Challenging Toyota’s Hybrid Hegemony April 30, 2006
Toyota’s market domination of the entire class of eco-friendly vehicles is coming under assault from some of the auto industry’s top engineers.
But with a mix of creative engineering, clever promotion and fortunate timing, Toyota has set the de facto standard for the entire class of eco-friendly vehicles. It has licensed its software to Ford and is selling hybrid components to Nissan. Toyota has half a dozen hybrid models in showrooms or on the way ? twice as many as any other automaker ? ranging from the miserly Prius to the $100,000-plus Lexus LS 600hL.
Yet the domination of Toyota’s Hybrid Synergy Drive is coming under assault from some of the auto industry’s top engineers. For more than a year, in nondescript buildings in Troy, Mich., north of Detroit, 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 unveiled that system, which they call a two-mode hybrid, at an industry conference in Vienna. Until then, most important details were kept under wraps by the joint development group, called the Global Hybrid Cooperation.
The two-mode system will be available in a wide range of cars, trucks and S.U.V.’s made by the three companies, starting with the 2008 Chevrolet Tahoe that goes on sale in fall 2007. G.M. 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. Like 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 S.U.V.’s ? the biggest gas hogs in Americans’ garages ? where it will have the greatest impact on overall fuel consumption.
Larry Nitz, hybrid engineering director of G.M. and an executive in the consortium, noted that hybrid technology had not gained a foothold in these heavy vehicles. Big luxury cars from BMW, Cadillac and Mercedes-Benz are also candidates for the system.
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 gas engine. But at higher speeds, when the engine is needed, using the electric motors has much less 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 by 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 system adds two clutches, which can engage different gear combinations to provide an overlay of four fixed (not variable) gear ratios. To the driver, these feel and function like the stepped gear changes of an automatic transmission.
Because the torque is multiplied by the gears, the electric motors can be much smaller ? small enough, in fact, to fit in the same housing as the transmission. And because the whole package is so tidy and integrated, it can be manufactured in modules that each of the three companies can install on its own cars and trucks.
“Ours offers the mechanical power path that’s more efficient than a one-mode’s mostly electric path,” Mr. Nitz, the G.M. engineer, said.
- Posted in : Toyota,Uncategorized
- Author : arnold
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