GMC Sierra 1500 Hybrid is the only hybrid in the full-size pickup segment, delivering an estimated 23 mpg on the highway and 20 mpg in the city (2WD and 4WD models). Compared with non-hybrid models, that’s 33 percent greater city fuel economy and a 23.5-percent improvement in overall fuel economy.
Sierra Hybrid achieves its efficiency without compromising the capability customers expect in a full-size truck – including up to a 6,100-pound (2,767 kg) trailering capacity.
Power for the Sierra Hybrid comes from General Motors’ patented two-mode hybrid system and a powerful 6.0L gas V-8, which combine to deliver all-electric driving up to 30 mph (48 km/h). The system saves fuel using electric propulsion, even when towing a trailer.
Hybrid system details
GM’s advanced Electrically Variable Transmission (EVT) and 300-volt nickel-metal hydride Energy Storage System (ESS) work in concert with the standard 6.0L V-8 gasoline engine with Active Fuel Management (AFM) and late intake valve closing (LIVC) technology to enable the Sierra Hybrid’s efficient performance. This hybrid system not only enables the Sierra to launch and drive up to 30 mph on electricity alone, it also allows the 6.0L V-8 engine to operate in its more economical V-4 mode for longer periods.
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 following major components comprise the Sierra Hybrid’s unique powertrain system:
- Electrically Variable Transmission (EVT)
- Energy Storage System (ESS)
- Vortec 6.0L V-8 with Active Fuel Management (AFM) and late intake valve closing (LIVC).
Electronically variable transmission (EVT): The key to GM’s EVT is its unique assemblage of two 60 kW electric motors, three planetary gearsets and four traditional hydraulic wet clutches. This arrangement allows continuously variable operation, and provides four fixed gear ratios (with operation comparable to that of a standard electronically controlled automatic transmission).
A sophisticated Hybrid Optimizing System constantly receives torque-based data from the powertrain and other vehicle systems, and 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.
Energy storage system (ESS): A 300-volt nickel-metal hydride Energy Storage System (ESS) provides power to the EVT’s two electric motors. This battery pack is located under the second-row seat.
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.
Vortec 6.0L V-8 engine: Engineers chose the Vortec 6.0L V-8 gasoline engine for the Sierra Hybrid because of its favorable torque characteristics. This is especially important because GM engineers adapted the 6.0L V-8 to operate with late intake valve closing (Atkinson-cycle combustion process) for reduced pumping losses and better overall fuel economy.
Using flat-top pistons, cylinder heads borrowed from GM’s 5.3L high-output V-8 and a 10.78:1 compression ratio, the Vortec 6.0L V-8 produces 332 horsepower (248 kW) at 5100 rpm and 367 lb.-ft. of torque (495 Nm) at 4100 rpm, yet requires only regular unleaded fuel.
The Vortec 6.0L also features variable valve timing to control late intake closing, as well as Active Fuel Management, which allows four of the eight cylinders to be shut off during periods of light load. With the benefit of electric boost, the engine is able to stay in V-4 mode for longer periods in the Sierra Hybrid.
Auto Stop mode and regenerative braking
A key contributor to fuel economy is the gasoline engine’s Auto Stop mode. At vehicle speeds between 0 and 30 mph, the gasoline engine may be automatically shut down. By leaving the engine off and allowing the vehicle to move only under electric power up to 30 mph, such as during heavy stop-and-go traffic, fuel consumption is greatly reduced.
The regenerative braking system works in concert with the hydraulic braking system. The system uses a brake pedal emulator, which provides progressive resistance as the pedal is depressed. This consistent pedal feel is very much like that of a standard hydraulic braking system in operation.
Sierra Hybrid matches its gasoline-only siblings in comfort and convenience, with special attention paid to acoustic details that makes for a very quiet driving experience. Examples include:
- Exhaust system and resonator specially tuned for the 6.0L LIVC engine’s Active Fuel Management operation. It ensures comfortable interior acoustics and a pleasant exhaust note during both V-4 and V-8 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 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.