Toyota Motor Corp. continues to make news on the hybrid-electric vehicle front, while more auto makers position for a piece of the action.

In addition to the all-new ‘10 Prius that debuted earlier this year with an EPA rating of 51/48 mpg city-highway (4.6-4.9 L/100 km) and the Lexus HS 250h offering 35-34 city/highway (6.7-6.9 L/100 km), it debuted a plug-in version of the Prius at the recent Frankfurt auto show.

Toyota says its new Prius PHEV will be capable of traveling 12 miles (19 km) and achieve highway speeds in electric-only mode.

Beginning late this year, the auto maker will deliver 500 Prius PHEVs worldwide in a demonstration program. About 150 will be placed with select U.S. lease-fleet customers for market and engineering analysis.

The U.S. introduction no doubt will steal a little thunder from the introduction of the much-anticipated Chevy Volt extended range electric vehicle and the Nissan Motor Co. Leaf, both of which are expected to debut in late 2010 as ‘11 models.

Unlike the standard Prius, the PHEV will use lithium-ion, rather than nickel-metal-hydride, batteries. Panasonic EV Energy Co. Ltd., owned 60% by Toyota, will supply the batteries.

One of the most interesting bits of technology available on the standard new Prius has nothing to do with its powertrain. Instead, the car can be ordered with solar panels embedded in the moonroof that power a fan that lowers the interior temperature as much as 30° F when the car is parked.

In the summertime, the temperature inside a vehicle can reach nearly 200°F (93° C).

Volumes will be relatively tiny, but after insisting for years that high-efficiency diesels were the only answer to increasing fuel efficiency and lowering carbon-dioxide emissions, the major German auto makers now are jumping into HEVs and EVs with enthusiasm. They still are trying to market diesels in the U.S., as well, even though others have mostly given up on the idea.

Mercedes-Benz AG is bragging it is the first to offer an HEV powered with lithium-ion batteries. U.S. deliveries of the S400 Hybrid HEV began in September, and engineers already are working on developing an all-wheel-drive version for buyers in the Northeast.

The HEV is based on the V-6 S-Class and features combined fuel economy of 29 mpg (8 L/100 km), a 30% increase from the V-8 S550. The modified 3.5L gasoline engine develops 275 hp, while the electric motor generates 20 hp.

Mercedes also showed off a PHEV S500 concept at Frankfurt, underscoring its growing commitment to electric power.

Likewise, BMW now is jumping into electrification with both feet and will be introducing an X6 HEV in the U.S. at the end of this year and a 7-Series mild hybrid in April 2010.

BMW calls the new ActiveHybrid X6 “the world's fastest all-wheel-drive hybrid.” It combines a twin-turbo V-8 with two electric motors. Compared with the conventional X6, it is 20% more fuel-efficient.

BMW claims the ActiveHybrid 7-Series is “the first car in the world to combine a gasoline V-8 engine, 8-speed automatic transmission and an electric motor as a mild hybrid concept. The electric motor basically serves as an “electric turbo” and means the HEV's acceleration is even better than that of the standard V-8 powered 750i, even though it delivers 15% better fuel economy.

Audi AG and Porsche AG also are introducing HEVs in 2010, and Audi displayed an all-electric concept at Frankfurt as well.