High-speed electric motor drives are also being developed with MiTi compliant foil bearings. A compact 32 kW, 60,000 rpm induction motor drive supported on foil bearings is currently in development testing. Elimination of the oil lubrication system will reduce maintenance and operating costs and substantially reduces noise levels.

or more information, view the pdf brochure of the 150 HP compressor (pdf).

RELATED NEWSLETTER(S):

Foil Gas Bearings Enable Oil-Free Compressor Breakthrough
MiTi has enabled the breakthrough development of a truly oil-free plant air compressor. Working with Samsung Techwin Co., Ltd. of Korea, MiTi applied its proprietary compliant foil gas bearing design to mount a 125 lb. rotor with integral permanent magnet motor on two radial bearings. (Volume 19 - September 2004)

Mohawk Innovative Technology, Inc. (MiTi) has recently demonstrated operation of a totally oil free turbocharger rotor simulator system supported on MiTi's compliant foil gas bearings. Two major breakthroughs have been accomplished. A landmark speed of 121,500 rpm with a prototype turbocharger rotor system was achieved at MiTi. In parallel testing completed at NASA under a multi-year collaborative effort, bearing startup/shutdown life of 100,000 cycles was also demonstrated under the very severe conditions of 1200°F and 2 ½ times normal design static startup loading. This high speed operation and demonstrated bearing life exceeds requirements for even the most rigorous high speed rotating machinery applications. Combining the above with the fact that this system operates with the process gases as the lubricant, these advances would appear to meet also fuel cell requirements for delivery of high purity compressed gases.

Several key features to be noted from these tests and which are of importance to advanced high efficiency compressors are the speed achieved for the size of the rotor system. First it should be noted that the rotor was successfully taken to the limiting speed of the test apparatus. The limit was set by the maximum permissible surface tip speed of the thrust runner at approximately 1900 ft/sec. Additionally, at maximum speed the journal bearings operate at 4.4 million DN (Diameter in mm times speed in rpm) which is well beyond the capability of any advanced oil lubricated rolling element or conventional gas lubricated bearings manufactured today. The tested prototype hollow oil-free turbocharger rotor is 254 mm (10 in.) in length and incorporates an integral 95.5 mm ( =3.6 in.) thrust runner and double acting foil thrust bearings. This 2-Kg (4.41 lb.) turbocharger simulator rotor system, which is consistent with a typical 95,000 rpm 150 HP turbocharger unit, is supported on a pair of 36.5 mm (1.4375 in.) MiTi advanced aerodynamic foil journal bearings. System and bearing thermal stability have also been demonstrated to rotor speeds of 120,000 rpm.

These breakthroughs in rotor-bearing system performance were achieved due to recent advancements in our compliant foil bearing and rotor-bearing system designs. In particular, our new bearings have been designed with increased damping and shock tolerance to provide stable and durable operation at speeds and loads well above any published in the literature.

The promise of engineering lies in its ability to anticipate the needs of tomorrow. We at MiTi are proud of the role we play in fulfilling that promise. The breakthrough in foil bearing technology has become reality based upon the sustaining interest and support of our allies in government and industry who have seen the promise and potential offered by oil-free compliant foil gas bearings. The promise of foil bearings has always been in their design philosophy, namely to have a built-in ability to accommodate changing operating conditions, much like elements of the human anatomy. For example, the characteristics of synovial fluid in human joints change with changing loads and amplitudes to damp out impact loads and thereby protect our joints. Likewise, the characteristics of MiTi's self-acting compliant foil gas hydrodynamic bearings, change with operating conditions. Under light load and speed, the foil bearing maintains its softer character, while under high load and speed, it stiffens up to provide stability and high load capacity. Additionally, the higher the amplitude of vibration, the greater the damping value becomes to dissipate vibrations and make for a smoother operating system; as vibrations are reduced and operation becomes smoother, the bearing system damping automatically reduces as well.

Thus, MiTi's novel foil bearing's structural compliance automatically makes necessary adjustments and quickly responds to changes in the system. It is these features that are allowing the promises of foil bearings to be realized in practical applications that will truly meet the needs of tomorrow.

It is our earnest belief that clean, gas producing, environmentally safe turbo-alternators, motor driven high speed compressors and other high speed oil-free systems including small gas turbine engines for aircraft, can be successfully developed and implemented with the use of MiTi's foil bearings. In particular, we believe that with our recent experiences in collaboratively developing high speed oil-free machinery employing our foil bearings, we can assist interested parties in developing compact, light weight, highly efficient and durable oil-free turbomachinery. These pages contain information showing the performance discussed above and a photo of a foil bearing supported Oil-Free Turbocharger Demonstrator Unit. Should you have any technical questions, or require any further information regarding the development and application of oil-free turbomachinery, please contact Mr. James F. Walton, II of MiTi.