GB2570467A

GB2570467A - Scroll pump

Info

Publication number: GB2570467A
Application number: GB1801250.0A
Authority: GB
Inventors: Ernest Kinnaird Holbrook Alan; Turner Neil; Alan Turrell David
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2018-01-25
Filing date: 2018-01-25
Publication date: 2019-07-31
Also published as: WO2019145677A1; GB201801250D0

Abstract

A scroll pump with two interleaving scrolls 15a,15b which are mounted on offset parallel axes such that they undergo relative orbital rotation and an anti-rotation device comprising a flexible belt 10 which is mounted around and in contact with at least a portion of the outer perimeter of the two scrolls, such that the flexible belt resists relative angular rotation between the two scrolls. The flexible belt and scrolls may comprise teeth which co-operate with each other. There may be a portion 14 of the scroll which extends radially outwards beyond the belt, such that the belt is stopped from slipping off. One of the scrolls may be fixed and the other rotate or both scrolls may rotate in synchronisation with each other. One scroll may be driven and transfer rotational movement to the other scroll through the belt or both scrolls may be caused to rotate by the belt. The pump may be a vacuum pump.

Description

A scroll pump is a pump formed of two interleaving scrolls one of which has an orbital motion with respect to the other thereby trapping and pumping or compressing pockets of fluid between the scrolls. In some cases, one of the scrolls is fixed, while the other is mounted on a drive shaft with an eccentric centre such that it orbits eccentrically without rotating. Another method for producing the relative orbiting motion is by co-rotating the scrolls, in synchronous motion, but with offset axes of rotation. Thus, in this case the two scrolls are mounted on parallel shafts and the relative motion is the same as if one were orbiting and the other stationary.

In the case of fixed and orbiting scrolls an anti-rotation device may be used connected to the scrolls to resist relative rotation between them and thereby allow the radial clearances to be accurately maintained as the scrolls pump. The antirotation device should resist rotational movement but also allow the relative orbiting motion required for the pumping.

Figure 1 shows an anti-rotation device according to the prior art, where a flexible bellows arrangement formed from a crimped pipe is used as an anti-rotation device in a scroll pump with one scroll fixed. This bellows arrangement is located on the orbiting scroll side of the pump and resists rotation of the orbiting scroll but is sufficiently flexible to allow the orbiting motion.

A drawback of such a device is that the bellows need to be quite long to keep the stress in the bellows below fatigue limits, and thus, pumps with bellows are physically quite big for their displacement. An alternative more compact antirotation arrangement is shown in Figure 2 and disclosed in WO2011/135324. The anti-rotation device here comprises a central body portion from which two

-2perpendicular pairs of arms extend, a first pair being connected to the fixed scroll and a second pair to the orbiting scroll, the first pair flexing to allow movement of the orbiting scroll relative to the fixed scroll in a first direction and the second pair flexing to allow movement of the orbiting scroll in a second orthogonal direction. This provides a more compact arrangement than the bellows, but it has proved difficult to scale up, because there are only two pairs of legs to share the stresses, and there is an unbalanced mass which introduces vibration to the pump.

Other existing mechanisms in the market include Oldham couplings, the use of three small crank shafts and the use of a thrust bearing.

It would be desirable to provide a scroll pump where the anti-rotation device is compact, robust, low cost and provides effective relative rotational resistance, while allowing relative orbiting motion between scrolls.

SUMMARY

A first aspect provides a scroll pump comprising: two interleaving scrolls mounted on parallel offset axes, said interleaving scrolls being mounted for relative orbital rotation, such that at least one scroll is mounted to rotate about an axis offset with respect to the axis of the other scroll; and an anti-rotation device for resisting relative angular rotational movement between said two scrolls; wherein said antirotation device comprises a flexible belt mounted around an outer perimeter and in contact with at least a portion of said outer perimeter of said two interleaving scrolls, such that relative angular rotational movement between said two scrolls is resisted by said flexible belt.

Scroll pumps typically have two interleaving scrolls which pump fluid by providing relative motion between the scrolls. This means the locations of the small gaps between the two scrolls change as one of the scrolls orbits and the fluid is pumped through the device. This relative orbiting motion may be produced by one scroll being fixed and the other orbiting eccentrically or by both scrolls

-3rotating in synchronous motion but with offset but parallel axes of rotation. The radial clearances between the two scrolls should be accurately controlled and it is therefore important that relative rotation between the scrolls is resisted while translational movement which allows the orbiting motion is permitted. Embodiments seek to provide a scroll pump with an anti-rotation device that is easy to assemble, has a low number of parts, has a long life and yet provides effective resistance to relative rotation. This is achieved by the use of a flexible belt around the outer perimeter of the scrolls. This flexible belt is a simple yet elegant way of providing resistance to relative rotation while allowing the orbital motion. Furthermore, it is simple to assemble and is robust and therefore has a long life. Furthermore, this solution is entirely scalable so that it can be used for pumps of any size.

In some embodiments, said flexible belt comprises teeth on an inner surface.

It is important that there is no, or at least very little, slippage of the belt that might allow relative rotation of the two scrolls. Thus, in some embodiments the inner surface of the belt may be roughened or treated in some way to increase friction and/or the outer circumferential surfaces of the scrolls may also be roughened or treated. Alternatively, the inner surface of the belt may comprise teeth that may be configured to cooperate with corresponding teeth on the outer circumferential surfaces of the two scrolls.

In some embodiments, at least a portion of said outer circumferential surface of each scroll extends axially towards the other scroll, such that said outer circumferential surfaces of each scroll do not overlap with said the other scroll.

In some embodiments, said outer circumferential surface of each scroll extend from an outer edge towards a mid point between respective scroll plates of said scrolls.

-4ln order for the outer circumferential surface of each scroll to contact the belt for at least some of the circumference, in preferred embodiments, the outer axially extending surface extends towards a mid point between the two scrolls such that the circumferential surfaces can cross during orbital motion and one of the circumferential surfaces is not always within the outer circumference of the other. Providing the surfaces as far as, or nearly as far as, the mid point increases the length of the surfaces while avoiding overlap allowing for an effective interlock between the teeth of the belt and the teeth on the outer circumferential surfaces. For the sake of this application, nearly as far as is considered to be any point up to or over 90% of the mid point.

In some embodiments, the outer circumferential surface of each scroll is a surface with a same sized circular cross section, the surface being a dedicated surface for supporting the belt. Each surface extends to a same axial distance around the whole circumference and in some embodiments both surfaces have a same axial length, while in other embodiments they may have different lengths.

In some embodiments, each surface comprises axially extending teeth around the whole circumference, the teeth being configured to cooperate with teeth on the belt.

In some embodiments, the teeth extend across the whole axial length of the outer surface, while in other embodiments, they extend across a portion of the length.

In some embodiments, each of said scrolls comprises a rim extending parallel to a respective scroll plate and out from an edge of said scroll, said rim being configured to retain said flexible belt.

It may be advantageous to provide some sort of extension outward from the scroll in the form of a rim that can act to help retain the flexible belt in position on the scrolls. In some embodiments, said rim is configured to extend out from an outer

-5edge of said circumferential surface of said scroll such that an inner surface of said rim is coplanar with an inner surface of said scroll plate.

In the above case the rim is provided to in effect extend the scroll plate surface and retain the belt within the whole width of the scroll. In other embodiments, said rim is configured to extend out from said outer circumferential surface of said scroll inset from said scroll plate. In the latter case, the belt is retained within a central portion of the scroll and will have a smaller width.

In some embodiments, each of said rims has a length such that they extend up to or beyond said flexible belt at all positions of said scrolls.

One scroll orbits with respect to the other such that one scroll is displaced with respect to the other scroll as it rotates. It may be advantageous for the rims to be long enough such that they extend up to or beyond the flexible belt no matter what the current displacement, thereby providing an effective means of retaining the belt in position. To achieve this the length of each rim may be greater than or equal to an offset distance between the two axes of said two scrolls plus a width of said drive belt.

In some embodiments, a width of said flexible belt is equal to or less than a distance between the two scroll plates of the two scrolls, and greater than 60% of said distance, preferably greater than 80% of said distance between said two scroll plates.

It may be advantageous for the belt to be wide and extend across all or at least most of the outer circumferential surface of the scrolls providing an effective way of preventing or at least impeding slippage. In any case it will want to extend across at least some of each of the scroll’s outer surfaces.

In some embodiments, one of said scrolls is a fixed scroll and the other scroll is mounted to orbit.

-6ln other embodiments, said two scrolls are each configured to rotate, said two scrolls being constrained by said belt to rotate in synchronisation with each other.

In some embodiments, said scroll pump comprises a motor configured to drive one of said scrolls, said belt being configured to transmit torque from said one scroll to the other scroll and to resist relative angular rotation of said two scrolls.

Where the two scrolls both rotate, the belt can be used to drive one of the scrolls, such that a rotational force is transmitted from the driven scroll to the non-driven scroll via the belt. This avoids the need for both shafts to be driven, which arrangement is more cost effective and requires less maintenance than the alternative solution of providing gears to drive the second shaft, or providing two drive motors.

In some embodiments, said scroll pump comprises a motor configured to drive a drive wheel located in a same plane as said scrolls, said flexible belt passing around said drive wheel and contacting a portion of said outer perimeter of each of said two scrolls, such that rotational movement of said drive wheel is transferred to said scrolls via said belt.

As noted above the flexible belt is a convenient way of transferring a rotational driving force. In some cases it can be used with an additional drive wheel that is located such that the flexible belt passes around the drive wheel and the scrolls, and driving of the drive wheel causes the belt to rotate and drive the scrolls, the belt acting as a drive belt for the scrolls. This allows the scrolls to be mounted simply on rotational bearings and the motor to be located remotely from the scrolls. Where the flexible belt has teeth on its surface then the drive wheel will have corresponding teeth on its outer circumferential surface.

In some embodiments, said flexible belt is mounted such that it is in contact at least with a portion of said outer circumferential surface of each scroll.

-7The flexible belt should contact each scroll across enough area on the outer surfaces to provide effective resistance to relative rotation. It may be advantageous for it to contact the outer surfaces at all portions of the outer surface where the two scrolls do not overlap.

In some embodiments, said scroll pump has a volumetric pumping capacity of more than 0.1 m³/hour, in some cases more than 3 m³/hour and preferably more than 10 m³/hour, more preferably greater than 20 m³/hour.

As noted previously this anti-rotation solution is scalable, so that it can be used on larger pumps, where some of the alternative solutions such as that shown in Figure 2 struggle with the forces imparted along the flexible members.

Although the scroll pump could be used in a number of applications, in some embodiments said scroll pump comprises a vacuum pump.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figure 1 illustrates a section through a scroll pump with bellows to align the orbiting scrolls according to the prior art;

-8Figure 2 illustrates a flexible arm coupling for aligning the orbiting scrolls according to the prior art;

Figure 3 illustrates a scroll pump according to an embodiment;

Figure 4 illustrates a cross section through the scrolls and belt of a pump according to an embodiment;

Figure 5 illustrates a cross section through the scrolls and belt with offset rims according to an embodiment; and

Figure 6 illustrates a scroll pump driven by a side shaft according to a further embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided.

Embodiments provide the use of a belt wrapped around the perimeter of the scrolls and contacting a portion of their outer circumferential surfaces to preserve the orientation of one scroll relative to the other. The belt is preferably a toothed belt and the outer circumferential surfaces of both scrolls have complementary ridged profiles configured to align with the teeth of the belt and thereby prevent or at least impede slippage of the scroll components relative to the belt. Both scrolls have a rim extending parallel to the scroll plate to prevent or at least impede the belt from coming off the scrolls.

The use of a belt provides a device that is simple to assemble, low cost, robust and easy and cheap to replace.

Embodiments can be applied to both common scroll pump configurations: Type 1 in which one scroll is stationary and the other orbits, and Type 2 in which both scroll components rotate.

Figure 3 shows a scroll pump according to an embodiment. This embodiment comprises a fixed scroll 15a and an orbiting scroll 15b the belt 10 passing around

-9their outer circumferential surfaces and providing resistance to relative rotational movement. Rims 14 extend from each scroll plate to hold the belt in position. Inlet ports 3 are provided towards the outer edge of the orbiting scroll 15b.

The pump's shaft rotates about an axis that passes through the centre of the fixed scroll. The orbiting scroll is rotatably mounted on an axis on the shaft that is offset from the shaft's rotational axis, and this provides the orbiting motion.

Figure 4 shows a cross section of the scrolls and belt 10 of the pump of figure 3. As can be seen the non-fixed scroll 15b is mounted on a drive shaft 20 on an offset shaft 22, this provides the orbiting motion relative to the fixed scroll 15a. Relative rotation between the two scrolls is resisted by the toothed belt 10 mounted around the perimeter of the pump and interlocking with corresponding teeth on the outer circumferential surface of both scrolls. The teeth and outer circumferential surfaces extend towards the mid point between the two scroll plates, while the scrolls themselves extend up to the opposing scroll plate. Inlet 3 is provided towards the outer edge of the orbiting scroll 15b and is in fluid communication with the volume at the outer edge of the two scrolls, which acts as the inlet to the pump, the scroll pump pumping fluid from the outside to the centre from where it is exhausted. Although the inlet is shown on the orbiting scroll it could also be formed in the fixed scroll.

Rims 14 can be seen extending from the scroll plates and acting to retain the belt. They extend far enough to extend beyond the belt at any point of the orbiting motion.

Figure 5 shows an alternative embodiment, where the rims 14 are offset in an inward direction from the scroll plates and the belt is narrower than in the embodiment of Figure 4. The offset rims retain the belt on the scrolls. In other embodiments (not shown) the rim may be offset outwards from the scroll plates to accommodate a belt that is wider than the scrolls.

- 10Figure 6 shows an alternative embodiment where both scrolls 15 rotate and the scrolls are driven via the belt 10 which passes around the two scrolls 15 and a drive shaft 20 located in the same plane as the scrolls but to one side of them. Rotation of the drive shaft 20 causes the belt 10 and thus, the scrolls 15 to rotate.

In this way neither of the scrolls need be mounted on shafts that are themselves driven, the driving force being provided by a drive shaft 20 located to one side and the driving force being transmitted via the belt. In other embodiments, the drive shaft may be the shaft on which one of the scrolls is mounted and the rotational force may be transmitted to the other scroll via the belt. This avoids the io need for both shafts to be driven, or for gears to impart rotational movement from one to the other.

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

- 11 REFERENCE SIGNS

Inlets 3

Belt 10

Rim 14

Scrolls 15

Fixed Scroll 15a

Orbiting Scroll 15b

Drive shaft 20 io Offset shaft 22

Claims

1. A scroll pump comprising:

two interleaving scrolls mounted on parallel offset axes, said interleaving scrolls being mounted for relative orbital rotation, such that at least one scroll is mounted to rotate about an axis offset with respect to the axis of the other scroll; and an anti-rotation device for resisting relative angular rotational movement between said two scrolls; wherein said anti-rotation device comprises a flexible belt mounted around an outer perimeter and in contact with at least a portion of said outer perimeter of said two interleaving scrolls, such that relative angular rotational movement between said two scrolls is resisted by said flexible belt.

2. A scroll pump according to claim 1, said flexible belt comprising teeth on an inner surface.

3. A scroll pump according to claim 2, wherein an outer circumferential surface of each of said scrolls comprises teeth configured to cooperate with said teeth of said flexible belt.

4. A scroll pump according to claim 3, wherein at least a portion of said outer circumferential surface of each scroll extends axially towards the other scroll, such that said outer circumferential surfaces of each scroll do not overlap with said the other scroll.

5. A scroll pump according to claim 3 or 4, wherein said outer circumferential surface of each scroll extend from an outer edge towards a mid point between respective scroll plates of said scrolls.

6. A scroll pump according to any preceding claim, wherein each of said scrolls comprises a rim extending parallel to a respective scroll plate and out from an edge of said scroll, said rim being configured to retain said flexible belt.

7. A scroll pump according to claim 6, wherein said rim is configured to extend out from an outer edge of said circumferential surface of said scroll such that an inner surface of said rim is coplanar with an inner surface of said scroll plate.

8. A scroll pump according to claim 6, wherein said rim is configured to extend out from said outer circumferential surface of said scroll inset from said scroll plate.

9. A scroll pump according to any one of claims 6 to 8, wherein each of said rims has a length such that they extend up to or beyond said flexible belt at all positions of said scrolls.

10. A scroll pump according to any preceding claim, a width of said flexible belt being equal to or less than a distance between the two scroll plates of the two scrolls, and greater than 60% of said distance, preferably greater than 80% of said distance between said two scroll plates.

11. A scroll pump according to any preceding claim, wherein one of said scrolls is a fixed scroll and the other scroll is mounted to orbit.

12. A scroll pump according to any one of claims 1 to 10, wherein said two scrolls are each configured to rotate, said two scrolls being constrained by said belt to rotate in synchronisation with each other.

13. A scroll pump according to claim 12, said scroll pump comprising a motor configured to drive one of said scrolls, said belt being configured to transmit torque from said one scroll to the other scroll and to resist relative angular rotation of said two scrolls.

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14. A scroll pump according to claim 12, said scroll pump comprising a motor configured to drive a drive wheel in a same plane as said scrolls, said flexible belt passing around said drive wheel and contacting a portion of said outer perimeter of each of said two scrolls, such that rotational movement of said drive wheel is transferred to said scrolls via said belt.

15. A scroll pump according to any one of claims 1 to 14, wherein said flexible belt is mounted such that it is in contact at least with a portion of said outer circumferential surface of each scroll.

16. A scroll pump according to any preceding claim, said scroll pump having a volumetric pumping capacity of more than 3 m3/hour and preferably more than 10 m3/hour, more preferably greater than 20 m3/hour.

17. A scroll pump according to any preceding claim, wherein said scroll pump comprises a vacuum pump.