WO1991018206A1

WO1991018206A1 - Pump assembly

Info

Publication number: WO1991018206A1
Application number: PCT/SE1991/000246
Authority: WO
Inventors: Anders Wikborg
Original assignee: Johnson Pump Aktiebolag
Priority date: 1990-05-16
Filing date: 1991-04-03
Publication date: 1991-11-28
Also published as: SE466167B; AU7884391A; SE9001754L; SE9001754D0

Abstract

The present invention relates to a pump assembly of displacement-type, comprising a pump housing (1) having a pump housing chamber (14) with inlet and outlet conduits (13, 17) for the pump medium, pump rotors (19) in said pump housing chamber (2), which interact with each other, said assembly also comprising two electrical motors, one for each pump rotor, each one with a motor rotor, enclosed in the pump housing and designed to drive the respective pump rotor, each one of said motor rotors and the corresponding pump rotor forming a motor rotor-pump rotor-unit (18), integrated in the pump housing. In accordance with the invention each one of said motor rotor-pump rotor-units is provided with the rotary part (25) of a unit designed to detect the angular position and the rotary speed of the motor rotor-pump rotor-unit, whereas the other part (33) of said unit is stationarily mounted. Also, a common electronic unit (26) for the two detection units is mounted, designed to control said motors and then also said pump rotors angle-synchronously, dependent on said detection.

Description

PUMP ASSEMBLY

TECHNICAL FIELD

The present invention relates to a pump assembly of displacement-type, comprising a pump housing having a pump housing chamber with inlet and outlet conduits for the pump medium, two pump rotors in the pump housing chamber, which interact with each other, and the assembly comprising also two electrical motors, one for each pump rotor, each one with a motor rotor, encased in the pump housing and designed to drive the respective pump rotor, each motor rotor and the matching pump rotor forming an integrated motor rotor-pump rotor-unit in the pump housing.

BACKGROUND ART

So called positive displacement pumps, i.e. pumps of the type which comprises two units, which rotate against each other and between themselves displace the pump medium outwards in one direction, e.g. lobe rotor pumps, usually are driven by means of one single electric motor via a gearing transmission to the two rotors. However, assemb¬ lies of the type described in the introduction above are also known. Such a construction is described in GB-2 123089. One problem with these pumps relates to the synchronization of the two motors and then also of the pump rotors. The shaft sealings between the pump housing and the motors disposed outside the pump housing are another most troublesome problem.

in order to solve this sealing problem an encasing of the motors jointly with the pump rotors in the pump housing has also been suggested, to avoid using shaft sealings. Such a soiution is described in US-A-4 758 132. However, the synchronization of the assembly is still a problem. Also, the construction according to US-A-4 758 132 is not ideal for other reasons, which will be illustrated when comparing w th the pump assembly according to the present invention in the subsequent description.

IIHSTITUTE DISCLOSURE OF THE INVENTION

The object of the present invention is i.a. to solve the above- mentioned problems. Another object of the invention is to suggest a pump assembly designed for primarily the high requirements as to sanitation and asepsis of the food industy and the pharmaceutical industry. Also, another object is to suggest a pump assembly having pump rotors, which function in a closed pump housing without any driving shafts and mechanical sealings.

These and other objects can be attained by providing each one of the motor rotor-pump rotor-units with the rotary part of a unit for detecting the angular position and the rotational speed of said motor rotor-pump rotor-unit, while the other part of said unit is stationa- rily mounted, and by using a common electronic unit for the two detecton units in order to control the motors and then also the pump rotors at least roughly angle-synchronously, dependent on said detection.

The pump rotors are provided with displacement elements, designed as wings, collars, lobes, cogs or the like. In those instances when the displacement elements are wings or collars they usually two in number, but pump rotors may also have merely one displacement element. Pump rotors may also have more than two displacement elements. One special type of pump rotors is piston rotors, in which the displacement elements are designed as one several, usually two, arched "pistons", designed to run in ringshaped "cylinders".

The detection units comprise so called resolvers and are of a type known per se. They basically comprise coil groups provided in an even number of poles, at least two and normally not more than twelve, which are mounted in the non-movable as well as in the moveable unit and distributed along the turn. Since they belong to the known art, they will not be described in detail in this text, however, it ought to be stated that they operate with induced electric currents and that they operate with certain tolerances. Consequently, the pump rotors must be designed in such a way that they also can function within the scope of the maximum deviations from an absolute synchronization, which has to be expected due to the dynamics of the control unit. For these reasons each one of the active displacement elements of the pump rotors has a total arc length, which is somewhat smaller than the arc length of the space between the displacement elements and somewhat smaller than half the revolution respectively, in case the pump rotor is provided with one single displacement element. The difference is more precisely at least two times the operative tolerance of the detection units, expressed as the corresponding arc angle. Today's technology offers resolvers, which operate with an accuracy of ± 4°. Consequently, the difference in arc length with these resolvers ought to be at least 8°, However, tomorrow's technology maybe will create resolvers having even smaller operative tolerances, and then it will be possible to lower the difference between the arc length of the active pump elements and the spaces correspondingly. Generally, the difference must be larger than the accuracy of the electronic control unit, with a certain safety margin.

In accordance with a first preferred embodiment the pump rotors are wing rotors (pump impellers) an in accordance with another preferred embodiment they are piston rotors. In each case - and in the case with pump rotors having other displacement elements than wings or arched pistons, e.g. displacement elements of some of the additional varities mentioned above - very compact assemblies having high^'pump rotor torques can be consructed. Their design may allow a cleaning without any dismantling, which is important, when the pump assembly is to be used in the food industry or the pharmaceutical industry.

An additional advantage and an additional object of the present invention is to achieve a very firm mounting of the rotors, as compared to e.g. the construction shown in US-A-4 758 132, in which the mounting must be done with considerably weaker dimensions in the central parts of the assemly. Thus, in accordance with one aspect of the invention it is possible to mount the respective motor rotor-pump rotor-unit floatingly, its exterior side bearing on at least one cylindrical wall of the respective motor rotor chamber. Additional advantages as well as characterizing features and aspects of the present invention will be set forth in the following patent claims as well as in the following description of two preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following description of two preferred embodiments reference will be made to the accompanying drawings, in which:

- Fig. 1 is an end view of a pump assembly according to a first preferred embodiment of the present invention, an end wall or cover having been removed in the left part of the figure;

- Fig. 2 shows the same pump assembly in section along line II-II in Fig. 1. Also, in Fig. 2 the electronic control system for the motors is shown schematically; - Fig. 3 is a longitudinal section of a pump assembly according to a second preferred embodiment of the invnetion, corresponding to a view III-III in Fig.4; and

- Fig. 4 is a view IV-IV in Fig. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS

Generally, in Figs. 1 and 2 a pump housing 1 is shown. All parts of pump housing 1 are made of a non-magnetic material, e.g. an acidproof, autenitic stainless steel, and it comprises a pump housing chamber housing 2, which against one of its sides (the left side in Fig. 1) is covered by a cover 3, by means of which the two pump units of the assembly jointly are covered, and comprises in the opposite direction two circular, larger openings, each of. which is covered by a cylind¬ rical motor rotor housing 4, which is welded to the pump housing chamber housing. Inside each motor rotor housing 4 an interior stator housing 5 is disposed, coaxially in relation to the respective motor rotor housing 4, and one of the end walls 6 of which (the left one in Fig. 2) extends almost up to common cover 3. The respective stator housing is covered at its opposite end by a cover 7. Inside each stator housing 5 a central radiator tube 8 is disposed having inlet and outlet conduits 9, 10 for cooling water. Between radiator tube 8 and an interior cooling water conduit 11 a screw 12 is disposed, designed to circulate the cooling water in the return conduit between interior conduit 11 and radiator tube 8. The pump assembly is entirely symmetrically constructed, and motor rotor housings 4, stator housings 5 and their interior parts are identical.

Inside pump housing chamber housing^' 2 a pump housing chamber 14 is disposed having an inlet conduit 13 and an outlet conduit 17. Between motor rotor housing 4 and stator housing 5 a cylindrical motor rotor chamber 15 is disposed and between stator housing 5 and radiator tube 8 a stator chamber 16 is disposed. In each one of pump housing chambers 14 and motor rotor chambers 15 an integrated motor rotor-pump rotor-unit 18 is disposed, for the sake of simplicity termed an MP-rotor unit in the following descripiton. An MP-rotor unit 18 is, according to this embodiment, mainly made of carbon, more precisely hard coal. Alternative feasible materials are some ceramics and some plastics. Also, composite materials are possible, which at least partially are made of carbon, ceramics and/or plastics. The present parts, made of carbon or similar alternative materials, comprise according to this embodiment partly a wing-rotor (pump impeller) 19 in pump housing chamber 14 and partly a cylindrical part 20, which forms an extension of the pump impeller and extends into motor chamber 15 along the letter's length almost up to the right end of motor chamber 15. Inside cylindrical rotor portion 18 a cylindrical ring 21 made of soft iron is disposed, recessed in rotor portion 20. Also, in the interior wall of soft iron ring 21 a number of permanent magnets 22, evenly distributed along the turn, are recessed, which are magnetically short-circuited with each other via soft iron ring 21. Between MP-rotor unit 18 and stator housing 5 there is a narrow gap 23. On the contrary, cylindrical portion 20 of the MP-rotor unit bears on the interior wall of motor rotor housing 4 and consequently is slidingly mounted against the motor rotor housing with a part, which preferably is made of carbon. Also, pump impeller 19 with its left side bears on the interior side of common cover 3. How this pressing is done will be explained in the following text. Each pump impeller 19 is provided with two collars or wings 35, and there is a space 36 between wings 35. Wings 35 of one of the pump impellers mesh with spaces 36 of the other pump impeller. The displacement volumes are formed by spaces 37 between respective pump impeller 19 and interior wall 2 of the pump housing where spaces 36 are located. Wings 35 as well as spaces 36 have cylindrical exterior walls, i.e. wings 35 of one of the pump impellers roll against the cylindrical bottoms of spaces 36 of the other pump impeller. Conse¬ quently, the two pump impellers 19 are pumping alternatingly according to principles known per se.

A typical feature of this embodiment according to the invention is that the height of rotor wings 35 above the bottoms of spaces 36 is comparatively low. The reason for this is a need of adjusting the construction to the situation, that pump impellers 19 do not move completely synchronously with each other. For the same reason each rotor wing 35 takes up an arc length V , which is smaller than arc length 'V of spaces 36. In case the synchronization e.g. has a tolerance of ± 4°, then V^* -V is at least 8°, i. e. at least the double tolerance.

In an interior ring-shaped groove in pump impeller 19 rotating poles 25 of a resolver is disposed. In stator chamber 16 the stationery part, also called stator 29, of the motor is disposed. It comprises in a known way coils of winding on a packet of stampings. Stator 29 is only shown schematically. Ends 30 of the coils of winding are shown. Stator chamber 16 is completely closed and does not communicate with pump housing chamber 14. Thus, the pump medium cannot penetrate into stator chamber 16. Electrical connection leads 31 to the stator windings are shown symbolically.

In the interior part of stator chamber 16, between stator 29, radiator tube 8 and end wall 6 of the stator housing, a cylindrical body of an electrically insulating material, preferably a plastic material, is disposed. In an exterior groove in body 32 stationary poles 33 of said resolver is disposed. These poles are known in the art, but it will in this connection briefly be explained how they fundamentally are constructed and operate. A coil group 33A in stator poles 33 of the resolver is fed with an electric current from electronic unit 26. Coil group 33A generates a field, which induces a current in coil group 25A of the oveable pole, sensor 25. A current is conducted to a second coil group 25B of sensor pole 25, which in its turn induces a current in a pickup-winding 33B in stator pole 33 of the resolver. This current is detected as a voltage in electronic unit 26 and provides an angular measurement. An even number of poles - the same number in the stator as in the rotor - each including coil groups of the described type, are distributed along the turns of the stator and the rotor and generate basic electric data relating to the angle position of the rotor in relation to the stator for the two motors, which is processed in the electronic unit 26 to provide data and instructions for the computerized synchronization of the two MP-rotor units by means of the electronic unit 26.

When MP-rotors 18 are rotating, the interior wall of motor rotor housings 4 functions as a sliding bearing against cylindrical part 20, made of carbon, of respective MP-rotor 18. At the same time respective pump impeller 19 is sliding with its left side on the interior wall of common end wall 3. Said bearing and sliding jointly stabilize the rotating units in a satisfactory way.

Stator 29 and consequently also cylindrical body 32 are pressed on end wall 6 of the stator housing by means of a number of springs 34 bet¬ ween stator 29 and cover 7. This effect is obtained, because springs 31 press stator 29 to the left and the magnetical field, which is generated by the stator part, also brings with it magnets 22 of MP-rotor 18 in the axial direction and presses pump impellers 19 against cover 3.

In Figs. 3 and 4, showing a piston rotor pump assembly, a first motor rotor-pump rotor-unit (MP-rotor unit) 40 is disposed on the vacuum side and a second motor rotor-pump rotor-unit (MP-rotor unit) 41 is disposed on the compression side. Each one of MP-rotor units 40, 41 is made, in a preferred embodiment, mainly of hard coal and comprises a long, tubular part 42 and 43 respectively. However, as was the case with the embodiment described above, also other materials than carbon are feasible, e.g. certain ceramics and plastics or composite materials, which^* partially can be composed of any of the mentioned materials. In one end the interacting displacement elements 44 and 45 respectively are disposed and in the other end the movable units 46, 47 are disposed in two resolvers (sensors) of the same type as has been described in connection with the preceding embodiment. Displace- ment elements 44 and 45 respectively comprise arched "pistons", designed as two sectors of a cylinder, which displacement elements extend in the same axial direction from long, tubular portions 42 and 43 respectively of MP-rotor uits 40,41.

It is best shown in Fig. 3, that the two MP-rotor units 40, 41 are placed side by side, the vacuum and compression sides being turned away from each other but meshing with each other through pistons 44, 45.

A long, angular pump housing, made of an austenitic, stainless, non-magnetic steel, comprises a first pump housing part 50, having mainly the same axial length and extension as the first MP-rotor unit 40, and a second pump housing part 51, having mainly the same length and extension as said second MP-rotor unit 41. The two pump housing parts 50, 51 are connected with each other through screws 52. First pump housing part 50 of pump housing 49 is provided at one of its ends an inlet conduit 53 with an inlet hole 55 for the pump medium. Down¬ stream of inlet conduit 53 first pump housing part 50 is provided with a first cylindrical portion 54 having a larger diameter than inlet conduit 53 and housing the static parts 86 of the resolver. After first cylindrical portion 54 a second, very thin-walled cylindrical portion 56 is disposed. All of the portions of first pump housing part 50 mentioned so far, namely inlet part 53, first cylindrical portion 54 and second cylindrical portion 56, which has a larger diameter than first cylindrical portion 54, are coaxial with first MP-rotor unit 40, the rotational center of which is denoted 48. After said second cylindrical portion 56 a flange portion 57 follows, which bears on and is connected to the end of second pump housing part 51. A first hub 58 projekts axially and outwards from flange portion 57 and is designed as a casing, open in its exterior end and in one of its sides. Hub 58 is shifted from center axis 48 of the vacuum side and is instead disposed concentrically with center axis 49 of the compression side.

Second pump housing part 51 is partly constructed in a similar way as first pump housing part 50 and thus is provided with, form right in Fig. 3, an outlet conduit 63 having an outlet opening 65, a first cylindrical portion 64, which houses stationary resolver units 87, and a second thin-walled cylindrical portion 66. A flange portion 67 follows, having a second hub 68, which jointly with flange portion 57 and its hub 58 define the shape of pump housing chamber 82, in which the two MP-rotor units 40, 41 are disposed, designed to be able to function with their circular sector-shaped rotor pistons 44 and 45 respectively. Flange portion 57 is provided with two semi cylinder- shaped borings 70 and 71, which are concentric with center axes 48 and 49 respectively of the vacuum side and the compression side respecti- vely. Second hub 68 has, according to Fig. 4, the same shape as said first hub 58 on first pump housing part 57, but it is mirror-inverted in relation to the same.

Rotor pistons 44 are designed to rotate in and when they are rotating fill ring-shaped groove or "cylinder" 72 between the interior side of first semi cylinder-shaped boring 70 and the exterior side of hub 68.

In a similar way said second MP-rotor unit is designed to rotate, with its pistons 45, in a corresponding groove 73 on the compression side.

The spaces between pistons 44 in the space for said groove 72 and the corresponding space on the compression side respectively constitute the displacement volumes of the pump.

Hub 68 is on its exterior side provided with a recess 74 for rotor pistons 45, and in a similar way hub 58 is provided with, on its exterior side, a cylinder-shaped recess 75 for pistons 44. In flange portion 57 a recess 76 is provided in the area of hub 58, and this recess also extends obliquely outwards and beyond lateral opening 77 of hub 58. That portion of recess 76, which extends beyond lateral opening 77, is denoted 78. In corresponding way a recess having a central part 79 and a peripherical part 80 is provided on the vacuum side, the opening in the side of casing portion 68 is denoted 81.

Generally, the pump housing chamber is denoted 82, Fig. 3. Its vacuum side part is denoted 82A and its compression side part is denoted 82B, Fig. 4. When one of pistons 44 blocks opening 81, tube-shaped volume 99 of MP-rotor unit 40 communicates with vacuum side 82A of the pump housing chamber via recess 79-80 outside the outer edge of piston 44. In a similar way a communication between the compression side of pump housing chamber 82B and volume 100 is provided, when opening 77 in hub 58 is blocked by one of pistons 45, the communication being established through recess 76-78 past the exterior edge of piston 45.

MP-rotor units 40, 41 are, in the area of their long portion 42 and 43 respectively, provided with a number of permanent magnets 88, 89, evenly distributed along the turn and recessed on the exterior side of a soft iron ring 90 and 91 respectively, which in its turn is disposed on the exterior side of long portions 42 and 43 respectively of MP-rotor units 40, 41 inside said two other cylindrical, thin-walled portions 56 and 66 respectively of the pump housing, made of a material, which is permeable for magnetic fields of force, preferably an austenitic stainless steel.

Outside said second cylindrical thin-walled portions 56 and 66 stator windings 92, 93 of the motors are disposed in a motor hood 94 and 95 respectively. The exterior side of first MP-rotor unit 41 bears with the exterior side of its long portion 42 against the interior side of second cylindrical portion 56 of first pump housing part 50 and is with its rotor pistons 44 mounted in cylindrical boring 70 in main part 67 of second pump housing part 51. Also, rotor pistons 44 bear with their interior side against the exterior side of hub 68. In a similar way second MP-rotor unit 41 bears with its exterior side against the interior side of second cylindrical portion 66 of second pump housing part 51 and with rotor pistons 45 against cylindrical boring 71 in main part 67 of the pump housing.

In order to facilitate the cleaning of the pump and also in order to render the cleaning more effective, without the need of dismantling the pump a number of ducts 96, 97 (suitably more ducts 96, 97 than those depicted in Fig. 3 are used) are arranged in MP-rotor units 40, 41. These ducts 96, 97 communicate with a narrow gap inside second cylindrical portions 56 and 66 respectively of the pump housing parts.

As in the case with the embodiment described above an electronic unit 26 is provided, which leads an electrical current to a transmitting winding in stator parts 86 and 87 respectively of the resolvers and receives signals from the pickup-windings in stator parts 86 and 87 respectively of the resolvers, and in this way the angle positions and the rotational speeds of MP-rotor units 40, 41 can be measured and controlled, and in this way rotor pistons 44 and 45 can be rotated mainly synchronously with each other. However, resolvers 46/86 and 47/87, as is the case with embodiment described above, can not guarantee a total synchronism between rotor units 40, 41. In order to prevent all risks for a situation, in which rotor pistons 44 and 45 hit each other, they take up, by analogy with the embodiment described above, an arc angle V , which is somewhat smaller than arc angle V for the spaces between rotor pistons 44 and 45 respectively.

The pump assembly described in this way operates in the following way. First MP-rotor unit 40 on the vacuum side rotates in counter clockwise direction, with reference to Fig. 4, while MP-rotor unit 41 on the compression side rotates in clockwise direction, with reference to Fig. 4. Liquid, which in the vacuum side is sucked through opening 55 and passes through tubular interior 99 of MP-rotor unit 40, is conducted from the interior of casing portion 68, which forms a continuation of interior 99 of MP-rotor unit 40, via opening 81 and recess 80 (when opening 81 is closed, only via recess 80) to vacuum side 82A of pump housing chamber 82. From here the pump medium flows into ring-shaped "cylinders" 72 and 73 in those angular positions of the pump rotors, when these spaces communicate with vacuum side 82A. The pump rotors function with their pistons 44, 45 alternately in ring-shaped cylinders 72 and 73 respectively and transport in this way the pump medium from vacuum side 82A to compression side 82B without pulsations and thus generates a negative pressure on the compression side and an even flow.

Constantly one of the two circular segment-shaped pistons 44 with some part of its exterior side meshes with cylindrical surface 75 on hub 58 and with its interior side with some part of second hub 68 and/or one of pistons 45 meshes with its exterior side with cylindrical surface 74 of hub 68 and with its interior side with some part of the exterior side of first hub 58. Due to the long sealing stretches a return leakage from the compression side to the vacuum side is minimized.

For the rest, the pump assembly according to the embodiment shown in Figs. 3 and 4 and desribed above has the same advantages as the first embodiment, which is described above with reference to Figs. 1 and 2, namely absence of shaft sealings, bearing between parts having coarse dimensions as well as high torque of the pump rotors, i.a. since the rotor pistons and the magnets essentially are d sposed on the same radial level. Also, the latter embodiment has a few additional advantages as compared to the first embodiment. Thus, it is much easier to clean it, since it is easy to wash it with a cleaner. Also, it is long with an inlet opening in the axial direction in one end and an outlet opening in the axial direction in the other end with only a small radial offset between the inlet conduit and the outlet conduit, which facilitates a mounting in the tube system, in which the pump will form an integral part. An additional advantage is that a return leakage essentially is stopped, which increases the efficiency of the pump. Also, it is possible to increase the capacity of the pump without substantially increasing its demensions by increasing the size if rotor pistons 44, 45 and the corresponding displacement volumes in cylinders/grooves 71, 72 in the axial direction.

Claims

1. A pump assembly of displacement-type, comprising a pump housing (1) having a pump housing chamber (14) with inlet and outlet conduits (13, 17) for the pump medium, pump rotors (19) in the pump ^"housing chamber (2) interacting with each other, the pump assembly also comprising two electric motors, one for each pump rotor, each with a motor rotor, encased in the pump housing and designed to drive the respective pump rotor, each motor rotor and the corresponding pump rotor forming a motor rotor-pump rotor-unit (18), integrated in the pump housing, c h a r a c t e r i z e d int that each one of said motor rotor-pump rotor-untis is provided with the rotary part (25) of a unit, designed to detect the angular position and the rotational speed of the motor rotor-pump rotor-unit, whereas the other part (33) of said unit is stationarily mounted, and in that a common electronic unit (26) for said two detection units is mounted and designed to contol the motors and then also the pump rotors angle-synchronously, dependent on said detection.

2. A pump assembly according to claim 1 of the type, in which the pump rotors are provided with one or several displacement elements (35, 44, 45) , projecting in a radial and/or axial direction, as well as alternately spaces (36, 72, 73), c h a r a c t e r i z e d in that each one of said displacement elements has an arc length, which is smaller than the arc length of each one of said spaces.

3. A pump assembly according to claim 1, c h a r a c t e r i z e d in that said motor rotor-pump rotor-units comprise encased permanent magnets (22) and form rotors in said motors, the stationary parts (29) of which comprise the respective motor winding and form stators.

4. A pump assembly according to any of claims 1-3, c h a r a c t e¬ r i z e d in that the respective motor rotor-pump rotor-unit (18) is floatingly mounted, its exterior side bearing on at least one cylinder wall of the respective motor rotor chamber.

5. A pump assembly according to any of claims 1-4, c h a r a c t e¬ r i z e d in that the stationary part of the respective detection unit is mounted in an end of said stator chamber.

6. A pump assembly according to any of claims 1-5, c h a r a c t e¬ r i z e d in that at least those parts of said motor rotor-pump rotor—units, which slidingly contact the pump housing walls, totally or partially are made of carbon, ceramics or plastics or of a compo¬ site material, which includes some of said materials.

7. A pump assembly according to any of claims 1-6, c h a r a c t e¬ r i z e d in that said motor rotor-pump rotor-units are mounted side by side, the pump rotors extending in the same direction.

8. A pump assembly according to claim 7, c h a r a c t e r i z e d in that said pump housing comprises two cylindrical motor rotor chambers (15), in one of its ends an end wall (7) for each motor rotor chamber and in the other end a cover (3) for said pump housing chamber (14), which is mounted between said cover (3) and the two motor rotor chambers (15).

9. A pump assembly according to claim 7 or 8, c h a r a c t e r ¬ z e d in that two cylindrical stator chambers (16), separated from the pump medium, are mounted inside said pump housing, one for each stator (29).

10. A pump assembly according to claim 9, c h a r a c t e r i z e d in that said stators are mounted in said stator housing and d splace- able in the axial direction, designed to adjust the magnetic fields of said rotors.

11. A pump assembly according to any of claims 8-10, c h a r a c t e¬ r i z e d in that said motor rotor-pump rotor-units (18) are designed to bear on said cover (3) and when they are rotating glide on said cover (3) .

12. A pump assembly according to claim 11, c h a r a c t e r i z e d in that said motor rotor-pump rotor-units are pressed in the axial direction against said cover (3) by means of springs (34), which are designed to press the respective stator (29) in the axial direction against said cover, the pressing force being transmitted through the magnetic action of the stator windings onto said motor rotor-pump rotor-unit.

13. A pump assembly according to any of claims 8-12, c h a r a c t e- r i z e d in that in the center of each one of said stator chambers at least one radiator tube (8) for liquid cooling of said motor windings is disposed.

14. A pump assembly according to any of claims 6-13, c h a r a c t e- r i z e d in that said pump rotors are wing rotors (pump impellers) having wing-shaped displacement elements (35) and in that the height of the rotor wings (35) is less than 20% and preferably less than 15% of the radius of said wing rotors in the area of the wings.

15. A pump assembly according to any of claims 1-6, c h a r a c t e¬ r i z e d in that said motor rotor-pump rotor-units (40, 41) are provided with displacement elements, designed as circular arc-shaped pistons (44, 45) .

16. A pump assembly according to claim 15, c h a r a c t e r i z e d in that said motor rotor-pump rotor-units (40, 41) are mounted in a pump housing (50), on the exterior side of which the stator windings (92,93) of the motors are mounted, in that said pump housing (50) is provided with an inlet opening (55) in one end of said assembly and an outlet opening (65) in its opposite end, and in that each one of said motor rotor-pump rotor-units in its end, which is turned away from said inlet opening and from said outlet opening respectively, is provided with pump rotors, which interact with each other and comprise said circular arc-shaped pistons (44, 45).

17. A pump assembly according to any of claims 15 and 16, c h a r a c¬ t e r i z e d in that said pistons (44, 45) are designed to rotate in ring sector-shaped spaces (72, 73) between cylindrical borings

(70, 71) in said motor housing and cylindrical exterior walls of hubs (58, 68) in said pump housing, which hubs are coaxial with said two motor rotor-pump rotor—units (40, 41).

18. A pump assembly according to claim 17, c h a r a c t e r i z e d in that said hubs are provided with openings (77, 81) in their sides _Q for approach flow of a liquid pump medium from said inlet conduit to the vacuum side (82A) of said pump housing chamber and for transmit¬ ting said liquid pump medium to the compression side (82B) of said pump housing chamber respectively.

-_j_5

19. A pump assembly according to claim 18, c h a r a c t e r i z e d by recesses (76, 78/79, 80) in the end walls of said pump housing chamber, through which recesses said inlet conduit can communicate with the vacuum side (82A) of said pump housing chamber, and the compression side (82B) of said pump housing chamber can communicate

20 with said outlet conduit, also when said openings (77, 81) in the sides of said hubs (58, 68) are closed by means of some of said arc-shaped pistons.

20. A pump assembly according to any of claims 15-19, c h a r a c t e- 25 r i z e d by a long duct (99, 100) in the interior of the respecitve motor rotor-pump rotor-unit (40, 41), which duct is coaxial with the inlet opening and with the outlet opening respectively as well as with the respective hub.

30 21. A pump assembly according to any of claims 15-20, c h a r a c t e¬ r i z e d in that said permanent magnets are mounted mainly on the same radial level as the arc-shaped pistons.

35