The Chevrolet Tahoe Hybrid I drove recently has a 6.0-liter (364 cu-in) V-8 gasoline engine producing a healthy 3322 hp and 367 lb-ft of torque. At part throttle, the engine handles the 5617-lb (dry) vehicle plus payload with ease.
Under the second row of seats, so it's out of the way, sits a bank of nickel-metal hydride (NiMH) batteries. It forms the heart of the Energy Storage System. It contains batteries and a logic unit that directs 300 volts to power the vehicle, 42 volts to the electric power steering system. and 12 volts for the vehicle battery and electrical accessories.Behind the wheel
No additional skills are needed to drive a additional skills needed drive hybrid, but there are new sensations to get used to. There is no separate starter motor to crank the engine. When starting, the electric motor engages the engine and suddenly, it is running.
If already hot, the engine may not turn over when you turn the key. Ease down on the gas pedal and the SUV starts rolling on pure electric power. The engine stays off. To accelerate more quickly, step down harder and all of a sudden, the engine is on. A computer determines which source of power is best. For really quick starts, both forms of power are blended seamlessly and optimally.
Stepping on the brakes feels different in the Tahoe. The sophisticated regenerative braking system works in tandem with the hydraulic brakes. The system uses the SUV's energy, turning the motor into a generator. The electrical energy is stored in the NiMH batteries, available when needed. A brake pedal emulator provides resistance in the brake pedal, so the feel of stopping is the same as with conventional brakes. There was a noticeable clunk each time, but only when I started braking.
One way to save fuel is to shut the engine off. That's what Auto Stop does when the engine is warm and you stop. Restarting is electric up to 30 mph. Then the V-8 blends in. When loafing along on level ground or running downhill, the computer switches off four cylinders, turning the V-8 into a V-4. When you need more power, the engine turns all cylinders back on. If I didn't see the dashboard indicator, I would not have known.
Around town, the Tahoe Hybrid's fuel economy is comparable to a four-cylinder Chevy Malibu (21 mpg vs. 22 mpg, respectively). In actual driving on a 94-mile test run, I achieved 21.6 mpg in town and 24.1 mpg on the highway. Of course, I was driving to maximize fuel economy, but those are achievable numbers.
One note of caution: Beware of high voltage. Train your technicians before letting them work on hybrids. Even 42 volts can injure, and 300 volts can kill.
Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Association and is currently on the Board of Truck Writers of North America. E-mail firstname.lastname@example.org.