Chevy Silverado Hybrid truck burns regular fuel up to 22 mpg
Bob Plunkett, Sun, 28 Jun 2009 08:02:07 PDT
SAN ANTONIO, Tex. -- Along Commerce Street, which cuts a broad swatch across San Antonio, we're driving Chevrolet's Silverado 1500 Hybrid, a gas/electric truck that delivers respectable fuel economy figures.
General Motors constructs this hybrid electric vehicle (HEV) off the Chevrolet Silverado 1500, a full-size pickup in the half-ton/light-duty class, and casts an equivalent model off the GMC Sierra truck.
The HEV version looks virtually identical to a conventional Silverado (or Sierra).
Its two-box body features a predominant prow flashing a chrome-bar grille, the tall cabin contains four doors and seats for five adults, and a rear truck box, stretching to 69.3 inches, almost six feet long -- remains concealed by a tri-part hard tonneau lid.
Yet the powertrain tucked inside Silverado's squarish engine bay is certainly not conventional.
It's a special hybrid propulsion system developed by GM -- working with Chrysler, BMW and Mercedes-Benz -- to improve fuel economy scores. First, there's a powerful 6.0-liter V8 aboard that runs on gasoline.
It knocks out 332 hp at 5100 rpm and high torque up to 367 lb-ft at 4100 rpm. But the Silverado Hybrid truck carries other power sources too.
Specifically, there are two 60-kW electric traction motors aboard. These electric motors are packaged with three planetary gearsets and four hydraulic wet clutches as components of GM's electrically variable transmission (EVT).
A high-tech control unit -- the Hybrid Optimizing System (HOS) -- manages all energy produced by the on-board gas/electric engines and applies it directly to Silverado's wheels in variable measures, as well as providing four fixed-gear ratios so it can mimic the shift pattern of a four-speed automatic transmission.
Power to run the electric motors flows from a 300-volt nickel-metal hydride battery pack, labeled the Energy Storage System (ESS), which is stowed in Silverado's cabin below the second-row bench seat. The ESS also stores energy produced during regenerative braking and may be charged by the V8 engine with one of the electric motors used as a generator.
GM describes the hybrid apparatus for Silverado Hybrid as a two-mode hybrid propulsion system. At low speed the truck can move forward or backward using an electric motor or the gas-fired V8 or a combination of the V8 and electric motor.
At highway speed Silverado's second mode works with all eight cylinders of the gasoline engine pumping when commanded, or with only four cylinders firing through GM's Active Fuel Management (AFM) technology which pares the number of cylinders in the combustion process to conserve fuel.
And when the Silverado HEV stops, its V8 engine shuts down, leaving only electric motors running. An electric motor may also propel this Silverado up to a speed of about 30 mph, and it works even when the truck is pulling a trailer.
So what's the point of packing a big pickup truck with so much compicated hardware? It's to improve the fuel economy numbers.
GM tests indicate that the Silverado 1500 Hybrid earns fuel economy figures up to 21 mpg for in-town driving in the two-wheel-drive (2WD) version, or 20 mpg with the optional four-wheel-drive (4WD) system.
For a big truck stretching 19 feet long and weighing nearly three tons, these fuel economy scores are huge -- representing up to 40 percent improvement for in-town driving over a Silverado 2WD with a 315-hp 5.3-liter V8 aboard earning only 14 mpg in city tests. So there's obvious savings to be earned with Silverado Hybrid's elevated fuel economy figures.
Note, though, that while fuel economy scores increase with Silverado's hybrid treatment, the truck's towing capacity actually decreases. GM rates the tow load for Silverado Hybrid at 6100 pounds (2WD) or 5900 pounds (4WD).
By comparison, a conventional Silverado Crew Cab truck with the 5.3-liter V8 aboard plus a tow package can tug up to 9600 pounds (2WD) or 9500 pounds (4WD). And the front-end cost to add all of the hybrid equipment to Silverado increases the bottom line by almost $7,000. GM sets the MSRP for a 2009 Silverado Hybrid truck at $38,100 (2WD) or $41,200 (4WD).
The MSRP for a 2009 Silverado LT Crew Cab without hybrid equipment tallies to $31,100 (2WD) and $34,300 (4WD).
Variances with Silverado Hybrid include the electric power steering (EPS) system with an electrically driven 42-volt variable-assist power steering rack. It eliminates the conventional hydraulic apparatus along with the power losses of an engine-driven pneumatic pump, and also pares pounds.
The brake system consists of a big disc at every wheel and a four-wheel anti-lock brake system (ABS) for straight-line brake tracking, plus StabiliTrak, GM's anti-skid device.
And the HEV has that regenerative braking system to capture electricity generated through vehicle braking and decelerating to recharge the ESS so it never needs to be plugged in for recharging like an electric vehicle.
Silverado Hybrid also has modifications to pare the body weight and improve aerodynamics.
* Its prow dips for aerodynamic efficiency and the front air dam rises slightly higher to trim the air drag.
* The P265/65R18 tires were selected for their low-rolling resistance to reduced road noise.
* A three-segment rigid tonneau covering the rear truck box enhances aerodynamic efficiency.
In the cabin, the Silverado HEV has Chevy's Crew Cab configuration with four doors and two rows of seats -- a pair of front buckets (or optional bench for three) and a rear bench for three.
Included on the dashboard is an eight-inch touch screen with animated graphics indicating the energy flow from gasoline engine or electric motors -- or perhaps all at once.