WO1991017361A1

WO1991017361A1 - Compressor having magnetic bearing assembly

Info

Publication number: WO1991017361A1
Application number: PCT/FI1991/000122
Authority: WO
Inventors: Jaakko Larjola; Jari Backman; Olli Lindgren; Mikko PAAVOSEPPÄ
Original assignee: Oy High Speed Tech Ltd.
Priority date: 1990-05-08
Filing date: 1991-04-26
Publication date: 1991-11-14
Also published as: FI902308A0; FI902308A

Abstract

The invention relates to a compressor, comprising an aggregate consisting of an electric motor (3), journalled inside a body (1) and serving as a compressor power unit, and of at least a single-step compressor unit (2). The compressor includes rotating components (4, 5, 7, 8) which are adapted to rotate concentrically. The journalling of such rotating compressor components in radial direction is essentially effected by means of a gas bearing assembly (9). The axially directed journalling of the compressor is effected by means of a magnet bearing assembly (6), which is adapted to receive its control from a means (11) measuring the axial position of the rotating compressor components. The type of compressor is a so-called high-speed compressor, whereby its speed of rotation is selected to be at least 2 x 104 rpm.

Description

Compressor having magnetic bearing assembly.

The present invention relates to a compressor, com¬ prising a body as well as an aggregate consisting of an electric motor journalled inside the body and serving as a compressor power unit and of at least a single-step compressor unit, the rotating components of said compressor being adapted to rotate concentri¬ cally and the journalling of the rotating compressor components in radial direction being essentially effected by means of a gas bearing assembly.

A blower unit as described above is disclosed e.g. in the publication US 3 933 416. However, the cited publication discloses the use of a motor operating on low speeds of rotation and intended particularly for pumping corrosive gases.

In several industrial processes, e.g. in pharmaceutical industry, food industry, textile industry etc., it is of extreme importance to obtain oilless compressed air. In so-called oilless compressors, traditionally designed for such purposes, the access of oil into compressed air is prevented by means of sealings or a like method but, in principle, an oil leak is always a possibility and, thus, the use of this type of constructions always involves considerable risks. In principle, the blower unit set forth in the publication US 3,933,416 operates without oil lubrication but its construction is unfavourable in applications which require a compact compressor and at the same time reasonable outputs. Such requirements lead to high rotating speeds for the rotating compressor components. In particular, a blower unit as set forth in US publication 3 933 416 is not capable of handling axial stresses in such applications. An object of this invention is to introduce a compres¬ sor which is capable of eliminating the above drawbacks in applications that require a compact, high-capacity and reliable compressor. In order to achieve this object, a compressor of the invention is primarily characterized in that the axial journalling is carried out by means of a magnet bearing assembly, adapted to receive its control from an element measuring the axial position of the rotating compressor components, and that the effective rotating speed of the compressor is selected to be at least 2 x 10⁴ rpm. Thus, a compressor designed as described above operates entirely on oilless bearing assemblies, so an oil leak into the compressed air to be pumped is impos- sible. Hence, a compressor of the invention can be used safely in. industrial processes which are sensitive to oil. On the other hand, the gas and magnet bearing assemblies have constructionally a long service life. Since it is further possible to construct a compressor- so as to be only fitted with non-contact sealings, such compressor is as good as free of maintenance in clean conditions. In most applications, a gas bearing assembly is very simple of set up, nor does it require adjustments during operation. An axially operating dynamic magnet bearing assembly can be set up by means of several different constructive methods. A magnet bearing assembly requires an element measuring- the axial position of the rotating components of a compressor and a control circuit for providing dynamic qualities, since the positional stability of the rotor wheel of a high-speed compressor is subject to strict requirements, particularly due to small clearan¬ ces. Nevertheless, such a control circuit is relati¬ vely simple to design. If the electric motor employed is a permanently magnetized electric motor, which is quite obviously the most preferred option, the compres¬ sor can be provided with a high efficiency and rotor dissipations are extremely low, so the compressor cooling can be readily carried out. Typically, a compressor of the invention can be given the following ratings, capacity: 10-500 kW, speed of rotation 2 x 10⁴ - 10⁵ rp , and trouble-free service life in reason¬ able conditions appr. 10 years.

Some preferred embodiments for a compressor of the invention are set forth in the annexed non-independent claims.

The invention will be described in more detail in the following specification with reference made to the accompanying drawing, which shows in a cross-section one embodiment for a compressor of the invention.

A compressor of the invention comprises as its main components a body 1, a compressor unit 2 and an electric motor 3. The rotating components of a compressor, i.e. a rotor wheel 4 included in compressor unit 2, a rotor 5 included in electric motor 3, and a radial plate 7 included in a magnet bearing assembly 6, are all mounted on a main shaft 8 to rotated concentrically around the centre axis of said main shaft 8 upon a bearing assembly included in body 1. Said bearing assembly comprises first of all a radial gas bearing array 9 whose component 9a and 9b are mounted on body 1 on either side of electric motor 3 in the longitudinal direction of main shaft 8. Secondly, said bearing assembly includes e.g. a magnet bearing array 6 which in the illustrated embodiment is mounted on the end of body 1 furthest away from compressor unit 2. Said body 1 includes integral body sections la and lb for an electric motor and a compres¬ sor unit. The compressor unit 2 includes a stator section 10 whose intake duct 11 is fitted with a means 12 measu¬ ring the position of the rotating compressor compo¬ nents, especially that of rotor wheel 4, said means being electrically 13 connected with a control circuit 14 for controlling the operation of magnet bearing assembly 6. Power supply is arranged from control circuit 14 along conductors 15a, 15b to means for the regulation of field strength, particularly to electro- magnets 16a, 16b. Electromagnets 16a, 16b are located in a chamber 17 surrounding said main shaft 8 and extending transversely, preferably perpendicularly, to its longitudinal direction, and fastened to its opposite, radially-directed walls 18a, 18b. Said chamber 17 is provided with a radial plate 7 mounted on main shaft 8, and particularly on rotor wheel 4. As described above, a compressor can be provided with a bilateral dynamic magnet bearing assembly which controls the axial position of main shaft 8 by means of control circuit 14 on the basis of measuring data supplied by said measuring means 12 associated with compressor unit 2.

On the opposite side relative to intake duct 11 of rotor wheel 4 said body is provided with a non-contact sealing 19 between the rotating compressor components and body 1. By way of reference, the drawing further shows an extension 20 for main shaft 8 as well as measuring elements 21, located in a recess included in body l and intended particularly for an angle of position, said elements being intended for a possible self-commutating circuit. Such circuit is particularly useful whenever said electric motor 3 comprises a brushless permanently magnetized direct-current machine. The drawing shows diagrammatically a current- supply system 22 applicable in this alternative electric motor design, which system can be mounted on the end of body 1. Elements 21 are connected to a control unit 23 which is fitted in a housing or a like 24. The supply of power occurs along a cable 25 to the control unit which includes an alternating transformer as mentioned above.

A compressor of the invention can be provided with several types of electric motors as well as several means of controlling such electric motors. The selec¬ tion of a motor type can be effected particularly according to the requirements set by the intended application of the compressor. As for the type of electric motor, said motor can be either a short- circuit machine, a permanently magnetized synchronous machine or a brushless permanently magnetized direct- current machine. Every electric motor of this type is provided with a similar stator. Thus, in terms of manufacturing technique, the construction will be preferable since the compressors applicable to various purposes are provided with identical bodies and stators. A permanently magnetized motor has a high efficientcy and rotor dissipations are negligible, whereby the cooling is easily arranged. On the other hand, the rotor of a short-circuit machine is mechani¬ cally simple but, at least in certain applications, it is hampered by more significant dissipations. Thus, a short-circuit machine is useful in applications where cooling is easily arranged. The supply of power in both a permanently magnetized synchronous machine and in a short-circuit machine can be effected by means of a frequency transformer. The supply of power in a brushless permanently magnetized direct- current machine is effected by means of an inverter, whose control can be carried out by measuring the angle of position of the magnetic axis of the rotor. Such control is particularly suitable for the supply of high-speed electric machines as it can be effected in a simple manner if compared to conventional frequen¬ cy transformers. In addition, an inverter and a control unit required for measuring the angle of position of the magnetic axis of a rotor are compact in size and, hence, can be permanently fixed to the body of a compressor.

A compressor of the invention can be designed in many different ways, particularly in terms of bearing assemblies. Thus, the magnet bearing assembly may consist of two sections, whereby a first electromagnet e.g. 16a is fitted e.g. in a chamber provided between a gas bearing 9a and a non-contact sealing 19, said chamber being provided with a plate corresponding to radial plate 7, and whereby a second electromagnet 16b and other constructive components shown in the drawing are identical to those shown in the drawing for magnet bearing assembly 6. It is of course obvious that the components of a two-component or multi- component magnet bearing assembly 6 can both, either one or some comprise a bilateral construction.

Claims

1. A compressor, comprising:

- a body (1) , as well as an aggregate consisting of an electric motor (3) , journalled inside said body (1) and serving as a compressor power unit, and of at least a single step compressor unit (2) , whereby rotating compressor components (4, 5, 7, 8) are adapted to rotate concentrically, and whereby the journalling of such rotating compressor compo¬ nents in radial direction is essentially effected by means of a gas bearing assembly (9) ,

ch-aracterized in that the axially directed journalling is effected by means of a magnet bearing assembly (6) , which is adapted to receive its control from a means (12) measuring the axial position of the rotating compressor components, and that the effective speed of rotation of the compressor is selected to be at least 2 x 10⁴ rpm.

2. A compressor as set forth in claim 1, characterized in that said means (12) measuring the axial position of rotating compressor components (4, 5, 7, 8) is mounted in connection with compressor unit (2) .

3. A compressor as set forth in claim 2, characterized in that said means (12) measuring the axial position of rotating compressor components (A , 5, 7, 8) is mounted adjacent to a compressor unit rotor wheel (4) in an intake duct (11) .

4. A compressor as set forth in any of claims 1-3, characterized in that said means measuring the axial position of rotating compressor components (4, 5, 7, 8) is connected with a control circuit (14) for regulating the field strength of magnet bearing assembly (6) .

5. A compressor as set forth in any of claims 1-4, characterized in that said magnet bearing assembly (6) is bilateral.

6. A compres.sor as set forth in any of claims 1-5, characterized in that said magnet bearing assembly

(6) includes at least one chamber (17) or a like, designed in body (1) and extending transversely, preferably perpendicularly, to the axial direction of the rotating compressor components, at least one of the radially directed walls (18a, 18b) of said chamber being fitted with elements for producing a magnetic field (16a, 16b) , and that said at least one chamber (17) is provided with a radial plate (7) or a like fastened to the rotating compressor components.

7. A compressor as set forth in any of claims 1-6, characterized in that at least a part of magnet bearing assembly (6) is positioned in a manner that said electric motor (3) is located in the longitudinal direction of the compressor between compressor unit (2) and a part of magnet bearing assembly (6) or the above-mentioned part thereof.

8. A compressor as set forth in claim 1, characterized in that the type of electric motor (3) is a permanently magnetized synchronous motor or a short-circuit machine, whose power supply is effected by means of a frequency transformer.

9. A compressor as set forth in claim 1, characterized in that the type of electric motor (3) is a brushless direct-current machine, whose power supply is effected by means of an inverter having its control based on measuring the angle of position of rotating compressor components (4, 5, 7, 8).

10. A compressor as set forth in claim 1, charac¬ terized in that on the side of the body furthest away from said intake duct (11) of rotor wheel (4) , said body (1) is fitted with a non-contact sealing (19) between rotating compressor components (4, 5, 7, 8) and body (l .