Competition for Toyota's Hybrids
he crossword puzzle clue is "hybrid car," the answer is probably "Prius." Since Toyota brought that model to the United States six years ago, the company has basked in a green public-relations glow - even though Honda Motor was first with a modern gas-electric car (the Insight) and Ford sold the first hybrid sport utility vehicle (the Escape).
But with a mix of creative engineering, clever promotion and fortunate timing, Toyota Motor has set the de facto standard for the entire class of eco-friendly vehicles. It has licensed its software to Ford Motor and is selling hybrid components to Nissan Motor.
Toyota has half a dozen hybrid models in showrooms or on the way - twice as many as any other automaker - ranging from the Prius to the Lexus LS600hL.
The domination of Toyota's Hybrid Synergy Drive, however, is coming under assault from some of the industry's top engineers. For more than a year, in nondescript buildings in Troy, Michigan, a German-American consortium of BMW, DaimlerChrysler and General Motors has been working quietly to develop a distinctly different type of hybrid powertrain.
On Friday, the consortium's top executives formally introduced that system, which they call a two-mode hybrid, at an industry conference in Vienna. Most important details of the project had previously been shielded by the group, called Global Hybrid Cooperation.
The two-mode system will be available in a wide range of cars, trucks and sport utility vehicles made by the three companies, starting with the 2008 Chevrolet Tahoe, which is to go on sale in the autumn of 2007. GM says that compared with conventional Tahoes, the hybrid version will achieve 25 percent better mileage in combined city and highway driving.
While the two-mode system takes a new approach to hybrid drive technology, there are some similarities. Like all hybrids, the two-mode combines the power of a gasoline engine with that of electric motors; it captures energy from braking that would otherwise be lost; and it shuts off the engine at a stop. As in most of today's hybrids, batteries alone can power the vehicle at low speeds.
But the new technology is different in some crucial respects. It has the potential to operate much more efficiently at highway speeds, with a greater boost from the electric motors. The components are lighter and more compact and can be readily adapted to different types of vehicles. It is particularly well suited to large trucks and sport utility vehicles, where it will have the greatest impact on overall fuel consumption.
Existing hybrid systems have a single mode of operation, using a single planetary gear set to split the engine's power - routing it to drive the wheels or charge the battery - for both city and highway driving.
These systems are effective at low speeds because they can move the car without running the gasoline engine. But at higher speeds, when the engine is needed, using the electric motor offers much less of a benefit.
Sending power through electric motors and a variable transmission is roughly 20 percent less efficient than driving the car through a purely mechanical power path, using gears. Also, driving a single-mode vehicle at higher speeds on electric power requires larger, heavier, costlier electric motors and is less than ideal for towing or hauling.
The two-mode system also has a variable transmission but adds two planetary gear sets (which multiply the torque from the power source). This arrangement provides two operating modes for the electric motors. The first is for accelerating from a standstill to second gear; another phase takes the car from second gear to overdrive.
The two-mode system makes better use of cylinder-deactivation systems of the GM and Chrysler V-8s that will power many of the hybrid trucks and sport utility vehicles. Their systems shut down half the cylinders when not needed, improving gasoline mileage.
Hybrid sales in the United States have roughly doubled in four of the past five years, a fact regularly cited by supporters of the technology. But the roughly 206,000 hybrid cars and trucks sold in the past year amounted to only 1.2 percent of the total auto market. The Prius accounted for slightly more than half of hybrids sold in 2005.
"There is still a lot of guessing about the hybrid customer," said Andreas Truckenbrodt, an executive director of the two-mode consortium who works for DaimlerChrysler. "And how long will he be willing to pay extra for hybrids?"
The consortium's two-mode system is a scaled-down evolution of a heavy- duty hybrid powertrain developed by Allison, a unit of GM's powertrain group, that is used in more than 400 hybrid-electric city buses. Development began in the 1990s as an outgrowth of GM's short-lived EV-1 electric car.
GM and DaimlerChrysler formed the consortium in 2005 after learning that they were working on similar approaches. BMW then signed on.
Because the two-mode design uses some off-the-shelf components and spreads costs across three companies, it should be less expensive. High costs have hindered mainstream acceptance of hybrids, said Wolfgang Epple, vice president for BMW's program and a consortium director.
Despite the common parts, the system will be calibrated to match each company's engines and brand character, Epple said.
He promised that a two-mode installed in a BMW X5 sport wagon, for example, would feel and perform differently from one installed in a Cadillac Escalade or Dodge Durango.
The system is being configured for rear- and front-drive applications and is designed to be easily scaled up or downsized, depending on a vehicle's type, size and power.
Eric Fedewa, director of global powertrain forecasting at CSM, said the two-mode system would bring benefits beyond fuel efficiency to larger trucks and cars.
"Smooth running on the battery alone at low speed gives added refinement to trucks in particular," he said
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