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NTN Develops “Resin Mold Insulated Bearing” for e-Axle
May 23, 2024New Products

  • Responding to the increase in battery voltage of EVs with an excellent electrical pitting resistant insulating resin layer

NTN Corporation (hereafter, NTN) has developed a “Resin Mold Insulated Bearing” for e-Axles used in electric vehicles (EVs). This bearing mitigates electrical pitting by offering insulation performance of 1,000 V or more. This is achieved by injection molding an insulating resin layer onto the bearing's outer diameter and width surface to support the use of high-voltage batteries. Furthermore, this bearing demonstrates durability across a broad temperature range, required by e-Axles. This durability was attained by selecting a resin material robust enough to endure temperature fluctuations and to optimize the molding techniques.

Photo:“Resin Mold Insulated Bearing” for e-Axle “Resin Mold Insulated Bearing” for e-Axle
Figure:Applied areas in parallel axis e-Axle (red circle) Applied areas in parallel axis e-Axle (red circle)

Background of development

In the automotive industry, the evolution and adoption of EVs are rapidly progressing with the aim to reduce environmental impact. The bearings used in the e-Axle, the power source in EVs, are required to counteract electrical pitting caused by motor current leakage.

NTN has been developing and supplying bearings such as ceramic bearings, where the ceramic rolling elements serve as insulators, and “Bearing with Insulating Coating” *1, where an insulating coating is applied to the bearing's outer diameter and width surface. Electrical pitting resistance, low torque, and efficient heat dissipation are critical for the performance of these electrical pitting resistant bearings. However, these requirements are continually evolving due to variations in the operating environments of bearings, which are influenced by vehicle designs. To address these diverse customer needs, NTN has newly developed the “Resin Mold Insulated Bearing”.

  1. Press release on May 24, 2023:
    NTN Develops “Bearing with Insulating Coating” for e-Axle


1. Electrical pitting resistance The bearing's outer diameter and width surfaces are injection-molded with a resin with excellent insulation properties. This resin mold inhibits the flow of electric current into the bearing, thereby achieving an insulation resistance performance exceeding 1,000 V. This product is designed to endure battery voltages up to 800 V, a threshold anticipated to rise in the future. *2
2. Durability Differences in thermal expansion and shrinkage between resins and metals can lead to resin cracking due to temperature changes. For this reason, a resin material that can withstand the required strength across a wide temperature range was selected for this product. Subsequently, molding methods that provide sufficient strength for the entire insulating resin layer were adopted as well. This resulted in a product that offers durable performance over a wide range of temperature environments found in e-Axles.
  1. The voltage applied to bearings for e-Axle is assumed to be less than 10% of the battery voltage

Photo:Raceway surface of outer ring after electrical pitting test Raceway surface of outer ring after electrical pitting test
(Left: Developed product, Right: Standard product)
Corrugated pattern damages are seen in standard product

In the future, as EV voltage increases, we anticipate a growing demand for electrical pitting resistant bearings. NTN is committed to meeting this demand by offering a diverse range of these bearings globally, aiming to enhance the functionality of EVs and HEVs.

NTN will showcase this product at the “Automotive Engineering Exposition 2024 YOKOHAMA”, taking place at PACIFICO Yokohama from May 22 to 24.


e-Axle for EVs and HEVs (motors and gearboxes)


Impact of higher battery voltage on e-Axle electrical pitting

EV batteries are advancing towards higher voltages to extend vehicle range and decrease charging time. Batteries operating at approximately 800 V are anticipated to be widely used in the future. This increase in voltage could significantly intensify bearing damage caused by sparks in the bearings. Moreover, as inverter control frequencies increase to enhance motor control efficiency, we expect a corresponding rise in spark occurrences. This, in turn, could potentially result to a higher incidence of electrical pitting.

Lineup of NTN's bearing resistant to electrical pitting

Figure:Lineup of NTN's bearing resistant to electrical pitting

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