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2008 GMC Yukon Two-Mode Hybrid Review

September 2007
Filed under: GMC Car News | GMC Headlines
Last year, the GMC Yukon and Yukon XL full-size SUVs were all-new, delivering more power and better fuel economy than the vehicles they replaced. They build on that segment-leading reputation with changes and innovations for the 2008 model year, including the introduction of the Yukon Hybrid and a new six-speed automatic transmission for the Yukon XL 2500 heavy-duty model.

The Yukon Hybrid features the world’s first production 2-Mode full hybrid propulsion system in an SUV, which offers an estimated 25-percent overall improvement in fuel economy. Better still, the fuel-saving advantages are balanced with a superior driving experience and uncompromised capability. The Yukon Hybrid can tow up to 6,200 pounds (2,812 kg); and to maximize its efficiency, its Vortec 6.0L V-8 engine is equipped with GM’s Active Fuel Management technology, which switches between four- and eight-cylinder power in certain driving situations.

“The innovative Hybrid system is designed to deliver optimum fuel efficiency in both city and highway driving, the way most Americans use their vehicles,” said Tom Stephens, group vice president, GM Powertrain. “The Yukon Hybrid doesn’t sacrifice a thing; it delivers 25-percent improvement in overall fuel economy and the capability that the Yukon name has always represented.”

The Yukon and Yukon XL are based on GM’s acclaimed full-size SUV platform and feature distinctive styling, spacious and refined interiors, exceptional driving characteristics and segment-leading safety features. Indeed, safety also is enhanced for ’08, as head curtain side air bags are now standard for all seating rows on all models. Previously they were optional on some models.

Additional changes for ’08 are minor, reflecting customer preferences and enhancing Yukon ’s style. They include a change to a 40/20/40-split front bench seat in the base SLE model that provides convenient storage space in the center section; and there are also two new exterior colors: Stealth Gray Metallic and Sonoma Red Metallic.

Yukon XL 2500 ¾-ton features standard StabiliTrak electronic stability control system and available, chrome-finish 17-inch aluminum wheels, along with its new, fuel-saving six-speed automatic transmission. It’s hooked to a powerful 6.0L V-8.

Yukon Hybrid
The V-8 powered Yukon Hybrid is expected to deliver a composite fuel efficiency improvement of an estimated 25 percent when combined with Active Fuel Management™ cylinder deactivation technology. It is available in 2WD and 4WD configurations and a Vortec 6.0L V-8 engine with more than 300 horsepower is the standard engine. A special four-speed automatic hybrid transmission is paired with the engine, enabling a maximum towing capacity of 6,200 pounds (2,812 kg).

The Yukon Hybrid has a distinctive look befitting its unique powertrain; it is 10 mm lower in the front and has additional aerodynamic features, such as a new, streamlined hood, new front and rear fascias, refinements to the rear pillars, a small spoiler above the liftgate and a closeout panel at the rear of the vehicle. To reduce overall mass, the hood, liftgate and wheels are made of lightweight aluminum. Prominent hybrid badging completes the look.

GM, BMW and DaimlerChrysler have co-developed the 2-Mode full hybrid system that will leverage automatic transmission technology and electronic controls in an integrated, powerful and compact system that can be used with both gas and diesel engines. GM’s 2-Mode full hybrid system in transit buses has been established as the starting point for the GM-BMW-DaimlerChrysler collaboration. The design integrates proven automatic transmission technology with a patented hybrid-electric drive system to deliver the world’s first 2-Mode full hybrid in an SUV.

The 2-Mode is patented hybrid technology with two modes optimized for city and highway driving. In the first mode, at low speed and light loads, the vehicle can operate in three ways: electric power only, engine power only or in any combination of engine and electric power. When operating with electric power only, it provides all the fuel savings benefits of a full hybrid system. Leaving the engine shut off for extended periods of time and moving under electric power at low speed is key to reducing fuel consumption in heavy stop and go traffic.

The second mode is used primarily at highway speeds. In addition to electric assist, the second mode provides full eight-cylinder engine power when conditions demand it, such as when passing, pulling a trailer or climbing a steep grade. The second mode integrates sophisticated electronic controls, such as Active Fuel Management, cam phasing, and late-intake valve closure, allowing even more efficient engine operation.

Yukon ’s 2-Mode system innovations allow for more compact packaging because its compact and powerful electric motors are designed to fit within the approximate space of a conventional automatic transmission – an efficiency advantage compared with today’s typical single-mode systems that rely on much larger electric motors.

A sophisticated controller determines when the vehicle should operate in either mode of the 2-Mode drive system. Input from the controller determines the necessary torque for the driving conditions and sends a corresponding command to the engine and electric motors. The engine and electric motors transfer torque to a series of gears in the transmission, which multiply torque similar to a conventional automatic transmission to propel the vehicle. But unlike conventional continuously variable transmissions, the 2-Mode full hybrid’s electrically controlled system uses no mechanical belts or bands. Shifts between the two modes are synchronous, which means no engine speed changes are necessary for the mode shift to occur, resulting in ultra smooth accelerations.

The 300-volt battery pack provides electric power for the system, and while it is larger than a typical automotive battery, it is designed to fit in the vehicle without compromising passenger space. Special converters located under the vehicle’s hood convert the motors’ AC output to DC current and power conventional 12-volt accessories, such as interior lighting, climate control and the radio. The vehicle’s internal combustion engine provides power to charge the battery pack, so the vehicle doesn’t have to be plugged in to keep the battery pack maintained.

Because the architecture can be scaled to fit multiple vehicles and adapted to gasoline or diesel engines, the 2-Mode full hybrid can be applied globally. In Europe , for example, where diesel engines are common in passenger vehicles, it can provide a significant reduction in fuel consumption, which would help automakers meet the region’s ever-stringent carbon dioxide emissions standard.

To maximize efficiency, the front of the GMC Yukon Hybrid is lowered 10 mm compared the non-Hybrid version, which provides additional aerodynamic benefits as well as a smoother and sleeker appearance. The hood and liftgate are made of aluminum to trim weight, and the leading edges of the hood have been streamlined.

The Yukon Hybrid retains GMC’s trademark grille design, but with a larger intake to accommodate the hybrid powertrain’s higher airflow requirement for cooling. The fascias are tuned at the corners and air dam, and the running boards are flared in front in an effort to guide airflow around the wheel openings. Hybrid badging appears on the C-pillar, on the rear liftgate and on the hitch cover.

Other aerodynamic refinements include sharpening of the D-pillar rearward, including the taillamps, a CHMSL appliqué detail spoiler over the rear hatch and a closeout panel under the back of the vehicle to facilitate airflow.

Lightweight, aero-efficient wheels with the lowest rolling-resistance tires available for full-size trucks further trim fuel use, and are complemented with a tuned ride to provide the ride and handling performance and attention to detail that customers expect from a totally integrated vehicle.

Yukon and Yukon XL lineup
Yukon rides on a 116-inch (2,946 mm) wheelbase, with an overall length of 202 inches (5,130 mm). It rides on a wider track that, along with the long wheelbase, provides a smooth, confident and secure driving experience. Yukon XL models have exterior dimensions similar to the regular models, but are about 14 inches longer in wheelbase and 20 inches longer in overall length.

Both Yukon and Yukon XL are available in SLE (cloth trim) and SLT trim (leather appointments), as well as 2WD and 4WD configurations. A third-row seat is standard on Yukon XL models and available on Yukon . The third-row seat is available in two configurations: two-passenger or three-passenger.

Yukon and Yukon XL models feature a 5.3L V-8 with GM’s fuel-saving Active Fuel Management technology. A 4.8L V-8 is the standard engine on the Yukon 2WD base model only, and a new 6.0L all-aluminum V-8 with variable valve timing is available on Yukon XL. Several available engines are capable of running on E85, a renewable fuel made of 85 percent ethanol and 15 percent gasoline; in fact, all Yukon 4WD and Yukon XL half-ton models come standard with the E85-capable version of the 5.3L V-8. GM vehicles with E85 capability can run on 100 percent gasoline or on E85 or on any combination of the two.

Design details
Yukon and Yukon XL have a sleek, taut form. Wraparound front and rear fascias, styled mirrors and integrated running boards provide a seamless, contemporary appearance. Craftsmanship is found in elements such as tight tolerances between exterior components and a tuned, wheels-to-the-corners proportion. The toned look on all models is created with a fast windshield angle of 57 degrees, which flows gracefully into the roofline. This improves aerodynamic performance, which bolsters fuel economy and helps reduce wind noise. Jewel-look lighting elements and doors that extend over the rockers accent the vehicles’ precise and refined design elements.

Features such as power articulating running boards and a power liftgate enhance accessibility. The liftgate’s easy-to-operate assist feature is designed to help the operator by using the mass of the tailgate to almost open or close itself once the liftgate is past the halfway-open position. A switch inside the vehicle activates the power assist.

Refined, spacious interiors
Interior space has a spacious, refined environment, thanks to a premium tone-on-tone color scheme and a lower-positioned instrument panel. Sculpted seat designs and detailed trim affirm the vehicles’ craftsmanship, which is bolstered by optional amenities, such as heated seats for first- and second-row passengers. Also, the front seats offer plenty of fore/aft and recline travel, and the second-row seats have a comfortable angle for the seatback recline.

The upscale styling is complemented by soft, low-gloss materials for the instrument panel and other trim pieces. The harmonious color and grain of the materials were carefully selected to provide a premium feel as well as durability. Flush-mounted HVAC controls and radios, with almost imperceptible gaps, convey precision and integration. Chrome accents are used on instrument surrounds, vents and other trim.

Craftsmanship also is revealed in unexpected areas, such as distinctive sill plates that greet occupants when the doors are opened, and there are no exposed fasteners or hardware on the pillars, seats or seat tracks. The seats have “close-outs” that surround the seat bottoms and seat tracks, creating a more finished appearance. The undersides of the seats are covered, too, when folded.

The Yukon family also offers an industry-exclusive power fold-and-tumble second-row seat feature that eases access to the third-row seat. The power fold-and-tumble second-row seats feature release buttons accessible by the driver on the overhead console or on the interior C-pillar to provide an easy, immediate release of the seat and an access path to the third-row seat or cargo area

Remote start is available and enables the climate system to heat or cool the vehicle’s interior prior to occupant use. A wide array of audio, infotainment and safety options also is available and includes an available touch-screen navigation system, as well as a DVD system with a large flip-down screen positioned in front of the second-row seats.

Yukon and Yukon XL interiors are versatile, too. The third-row seats fold flat and are easily tumbled forward or removed for maximum cargo area. Also, the center console storage compartment, at 20.1 liters of capacity, is the segment’s largest. The glove box offers significant storage space, too, and features damped opening operation that bolsters quietness and refinement.

Responsive suspension, solid chassis
The Yukon and Yukon XL are built on GM’s full-size SUV platform, which incorporates features such as a fully boxed frame, coil-over-shock front suspension and rack-and-pinion steering. The frame supports wide front and rear tracks that enhance stability and driving confidence through a more secure road feel and a lower center of gravity. The front suspension consists of a coil-over-shock design that delivers linear, solid and unwavering ride and handling characteristics on all road surfaces.

A rack-and-pinion steering system provides precise and responsive control and enhanced on-center feel. Yukon and Yukon XL 1500 models use a highly refined five-link rear suspension that provides superior isolation and ride, with larger, firmer brackets that also contribute to the vehicles’ precise driving manners.

Large, four-wheel disc brakes and a sophisticated ABS system ensure braking performance at the top of the segment. Larger vented front and rear brake rotors, stiff dual-piston calipers and long-life brake pads contribute to enhanced pedal feel, reduced brake noise, predictable, linear brake response and shorter braking distances. A Bosch 8.0 next-generation four-channel ABS system is standard. The ABS system works with the standard StabiliTrak electronic stability control system. It incorporates rollover mitigation – software algorithm technology that uses sensors to proactively predict vehicle “tip-up” and applies appropriate brake forces to help prevent such events.

Enhanced driving control and ride smoothness is offered with the available Autoride real-time damping system, which uses electronically controlled shock absorbers to make nearly instantaneous damping adjustments. The system “reads” the road and anticipates the best damping rates. Seventeen-inch wheels are standard on Yukon and Yukon XL; 20-inch wheels are available. The wheels are designed with premium-appearance faces, including available chrome or polished finish. New tires are tailored to the vehicles to provide excellent balance of handling, quietness and safety. Yukon 2500 comes standard with 16-inch wheels and new, 17-inch wheels are available.

Powertrain
The Gen IV small-block V-8 family powers the Yukon and Yukon XL. An iron-block Vortec 5.3L V-8 with 320 horsepower (239 kW)* and 340 lb.-ft. of torque (461 Nm)* offering Active Fuel Management technology is standard on all models except the base Yukon 2WD; Yukon XL with 4WD (5.3L with aluminum cylinder block) delivers 310 hp (231 kW) and 335 lb.-ft of torque (454 Nm).* Active Fuel Management enables better fuel economy by switching between eight-cylinder and four-cylinder operation in appropriate, lower-demand situations. Operation is automatic and seamless to the driver. The engine uses less fuel when operating in four-cylinder mode.

A Vortec 4.8L V-8 is standard on the Yukon 2WD base model. A Flex-fuel E85 version of the 5.3L engine, which is capable of running on E85 ethanol fuel or any mixture of E85 and gasoline, is standard on 4WD models and available on 2WD models. E85 is comprised of 85 percent ethanol, a renewable resource fuel produced in the United States that reduces carbon dioxide emissions

Available on Yukon XL is an all-aluminum 6.0L V-8 with variable valve timing (VVT). It is rated at 366 horsepower (273 kW).* VVT helps optimize camshaft timing to improve low-rpm torque and high-rpm horsepower. The system is enabled by a unique cam phaser – the industry’s first application of VVT on a mass-produced V-8 cam-in-block engine. The unique cam phaser adjusts the camshaft timing at the same rate for both the intake and exhaust valves.

Safety and security
The Yukon and Yukon XL are designed to be among the industry's safest and most secure vehicles, with a 360-degree perimeter safety system of occupant protection and crash avoidance technologies. Standard features include r head curtain side air bags for all seating rows and front-seat safety belt pretensioners that are linked to the vehicle's sensing system to provide segment-exclusive deployment in rear-end crashes. These features are integrated into a stronger vehicle structure that is also designed for improved compatibility with other vehicles.

The head curtain air bags include design features that provide increased rollover protection and occupant containment. Sensors located at the front of the vehicle, in the side doors, and within the occupant compartment provide increased and more immediate crash detection. The vehicle's sensing system provides segment-exclusive capability to deploy front seat safety belt pretensioners during certain rear-end collisions, enhancing the belt system's ability to hold the occupants firmly in place.

The head curtain side air bag system incorporates one of the segment's first rollover indication sensors, which is located on the vehicle's center tunnel in the occupant compartment. The sensor monitors the vehicle's acceleration and roll rate. If these signals indicate an impending rollover, the roof-mounted head curtain side air bags deploy to provide an extra measure of occupant protection and containment. These head curtain side air bags stay inflated longer than airbags developed only for side impacts because rollover incidents can last longer. The deployment duration and other design features of the head curtain air bags combine to provide increased occupant protection and the ability to help keep occupants inside the vehicle.

Crash avoidance is bolstered through enhanced design and driver control dynamics, such as wider front and rear tracks, as well as more responsive suspensions – including a new coil-over-shock front suspension design and new rack-and-pinion steering. The vehicles are built on a stronger and stiffer, fully boxed frame that contributes to enhanced crash energy management. The front frame section has been designed to optimize crush progression resulting in improved energy absorption efficiency. The improved crush performance, enabled by hydroformed frame rails and efficient chassis component packaging, also comprehends design provisions for improved vehicle-to-vehicle compatibility in the event of a frontal impact with a smaller vehicle.

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