GB2470388A

GB2470388A - A turbo compressor unit including at least two conical journal air bearings

Info

Publication number: GB2470388A
Application number: GB0908746A
Authority: GB
Inventors: Thomas Hild
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2009-05-21
Filing date: 2009-05-21
Publication date: 2010-11-24
Also published as: GB0908746D0

Abstract

A turbo compressor unit 10 comprises: a rotor shaft 11; and a compressor wheel 12 disposed thereon in a coaxial fashion. The rotor shaft 11 is supported by at least two conical journal air bearings 13a, 13b which are arranged, with respect to one another, in opposing orientation.

Description

Conical air bearings for turbo compressor

Description

The invention relates to conical air bearings for turbo compressors.

The term "turbo compressor" relates to all kinds of axial-flow compressors comprising at least one fan, or rotor blade.

Such turbo compressors are for example being used in fuel cells. In order to achieve very high fuel utilization, it is necessary to reduce the amount of hydrogen exiting the fuel cell. The said turbo compressors serve to impel fuel recycle gas from fuel flow exits to fuel flow inlets, thereby increasing fuel efficiency.

Other applications include turbocharged combustion engines, aircraft jet engines, or gas turbines.

In order to cope with high rotation speeds (in some applications rotation speeds of > 300000 min' may occur), air bearings have been introduced, as for example disclosed in US4503683. These air bearings help to overcome the problem of lubricant breakdown, and they reduce the bearing wear of a spinning turbo to zero, in addition to reducing lag.

Unlike contact-roller bearings, air bearings utilize a thin film of pressurized air to provide an exceedingly low friction load-bearing interface between surfaces. The two surfaces don't touch. Being non-contact, air bearings avoid the traditional bearing-related problems of friction, wear, particulates, and lubricant handling, and offer distinct advantages in precision positioning and high-speed applications.

The fluid film of the bearing is air that flows through the bearing itself to the bearing surface. The design of the air bearing is such that, although the air constantly escapes from the bearing gap, the continual flow of pressurized air through the bearing is enough to support the working loads.

In turbo compressor units according to the state of the art which supported by air bearings, at least two journal air bearings are used in connection with at least one thrust air bearing. While the former are thought to absorb radial forces, the latter is thought to absorb axial forces. By these means the turbo compressor unit is stabilized both radially and axially.

It is a disadvantage of such kind of a turbo compressor unit that the said design is labor-and cost intensive, requires considerable space and incurs comparatively high maintenance efforts.

It is the object of the invention to provide a turbo compressor unit, or a support for such unit, which avoids the said disadvantages.

The solution of the object is achieved by the features of claim 1. Preferred embodiments are given by the dependent claims.

These and other aspects of the invention will be apparent from and elucidated with reference to a preferred embodiment described hereinafter.

In the drawings: Fig. 1 is a schematic drawing of a turbo compressor unit according to the invention, and Fig. 2 is a schematic drawing of a turbo Is compressor unit according to the state of the art.

In Fig. 1, a turbo compressor unit 10 is shown, which comprises a rotor shaft 11 and a compressor wheel 12, the latter being the actual "turbo". The compressor wheel is disposed on the rotor shaft in a coaxial fashion. Furthermore, Fig. 1 show that the rotor shaft is supported by two conical journal air bearings 13a and 13b, which are arranged, with respect to one another, in opposing orientation.

The term "opposing orientation" of the conical journal air bearings means that the directions of the cones of at least two bearings are opposite to one another.

The opposing orientation accounts for the fact that the bearings absorb both axial and radial forces, and provides for a stabilization of the rotor shaft in an axial direction. Therefore, it renders a thrust air bearing, which in turbo compressors according to the -.4-state of the art stabilizes the rotor shaft in an axial direction, obsolete.

This again leads to a substantial reduction of space requirements, manufacturing efforts and material usage, and thus to a considerable reduction of costs, while maintenance efforts will be reduced as well.

The technological field of air bearings for high

speed applications like turbo compressors is still not well explored. For this reason, the skilled person has safety issues (particularly related to stability) in mind when considering the use of an air bearing to support a turbo compressor, which in the past made a thrust air bearing seem indispensable.

Conical air bearings have only recently been developed, and they have not yet found widespread application. It is the merit of the inventor of the present invention that he has for the first time described that conical air bearings meet all safety and stability requirements to be set of journal bearings supporting a turbo compressor unit.

Furthermore, the said unit shown in Fig 1 further comprises an electric motor which is disposed, in a coaxial fashion, on the rotor shaft, and comprising a stator 14a and a magnetic rotor 14b. Such electric motor is necessary in some applications to drive the turbo compressor. Other electric motor arrangements (e.g. comprising a belt drive or a gearbox to drive the rotor shaft), or other electric motor types can be used as well by the person skilled in the art.

However, in some applications, like turbocharged combustion engines, the turbo compressor is driven by a rotor which is disposed in the exhaust tube. Therefore, in such applications the said electric motor is not necessary.

In a preferred embodiment, the turbo compressor unit according to the invention is integrated into a fuel cell environment.

In other preferred embodiments, the turbo compressor unit according to the invention is integrated into a device selected from the group consisting of turbocharged combustion engines, aircraft jet engines, and/or gas turbines.

In variance to Fig. 1, the turbo compressor unit according to the invention may as well comprise a) more than one compressor wheel (e.g. and array of 5 -10, as is the case in gas turbine engines, b) two rotor shafts disposed to one another in a concentric fashion (i.e. the outer of which is hollow), and supporting to different compressor wheels, wherein at least one rotor shaft is supported by the said at least two conical air bearings, c) at least one rotor wheel on the opposite side of the rotor shaft and disposed in the engine exhaust (as is the case in turbocharged combustion engines), and/or d) at least one turbine wheel on the opposite side of the rotor shaft, as is the case in jet engines.

Fig. 2 shows a turbo compressor unit 20 according to the state of the art, comprising a rotor shaft (21) and a compressor wheel (22) disposed thereon in a coaxial fashion. The rotor shaft is supported by two non-conical journal air bearings (23a, 23b) and a thrust air bearing (23c). While the former are thought to absorb radial forces, the latter is thought to absorb axial forces. By these means, the turbo compressor unit is stabilized both radially and axially. See above as to the disadvantages of this conventional design.