Story: Development of Gen III Prius

The third-generation Prius achieves excellent fuel efficiency and comfortable driving characteristic of a hybrid vehicle

The third-generation Prius was introduced in May 2009. Akihiko Otsuka, chief engineer of the third-generation Prius project, says the two key points in developing the new Prius were an affordable price and improved fuel efficiency.

As measures related to energy and global warming issues, it is necessary to expand the use of highly fuel-efficient vehicles such as the Prius. For that reason, setting the price of the Prius—Toyota’s entry model hybrid vehicle—at an affordable level was seen as one of Toyota’s missions. “Although we tackled development with a fuel efficiency target of 38km/L, it was a tough level to achieve because engine efficiency had already been substantially improved,†explained Otsuka regarding the difficulties met in improving fuel efficiency. “In order to lower the vehicle’s overall energy loss, we aimed at increasing system efficiency to 60% and vehicle efficiency to 40%.â€

In order to combine an affordable price with improved fuel efficiency, particular efforts were made to improve engine efficiency and reduce the size and weight of parts. To improve engine efficiency, the inline four-cylinder engine was switched from the previous 1.5-liter model to a newly developed 1.8-liter one. The increased displacement gave the engine more output torque, making it possible to reduce engine rpm during high-speed driving, thereby improving engine efficiency in all speed ranges and improving fuel efficiency. The new Prius also has a 0.25 coefficient of drag, contributing to a 0.3km/L improvement in fuel efficiency.

To reduce the size of parts and make them lighter, all 30,000 parts used in the Prius were checked carefully over and over. Using fewer raw materials in hybrid systems resulted in about a 20% size reduction, at the same time lowering costs by 30% and improving fuel efficiency. To reduce costs further, the new Prius shares 90% of the parts in the platform and 50% of the parts in the suspension with existing models. Toyota’s basic stance is to prioritize the setting of prices that customers can afford and the reduction of costs to realize those prices. These combined efforts helped to achieve a fuel efficiency of 38km/L for the third-generation Prius.

Besides environmental performance, safety features were also bolstered, such as through the use of Steering-assisted Vehicle Stability Control (S-VSC), Supplemental Restraint System (SRS) side impact airbags, and SRS curtain-shield airbags. Retail prices in Japan start at 2.05 million yen, and sales will cover 80 countries, double the number for the second-generation Prius. Toyota also introduced the Prius Cup, an initiative for drawing cars and customers closer together in a move to nurture the automobile culture (see pp 8-9 for more details). The new Prius seeks to achieve a balance between advanced environmental features, driving performance that is unique to a hybrid vehicle, and the excitement of ‘driving the future’ as an electric car when running on batteries. In the first month after launch, sales in Japan topped 180,000 units. The third-generation Prius is not simply an environmentally-considerate vehicle: it is a next-generation vehicle that will satisfy even car enthusiasts.

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