Toyota Prius Plug-In Hybrid

Now that Toyota’s plug-in hybrid development is no longer a secret, the company is putting plug-in prototypes on the road in Japan and California to further improve the technology. The Toyota Plug-in HV, a test platform based on the production hybrid Prius, has been approved for public road use by Japan’s Ministry of Land, Infrastructure and Transport – the first certification of its kind. Toyota will field eight vehicles in Japan to verify the electric-only cruising range and optimal battery capacity.

Toyota will also provide plug-in prototypes to the Advanced Power and Energy Program at the University of California, Irvine (UCI) and the Institute of Transportation Studies at the University of California, Berkeley (UCB), through an on-going sustainable mobility development program with the two UC campuses. The vehicles will also be used as part of a program jointly developed by the California Air Resources Board (CARB) and the California Energy Commission (CEC) that’s designed to create incentives for the use and production of alternative fuels and vehicles.

The Plug-in HV features two major changes over the production Prius. Toyota has doubled the battery capacity to 13 amp-hours by installing a larger nickel-metal-hydride (NiMH) battery pack. Accordingly, the overall weight of the prototype is about 70 pounds greater than a stock Prius. Toyota says the larger NiMH battery pack is meant to simulate the level of performance the company expects to achieve when it eventually develops its own more compact and powerful battery systems, presumably with lithium-ion batteries. The other major modification is the addition of plug-in capability. Plugging into a standard 110-volt household outlet via a socket located on the rear fender will fully replenish the batteries in three to four hours.

The increased battery capacity means electric-only driving range is extended to approximately eight miles. The Plug-in HV is also capable of driving electrically at speeds up to 62 mph before the 1.5-liter gasoline engine turns on. Maximum electric-only cruising speed in the production Prius is 42 mph. This electric-only range is not as great as some of the unofficial Prius conversions that have been demonstrated in California and elsewhere. Nevertheless, Toyota reportedly claims that even with this experimental number, substantial gains in fuel economy and a major reduction in total tailpipe emissions over current conventional hybrid systems can be achieved.

Unlike Chevrolet’s Volt concept and its underlying E-Flex powertrain, which is conceived as an electric propulsion system that uses an internal combustion engine or some other power source to supplement the batteries, Toyota’s Plug-in HV is built off the same hybrid system that powers the company’s current hybrids. Toyota’s approach is unsurprising given its success on the market: The company’s cumulative hybrid sales recently surpassed the one million mark, and it expects to sell as many annually beginning early next decade. Still, both companies claim substantial development work is left to be done, particularly in the battery arena, before any form of plug-in is mass-produced.