Widely seen as the wave of the future, electric vehicles have faced a serious hurdle in pushing the technology to match or surpass the distance that traditional vehicles can drive in a single charge.
To overcome this hurdle, a research group at the University of Tokyo has been developing wireless technology that relies on in-wheel motors to receive a charge while driving in a charging lane or on sections of roads embedded with power transmission coils. That, the group says, will allow the vehicles 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 electric vehicles 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 roads with the proper infrastructure),” said team leader Hiroshi Fujimoto, an associate professor at the university’s Graduate School of Frontier Sciences.
The research is being conducted jointly with Toyo Denki Seizo, an electrical equipment manufacturing company, and NSK, a manufacturer of bearings.
Japan is targeting next-generation vehicles taking a 50 percent to 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 electric vehicles have been conducted on onboard motor vehicles, which are designed to recharge a battery in the body, the in-wheel system is designed to directly receive electric power from road infrastructure with reception coils placed on 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 industry has faced a dilemma since the vehicles need larger batteries to travel longer distances, as 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 percent to 40 percent, 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 drive shaft and differential gears,” which also contributes to mechanical power loss, Fujimoto said in a recent interview at the university’s Kashiwa campus in Chiba Prefecture.
The team was initially researching in-wheel motor electric vehicles with cables and wires, as they can provide various benefits, such as improved safety, eco-friendliness and improved comfort, compared with cars using 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 wires and cables.
This presents a risk of power disconnection 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 the wireless in-wheel vehicle that would eliminate the risk of breakage, and unveiled the prototype in May 2015.
They have since 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.
The technology allows drivers to travel long distances without worrying about the battery level, Fujimoto said. Excess power harnessed from the road can be stored in capacitors in the wheels and the battery and can be used when the car moves off a road with charging infrastructure.
“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, Fujimoto said.
Still, a number of challenges exist in bringing about the practical application of the technology. Commercialization must be achieved in accordance with various legal regulations, notably regarding road infrastructure, said Tatsuya Maruyama of Toyo Denki Seizo’s public relations department.
“Also, environmental assessments, system efficiency, and costs can be mentioned as challenges,” Maruyama said via email, adding that wireless charging technology is expected to diversify ideals of electric vehicles and expand the improvement of infrastructure.
“It is expected to accelerate the movement of electric motorization of vehicles as various means of transportation,” Maruyama said.