"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 GMC 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
"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 GMC 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.
