General Motors' Two-Mode hybrid system is the most significant gasoline-electric propulsion advancement since the original Toyota Prius. Chevrolet Tahoes and GMC Yukons equipped with this technology can achieve 20 mpg or more, which is equivalent to that of a four-cylinder mid-size sedan in city driving.
With oil approaching $100 per barrel and a trip to the pumps capable of inflicting a like-size dent in your wallet, big trucks that don't guzzle gas on an ordinary commute seem like manna from the Middle East. To celebrate their arrival, we're saluting GM's Two-Mode as Automobile Magazine's 2008 Technology of the Year.
Like Honda's Integrated Motor Assist and Toyota's Hybrid Synergy Drive, Two-Mode blends the best attributes of internal combustion and battery-powered electric motors. But that's the only thing these three prevailing hybrid systems have in common.
GM's hybrid powertrain consists of a husky 332-hp, 6.0-liter V-8 bolted to what looks like an overgrown automatic transmission. Actually, that box (pictured above) is packed with the following hybrid components:
- two 80-hp AC motors;
- three planetary gear sets;
- four multiplate clutches;
- two hydraulic oil pumps.
A metal container located under the second-row seats contains the 300-volt nickel-metal hydride battery pack. A second box mounted under the hood is loaded with power inverters and control circuits.
Because Two-Mode is a second-generation approach conceived by transmission experts instead of engine specialists, gasoline and electric power sources are more ingeniously combined with fixed and variable gear ratios to achieve higher efficiency over a broader range. Alterations to the vehicle--weight savings from aluminum body panels and wheels, elimination of the spare wheel and tire, and subtle aerodynamic tweaks--also contribute to heightened efficiency.
Since GM partnered with BMW and the former DaimlerChrysler to develop Two-Mode for front-, rear-, and four-wheel-drive applications with gasoline and diesel engines, you'll see it in more cars, pickups, SUVs, and crossover applications. And not a moment too soon.
Here's how it works
- In Auto Stop mode (engine switched off), motor B propels a lightly loaded vehicle up to 30 mph as long as the driver maintains gentle pressure on the accelerator pedal.