A New Proprietary Lubrication Mechanism Significantly Reduces the Necessary Lubricant Supply, Contributing to Longer eVTOL Flight Range

● Newly developed lubrication mechanism reduces required bearing lubricant supply by nearly 80%.

　The new design allows oil supply scavenge pumps and the lubricant tank to be lighter weight.

● Improved lubrication mechanism reduces the oil supply amount, cutting bearing power loss by nearly 30% compared to previous models.

 　NSK Ltd. has released a new gas turbine generator bearing for eVTOLs1 including large drones, which is expected to extend drone flight range.

　The new product was used for the gas turbine generator of a large drone (high payload emergency supply delivery drone equipped with a gas turbine generator) equipped with an 80-kw hybrid drive system for a regional reconstruction and practical development promotion project in fiscal 2023, and delivered to Fukushima Prefecture on February 21, 2024.

　NSK aims to achieve annual sales of 1.0 billion yen by 2030 for this product.

1.    Background

　In recent years, development of eVTOLs has been moving forward as a new means of transportation, with a predicted market size of 20 trillion yen by 2035. Previously, mainstream eVTOL propulsion systems were completely motorized, but to meet the growing need for longer flight range and improved transportation capabilities, demand for high-output, compact, lightweight hybrid motors is expected to continue growing. Gas turbine generators stand out from other hybrid motorized models because they can use various fuel sources such as biofuels and hydrogen, making them attractive from a carbon neutrality perspective. Now, gas turbine generators are the strongest contender for practical propulsion mechanisms.

　To contribute to longer flight range, reducing weight (i.e., making oil supply scavenge pumps and the lubricant tank lighter), and delivering high-speed revolution performance is required of gas turbine generator bearings. To meet this need, the market challenge is ensuring high-speed revolution performance (over 2.5 million dmn) with minimal lubrication.

2. Features

　NSK has developed a new lubrication mechanism that reduces the amount of lubricating oil the bearing requires while also lowering power loss. This design ensures high-speed revolution performance (over 2.5 million dmn) with the optimal, minimal amount of lubricating oil.

1) Reducing the amount of lubricating oil

　The new product reduces the amount of lubricating oil to one quarter of the conventional jet lubrication mechanism.

⇒Lightweight oil supply scavenge pumps and lubricant tank

2) Reducing energy loss (power loss)

　The new product reduces the power loss to two thirds of the conventional jet lubrication mechanism.

3) Ensuring high-speed revolution performance (over 2.5 million dmn)

3. Technology

1) Overview of the new lubrication mechanism

　The problem with jet lubrication, a common lubrication mechanism used for high-speed bearings, is that it requires a large amount of lubricating oil and causes high power loss. NSK’s new product resolves this issue by incorporating under-race lubrication as used in higher revolution applications, delivering reduced power loss and lubricating oil volume.

2) Issues with the conventional lubrication mechanism

　Jet lubrication uses highly compatible parts, spacers, in the oiling mechanism, making it versatile and cost-effective, but a large volume of oil is forcibly supplied at high pressure from outside the bearing, resulting in large volume lubricating oil usage and significant power loss.

　On the other hand, under-race lubrication uses dedicated flow channels in the shaft and bearing inner race to directly supply oil, a method which has low versatility and high cost. The benefit is that, since only the necessary amount of oil (minimal) is supplied via centrifugal force, this method is offers minimal power loss and oil usage.

3) New lubrication mechanism

　NSK’ new lubrication mechanism features an improved spacer shape allowing for direct supply of the necessary amount of oil (minimal) to the inside of the bearing using centrifugal force. This solution reduces the amount of lubricating oil and power loss, yielding a new highly versatile, low-cost lubrication mechanism.