Setting The Standard For Hybrid Cars

The electric motor connects to the ring gear of the gear set. It also links directly to the differential that drives the wheels. Therefore, the rate of spin of the electric motor and the ring gear determines the car's speed.

The generator is connected to the sun gear of the gear set, and the engine connects to the planet carrier. The ring gear's speed depends on all three components, which must work together at all times to control the output speed.

A proprietary 32-bit microprocessor unit is used for the engine-control module (ECM), the high-voltage electronic-control unit (ECU), the battery's ECU, and the skid-control ECU. This represents an upgrade from earlier 16-bit designs. Intercommunication takes place over a controller-area-network bus.

AN ADVANCED BATTERY DESIGN Consisting of 168 1.2-V dc cells, the NiMH battery is interconnected using 28-cell modules, for a nominal voltage of 201.6 V dc. It's housed in a crash-resistant case located under the backseat of the car. The constantly improving battery is now in its third generation. (The battery used for Toyota's Lexus RH 400h and Highlander sports utility vehicles is a fourthgeneration design.) Located under the hood are the engine, the inverter assembly, and the hybrid transaxle (Fig. 7).

Toyota says it has always been asked about the battery's lifetime and replacement cost. For one thing, the battery pack and all hybrid components are considered "life-of-the-car" components. They're warrantied for eight years or 100,000 miles of driving, whichever comes first. That warranty is even better (10 years and 150,000 miles) in U.S. states with California-type emission standards (California, Connecticut, Massachusetts, Maine, New Jersey, New York, Rhode Island, Vermont, Washington, and soon Oregon). And since the Prius went on sale in the U.S. five years ago, there has never been a failure of the battery requiring replacement.

"Our batteries have been tested to a simulated 180,000 miles without failure," claims a Toyota spokesman. "A first-generation Prius in taxi use in the Pacific Northwest has gone more than 200,000 miles on its original battery."

Still, much speculation persists about the replacement should it fail beyond the warranty period. While no specific cost figure exists due to no history of battery failure, a check with an energy storage expert estimated a price of $3000 to $4000.

According to the expert, "A key issue in a battery's life is good energy management. Using the battery properly (i.e. no deep discharges or charges, keeping it operating at the right temperature, etc.) adds to battery life."

He regards the Prius' synergistic design with its high-voltage battery as a milestone, though not necessarily the final and most efficient answer for energy storage. He foresees even newer technologies on the horizon that will make driving more efficient and more environmentally friendly.

One such technology is supercapacitors. They aren't batteries. Rather, they're ionicenergy storage devices that have greater lifetimes than batteries of eight to 10 years. Additionally, they possess 20% or more energy storage capability. But he credits the Prius design for starting this revolution in automotive energy savings and pollutionlowering technologies.

Indeed, the hybrid gasoline-electric car movement is just beginning, and it's certain to expand considerably. By 2008, other auto manufacturers worldwide are all expected to penetrate the market.

Last month, Toyota issued a voluntary recall for 75,000 Priuses sold in the U.S. (160,000 worldwide) for a potential software glitch that could cause the car to stall or shut down. According to Toyota, no accidents or injuries have occurred as a result. It says the problem is a minor one that the company already has dealt with successfully.