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 thrust bearing assembly comprises a first plate fixed to the orbiting scroll, a second plate spaced apart from the first plate, and a ball 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. 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, wherein the coupling structure comprises a thermal break for reducing heat transfer from the second plate to the coupling structure during operation of the non-contacting scroll pump.

The coupling structure may comprise a pin comprising a hollow section. The hollow section may extend axially from proximate to an end of the pin which is in contact with the second plate. The thermal break may be provided at least partially by the hollow section.

The pin may have the same thermal expansion co-efficient as a section of the housing from which it extends.

The coupling structure may comprise one or more inserts located between the second plate and the rest of the coupling structure, wherein the thermal break is provided at least partially by the one or more inserts.

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.

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 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 assemblies further comprises a coupling structure extending between the housing and the second plate to couple the housing to the second plate, wherein the coupling structure comprises a thermal break for reducing heat transfer from the second plate to the coupling structure during operation of the non-contacting scroll pump. 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 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 perspective view of a plurality of thrust bearing assemblies of the non-contacting scroll pump; and

Figure 4 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 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 embodiment, the drivet 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 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.

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

The adjustment pin 175 has the same thermal expansion co-efficient as the housing portion 110. This is to prevent changes in ambient temperature from expanding the housing portion and the adjustment pin 175 at different rates, which would cause undesirable offsets in the axial position of the orbiting scroll 130. During operation of the scroll pump 100, the orbiting scroll 130, first plate 171 , second plate 172, ball bearing cages 173a, 173b and ball bearings 174 all heat up at a much greater rate than the rate with which the housing portion 110 heats up. The adjustment pin 175 is in thermal contact with the second plate 172 and so is in thermal contact with the hotter components of the scroll pump 100. It is desirable for the adjustment pin 175 to heat up at the substantially the same rate at the housing portion 110 (i.e. slower than the second pad 172) so that the thermal expansion of the adjustment pin 175 can be matched to the thermal expansion of the housing portion 110. Again, this is to prevent undesirable offsets in the axial position of the orbiting scroll 130 during operation of the scroll pump 100.

In order to match the thermal expansion rate of the adjustment pin 175 to the thermal expansion rate of the housing portion 110 during operation, the adjustment pin 175 further comprises a hollow section 300. The hollow section 300 extends axially from the second end 175b such that there is still sufficient material (e.g. at least 1 mm thickness) at the second end 175b to withstand the axial force of being in contact with the second plate 172. The hollow section 300 acts as an insulating thermal break which reduces the transfer of heat from the second plate 172 to the adjustment pin 175 as a whole. This tends to help thermally insulate the adjustment pin 175 from the second pad 172 so that the adjustment pin 175 remains at substantially the same temperature as the housing portion 110. Since the adjustment pin 175 and the housing portion 110 have the same thermal expansion co-efficient, they expand at substantially the same rate.

In this embodiment, the hollow section 300 is cylindrical but it will be appreciated that other shapes may be used provided the hollow section 300 still acts as an appropriate thermal break.

As an alternative or further thermal break to the hollow section 300, the thrust bearing assembly 170 may comprise one or more inserts (not shown) located between the second end 175b of the adjustment pin 175 and the second plate 172. The one or more inserts act as physical barriers thereby providing a thermal break to help reduce heat transfer from the second plate 172 to the adjustment pin 175. The one or more inserts may be formed from steel or ceramic material. The casing 176 surrounds the adjustment pin 175 and acts as a barrier to prevent escape 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. In this embodiment, the casing 176 has a bellows shape.

Figure 3 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 4 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 4 illustrates a close-up view of the first and second 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 4).

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.

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

300: hollow section