US3762839A

US3762839A - Centrifugal pump with magnetic drive

Info

Publication number: US3762839A
Authority: US
Inventors: N Laing
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-02-10
Filing date: 1971-05-17
Publication date: 1973-10-02
Anticipated expiration: 1990-10-02
Also published as: FR2030407A1; GB1305651A; JPS4933308B1; BE745684A; DE2048286A1; GB1305652A; DE2005803A1; DE2048286B2; CA928755A

Abstract

In a centrifugal pump in which the impeller and a first pole ring of a magnetic transmission form a unitary structure, the latter is driven through a magnetically permeable separating wall. The magnetic transmission has a second pole ring and, between it and the separating wall, a conductor pole ring comprising a plurality of conductors with the two pole rings being independently arranged for rotation with respect to one another. The two pole rings each have a plurality of pole faces of alternating polarity with one of the pole rings having more pole faces than the other, whereby rotation of one of the pole rings with respect to the other pole ring will be at a predetermined ratio.

Description

United States Patent Laing 1 1 Oct. 2, 1973 [54] CENTRIFUGAL PUMP WITH MAGNETIC 3,490,379 1/1970 Laing 417/420 DRIVE [76] lnventor: Nikolaus Laing, Hofener Weg 35-37, Primary Examinerwilliam Freeh Aldingen bei Stutt t, Germany Assistant Examiner-John T. Winburn Att0rneyPennie, Edmonds, Morton, Taylor & Adams [22] Filed: May 17,1971

AppL No.: 144,200

Related U.S. Application Data Division of Ser. No. 9,916, Feb. 9, 1970, Pat. No. 3,645,650

{57] ABSTRACT In a centrifugal pump in which the impeller and a first pole ring of a magnetic transmission form a unitary structure, the latter is driven through a magnetically permeable separating wall. The magnetic transmission has a second pole ring and, between it and the separating wall, a conductor pole ring comprising a plurality of conductors with the two pole rings being independently arranged for rotation with respect to one another. The two pole rings each have a plurality of pole faces of alternating polarity with one of the pole rings having more pole faces than the other, whereby rotation of one of the pole rings with respect to the other pole ring will be at a predetermined ratio.

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PATENTED E 21973 SHEET 15 [1F 16 INVENTOR BY jm 4 d d PATENTED 2 SHEET 18 [1F 16 INVENTOfQ CENTRIFUGAL PUMP WITH MAGNETIC DRIVE RELATED APPLICATION This application is a division of my copending application Ser. No. 9,916 filed Feb. 9, 1970 now U.S. Pat. No. 3,645,650.

BACKGROUND OF THE INVENTION The invention relates to centrifugal pumps for liquids or gases, whose impeller forms a unit with a magnetic pole ring and which is driven by a rotating magnetic field, the rotating magnetic field being produced by a motor-driven pole ring having a number of poles which is greater than that of the said magnetic pole ring.

The invention thus relates to centrifugal pumps, whose impellers work at a speed different from that of the rotor of the driving motor. The transmission arrangement is not a magnetic coupling, but a magnetic transmission.

DESCRIPTION OF THE PRIOR ART A magnetic transmission with three relatively coaxially arranged elements, at least two of which are rotatable independently of each other, is known. Two of these elements consist of rings, separated by an air gap, with non-meshing, magnetically conductive teeth, which form regions of alternately high and low magnetic reluctance, the difference between the number of teeth on the two rings being small, so that, on one diameter only, two teeth of the outer ring are positioned exactly opposite two teeth of the inner ring. One of these rings may be permanently magnetised or provided with a winding which magnetises the ring so that a magnetic field is produced which causes alignment of two oppositely positioned teeth of the rings. This transmission constitutes the magnetic analogue of the mechanical hypocycloid gear in which only two teeth of the outer ring mesh at any one time. Whereas extremely high stresses for power transmission can be employed with gears, only very small shear forces can be transmitted by magnetic transmissions with poles on either side of an air gap which enables contactless running. In consequence, only small torques can be transmitted by any known magnetic transmissions, so that they cannot be considered for the transmission of larger powers. Moreover, this kind of transmission is possible only for very high transmission ratios of, for example, 1:20 or 1:50 but not transmission ratios of 1:2 or 1:5, so that this kind of transmission does not present a usable substitute for gears for the transmission of larger powers.

A frictionless magnetic transmission is also known, in which ferro-magnetic coupling elements are separated by a predetermined distance from a driving and a driven part, the whole assembly being accommodated in a housing which provides a closed magnetic circuit. In this form of transmission, only one coupling element at a time carries the maximum magnetic flux, so that therefore only the principle of the stepping gear is applied, in which only a very small region of the circumference is actively employed for the transmission of torque at any one time This magnetic transmission also has the disadvantages already mentioned.

Furthermore, a magnetic transmission is known, in which a driven magnetic system is coupled to a driving magnetic system by fields of magnetic force and the transmission ratio is formed by branching of the magnetic flux in a ferromagnetic coupling member. In a simple construction the direction of rotation of the output of this transmission is not defined. Only by means of a plurality of systems which are angularlydisplaced and axially juxtaposed, can the direction of rotation of such transmissions be predetermined. The latter, however, has the disadvantage that the effective flux is at any one time confined to a region of not more than one-third of the axial length and that the magnetic paths become very large; for this reason again they are not suitable for the transmission of large powers.

By comparison, it is the purpose of the invention to provide centrifugal pumps having magnetic transmissions, capable of transmitting large mechanical powers with minimum material cost and any desired transmission ratio, and particularly at low transmission ratios.

GENERAL DESCRIPTION OF THE INVENTION In a construction according to the invention, this is achieved by constructing the conductors in such a way that the magnetic flux flowing through a pole of the pole ring with the smaller number of poles is distributed over at least two poles of the pole ring with the greater number of poles. In a practical embodiment of this kind according to the invention at least one conductor has at least two pole faces facing the pole rings with the larger number of poles.

In another embodiment, the problem underlying the invention is solved by making at least one face of the conductor facing the pole ring with the larger number of poles at least as wide as the distance between two adjacent pole centres of this pole ring.

Preferably the three elements of a magnetic transmission according to the invention are arranged in the form of three concentric rings. If with this arrangement the number of the conductors equals twice the number of the poles of the inner pole ring which has the higher speed, then the alternating magnetic field which the driving pole ring produces in each conductor can be transformed into a two-phase, phase-symmetrical, circular and substantially sinusoidal rotating field, so that the same conditions apply to the driven pole ring as to the rotor of a three-phase induction motor.

The radial flux, which in an electric motor is provided by windings, is generated by permanent magnets of a rotating pole ring in these magnetic transmissions. By the use of high quality magnetic materials, the same induction as in the case of an electric motor can be provided, so that the transmittable torques correspond to those of electric motors having rotors of the same size. By contrast with simple motors, magnetic transmissions may also be built in synchronous form, if the driven pole ring is not in the form of an induction rotor (squirrel cage rotor) as in the case of an electric motor, but in the form of a permanent magnet rotor. This is not possible in the case of an electric motor, since the rotor would have to be accelerated to its full speed in onefiftieth (or one-sixtieth) of a second, whereas the magnetic transmission is driven and therefore accelerated over a longer period at a lower angular acceleration.

By providing two permanent magnet pole rings for the input and output, all eddy current losses are eliminated; in the case of an electric motor, these usually account for more than 50 percent of all losses. The only source of losses left is the iron loss in the conductors, which however only amounts to a few watts per kilogram of iron. The efficiency of the new magnetic transmission, if both pole rings contain permanent magnets,

is therefore nearly unity, which is of decisive importance, having regard to the large power which are to be transmitted.

The main area of application of the centrifugal pumps having magnetic transmissions is the conversion of the speed of mains-fed induction motors whose maximum speed is limited. Since the output of centrifugal pumps for given dimensions of the casing increases as the speed, a step-up transmission results in spaceand material saving constructions. Basically, however, the invention may also find application for centrifugal pumps whose impeller speed is less than that of the mtor, particularly in the case of drivingor medium frequency motors.

lf the number of conductors is three times that of the poles of the high speed pole ring with the smaller number of poles, it is also possible to produce a three-phase circular rotating field, which however is of advantage only where the degree of lack of uniformity of rotation which is dependent on the number of poles could be objectionable.

It is emphasised that in a centrifugal pump having a magnetic transmission according to the invention any one of the three elements can be the driving and any one of the three elements the driven element. It is further emphasised that one of the three elements must be held stationary or supported by a stationary system, which is usually done by supporting it by a housing element.

Transmissions for centrifugal pumps according to the invention may be built up in the form ofa cylinder, s'uperirnposd by a hollowcylinder and a further hollow cylinder surrounding them. The inner and outer pole rings may also be arranged relatively eccentrically. The air gaps need, however, not necessarily lie on cylindrical envelopes; they may also lie on conical envelopes, spherical surfaces and planes. in the latter version the arrangement consists of three discs, and it is not necessary for the rotating discs to be geometrically co-axial.

In the case of high-speed centrifugal pumps, which require a high driving speed, the high-speed pole ring of the magnetic transmission is constructed as a unit with theimpeller wheel, whilst the low-speed pole ring is driven by the motor. The third element, the conductor ring, is separated from the pump impeller by a wall, so that hermetic sealing is effected. Hermetically sealed pumps with thin-walled magnetically permeable separating walls are known. The invention enables the construction of pumps in which the walls through which magnetic forces are fed into the interior of the pump, can be made of any desired thickness, so that hermeticallysealed pumps constructed with magnetic transmissions in accordance with the invention can be manufactured for pressures which can be practically as high as desired and at which thin-walled magnetically permeable separating walls of magnetic couplings would tear. In such constructions, the thin-walled separating wall only acts as a sealing element, whilst the conductor ring also acts as a mechanical support against high pressures. For such pumps also magnetic transmissions with a transmission ratio in l are meaningful.

Since the torque is transmitted by a rotating magnetic field, the new magnetic transmissions can also be combined with magnetic bearing systems, so that desides contactless transmission of the torque, the bearing can also be contactless, except for a support at the centre of a spherical section.

The magnetic transmissions for centrifugal pumps in accordance with the invention may be classified according to their geometric parameters; these include the number of poles of the low speed and high speed pole ring, the number of conductors, the number of pole areas of the conductors, as well as the spacing of the pole areas of adjacent conductors. Accordingly, let, by definition:

p= Number of poles of the low speed pole ring (large number of poles) q Number of poles of the high speed pole ring (small number of poles) m Transmission ratio of the transmission, where m always p/q r Number of conductors r Number of pole areas of the conductors facing the low speed pole ring r,, Number of pole areas of the conductors facing the high speed pole ring j Spacing of the pole centres of the pole areas facing the low speed pole ring, of different adjacent conductors, relative to the spacing of the centres of adjacent poles of the low speed pole ring.

The highest transmission ratio is always given by the ratio m (PM) In this case the conductor ring formed by conductors 17 is held stationary. if, instead of the conductor ring, the low speed pole ring is held stationary, then, for the same embodiment, we get the lower transmission ratio of the conductor ring to the high speed'pole ring Using the same transmission, we get the lowest transmission ratio when the high speed pole ring is held stationary. We then get between the low speed pole ring 11 and the conductor ring, the transmission ratio m (m/m 1).

All the transmissions for centrifugal pumps in accordance with the invention thus enable three transmission ratios to be obtained, the direction of rotation for the transmission ratio m changing in the case of the ratio 111,. These speed ratios are exactly true only where two pole rings are magnetised by permanent-or electromagnets. if one of the pole rings is in the form of a hysteresis magnet or a short-circuited rotor like the rotor of an electric motor, then the slip of such a pole ring is superimposed on the transmission ratio. In these magnetic transmissions it is not necessary for the driving portion to be provided with permanentor electromagnets. It is also permissible for the driven pole ring only to effect the magnetisation. According to a preferred feature of the invention, a claw pole construction is provided for the magnetic material, in which adjacent poles of the same polarity are short-circuited together by soft magnet rings, so that a iarge portion of the entire magnetic material is operative at all times.

The particular provision and construction of the conductors which conduct the magnetic flux between the pole rings in accordance with the invention results in the magnetically active material of the pole ring with i the greater number of poles being almost completely utilised and thereby the torque transmitted by the transmission being considerably increased compared with known magnetic transmissions, in which only a portion of the magnetically active mass corresponding to the transmission ratio contributes to the torque transmission at any one time.

BRIEF DESCRIPTION OF THE DRAWINGS Some advantageous embodiments of the invention will now be described with reference to the drawings.

FIG. 1 shows a pump with a magnetic transmission;

FIG. 2 shows a turbo-compressor drive with a magnetic transmission;

FIG. 3 shows a borehole pump with a step-up magnetic transmission;

FIG. 4 shows an axial-flow pump with a step-down magnetic transmission;

FIGS. 5a-5d are a plan view of a preferred form of a magnetic transmission constructed according to the invention with odd series cascading in one direction and having

transmission ratios

5, 9, l3 and 5 respectively;

FIGS. 6a-6c show a different embodiment of a magnetic transmission with odd series cascading in the opposite direction of rotation than in FIG. 5 and having the

transmission ratios

3, 7, 11 respectively;

FIGS. 7a-7d show a further embodiment of a magnetic transmission with even series cascading in one direction having

transmission ratios

2, 4, 8 and 6 respectively;

FIGS. Sa-Sd show a magnetic transmission having even series cascading in a direction opposite to the direction of rotation of FIG. 7 and having

tranmission ratios

4, 6, 8 and I0 respectively;

FIG. 9 shows a spherical construction of the magnetic transmission according to the invention, preferably for pumps with magnetic bearings;

FIG. 10 shows a developed view of a sheet metal strip for producing the conductors.

FIG. 11a is a plan view of a part of a low speed pole ring for use in a magnetic transmission where the ring has magnetically conductive pole shoes;

FIG. 11b is an enlarged section through a part of a different embodiment of a low speed pole ring; and

FIG. 11c is a section through a still further embodiment of a low speed pole ring having claw poles;

FIG. 12a is a plan view of a magnetic transmission similar to that shown in FIG. 5b illustrating the magnetic lines of flux in one position of the high speed pole ring;

FIG. 12b is a view similar to FIG. 12a illustrating the magnetic lines of flux in a different position of the high speed pole ring; and

FIG. 120 is a view similar to FIG. 12a illustrating the high speed pole ring in a still further position.

FIG. 13a illustrates the construction of a magnetic tramission having the ratio 1 to I wherein the conductors are arranged radially;

FIG. 13b is a view similar to FIG. 13a but where the conductors are arranged in a cross formation and where the direction of the rotation of the pole ring is opposite to that shown in FIG. 13a;

FIG. 14a is a plan view of a magnetic transmission with a three-phase rotating field;

FIG. 14b is a view similar to FIG. 14a having different conductor configurations;

FIG. 140 is a view similar to FIG. 140 having a different number of conductors; and

FIG. 14d is a view similar to FIG. 14a of a still further embodiment having a different number of conductors and conductor configurations;

FIG. 15 shows a short-circuited rotor in a magnetic transmission with a conductor ring of special construction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a pump according to the invention with a magnetic transmission for increasing the speed of the pump runner 123, whereby the pump may be constructed in a very compact manner. The conductors 17 are made up of foils arranged one above the other; the pole ring consists of radially magnetised permanent magnets which are joined to each other in magnetically conducting manner by the ring 121 for closing the magnetic circuit. The pole ring 122 drives the pump runner 123. A magnetically permeable separating wall 124, of spherical form, is provided for hermetically sealing the interior of the pump. The motor 125 drives the outer pole ring via the disc-like wheel 126.

FIG. 2 shows a turbo-machine of the same kind as that of FIG. 1, but designed as a compressor, particularly for refrigerants. In these compressors, hermetic sealing is of very great importance, since refrigerant is always lost through the shaft seals. Since compressors run at appreciably higher speeds than pumps, the invention provides for the conductors a construction of extremely thin laminae with minimum hysteresis and eddy current losses, such as those used in audio frequency transformers. Pole shoes 132 of soft magnetic material are provided between the permanent magnet pieces 131. of the outer pole ring and the conductors 130. The spherical separator 134 is preferably made of synthetic material, e.g. a glass fibre reinforced epoxy resin, which is made impereable to gasses by a very thin layer of metal by electroor vapour deposition.

FIG. 3 shows a bore hole pump, in which a motor 111, which is accommodated in a hermetically sealed housing 110, drives the pole ring 112 of the magnetic transmission with the conductor ring 113. The high speed pole ring 115 rotates in a conical, magnetically impermeable, separating wall 114, the pole ring being conical and provided with helical channels 116, which convey a small quantity of liquid into the magnetic air gap. This results in hydrodynamic lubrication, so that further bearings can be dispensed with.

Water is admitted through the orifices 118. The cap 119, which also rotates, prevents the ingress of sand into the space formed by the separating wall. Since the velocity pressure of the pump varies with the square of the speed, a pump runner 117 in a construction according to the invention with a transmission ratio of 3 1 takes the place of a total of nine conventional runners, with the result that the pump is considerably simplified.

FIG. 4 shows a stirring mechanism in the form of an axial-flow pump which is driven by a step-down magnetic transmission in accordance with the invention. The inner, high speed pole ring 102 is mounted on the motor shaft 101 of the motor (shown broken); the conductor ring is made up of laminar conductors 103 and, with its rotating field, drives the low speed outer pole ring 106 with the stirrer 105, whose hub is supported on a spherical bearing 107. A conical sheath 108 serves to support the spherical bearings, the sheath being hermetically sealingly joined to the separating membrane

Claims

1. A centrifugal pump for liquids and gases, having a pump chamber and an impeller, a first magnetic pole ring forming a unit with said impeller, a magnetically permeable separating wall which defines the wall of said pump chamber in the region of said first pole ring, and an arrangement for producing a rotating magnetic field for driving said first pole ring, wherein the improvement comprises providing a second pole ring (17) and a third pole ring (120) outside said pump chamber, said second pole ring (17) being separated from said first pole ring (122) by a first magnetic air gap and from said third pole ring (120) by a second magnetic air gap, and a motor driving one of said second pole ring (17) and said third pole ring (120), and said first pole ring (122) comprising magnets.

2. A centrifugal pump according to claim 1, wherein said first pole ring is constructed as a segment of a sphere and said second pole ring as a hollow sphere.

3. A centrifugal pump according to claim 1, wherein said first pole ring (115) has spiral grooves (116).

4. A centrifugal pump according to claim 1, including a housing for said pump and said motor and wherein said motor and said third pole ring are hermetically separated from said pump chamber in said housing by said separating wall.

5. A centrifugal pump according to claim 1, wherein said pump impeller (117) is connected to said pole ring (115) with its inlet side facing the lattEr.

6. A centrifugal pump according to claim 1, wherein said second pole ring is built up from a sheet metal spiral.

7. A centrifugal pump according to claim 1, wherein said third pole ring (120) defines a hollow cylinder and drives said first pole ring (122) via said second pole ring (17), the latter being assembled from sheet metal discs.

8. A centrifugal pump according to claim 1, wherein said first pole ring rotates at a higher speed than said third pole ring and the volume of magnetic material of said third pole ring (120) is several times as great as the volume of the magnetic material (122) of said first pole ring.

9. A centrifugal pump according to claim 1, wherein said spherical separating element (134) consists of non-metallic material.

10. A centrifugal pump according to claim 1, wherein said second pole ring is constructed in the form of a pressure cylinder.

11. A centrifugal pump according to claim 1, wherein said first pole ring and said third pole ring have the same number of poles.

12. A centrifugal pump according to claim 1, wherein said first pole ring is of spherical construction and forms a unit with said impeller said second pole ring defines a conductor ring the centres of the magnetic poles of said first pole ring and of said conductor ring are arranged on the surface of a sphere and said impeller is axially supported at its centre.

13. A centrifugal pump according to claim 12, wherein said second pole ring (130) is disposed between two concentric spherical shells.