Japanese researcher shows future of EVs with new wireless technology
Electric vehicles, although meant to be the wave of the future at a time when climate change has become a serious issue, face a major hurdle: getting them to travel as far as, or even surpass, fossil-fuel vehicles on a single charge.
To overcome this hurdle, a research group at the University of Tokyo has been developing a wireless technology that relies on in-wheel motors to receive a charge while driving on a charging lane or section of roads embedded with power transmission coils. That, the group says, will allow EVs to get more distance without heavily relying on large-capacity batteries.
The team recently announced the world’s first successful demonstration of wireless charging of in-wheel motor EVs while in motion using actual vehicles.
“With this technology, the driving range of EVs would become unlimited in the future (as long as vehicles drive on a road with the proper infrastructure),” said Hiroshi Fujimoto, an associate professor at the university’s Graduate School of Frontier Sciences, who leads the team.
The research is being conducted jointly with Toyo Denki Seizo K.K., an electrical equipment manufacturing company, and NSK Ltd., a manufacturer of bearings.
Japan is targeting next-generation vehicles taking a 50-70 percent share of vehicle sales by 2030, according to the Japan Revitalization Strategy revised in 2015.
Japan also pledged in its Intended Nationally Determined Contributions, submitted to the U.N. Framework Convention on Climate Change Secretariat, to cut emissions of energy-originated CO2 in the transport sector to 163 million tons in fiscal 2030 from 225 million tons in fiscal 2013.
While most of the studies of dynamic wireless power transfer for EVs have been conducted on onboard motor vehicles, which are designed to wirelessly recharge a battery in the body, the in-wheel motor system is designed to directly receive electric power from road infrastructure with reception coils placed at the wheels.
The road infrastructure consists of power transmission coils, inverters as well as vehicle sensor and control systems that allow it to transmit power only when vehicles enter a charging section.
The EV industry is faced with a dilemma since the vehicles need larger batteries to travel longer distances, but this makes the vehicles heavier and more energy consuming, according to the research team.
But using wireless in-wheel motors can reduce the weight of the drive unit by 30 to 40 percent and the size of the battery, the team said in a statement. It also eliminates the need for a bulky transmission and provides more space for passengers and cargo.
“By placing motors in a vehicle’s wheels, we no longer have to carry heavy mechanical components like a driveshaft and differential gears,” which also attributes to mechanical power loss, Fujimoto said in a recent interview with Kyodo News at the university’s Kashiwa campus in Chiba Prefecture, east of Tokyo.
The team was initially researching in-wheel motor EVs with cables and wires, as these types of vehicles can provide various benefits, such as improved safety, eco-friendliness and improved comfort, compared with cars with a transmission.
They handled and maneuvered better, thanks to the independent torque control of each wheel, but the problem was that electricity had to be delivered via the battery using the wires and cables.
Thus, there was a risk of disconnection of power by entrusting the power of each wheel to cables, which might break under wear and tear or environmental conditions like snow. So the team devised a wireless in-wheel motor vehicle that would eliminate the risk of breakage, and unveiled the prototype in May 2015.
They achieved a successful wireless transfer of electric power from a central battery to each wheel’s motor.
Now the in-wheel motors themselves can get electricity from both road infrastructure and the battery in the body of the car.
Most significantly, the technology allows drivers to travel long distances without worrying about the battery level, according to Fujimoto. Excess power harnessed from the road is stored in capacitors in the wheels and the battery and can be used when the car moves off a road with charging infrastructure.
Fujimoto said, “Technologically challenging areas in the research were to make every component fit into the compact in-wheel system” as well as the power management by controlling input and output of electricity with multiple power sources.
Still, a number of challenges exist in bringing about the practical application of wireless in-wheel motor EVs capable of being charged from the road, as the commercialization must be achieved in accordance with various legal regulations notably regarding road infrastructure, Tatsuya Maruyama at the public relations division of Toyo Denki Seizo pointed out.
“Also, environmental assessments, system efficiency, and costs can be mentioned as challenges,” Maruyama said via email, adding this wireless charging technology is expected to diversify ideals of EVs and expand into the improvement of infrastructure.
“It is expected to accelerate the movement of electric motorization of vehicles as various means of transportation,” Maruyama said.