Magnetic Material Solutions
Supporting Automotive Electrification

Automotive electrification, such as development of electric vehicles (EVs) or hybrid electric vehicles (HEVs), has advanced and components used for engine-driven vehicles have been shifted to those of electromagnetic actuators. Key components necessary for automotive electrification including motors and inverters have evolved mainly in non-automotive fields such as industrial equipment and rail industries, but meanwhile, development for increasing their power output and downsizing for on-board applications has been in progress.
Here are examples of Showa Denko Materials’ magnetic material solutions contributing to automotive electrification. They include solutions that can retain magnetic properties in motors or inverters even in their high operating frequency or downsize components through 3D magnetic circuit design with a high degree of freedom.

Application examples of magnetic materials

Motor [Isotropic bonded magnet]

Can be used at high motor operating frequency

Operating frequency of motors has become higher to increase the motor speed and achieve high-efficient drive of electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, due to a concern that magnetic properties may be degraded by heat caused by eddy current, 1,000 Hz has been considered as a limitation for conventional materials. Our bonded magnet is expected to retain its magnetic properties because the eddy current is suppressed even at high frequency exceeding 1,000 Hz with its high electric resistance (50μΩ・m)

solution

Magnetic properties can be retained at operation frequency over 1,000 Hz

In order to increase the motor speed and achieve high-efficient drive of electric vehicles (EVs) and hybrid electric vehicles (HEVs), operating frequency tends to increase. Conventionally, neodymium (NdFeB) sintered magnets used for motors have large eddy current loss, and magnetic properties cannot be retained if the operating frequency exceeds 1,000 Hz. For our bonded magnet manufactured by compression molding the mixed magnetic powder consisting of a neodymium magnetic powder and a binder resin, the magnetic powder particles have insulation layers on their surfaces, suppressing the occurrence of the eddy current. Therefore, it is expected that magnetic properties are retained at high frequency exceeding 1,000 Hz while a high electric resistance (50μΩ・m) is present.

Crushing strength reduction rate is 5% or less even in a high temperature environment over 150℃

Glass transition temperature of epoxy resin, which is widely used as a binder, is 150℃ or less. For this reason, the challenge was to prevent heat degradation of the binder layer to ensure its strength even in a high temperature environment exceeding 150℃. The epoxy resin we are using as a binder for bonded magnets has a heat-resistant structure in resin composition. This prevents heat degradation of the binder, allowing it to be used under a high temperature exceeding 150℃. Furthermore, a coupling agent that accelerates a reaction with the resin and the metal was added to strengthen the interface adhesion between the binder resin and magnetic powder, improving the crushing strength reduction rate due to heat from 70-80% to 5% or less.

Difference between conventional and our binder materials
Crushing strength reduction rate of conventional and our binder materials
* Shows the reduction rate when the crushing strength at room temperature is regarded as 100%. Reduction rate may vary depending on the shape of a molded body.

Product features

Heat-resistant and highly durable

A bonded magnet with a heat resistance temperature of 200℃ or more and a maximum of 380 MPa crushing strength can be produced. Showa Denko Materials provides bonded magnets with excellent durability that meet customers’ requirements and retain high strength in an environment where a high heat load is applied during motor driving.

High pressure compression that is approximately twice as the conventional one improves the filling factor of magnetic powder, increasing power output

Conventionally, powder was compressed with a pressure of 0.6 to 1 GPa. Using our compression stress analysis and optimum die designing, compression can be performed at high pressure up to 2 GPa. As the filling amount of magnetic powder can be increased due to high-pressure compression, a magnet that is the same size as the conventional one but provides high power can be manufactured.

Comparison of the flux density between conventional and our
high-pressure compression

Cutting after sintering is unnecessary, reducing machining cost

Sintered neodymium magnets that are manufactured through sintering and thermal treatment in a vacuum furnace significantly shrinks during sintering, and needs to be cut in accordance with product dimensions after manufacturing. A bonded magnet that is near-net-shape molded with a mold requires less machining. Therefore, reduction in the machining cost of customer process can be expected.

Integral compression molding with metal parts reduces machining process

Bonded magnets can be molded with peripheral metal parts. This reduces manufacturing processes and allows for more efficient production.

Comparison between conventional and our integral compression molding processes
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Motor [Core material]

Contributes to downsizing of motor through 3D magnetic circuit design

Along with a transition from engine drive to electromagnetic drive, the number of motors has been increasing, and in order to secure installation spaces, downsizing of motors is required. An improvement in design of a motor core, which is a main part of the motor, is essential for downsizing of motor. A motor core which consists of our pure iron soft magnetic composites allows a 3D magnetic circuit design with a high degree of freedom and its core axial length can be shorten, contributing to downsizing of motors.

solution

Downsizing of a motor core through 3D magnetic circuit design

Nearly 50 motors are used in an engine-driven vehicle, while the number of those used in an electric vehicle (EV) or a hybrid electric vehicle (HEV) has been increasing to 100 or more, posing an issue of downsizing and weight reduction of motors. A motor core, which is an important part of motor design, is conventionally manufactured by lamination steel with a high magnetic flux density. The magnetic flux can only go parallel to the laminated surfaces. Thus, due to restrictions on magnetic circuit design, the axial length has to be long, making it difficult to downsizing of motors.
Our pure iron soft magnetic composites <EU-67s> is manufactured by compaction of iron powder which is coated with an insulation layer. This does not restrict the magnetic flux direction, allowing 3D magnetic circuit design with a high degree of freedom. It also simplifies windings and an excellent winding space factor can be performed without causing extra winding wire (coil end) that goes out from the coil, which can shorten the coil axial length. The coil winding space factor, which is 30-40% for conventional materials, can be improved up to 80%. In particular, this is suitable for an axial motor or a claw pole motor where flux is preferentially passed though in the Z-axis direction.

Difference between a lamination steel core and our pure iron soft magnetic composite core
Comparison between a lamination steel core and our pure iron soft magnetic composite core

Product features

Achieves low core loss (40 W/kg) at operating frequency of 1T/400Hz

Through advancement in electrification technology, operating frequency of motors has been increasing up to 1,000 Hz or more. In such a frequency, core loss* of a lamination steel core increases, making it difficult to ensure necessary magnetic force. A pure iron soft magnetic composite core whose individual iron particles are insulated has a low eddy current loss, and the core loss at frequency of 1 T/400 Hz is approx. 40 W/kg. Even at high operating frequency of 1 T/1,000 Hz, core loss is low (100-130 W/kg), while it is 150 W/kg or more for the lamination steel core. Our motor core can be used at a frequency up to 5,000 Hz.

Structure of the pure iron soft magnetic composite core
Core loss: A loss caused in the iron core. This becomes a factor that causes a low efficiency of electrical machines such as motors.

Transverse Rupture Strength: 150 MPa

Transverse rupture strength of a conventional pure iron soft magnetic composites is used is 30-40 MPa. Therefore, it is difficult to use such parts for motor cores because resistance to the centrifugal force during high-speed rotation and the fatigue strength to withstand cyclic load are required. With our soft magnetic composites technology, the strength is increased five times to achieve 150 MPa of transverse rupture strength by applying a special heat treatment to the core material to fill surface pores, which are a cause of strength reduction.

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Reactor

Downsizing of a reactor with its high magnetic flux density

Needs of inverter downsizing and weight reduction have been increasing to improve power consumption of electric vehicles (EVs) and hybrid electric vehicle (HEVs). However, the challenge is that the part size has to be large to ensure necessary inductance when an alloy dust core is used as a core material of a reactor installed in an inverter. A reactor core consisting of our pure iron soft magnetic composites has a high magnetic flux density, allowing inverter downsizing.

Resolution of issues

20-30% downsizing of a reactor core

In order to increase energy efficiency, the booster circuit operating frequency is expected to be increased from 10-20 kHz to 30-40 kHz. This means that components installed in an inverter have to be compatible with a high frequency. In such case, an alloy dust core that is suitable for operation in a high frequency and has less core loss is generally used. However, due to its low magnetic flux density (1.2-1.5 T at 50,000 A/m), a core size has to be large to ensure a necessary inductance, making it difficult to downsize the core.
For our reactor core <EU-71> that consists of our pure iron soft magnetic composites, powder consisting of particles with insulation layer of inorganic oxide is used as magnetic material, suppressing the eddy current that may cause core loss. Accordingly, core loss level can be the same as that of conventional materials, and the core can be used in a high frequency. Furthermore, as its main constituent is “iron”, a high magnetic flux density (2.0 T at 50,000 A/m) is obtained, allowing a smaller design than conventional materials. Actually, we have an example of reactor downsizing by 20-30% that meets the same specifications as the conventional core.

Comparison between an alloy dust core and our pure iron soft magnetic composite core
Alloy dust core Our pure iron soft magnetic composite core
Core loss 100 100 Equivalent
Inductance 100 130 High inductance properties due to a high magnetic flux density
Power conditioner efficiency 100 100 Equivalent
Reactor volume 100 87 Downsizing and assembly process simplification are possible.
Number of cores/unit 100 60
Number of coil turns 100 85 The amount of copper wire used for a coil can be reduced.

* Comparison of our pure iron soft magnetic composites properties when the alloy dust core performance is regarded as 100.

Product features

A high magnetic flux core that can be used in a high frequency of 10-30 kHz

A lubricant that can ensure insulation is applied when our pure iron soft magnetic composites is compacted and plastic flow of the core is restricted, increasing the specific electric resistance 30 times. Low core loss level is kept and our core can be used in a high frequency.

High strength that is twice of the alloy dust core

A soft iron with a high shape retention property is used as a magnetic material and a high-pressure compacting is performed, resulting in a high strength twice the strength of the alloy dust core and a high durability.

Proposal of an optimum design of a reactor module through magnetic field analysis

With our vast knowledge on magnetic properties and a reactor design optimization simulation based on magnetic field analysis, Showa Denko Materials proposes core materials and peripheral modules that meet customer specifications.

Simulation example
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Actuator

Can shape complex design with integral compaction.

Due to automotive electrification, mechanically or hydraulically actuated components have been shifted to those of electromagnetic actuation type. As various actuators installed on such vehicles have complex structures and shapes, machining process is also complex and requires a long time. Therefore, simplification of machining process has been an issue. With our sintered magnetic core that can be manufactured by near-net-shape compaction, machining process can be simplified even if the shape is complex, and an improvement in manufacturing efficiency can be expected.

Resolution of issues

Multifunctional parts can be manufactured with integral compaction.

Due to automotive electrification, mechanically or hydraulically actuated components have been shifted to those of electromagnetic actuation type. Actuator mechanical components such as plungers, yokes, and sensor rotors installed on such vehicles have complex structures and shapes. Conventionally, those parts are manufactured by cutting bulk bodies made from lamination steel or electromagnetic steels, and they are assembled and welded after machining. Since this machining process is complex and requires a long time, an improvement in yield has been an issue. Our sintered magnetic cores are manufactured by compaction of magnetic powders such as Fe, Fe-Si, or stainless steel. Thus, machining process can be reduced and an improvement in yield can be expected. Also different materials can be bonded during sintering process. It is called Sintering Diffusion Bonding method. For example, a wear-resistant material used for the inner side and a highly magnetic responsive material for the outer side can be combined and bonded together to finish a part. This can reduce the process and cost of welding.

Difference between conventional process and diffusion bonding process

Product features

Magnetic flux density improvement by high-pressure compaction

Due to high-pressure compaction at 1 G-2 GPa, Our sintered core shows a high magnetic flus density.

Easy surface treatment

Due to high-pressure compaction, internal pores are isolated during sintering process. Therefore, sealing (resin impregnation) process is not required before anti-corrosion plating.

1.5 times higher strength compared to welding

Diffusion bonding is a metallic bond that utilizes the difference in coefficients of thermal expansion of parts compacted from different materials. Therefore, bonding strength is approx. 1.5 times higher than weld bonding and an excellent durability is obtained.

Bonding strength obtained through the conventional process and diffusion bonding

* Evaluation of diffusion bonding strength when the strength obtained through the conventional process is regarded as 100.

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