The Chevrolet Tahoe Hybrid, along with its GMC counterpart, the Yukon Hybrid, are the first vehicles to utilize the advanced two-mode hybrid powertrain developed jointly by BMW, DaimlerChrysler, and General Motors. This full-size SUV launches a new breed of larger vehicles that are significantly greener than their gas-powered versions. Maybe that's why the Tahoe Hybrid received the questionable title of “Green Car of the Year” at the 2007 Los Angeles Auto Show. The panelists may have jumped the gun a little, as this hybrid doesn’t even meet the corporate average fuel economy (CAFE) standard.

The crux of the Tahoe Hybrid’s powertrain is GM’s 6-liter Vortec V8 with cylinder deactivation technology. In other words, this engine can shut down four of its eight cylinders when the additional power is not needed. That saves fuel. Beyond the engine, there’s a 300-volt battery that hides below the second-row seats. The vehicle's two electric motors are housed within the transmission.

In order to keep the vehicle running at peak efficiency, this hybrid system is able to run in one of two separate modes—hence the name "two-mode hybrid." For low-speed, low-impact driving, the powertrain works just like other hybrids; it stops the V8 engine whenever possible so that it may draw power from one or both of the electric motors. The second mode is mostly for highway driving, at which time one or both electric motors can run concurrently along with the V8 engine in order to provide a power boost. The two-mode transmission is the key to the whole system, which attempts to keep the engine running at the optimum rpm for low fuel consumption. Essentially, it manages a balancing act between the V8 engine and the electric motors. It is also responsible for making the transitions between the two modes practically seamless.

All of this technology results in a 25 percent improvement in overall fuel economy over the Tahoe hybrid’s gas-powered counterpart. More impressive is a 40 percent improvement in city driving. The Tahoe Hybrid two-wheel drive model has an EPA rating of 21 city/22 highway, as compared to the conventional Tahoe’s 14 city/19 highway. Unbelievably, this huge SUV’s city fuel economy is equivalent to that of a four-cylinder Toyota Camry.

Aside from its efficient powertrain, the Tahoe Hybrid achieves greener motoring by utilizing a new power-conserving air-conditioning unit, and lightweight, low-resistant aluminum wheels. To that end, Tire Pressure Monitoring also comes standard.

Despite its focus on fuel-efficiency, the Tahoe Hybrid still delivers all the power and capability needed from a full-size SUV. It boasts 332 horsepower, and can tow up to 6000 pounds. And it is available in both two-wheel and four-wheel drive models. Its four-drive system is comparable to most trail-rated pickup trucks, allowing the Tahoe Hybrid to drive off-road or through difficult road conditions with excellent traction and stability. On normal, dry pavement, this SUV offers a comfortable and smooth ride, as opposed to the rigid feel of many larger vehicles.

The Tahoe Hybrid grants plenty of capability for work-related endeavors, and an abundance of space and amenities for large families, even up to eight.

In the next year or two, it will be joined by a roster of full-size two-mode hybrid SUVs and trucks, including the Chrysler Aspen, the Dodge Durango, the Cadillac Escalade, the Chevrolet Silverado, and the GMC Sierra.

The Tahoe Hybrid has virtually the same truck-like body as the regular Tahoe, with a few minor modifications. It rides slightly lower to the ground, which enhances its aerodynamics. It also has a revised D-pillar and flared ends for the running boards, both of which help to reduce wind resistance, and in turn, increase efficiency. The Tahoe Hybrid also has a larger air intake up front for more effective engine cooling.

To save weight, the hood and liftgate are made of aluminum—which especially helps since the hybrid powertrain is 400 pounds heavier than the conventional gas-powered one.

Furthermore, the wheels have been outfitted with low-rolling-resistance tires, again to improve efficiency.

The Tahoe Hybrid identifies itself with special badging on the C-pillars and liftgate.

Inside, the Tahoe Hybrid offers the same handsome, spacious and comfortable cabin as the standard Tahoe. It offers seating for eight and vast cargo room, whether it be for luggage, groceries, or lumber. The second row shows the biggest difference, having been redesigned to accommodate the hybrid battery pack hidden below.

Up front, the driver and front passenger enjoys plush and supportive seats, as well as excellent visibility. And the instrument cluster includes an economy meter with a “green range” that tells how efficiently the hybrid motor is operating.

This family-centric SUV grants options and amenities galore. Favorites include a premium audio system, DVD entertainment system, navigation, and a back-up camera. And on a more basic level, Chevy even made sure that all passengers have a cupholder of their own, a simple convenience that is often overlooked by vehicle planners.

As a work truck, the Tahoe Hybrid is as tough as any. It is rugged enough to handle the abuses of higher-impact environments like construction sites. The interior has been built to handle heavy-duty tasks, such as hauling tools, equipment, and building materials.

Passenger safety comes from an array of airbags: front, side, and head curtain canopy with rollover sensors.

“The 2008 Tahoe Hybrid uses cutting-edge technology to combine improved fuel economy with full-size SUV performance and practicality.”

“Helping you have your cake and eat it too, the Active Fuel Management system, which cuts the operation of four cylinders when they are unneeded, enhances fuel economy.”

“Marrying Active Fuel Management with a two-mode, full hybrid system is the latest in fuel conservation science.”

A hybrid electric vehicle (HEV) is a vehicle which combines a conventional propulsion system with an on-board rechargeable energy storage system (RESS) to achieve better fuel economy than a conventional vehicle without being hampered by range from a charging unit like an electric vehicle. The different propulsion power systems may have common subsystems or components.

Regular HEVs most commonly use an internal combustion engine (ICE) and electric batteries to power electric motors. Modern mass produced HEVs prolong the charge on their batteries by capturing kinetic energy via regenerative braking, and some HEVs can use the combustion engine to generate electricity by spinning an electrical generator (often a motor-generator) to either recharge the battery or directly feed power to an electric motor that drives the vehicle. This contrasts with battery electric vehicles which use batteries charged by an external source. Many HEVs reduce idle emissions by shutting down the ICE at idle and restarting it when needed. An HEV's engine is smaller and may be run at various speeds, providing more efficiency.

Engines and fuel sources Gasoline engines are used in most hybrid electric designs, and will likely remain dominant for the foreseeable future. While petroleum-derived gasoline is the primary fuel, it is possible to mix in varying levels of ethanol created from renewable energy sources. Like most modern ICE-powered vehicles, HEVs can typically use up to about 15% bioethanol. Manufacturers may move to flexible fuel engines, which would increase allowable ratios, but no plans are in place at present. Diesel-electric HEVs use a diesel engine for power generation. Diesels have advantages when delivering constant power for long periods of time, suffering less wear while operating at higher efficiency. The diesel engine's high torque, combined with hybrid technology, may offer substantially improved mileage. Most diesel vehicles can use 100% pure biofuels (biodiesel), so they can use but do not need petroleum at all for fuel (although mixes of biofuel and petroleum are more common, and petroleum may be needed for lubrication). If diesel-electric HEVs were in use, this benefit would likely also apply. Diesel-electric hybrid drivetrains have begun to appear in commercial vehicles (particularly buses); as of 2007, no light duty diesel-electric hybrid passenger cars are currently available, although prototypes exist. Peugeot is expected to produce a diesel-electric hybrid version of its 308 in late 2008 for the European market. PSA Peugeot Citroën has unveiled two demonstrator vehicles featuring a diesel-electric hybrid drivetrain: the Peugeot 307 and Citroën C4 Hybride HDi.Volkswagen made a prototype diesel-electric hybrid car that achieved 2 L/100 km (118 mpg–U.S. / 141 mpg–imp) fuel economy, but has yet to sell a hybrid vehicle. General Motors has been testing the Opel Astra Diesel Hybrid. There have been no concrete dates suggested for these vehicles, but press statements have suggested production vehicles would not appear before 2009.

Benefits of the hybrid electric design include:

Fuel consumption

Current HEVs reduce petroleum consumption (compared to otherwise similar conventional vehicles) primarily by using three mechanisms: a) Reducing wasted energy during idle/low output, generally by turning the ICE off;
b) Recapturing waste energy (i.e. regenerative braking);
c) reducing the size and power of the ICE engine, and hence inefficiencies from under-utilization, by using the better torque response of electric motors to compensate for the loss in peak power output from the smaller ICE. Any combination of these three primary hybrid technologies may be used for different fuel usage, power, emissions, weight and cost profiles. The ICE in an HEV is smaller, lighter, and more efficient than the one in a conventional vehicle, because the combustion engine can be sized for slightly above average power demand rather than peak power demand. A standard combustion engine is required to operate over a range of speed and power, yet its highest efficiency is in a narrow range of operation; in an HEV, the ICE operates within its range of highest efficiency. The power curve of electric motors is better suited to variable speeds and can provide substantially greater torque at low speeds compared with internal-combustion engines. The greater fuel economy of HEVs has implication for reduced petroleum consumption and vehicle air pollution emissions worldwide

Durability

Reduced wear on the gasoline engine, particularly from idling with no load. Reduced wear on brakes from the regenerative braking system use.

Environmental impact

Reduced noise emissions resulting from substantial use of electric motor at low speeds, leading to roadway noise reduction and beneficial noise health effects(although road noise from tires and wind, the loudest noises at highway speeds fron the interior of most vehicles, are not affected by the hybrid design alone). Note, however, that this is not always an advantage; for example, people who are blind or visually-impaired, and who rely on vehicle-noise while crossing streets, find it more difficult to do safely. Reduced air pollution emissions due to lower fuel consumption, leading to improved human health with regard to respiratory and other illness. Pollution reduction in urban environments may be particularly significant due to elimination of idle-at-rest.