Japanese University Discloses Solar Race Car

Jul 24, 2013
Masaru Yoshida, Nikkei Monozukuri & Motohiko Hamada, Nikkei Automotive Technology
The "Practice" solar car developed by Kogakuin University and the main members of the project. Hiroto Hamane, who leads the project, is the third person from the left.
The "Practice" solar car developed by Kogakuin University and the main members of the project. Hiroto Hamane, who leads the project, is the third person from the left.
[ If it clicks, the expanded picture will open ]
The tire of the solar car was developed by Bridgestone Corp. It has a low rolling resistance.
The tire of the solar car was developed by Bridgestone Corp. It has a low rolling resistance.
[ If it clicks, the expanded picture will open ]
The wheel bearing developed by NTN Corp was made by using a ceramics ball. Its rotation torque was reduced by 50% by using a low-viscosity grease.
The wheel bearing developed by NTN Corp was made by using a ceramics ball. Its rotation torque was reduced by 50% by using a low-viscosity grease.
[ If it clicks, the expanded picture will open ]

Kogakuin University announced a new solar car that it developed for the World Solar Challenge 2013 (WSC 2013), a solar-powered car race that attracts teams from around the world.

With the car, "Practice," the university will run the race for the first time.

The WSC 2013 is the largest solar-powered car race in the world and will take place from Oct 6 to 13, 2013. Race participants drive their cars from Darwin to Adelaide, Australia (about 3,000km).

Since the university launched its "solar car project" in 2009, it has been engaged in the development of solar cars. In 2012, it became the overall champion of World Green Challenge 2012 (WGC 2012), which took place in Japan.

The Practice is a four-wheeled solar car that was developed based on the car that the university used for WGC 2012. The university employed new parts and technologies with help from companies.

For example, Bridgestone Corp newly developed a tire with low rolling and air resistances for the Practice based on its "Ecopia" fuel-efficient tire. Also, the company improved the tread pattern so that it becomes suited for driving straight on a dry road.

As a wheel bearing, the university employed a deep groove ball bearing using a ceramics ball. NTN Corp developed it for the Practice. The bearing has an accuracy of "JIS-5," which is two levels higher than "JIS-0," or the standard accuracy for bearings, improving rotation accuracy.

By replacing a steel ball with the ceramics ball to optimize the curvature of the spinning area and reduce contact area and employing a grease with a low viscosity, NTN reduced resistance to stirring. As a result of those improvements, rotation torque was reduced by 50%, compared with the company's existing product.

Furthermore, NTN used non-contact rubber sealing in place of steel-plate sealing to prevent the ingress of foreign objects at the time of driving in desert areas.

The carbon fibre-reinforced plastic (CFRP) used for the body of the Practice was provided by the Teijin Group. Specifically, the CFRP is made by using Toho Tenax Co Ltd's ultra-thin carbon fiber, whose strength is equivalent to that of normal carbon fibers and mass is about 1/3.

The CFRP is also used for the bodies of Formula One cars. It contributed to the low mass of the car (160kg), which is more than 30% lighter than the mass of the car that the university used in WGC 2012 (230kg).

The motor of the Practice was provided by Mitsuba Corp. The company developed it by, for example, optimizing the coil. The university did not disclose the details of the car's battery.