Realized by MinebeaMitsumi's global production network
Trump card for fuel economy improvement and engine downsizing

Bearings

High-heat-resistant ball bearing unit for automobile turbochargers

As public eco-awareness has been rising and environmental regulations are being strengthened worldwide, automobile manufacturers devote themselves to the realization of new eco-friendly vehicles. One solution to do this is engine downsizing, and a turbocharger, which increases an engine's efficiency and power output while maintaining the performance of conventional engines, has come into the spotlight. MinebeaMitsumi succeeded in developing a next-generation, high-heat-resistant ball bearing unit that directly improves turbocharger performance.

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High-heat-resistant ball bearing unit for automobile turbochargers

Turbocharger with potential for rapid demand expansion

Turbochargers, in their heyday in the 1980s, were installed in many racing cars and sports cars to enhance the speed and maximum output of the automobiles. In those days, there was a trade-off relationship between the turbocharger and fuel consumption. Recently, a turbocharger has attracted attention once again as a device for boosting the insufficient output of engines that are downsized to meet environmental restrictions. Thus, its arena of applications has been expanded to general automobiles and eco-cars as well.


Bearings that determine a turbocharger's performances

A turbocharger is a device to increase an engine's power output with a smaller engine capacity by improving the engine's combustion efficiency through the recycling of exhaust gases that are normally discarded.

Mechanism of turbocharger

A turbocharger harnesses exhaust gas pressure emitted from the engine cylinder to drive a turbine and a compressor mounted on the same shaft. Air taken in by an automobile is compressed by the compressor and sent to the cylinder, which increases air intake and improves combustion efficiency. The turbine and compressor both play important roles to efficiently send compressed air to the engine. In 2008, MinebeaMitsumi started developing a new type of bearings for a turbine main shaft that directly influences the rotational efficiency.

The bearing for turbine main shafts is used for the turbine driven by ultrahigh-temperature exhaust gases exceeding 800°C as the power source, and it must withstand ultrahigh speed of over 200,000 revolutions while continuously immersed in oil. For this reason, many turbochargers for general automobiles used oil-lubricating bearings that are highly resistant to harsh environments. However, since the friction resistance of oil-lubricating bearings increases at the time of acceleration and deceleration due to its structure, the speed following capability is inferior to that of ball bearings (particularly when an engine starts at the low temperature). This generates a time lag between the increase in intake air pressure and the step-in operation of the accelerator pedal. Consequently, the driver feels the acceleration to be slow, and depresses the accelerator pedal more than necessary, thereby resulting in poor fuel economy. In actual city driving, since acceleration and deceleration are frequently repeated, a series of those steps tend to affect practical fuel economy.

Conventional oil-lubricating bearing (also known as sleeve bearing or metal bearing)

Small size, Low torque, Durability, Heat resistance

Requirements for the new bearing

To address these issues, we had to improve the following four main points for the new type of ball bearing unit: Downsizing along with an engine unit downsizing, high durability, high-heat resistance and low torque. In addition, we had to mass produce the bearings so that they would be widely adopted for use in general automobiles and eco-cars. MinebeaMitsumi, which has been continuously improving bearing production technologies since its establishment, has begun to tackle this challenge.


Development of high-heat-resistant ball bearing unit to meet various requirements

MinebeaMitsumi has improved combustion efficiency and reduced the time lag between the pedal operation and automobile acceleration by adopting high-heat-resistant ball bearings instead of oil-lubricating bearings.

Three shaft diameters, 6 mm, 10 mm and 12 mm, are available. Displacements from 1.4 to 10 L are supported.

Compared to oil-lubricating bearings, the structure of high-heat-resistant ball bearings is more complicated. However, we solved the issues of durability and heat resistance by combining parts made from different materials. For the inner race and outer race, we adopted M50 bearing steel that is also used for the main bearings of aircraft jet engines; and for balls, we adopted lightweight ceramic materials with low calorific value that are suitable for high revolution. We also applied special surface treatment to the retainer to improve the balls' rotation efficiency. Besides downsizing, unitization allowed us to reduce the assembly work in the turbocharger manufacture and improve the stability and balance of the entire part.

Sectional view of ball bearing unit

Comparison of the mechanical losses of ball bearing and oil-lubricating bearing

Screen of actual fluid analysis

Realization of advanced product development through the global coordination within MinebeaMitsumi

MinebeaMitsumi's global technical development capability and production system were indispensable for the processes from the development to mass production of the new type ball bearing unit. Our German affiliate, myonic, conducted the basic design and development and another German affiliate, PMDM, worked on the fluid and heat analyses. Then, our Karuizawa Plant carried out the prototype/mass production designing and the Bang Pa-in Plant in Thailand took charge of the mass production. As such, the comprehensive strength of MinebeaMitsumi Group, which is expanding business globally, is fully utilized.

Our (German) subsidiary myonic, which joined the MinebeaMitsumi Group in 2008, is a long-established manufacturer with a history of over 70 years, and it manufactures special ball bearings for aircraft and medical products. PMDM has advanced technologies in fluid and heat analyses cultivated in the hard disk drive (HDD) development. Both companies conducted heat analyses for durability and heat resistance and fluid analyses for ball bearing lubricating oils. Through repeated prototyping and testing, they advanced the development of products that met various requirements. One of the mother plants of MinebeaMitsumi's global production system, the Karuizawa Plant, reiterated prototyping time and again in tandem with the developments in myonic and PMDM to tailor the design of the new type of ball bearing unit so that it could shift the product to mass production. Our main production base, the Bang Pa-in Plant in Thailand, is continuously producing high-heat-resistant bearing units that support the heart of general automobiles and eco-cars in the world, under strict, uncompromising quality control.

Interview : Technological superiority and enhanced global coordination within the MinebeaMitsumi Group - Ball Bearing Business Unit, Karuizawa Plant

Since its establishment as Japan's first specialized manufacturer of miniature ball bearings in 1951, MinebeaMitsumi has been leading the development and production of the world's miniature ball bearings and conducting R&D constantly to meet the needs of the age. We have realized the mass production of a high-performance product, i.e., the high-heat-resistant ball bearing unit introduced this time, by applying MinebeaMitsumi's technologies cultivated over the years. Our engineers in Germany, Japan and Thailand cooperated to achieve the same goal through the development and production of a single product, and they have created an organic linkage in MinebeaMitsumi Group. No matter how complicated it may be, MinebeaMitsumi has the technologies to create any type of ball bearings only with drawings. As a leading manufacturer of miniature ball bearings, we are proud that there is no miniature ball bearing that we cannot create.


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