Green by Design
Part 6: Hybrids—Today and Tomorrow

A Hybrid Overview

Among cutting-edge vehicles entering the market today, hybrid-electrics continue to draw the most attention from environment-minded audiences. And for good reason: for the most part, their tailpipe emissions are low, and their fuel economies, excellent. Hybrids both in the showroom and on the way include a host of sophisticated technologies. One ingenuity they all feature is engine power management.

The use of engine power in a conventional vehicle varies greatly, depending on driving requirements. During hard acceleration, a vehicle uses its power to the fullest. But during the vast majority of driving, the extra engine power is not used, and the larger engine simply adds higher frictional losses and extra weight to the vehicle. Still, in conventional vehicles, engineers must design the engine to meet the most demanding requirements. This poses an inherent energy loss in conventional vehicles.

The larger a combustion engine is and the faster it revs, the more power it provides. Unfortunately, the larger it is, the more fuel it will use as well, as energy is required to overcome its own weight and friction, including the energy needed to pump air into the cylinders. Furthermore, combustion engines use more fuel when running at higher revs. The higher the revolutions-per-minute (rpm), the more friction gets generated; and friction always wastes energy.

Smaller gasoline engines, or those running at a lower rpm where efficiency is better, offer higher fuel economy, but they also provide only a limited amount of power. However, by coupling an electric motor to a smaller engine, it's possible to engineer a system that makes practical use of both engine size and power. Electric motors efficiently provide great torque at low rpm, so pairing one with a small, efficient engine yields the magic of hybrid-electric design: use a smaller engine and keep it at low revs, and then use the electric motor to restore the performance that would otherwise be lost.

But where does the electric motor get its power? Another feature of hybrid vehicles is that they make their own electricity. The battery is charged using power generated by recovering energy when the car is braking or at other times when the gasoline engine produces more power than needed to drive the wheels. Thus, hybrids need not be plugged in, and their ability to recover energy yields another boost in efficiency.

In short, a hybrid-electric design can optimally integrate an electric motor with an efficient combustion engine, maximizing the strengths of both and yielding higher fuel efficiency.

Bear in mind, however, that today's eco-friendly notion of the hybrid may not necessarily hold true with upcoming hybrid designs. While a number of hybrids on the road today offer dramatic fuel economy improvements over their conventional counterparts, the technology can also be utilized simply to boost performance in vehicles. By not downsizing the gasoline engine, for example, fuel savings can essentially be substituted for even greater acceleration and power. The industry is now beginning to produce some of these "performance hybrids," though it remains unclear how they will be received in the market. Getting additional hybrids into the market may help automakers drive hybrid costs down through economies of scale. However, the emerging national consensus that the nation needs to conserve oil suggests that the focus of hybrids should remain on fuel economy.

Numerous hybrids are now on the market in a wide range of types: two-seaters; compact and midsize cars; compact and midsize SUVs; full-size pickups; and economy and luxury models. Some of these vehicles, such as the Honda Insight, Toyota Prius, and Honda Civic Hybrid, have been the focus of previous Green by Design articles. While the hybrid models now on the road are well-documented, a number of automakers have recently unveiled plans for upcoming models. The details below illustrate just a few of the numerous approaches automakers are taking in designing tomorrow's hybrids. Some models employ electrical system advancements to achieve minor fuel economy gains at moderate cost. Others use full-fledged, dual-source powertrains that use an electric motor (or sometimes two) in conjunction with an internal combustion engine, to make even greater improvements in fuel economy.

Saturn Hybrids

Saturn is entering the hybrid market with a mild-hybrid version of two of its vehicles, the Vue sport utility vehicle and Aura midsize sedan. Branded the Vue Green Line and Aura Green Line, and available in mid- and late-2006 respectively, these models will offer modest improvements in fuel economy at modest cost. They represent the intermediate level of a three-tiered hybrid technology strategy at GM. The current Chevrolet Silverado Hybrid and GMC Sierra Hybrid pickups, which include certain hybrid-electric design components but do not use an electric motor to directly move the vehicle, represent the low level, while GM's upcoming "Two-Mode" hybrids represents the upper level.

The foundation of the 2007 Saturn Vue Green Line is GM's belt alternator starter (BAS) system, which provides engine idle-off and regenerative braking capability, and enables fuel cutoff to the engine during deceleration. On the Vue Green Line, however, the BAS system is supplemented with design enhancements to provide brief allotments of boost power from a very small electric motor during acceleration, and torque smoothing for a more even ride.

Combining these design elements with a 2.4-liter variable valve timing Ecotec engine and four-speed automatic transmission results in roughly a 20 percent overall improvement in fuel economy, achieving 27 mpg in the city and 32 mpg on the highway. Approximately half of the fuel economy gains are attributed to the BAS system, with the remainder attributed to weight, engine, and aerodynamic design enhancements. While a similar BAS-based system will be implemented on GM's Chevy Malibu next year, it is yet unclear what additional enhancements will make it on that model.

While the "Green" in Saturn's Green Line moniker is a sure reference to the environment, it could equally be viewed as a nod to the green in customers' wallets. The small battery pack and motor admittedly offer limited gains in fuel economy, but with a price premium of less than $2000, the Vue Green Line offers consumers a hybrid alternative that won't necessarily break the bank.

Although official design specifications of the Aura Green Line are still sparse, Saturn has confirmed that it will also use the same underlying system found on the Vue Green Line: a BAS system, 2.4-liter Ecotec engine, and 36-volt nickel-metal hydride battery pack. Fuel economy estimates for the Aura Green Line have not been announced, although they should be significantly higher than the conventional Aura, which is outfitted with a base 3.5-liter engine.

GM Two-Mode Hybrids

As noted above, the upper level of GM's three-tiered hybrid technology strategy is the "Two-Mode" hybrid, based upon joint research with DaimlerChrysler and BMW Group. Slated to first appear on the Chevrolet Tahoe and GMC Yukon SUVs in late 2007, this design is noteworthy since its marks the first attempt at applying hybrid technology to full-sized SUVs.

The Two-Mode gets its name from the system's number of operation modes. Under the first mode, when the vehicle is under light loads and low speeds, the vehicle will operate in one of three different configurations, depending on driving conditions: solely using electricity, solely using the engine, or a combination of both. Under the second mode, when the vehicle is running at highway speeds, the system engages a unique second gearset to offer the vehicle improved efficiency.

Utilizing two planetary gearsets, two 60 kW electric motors, a 300-volt battery pack, and a V8 gasoline engine, GM claims the Two-Mode Tahoe and Yukon offers a 25% improvement in fuel economy over their gasoline counterparts, although a portion of that improvement is attributable to the engine's "displacement on demand" cylinder deactivation (at highway speeds), low rolling resistance tires, aerodynamic improvements, and an aluminum hood and tailgate. Still, that improvement raises the combined city/highway average fuel economy from roughly 17 to 21 which equates to approximately two fewer tons of global warming-inducing CO2 being emitted from each vehicle, each year.

Automakers affiliated with the Two-Mode design have stated it will be incorporated on a number of upcoming models after the Tahoe and Yukon release, including the Dodge Durango, Cadillac Escalade, rear-wheel-drive luxury Mercedes-Benz passenger cars, and yet-to-be-named BMW models.

Lexus Hybrids

With the Lexus RX 400h now on the market, Toyota plans to continue its foray into the luxury hybrid segment with the 2007 Lexus GS 450h and 2008 LS 600h. Slated to be released in mid-2006 and mid-2007, respectively, these models are redefining hybrid design. The focus of both of these vehicles is power and performance, a design characteristic embraced unapologetically by Lexus. The GS 450h, expected to be the world's first rear-wheel drive hybrid, mates a 296 hp, 3.5L V6 engine to a 200 hp electric motor yielding a combined peak output of 339 hp and a 0-60 time of 5.2 seconds. The model is claimed to have a combined city/highway fuel economy averaging in the high 20s. The GS 450h is expected to meet California SULEV II and Federal Tier 2 bin 3 emissions levels.

The LS 600h L gets the distinction of being the first hybrid vehicle to utilize an 8-cylinder engine. The 430+ horsepower model combines a V8 5.0-liter gasoline engine with a high-output electric motor and recently-designed larger battery pack to provide the performance of a 12-cylinder engine. Operating full-time as an all-wheel drive vehicle, the model also includes a dual-stage, electronically controlled CVT to provide smooth acceleration under a range of driving conditions. Noise, vibration, and harshness-known in the industry as NVH-is reduced through the hybrid design and, in fact, is one of the vehicle's chief selling points. Don't expect to see this model sitting on the Greenest Vehicles list, however; while the model is expected to achieve SULEV II emissions levels (and a comparable Federal certification), Lexus claims the fuel economy will only be similar to that of a conventional V8-powered vehicle, likely in the low-20s.

Continue to Part 7: Greener Tech Tomorrow