When I was a kid, there was one particularly long hill where my Dad would always shift our truck into Neutral and coast for a mile or so down the gentle grade. I'd seen him do it many times before it occurred to me one day to ask him why.
"Why pay for gas when gravity does the work for free?" he replied.
That thought, in a simple way, is at the heart of the hybrid that General Motors has built into its line of Chevy and GMC pickup trucks. Running on a combination of gasoline and electrical power the hybrid uses a mix of both to gain the most frugal use of each type of energy. Equipped with a standard 6.0L Vortec V-8, the truck also generates its own power by using gravity each time the truck slows-recharging the 300-volt batteries that will then feed the voltage back after the next stop. Of course, there is a bit more to it then that, but the key idea is that this hybrid system re-captures energy that the truck produces anyway (just plain physics, really), energy that in other vehicles is wasted as byproducts of combustion.
What makes it work are GM's Electrically Variable Transmission (EVT) and the 300-volt nickel-metal hydride Energy Storage System (ESS) that saves and gives back that untapped power. This EVT is a unique setup of two 60kW electric motors, three planetary gearsets and four traditional hydraulic wet clutches. This arrangement is continuously in variable operation, offering the greatest efficiencies at any given moment under any specific load.
From a standstill, the Silverado launches and drives up to 30 mph on electricity alone, then the 6.0L gas engine takes over; but this V-8 engine also has Active Fuel Management (AFM) and Late Intake Valve Closing (LIVC) technology, which lets it operate in "V-4" mode once its reached highway speeds. To help it stay in V-4 mode as long as possible, the EVT also offers the equivalent of a 30hp boost of electric power, when needed at high speeds. Again, its all about physics-minimize friction, use gravity to make electricity and maintain motion using the least amount of energy.
I drove this truck, over the holidays last year, for a total of 1,000 miles around town and with a trip to Ottawa thrown in. My total mileage broke down to about a 60/40 split between highway driving and a mix of city and in-town expressways.
The four-speed EVT transmission...
The four-speed EVT transmission can trace its roots to GM's hybrid passenger bus drivetrains.
And how did I drive it? Well, I hauled a couch, delivered an ATV, took Christmas gifts to Grandma's, fought for parking at the mall, and ferried four turkey-stuffed family members around. Finally, I shipped my son back to University of Ottawa with the bags of laundry his mom washed, and at least 50 pounds of cakes and cookies to feed the other dorm inmates. In short, I did nothing out of the ordinary testing this truck-including ignoring the hybrid function, 'cause I know that is what most buyers will do. I simply drove it; in snow, rain, ice, and at temperatures of just above freezing to around zero degrees Fahrenheit.
And that is the beauty of this hybrid-while it's great to understand how it works, you don't have to; inside, the only indication that you are even driving a hybrid is the gauge cluster that includes a tachometer with an "Auto Stop" indicator (this signals when the gas engine is shut down, though all functions like the heater remain on). The only other clue is the economy gauge to the left of the tach that is meant to help you maintain the most efficient driving style
While I paid little attention to that gauge, a funny thing happened when I did my first calculations-my fuel consumption was better in the city than on the highway (exactly backwards for a straight gas engine). This strange result is a feature of the engine shutting off at stoplights and while idling-also at low speeds and in stop-and-go traffic, the electric motors propelled the truck exclusively. During the first ten days of my test (which was mostly city driving), I averaged 18.7 mpg
Among the readouts in the Silverado instrument cluster is "instant fuel economy" as well as "average economy," but for my purposes I calculated my usage old-school-using a pencil-but I did compare my figures with the truck's readouts, and I found the vehicle's computer was 99-percent accurate.
The day we did the highway run to Ottawa (from Brampton, Ontario) it was clear but cold at around five degrees. There were five of us in the truck, and the bed was stuffed (with a brilliant red beanbag chair bungeed on top of the pile). I set the cruise at 75 mph and did the trip of 312 miles on 19.8 gallons of regular fuel-15.8 mpg). The return trip data was almost identical.
As for the truck itself, the hybrid system uses the GMT900 truck (all new in '07) as its host. Specifically, one model is currently available, a crew cab shortbox model; mine was the 4x4 version with a curb weight of 5,881 pounds. From the outside, the only thing that sets it apart from a normal Silverado is a hybrid badge and some stenciling. Under the hood it's also much the same, apart from the fact that things like the water pump, power steering pump and A/C unit are electrically driven (so they will continue to run when the gas engine is off). That's it, really-no other major body changes were necessary because the hybrid electric motors are neatly fitted into the EVT transmission housing (this makes it easy to mate to other vehicles like the Tahoe and Escalade, which GM has already done) while the battery array is located in a sealed box under the rear seat. That's it; and with a warranty of eight years/100,000 miles on the ESS, little or no thought need ever be given to the hybrid function at all.
The 6.0 V-8 has Active Fuel...
The 6.0 V-8 has Active Fuel Management and Late Intake Valve Closing, which allows it to run on half its cylinders at highway speeds.
An issue with some other hybrids currently on the market is towing. Specifically, they can't. Not so with the GM system. This tranny will handle up to 5,900 pounds (4x4 version) or 6,100 pounds for the 4x2 truck using the variable electric/gas operation and fixed-gear ratios in the transmission for heavier loads. Interestingly, much of this technology and build experience was gained from GM's development of hybrid passenger bus drivetrains.
Earlier this year I set up a towing test with the identical hybrid system in an early-build Chevy Tahoe. My choice of trailer (2008 Keystone Sprinter: length, 28'11"; weight, 6,318 pounds) pushed the Tahoe to just past the limit set by GM.
I towed it with an equalizing hitch and found, in general, it didn't feel like it was a burden to any aspect of the powertrain. I also noted that from a standing start, the electric motors alone moved the trailer easily, and at higher speeds (sticking to the speed limits) the V-4 would still stay engaged on level pavement at 50 mph. I also ran the unit in cruise control, and the truck maintained its speed all up and down through the hilly Oakridge's Moraine countryside, popping in and out of V-8 mode as dictated by the rise or fall of the highway.
So, even with the trailer attached, our Silverado always chose the most economical mix of power options available-mind you, in several merge situations, I floored the pedal and the truck responded instantly, easily pulling the trailer into the traffic stream.
For this test, I drove 60 miles and certainly I felt the gas engine working harder than normal to tow this load-and that was reflected in the fuel consumption (which was an average of 11.9 mpg). But it tows-so there is no need to give up that option because of your choice of a hybrid.
So, what's the cost of economy or being green? About $10,000 more than a non-hybrid truck. You can narrow that gap somewhat if you go with the 4x2 version which knocks $4,150 off my 4x4 tester's price. Does buying one make (dollars) sense? You decide.
Quick Specs
Vehicle: Chevrolet Silverado 2-Mode Hybrid pickup truck
Base price: $50,875
Price as tested: $52,225 (4x4)
Engine: GM Vortec 6.0L V-8 with VVT and AFM
Rated horsepower/torque (lb-ft) @ rpm: 332 @ 5,100/367 @ 4100
Transmission: 4-speed EVT
Brakes: Power-assisted four-wheel discs with fully blended regenerative braking control, standard stability control, traction control
ABS: Four-channel
Wheels: 18-in chromed aluminum
Tires: P265/65R18 all-season
EPA estimated fuel economy, city/hwy: 15/21
Standard features: AutoTrac automatic 4WD, locking rear differential, Z/85 handling/trailering suspension, HD trailer package, four-wheel ABS, StabiliTrak, tinted glass, chrome wheels, power heated mirrors, soft tonneau cover, intermittent wipers, Bluetooth, automatic HVAC, power windows, steering, brakes, locks and cruise control. Leather-wrapped tilt wheel w/audio controls, driver info centre w/tire pressure monitoring, 40/20/40 split bench w/lockable storage under armrest, stadium-style rear split folding bench seat, colour-keyed carpet and floor mats, and engine block heater. Dual stage front airbags, head curtain side-impact airbags, latch child seat anchors, OnStar-one year Safe and Sound included