Corriente de Humboldt

The HEVTA has focused on a midsized passenger car, primarily because this is the focus of the current Partnership for a New Generation of Vehicles (PNGV) research and because the results can be applied, with some caution and modification, to most of the light-duty vehicles in the U.S. fleet. The current vehicles on which the HEVTA vehicles are based – the Chrysler Intrepid, Chevrolet Lumina, and Ford Taurus – are assumed to be slightly downsized (in external dimensions) for the timeframe of the analysis, 2005-2020. They are also assumed to have

advanced low rolling resistance tires and greatly improved aerodynamics.

For sizing, we have chosen the current Chrysler Cirrus and Chevrolet Malibu as having the approximate external dimensions of a future midsize car that has undergone a process of interior space and structural redesign accompanied by substantial weight reduction. The current cars weigh about 1,418 kg (3,125 lb). By 2010, with an ultralight steel (ULS) body, these cars would be expected to weigh about 1,255 kg (2,767 lb), with the body and chassis (basically, the car without its drivetrain) assumed to contribute 73.5% of the vehicle mass, or 922 kg (2,029 lb). When these vehicles are converted to hybrid electric vehicles (HEVs), their body and chassis weight is assumed to increase by 5% to account for any additional structural strength needed to support the battery pack and power-electronic components.47

As discussed previously, to obtain a fair comparison between hybrid and conventional vehicles, we have assumed that all the vehicles share the same body characteristics and similar performance, measured as zero to 60 mph acceleration (Z60) time. All of the vehicles are essentially identical except for differences in their drivetrains and the 5% structural weight difference. The hybrids also must satisfy a gradeability requirement, although the conventional vehicles have better gradeability due to their larger, more powerful engines. Table 4-1 shows the basic body characteristics assumed for the 2010 and 2020 vehicle.

47_{Note that this 5% factor is somewhat arbitrary, for two reasons: first, it is possible to design the battery} pack in such a way that it becomes an integral and supporting part of the body structure, thus reducing or eliminating the need for added structural weight; and second, the size and weight of the battery pack and electronic components, thus the added structural weight required, will vary significantly depending on the vehicle’s performance requirements and on whether it is expected to be capable of operating all- electrically, with some recharging from the grid.

Table 4-1 Midsize HEV Characteristics

Vehicle Characteristics 2010 2020

Body and chassis mass in kg (lb in parenthesis)

Ultralight steel body 969 (2,136) 959 (2,114)

Aerodynamic and rolling

Frontal area (square meters) 2.06 2.01

Coefficient of drag (Cd) 0.26 0.24

Coefficient of rolling resistance (Cr) 0.0075 0.0065

We examine a number of different types of hybrid design, including:

Parallel grid-independent full hybrid, with engine sized to provide the power to maintain

gradeability requirements, and battery/motor sized to provide adequate boost to the engine to allow attainment of the Z60 requirement.

Parallel grid-independent mild hybrid, with less battery and motor power and more engine

power than the parallel grid-independent hybrid. Engine power is precisely midway between the conventional vehicles (CVs) and full hybrid’s engine power, with battery and motor power consequently sized to provide enough boost to satisfy the Z60 requirement.

Series grid-independent full hybrid, with engine and electric motor (continuous rating) sized for

gradeability, battery sized to provide boost for acceleration requirements, and electric motor (maximum power) sized for full acceleration power requirements.48

Parallel and series grid-dependent hybrids, designed to operate part of the time as full electric

vehicles, so battery and electric motor are sized to satisfy a separate electric vehicle (EV) acceleration requirement, and the engine is sized to provide full HEV gradeability. For the parallel hybrids we examined, this combination tends to allow especially rapid acceleration when both engine and battery/motor are engaged simultaneously, because the battery and motor are considerably larger than those found in a parallel grid-independent hybrid.

For the grid-independent vehicles, we examine power levels that will allow Z60 times of 8, 10, and 12 seconds. The original PNGV guidelines call for Z60 times of 12 seconds, but this value has been outrun by changes in the fleet. The current average Z60 time for midsize cars is 10.5 seconds, vs. 11.4 seconds in 1994 when the guidelines were established (Heavenrich and Hellman 1999). Trends of increasing power and decreasing Z60 times appear to be robust. For grid-connected vehicles, we examine power levels that will allow all-electric Z60 times of 12, 14, and 16 seconds. Keeping all-electric Z60 times for these vehicles more modest makes sense because the powerful and very expensive electric motors needed to allow faster acceleration

48_{In other words, there are two separate sizing criteria for the electric motor. Although the gradeability} criterion requires less power than the acceleration criterion, the motor’s continuous power rating will be lower than its peak rating. Therefore, actual motor size may be determined by either the acceleration or the gradeability criterion, depending on motor design and the gradeability and acceleration criteria used.

would make these vehicles extremely expensive (they are already considerably more expensive than the grid-independent hybrids).

The drivetrain components of both conventional and hybrid vehicles will likely be

substantial improvements over those available today. For example, it seems quite possible that, by 2010, the engines driving both conventional and hybrid vehicles will be mature versions of recently-introduced direct injection stratified charge (DISC) gasoline engines, direct injection (DI) diesels (if emissions problems are solved), or other advanced technologies. Recent progress in electrical drive technology implies that batteries, motors, and power electronics will have both higher efficiency and higher specific power than those available today. All such developments will increase the efficiency of hybrid vehicles, although use of advanced engines and

transmissions in conventional vehicles may shrink the relative efficiency advantage of the hybrids (see Section 2.5.5).

Tables 4-2 and 4-3 show the assumed characteristics of the batteries and other hybrid drivetrain components for 2010 and 2020. The study team decided not to try to simulate an advanced engine, in part because appropriate engine maps were not available. The base engine, from which the HEV and CV engines were scaled, is a 1994 version of a 63 kW (85 horsepower) single overhead cam (SOHC) 1.9-L Saturn engine. The battery characteristics are based on the results of a Delphi study conducted by ANL as well as published characteristics of the batteries used in Toyota’s Prius hybrid (Japanese market version49_{) and RAV-4 electric vehicles. The} motor, generator, and inverter characteristics are based on the performance of a Unique Mobility SR218H permanent magnet motor and CA40-300L inverter, with assumed improvements over time. The efficiencies shown in Table 4-3 are those attained during high-power acceleration (that is, during peak loading of the components) and are used to determine the battery power capacity needed to allow the vehicle to achieve acceleration goals. Future analysis will explore the effects of changing the various component assumptions.

Table 4-2 Nickel Metal Hydride Battery Characteristics High-Energy/ Low-Power Intermediate Low-Energy/ High-Power Battery Characteristic 2010 2020 2010 2020 2010 2020 Specific power (W/kg) 184 203 350 386 520 573 Specific energy (Wh/kg) 73 79 54 58 46 50 Cost ($/kWh) 426 382 533 478 567 508 Cost ($/kW) 169 149 82 72 50 44

49_{The version of the Prius introduced into the U.S. market has an upgraded battery pack attaining a specific} power of 880 W/kg, versus the earlier Japanese version’s 500 W/kg. We based our battery on the earlier Japanese version.

Table 4-3 Specific Power and Efficiency Values for HEV Drivetrain Components

Component Type 2010 2020

Specific Power (W/kg)

Motor and generator Permanent magnet 1,300 1,400

Auxiliary power unit Gasoline 330 340

Motor with inverter 1,025 1,110

Transmission (parallel HEV) 1,320 1,360

Transmission (series HEV) 1,650 1,700

Efficiency (%)

Motor and inverter Permanent magnet 90 93

Battery (one-way) Nickel metal hydride 93 95

Transmission 93 95