2009 GMC Sierra Hybrid Preview

Introduction

When GMC brings the 2009 Sierra Hybrid to market this fall, expect to see a full-size pickup truck that delivers a 25-percent improvement in overall fuel economy-and a full-size truck's capability. This includes a 6,100-pound towing capacity. The use of GM's patented 2-mode hybrid system, along with the Vortec 6.0-liter V-8 engine, allows for the increased fuel efficiency. All-electric driving (up to 30 mph) permits fuel savings even with a fully-loaded truck, or towing a trailer, the automaker says.

Announced at the 2008 Chicago Auto Show, the 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 automaker says. According to GM, the GMC Sierra Hybrid and Chevrolet Silverado Hybrid are the only two full-size pickups offering a hybrid powertrain.

Model LineupThe 2009 GMC Sierra Hybrid is a front-engine, full-size, 4-door pickup that will be available in 2WD and 4WD when it goes on sale in the fourth quarter of 2008. The Hybrid is based on the Sierra platform that GMC introduced in model year 2007. The Hybrid will be offered in a Crew Cab body style, equipped with standard locking rear axle, electronic stability control system and trailering package.

GMC claims the hybrid is exceptionally quiet. This is due to:

• Low-rolling-resistance, "quiet-tuned" tires


• Electrically driven 300-volt air conditioning compressor that reduces vibration and allows the passenger compartment to cool even when the gas engine is shut off


• New exhaust system and resonator tuned to the 6.0-liter V-8 engine's Active Fuel Management system


• Additional engine intake induction tuning


• Electrically driven, 42-volt, variable-assist power steering


• Energy Storage System (ESS) cooling system internal fan tuned for quiet at low speeds

Hardware

The power and efficiency in the 2009 GMC Sierra Hybrid comes from the combination of the GM 2-mode hybrid system, featuring an electrically variable transmission (EVT), energy storage system (ESS), and Vortec 6.0-liter V-8 engine with Active Fuel Management and late-intake valve closing. GMC says it designed the EVT specifically to achieve the best in city/highway fuel economy, when used in concert with the 6.0-liter V-8. The Hybrid's drivetrain has three major components: EVT, ESS and the Vortec 6.0-liter V-8 engine.

Hybrid Details

The EVT is a unique assembly consisting of two 60-kW electric motors, three planetary gear sets and four traditional hydraulic wet clutches. The electric motor is less than half the size of those in single-mode hybrid systems. A hybrid optimizing system (HOS) receives torque-based data from the Sierra Hybrid's powertrain and other systems and determines the most efficient means of moving the vehicle: all-electric power, gasoline engine power, or a combination of the two. Think of EVT as basically two transmissions: a fixed-ratio drive for high-load situations, and a continuously variable drive for light-load conditions.

A 300-volt nickel-metal hydride Energy Storage System (ESS) provides power to the EVT's two electric motors. The battery pack, located underneath the rear seat, takes up little additional space. Besides providing power to the EVT, the ESS also stores captured energy produced during regenerative braking. It allocates power to the air conditioning compressor and accessory power module. The ESS is warranted for 8 years/100,000 miles as part of the vehicle's emission control system.

Regenerative brakes, used along with standard hydraulic brakes, slow and stop the 2009 GMC Sierra Hybrid. Hydraulic brakes may not even be used, depending on the amount of braking required. In addition, the ABS and electronic stability control modulator have been adapted to allow interaction between the hydraulic and regenerative braking systems.

The Vortec 6.0-liter V-8 engine (which runs on regular unleaded gasoline) pumps out 332 hp at 5100 rpm and 367 lb.-ft. of torque at 4100 rpm. The engine's Active Fuel Management and late-intake valve closing reduce pumping losses and achieve better overall fuel economy, the automaker says. The gasoline engine has an Auto Stop mode that automatically shuts it down when the vehicle reaches 60 mph, allowing the truck to proceed in all-electric power. In situations such as heavy stop-and-go city traffic, the consumption of fuel is dramatically reduced. Under these conditions, the engine restarts automatically using EVT's powerful internal electric motors.

Safety

The 2009 GMC Sierra Hybrid will offer dual-stage frontal air bags and head curtain side air bags. Information from GM states that Sierra Hybrid is "the only full-size truck with 5-star side-impact ratings in federal crash tests." In addition, the Sierra Hybrid will feature standard electronic stability control, traction control, and 4-channel anti-lock brakes.

Technology

Besides the patented GM 2-mode hybrid technology, not much else in the way of technology features is yet known. Most likely the standard or optional list will include a navigation system, AM/FM stereo with CD/MP3 player and auxiliary input jack.