GB2394512A

GB2394512A - Pump rotor set with increased fill limit

Info

Publication number: GB2394512A
Application number: GB0224519A
Authority: GB
Inventors: Stephen Mark Hodge
Original assignee: Concentric Pumps Ltd
Current assignee: Concentric Pumps Ltd
Priority date: 2002-10-22
Filing date: 2002-10-22
Publication date: 2004-04-28
Also published as: AU2003274358A1; GB0224519D0; WO2004038223A1

Abstract

The rotor 10 or annulus (stator) 60 of a pump has a number of teeth 14, 64 and a number of blind filling slots 18, 66 between the teeth and extending from an end face of the rotor 10 or annulus 60. Two annulus with filling slots 66 in their end faces may be fitted back-to-back (figs. 5,6) so that peripheral filling windows (102, 122) are formed. The filling slots are provided in order to increase the "single end filling limit", ie the amount of fluid that a particular rotor/annulus set can admit through one end without cavitation/flow truncation occurring, and may also increase the "double end fill limit", ie the amount of fluid that can be admitted into a rotor set from both ends.

Description

! 2394512

Improvement in or relating to pumps The present invention relates to improvement in, or relating to, pumps.

5 All rotor sets have a "single end fill limit" and "double end fill limit" in relation to the amount of oil that can pass into a rotor set under dynamic conditions, above which "cavitation" commences. Cavitation will initially be seen as flow truncation, which, if at sufficient levels, and present over a period of time, can result in material damage to both rotor and annulus forms. This potential for damage can be offset by careful selection of materials, but ideally 10 cavitation of any significance should be avoided. In practice a flow truncation of up to about 5% is deemed acceptable for limited periods.

Actual fill limits, are dependent on several factors, and can vary between pump configurations, even for the same rotor set. Inlet and outlet geometry, fluid viscosity and pump speed are all 15 likely to have an influence on the apparent fill limit of a particular rotor set.

Fill limits are essentially a function of pocket area available at the end faces of the rotor set as they pass the inlet port, and the rotor set length. This determines the volume of oil that has to enter the rotor set in the time the pocket passes the inlet port.

An aim of the invention is to increase the 'single end filling limit', this being the amount of fluid that a particular rotor and annulus set can admit through one end without cavitation/flow truncation taking place. In practice, the modification may also increase the "double end fill limit" i.e. the amount of fluid that can be admitted into a rotor set from both ends. Primarily, 25 the aim is to increase the single filling limit on pump designs where double tilling is not practicable because of installation constraints.

According to a first aspect of the invention there is provided a pumping member for a pump, the pumping member comprising a plurality of teeth defining a plurality of recesses between 30 successive teeth, the recesses being arranged to admit fluid, the pumping member also comprising a plurality of supplementary filling apertures in an end face of the pumping member.

The supplementary filling apertures are preferably located between the teeth of the pumping member. In one preferred embodiment, the pumping member is a rotor In another preferred embodiment, pumping member is an annulus.

According to a second aspect of the invention there is provided a rotor for a pump, the rotor comprising a plurality of teeth defining a plurality of recesses between successive teeth, the 10 recesses being arranged to admit fluid, the rotor also comprising a plurality of supplementary recesses in a bore of the rotor.

The supplementary recesses are preferably in the form of slots.

15 The slots preferably extend substantially axially.

Preferably, the supplementary recesses extend for less than half the pumping members, axial length. Most preferably, the slots extend for about one third of the axial length of the pumping member. The supplementary recesses are preferably sintered.

In one preferred embodiment of the invention, the supplementary recesses connect a bore of the rotor to the form.

The supplementary recesses of the pumping member are preferably rounded.

Arrangements exist in the prior art whereby peripheral slots are formed as windows in a single

piece annulus.

According to a third aspect of the invention there is provided a method of making an annulus for a pump, the method comprising providing a first annulus comprising a plurality of teeth defining a plurality of recesses between successive teeth, the recesses being arranged to admit fluid, the annulus also comprising a plurality of supplementary filling apertures between the

teeth, and in an end face thereof, and attaching the first annulus to a second annulus in end-to-end manner.

The second annulus preferably comprises an annulus having one or more filling slots in an end 5 face thereof. Most preferably, the slot(s) of the first annulus correspond in size and location to the slot(s) of the second annulus.

According to a fourth aspect of the invention there is provided a pump housing for a pump, the housing comprising an inlet port and an outlet port, wherein the position of the ports 10 corresponds to the position of, supplementary recesses of a pumping member in accordance with the first aspect of the invention, or, supplementary recesses of the rotor in accordance with the second aspect of the invention.

In this way, fluid can flow freely into, and out of, the pump housing.

According to a fifth aspect of the invention there is provided a pump assembly comprising a pumping member in accordance with the first or second aspect of the invention.

Preferably, the pump comprises two pumping members in accordance with the first aspect of 20 the invention, one being an annulus, the other being a rotor.

Pumping members for pumps in accordance with the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which, 25 Figure I is a perspective view of a first rotor in accordance with the invention, Figure 2 is a perspective view of a second rotor in accordance with the invention, Figure 3 is a perspective view of a first annulus in accordance with the invention, Figure 4 is a perspective view of a second annulus in accordance with the invention, Figure 5 is a perspective view of a third annulus in accordance with the invention, 35 Figure 6 is a perspective view of a fourth annulus in accordance with the invention,

Figure 7 is a perspective view, showing the rotor of Figure 2 installed on the annulus of Figure 4, and Figure 8 is a perspective view, showing the rotor of Figure 1 installed on the annulus of Figure 5 3. 1. Filling Slots in Rotor End Faces Depending on the set in question, these slots may be of limited depth, or may, in the case where the material thickness between the minor rotor form diameter and rotor bore is small, 10 connect the rotor bore to the form. In either case, in order to maintain adequate annulus support, it is thought preferable for the slots to be present for only a proportion of the total rotor length, perhaps one third. If the slots connect to the bore, the bore under the slot should be a close clearance on the shaft so as not to cause local rotor form growth which may erode running clearances with the annulus. This clearance on the shaft should also not be sufficient 15 to produce a short cut from inlet to outlet via these slots (see Figure 2).

For test purposes, the slots may be milled, but for optimum performance in production they should be sintered to a form that optimises the flow. The porting minor diameter will need to be modified so as to allow fluid to enter the slots freely.

Referring to Figure 1, a rotor 10 consists of a generally cylindrical part 12 and six, spaced apart, radially extending, teeth 14, which run longitudinally on the periphery of the cylindrical part. The cylindrical part 12 has an axial bore 16 extending through it. The rotor 10 also has six "blind" filling slots 18, (two of which are referenced) defined in the cylindrical part 12 25 between each pair of successive teeth 14. The slot 18 profile shown represents what may be preferable for a production part with well-rounded corners.

The major form diameter is measured from the tip of a lobe (tooth 16) to the tip of an opposite lobe, through rotor bore. The minor form diameter is measured trough to trough 30 through the rotor bore. The rotor in Figure 1 is numbered 67140. The numbers are as follows: 6 = Number of lobes on inner form.

7 = Number of lobes on outer form.

140= 0.140 inches apart between two axis (of rotor and annulus).

The difference between major and minor form diameters is a function of the offset between the inner and outer form. Since cavities are proportionately larger, the difference tends to be larger with a lower no. of lobes.

5 It will be appreciated that a 4/5 (the no. of male lobes on inner rotor/no. of male lobes on outer rotor) set, which has a relatively large difference in major to minor form (rotor or annulus) diameters would tend to have a larger fill capacity than a similarly sized 6/7 or 8/9 set, the pockets on these sets being relatively small with the rotor and annulus blocking off a large proportion of the available port area.

Referring to Figure 2, another rotor 30 (of 45216 type) has a plate-like part 32, which has a bore 34, extending through it, perpendicular to the plane of the plate-like part. The rotor 30 has four teeth 36. Each tooth 36 defines a through-bore 38, which runs parallel to the bore 34.

15 The rotor 30 has four "blind" filling slots 40. The slots 40 connect to the bore 34 for about one third of bore length, the bore being relieved slightly to prevent form growth. Note: when the slots 40 connect to the bore there is potential for short circuit from pressure to suction via the slots 40 and shaft journal chamfer, or via the clearance between the end of the shaft and pump cover when shaft is flush with shaft end.

2. Filling Slots in Annulus End Faces These are positioned the same as with the rotor in that they lie in the non-critical part of the form, and are again present for perhaps one third of the annulus length. Again, the profile of the slots can be optimised for production to encourage smooth flow. The inlet port major 25 diameter will need to be increased to match the annulus outside diameter to realise the full potential of the end slots.

Another consideration is the potential effect of the slots on the hydrodynamic film generation around the annulus periphery. The annulus outside diameter is now broken, which may be 30 detrimental to the film generation, although the slots also provide for pressurised oil to be fed directly to the annulus bore which may improve the lubrication. It may be advantageous to "round off' the slots where they met the outside diameter so as to minimise the scraping effect (see Figure 4).

Referring to Figure 3, an annulus 60 (of 67140 type) comprises an annular part 62 which has seven teeth 64 extending parallel to the longitudinal axis. The teeth 64 define seven filling slots 66 (only two of which are referenced) between each pair of successive teeth 64. Note rounded edges to slots to discourage 'scraping' of oil from annulus bore.

Referring to Figure 4, an annulus 80 (of 45216 type) comprises an annular part 82 which has five teeth 84 extending parallel to the longitudinal axis. The teeth 84 define five filling slots 85 and through-holes 86.

0 3. Filling Slots in Annulus Outside Diameter This technology allows the rotor set to be filled (and exhausted) within it's own length, resulting in a shorter pump assembly. The peripheral slots can be used in conjunction with conventional end face porting to achieve maximum filling potential. Disadvantages are that the slots are difficult to produce in sintered parts and an inlet core needs to be added in the annulus 15 bore wall. The core and slots will have an effect on the lubrication of the annulus outside diameter. The problem of sintering the slots in the annulus periphery can be overcome by using two annulus of the type with end filling slots as discussed above in 2) and fitting them back to 20 back. End clearances will of course be impacted by the tolerance accumulation (see fig. 3).

Referring to Figure 5, an annulus 100 (of 67140 type) is formed by putting a pair of annulus 80 back to back to produce peripheral windows 102.

25 Referring to Figure 6, an annulus 120 (of 45216 type) is formed by putting a pair of annulus 80 back to back to produce peripheral windows 122.

Referring to Figure 7, the cooperating rotor 30 and annulus 80 are arranged such that the slots 40, 85 open at the same end of the set.

Referring to Figure 8, the slots 18, 66 of the rotor 10 and annulus 60 also open at the same end of the set.

In use, a rotor 10, 30 and annulus 60, 80 pair (such as that shown in Figures 8 and 9) is 35 installed in a pump.

In Summary if one is to stay with the current form generation method, then to increase the

filling capacity of a given rotor set configuration, one must increase the area through which fluid can pass into the pockets as they pass the inlet porting. This can be achieved by 5 incorporating one or more of the following features: 1. Filling slots in rotor end faces, 2. Filling slots in annulus end faces, 3. Filling slots in annulus outside diameter, and 10 4. Filling slots in rotor bore.

Option 4 can be discarded as being impracticable for most oil pump applications where shaft diameter would normally be prohibitive.

Claims

1. A pumping member for a pump, the pumping member comprising a plurality of teeth defining a plurality of recesses between successive teeth, the recesses being arranged to admit 5 fluid, the pumping member also comprising a plurality of supplementary filling apertures in an end face of the pumping member.

2. A pumping member according to Claim 1, wherein the supplementary filling apertures are located between the teeth of the pumping member.

3. A pumping member according to Claim 1 or 2, wherein the pumping member is a rotor

4. A pumping member according to Claim 1 or 2, wherein the pumping member is an annulus.

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5. A rotor for a pump, the rotor comprising a plurality of teeth defining a plurality of recesses between successive teeth, the recesses being arranged to admit fluid, the rotor also comprising a plurality of supplementary recesses on the recesses of the rotor.

6. A rotor according to Claim 5, wherein the supplementary recesses are in the form of slots.

7. A rotor according to Claim 6, wherein the slots extend substantially axially.

8. A rotor according to Claim 5, 6, or 7, whirred the supplementary recesses extend for less than half the axial length of the pumping members.

9. A rotor according to Claim 6, 7 or 8, wherein the slots extend for about one third of the axial length of the pumping member.

10. A rotor according to any of Claims 5 to 9, wherein the supplementary recesses are sintered.

1 1. A rotor according to any of Claims 5 to 10, wherein the supplementary recesses connect a bore of the rotor to the form.

12. A rotor according to any of Claims 5 to I 1, wherein the supplementary recesses of the 35 rotor arc rounded.

13. A method of making an annulus for a pump, the method comprising providing a first annulus comprising a plurality of teeth defining a plurality of recesses between successive teeth, the recesses being arranged to admit fluid, the annulus also comprising a plurality of S supplementary filling apertures between the teeth, and in an end face thereof, and attaching the first annulus to a second annulus hi an end-toend manner.

14. A method of making an cumulus according to Claim 13, wherein the method comprises providing a second annulus which has one or more filing slots he an end face thereof.

I S. A method of making an annulus according to Claim] 3, wherein the method comprises providing a slot or slots of the first annulus corresponding ha size and location to the slot or slots of the second annulus.

15

16. A pump housing for a pump, the housing comprising an inlet port and an outlet port, wherein the position of the ports corresponds to the position of supplementary recesses of a pumping member in accordance with one or more of Claims 1 to 4, or, supplementary recesses of the rotor in accordance with any one or more of Claims 5 to 12.

20

17. A pump assembly comprising a pumping member in accordance with one or more of Claims] to 4 or one or more of Claims 5 to 12.

18. A pump assembly according to Claim 17, wherein the pump comprises two pumping members in accordance with one or more of Claims 1 to 4, one being an annulus, the other 25 being a rotor.