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Toyota's Plug-in Hybrid

Debut of prototype is near

  • January 29, 2007

Toyota Motor Corp., leading the automobile industry in hybrid technologies, is proceeding with its development of new hybrid vehicles (HVs). It's the plug-in HV with batteries that are rechargeable from home electric outlets.

To put it to practical use, it would be necessary to load next-generation, high capacity but compact lithium ion batteries as secondary batteries. According to people closely associated with Toyota, the public appearance of the prototype will occur in the not-too-distant future.

Perhaps the Tokyo Motor Show scheduled for this fall will set the stage for its debut. It's a little advantageous and exciting system of charging the car's energy at home.

The plug-in HV now being developed will drive within city limits using the electric vehicle (EV) mode without emitting any exhaust gas. But they can be driven in suburban areas using the engine and motor. The secondary batteries will be larger in capacity and output than those in current HVs such as the Prius, and will be rechargeable from house current outlets and other outside power sources.

A user may also be able to cut down on fuel costs by signing up for a midnight power contract. Moreover, a family using the solar system may be able to minimize environmental impact and lessen the cost of driving by selling the solar energy saved during the day to the power company and recharge the car with midnight energy.

GM and Ford exhibiting in Detroit

The plug-in system is fast becoming one of the world's environmental technologies befitting the current times. Nissan Motor Co. disclosed plans to develop the system last December, and U.S. General Motors (GM) came up with its plug-in EVs to operate in combination with the engine, while Ford Motor Co. exhibited plug-in EVs loaded with fuel cells at the Detroit Auto Show held this month.

Of the models displayed by the two U.S. automakers, a more realistic model is GM's "Chevrolet Volt." Its lithium ion batteries can be fully charged in 6 to 6.5 hours from a 110 volt home electric outlet. As it is, the batteries alone enable the vehicle to drive 40 miles (64 kilometers).

Chevrolet Volt also carries a 1-liter turbo engine adaptable to the E85, which runs on gasoline containing up to 85% ethanol. The device works in such a way that when the battery life is reduced beyond a certain level, the engine starts up to recharge the battery.

It is said that if its 55-liter fuel tank filled to full capacity is used for power generation, the vehicle's mileage can be extended to 640 miles (1,024 kilometers). A trial calculation of the vehicle's 80-mile (128 km) drive using the engine recharging system in combination shows that its fuel consumption per liter is 42 kilometers.

Improvement of lithium ion battery remains to be a problem

GM released this vehicle as an "EV," but it's actually a "Series-type HV" that uses the engine exclusively for recharging. The plug-in HV being developed by Toyota adopts the "parallel system" requiring a higher level of control technology and uses the engine both for driving and recharging as in the case of the company's existing HVs. The difference in the two firms' accumulation of HV technology seems apparent.

But Toyota also agrees that "a drastic improvement of secondary batteries would be required" before its plug-in HV can be put to practical use, according to Vice President Masatami Takimoto in charge of power train development. The company expects it would require considerable length of time. According to Takimoto, to drive 60 kilometers as an EV just as GM's Chevrolet Volt, 12 of the batteries (nickel hydrogen battery = capacity 6.5Ah) loaded on the current Prius would be required.

For that reason, lithium ion is most likely to be used as the secondary battery for plug-in HV. Lithium ion batteries are already in common use for notebook type PCs and mobile phones, but when it comes to automotive use, problems arise not only in terms of efficiency, including capacity, but also from the standpoint of cost efficiency and safety.

It has been almost 10 years since the Prius debuted. Of the global sales plan for this year, Toyota expects about 440,000 units or 5%-plus to be HVs, and will make steady efforts for further expansion. Although putting the plug-in HV to practical use is certain to come up against the wall of battery technology, it's this type of vehicle that will lead to opening the floundering domestic automobile market. Hopes in the market are being held high for the Tokyo Motor Show.

(Haruo Ikehara, Business Journalist)

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