WO1997035096A1

WO1997035096A1 - Magnetic drive and suspension system for positive displacement planetary vane pumps

Info

Publication number: WO1997035096A1
Application number: PCT/AU1997/000165
Authority: WO
Inventors: William Wesley Martin
Original assignee: William Wesley Martin
Priority date: 1996-03-15
Filing date: 1997-03-14
Publication date: 1997-09-25
Also published as: AUPN871096A0

Abstract

A positive displacement pump (10) having a magnetic drive, characterised in that the pump (10) comprises a pump housing (12) defining a cavity (14) therein through which a fluid may be pumped or metered, at least one vane (50, 52) being located in the cavity (14), the pump housing (12) having provided at each opposed end thereof a gear housing (16), the gear housing (16) having located therein at least one guide member (38, 44), wherein there are provided a complementary number of guide members (38, 44) and vanes (50, 52) forming pairs thereof, these pairs having provided therein magnetic coupling means such that movement of a guide member (38, 44) induces movement in a complementary vane (50, 52).

Description

Title

MAGNETIC DRIVE AND SUSPENSION SYSTEM FOR POSITIVE DISPLACEMENT PLANETARY VANE PUMPS

Field of the Invention

The present invention relates to a magnetic drive and suspension system for positive displacement planetary vane pumps. The magnetic drive enables the elimination of seals to the pump wall or cavity.

Discussion of the Prior Art

Positive displacement planetary vane pumps have a broad range of applications both in the domestic and industrial arenas. However, positive displacement planetary vane pumps require that drive shafts for vanes, blades or the like penetrate the pump chamber or cavity to drive same. This introduces a requirement to provide seals to the pump chamber or cavity.

The need to provide drive shafts and seals into the pump chamber or cavity results in leakage into or through the seal. Such positive displacement planetary vane pumps may be seen in, for example, US Patents 1101329, 1394861 , 2919062 and 5156541. The particular design of positive displacement planetary vane pumps as described in PCT/AU94/00584 (WO 95/09973) is ideally suited to the pumping, without damage, of blood for use in a left ventricular assist device. This application however requires the pump to be fitted with a sealless magnetic drive. Other forms of rotary pumps are inefficient in such an application. Other non-rotary positive displacement pumps are too large for such an application.

The present applicant has described previously a positive displacement planetary vane pump, see for example PCT/AU94/00584 (WO 95/09973) wherein a plurality of vanes are shown to rotate through a pump chamber in both positive displacement and non-positive displacement portions of rotation. However, such an arrangement still required the provision of drive shafts for each vane with accompanying seals. Furthermore, a seal is required for the rotating drive disc employed to rotate the vanes through the pump chamber. Still further, the need to accommodate seals on the interior surface of the pump chamber causes the adhesion of blood components and clotting when the pump is used as a blood pump.

Other forms of non-planetary rotary pumps can be magnetically driven and suspended by a rotary magnetic drive. The planetary nature of the positive displacement planetary vane pump requires a magnetic drive which matches the planetary vane orbit.

Various forms of magnetic drive are used on non-positive displacement rotary pumps and non-rotary positive displacement pumps at present. The non-positive displacement rotary pumps can be magnetically driven or both magnetically driven and suspended. The magnetic drives can be provided in the form of a drive disc with magnetic couplings which require, in turn, a thrust bearing in the fluid being pumped. The impeller may double as the electric motor rotor or armature if the drive is electric. The magnetic drive can be symmetrical and can provide drive from both sides of the impeller. Such an arrangement is typically used where magnetic suspension and rotation are required. Electromagnetic control of the magnetic field is required to maintain the impeller in suspension. This arrangement eliminates the need for the thrust bearing in the fluid.

Non-rotary positive displacement pumps of the diaphragm type may comprise an electromagnet that is switched on and off to expand and contract the diaphragm. Piston pumps may have a series of electromagnets along the cylinder that serve to drive the piston in either direction along the cylinder by sequential switching of the electromagnets. The magnetic drive and suspension system for positive displacement planetary vane pumps of the present invention has as one object thereof to overcome or reduce the abovementioned problems associated with the prior art.

Brief Description of the Invention

In accordance with the present invention there is provided a magnetic drive for a positive displacement planetary vane pump, characterised in that the magnetic drive comprises at least one drive guide member provided in at least one gear housing, the or each drive guide member being supported in a rotatable manner on or by a rotatable drive support through the rotation of which the or each guide member may be moved through a circular arc within the or each gear housing, whereby the or each guide member is caused to rotate about its own axis as the or each guide member moves through the circular arc driven by the rotation of the rotatable drive support and wherein a gearing arrangement is provided such that rotation of the rotatable drive support produces consequent axial rotation of the or each guide member.

Preferably, the magnetic drive is provided in combination with a pump housing, the pump housing containing at least one vane in a cavity defined thereby. The or each guide member preferably being arranged so as to induce movement in a corresponding vane through the pump cavity.

The pump cavity and the gear housing are preferably in fluid tight isolation whereby the fluid being pumped through the pump cavity cannot enter the gear housing and similarly the content of the gear housing cannot contaminate the fluid being pumped.

Preferably, the or each guide member and corresponding vane are provided with a magnetic coupling means whereby movement of the or each guide member induces movement in the corresponding vane. The magnetic coupling is preferably provided in the form of a balanced repulsive axial magnetic force and provides a consequent suspension of the or each vane within the pump cavity. Still preferably there is provided at least a single mechanical holding point for each vane within the pump cavity, the mechanical holding point may be provided as a moving contact with the pump housing.

Preferably, the magnetic coupling is achieved by way of permanent magnet pairs provided in the drive guide member and corresponding vane. The magnet pair preferably comprises a broad "female" magnet in the guide member and a thinner "male" magnet in the vane such that the field generated by the "male" magnet is held within the boundaries of the "female" magnet.

It is preferable that where two or more guide members are provided they are proportioned such that during rotation they do not collide.

The rotatable drive support is preferably driven to rotate by a drive shaft received at a midpoint thereof, the shaft projecting into the gear housing through an outermost portion thereof from a point outside same. The drive shaft having a non-rotating gear formed thereabout through a depending projection of the outermost housing portion. Two intermediate planetary gears are provided interconnecting the non-rotating gear with a gear provided on a drive shaft associated with each guide member. The drive shaft associated with each guide member is held rotatably in the rotatable drive support.

In accordance with the present invention there is further provided a positive displacement pump having a magnetic drive, the pump comprising a pump housing defining a cavity therein through which a fluid may be pumped or metered, at least one vane being located in the cavity, the pump housing having provided at each opposed end thereof a gear housing, each gear housing having located therein at least one guide member, wherein there are provided a complimentary number of guide members and vanes forming pairs thereof, these pairs having provided therein magnetic coupling means such that movement of a guide member induces movement in a corresponding vane. The guide members of both gear housings are preferably caused to move in a synchronised manner. Such synchronisation may be achieved by gearing, for example bevel gears.

Preferably, the magnetic coupling of the pairs of guide member and vane allow the pump cavity to be formed without seals, such a construction allows complete isolation of the fluid flow from the content of the gear housings.

Brief Description of the Drawings

The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:

Fig. 1 is a top plan view of a magnetic drive for a positive displacement pump in accordance with the present invention showing the gear housing in cut-away and the gearing thereof in part only;

Fig. 2 is a cross-sectional elevational view of the magnetic drive and positive displacement pump of Fig. 1 along line A-A showing both gear housings and the pump housing with which they are associated;

Fig. 3 is a top plan view of the magnetic drive for the positive displacement pump of Figs. 1 and 2 showing a first position of two vanes;

Fig. 4 is a top plan view in accordance with Fig. 3 showing a second position of the two vanes;

Fig. 5 is a top plan view in accordance with Fig. 3 showing a third position of the two vanes;

Fig. 6 is a schematic view showing the interaction of the magnetic fields generated by the magnets of the guide members and vanes; and Fig. 7 is a plan view of a guide track provided in the intermediate walls and for use in electromagnetically driving the vanes through the pump cavity.

Description

In Figs. 1 to 5 there is shown a positive displacement pump 10 comprising a pump housing 12 defining a pump cavity 14 therein. The pump housing 12 has associated therewith in an opposed manner a pair of gear housings 16, as is best seen in Fig. 2. Each gear housing 16 is of identical construction.

The gear housings 16 comprise an outermost portion 18 encasing a pair of outermost gears 20 and 22. The outermost gears 20 and 22 engage a pair of intermediate planetary gears 24 and 26. The intermediate gears in turn engage a non-rotatable sun gear 28. The sun gear 28 is formed from an inwardly depending portion of the outermost portion 18 of the gear housings 16.

A drive shaft 30 is received through the outermost portion 18 and is supported rotatably therein in a bearing means 32. The drive shaft 30 extends through the sun gear 28 and attaches to, or is formed integrally therewith, a rotatable drive support, for example a drive disc 34. The drive disc 34 rotates freely within the gear housing 16 without the need for seals. It is to be understood that the rotatable drive support^'need not necessarily be circular in plan view.

The gear 20 has received rigidly therein a drive shaft 36 which projects therefrom through the drive disc 34 and attaches to a mid-point of a first vane guide member 38. The drive shaft 36 is received rotatably through the drive disc 34 by way of a bearing means 40 provided therein.

The gear 22 has received rigidly therein a drive shaft 42 which projects therefrom through the drive disc 34 and attaches to a mid-point of a second vane guide member 44. The drive shaft 42 is received rotatably through the drive disc 34 by way of a bearing means 46 provided therein. The gear housings 16 are isolated from the pump cavity 14 by intermediate walls 48. In this manner the pump cavity 14 is distinguished in not having any seals bordering thereon. As such any fluid flow through the pump cavity 14 is isolated from the gear housing 16.

The pump cavity 14 contains a pair of vanes 50 and 52. The vanes 50 and 52 form functional pairs with the guide members 38 and 44 through magnetic coupling therebetween whereby movement and rotation induced in the guide members 38 and 44 through the gear housings 16 will be mirrored by the vanes 50 and 52 through the pump cavity 14. The specific nature of the movement of the vanes 50 and 52 is discussed at length in the specification of PCT/AU94/00584 (WO 95/09973) in the name of the present applicant and the entire content thereof is incorporated hereby by reference. The significant improvement in the present invention from that described in the prior specification being in part the change from direct mechanical manipulation of the vanes 50 and 52 to the magnetic coupling of the vanes 50 and 52 to the guide members 38 and 44, it being the guide members 38 and 44 now that are directly mechanically manipulated.

It is envisaged that the magnetic coupling of the guide members 38 and 44 and vanes 50 and 52 may be achieved in at least two forms. One form is demonstrated, at least schematically, in Fig. 2 whereby high energy density permanent rare earth magnets 54 and 55 are positioned in the axial extremities, top and bottom edges as shown in Fig. 2, of the guide members 38 and 44 and vanes 50 and 52, respectively so as to lie substantially adjacent across the intermediate walls 48. For example, neodymium-iron-boron magnets may be utilised. It is envisaged that magnetic coupling may be achieved through use of either attractive or repulsive forces between guide members and vanes. However, it is preferable that repulsive forces be utilised, as shown in Fig. 2 with the deliberate orientation of like poles of the rare earth magnets, as friction force between the vanes 50 and 52 the intermediate walls 48 is minimised due to the elimination of strong magnetic attractive forces normally associated with a magnetic coupling.

With reference to Figs. 2 and 6 the vanes 50 and 52 have a pair of the magnets 55 located adjacent the axial extremities thereof. It is important to note that such are spaced from the lateral extremities of the vanes 50 and 52 so as to avoid interference between the magnets on each vane 50 and 52 as same pass through the return slot 57 of the pump cavity 14. It is at that point during rotation that the vanes 50 and 52 are closest and it is necessary to prevent destabilisation of the magnetic drive.

The magnets 54 are positioned with a depression in their face bordering the intermediate wall 48 of the pump cavity 14. In this manner the magnets 54 resemble a solid block having had one surface hollowed out. The magnets 54 are also broader than the magnets 55. This coupling between the pairs of magnets 54 and 55 ensures that a magnetic field 59 generated by the magnet 55 is effectively "held" within the magnetic field 61 generated by the magnet 54, as can be best seen in Fig. 6. The coupling between the magnets 55 and 54 may consequently be described as male/female, respectively.

A further manner in which the required magnetic coupling may be achieved is envisaged to be the computer controlled electromagnetic balancing between the permanent magnets provided in the vane and electromagnets in the drive member. Instant adjustment of minor variations in field intensity keep the vanes from contacting the pump walls. Such an electromagnetic arrangement will require sensors and suitable feedback to a governing computer or PLC whereby the position of the vanes may be continuously adjusted. The positive displacement planetary vane pump requires a magnetic drive that duplicates the planetary orbit described by the vanes, however many may be provided. As noted above, this may be achieved with a magnetic coupling to each of two gear boxes (the gear housings 16 noted above) at opposed ends of the pump 10, as shown in Fig. 2. Alternatively, again as noted above, a series or array of small electromagnets in the walls of the pump bordering the pump cavity 14 that activate/deactivate sequentially to drive the vanes to move through the pump cavity 14.

Unlike the magnetic piston pump of the prior art the electromagnetics can not be provided in a ring structure but must be provided as small points on the pump wall. The array of electromagnets is required to duplicate the planetary orbit described by the vanes as the orbit through the pump cavity. It is envisaged that the electromagnets will not always be driving the same magnet in the vanes as some planetary pumps utilise vanes that are rotated end over end alternately during rotation. The electromagnetic drive described duplicates the male/female repulsive coupling by a combination of permanent and electromagnets. The male component may be provided in the form of the permanent magnet 55, as described previously. A guide track 80, shown in Fig. 7, is provided in the intermediate wall 48 to simulate the female magnets 54 of the embodiment of Fig. 2. Two paths 82 of permanent magnet flank an orbit path 84 comprised of a series of electromagnets 86. The electromagnets 86 are activated sequentially to achieve drive for the vane 50 in the direction of Arrow 88, as shown in Fig. 7.

After the vanes 50 and 52 pass through the return slot 57 the electromagnet guide track 80 splits into two drive tracks. A break in the guide track 80 allows the vane tip to follow either an outer or inner orbit as required. The computer or PLC governing the switching of the electromagnets 86 will be required to generate the break in the guide track 80 at an appropriate time during the orbiting motion of each vane 50 and 52. Furthermore, it is envisaged that a sensing and compensating system to suspend the vanes may be incorporated into this form of the invention.

With reference again to Fig. 2 in the absence of electromagnetic suspension it is envisaged that the vanes 50 and 52 have at least a close clearance, low friction interface with the pump cavity 14. Further, both the vanes 50 and 52 and the pump cavity 14 may be coated with or formed from a low friction, wear resistant and non-thrombogenic material. For example, pyrolytic carbon has been demonstrated to have a good combination of biocompatibility and high strength and might be utilised.

It is envisaged that a functional "slide" fit between the vanes 50 and 52 and the walls of the pump cavity 14 may be achieved. Such will provide increased efficiency and minimal stress to fluids, for example blood, pumped therethrough. However, a series of lugs may be utilised on the vanes 50 and 52, if such a "slide" fit is inappropriate, such that the lugs engage the intermediate walls 48, the thrust portion of the pump cavity wall 15 and the upstand 63 during rotation and consequently provide the necessary mechanical holding point for the balancing of magnets by magnetic coupling, as explained by the Earnshaw theorem. It is to be noted that each axial and lateral extremity of the vane would preferably have two such lugs to prevent rocking of the vane about lateral and axial axes.

In Figs. 3 to 5 there is shown the progressive positions of the vanes 50 and 52 with the pump cavity 14 driving the pumping of fluid flow 56 therethrough. As noted above, the movement of the vanes 50 and 52 through their circular path 58 is induced through rotation of the drive discs 34 whereas the independent rotation 60 of the vanes about their axes X is imparted via intermediate gears 24 and 26, and the non-rotating sun gear 28. Such produces a substantially continuous or non-pulsing flow without significant resistance thereto through passage of the vanes between the non positive displacement and positive displacement phases of rotation.

The two drive shafts 30 shown in Fig. 2 are preferably coupled, perhaps by way of bevel gears, so as to ensure they are driven evenly and at the same rate. It is obviously important that the guide members 38 remain rotating and revolving in unison. Such bevel gears may be provided within an additional housing.

The magnetic drive for positive displacement pumps of the present invention can be seen to provide a pump having a cavity therein without the need for drive shafts to project therein to drive the vanes thereof and with a consequently sealless pump casing. Such benefits the pumping of clotting fluids such as blood and the present invention is consequently seen to have particular application as a blood pump.

It is envisaged that the drive support may be magnetically coupled and driven so as to eliminate the shaft seal to the gear housing 16. This prevents cross contamination between the content of the gear housing 16 and a human body in which the pump housing is positioned.

Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims

CLAIMS:

1. A magnetic drive for a positive displacement planetary vane pump characterised in that the magnetic drive comprises at least one drive guide member provided in the or each gear housing, the or each drive guide member being supported in a rotatable manner on or by a rotatable drive support through the rotation of which the or each guide member may be moved through a circular arc within the or each gear housing, whereby the or each guide member is caused to rotate about its own axis as the or each guide member moves through the circular arc driven by the rotation of the rotatable drive support and wherein a gearing arrangement is provided such that rotation of the rotatable drive support produces consequent axial rotation of the or each guide member.

2. A magnetic drive according to claim 1 , characterised in that the magnetic drive is provided in combination with a pump housing, the pump housing containing at least one vane in a cavity defined thereby.

3. A magnetic drive according to claim 2, characterised in that the or each guide member is arranged so as to induce movement in a corresponding vane through the pump cavity.

4. A magnetic drive according to claim 3, characterised in that the pump cavity and the gear housing are in fluid tight isolation whereby the fluid being pumped through the pump cavity can not enter the gear housing and similarly the content of the gear housing cannot contaminate the fiuid being pumped.

5. A magnetic drive according to claim 3 or 4, characterised in that the or each guide member and its corresponding vane are provided with a magnetic coupling means whereby movement of the or each guide member induces movement in the corresponding vane.

6. A magnetic drive according to claim 5, characterised in that the magnetic coupling is provided in the form of a balanced repulsive axial magnetic force and provides a consequent partial suspension of the or each vane within the pump cavity.

7. A magnetic drive according to claim 5 or 6, characterised in that the magnetic coupling is achieved by way of permanent magnet pairs provided in the drive guide member and corresponding vane.

8. A magnetic drive according to claim 7, characterised in that the magnet pairs comprise a broad "female" magnet in the guide member and a thinner "male" magnet in the vane such that the field generated by the "male" magnet is held within the boundaries of the "female" magnet.

9. A magnetic drive according to any one of the preceding claims, characterised in that where two or more guide members are provided they are proportioned such that during rotation they do not collide.

10. A magnetic drive according to claims 5 to 9, characterised in that there is provided at least a single mechanical sliding holding point for each vane within the pump cavity.

11. A magnetic drive according to any one of the preceding claims, characterised in that the rotatable drive disc is preferably driven to rotate by a drive shaft received at a mid point thereof, the shaft projecting into the gear housing through an outermost portion thereof from a point outside same.

12. A magnetic drive according to claim 11 , characterised in that the drive shaft has a non-rotating sun gear formed thereabout through a depending projection of the outermost housing portion.

13. A magnetic drive according to claim 12, characterised in that two intermediate planetary gears are provided interconnecting the non-rotating sun gear with a gear provided on a drive shaft associated with each guide member.

14. A magnetic drive according to claim 13, characterised in that the drive shaft associated with each guide member is held rotatably in the rotatable drive support.

15. A positive displacement planetary vane pump having a magnetic drive, characterised in that the pump comprises a pump housing defining a cavity therein through which a fluid may be pumped or metered, at least one vane being located in the cavity, the pump housing having provided at each opposed end thereof a gear housing, the gear housing having located therein at least one guide member, wherein there are provided a complimentary number of guide members and vanes forming pairs thereof, these pairs having provided therein magnetic coupling means such that movement of a guide member induces movement in a complimentary vane.

16. A positive displacement pump according to claim 15, characterised in that the magnetic coupling of the pairs of guide member and vane allow the pump cavity to be formed without seals, thereby providing isolation of the fluid flow from the content of the gear housings.

17. A positive displacement planetary vane pump characterised in that it comprises a pump housing defining a cavity therein through which a fluid may be pumped or metered, at least one vane being located in the cavity, the pump housing having provided at each opposed end thereof an array of electromagnets, the array of electromagnets describing the planetary path of rotation of the or each vane, the or each vane being driven through the sequential switching of the electromagnets.

18. A positive displacement planetary vane pump according to claim 17, characterised in that the array of electromagnets comprises a guide track having a series of electromagnets bordered by lines of permanent magnets, the permanent magnets acting to prevent lateral displacement of the vanes.

19. A positive displacement planetary vane pump according to claims 17 or 18, characterised in that a computer or PLC is provided to govern switching of the electromagnets in the guide track.

20. A magnetic drive for a positive displacement planetary vane pump substantially as hereinbefore described with reference to the accompanying drawings.

21. A positive displacement planetary vane pump having a magnetic drive substantially as hereinbefore described with reference to the accompanying drawings.