WO1998042985A1

WO1998042985A1 - Gear pump with magnetic coupling

Info

Publication number: WO1998042985A1
Application number: PCT/DK1998/000114
Authority: WO
Inventors: Bent Hedebo Hansen
Original assignee: A/S De Smithske
Priority date: 1997-03-24
Filing date: 1998-03-23
Publication date: 1998-10-01
Also published as: AU6612498A

Abstract

Gear pump comprising a pump rotor (8) and an idler wheel (38), which is arranged within the pump rotor (8) and is being driven by engagement with the rotor. A magnetic coupling (30, 31) for the transmission of a drive force to the pump rotor (8) is established between axially adjacent ends of the shaft parts (14, 32). Hereby is obtained an especially short pump housing (2, 28). During performance of the internal gear pump according to the invention, the magnetic transmission force is exerted axially instead of radially as by the prior art pumps. The inventor has discovered, that apparently is provided a secondary support of the rotor due to the arrangement of the axially adjacent ends establishing the magnetic coupling, whereby the rotor surprisingly is stabilised without slanting of the predetermined axial direction of the rotor. Further support as by arrangement of further bearings is thereby avoided.

Description

Gear pump with magnetic coupling

Technical field

The present invention relates to a gear pump of the type wherein the pump casing comprises one or several pump rotors, which rotate between parallel, inner wall parts within the pump casing and is driven by a shaft part, which by means of a magnetic coupling is in drive connection with a motor-driven hub through a separating housing of non-magnetic material, and which housing is totally closed to the out- side and is tightly assembled with the pump casing. The only admittance to the pump chamber within the pump housing is through a connection at the suction side and a connection at the discharge side of the chamber, respectively.

Prior art

Gear pumps are so-called positive displacement pumps whereof the internal gear pumps comprise an idler wheel, which is arranged within the pump rotor and is being driven by the rotor. The pump rotor has an inner gear, which is engaged with an outer gear of the idler wheel thereby providing intermediary spaces between the teeth of the respective gears adapted for the transportation of liquid through the pump when it being driven by a motor.

A fixed, rib-shaped support part extends at the part of the periphery where the idler wheel is out of engagement with the rotor wheel, with the purpose of sealing of the intermediary spaces between the teeth of the respective gears at that part of the periphery.

These pumps were invented in the beginning of this century, and has since then been some of the most dominating types of positive displacement pumps. Pumping in both directions through the chamber are possible, and the pumps has proven to be especially reliable due to their sturdy and simple construction comprising only two rotating parts, being the idler wheel and the rotor, as well as comprising only one shaft seal for the transmission to the rotor. Due to the liquid flow direction being changed only slightly through the pump chamber, a gentle liquid handling is achieved as well as superior self-priming capability. The gear pumps are furthermore used for a wide range of liquids, and especially highly viscous liquids may be referred to.

A drive force is exerted by the drive shaft of a drive motor to the pump rotor. These drive motors are normally electromotors, which are flanged to the pump casing of the gear pump.

These types of pumps are used within fields where a full security against leakage from the pump is desired by use of tight shaft seaiings. These sealings will inevitable cause a gaseous exchange between the pump medium and the atmosphere or simply cause a leakage from the pump. The fully closed separating housing, which is arranged in a suitable resistant manner will secure, that the pump medium under no circumstances penetrate through the drive connection.

Hereby it is a condition, that means are arranged in the inner of the separating housing, which means are adapted to achieve a total stabilisation of the driven rotor part, which stabilisation otherwise may be obtained by use of various bearings for a drive shaft, which extends directly to the motor. The matter is typically a pair of ra- dial bearings arranged with a mutual axially distance ensuring that slanting of the driven rotor part is avoided, as well as one or two axial bearings securing positioning of the shaft axially. The rotor part is arranged between the opposite wall parts of the pump casing without any galling or friction creating engagement with these, however the rotor part is arranged in such an extremely short distance thereof, that no signifi- cant return flow of pump medium from the discharge side to the suction side through the mentioned chambers or gaps may occur.

For the conventional pumps are these conditions fully considered by arranging a bracket at the inner of the separating housing, which bushing projects from the pump casing and supports a shaft part, which projects from the rotor part. The bracket comprises the parts, which are necessary for restricting the shaft part radially, as well as axially, as the bushing at its outer end is connected to a radially extending flange, from which a cylindrical means extends in the reverse direction along the outside of the bracket, which cylindrical means on its periphery carries several magnets. These magnets interacts with a correspondingly magnet provided inner side of a cup-shaped hub through the non-magnetised cylindrical wall of the separating housing, which hub is in rotary drive connection with a motor drive shaft through a central shaft part.

By these known gear pumps, the matter is, that the magnetic coupling is arranged between axially extending, magnetic surfaces provided at adjacent, coaxial surfaces of a drive shaft and of a cylinder, respectively. The magnetic transmission force is thereby exerted radially to the drive shaft and the magnetic coupling is established between radially adjacent surfaces. As explained in further details above, the axial extension of the magnetic surfaces necessitates a rather long extension of the drive shaft by these known pumps, which results in an undesirable, long extension of the pump housing as well.

Core of the invention

The present invention departures of several reasons with the traditional pump layout as it strives for a simplification of the construction. By the present invention, it has been realised, that especially for pumps constructed to a moderate performance it is fully satisfactory, that the magnetic coupling is established between axially adjacent ends of shaft parts, and that is without use of any cylindrical, cup-shaped drive means extending in the longitudinal direction of the drive shaft part of the rotor part.

Hereby is obtained an especially short pump housing. During performance of the gear pump according to the invention, the magnetic transmission force is exerted axially instead of radially as by the prior art pumps. The inventor has discovered, that apparently is provided a secondary support of the rotor due to the arrangement of the axially adjacent ends establishing the magnetic coupling, whereby the rotor surprisingly is stabilised without slanting of the predetermined axial direction of the rotor. Further support as by arrangement of further bearings is thereby avoided.

The axially adjacent ends may be comprised by a shaft part of the rotor and the drive shaft of the motor, respectively. As a further aspect of the invention it has also been possible to improve the drive shaft part of the rotor further by providing it with a very short length, and arranging it in only one single radial bearing. When this bear- ing is laid out as a radial angular contact ball bearing, the drive shaft part will be secured against slanting by means of a firm, axially restraining of the outer collar of the bearing.

Remaining is the required axially stabilisation, but by the present invention it has exactly been realised that this stabilisation follows inevitably as a consequence of the use of a magnetised drive transmission between the adjacent ends of the respective shaft parts. Hereby is provided a drive transmission for transferring a rotation through a non-magnetic gap wall and through narrow gaps between this inte- grated gap wall and the respective adjacent ends of the shaft parts, which narrow gaps being filled with air or liquid. Such a drive transmission is however based on the fact, that a mutual axially attraction is established between the ends of the shaft parts, so that the drive transmission is established by rotation of the poles and antipoles of the arrangements of the magnets. By the mentioned prior, cylindrically magnetised transmissions is an attraction force established between the interacting magnetised poles of the two cylindrical transmission surfaces, establishing nothing else that exactly a radially transmission of rotation by the rotation the poles.

By the present invention the rotor is axially stabilised, as it by means of the magneti- sation force exerted to the short drive shaft part is forced in direction against the

"pump side" of the mentioned ball bearing. On basis of this well defined support the rotor may well be fabricated with fine tolerances, so that it ends very close to the outer end wall of the pump chamber and to the gap wall, respectively, which gap wall is arranged in the magnetised gap at the free end of the short drive shaft part of the rotor.

By a preferred embodiment of the pump according to the present invention, the gap wall arranged in the mentioned magnetised gap may be comprised as an integrated bottom part of a cup-shaped means, which is part of the pump construction as it at its outer bottom area is sealingly tightened against the pump casing and from there projects to a ring shaped, flange area for being tightened to a connection part of a drive motor. At the inner of this house- or cup-shaped part is arranged an hub, which to the outside is drive connected with the motor shaft, and with its inner end is provided with the driving, magnetised arrangement. The hub may be provided as a fly wheel, which due to its inertia reduces the start rotation of the motor shaft, so that the magnetised arrangement with a good margin is able to accelerate the pump rotor slowly enough in a well defined magnetised engagement without it being necessary to adapt other and more expensive ar- rangements for securing, that the motor shaft during start up does not rotate so fast, that the magnetised transmission is out of engagement. By the mentioned pumps of the prior art this has been affected by use of the driving, magnet carrying cylindrical part of the motor shaft, but by the present invention this arrangement is totally omitted, and therefore it is an advantage to use the mentioned "fly wheel" with the axially arranged driving magnet system of the present invention.

This system may in a simple manner comprise of radially orientated triangulary segments of magnetised plate material, which are magnetised and arranged in such a manner, that the segments, seen in the direction of the periphery alternately will provide outer pole surfaces with north and south polarisation, respectively. Of a natural course, an equal number of these differently polarised segments must be adapted, and a natural number would be two, four or six segments, however without excluding a higher number.

Detailed description

The invention is explained further below by referring to the drawing, at which

Fig. 1 shows a section of a pump according to the invention,

Fig. 2 shows a vertical section of an gear in the pump chamber of the pump,

Fig. 3 - 5 show different positions during rotation of the internal gear of the pump,

Fig. 6 shows an enlarged central part of the section of fig. 1 , and

Fig. 7 shows part of fig. 6 in an even further enlarged view.

The pump disclosed in the fig. 1 comprises at it's left side a pump casing 2, which has opposite inlet- and outlet connections 4, and which at the front is closed by a front cover 6. The front cover 6 extends with a plug part somewhat into the pump casing in which it provides an end wall surface 7 adjacent to the end 9 of a pump rotor 8. By means of stippled partitioning lines is disclosed that the pump rotor 8 is comprising a toothed rim part 10, a basic part 12, and a shaft part 14, the last mentioned being accommodated in a ball bearing 16. The toothed rim part is furthermore disclosed from the end at fig 2. The outer collar of the ball bearing 16 is restrained in the pump casing 2 by means of the bottom part 18 of a projecting cup- shaped housing 20, which by means of stay bolts 22, is tightened against the pump casing 2.

By means of a sealing ring 26 is obtained, that the mentioned bottom part 18 of the cup-shaped housing provides tight closing of the pump chamber. Furthest therefrom is the cup shaped housing 20 at it's opposite end flanged to an electromotor 24.

The central area 28 of the bottom part 18 provides an gap wall in a magnetically transmission comprising a number of permanently magnetised disc-shaped segments 30, arranged at both opposite sides of the wall, that is at the end of the shaft part 14, and at the front end of an inertia hub 32, respectively, which hub essentially fills out the cup-shaped housing 20, and is in engagement with the motor shaft 34.

As disclosed, provides a wall opening 36 in the cup-shaped housing admittance to a binding screw, which secures the hub 32 axially on the motor shaft 34. Thereby, it is possible to adjust the position of this means 32, so that it is secured, that its mag- netised segments are positioned at a very short distance from the wall 28. The same must apply for the magnets at the end of the shaft part 14, which how- ever may be established by the construction on basis of the known width of the ball bearing 16. This is a so-called radial angular contact ball bearing, the outer collar of which is adapted to accommodate the force, which is directed towards the right, and which force is performed by the basic part 12 of the rotor against the inner collar of the ball bearing due to the magnetic attraction through the wall 28.

Thus, the rotor is supported in a fully stabilising manner during operation, so that the required fine tolerances for the width of the gaps at the opposite sites or ends of the rotor may be obtained regardless of further supporting means. By the disclosed embodiment, the pump unit functions according to a well known principal, as the toothed rim part 10 interacts with a smaller and eccentrically positioned idler wheel 38, which is arranged to rotate freely on a shaft part 40, protruding from the front cover to the inner, as more clearly disclosed in fig. 2. The available free distance between the two gears is taken up by a crescent- and rib-shaped support part 42, which protrudes from the front cover wall as well, and which by interact with the respective gears secures, that the liquid is pumped forward by passage of the teeth spacings along the two opposite sides of that support part. In the opposite, upper area is by means of the gears obtained a transmission of the drive force from the driven toothed rim part 10 of the rotor and to the freely running idler wheel 38, under more or less filling of the spacings between the teeth of the gears, whereby only an insignificant flow of the pump medium is returned.

However, the invention is not restricted to the disclosed embodiment of the pump system.

In fig. 2 is by means of stippled lines disclosed, that at the end of the central shaft part 14 are on the rotor 8 arranged four plate shaped segments, which are referred to by N and S, which refers to their magnetic polarisation. It is inferior if these segments which may be present in other numbers as disclosed, extends all the way into the central area, as their exerted drive force of course are greatest at the periphery. However, it must be observed, that according to the invention the actual attraction in the magnet transmission is of significance, and in relation to this, the central area supports to the same extension as corresponding areas at the periphery.

It should be observed, that an especially strong magnetic coupling force is provided when the axially adjacent ends of the shaft parts are provided with axial magnetised rare earth magnets.

In fig. 3-5 is more clearly disclosed how the liquid is pumped through the pump chamber within the pump casing. For the purpose of clarifying the flow direction only different parts of the total flow is shown in the respective figures, by being marked with dots. The rotor 8 is shown driven to anti-clockwise rotation by the inventive magnetic coupling. In fig. 3 is shown, that the liquid enters the pump chamber at the connection of the suction side S of the pump chamber.

In fig. 4 is shown that the dotted liquid volume of fig. 3 is now being transported through the pump chamber. The liquid volume is being trapped in the intermediary pockets between the teeth 39 of the idler wheel 38 as well as in the intermediary pockets between the teeth 10 of the rotor 8. The pockets is restricted by the upper and the lower surfaces of the rib-shaped part 42, respectively.

In fig. 5 is shown, that the liquid volume has been transported to the discharge side D of the pump, where it is delivered for further treatment.

It should be mentioned, that pumping in both directions through the chamber are possible. The pump has proven to be especially reliable due to its sturdy and simple construction comprising only two rotating parts, being the idler wheel and the rotor. Due to the liquid flow direction being changed only slightly through the pump chamber, a gentle liquid handling is achieved.

An enlarged magnetic coupling of the pump according to the invention is disclosed in fig. 6 corresponding to the central part of the section of fig. 1. It should be ob- served, that by the enclosed embodiment the primary support of the rotor 8 is arranged completely within the pump casing, as the shaft part 14 of the rotor is supported in the inner collar 43 of the radial angular contact ball bearing 16. The radial angular bearing 16 is adapted to support the rotor by a radial as well as an axial force component, r and a, respectively. The result is support by an angular force component c.

Astonishingly, the axial attraction force of the magnetic coupling provides a secondary support of the rotor, whereby the rotor surprisingly is stabilised without slanting of the predetermined axial direction of the rotor. Further support as by arrangement of further bearings is thereby avoided.

It should further be observed, that by the disclosed embodiment, the wall 28, which is part of the housing that closes of the pump chamber to the outside, extends through the gap between the axially adjacent ends 16, 32 establishing the magnetic coupling. Rotary parts extending through openings in the pump housing is thereby totally avoided, and a fully tight housing is the result. Therefore the gear pump according to the invention may furthermore be used for a wide range of liquids, and especially low viscous liquids and gaseous liquids may be referred to as the danger of leakage is excluded.

The diameter of the integrated gap wall 28 corresponds to the diameter d of the axially adjacent ends of the shaft parts 14, 32, respectively, constituting the magnetic coupling. The thickness t of the wall 28 chosen depends of the diameter d and the maximal pressure peaks experienced for the pump chamber. By a static pressure in the chamber of around 30 bar, a relation of 1 :20 between the thickness t and the diameter d proved to be satisfactory when the pump casing was fabricated from stainless steel. However, relations between t:d in the interval between 1 :5 and 1 :100 has been possible to achieve the desired drive forces of the magnetic coupling as well.

Claims

1. Gear pump comprising a pump rotor (8) arranged in a pump chamber (3) as well as a magnetic coupling (30, 31 ) for the transmission of a drive force to the pump rotor (8) via shaft parts (14, 32), whereby the magnetic coupling (30, 31) is established between axially adjacent ends of the shaft parts (14, 32).

2. Gear pump according to claim 1 , whereby the axially adjacent ends are comprised by a shaft part (14) of the rotor (8) and the drive shaft (32) of the motor (24), respectively.

3. Gear pump according to claim 1 , whereby the end of the shaft part (14) comprised by the rotor (8) is arranged within the pump chamber (3).

4. Gear pump according to claim 1 , whereby the wall (28), which is part of a pump housing closing of the pump chamber (3), extends through the gap between the axially adjacent ends establishing the magnetic coupling (30, 31 ).

5. Gear pump according to claim 1 , whereby the relation t:d between the thickness (t) of the gap wall (28) and the diameter (d) of the axially adjacent ends of the shaft parts (14, 32, respectively), constituting the magnetic coupling is in the interval between 1 :5 and 1 :100.

6. Gear pump according to claim 1 , whereby both of the axially adjacent ends estab- lishing the magnetic coupling are arranged inside the pump chamber.

7. Gear pump according to claim 1 , whereby both of the axially adjacent ends establishing the magnetic coupling are arranged outside the pump chamber.

8. Gear pump according to claim 1 , whereby the axially adjacent ends establishing the magnetic coupling (30, 31 ) comprise axially magnetised magnets (N, S).

9. Gear pump according to claim 1 , whereby radially orientated triangulary segments (30, 31 ) of magnetised plate material are arranged in such a manner, that the seg- ments, seen in the direction of the periphery alternately will provide outer pole sur- faces with north and south polarisation (N, S), respectively.

10. Gear pump according to claim 1 , whereby primary support (16) of the rotor (8) is arranged within the pump housing (2, 28).

1 1. Gear pump according to claim 1 , whereby the primary support (16) of the rotor (8) is adapted to exert a radial force component (r).

12. Gear pump according to claim 1 , whereby the primary support (16) of the rotor (8) is adapted to exert an axial force component (a).

13. Gear pump according to claim 1 , whereby the primary support of the rotor (8) is obtained by a radial angular ball bearing (16) in which the drive shaft part (14) of the rotor (8) is arranged.

14. Gear pump according to claim 1 , whereby the one of the axially adjacent ends establishing the magnetic coupling (30, 31 ) is comprised by an hub (32), which to the outside is drive connected with the motor shaft (34), and which with its inner end is provided with the driving, magnetised arrangement (30).

15. Gear pump according to claim 1 , further comprising an idler wheel (38), which is arranged within the pump rotor (8) and is being driven by engagement with the rotor.

16. Gear pump according to claim 1 , whereby the pump rotor (8) has an inner gear (10), which is engaged with an outer gear (39) of the idler wheel (38) thereby providing intermediary spaces between the teeth of the respective gears (10, 39) adapted for the transportation of liquid through the pump.

17. Gear pump according to claim 1 , whereby the origin of rotation of the idler wheel (38) is arranged eccentrically to the origin of rotation of the pump rotor (8).

18. Gear pump according to claim 1 , whereby a fixed, rib-shaped support part (42) extends at least part of the periphery where the idler wheel (38) is out of engagement with the rotor wheel (8) for sealing of the intermediary spaces between the teeth of the respective gears (39, 10) at that part of the periphery.

19. Rotor (8) for a gear pump and which comprises a shaft part (14), which is adapted to be arranged in a magnetic coupling (30, 31 ) being established between the end of the shaft part (14) of the rotor (8) and an axially adjacent end of another shaft part for transmission of a drive force to the rotor.

20. Rotor (8) according to claim 19, wherein the end of the shaft part (14) of the rotor comprise one or several axially magnetised magnets (31)

21. Casing (20) for a gear pump and comprising a radially extending wall (28), which closes off the pump chamber to the side from which a drive force is transmitted to the pump rotor, which wall (28) is uninterrupted at the centre.