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SCROLL PUMP

FIELD OF THE INVENTION

The present invention relates to scroll pumps.

BACKGROUND

Scroll pumps are a known type of pump used in various different industries to pump fluid. Scroll pumps operate by using the relative motion of two intermeshed scrolls (known as a fixed scroll and an orbiting scroll) to pump fluid. Each of the fixed and orbiting scrolls includes a spiral wall extending from a base.

One type of scroll pump is a non-contacting scroll pump. In a non-contacting scroll pump, there is no contact between the tip (i.e. the end of the spiral wall) of each of the fixed and orbiting scrolls and the other scroll. Furthermore, in a noncontacting scroll pump, there is no tip seal between the tip of each of the fixed and orbiting scrolls and the other scroll. Therefore, in non-contacting scrolls pumps, there is a small gap (or clearance), e.g. of 10-20 microns, between the tip of each of the fixed and orbiting scrolls and the other scroll. In order to maintain said gap, non-contacting scroll pumps typically include a thrust bearing assembly engaged with one of the scrolls to keep the scroll in the correct axial position relative to the other scroll.

SUMMARY OF INVENTION

In an aspect of the invention, there is provided a non-contacting scroll pump, the non-contacting scroll pump comprising a housing, an orbiting scroll located within the housing, and a thrust bearing assembly located within the housing for axially supporting the orbiting scroll. The orbiting scroll comprises a base and a spiral wall extending perpendicularly from the base. The thrust bearing assembly comprises a first plate fixed to the orbiting scroll, a second plate spaced apart from the first plate, a ball bearing located between the first plate M2 IB 154

- 2 - and the second plate, the ball bearing being configured to roll against the first and second plates during orbiting of the orbiting scroll. The thrust bearing assembly further comprises a coupling structure extending between the housing and the second plate to couple the housing to the second plate, and a casing. The first plate, the second plate, and the ball bearing are located within a recess in the base of the orbiting scroll. The casing encloses the recess. The casing comprises a sealing structure.

The sealing structure may be an elastomeric face seal.

The sealing structure may be a spring loaded ring seal.

The sealing structure may be a plurality of shields.

Each of the plurality of shields may comprise an annular lip and the shields may form a seal at least partially by overlapping of the annular lips with each other.

The non-contacting scroll pump may further comprise a first ball bearing cage sandwiched between the first plate and the second plate, and a second ball bearing cage sandwiched between the first plate and the second plate, wherein the first and second ball bearing cages house the ball bearing to constrain movement of the ball bearing.

The first ball bearing cage may be fixed to the first plate and the second ball bearing cage may be fixed to the second plate.

The first and second ball bearing cages may each comprise a hole, the hole of the first ball bearing cage overlapping with the hole of the second ball bearing cage, and wherein the ball bearing is accommodated within the overlapped holes of the ball bearing cages.

The non-contacting scroll pump may comprise three thrust bearing assemblies, wherein each of the three thrust bearing assemblies comprises a first plate fixed to the orbiting scroll, a second plate spaced apart from the first plate, a ball M2 IB 154

- 3 - bearing located between the first plate and the second plate, the ball bearing being configured to roll against the first and second plates during orbiting of the orbiting scroll. Each of the three thrust bearing assembly further comprises a coupling structure extending between the housing and the second plate to couple the housing to the second plate, and a casing. The first plate, the second plate, and the ball bearing are located within a recess in the base of the orbiting scroll. The casing encloses the recess. The casing comprises a sealing structure. The three thrust bearing assemblies may be evenly angularly distributed around the rotation axis of the orbiting scroll in a triangular formation.

The coupling structure may be a pin.

The coupling structure may be for adjusting the axial position of the orbiting scroll.

In another aspect of the invention, there is provided a vacuum pumping system comprising a plurality of vacuum pumps, wherein one of the vacuum pumps is the non-contacting scroll pump of the above aspect.

In yet another aspect of the invention, there is provided the use of the noncontacting scroll pump of any of the above aspects to pump fluid.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic illustration (not to scale) showing a cross-sectional view of a non-contacting scroll pump;

Figure 2 is a schematic illustration (not to scale) showing a close-up cross- sectional view of a thrust bearing assembly of the non-contacting scroll pump;

Figure 3 is a schematic illustration (not to scale) showing a close-up cross- sectional view of an alternative thrust bearing assembly of the non-contacting scroll pump; M2 IB 154

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Figure 4 is a schematic illustration (not to scale) showing a close-up cross- sectional view of yet another alternative thrust bearing assembly of the noncontacting scroll pump;

Figure 5 is a schematic illustration (not to scale) showing a perspective view of a plurality of thrust bearing assemblies of the non-contacting scroll pump; and

Figure 6 is a schematic illustration (not to scale) showing a close-up perspective view of part of a thrust bearing assembly of the non-contacting scroll pump.

DETAILED DESCRIPTION

Figure 1 is a schematic illustration (not to scale) showing a cross-sectional view of a non-contacting scroll pump 100.

The scroll pump 100 comprises housing portions 110, a fixed scroll 120, an orbiting scroll 130, a drive shaft 140, an actuator 150, a main bearing assembly 160, and a plurality of thrust bearing assemblies 170.

In this embodiment, the housing portions 110 and the fixed scroll 120 together define an overall housing of the scroll pump 100 within which other components of the scroll pump 100 are located. However, it will be appreciated that, in other embodiments, the fixed scroll 120 may not define any of the overall housing of the scroll pump 100 and instead may be located entirely within an overall housing. In this embodiment, the orbiting scroll 130 is located within the overall housing of the scroll pump 100.

The orbiting scroll 130 is intermeshed with the fixed scroll 120 to define a space (or channel) which is used by the scroll pump 100 during operation to pump fluid (e.g. a gas). The orbiting scroll 130 is configured to orbit relative to the fixed scroll 120 to pump fluid from an inlet (not shown) of the scroll pump 100 to an outlet (not shown) of the scroll pump 100. The precise physical mechanism by which fluid is pumped by the orbiting of the orbiting scroll 130 relative to the M2 IB 154

- 5 - fixed scroll 120 is well understood and will not be described herein for the sake of brevity.

The fixed scroll 120 comprises a first base 122 and a first spiral wall 124. The orbiting scroll 130 comprises a second base 132 and a second spiral wall 134. The first spiral wall 124 and second spiral wall 134 are intermeshed with each other. Furthermore, the first spiral wall 124 extends perpendicularly from the first base 122 towards the second base 132 such that an end surface (also known as the tip) of the first spiral wall 124 is proximate to (e.g. 10-20 microns away) but not in contact with an opposing surface of the second base 132. The second spiral wall 134 extends perpendicularly from the second base 132 towards the first base 122 such that an end surface (or tip) of the second spiral wall 134 is proximate to (e.g. 10-20 microns away) but not in contact with an opposing surface of the first base 122. Thus, there is a gap or clearance (e.g. of 10-20 microns) between the end surfaces of the first and second spiral walls 124, 134 the respective opposing surfaces of the first and second bases 122, 132. The distance between the end surface of the first spiral wall 124 and the opposing surface of the second base 132 is the same as the distance between the second spiral wall 134 and the opposing surface of the first base 122. The gaps are empty in the sense that there are no objects or other scroll pump parts located within the gaps. For example, there are no tip seals within the gaps. Accordingly, the end surfaces of the first and second spiral walls 124, 134 are not in contact with any objects or other scroll pump parts.

In this embodiment, the first base 122 and first spiral wall 124 are integrally formed with each other, and the second base 132 and second spiral wall 134 are integrally formed with each other. However, in other embodiments, one or both of the spiral walls 124, 134 are not integrally formed with their respective bases 122, 132.

The drive shaft 140 is coupled to the orbiting scroll 130 and configured to rotate to drive the orbiting of the orbiting scroll 130. The drive shaft 140 is located within the overall housing of the scroll pump 100 and mounted via the main bearing assembly 160 which facilitates rotation of the drive shaft 140. In this M2 IB 154

- 6 - embodiment, the drive shaft 140 extends through both the fixed scroll 120 and the orbiting scroll 130, and the orbiting scroll 130 is mounted at an end of the drive shaft 140.

The actuator 150 (e.g. an electric motor) is coupled to the drive shaft 140 and configured to actuate the drive shaft 140 to cause the drive shaft 140 to rotate to drive the orbiting of the orbiting scroll 130. The actuator 150 is located within the overall housing of the scroll pump 100 and mounted around the drive shaft 140.

The main bearing assembly 160 mechanically couples the drive shaft 140 to the orbiting scroll 130 and the overall housing of the scroll pump 100 such that the drive shaft 140 is able to rotate within the scroll pump 100 to drive the orbiting scroll 130. In this embodiment, the main bearing assembly 160 comprises a bearing located between (and mechanically coupling) a first end of the drive shaft 140 and the overall housing of the scroll pump 100, a bearing located between (and mechanically coupling) the orbiting scroll 130 and a second end of the drive shaft 140 opposite to the first end, and a bearing located between (and mechanically coupling) the fixed scroll 120 and the drive shaft 140.

The plurality of thrust bearing assemblies 170 are each located between the orbiting scroll 130 and a housing portion 110 which is axially spaced apart from the orbiting scroll 130. Each thrust bearing assembly 170 is coupled to (and engaged with) the orbiting scroll 130 to constrain and/or control the axial position of the orbiting scroll 130 relative to the fixed scroll 120. In this embodiment, there are three thrust bearing assemblies 170 evenly angularly distributed around the central rotation axis of the orbiting scroll in a triangular formation to provide a stable axial force on the orbiting scroll 130 (this is illustrated further in Figure 3). The precise structure of each of the thrust bearing assemblies will be described in more detail with reference to Figure 2.

Figure 2 is a schematic illustration (not to scale) showing a close-up cross- sectional view of a thrust bearing assembly 170 of the non-contacting scroll pump 100. M2 IB 154

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The thrust bearing assembly 170 comprises a first plate 171 , a second plate 172, a first ball bearing cage 173a, a second ball bearing cage 173b, a plurality of ball bearings 174, an adjustment pin 175, and a casing 176. Via these structures, the thrust bearing assembly 170 provides axial support to the orbiting scroll 130 while also facilitating the orbiting of the orbiting scroll 130 during operation, as will be described in more detail below.

The first and second plates 171 , 172 each have a first side facing towards the orbiting scroll 130 and a second side opposite to the first side facing away from the orbiting scroll 130. The first and second ball bearing cages 173a, 173b also each have a first side facing towards the orbiting scroll 130 and a second side opposite to the first side facing away from the orbiting scroll 130. The first side of the first plate 171 is fixed to a back surface of the orbiting scroll 130, and the second side of the first plate 171 is fixed to the first side of the first ball bearing cage 173a. The second side of the first ball bearing cage 173a is spaced apart from the first side of the second ball bearing cage 173b by the ball bearings 174, thereby allowing relative motion of the first and second ball bearing cages 173a, 173b. The second side of the second ball bearing cage 173b is fixed to the first side of the second plate 172. The second side of the second plate 172 is engaged with an end of the adjustment pin 175.

The first and second ball bearing cages 173a, 173b each comprise a plurality of holes within which the plurality of ball bearings 174 are located. Each hole of the first ball bearing cage 173a partially overlaps with a corresponding hole of the second ball bearing cage 173b to form a plurality of hole pairs. Each hole pair houses a single ball bearing 174. The partial overlap of the holes enables the first and second bearing cages 173a, 173b to accommodate the orbiting motion of the orbiting scroll 130 during operation while constraining the movement of the ball bearings 174. This is illustrated further in Figure 4.

The plurality of ball bearings 174 are sandwiched between the first and second plates 171 , 172 such that each of the first and second plates 171 , 172 are in contact with the ball bearings 174. Each ball bearing 174 of the plurality of ball M2 IB 154

- 8 - bearings 174 is housed within a respective hole pair of the first and second ball bearing cages 173a, 173b. The plurality of ball bearings 174 may be formed from steel or ceramic.

During operation, to facilitate the orbiting of the orbiting scroll 130, the plurality of ball bearings 174 roll against the first and second plates 171 , 172 within the hole pairs of the first and second ball bearing cages 173a, 173b. During operation of the scroll pump 100, the first plate 171 and first ball bearing cage 173a, which are fixed to each other and to the orbiting scroll 130, move together with the orbiting scroll 130. Thus, during operation, the first plate 171 , first ball bearing cage 173a and orbiting scroll 130 all move together relative to the second plate 172 and the second ball bearing cage 173b on the plurality of ball bearings 174.

The adjustment pin 175 extends axially between a housing portion 110 of the scroll pump 100 and the second plate 172. A first end 175a of the adjustment pin 175 is attached to the housing portion 110, and a second end 175b opposite to the first end 175a of the adjustment pin 175 is engaged with the second side of the second plate 172. The first end 175a of the adjustment pin 175 is threaded and coupled to the housing portion 110 via a corresponding threaded nut 175c. The threaded nut 175c is at the first end 175a of the adjustment pin 175 and is rotatable on the threading of the first end 175a to adjust the axial position of the adjustment pin 175, thereby facilitating control of the axial position of the orbiting scroll 130 via the rest of the thrust bearing assembly 170.

The second end 175b of the adjustment pin 175 sits in a tapered recess 172a in the second side of the second plate 172. The tapered recess 172a has a generally conical shape. More specifically, the second end 175b of the adjustment pin 175 comprises a rounded surface which is engaged with a surface of the second side of the second plate 172 which defines the tapered recess 172a. In this way, the rounded surface of the second end 175b of the adjustment pin 175 and the surface defining the tapered recess 172a together form a ball and socket joint, which enables the second plate 172 and the M2 IB 154

- 9 - second ball bearing cage 173b to articulate/rotate on the first end 175b of the adjusting pin 175.

The first plate 171 , second plate 172, first ball bearing cage 173a, second ball bearing cage 173b and ball bearings 174 are all located within a recess in the base 132 of the orbiting scroll 130. The casing 176 surrounds the adjustment pin 175 and acts as a barrier to prevent escape, from the recess, of lubricant (e.g. oil or grease) used for the ball bearings 174, the first and second bearing cages 173a, 173b, and the first and second plates 171 , 172. The casing 176 comprises a tubular section 176a and a plate section 176b. The tubular section 176a extends axially between the housing portion 110 and the plate section 176b. The plate section 176b has a central hole through which the adjustment pin 175 extends to reach the second plate 172. The plate section 176b is located over the opening of the recess to cover the opening of the recess except for a small gap between the plate section 176b and the adjustment pin 175 due to the central hole. The tubular section 176a abuts against the plate section 176b to fully enclose the recess to prevent escape of lubricant from the recess into other parts of the scroll pump. In order to maintain a tight seal at the interface between the tubular section 176a and the plate section 176b, the casing 176 further comprises an annular elastomeric face seal 177 located at the interface between the tubular section 176a and the plate section 176b. The annular elastomeric face seal 177 extends around the adjustment pin 175 to seal the interface between the tubular section 176a and the plate section 176b.

Figure 3 is a schematic illustration (not to scale) showing a close-up cross- sectional view of an alternative thrust bearing assembly 170 of the noncontacting scroll pump 100. The embodiment of Figure 3 is the same as the embodiment of Figure 2 except that the annular elastomeric face seal 177 of the embodiment of Figure 2 is replaced with a spring loaded ring seal 178 at the interface between the tubular section 176a and the plate section 176b. The spring loaded ring seal 178 extends around the adjustment pin 175 to seal the interface between the tubular section 176a and the plate section 176b. M2 IB 154

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Figure 4 is a schematic illustration (not to scale) showing a close-up cross- sectional view of yet another alternative thrust bearing assembly 170 of the noncontacting scroll pump 100. The embodiment of Figure 4 is the same as the embodiment of Figure 2 except that the annular elastomeric face seal 177 is replaced with a first annular shield 179a and a second annular shield 179b at the interface between the tubular section 176a and the plate section 176b. The first annular shield 179a is an annular lip extending axially from an end of the tubular section 176a towards the plate section 176b and abutting the plate section 176b. The second annular shield 179b is an annular lip extending axially from the plate section 176b towards the tubular section 176a and abutting the tubular section 176a. The first and second annular shields 179a, 179b extend around the adjustment pin 175 to seal the interface between the tubular section 176a and the plate section 176b. The first and second annular shields 179a, 179b form a tight seal by the annular lips overlapping with each other whilst abutting against the plate section 176b and tubular section 176a respectively. In this embodiment, the first annular shield 179a is integrally formed with the tubular section 176a and the second annular shield 179b is integrally formed with the plate section 176b.

Advantageously, in the embodiments of Figures 2 to 4, the use of a sealing structure 177, 178, 179a, 179b to seal the interface between the tubular section 176a and the plate section 176b provides a low cost and compact way of providing a tight seal to prevent escape of lubricant.

Figure 5 is a schematic illustration (not to scale) showing a perspective view of the plurality of thrust bearing assemblies 170 of the non-contacting scroll pump 100. As shown, in this embodiment, the scroll pump 100 comprises three thrust bearing assemblies 170 which evenly angularly distributed around the central rotation axis of the orbiting scroll in a triangular formation to provide a stable axial force on the orbiting scroll 130.

Figure 6 is a schematic illustration (not to scale) showing a close-up perspective view of part of a thrust bearing assembly 170 of the non-contacting scroll pump 100. Specifically, Figure 6 illustrates a close-up view of the first and second M2 IB 154

- 11 - bearing cages 173a, 173b of the thrust bearing assembly 170. As shown, each hole of the first ball bearing cage 173a partially overlaps with a corresponding hole of the second ball bearing cage 173b to form a plurality of hole pairs. The ball bearings 174 are each located within a respective hole pair (only one ball bearing 174 is labelled in Figure 6).

The above-described non-contacting scroll pump 100 may be used as part of a vacuum pumping system including multiple pumps and/or other components.

It will be appreciated that various modifications/deviations may be made to the above described embodiments without departing from the scope of the invention.

In the above-described embodiments, the scroll pump comprises three separate thrust bearing assemblies. However, in other embodiments, the scroll pump comprises a different number of thrust bearing assemblies, e.g. only one, two or more than 3.

In the above-described embodiments, the thrust bearing assembly comprises a plurality of ball bearings. However, in other embodiments, the thrust bearing assembly comprises only one ball bearing.

In the above-described embodiments, the thrust bearing assembly comprises ball bearing cages to constrain the movement of the ball bearings. However, in other embodiments, the ball bearing cages are omitted.

In the above-described embodiments, an elongate adjustment pin is used to couple the housing to the second plate. However, in other embodiments, a different type of coupling structure may be used, e.g. a different type of elongate member. M2 IB 154

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REFERENCE NUMERAL LIST

100: non-contacting scroll pump

110: housing

120: fixed scroll

122: base of fixed scroll

124: spiral wall of fixed scroll

130: orbiting scroll

132: base of orbiting scroll

134: spiral wall of orbiting scroll

140: drive shaft

150: actuator

160: main bearing assembly

170: thrust bearing assembly

171 : first plate

172: second plate

172a: recess

173a: first ball bearing cage

173b: second ball bearing cage

174: ball bearing

175: adjustment pin

175a: first end of adjustment pin

175b: second end of adjustment pin

175c: nut

176: casing

176a: tubular section

176b: plate section

177: elastomeric face seal

178: spring loaded ring seal

179a: first annular shield

179b: second annular shield