Trucks: Chevrolet’s Tahoe Hybrid
| May 03, 2008 |
GM is touting its Chevy Tahoe Hybrid as the most fuel-efficient SUV available and it’s hard to argue with their logic. The fuel economy claims are impressive: The Tahoe’s two-mode hybrid drive system delivers 30 percent better overall fuel efficiency than a conventionally powered Tahoe equipped with a smaller V-8 engine; and Chevy says the hybrid gets 50 percent better in-city fuel economy than a conventional Tahoe, including a 21-mpg in-city rating. For perspective, that’s the same rating a four-cylinder Toyota Camry gets in urban driving conditions.
GM hasn’t scaled down the basic Tahoe platform one whit. The only giveaways are some battery systems instrumentation, somewhat flashy graphics that display the hybrid’s actions in real time on the center-dash navigational screen (if you select that option from the main menu) and the large, albeit invisible battery located under the second-row rear passenger seat.
From the driver’s seat, the Tahoe Hybrid behaves in traffic and on the open road exactly as a purely gasoline-powered model would. The SUV comfortably seats up to eight adults, and both the second- and third-row seats fold down to provide ample, secure cargo capacity. All the usual bells and whistles, from heated front- and second-row seats, power windows and mirrors to the premium Bose stereo with Onstar and real-time GPS navigation system are offered as well. And aside from the optional “Hybrid” graphics emblazoned on the sides and windshield, it’s virtually impossible to tell a conventional Tahoe from a Hybrid model.
A combination of forward-thinking technologies
GM was able to achieve such impressive in-city fuel economy for the Tahoe Hybrid by bringing a couple of pertinent technologies together on the truck and integrating them seamlessly together.
Early Silverado hybrid trucks showcased the viability of the two-mode drive system, but there were some definite quirks that needed to be worked out of the system. Most notable was that the engine re-start was tied directly into the truck’s brake pedal. In other words, the on-board computer would shut the gasoline engine down once its rpms fell below a certain point (roughly 1,000 rpms or so) at a traffic light or stop sign. But as soon as the driver released the brake pedal, the engine would restart. All told, it made for a highly inefficient hybrid system – particularly in stop-and-go driving conditions.
The 2008 version of GM’s two-mode drive system is much more sensibly designed. As with the earlier hybrid systems, the computer shuts the engine down once its rpms drop off into idle range. The actual power transition is transparent: You’ll note the engine oil pressure gauge dropping to zero, and the tachometer dropping below 1,000 rpms into a new “Auto Stop” zone. At this point, the Tahoe is essentially a big golf cart running on electric power captured when the SUV is braking or coasting in normal driving conditions.
As long as you keep the tachometer below 1,000 rpms and vehicle speed under 20 mph or so, the Tahoe moves quietly along just fine on electric power. It’s an outstanding system in traffic congestion, on neighborhood streets, parking lots and fast food drive-through lanes. When it’s time to go, simply step on the accelerator normally and the computer will instantly re-start the gasoline engine. The SUV emits zero emissions and burns no fuel when operating in this mode.
It’s on the open road that the second piece of GM’s innovative fuel-economy technology comes into play. The Tahoe Hybrid comes standard with Active Fuel Management. This is essentially a computer-controlled displacement system. The Tahoe’s onboard computer compares multiple variables such as engine rpm, accelerator inputs and vehicle speed and determines if the engine needs to be running on all eight cylinders or if can get by on four. A readout in front of the driver lets you know how many cylinders are currently in use – a helpful tool because the actual engagement and disengagement of the cylinders is virtually impossible to detect from inside the vehicle.
It’s a pretty slick system. And it’s a good feeling to check the mileage readout and see that you’re logging 43 mpg at 70 mph in a vehicle as large as a Chevy Tahoe. Still, it’s worth noting that the Hybrid Two Mode power system works best and delivers its greatest benefits in city driving conditions. The Tahoe Hybrid’s highway mileage is exactly the same as a conventional Tahoe equipped with Active Fuel Management, simply because its electric drive system has no influence on high-speed road performance.
The Tahoe Hybrid is a good choice for contractors working and driving in dense urban traffic. Price-wise it’s not a bad deal, either. A fully tricked out gasoline-burning Tahoe currently lists for around $48,000, while a Hybrid version (with a full host of creature comforts) retails for around $50,000.
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