If it doesn't already, your fleet soon will include hybrid trucks. Given high fuel prices, concern for the environment, and the goodwill generated by setting an example for your community, it's inevitable.
The EPA's Smartway program rewards both public and private owners of fuel-efficient, less-polluting vehicles. In a growing number of cities, hybrids can use high-occupant vehicle (HOV) lanes on expressways. Financial incentives such as development grants make it easier for governments to afford these higher-priced technologies. Thanks to diesel prices that have reached $4.50/gallon or more, payback on the initial investment is shorter than ever.
Two types of hybrids
Just as corn is bred to provide the best characteristics of each parent strain—yield/acre and pest resistance, for example—hybrid vehicle combines the best characteristics of two technologies to get each one's advantages.
Gasoline-electric is most common, combining the combustion engine's power with the electric motor's energy efficiency and emissions-free operation.
For commercial applications, diesel is more energy efficient. Diesel-hydraulic hybrids are developed for frequent stop-and-go driving; instead of using only service brakes to slow and stop, the trucks convert their kinetic energy into hydraulic pressure stored in a tank. Pressure is released to turn hydraulic motors to assist acceleration, relieving the burden on the engine and reusing energy lost as heat from the brakes.
All hybrid systems combine power sources for acceleration and use hydraulic or electric motors for regenerative braking. The reuse of braking force is why hybrid vehicles often get better fuel economy in cities than on highways. General Motors' full-size hybrid pickups—the Silverado and Sierra, and the SUVs built on the same platforms—the Tahoe and Yukon, get similar city and highway mileage, according to EPA estimates. They have the same general configuration and dimensions as the conventional models, but towing capacity and payload are reduced, most likely to avoid overstressing the electric motor.
A Chevrolet Tahoe Hybrid with a 6.0-liter V-8 gasoline engine produces a healthy 332 hp and 367 foot-pounds of torque. At part throttle, the engine handles the 5617-pound (dry) vehicle plus payload with ease. Nickel-metal hydride (NiMH) batteries form the heart of the Energy Storage System, which contains batteries and a logic unit, that directs 300 V to power the vehicle, 42 V to the electric power steering system, and 12 V for the vehicle battery and electrical accessories.
A different type of ride
No additional skills are needed to drive a hybrid, but there are new sensations to get used to. There's no separate starter motor to crank the engine. When starting, the electric motor engages the engine and, suddenly, it's 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 the engine turns on. A computer determines the best source of power. For really quick starts, both forms of power are blended seamlessly and optimally.
Stepping on the brakes feels different in the Tahoe. The regenerative braking system works in tandem with the hydraulic brakes, using the SUV's energy, turning the motor into a generator. The electrical energy is stored in the NiMH batteries and is available when needed. A brake pedal emulator provides resistance in the pedal, so stopping feels almost the same as with conventional brakes. During a test drive, there is a noticeable clunk each time the vehicle stopped, but only when braking began.
One way to save fuel is to shut off the engine. 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 kicks in. 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, all cylinders come back on.
Around town, the Tahoe Hybrid's fuel economy is comparable to a four-cylinder Chevy Malibu. While driving a 94-mile test run, the vehicle achieved 21.6 mpg in town and 24.1 mpg on the highway.
Beware of high voltage. Train your technicians before letting them work on hybrids. Even 42 V can cause injury, and 300 V can kill.
This article first appeared in our sister publication, Public Works magazine, and is reprinted with permission.
Technology and Maintenance Council of the American Trucking Association