by Larry Carley, c2000
Exhaust emissions from the Prius are extremely low. Toyota says carbon monoxide (CO), hydrocarbon (HC) and oxides of nitrogen emissions are reduced 90 percent. This allows the vehicle to exceed California's Super Ultra Low Emission Vehicle (SULEV) standards.
Power output from the gasoline engine is split between the drive wheels and a generator. The generator, in turn, is used to run the electric motor and/or to recharge the 40 7.2 volt sealed Nickel-Metal Hydride (NHM) batteries.
The electric motor is a permanent magnet design which needs no maintenance because its "no touch" internal components do not wear. It produces its maximum power of 30 kilowatts (40 horsepower) from 940 to 2000 rpm, and maximum torque of 31.1 kg-m (225 lb./ft.) from 0 to 940 rpm.
The U.S.-spec Prius will benefit from a more powerful, more compact, and lighter battery pack. Peak battery-pack power has been increased by 20 percent to 25 kilowatts (kW), or 34 horsepower. Each of the 38 modules within the pack is only three-quarters of an inch thick and 20 percent lighter in weight than the units in the Japan-version Prius. The new lighter batteries will reduce battery pack volume by 40 percent and will allow for more cargo area in the trunk.
Operation of the hybrid combination is seamless and virtually imperceptible to the driver and passengers. It five main operating modes are:
1. When pulling away from a stop or under a light load, only the electric motor powers the vehicle.
2. For normal driving, a combination of gasoline and electric power is used.
3. Under full-throttle acceleration, the electric motor receives additional power from the 40 batteries.
4. During deceleration or braking, the electric motor functions as a generator to recharge the batteries.
5. The batteries are regulated to maintain a constant charge. When charging is needed, power from the engine is used to drive the generator. This eliminates the need for an external charger or power connection.
The key to the Toyota Prius system is a power split device in the transmission which sends engine power either directly to the wheels or the electric generator. The generator, in turn, powers the electric motor and recharges the batteries. The power split device uses a planetary gear to constantly vary the amount of power supplied from the engine to either the wheels or generator. The electronically controlled transmission controls engine speed, generator output and the speed of the electric motor to handle changing driving modes.
The system is designed to keep the engine running within its most efficient rpm range. When increased driving loads lug down the engine's speed, the control system shuts off fuel to the engine and kills the engine. The electric motor then takes over and provides 100 percent of the driving power. If additional power is needed, the engine is restarted and adds its power output until the extra power is no longer needed. At that point, the electric motor cuts out and the engine resumes its light load operation in its optimum speed range.
The hybrid drivetrain has proven itself to be trouble-free, says Toyota. The car has been on sale in Japan since December 1997, and has sold more than 35,000 units.
Standard equipment includes Anti-Lock Brakes, automatic transmission, climate-control air conditioning, power windows, door locks and mirrors, AM/FM/cassette stereo, an eight-year/100,000-mile battery and hybrid system warranty, and free seven-day/24-hour roadside assistance.
FOLLOW-UP REPORT (5/01)Demand for this car has far exceeded Toyota's ability to produce. Annual production is currently only about 9,000 cars for the U.S. market. Toyota claims it is losing money on every Prius it builds. Even so, soaring fuel prices are generating tremendous interest in fuel-efficient vehicles, especially ones like this that get such great mileage.According to our local Toyota dealer, the waiting list for the Prius is six to eight months -- with a cash deposit! The dealer wouldn't quote a final price but said that some dealers are adding an additional "market premium" of up to several thousand dollars to the list price of this car because of the high demand. So be prepared to pay full list price plus for this hot little car. |
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