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GM @ Chicago 2008: '09 GMC Sierra Hybrid

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For release: Feb. 3, 2008, 12:01 a.m. EST



CHICAGO – GMC announced the 2009 GMC Sierra Hybrid, a powerful full-size pickup that achieves 40-percent greater city fuel economy and a 25-percent improvement in overall fuel economy while delivering the capability expected of a full-size truck – including a 6,100-pound (2,767 kg) towing capacity.

Partnering General Motors’ patented two-mode hybrid system and a powerful 6.0L gas V-8, the Sierra Hybrid delivers highly efficient performance, including all-electric driving up to 30 mph (48 km/h). That allows fuel savings to be realized even when the truck is fully loaded or towing a trailer.

“The Sierra Hybrid represents GMC’s commitment to engineering excellence, delivering a fully functional truck that offers a significant improvement in fuel economy,” said Jim Bunnell, GMC general manager. “Sierra Hybrid will deliver fuel economy that is expected to be the best in the full-size pickup segment, exceeding the current mileage leader – the non-hybrid Sierra.”

The Sierra Hybrid goes on sale in the fourth quarter of 2008 and is based on the strong and capable Sierra platform that was introduced for the 2007 model year. It will be offered in the Crew Cab body style on both 2WD and 4WD models. Each model is equipped with several standard, popular features, including StabiliTrak electronic stability control system, a locking rear axle and a trailering package. Sierra Hybrid also offers dual-stage frontal air bags and head curtain side air bags, and it is the only full-size truck with five-star side-impact ratings in federal crash tests.

Hybrid details

The Sierra Hybrid’s fuel-saving performance is derived from GM’s advanced Electrically Variable Transmission (EVT) and 300-volt nickel-metal hydride Energy Storage System (ESS), which work in concert with the standard 6.0L V-8 gasoline engine with Active Fuel Management (AFM) and late intake valve closing (LIVC) technology. GM’s hybrid technology system not only enables the Sierra to launch and drive up to 30 mph on electricity alone, it also allows the Vortec 6.0L V-8 engine to operate in its more economical V-4 mode for longer periods.

As part of the vehicle’s emission control system, the ESS is warranted for eight years/100,000 miles.

With GM’s two-mode hybrid system, the electric power used to propel the vehicle is generated by the hybrid system itself. When the brakes are applied or the vehicle is coasting, the electric motors within the hybrid system create electricity that is stored in the 300-volt battery. This stored energy is used to move the vehicle and the regenerative braking cycle is renewed.

The two-mode hybrid system provides seamless, dependable power on demand in an efficient package. In fact, its electric motor is less than half the size of those in single-mode hybrid systems. This technology was developed and is still used in fleets of hybrid transit buses in more than 70 North American and European cities. Scaled-down for use in passenger vehicles, the two-mode system delivers fuel savings where it is needed most – in large vehicles with high levels of capability. The two-mode system was first introduced on the 2008 Yukon Hybrid. It is a core part of GM’s energy diversity efforts, which are centered on reducing dependence on petroleum, improving fuel economy, reducing emissions and minimizing the automobile’s impact on the environment.

With the fuel savings of the hybrid system and Sierra’s 26-gallon (98-liter) fuel tank, the Sierra Hybrid has a cruising range of more than 500 miles (800 km).

Quiet and smooth

Integration of the hybrid system on the Sierra is seamless – the battery pack is located beneath the rear seat – and perceptible only in what it lacks: noise.

“The Sierra Hybrid is exceptionally quiet,” said Mark Cieslak, vehicle chief engineer. “From a passenger’s perspective, the refinement of the hybrid system is quite evident throughout the driving experience, and showcases itself when the vehicle is moving under electric power.”

Contributors to the quiet driving experience include:

-New exhaust system and resonator tuned for the 6.0L engine’s Active Fuel Management operation

-Additional engine intake induction tuning for reduced interior noise and pleasing sound quality

-Low-rolling resistance, “quiet-tuned” P265/65R18 tires for reduced road noise

-Electrically driven 300-volt air conditioning compressor reduces vibration and allows the standard, tri-zone HVAC system to cool the passenger compartment even when the gasoline engine is shut off

-Electrically driven 42-volt variable-assist power steering reduces vibration and provides up to a 0.5-mpg fuel economy improvement by reducing parasitic losses common in belt-driven hydraulic systems

-Energy Storage System (ESS) cooling system internal fan is tuned to be quiet at low vehicle speeds when the fan could more easily be heard by the occupants.

Along with quietness, the Sierra Hybrid also delivers exceptional driving smoothness, thanks to specifically tuned shocks for its Z85 suspension and a new hydraulic body mount. Located on the passenger side of the chassis, the hydraulic mount provides a dramatic improvement in highway driving smoothness, particularly on rough or choppy road surfaces.

“The hydraulic mount makes a dramatic improvement in ride quality,” said Cieslak.

Additional details specific to the Sierra Hybrid include aerodynamic aids. A slightly deeper front air dam and a tonneau cover for the bed reduce air drag, fostering maximum efficiency.

Trailering performance

In addition to increased fuel economy, the Sierra Hybrid’s electrically variable transmission also provides tremendous trailering capability, enhancing driving smoothness and quality when towing. Electric drive is enabled up to approximately 30 mph (48 km/h), even when towing, allowing fuel savings when the truck is towing a trailer.

“Along with being very smooth, the EVT always provides abundant torque at all rpm levels for easy towing,” said Cieslak. “It is particularly helpful on grades, as the EVT’s greater ratio spread allows the engine to hold optimal rpm for smooth, steady performance, with no hunting between higher and lower gears.”

The EVT incorporates grade braking and tap up/tap down shift control. It also benefits towing on curves or lower-speed back roads, as exceptionally smooth gear transitions eliminate the “shift shock” torque disruption that can occur during abrupt shifts, such as when slowing or braking.

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For release: Feb. 3, 2008, 12:01 a.m. EST



CHICAGO – The 2009 GMC Sierra Hybrid delivers greatly improved fuel economy without sacrificing the strength and capability expected of a full-size, V-8-powered truck. This is enabled by GM’s patented two-mode hybrid system, featuring an electrically variable transmission (EVT).

Sierra Hybrid offers the best of both worlds: hybrid benefits while operating in both stop-and-go traffic or on the highway. This is different from single-mode hybrids that provide benefits only when in a slower city driving environment. The Sierra joins the Chevrolet Silverado as the only full-size pickups offered with hybrid powertrains.

Drawing on experience gleaned in the development of hybrid bus propulsion systems, GM designed the two-mode EVT to provide the best combination of city and highway fuel economy; it is used in concert with the Vortec 6.0L V-8 engine with Active Fuel Management. Furthermore, the EVT is designed to bolt directly to the standard four-wheel-drive transfer case found on the gasoline-only models for true four-wheel-drive capability.

The Sierra Hybrid’s drivetrain is made up of the following major components, each of which works together to provide seamless, economical and comfortable operation that goes virtually unnoticed by the driver and passengers:

-Electrically Variable Transmission (EVT)

-Energy Storage System (ESS)

-Vortec 6.0L V-8 with Active Fuel Management (AFM) and late-intake valve closing (LIVC)

Electrically Variable Transmission (EVT)

The key to GM’s all-new EVT is its unique assemblage of two 60 kW electric motors, three planetary gear sets and four traditional hydraulic wet clutches. This arrangement allows continuously variable operation, as well as providing four fixed gear ratios (with operation comparable to that of a standard electronically controlled automatic transmission).

The design was selected because of the operational characteristics of electric motors, which are very efficient when turning at low speeds, but much less efficient as motor rpm increases. Current hybrid passenger vehicles run their electric motors almost continuously throughout the entire drive cycle, which can be very inefficient under high loads and at highway speeds. The opposite is true with GM’s EVT, which can activate any of its four hydraulic clutches to allow power to be transferred via the fixed-gear ratios whenever high load conditions are experienced.

A sophisticated Hybrid Optimizing System (HOS) constantly receives torque-based data from the powertrain and other vehicle systems, and then determines the most efficient means of propelling the vehicle – either via electric power, gasoline engine power or a combination of the two. The EVT is like having two transmissions in one – continuously variable drive for light-load conditions and fixed-ratio drive for high-load situations.

All functions of the EVT are controlled by the HOS, which constantly searches for the optimal transmission operation (using either variable or fixed ratios) to meet current operating conditions. The HOS also bases its decisions on allowing the Vortec 6.0L V-8 to take full advantage of its Active Fuel Management system and, because of an equivalent 30-horsepower (22 kW) boost of electric power, remain in V-4 mode as long as possible for maximum fuel economy. This is the key to Sierra Hybrid’s 25-percent improvement in combined city/highway fuel economy.

Unlike less advanced hybrid systems, this new GM system occasionally shuts down the electric motors, allowing the EVT to function as a conventional automatic transmission. Typically, this fixed-ratio operation occurs at highway speeds or when hauling heavy loads, and can actually be more efficient than operating in electric-gasoline hybrid mode under the same conditions. This is because under high-load situations, when the fixed gears are in use, the electric motors can be used to generate electricity – or, if needed, they can be called on to supply additional torque for improved performance.

Energy Storage System (ESS)

Providing power to the EVT’s two electric motors is a 300-volt nickel-metal hydride Energy Storage System (ESS). This battery pack is located under the rear seat, where it takes up virtually no additional space.

The primary function of the ESS is to provide power (300 volts) to the EVT via the Traction Power Inverter Module (TPIM) and to store captured energy produced during regenerative braking. The ESS can also be charged, when necessary, by the gasoline engine via one of the two electric motors when operated in generator mode.

In addition to supplying power to the EVT, the ESS also provides power to the air conditioning compressor and the Accessory Power Module (APM), which converts the high-voltage supply to 42 volts for the electric power steering system, and 12 volts for the vehicle battery and other 12-volt electrical accessories.

Battery pack durability and reliability are maintained via optimized charge and discharge cycles, as well as a dedicated cooling system that draws air from the passenger compartment. As part of the vehicle’s emission control system, the ESS is warranted for eight years/100,000 miles.

The ESS also has numerous safety features that prevent overcharging, overheating, unintended access to high-voltage components and infiltration from liquid spills.

Regenerative braking

The Sierra Hybrid features fully blended regenerative braking to capture energy that would otherwise be lost during vehicle deceleration. By using one or both of the EVT’s traction motors as a generator, braking energy is converted to electrical energy and stored in the ESS for future use to propel the vehicle.

The regenerative brakes are used along with the standard hydraulic brakes to slow the vehicle and/or bring it to a stop. Depending on the amount of braking force required, the hydraulic brakes may not even be used, such as during mild deceleration when slowing to allow space for merging traffic near a highway on-ramp.

When additional braking is called for, based on a change in the position of and/or the force applied to the brake pedal emulator, the hydraulic braking system will be called on to assist the generator(s) in slowing or stopping the vehicle. The anti-lock braking system (ABS)/Electronic Stability Control (ESC) modulator used on the Sierra Hybrid has been adapted to allow this interaction between the hydraulic brakes and the regenerative braking system.

The use of cooperative control between the regenerative braking system and the hydraulic brakes results in excellent braking control and maximum energy recovery. The system also provides feedback in the form of brake pedal resistance, which gives the driver the same feel as would be experienced with a normal hydraulic braking system.

Regenerative braking has the additional benefit of extending the life of the friction materials used in the hydraulic braking system, as well as improving braking performance in the form of shorter stopping distances.

Vortec 6.0L V-8 engine

The Sierra Hybrid’s Vortec 6.0L V-8 engine is unique. It features Active Fuel Management and late-intake valve closing (modified Atkinson-cycle combustion process) for reduced pumping losses and better overall fuel economy.

The engine uses flat-top pistons, cylinder heads borrowed from GM’s 5.3L high-output V-8 and a 10.8:1 compression ratio, producing 332 horsepower (248 kW) at 5,100 rpm and 367 lb.-ft. of torque (497 Nm) at 4,100 rpm. It runs on regular unleaded fuel.

A key contributor to the Sierra Hybrid’s fuel economy is the gasoline engine’s Auto Stop mode. Once the vehicle reaches 0 mph, depending on the current state of the battery charge, the gasoline engine can automatically shut down. By leaving the engine off and allowing the vehicle to move only under electric power, such as during heavy stop-and-go traffic, fuel consumption is greatly reduced.

However, when extra power is required, such as for wide-open-throttle acceleration from a standing stop, the Vortec 6.0L V-8 is seamlessly restarted so it can deliver the necessary power and torque. In this case, the engine is restarted effortlessly from the Auto Stop mode using the EVT’s powerful internal electric motors; there is no traditional starter motor.

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