With the rise of new energy vehicles, the structure of cars has become simpler. So simple that a battery pack and a motor can replace traditional engines. Can you believe there’s a technology that can eliminate the entire transmission system? Yes, it’s the hub motor technology!
If you want to know about “hub motor“, please read this article.
Hub Motor Technology
The traditional electric vehicle transmission scheme delivers the motor’s output torque to the wheels through a gearbox, differential, and other components.
Some might ask: why make it so complex? Can’t we just mount the motor directly on the wheel?
Bingo! In-wheel motor technology mounts the motor inside the wheel hub, directly driving the wheel without any mechanical transmission structures. It’s that simple and straightforward!
Currently, the low-speed outer rotor motors and high-speed inner rotor motors used in electric wheels are radial flux permanent magnet motors.
Electric Motor Rotor + Stator
The outer rotor permanent magnet motor serves as the actuator for directly driving electric vehicles. The brushless wheel hub motor uses a surface-mounted NdFeB magnet outer rotor with a multi-pole, few-slot stator structure.
Why use an outer rotor structure?
The outer rotor structure increases the armature diameter under the constraint of fixed wheel diameter, enhancing motor energy. However, it worsens heat dissipation, which impacts its long-term overload capability.
What are the characteristics of the in-wheel motor stator?
The stator uses a multi-pole, few-slot structure to reduce volume and simplify the design. This helps generate the required harmonic potentials, improving power performance indicators.
The permanent magnet rotor position sensor uses a reluctance-type multi-pole rotary transformer integrated with the motor body for compact installation. Typically, in-wheel electric vehicles have two or four wheel-side motors, with multiple motors coordinated through advanced control.
Current Applications of In-Wheel Motors in Electric Vehicles
TM4 in Canada
This company designs and manufactures integrated in-wheel motors. It uses an outer rotor permanent magnet motor, directly integrating the motor rotor housing with the wheel rim. The motor housing becomes part of the wheel rim.
This integrated in-wheel motor system’s permanent magnet brushless DC motor delivers a rated power of 18.5 kW, a peak power of 80 kW, a peak torque of 670 Nm, a rated speed of 950 rpm, and a maximum speed of 1385 rpm. Its average efficiency under rated conditions reaches 96.3%.
SIM-Drive in Japan
The Japanese venture company SIM-Drive, focused on electric vehicle development, announced the completion of a prototype vehicle from its “First Phase Leading Development Car Project” conducted from January 2010 to March 2011. The prototype vehicle, SIM-LEI, achieved a range of 333 km (JC08 mode), which is 1.5 times greater than the Nissan Leaf, despite having a comparable lithium-ion battery capacity.
LEI stands for “Leading Efficiency In-wheel motor.” During its development, SIM-Drive aimed to achieve goals directly linked to mass production.
The SIM-LEI in-wheel motor adopts an outer rotor structure, replacing the conventional inner rotor design. While the outer rotor is more complex than the inner rotor, it can output larger torque more easily.
Because the motor itself ensures sufficient torque, gear reducers are no longer necessary, reducing friction losses. “With no main drive gears, differential gears, or drive shafts, friction losses are reduced by about 10%,” said Tomoyuki Maebe, General Manager of SIM-Drive’s Vehicle Development Department.
Ford
In 2013, Ford demonstrated an eWheelDrive in-wheel motor-driven vehicle based on the Ford Fiesta. The eWheelDrive system integrates independent motors into two rear wheel hubs. Its new steering system allows vehicles to move sideways directly into parking spots without steering.
The motor uses liquid cooling, with a single motor providing a maximum power of 40 kW (54 hp). The average power output during operation is 33 kW per motor, with the two motors providing a combined maximum power of 80 kW (109 hp) and a continuous average power output of 66 kW (90 hp). The motor, electronic controller, cooling system, and brake system are all integrated inside the wheel rim.
Ford collaborated with Schaeffler, a globally renowned auto parts manufacturer, to develop the eWheelDrive system. This innovative technology lays the foundation for smaller, more flexible vehicles, addressing urban parking challenges.
eWheelDrive integrates independent motors into two rear wheel hubs, replacing traditional drivetrain systems, including engines, gearboxes, and central generators for electric vehicles, saving significant space.
Tyt In-Wheel Motors
Hubei Tyt’s e-Traction in-wheel motor integrates the tire, wheel hub, permanent magnet synchronous outer rotor, stator, inverter, and pressure plate inside the wheel. It delivers peak output torque between 6000–10200 Nm and achieves a maximum speed of 500 rpm/85–97 km/h, making it a low-speed, high-torque motor.
BYD Wheel-Side Motors
BYD’s first mass-produced wheel motor has the following parameters: maximum power 90 kW (122 hp), maximum speed 7500 rpm, and operating voltage 640 V.
These have been applied to K9 electric buses, which are exported globally.
In terms of research and development, the reducer matching the wheel motor reduces the driving force to a normal range through three to four sets of gears (including important planetary gears) (the motor speed can reach 7000-12000 rpm under normal conditions, and the reducer reduces the high speed of the motor to 500-5000 rpm).
Other EV In-Wheel Motors
| Model | Power Type | Electric Drive Form |
| IZA | Electric | Four-wheel in-wheel drive |
| Eco | Electric | Rear-wheel in-wheel drive |
| Luciole | Electric | Rear-wheel in-wheel drive |
| KAZ | Electric | Four-wheel in-wheel drive |
| Eliica | Electric | Eight-wheel in-wheel drive |
| AUTOnomy | Fuel Cell | Four-wheel in-wheel drive |
| Chevrolet S-10 | Hybrid | Rear-wheel in-wheel drive |
| Peugeot QUARK | Fuel Cell | Four-wheel in-wheel drive |
| GM Squel | Fuel Cell | Rear-wheel in-wheel drive |
| Mitsubishi Colt | Electric | Rear-wheel in-wheel drive |
| Honda FCX concept | Fuel Cell | Rear-wheel in-wheel drive |
| Italian CNR-T2 | Hybrid | Rear-wheel in-wheel drive |
| Mitsubishi CT-MIEV | Hybrid | Rear-wheel in-wheel drive |
Why Haven’t In-Wheel Motors Achieved Mass Production Yet?
The primary challenge is motor heat dissipation. Experts have expressed various opinions:
Professor Song Jian, Tsinghua University
“During vehicle braking, a large amount of heat is generated, which transfers directly to the motor. Generally, when motor materials exceed 200°C, demagnetization occurs, and currently, no technology can address this issue.”
Professor Lian Xiaomin, Tsinghua University
While thermal demagnetization is real, a good cooling system can dissipate heat effectively, preventing demagnetization. Water cooling has already been designed, using water to cool the stator and air to cool the rotor.
Protean Electric CEO Chen Guoxian
Chen Guoxian, CEO of Protean Motor, who has been deeply involved in the field of wheel hub motors for many years, believes that demagnetization will occur when the temperature of the motor permanent magnet reaches 140℃. So, how to keep the magnet below 140℃?
“Our method is to place silicon steel sheets in the brake disc for protection. The heat generated by the friction of the car during braking will be treated with heat insulation layer by layer, and cooling water is used in the motor stator for cooling treatment, so that the motor material can reach a temperature that will not demagnetize.”
Chen Guoxian said that the experimental results obtained through finite element analysis show that the temperature of the permanent magnet can be controlled at around 90℃.
For traditional car companies, the tradition has always been that transmission belongs to transmission, drive belongs to drive, and chassis belongs to chassis.
Once the wheel hub motor is popularized, the transmission system will be cancelled, and the drive and chassis will be deeply integrated, which is a very big challenge for the organizational structure of traditional car companies.
Lamnow – Electric Wheel Hub Motor Lamination Manufacturer
Lamnow utilizes advanced processes such as stamping, laser cutting, and wire cutting, to ensure precision and efficiency in manufacturing electric hub motor laminations. Our comprehensive services include in-wheel motor winding, impregnating insulation, and lamination bonding processes.
Whether it’s for electric cars motors, electric bicycle motors, electric motorcycle motors, electric scooter motors, or other applications, our laminations play a crucial role in powering the future of transportation. Contact Lamnow for superior quality, reliability, and innovation in hub motor lamination solutions.
