How the Toyota Prius Works

Chances are if you've heard of hybrids, you've heard of the Prius, too.
Chances are if you've heard of hybrids, you've heard of the Prius, too.
Bryan Mitchell/Getty Images

In December 1997, the world's leading nations were meeting in Tokyo, Japan to discuss the Kyoto Protocol. In addition to setting up a specific proposal that would aim to reduce the world's carbon emissions, the Kyoto Protocol was a clear sign that people from all around the world were recognizing energy consumption as an important topic. Even at that point in our history, many drivers had an understanding that the fuel used to power our cars and trucks contributes heavily to global warming, and without a significant change in technology and driving habits, climate change would eventually harm the environment.

Several months before that conference, Toyota introduced a new model to the Japanese market. The car sold reasonably well for a new model -- about 18,000 people bought one -- but it would be a few years before it would become a worldwide success. The vehicle was the Toyota Prius.


If you bring up the topic of hybrid cars during a conversation, it's likely the Prius will be mentioned, too. Unlike many of the cars coming off the assembly line during the auto industry's hard times, the Toyota Prius is a relative success story. The name Prius -- which means "to go before" in Latin -- is nearly synonymous with hybrid car technology and has become somewhat of a household name.

And "going before" seems to be the main focus driving Toyota's agenda in terms of the Prius. While most automakers are still catching up to develop their own gasoline-electric hybrid technologies, Toyota is about to release its third generation of the Prius. And although the U.S. government has mandated an increase in average fuel economy up to 24 miles per gallon for all car manufacturers by the year 2020, the Toyota Prius has been surpassing that milestone for several years.

The Prius also consistently tops consumer satisfaction reports [source:]. So what is it about the Toyota Prius that makes its drivers so enthusiastic? How does its hybrid gasoline-electric engine get the mileage it does, and what sets it apart from other hybrids? Find out on the next page.


Toyota Prius Design

A view from inside a Toyota Prius hybrid vehicle in San Anselmo, Calif.
Although it's a conservative-looking sedan, the design for the Prius is compact and aerodynamic, allowing it to save the extra bit on fuel economy.
Justin Sullivan/Getty Images

The Toyota Prius has been, historically, fairly conservative in regards to its outward appearances. Since its release in Japan and America, the Prius has closely resembled most compact cars on the road. The design, however, has become sleeker as the years have gone by, with a significantly more aerodynamic body to allow air to flow more quickly over the top of the car and create less drag.

The current 2010 Toyota Prius, the third generation of the popular hybrid, underwent some slight yet influential changes. Toyota wanted to keep the general design intact since the Prius has become a relatively recognizable hybrid, but small additions and subtractions count. The body is about four inches (10 centimeters) longer than the previous model and an inch (2.5 centimeters) wider, too, and several small tweaks, including sharper corners and carefully designed lines for better air release, make the Prius look more modern. This all adds up to a decrease in overall wind resistance, and the drag coefficient (Cd) is currently 0.25 compared to 0.26 for the 2009 model. That number might seem small, but in the end it adds a significant amount more to the miles per gallon average.


All three generations of the Prius have been equipped with an energy monitor, one of the vehicle's biggest draws for costumers concerned about fuel efficiency. A multi-function display (MFD) monitors energy flowing to and from the engine and battery, along with information about the vehicle's regenerative braking and battery levels. This lets aware drivers keep an eye on how much fuel they're using, and, if they pay attention, it can even encourage more fuel-efficient driving practices. Digital gauges that display vehicle speed, engine RPMs and other vital stats, are under a centrally located hood high atop the vehicle's dashboard.

So that's how a Prius looks, but what makes a Prius run? We'll tell you on the next page.


Toyota Prius Specs

The Toyota Prius is a combination series-parallel hybrid, allowing it to sample the best of both technologies when necessary.
The Toyota Prius is a series-parallel hybrid, allowing it to sample the best of both technologies when necessary.
Justin Sullivan/Getty Images

There are generally two types of hybrid cars available on the market. There are parallel hybrids, where there are several power options -- the electric motor can operate by itself to power the car, the gasoline engine can operate by itself or both the electric motor and the gasoline engine can work together. There's also the option of the series hybrid, where the gasoline engine, instead of directly powering the wheels, serves only to charge the vehicle's battery to provide power to the electric motor.

The Toyota Prius is somewhat unique among hybrids. It's a combination of both of the previous types and is known as a series-parallel hybrid. This is possible because of the Prius' power split device, a special gearbox that connects the gasoline engine, electric motor and generator together into one unit. The device, which was introduced in the second generation Prius, contains a planetary gear set, and it allows the car's various power technologies to work together to move the vehicle. The electric motor is attached to a ring gear, which transfers the power of the motor to a reduction gear unit that's connected to the final drive. The planetary gear set also contains a smaller sun gear and a series of planet gears. All of these gears moving together not only provide power for the car, but they also provide power for the vehicle's generator. When the sun gear simply can't spin any faster, this is the limit of the car's fully-electric operation and the vehicle's internal combustion engine is switched on. This setup allows for increased efficiency since the electric motor and generator run as long as possible before the gasoline engine starts up and begins to burn fuel.


The engine in the third generation Prius grew from 1.5 to 1.8 liters, giving the hybrid a boost in horsepower from 110 to 160, an important factor for those wary of the supposed weakness of hybrid cars. Also, the Prius doesn't have to be recharged, since its generator constantly supplies power to the battery. With all of this, the third generation of the Toyota Prius aims to get 50 miles per gallon (21.3 kilometers per liter) in combined city and highway driving, compared to 46 miles per gallon (19.6 kilometers per liter) for the 2009 Prius and 41 miles per gallon (17.4 kilometers per liter) for previous models.

For more information about hybrid cars and other related topics, follow the links the next page.


Lots More Information

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More Great Links

  • Associated Press. "Prius tops Consumer Reports best value list." Feb. 27, 2009. (March 9, 2009)
  • "Toyota Prius, again, tops Consumer Reports Satisfaction Survey." Dec. 29, 2008. (March 9, 2009)
  • "2010 Toyota Prius Breaks 50 MPG." Jan. 12, 2009. (March 9, 2009)
  • "History of Hybrid Vehicles." March 27, 2006. (March 9, 2009)
  • "2010 Toyota Prius: Design Dissected." Jan. 12, 2009. (March 9, 2009)
  • Lavelle, Marianne. "Fuel Efficiency Plan Aims for Big Savings." U.S. News and World Report. April 22, 2008. (March 9, 2009)
  • "Toyota Prius." (March 9, 2009)