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Jan. 15, 2020

Magnet solutions that improve the efficiency of drive motors for EVs

Electric vehicles (EVs) have been spreading widely as a solution for the environmental problems faced worldwide. However many technical hurdles must be cleared so that EVs can run safely and with comfort on a full scale across the world. One solution is the higher performance of the drive motor (i.e.via reduced size, lighter weight, and higher efficiency). To achieve motors that can meet higher technical requirements, the evolution of magnets, which are components that affect motor performance, is an essential step.

Technical challenges in use of EV drive motors

The electrification of cars is progressing steadily all over the world. Especially in Europe and India, “EV shift” efforts have been made with specific deadlines to phase out the sale of ICE (internal combustion engine)-driven vehicles. This global EV trend is expected to accelerate further across the globe.

Market forecast for motor-powered cars

Market forecast for motor-powered cars

Source: Fuji Keizai Co., Ltd. 2019 In-depth Analysis Survey of HEV- and EV-related Markets

EV,FCV and PHEV are expected to increase steadily to become the mainstream of electric and hybrid vehicles (xEV).

There is a clear difference between EVs , HEVs and PHEVs. While EVs are mainly powered only by motors, HEVs (hybrid vehicles) are driven by both motors and internal combustion engines, PHEVs (plug-in hybrid vehicles) are the advanced versions of HEVs, which can run on ICEs, in case of need, when their motor malfunctions. Moreover, they offer the choice of using the motor and ICE according to the driving situation, allowing to perform optimal energy-saving driving.

On the other hand, EVs have only the motor to rely on as the driving source. EV drive motors are required to run efficiently and with less power in all sorts of driving scenarios, including traffic jams requiring frequent stops and starts, off-road driving on steep mountain roads and bumpy roads, driving on highways, and driving with different numbers of passengers and luggage. Furthermore, the miniaturization and weight reduction of the motor itself is a must, given that these requirements will further improve efficiency. The important factor here is the evolution of magnets, which are components that affect motor performance.

Example of EV drive motor structure (image)

Example of EV drive motor structure (image)
EV drive motors mostly use a type of motor called a brushless motor. The drawing shows an example of the structure of the brushless motor. It consists of a rotor that rotates when supplied with electric current, and stator for rotating the rotor. The rotor contains a neodymium magnet.

Motor solutions applying high-powered magnets and magnet control technologies

EV drive motors require an extremely strong magnetic energy, and hence the most powerful permanent magnet, the neodymium magnet*1, is used. Of these magnets, TDK's Neodymium Magnets (NEOREC Series) have achieved one of the world's highest level of coercive force*2.
The powerful magnets provide a large rotational force to the motor, thereby contributing to its further miniaturization, lighter weight, and higher efficiency compared to those using conventional neodymium magnets.

The further reduction of the size and weight, and improvement of efficiency of EV drive motors would require to changing the motor shape and internal structure to more complex and diverse designs. This means that the neodymium magnets used would need to be more powerful and of a different shape, while providing magnetic field orientations for generating magnetic force more efficiently.

TDK has developed a technology that accurately creates various neodymium magnet shapes, and an orientation control technology*3 that can change the magnetic field freely. Optimizing the magnet according to the conditions/environment in use, these technologies have made it possible to provide optimum neodymium magnet solutions for a diverse range of motor designs.

Differences in orientation between flat plate-shaped and arc-shaped magnetic fields (image)

Examples of new shape and magnetic field orientation technologies for neodymium magnets
Differences in orientation between the flat plate-shaped and arc-shaped magnetic fields in interior permanent magnet (IPM) rotors (magnet embedded inside the metal core of rotor). The magnetic field orientation is one direction for the flat type, and in a radial direction for the curved type.

TDK has also developed a technique that minimizes the necessity of heavy rare-earth elements*4 in neodymium magnets, such as dysprosium (Dy) and terbium (Tb), which are difficult to procure. In 2012, the company released the industry’s first neodymium magnet that contains no Dy. Through these efforts, TDK aims to continue meeting motor design needs as well as to support the stable production of EVs by reducing supply-chain risk in magnet procurement.
TDK”s Magnet solutions meet new development requirements for EV drive motors and support EV driving with zero CO2 emissions.

Neodymium Magnets (NEOREC Series)

Neodymium Magnets (NEOREC Series)
Lineup of various magnetic properties. In addition to drive motors, TDK offers a wide selection of products for various applications. Selecting the most suitable design will dramatically reduce the size and thickness of the equipment using the magnet, as well as allowing higher power. See Product Center for details.

Terminology

  1. Neodymium magnet: Magnet composed mainly of neodymium, iron, and boron. Considered the most powerful of permanent magnets.
  2. Coercive force: Measure of resistance to weakening of the magnetic force during the use of magnets. Expressed by the force required to return the magnetized material to the unmagnetized state. As the unit of measure, the oersted (Oe) is used in centimeter–gram–second (CGS) system and ampere/meter (A/m) in International System of Units (SI).
  3. Orientation control: Processing to align the magnetic field in a specific direction.
  4. Heavy rare earth elements: Out of 17 rare earth elements, these are particularly rare and difficult to procure stably.
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