costs and other part costs, Battery (NiMH 21 kW) 1,000 including labor and overhead, for integrating the technology. Electrical accessories 100 Electric PS and water pump 200 Using the studies described in Chapter 3, the committee de- Automatic transmission −850 veloped a different markup factor for hybrids that relates the Regenerative brakes 250 definition of factory cost to RPE. Although different studies Electric A/C 300 use different definitions and allocations for items such as Engine downsize −120 profit, vehicle warranty, corporate overhead, transportation, Starter and alternator −95 marketing, and dealer costs, the committee concluded that High-voltage cables (Martec 500 V) 200 the factory markup for hybrids should be on the order of Body/chassis/special components 200 Total 3,385 1.33 rather than 1.5 for factory cost to RPE. The committee’s TABLE 6.3 Projections of the Future Factory Cost of a Mature Prius-type Hybrid in U.S. Dollars Factory Cost (B + C + D - A) 20 kW Cost Reductions (%) 2008 2015 2020 2025 Motor/generator/gears 5 1,100 1,050 990 940 Control electronics + dc/dc (1.2 kW) 15 1,100 940 800 680 Battery (NiMH 21 kW, Li-ion Martec) 15 1,000 850 720 720 Electrical accessories 5 100 90 90 85 Electric PS and water pump 5 200 190 180 170 Automatic transmission 0 −850 −850 −850 −850 Regenerative brakes 5 250 240 230 210 Electric A/C 10 300 270 240 220 Engine downsize 0 −120 −120 −120 −120 Starter and alternator 0 −95 −95 −95 −95 High-voltage cables (Martec 500 V) 10 200 180 160 150 Body/chassis/special components 10 200 180 160 150 Total 3,385 2,925 2,505 2,260

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94 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES FUEL CONSUMPTION BENEFITS OF HYBRID appropriate for each component are used. For example, ARCHITECTURES expected reductions are on the order of 15 percent for each 5-year period for the battery and control electronics, 5 per- As noted earlier, the average fuel consumption of produc- cent for the electrical machines, and no change in cost for tion hybrid HEVs was determined from fuel economy data the mature components such as engine downsizing, and the supplied by Oak Ridge National Laboratory and included as alternator. Table 6.A.1 in the annex at the end of this chapter. For sev- A similar analysis has been done for the other hybrid eral specific models, these data were compared to data from classes, and the summary results are shown in Table 6.4. It conventional (nonhybrid) vehicles of approximately similar should be noted that future costs for PHEVs and EVs are performance and physical specifications, and the results highly uncertain due to the uncertainties in future battery are shown in Table 6.5. As mentioned earlier, a significant chemistries and tradeoffs between power and energy. Li-ion contribution to the fuel consumption benefit of hybrid ve- batteries for consumer electronics are a commercial tech- hicles is due to modifications to the engine, body, and tires. nology, and costs have gone down along the learning curve. For example, the fuel economy of the Prius is significantly However, many OEMs and battery suppliers are expecting influenced by engine improvements and optimized operating large cost reductions for Li-ion batteries with increasing area. The 2007 model-year version of the Saturn Vue hybrid, applications in vehicles. Among its provisions related to which used a BAS design, exhibits a 25 percent improvement fuel economy, the Energy Independence and Security Act of in fuel economy on the FTP cycle, but approximately half of 2007 requires periodic assessments by the National Research that improvement is due to vehicle modifications, including Council of automobile vehicle fuel economy technologies. a more aggressive torque converter lockup and fuel cutoff Thus, follow-on committees will be responsible for respond- during vehicle deceleration (D. Hancock, General Motors, ing to this legislative mandate, including the periodic evalu- personal communications, November 30, 2007). ation of PHEVs, EVs, and other technologies and how these The Oak Ridge data did not include information on the technologies can help meet new fuel economy standards. Honda Accord, which was discontinued in 2007. The Accord has a motor/generator of 15 kW in motoring mode and a slightly higher 15.5 kW in regenerative mode (J. German, Honda, personal communication, February 28, 2008). The motor generator has high-energy-density magnets in an inte- TABLE 6.4 Retail Price Estimates for Various Types of rior configuration. It also has flat wire windings that provide Hybrids Projected to 2025 (using an RPE of 1.33) better packing density compared to round wire. The NiMH 2009 2015 2020 2025 battery has 132 cells with a nominal voltage and energy of Vehicle ($) ($) ($) ($) 144 V and 0.87 kWh, respectively (Iijima, 2006). Honda calls Prius-type power split 4,500 3,900 3,300 3,000 the system an integrated motor assist. BAS/12 V 670 570 490 440 BAS/42 V 1,500 1,200 1,100 1,000 Plug-In Hybrids ISG 12 kW/144 V 2,900 2,500 2,100 2,000 Prius-type PHEV 10 (Li-ion battery) 8,800 7,600 6,500 5,900 The rules for assigning fuel economy ratings to plug-in Series PHEV 40 (Li-ion battery) 13,000 11,000 9,800 8,900 hybrids are currently being developed by SAE (revision of HEV crossover (V6) 6,900 6,000 5,200 4,700 J 1711). Thus the committee cannot predict at this time what Large SUV/pickup (V8) 8,700 7,500 6,400 5,700 TABLE 6.5 Comparison of Fuel Economy, Fuel Consumption, Performance, and Physical Specifications of Hybrid and Comparable SI Engine-Powered Vehicles Acceleration Fuel EPA Edmund’s (Consumer Reports, mph/sec) Volume EPA Test Consumption Test Car MSRP Architecture Trunk (mpg, combined) (gal/100 mi) Weight 0 to 30 0 to 60 45 to 65 Price Prius Prius/Corolla 1.33 1.64 0.61 1.13 1.06 1.07 1.05 1.36 Prius/Camry 1.07 2.00 0.50 0.87 1.03 1.10 1.03 1.09 Honda Civic Civic hybrid/Civic SI 0.83 1.51 0.66 1.00 1.22 1.16 1.22 1.45 Chevy Tahoe 4WD Tahoe 4WD Hybrid/Tahoe 4WD SI N/A 1.53 0.65 1.00 1.15 1.07 0.96 1.30

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95 HYBRID POWER TRAINS the official fuel economy rating of a specific PHEV design builders, equipment suppliers, and government organiza- will be. At the time of this writing only two PHEVs have been tions, there remain significant problems requiring technical announced for production—the GM Volt, which is expected and economic resolution, including the following: to have a 40-mile range on battery alone, and the Toyota plug-in Prius, which will have a 12-mile all-electric range • Higher cost of fuel cells compared to other energy and the ability to cruise at highway speeds under all electric converters, power.6 GM has announced that LG Chem of Korea will be • Lack of a hydrogen distribution infrastructure, supplying the Volt’s Li-ion battery. • Need for a low carbon source of hydrogen (biomass or water electrolysis using electricity produced with low emissions), FUEL CELL VEHICLES • Need to demonstrate acceptable durability and reli- Fuel cell vehicles have the potential to significantly re- ability, and duce greenhouse gas emissions (depending on how hydrogen • Weight and volume of an on-board hydrogen storage is produced) as well as U.S. dependence on imported oil over tank sized for a range of 300 to 400 miles. the long term. However, fuel cell vehicle technologies have technical challenges that are severe enough to convince the Because of these factors, the committee does not expect committee that it is unlikely such vehicles will be deployed wide use of fuel cell vehicles before 2025. in significant numbers within the time horizon of this study. A recent report (NRC, 2008) states that under the follow- FINDINGS ing set of very optimistic assumptions, 2 million fuel cell Finding 6.1: The degree of hybridization can vary from vehicles could be part of the U.S. fleet in 2020: minor stop-start systems with low incremental costs and • The technical goals are met and consumers readily modest reductions in fuel consumption (i.e., the most basic accept such vehicles. stop-start systems may have a fuel consumption benefit of • Policy instruments are in place to drive their introduction. up to about 4 percent at an estimated incremental retail price • The necessary hydrogen production, supply, distribu- equivalent (RPE) cost of $670 to $1,100) to complete vehicle tion, and fueling infrastructure is present. redesign (e.g., Prius) and downsizing of the SI gasoline en- • Oil prices are at least $100/barrel by 2020. gine at a high incremental RPE cost ($3,000 to $9,000) and • Fuel cell vehicles are competitive on the basis of life- with significant reductions in fuel consumption. A significant cycle cost. part of the improved fuel consumption of production hybrid vehicles comes from vehicle modifications such as low- Although the committee agrees with that study’s con- rolling-resistance tires, improved aerodynamics, and the use clusions under these optimistic assumptions, it believes of smaller, more efficient SI engines. that achieving them is unlikely. Almost every major OEM Finding 6.2: In the next 10 to 15 years, improvements in has a fuel cell vehicle program, and several have deployed limited fleets of experimental vehicles. These fleets invari- hybrid vehicles will occur primarily as a result of reduced ably represent limited mission, localized experiments, city costs for hybrid power train components and improvements buses, or postal vehicles, for example. Through interviews in battery performance such as higher power per mass and and presentations, the committee can find little evidence that volume, increased number of lifetime charges, and wider a commercially viable fuel cell light-duty vehicle will be allowable state-of-charge ranges. available in significant numbers by 2020. The Japanese auto Finding 6.3: During the past decade, significant advances industry will not decide to pursue a commercial development program until 2015, thus making a 2020 introduction date have been made in lithium-ion battery technology. When very difficult. The committee confirmed this target decision the cost and safety issues associated with Li-ion batteries date with Japan’s NEDO, Japanese academics, and the OEMs are resolved, they will replace NiMH batteries in HEVs and themselves. All current fuel cell vehicle research assumes PHEVs. A number of different Li-ion chemistries are being stored hydrogen as the fuel. The monumental difficulty of studied, and it is not yet clear which ones will prove most providing the necessary hydrogen distribution infrastructure beneficial. is another factor mitigating against the presence of fuel cell Finding 6.4: Given the high level of activity in lithium-ion vehicles in significant numbers by 2020. For fuel cells, in spite of hundreds of millions of dollars battery development, plug-in hybrid electric vehicles will h aving been devoted to their development by vehicle be commercially viable and will soon enter at least limited production. However, improving the cost-effectiveness of PHEVs depends on the cost of fuel and whether significant 6 See http://www.reuters.com/article/pressRelease/idUS238743+09-Sep- reductions in battery cost are achieved. 2009+PRN20090909.

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96 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES Finding 6.5: The practicality of full-performance battery Grewe, T.H., B.M. Conlon, and A.G. Holmes. 2007. Defining the General Motors 2-mode hybrid transmission. SAE Paper 2007-01-0273. SAE electric vehicles (i.e., with driving range, trunk space, International, Warrendale, Pa. volume, and acceleration comparable to those of internal Iijima, T. 2006. Development of hybrid system for 2006 compact sedan. combustion-powered vehicles) depends on a battery cost SAE Paper 2006-01-1503. SAE International, Warrendale, Pa. breakthrough that the committee does not anticipate within Kalhammer, F.R., B.M. Kopf, D.H. Swan, V.P. Roan, and M.P. Walsh. the time horizon considered in this study. However, it is clear 2007. Status and Prospects for Zero Emissions Vehicle Technology. Report presented to ARB Independent Expert Panel, April 13, State of that small, limited-range, but otherwise full-performance California Air Resources Board, Sacramento. battery electric vehicles will be marketed within that time Nelson, P., K. Amine, and H. Yomoto, 2007. Advanced lithium-ion batteries frame. for plug-in hybrid-electric vehicles. Paper presented at 23rd Interna- tional Electric Vehicle Symposium, December, Anaheim, Calif. Finding 6.6: Although there has been significant progress in NRC (National Research Council). 2008. Transitions to Alternative Trans- portation Technologies: A Focus on Hydrogen. The National Academies fuel cell technology, it is the committee’s opinion that fuel Press, Washington, D.C. cell vehicles will not represent a significant fraction of on- Reilly, B. 2007. Battery Technologies. Presentation to the National Research road light-duty vehicles within the next 15 years. Council Committee on the Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy, October 25, Washington, D.C. Ricardo, Inc. 2008. A Study of Potential Effectiveness of Carbon Dioxide REFERENCES Reducing Vehicle Technologies. Prepared for the U.S. Environmental Protection Agency. EPA420-R-08-004. Contract No. EP-C-06-003. Amine, K. 2007. Advanced high power chemistries for HEV applications. Work Assignment No. 1-14. Ann Arbor, Mich. Available at http://www. Presentation to the National Research Council Committee on the Assess- epa.gov/oms/technology/420r08004a.pdf. Accessed June 29, 2009. ment of Technologies for Improving Light-Duty Vehicle Fuel Economy, Rousseau, A., N. Shidore, R. Carlson, and P. Nelson. 2007. Research on November 27, Washington, D.C. PHEV battery requirements and evaluation of early prototypes. Paper Andermann 2007. Lithium-ion batteries for hybrid electric vehicles: Oppor- presented at the Advanced Automotive Battery Conference, May 17, tunities and Challenges. Presentation to the National Research Council Long Beach, Calif. Committee on the Assessment of Technologies for Improving Light- Tate, E.D., M.O. Harpster, and P.J. Savagian. 2009. The electrification of the Duty Vehicle Fuel Economy, October 25, Washington, D.C. automobile: From conventional hybrid, to plug-in hybrids, to extended- California Air Resources Board. 2009. DriveClean. Available at http://www. range electric vehicles. SAE International 1(April):156-166. driveclean.ca.gov. Accessed June 29, 2009. Tesla Motors, Inc. 2009. Tesla Roadster Spec Sheet. Available at http:// Fushiki, S., and B. Wimmer. 2007. Perspectives from Toyota. Presentation www.teslamotors.com/display_data/teslaroadster_specsheet.pdf. Ac- to the National Research Council Committee on the Assessment of cessed June 29, 2009. Technologies for Improving Light-Duty Vehicle Fuel Economy, Novem- Transmission Technology International. 2008. ZF eight-speed hybrid. ber 27, Washington, D.C. September, p. 10.

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ANNEX TABLE 6.A.1 Performance of Production Hybrid Vehicles from 2009 CAFE Certification Data EPA Fuel Economy Volume (unadjusted mpg) EPA Test Acceleration (Consumer Reports) Edmund’s MSRP Make Type Model Drive Trunk City Comb. Hwy Car Weight 0 to 30 mph, sec. 0 to 60 mph, sec. 45 to 65 mph, sec. Price Toyota Split Highlander Hybrid 4WD NA 35 35 35 5000 3.4 8.2 5 $34,700 Toyota Highlander 4WD NA 21 25 31 4750 3 8 5.1 $29,050 HYBRID POWER TRAINS Toyota Split Prius FWD 16 67 66 65 3250 3.8 10.6 6.2 $22,000 Toyota Corolla FWD 12 35 40 49 2875 3.6 9.9 5.9 $16,150 Toyota Camry FWD 15 27 33 44 3750 3.7 9.6 6 $20,195 Toyota Yaris FWD 13 37 42 49 2625 4.1 11.4 6.9 $13,765 Toyota Split Camry Hybrid FWD 11 44 46 48 4000 3.5 8.5 5.1 $26,150 Toyota Camry FWD 15 27 33 44 3750 3.7 9.6 6 $20,195 Toyota Camry FWD 15 25 30 40 3875 3.3 7.1 4.4 $24,215 Ford Split Escape Hybrid FWD NA 45 44 43 4000 NA NA NA $29,645 Ford Escape FWD NA 26 30 39 3625 NA NA NA $21,645 Ford Escape FWD NA 23 27 36 3625 NA NA NA $24,465 Ford Split Escape Hybrid 4WD NA 37 37 37 4250 4.1 10.7 5.8 $31,395 Ford Escape 4WD NA 24 28 35 3875 3.3 10 6.4 $23,395 Ford Escape 4WD NA 22 26 33 3875 3 7.9 5.2 $26,215 Saturn Parallel Aura Hybrid FWD 16 33 39 48 NA NA NA NA $26,325 Saturn Aura FWD 16 28 34 47 4000 3.4 9.4 6.9 $22,655 Saturn Aura FWD 16 21 26 36 4000 2.8 6.6 4.3 $27,250 Saturn Vue Hybrid FWD NA 32 37 45 4000 4.2 10.9 7.3 $28,160 Saturn Vue FWD NA 24 28 37 4000 NA NA NA $23,280 Saturn Vue FWD NA 21 25 33 4250 NA NA NA $26,435 Honda Parallel Civic Hybrid FWD 10 55 59 65 3125 4.4 11.7 7.3 $23,650 Honda Civic FWD 12 33 39 51 3125 3.6 10.1 6 $16,305 Nissan Parallel Altima Hybrid FWD 10 47 47 47 3750 3.1 7.6 4.4 $26,650 Nissan Altima FWD 15 29 34 43 3500 3.2 8.1 5 $19,900 Mazda Split Tribute Hybrid FWD NA 45 44 43 NA NA NA NA $28,175 Mazda Tribute FWD NA 26 30 39 NA NA NA NA $21,790 Mazda Tribute FWD NA 23 27 36 NA NA NA NA $23,055 Mazda Split Tribute Hybrid 4WD NA 37 37 37 NA 4.1 10.7 5.8 $29,925 Mazda Tribute 4WD NA 24 28 35 NA 3.3 10 6.4 $23,545 Mazda Tribute 4WD NA 22 26 33 NA 3 7.9 5.2 $24,805 Mercury Split Mariner Hybrid FWD NA 45 44 43 NA NA NA NA $30,090 Mercury Mariner FWD NA 26 30 39 NA NA NA NA $22,650 Mercury Mariner FWD NA 23 27 36 NA NA NA NA $23,660 Mercury Split Mariner Hybrid 4WD NA 37 37 37 NA 4.1 10.7 5.8 $31,840 Mercury Mariner 4WD NA 24 28 35 NA 3.3 10 6.4 $24,400 Mercury Mariner 4WD NA 22 26 33 NA 3 7.9 5.2 $25,410 97 continued

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TABLE 6.A.1 Continued 98 Official EPA Volume (unadjusted mpg) EPA Test Acceleration (Consumer Reports) Edmund’s MSRP Make Type Model Drive Trunk City Comb. Hwy Car Weight 0 to 30 mph, sec. 0 to 60 mph, sec. 45 to 65 mph, sec. Price Chevrolet Parallel Malibu Hybrid FWD 15 33 39 48 3875 4.1 10.3 6.9 $25,555 Chevrolet Malibu FWD 15 27 33 43 3750 3.4 9.4 7 $21,605 Chevrolet Malibu FWD 15 23 28 40 NA 3 8.1 5.1 NA Lexus Split RX 400h Hybrid 2WD NA NA NA NA NA NA NA NA NA Lexus RX 350 2WD NA 20 22 25 4250 NA NA NA $37,700 Lexus RX 350 2WD NA 20 22 25 NA NA NA NA NA Lexus Split RX 400h Hybrid 4WD NA NA NA NA NA 2.9 7.4 4.6 NA Lexus RX 350 4WD NA 22 26 32 4500 NA NA NA $39,100 Lexus RX 350 4WD NA 22 26 32 NA 2.7 7.3 4.8 NA Lexus Split GS 450h Hybrid RWD 9 28 31 35 4500 2.5 5.9 3.9 $56,550 Lexus GS 350 RWD 13 24 28 37 4000 NA NA NA $45,000 Lexus Split LS 600h L AWD 12 25 27 30 5500 NA NA NA $106,035 Chevrolet Split Tahoe Hybrid RWD NA 27 28 30 6000 NA NA NA $50,455 Chevrolet Tahoe RWD NA 15 19 27 6000 NA NA NA Premium Chevrolet Tahoe RWD NA 17 20 27 5500 NA NA NA $39,315 Chevrolet Split Tahoe Hybrid 4WD NA 27 28 30 6000 3.9 9.6 5.5 $53,260 Chevrolet Tahoe 4WD NA 15 18 26 6000 3.4 9 5.7 $41,025 Chevrolet Split Silverado Hybrid RWD NA 27 28 30 NA NA NA NA $38,020 Chevrolet Silverado RWD NA 17 21 27 5500 NA NA NA NA Chevrolet Silverado RWD NA 18 21 27 5000 NA NA NA $26,915 Chevrolet Split Silverado Hybrid 4WD NA 27 28 30 NA $41,170 Chevrolet Silverado 4WD NA 17 20 27 5500 NA Chevrolet Silverado 4WD NA 18 21 27 5250 3 7.9 5.1 $30,065 GMC Split Yukon Hybrid RWD NA 27 28 30 NA NA NA NA $50,920 GMC Yukon RWD NA 15 19 27 NA NA NA NA Premium GMC Yukon RWD NA 17 20 27 NA NA NA NA $39,970 GMC Split Yukon Hybrid 4WD NA 27 28 30 NA 3.9 9.6 5.5 $53,730 GMC Yukon 4WD NA 17 20 27 NA 3.4 9 5.7 $41,765 GMC Split Sierra Hybrid RWD NA 27 28 30 NA NA NA NA $38,390 GMC Sierra RWD NA 17 21 27 5500 NA NA NA NA GMC Sierra RWD NA 18 21 28 NA NA NA NA $26,915 GMC Split Sierra Hybrid 4WD NA 27 28 30 NA NA NA NA $41,540 GMC Sierra 4WD NA 17 20 27 NA NA NA NA NA GMC Sierra 4WD NA 18 21 27 6000 3 7.9 5.1 $30,065 Dodge Split Durango Hybrid 4WD NA 25 27 30 NA NA NA NA $45,040 Dodge Durango 4WD NA 17 20 26 NA 2.8 7.4 5.2 NA Chrysler Split Aspen Hybrid 4WD NA 25 27 30 NA NA NA NA $45,270 Chrysler Aspen 4WD NA 17 20 26 NA 2.8 7.4 5.2 NA Cadillac Split Escalade Hybrid 2WD NA 27 28 30 NA NA NA NA $73,135 ASSESSMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES