GB2595882A

GB2595882A - Vacuum bearing

Info

Publication number: GB2595882A
Application number: GB2008733.4A
Authority: GB
Inventors: James Patey Alexander; Jonathan Grant Nicolas; Bilal Akhtar Muhammad
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2020-06-09
Filing date: 2020-06-09
Publication date: 2021-12-15
Also published as: GB202008733D0

Abstract

The present invention relates to a bearing with a cover which acts to selectively prevent fluid flow through the bearing in a vacuum machine, where one end of the bearing is proximal to a vacuum chamber and the other is distal from the chamber, the cover sealing the outer race to the inner race. The cover may be located distal from the chamber on the seal. The seal may act as an over-pressure relief valve. There may be a non-contact seal located at the opposite end of the bearing. The cover may be at least partially disengaged from one of the races.

Description

Vacuum Bearing

Field

[1] The present invention relates to rolling bearings and, in particular, rolling bearings for vacuum pumps, vacuum pumps, methods of operating a vacuum pump, and methods of assembling a vacuum pump.

Background

[2] Known vacuum pumps comprise a pump mechanism. The pump mechanism may typically comprise one or more rotors housed within a pump chamber and coupled to a rotatable drive shaft. The rotatable drive shaft may be driven by a motor and mounted on one or more rolling bearings.

[3] During operation of the vacuum pump the pressure within the pump chamber will decrease. This results in a pressure difference between the interior of the pump chamber, which is at a relatively low pressure, and a region exterior to the pump chamber, which will be at a relatively high pressure, for instance atmospheric pressure (e.g. 1.013 bar). Accordingly, it is important that unwanted fluid is prevented from entering the pump chamber, for example by leaking across gaskets or other sealing surfaces. Such unwanted fluid ingress may detrimentally affect the performance of the vacuum pump.

[4] Typically, the drive motor is positioned outside of the pump chamber.

Therefore, the drive shaft may extend into the pump chamber through an orifice in chamber wall, providing a potential route for unwanted fluid ingress into the pump chamber. To ameliorate the problem a face seal is typically employed.

[5] Disadvantageously, such a seal may increase the power required from the drive motor to achieve a given speed. Furthermore, during use, increased friction attributable to the seal may contribute to heating within the pump.

[6] In known vacuum pumps, when the pump is switched off, the pressure of the fluid within the pump chamber may gradually increase to be substantially equal to that of the fluid in the region exterior to the pump chamber. A contributing factor to this may be that fluid may leak into the pump chamber through the one or more bearings. This process may typically take a matter of minutes, depending on the volumes of the pump and the chamber being evacuated. It is important that the pressure within the pump chamber does not increase at too fast a rate, as this may result in contaminants from within the pump chamber being forced into the chamber being evacuated.

[7] Ideally, the pressure of the fluid within the pump chamber would be kept at the low pressure indefinitely to ensure that the chamber being evacuated remains free of contaminants. It would therefore be beneficial for a vacuum pump to retain the pressure difference between the pump chamber and the region exterior to the pump chamber for as long as possible.

[8] Thus, there is a requirement for a vacuum pump comprising an improved seal with reduced power losses. Preferably, said improvements may enable a reduction in pump size.

Summary

[9] In a first aspect, the present invention provides a vacuum pump. The vacuum pump comprises a pump mechanism including a pump chamber and a rolling bearing, also referred to as a rolling element bearing. The rolling bearing comprises an inner race, an outer race, and a plurality of rolling elements, the plurality of rolling elements being operatively engaged with said inner race and outer race. The rolling bearing is in fluid communication with the pump chamber. The rolling bearing is arranged such that a first end of the rolling bearing is proximal to the pump chamber and a second end of the rolling bearing is distal to the pump chamber. The bearing further comprises a shield positioned at the first end or the second end of the rolling bearing. The shield is configured to selectively seal the outer race to the inner race.

[10] In embodiments the rolling bearing separates interior of the pump chamber from a volume of relatively high pressure. Preferably, the bearing separates the pump chamber from a further cavity within the vacuum pump. Preferably, when the vacuum pump is in use fluid, e.g. gas, within pump chamber is at a lower pressure than fluid, e.g. gas, within the further cavity. Typically, the further cavity is at atmospheric pressure (e.g. 1.013 bar). The second cavity may be open or closed to the surrounding atmosphere, preferably open thereto.

[11] The vacuum pump may be a positive displacement pump, momentum transfer pump, or a regenerative pump. Preferably the vacuum pump may be selected from the group consisting of a scroll pump, a turbomolecular pump, a roots pump, and the like. Scroll pumps are particularly preferred. The skilled person will appreciate that the present invention may be employed in substantially any pump comprising a rolling bearing, wherein the rolling bearing is exposed to a first pressure at a first end, and a second pressure at a second end, wherein the first pressure is different to the second pressure. The skilled person will further appreciate that the present invention may also be employed in compressor pumps.

[12] The skilled reader will appreciate that the specific configuration of the pump mechanism will depend on the type of vacuum pump that is being employed. Typically, however, the pump mechanism may operate via the interaction between one or more moving components (e.g. a rotor or rotors) with one or more substantially stationary components (e.g. a stator or stators). Typically, the pump mechanism may further comprise drive means, such as an electric motor, coupled to the moving component of the pump mechanism. Typically, the drive means is coupled to the moving component by a drive shaft, sometimes referred to as the rotor shaft.

[13] Preferably the inner race of rolling bearing is coupled to a drive shaft of the vacuum pump. Preferably the outer race is coupled to the outer wall of the pump chamber.

[14] In a scroll pump, the pump mechanism may comprise an orbiting scroll (rotor) and a fixed scroll (stator). Typically, the orbiting scroll is coupled to a motor via a bearing coupled to an eccentric member coupled to a drive shaft. The eccentric member and drive shaft may be separate or unitary structures. Rotation of the drive shaft may impart the orbiting motion on the orbiting scroll.

[15] Generally, the pump chamber is a cavity of a vacuum pump in which the pump mechanism displaces the fluid being pumped. Accordingly, the pump chamber will contain the rotator(s) and stator(s) forming a part of the pump mechanism.

[16] Typically, the pump chamber is defined by one or more chamber walls.

Typically, the one or more chamber walls will substantially surround the pump mechanism. However, it will be appreciated that one or more components of the pump mechanism may themselves define the outer wall of the pump chamber or a portion thereof [17] In a scroll pump, for instance, the pump chamber may be defined by the orbiting scroll and the fixed scroll. Typically, a first orbiting portion of the pump chamber is coupled to a second fixed portion of the pump chamber by one or more gaskets. A first orbiting portion of the pump chamber may be defined by a base plate and/or scroll wall of the orbiting scroll. A second fixed portion of the pump chamber may be defined by the base plate and/or scroll wall of the fixed scroll. Thus, the pumping chamber may be defined by a fixed scroll base plate, a fixed scroll wall, an orbiting scroll base plate, and an orbiting scroll wall.

[18] Typically, the pump chamber comprises one or more inlets for allowing fluid to enter the pump chamber and/or one or more outlets through which fluid exits the pump chamber. Preferably, the pump chamber inlet is positioned upstream of a whole or part of the pump mechanism. The pump mechanism may interact with the fluid to be pumped so as to direct the fluid from the pump chamber inlet to the pump chamber outlet. Typically, the pump chamber inlet(s) or outlet(s) each comprise an aperture in an outer wall of the pump chamber.

[19] In use, the pump chamber inlet may allow fluid to flow from a region exterior to the pump chamber to within the pump chamber. The pump chamber inlet may be in fluid communication with a vacuum chamber (i.e. a further chamber which is going to be evacuated), typically by way of a conduit or channel. Preferably, the vacuum pump is configured to restrict, or substantially prevent, the flow of fluid from within the pump chamber to a region exterior the pump chamber via the inlet. More preferably, the pump chamber inlet may include a non-return valve.

[20] Typically, the pump chamber outlet is configured to allow fluid to flow from within the pump chamber to a region exterior to the pump chamber. Preferably, the pump chamber outlet may be configured to restrict, or substantially prevent, the flow of fluid from a region exterior to the pump chamber to within the pump chamber. More preferably, the pump chamber outlet may comprise a non-return valve, also referred to as an exhaust valve. The non-return valve may be configured to open at a threshold pressure difference. That is to say, when the fluid pressure within the pump chamber exceeds the fluid pressure of a region exterior to the pump chamber by a predetermined value.

[21] Typically, the pump chamber outlet is positioned at or towards a substantially downstream end of the a whole or part of the pump mechanism.

[22] The rolling bearing may comprise an inner race, an outer race, and a plurality of rolling elements operatively engaged with said inner and outer race. The inner race and the outer race may be rotatable relative to each other. Typically, the inner race and the outer race are substantially annular. Typically, in use, the outer race and inner race are substantially coaxially aligned. Typically, they share a common axis of rotation.

[23] Preferably, the rolling elements are substantially uniformly spaced around the inner race and the outer race. A bearing cage may be arranged between the inner race and outer race and may be configured to maintain the substantially uniform circumferential separation of the rolling elements.

[24] Typically, the inner race of the rolling bearing is coupled to a drive shaft of the pump mechanism, preferably directly attached thereto. Preferably, the inner race is coupled to the drive shaft of the pump mechanism via, for example, a press fit, an interference fit, fastening means, or engagement within a corresponding groove of the drive shaft. The drive shaft may comprise a section with increased diameter against which the inner race may axially abut. Additional sealing means, for example a gasket, may be positioned between the inner race of the rolling bearing and the drive shaft of the pump mechanism to aid sealing.

[25] Typically, the outer race of the rolling bearing is coupled to a component of the pump mechanism, preferably a static component of the vacuum pump. For instance, a component of the pump that does not move relative to the drive shaft of the vacuum pump when the vacuum pump is pumping.

[26] For example, in a scroll pump, the component of the pump mechanism to which the outer race is coupled may be the fixed scroll. Preferably, the radially outermost face of the outer race of the rolling bearing is directly attached to the fixed scroll via an interference fit with the fixed scroll. The fixed scroll may comprise a recess configured to receive the rolling bearing. Additionally, or alternatively, further sealing means, for example a gasket, may be positioned between the outer race of the rolling bearing and the component of the pump mechanism to aid sealing.

[27] Additionally, or alternatively, the outer race of the rolling bearing may be coupled to the pump chamber. Preferably, the outer race of the rolling bearing is coupled to a wall of the pump chamber. More preferably, the radially outermost face of the outer race of the rolling bearing is directly attached to a wall of the pump chamber.

[28] Preferably, the outer race of the rolling bearing is coupled to a component of the pump mechanism and/or the pump chamber via, for example, a press fit, an interference fit, fastening means, or engagement within a corresponding groove and/or abutment. Additional sealing means, for example a gasket, may be positioned between the outer race of the rolling bearing and the outer wall of the pump chamber to aid sealing. Most preferably, the outer race of the rolling bearing may be coupled to a component of the pump mechanism and/or the pump chamber via an interference fit.

[29] The rolling bearing may be mounted within the vacuum pump such that it is in fluid communication with the pump chamber. The rolling bearing may be mounted within the vacuum pump such that a first end of the rolling bearing is proximal to the pump chamber, and a second end of the rolling bearing is distal from the pump chamber.

[30] The first end of the rolling bearing may be in fluid communication with the pump chamber of the vacuum pump. For example, the rolling bearing may be mounted such that an inner race of the rolling bearing is coupled to the drive shaft and an outer race of the rolling bearing is coupled to an outer wall of the pump chamber and/or a component of the pump mechanism, such that the first end of the rolling bearing is in fluid communication with the pump chamber. Preferably, the rolling bearing is mounted such that a first end of the rolling bearing defines a portion of the pump chamber.

[31] The second end of the rolling bearing may be distal from the pump chamber with the remainder of the rolling bearing being positioned between the second end of the rolling bearing and the pump chamber. Preferably, the second end of the rolling bearing is in fluid communication with a region exterior to the pump chamber. Preferably, the second end may be in fluid communication with a secondary chamber or cavity that is within the vacuum pump and separated from the pump chamber by the rolling bearing. For example, the secondary chamber may comprise a chamber for housing the drive means.

[32] Typically, the shield of the rolling bearing may comprise a lip seal. Preferably, the shield may be of single lip or double lip construction. The shield may include an elastomeric portion, preferably a nitrile portion. Preferably the lip seal is elastomeric.

[33] In some embodiments, the shield may comprise a relatively rigid structural support portion and a relatively flexible sealing portion. The relatively rigid support portion may comprise a polymeric or metallic material, for example steel. The sealing portion may comprise an elastomeric material. The sealing portion may be configured to sealably engage the inner and/or outer race. In embodiments, the relatively rigid structural portion may be of a substantially annular metallic construction. The relatively flexible sealing portion may comprise nitrile. Typically, the sealing portion is substantially annular and may be coupled to and/or at least partially surround relatively rigid structural portion. Preferably, the relatively flexible sealing portion is in the form of a lip seal.

[34] The shield may be coupled to the inner race or the outer race of the rolling bearing. Preferably the shield is directly connected to the inner race or the outer race of the rolling bearing, for instance via snap fit, securing ring, or a spring. The shield may be directly connected to the inner race or the outer race of the rolling bearing via a snap fit. Preferably, the shield is directly connected to the inner race or the outer race of the rolling bearing by a snap fit.

[35] The shield may extend radially between the outer race and the inner race.

Preferably, the shield is attached to the outer race and extends substantially radially inwardly towards the inner race.

[36] Additionally, or alternatively, the shield is fixed to the inner race or the outer race and selectively sealably engages the other of the inner race or outer race. Preferably, in some configurations, the shield is fixed to the outer race and extends radially inwardly to sealably engage the inner race. This is preferable as the seal will typically remain stationary relative to the inner race during use.

[37] Preferably, the sealable engagement between the shield and the inner or outer race may include engagement between at least seal lip of the shield and a surface of the inner or outer race. Preferably, the sealable engagement may be such that fluid flow between the seal and the inner or outer race is selectively substantially prevented.

[38] In embodiments, the sealable engagement between the shield and the inner or outer race may be achieved by the shield engaging a substantially radially extending face of the inner or outer race. The inner or outer race may comprise a circumferential step comprising the substantially radially extending face. For example, the inner race may comprise a step defining a substantially radially extending face, wherein in use, the shield may sealably engage with the substantially radially extending face.

[39] In some embodiments, the sealable engagement between the shield and the inner or outer race may be achieved by the shield engaging a substantially axially extending face of the inner or outer race. For example, the shield may sealably engage a radially outermost face of the inner race.

[40] Typically, the sealable engagement may restrict, and/or substantially prevent, fluid flow when the inner and outer race are substantially stationary relative to each other. Preferably, the sealable engagement may substantially prevent fluid flow both during use, i.e. rotation of the rolling bearing when the inner race and outer race are in relative motion, and when the inner race and outer race are substantially stationary relative to each other.

[41] The shield may additionally restrict contaminants from entering the rolling bearing. Such contaminants may comprise particulates, such as dust.

[42] The rolling bearing will normally be lubricated. Preferably, the shield may be configured to retain lubricant within the bearing. The lubricant may be a bearing grease.

[43] The relatively flexible sealing portion of the shield may engage the inner race or outer race substantially tangentially thereto. Preferably, the seal lip of the shield may engage the inner race or outer race such that the angle of incidence is from about -20° to about 200, preferably from about -10° to about 10°.

[44] Advantageously, because the shield may selectively seal between the outer race and the inner race, the rolling bearing of the invention may be used to seal the pump chamber from regions exterior to the pump chamber without the need for a separate additional seal, such as a shaft seal. The shaft seal, may be for example a face seal, as is present in vacuum pumps of the prior art. Removal of the additional seal necessarily removes the friction caused by said additional seal and therefore advantageously may reduce the overall power requirements for the pump.

[45] Additionally, by removing the additional seal, the friction associated with that seal no longer contributes towards the heat generated within the pump. In pumps of the prior art, thermal control means may be required to address this additional heat. Whereas, in pumps of the present invention there is a reduced need for such thermal control means within the pump. This may beneficially enable a reduction in the size of the vacuum pump: and reduces part counts and costs.

[46] In general, the selectively sealable shield is positioned at the second end of the rolling bearing, i.e. distal to the pump chamber.

[47] For the purposes of the invention, the first and second ends of the inner and outer races correspond with the first and second ends of the roller bearing. Preferably, the selectively sealable shield may be securely connected at the second end of the outer race and extend substantially radially inwardly such that it may sealably engage with the second end of the inner race. Accordingly, the selectively sealable shield may preferably be positioned at the non-pump side of the rolling bearing.

[48] The rolling bearing may have a sealed configuration and/or an over-pressure configuration.

[49] In the sealed configuration, fluid within the pump chamber may be at a relatively low pressure, and fluid at the non-pump side may be at a relatively high pressure. The selectively sealable shield may restrict, and preferably substantially prevent, the flow of fluid from the second end to the first end of the bearing, e.g. by sealably engaging the inner or outer race.

[50] Preferably, in the sealed configuration, the fluid within the pump chamber may be at a pressure of from about atmospheric pressure (e.g. 1.013 bar) to about 10-3 mbar, preferably from about 20 mbar to about 10-2 mbar. Additionally, or alternatively, fluid at the second end of the rolling bearing may be at about atmospheric pressure (e.g. 1.013 bar).

[51] Additionally, or alternatively, the fluid within the pump chamber may be less than or substantially equal to the pressure of the fluid at the second end of the rolling bearing. By substantially equal to it will be understood that the pressure of the fluid within the pump chamber may be up to about 150 mbar greater than the pressure of the fluid at the second end of the rolling bearing.

[52] Preferably, in the sealed configuration, the selectively sealable shield may be configured such that the shield sealably engages with the inner race of the rolling bearing. More preferably, in the sealed configuration, the selectively sealable shield may be configured such that a sealing portion of the shield sealably engages with a radially extending surface of the inner race of the rolling bearing.

[53] The rolling bearing may be in the sealed configuration when the inner race is moving relative to the outer race and/or when the inner race is substantially stationary relative to the outer race.

[54] In the over-pressure configuration, fluid within the pump chamber may be at a relatively high pressure, and fluid at the non-pump side is at a relatively low pressure. The selectively sealable shield may permit fluid flow from the first end to the second end, e.g. by disengaging from the inner or outer race so as to provide a channel through which fluid may flow.

[55] Preferably, in the over-pressure configuration, the fluid within the pump chamber may be at a greater pressure than fluid on the non-pump side, for instance by at least about 200 mbar.

[56] The bearing may be configured to transition from the sealed configuration to the over-pressure configuration. Typically, this may occur when there is a blockage of an outlet port of the pump chamber, and/or a further fluid restriction downstream of the outlet port. Typically, during normal use of the pump, the bearing will remain in the sealed configuration. In normal use, the over-pressure configuration is unlikely to occur. During the transition deflection of the shield will typically provide a channel through which fluid may pass, typically a substantially annular channel about the outer circumference of the selectively sealable shield.

[57] Preferably, in the over-pressure configuration, the selectively sealable shield may be configured to permit fluid to flow from the first end to the second end of the rolling bearing, such that the pressure of the fluid within the pump chamber will not exceed about 800 mbar greater than the fluid pressure at the non-pump side. More preferably, the selectively sealable shield may be configured to permit fluid to flow from the first end to the second end of the rolling bearing such that the pressure of the fluid within the pump chamber will not exceed about 650 mbar greater than the fluid pressure at the non-pump side. Most preferably, the selectively sealable shield may be configured to permit fluid to flow from the first end to the second end such that the pressure of the fluid within the pump chamber may not exceed about 500 mbar greater than the fluid pressure at the non-pump side.

[58] Advantageously, this may ensure that the components of the pump are not subjected to pressure differences that could potentially cause damage thereto. For example, excessive over-pressure within the pump chamber may lead to bending and/or fracture of housing screws. Thus, the over-pressure configuration may minimise the risk of failure of the components, and accordingly may increase their life span.

[59] A rolling bearing which can provide both the sealed configuration and the over-pressure configuration may advantageously enable the rolling bearing to both restrict fluid ingress into the pump chamber in the sealed configuration, and enable fluid egress from the pump chamber in the over-pressure configuration. This may beneficially allow for efficient pumping, protect components from damage, and reduce the requirement for additional shaft seals.

[60] Typically, the bearing may further comprise a non-contact shield at the first end.

The non-contact shield may extend between the outer race and inner race. Preferably, the non-contact shield may be substantially annular.

[61] The non-contact shield may be coupled to one of the inner or outer race. As the name suggests, preferably the non-contact shield does not engage, or otherwise contact, the other of the inner race or outer race. Preferably the non-contact shield is coupled to the outer race. Preferably, the non-contact shield may extend substantially radially inwardly from the outer race. Typically, the non-contact shield provides a substantially annular channel through which gaseous fluid may flow.

[62] The non-contact shield may be fixed to the inner race or outer race by securing means. Preferably the securing means may comprise a spring, or a snap fit. Alternatively, the non-contact shield may be integrally formed with the inner race or outer race as a single unitary component.

[63] Typically, the non-contact shield may retain lubricant within the rolling bearing.

[64] The selectively sealable shield may be substantially annular. Preferably, the selectively sealable shield may comprise one or more substantially annular components. Alternatively, the selectively sealable shield may comprise a plurality of part-annular segments that together form a substantially annular component.

[65] Typically, the selectively sealable shield may be pivotally coupled to the inner race or outer race. Preferably, the selectively sealable shield may be pivotally coupled to the outer race.

[66] Typically, in the sealed configuration of the bearing, the selectively sealable shield may be sealably engaged with the inner race or the outer race, preferably the inner race.

[67] Typically, the selectively sealable shield may be pivotably mounted to the inner or outer race by a relatively flexible portion of the selectively sealable shield. Preferably, the relatively flexible portion may be a region of the selectively sealable shield with narrower thickness. Additionally, or alternatively, the relatively flexible portion may comprise an elastomeric material. The relatively flexible portion may be configured to flex 11.

when the bearing is exposed to a predetermined pressure difference between the first end and the second end of the rolling bearing. Typically, so as to break the seal radially opposing end of the shield and provide a channel through which gas may pass.

[68] Advantageously, said pivotable mounting of the selectively sealable shield to the inner or outer race may enable the selectively sealable shield to reversibly transition the bearing between a sealed configuration and an over-pressure configuration.

[69] Preferably, the selectively sealable shield may be biased towards a sealed configuration. Said biasing may occur as a result of biasing means, such as a spring, or alternatively due to the rigidity of the selectively sealable shield.

[70] As discussed above, the vacuum pump outlet may comprise an exhaust valve.

Typically the exhaust valve is downstream of the pump chamber. The exhaust valve may be configured to open at or above a threshold pressure difference between the fluid in the pump chamber and fluid on the egress side. The selectively sealable shield of the bearing may be configured to transition from the sealed configuration to the over-pressure configuration when the pressure difference between fluid at the first end of the bearing and fluid at the second end of the bearing is greater than the threshold pressure difference of the exhaust valve of the pump.

[71] Typically, during normal operation of the vacuum pump, the pressure difference between fluid at the first end of the bearing and fluid at the second end of the bearing is less than the threshold pressure difference of the exhaust valve of the pump. Accordingly, the selectively sealable shield will not normally transition from the sealed configuration to the over-pressure configuration during normal use.

[72] Preferably, during normal use of the vacuum pump, the pressure difference between the fluid at the first end of the bearing and fluid at the second end of the bearing may be less than about 200 mbar.

[73] Preferably, the pressure difference required to open the exhaust valve may be lower than the pressure difference required for the selectively sealable shield to transition from the sealed configuration to the over-pressure configuration. For example, the pressure difference required to open the exhaust valve may from about 0 mbar about 200 mbar, and the pressure difference required for the selectively sealable shield to transition from the sealed configuration to the over-pressure configuration may be from about 200 mbar to about 500 mbar.

[74] Advantageously, this may ensure that during normal operation, substantially all fluid exiting the pump chamber may pass through the exhaust valve. Preferably, during normal operation, the fluid flow rate through the exhaust valve may be sufficient such that pressure difference does not rise above the threshold to trigger a transition of the selectively sealable shield to the over-pressure configuration.

[75] An over-pressure configuration may occur, for example, if there is a blockage of the exhaust port. The blockage may be a partial blockage wherein some fluid may exit the pump chamber through the exhaust valve; or a total blockage wherein substantially no fluid may exit the pump chamber through the exhaust valve. Alternatively, an overpressure configuration may be triggered by a downstream fluid flow restriction caused by a narrow pipe, a silencer, or a blockage of a component downstream of the pump chamber exhaust valve.

[76] In such scenarios, the pressure difference between fluid at the first end of the bearing and fluid at the second end of the bearing may exceed the threshold pressure difference and therefore be sufficient for the selectively sealable shield to transition from the sealed configuration to the over-pressure configuration.

[77] Advantageously, this may prevent an unwanted pressure build-up within the pump chamber that may cause damage to components of the vacuum pump, and may even lead to failure of components. For example, if the pressure within the pump chamber exceeds a certain value, the housing screws within the pump may fracture.

[78] Typically, the fluid may be a gas.

[79] The rolling bearing may further comprise a second selectively sealable shield. The second selectively sealable shield may be positioned on the other end of the rolling bearing from the first selectively sealable shield [80] The rolling bearing may comprise a first selectively sealable shield at a first end of the rolling bearing, and a second selectively sealable shield at the second end of the rolling bearing. Typically, in such configurations, the rolling bearing may not comprise a non-contact shield.

[81] Typically, in embodiments wherein the rolling bearing comprises first and second selectively sealable shields, the rolling bearing may be configured to substantially prevent fluid flow between the first end of the bearing and the second end of the bearing.

[82] Advantageously, this may provide improved sealing to enable lower pressures to be achieved within the pump chamber, as fluid leakage across the seal may be reduced.

[83] Such configurations may advantageously enable a more gradual pressure increase within the pump chamber when the vacuum pump is switched off.

[84] In use, the inner race may be configured to rotate about the central axis of the rolling bearing and the outer race may be configured to remain substantially stationary. Preferably, the selectively sealable shield may be configured to remain substantially stationary relative to said central axis.

[85] Preferably, in configurations with two selectively sealable shields, both selectively sealable shields may be configured to remain substantially stationary relative to said axis.

[86] Typically, the vacuum pump may be a scroll pump.

[87] Typically, the rolling elements may be balls.

[88] Typically, there may be from about 4 and about 20 rolling elements within the rolling bearing, preferably from about 6 to about 12 rolling elements, for example 7 rolling elements.

[89] In a further aspect, the present invention provides a method of assembling a vacuum pump. The method comprises providing a vacuum pump, preferably a scroll pump. The method further comprises installing a roller bearing. The roller bearing may be installed on a rotor shaft of the vacuum pump. The roller bearing comprises an inner race, an outer race, and a plurality of rolling elements operatively engaged between said inner race and outer race. The rolling bearing may be in fluid communication with the pump chamber and arranged such that a first end of the rolling bearing is on a pump side, and a second end of the rolling bearing is on a non-pump side. The bearing further comprises a shield positioned at the first end or the second end of the rolling bearing. VVherein the shield is configured to selectively seal the outer race to the inner race.

Brief Description of the Figures

[90] Preferred features of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a cross-sectional view of a scroll pump according to the prior art.

Figure 2 shows a cross-sectional view of a rolling bearing according to the prior art.

Figures 3a and 3b show cross-sectional views of a rolling bearing as found in embodiments of the present invention.

Figure 4 shows a cross-sectional view of a rolling bearing as found in a further embodiment of the present invention.

Figures 5 show a cross-sectional view of a rolling bearing as found in an embodiment of the present invention.

Detailed Description

[91] Figure 1 shows a known scroll pump (1). The scroll pump (1) comprises a pump housing (2), and a drive shaft (3). The drive shaft (3) may, in use, be driven by a motor (4) such that the drive shaft (3) may rotate.

[92] The drive shaft (3) may comprise two or more portions. A first portion (3a) may rotate about its central axis. A second portion (3b) may have a central axis that is substantially eccentric from, but preferably substantially parallel to, the axis of rotation of the first portion (3a). Preferably, the first portion (3a) and second portion (3b) may be integrally formed as a single unitary component.

[93] The drive shaft (3) may be coupled to an orbiting scroll (5). Preferably, the drive shaft (3) may be coupled to the orbiting scroll (5) such that, in use, rotation of the shaft (3) may impart an orbiting motion to the orbiting scroll (5) relative to a fixed scroll (6).

[94] In use, the orbital motion of the orbiting scroll (5) relative to the fixed scroll (6) may pump fluid along a flow path between a pump inlet (7) and a pump outlet (8).

[95] The orbiting scroll (5) may comprise an orbiting scroll wall (9). The orbiting scroll wall (9) may extend from an orbiting base plate (10). Preferably the orbiting scroll wall (9) may extend from the orbiting base plate (10) in a direction substantially parallel to the orbit axis of the orbiting scroll (5).

[96] Similarly, the fixed scroll (6) may comprise a fixed scroll wall (11). The fixed scroll wall (11) may extend from a fixed base plate (12). Preferably, the fixed scroll wall (11) may extend from the fixed base plate (12) in a direction substantially parallel to the central axis of the fixed scroll (6).

[97] A pump chamber (13) may be defined by the orbiting scroll (5), the fixed scroll (6), and a portion of the outer wall of the pump housing (2). Preferably, the pump chamber (13) may be defined by a portion of the outer wall of the pump housing (2), the orbiting base plate (10) and orbiting scroll wall (9), and the fixed base plate (12) and fixed scroll wall (11).

[98] The pump chamber (13) may be positioned between, and fluidly connected to, the pump inlet (7) and pump outlet (8). In use, a first fluid pressure may be exhibited within the pump chamber (13). Typically said first fluid pressure may be from about 10-2 mbar to about 20 mbar.

[99] Typically, the pump inlet (7) may be in the form an aperture or conduit in a wall of the pump chamber (13). Preferably, the pump inlet (7) may include a non-return valve. Generally, in use, the inlet will be in fluid communication with the chamber which is to be evacuated (not shown).

[100] The pump outlet (8) may in include an aperture in the outer wall of the pump chamber (13). Preferably, the pump outlet (8) may be in the form of a conduit withing the fixed scroll (6). Generally, the pump outlet (8) includes a non-return valve (not shown). The pump outlet (8) may be coupled to a second pump (not shown).

[101] Typically, the pump inlet (7) may be at or towards a first end of the pumping chamber (13), and the pump outlet (8) may be at or towards a second end of the pumping chamber (13). Preferably, the second end may be downstream of the first end.

[102] There may be cavities within the vacuum pump region exterior to the pump chamber (13) that, in use, are at a relatively higher pressure compared to that within the pump chamber, for example in the motor housing (14). Typically, said fluid pressure in said cavities may be about atmospheric pressure (e.g. 1.013 bar).

[103] A first bearing (15) may support the drive shaft (3) for rotation relative to the fixed scroll (6). Preferably, the first bearing (15) may be coupled to the first portion (3a) of the drive shaft (3). More preferably, an inner race of the first bearing (15) may be coupled to the first portion (3a) of the drive shaft (3).

[104] Typically, the first bearing (15) may be coupled to the drive shaft (3), preferably the first portion (3a) of the drive shaft (3), by a press-fit. Preferably, the inner race of the first bearing (15) may be coupled to the first portion (3a) of the drive shaft (3) by a press-fit.

[105] The first bearing (15) may be coupled to the housing (2), and/or to the fixed scroll (6). Preferably, the first bearing (15) may be coupled to the fixed base plate (12) of the fixed scroll (6). Preferably, an outer race of the first bearing (15) may be coupled to the fixed base plate (12) of the fixed scroll (6).

[106] Typically, the first bearing (15) may be coupled to the fixed base plate (12) of the fixed scroll (6) via an interference fit. Preferably, the outer race of the first bearing (15) may be coupled to the fixed base plate (12) of the fixed scroll (6) via an interference fit.

[107] A first shaft seal (16) may be located between the drive shaft (3) and the fixed scroll (6). Preferably, the first shaft seal (16) may extend substantially radially outwardly from the drive shaft (3) to the fixed base plate (12) of the fixed scroll (6). The first shaft seal (16) may restrict, preferably substantially prevent, fluid, typically gas, from passing between the pump chamber (13) and the region exterior to the pump chamber (14) across said first shaft seal (16).

[108] A second bearing (17) may operatively connect the drive shaft (3) to the orbiting scroll (5). Preferably, the second bearing (17) may be coupled to the second portion (3b) of the drive shaft (3). More preferably, an inner race of the second bearing (17) may be coupled to the second portion (3b) of the drive shaft (3). Typically, the inner race of the second bearing (17) may be coupled to the second portion (3b) of the drive shaft via a press fit.

[109] Typically, the outer race of the second bearing (17) may be coupled to the orbiting scroll (5). Preferably, the outer race of the second bearing (17) may be coupled to the orbiting base plate (10) of the orbiting scroll (5).

[110] The second bearing (17) may enable the drive shaft (3), particularly the second portion (3b) of the drive shaft (3), to rotate relative to the orbiting scroll (5). Thereby enabling an orbital motion to be imparted to the orbiting scroll (5) from the rotary motion of the drive shaft (3).

[111] A second shaft seal (18) may be located between the orbiting scroll (5) and the drive shaft (3). Preferably, the second shaft seal (18) may extend substantially radially between the drive shaft (3) and the orbiting scroll (5). More preferably, the second shaft seal (18) may extend substantially radially outwardly from the drive shaft (3) to the orbiting scroll (5). The second shaft seal (18) may substantially prevent fluid, typically gas, from flowing into the pump chamber (13) across said second shaft seal (18).

[112] Typically, a counterweight (19) may be arranged to counterbalance the weight of the orbiting components of the pump, including the orbiting scroll (5) and second portion (3b) of the drive shaft. Preferably, the counterweight (19) may be coupled to the orbiting scroll (5) and the drive shaft (3), such that it may rotate therewith. Preferably, the counterweight (19) may comprise an extension from the second portion (3b) of the drive shaft. More preferably, said counterweight may extend from the second portion (3b) in a direction substantially radial to the central axis, and opposite to the direction of eccentricity from the central axis of the second portion (3b).

[113] An anti-rotation device (20) may connect the orbiting scroll (5) to the pump housing (2). The anti-rotation device (20) may be configured to substantially prevent rotation of the orbiting scroll (5), but to allow orbiting motion of the orbiting scroll (5) during use. The anti-rotation device (20) may be substantially lubricant free. In this example, the anti-rotation device (20) may be made from a polymeric material, and may be a one-piece polymer component.

[114] Figure 2 illustrates a cross-sectional view of a portion of a rolling bearing

according to the prior art.

[115] Such a rolling bearing may be suitable for use as the first bearing (15) or second bearing (17) as shown in Figure 1.

[116] The rolling bearing may comprise an inner race (37). The inner race (37) may be substantially annular. The inner race (37) may be configured to be coupled to a drive shaft of a vacuum pump (not shown) when in use. Preferably, in use, the inner race (37) may be coupled to a drive shaft of the vacuum pump via a press fit.

[117] Typically, the inner race (37) may comprise a metallic material, preferably steel, for example carbon chromium steel.

[118] The rolling bearing may further comprise an outer race (38). The outer race (38) may be configured to be coupled to the housing of a vacuum pump (not shown), or alternatively to a different component of the vacuum pump, for example the fixed base plate of fixed scroll. The outer race (38) may be substantially annular. Preferably, in use, the outer race (38) may be coupled to the housing or fixed scroll of the vacuum pump via an interference fit.

[119] Typically, the outer race (38) may comprise a metallic material, preferably steel, for example carbon chromium steel.

[120] The rolling bearing may further comprise rolling elements (39,40). Each rolling element (39,40) may operatively engage the inner (37) and outer (38) races.

[121] The rolling bearing may comprise from about 6 to about 20 rolling elements (39,40), preferably from about 6 to about 12 rolling elements (39,40), for example 7 rolling elements (39,40). The rolling elements (39,40) may be balls.

[122] The rolling elements (39,40) may comprise a metallic, polymeric, and/or ceramic material. Preferably, the rolling elements (39,40) comprise hardened chrome steel.

[123] The plurality of rolling elements (39,40) may be interspaced about the rolling bearing. The plurality of rolling elements (39,40) may be spaced about the outermost circumference of the inner race (37) by a bearing cage (41), also known as a ball bearing retainer or ball bearing separator. The bearing cage (41) may be configured to ensure substantially uniform spacing of the rolling elements (39,40), which may increase rolling efficiency of the rolling elements (39,40) and reduce vibration.

[124] The rolling bearing may have a central axis (X), about which, in use, the inner (37) and/or outer (38) races may rotate. The central axis (X) may be substantially coaxial with the central axis of the inner race (37) and/or outer race (38).

[125] The rolling bearing may have a first axial end (A), and a second axial end (B).

Wherein the first (A) and second (B) axial ends are substantially opposite each other.

[126] The rolling bearing may comprise a first non-contact shield (42). The first non-contact shield (42) may be positioned at a first axial end (A) of the rolling bearing. Preferably, the first non-contact shield (42) may extend between the outer race (38) and inner race (37).

[127] The first non-contact shield (42) may be substantially annular. The first non-contact shield (42) may be coupled to the outer race (38), preferably about the inner circumference of said outer race (38). Typically, the first non-contact shield (42) may extend substantially radially inwardly from the inner circumference of the outer race (38). Typically, the non-contact shields (42,43) may not operatively engage the inner race (37) to allows communication between a region exterior to the bearing and interior thereto.

[128] Typically, the first non-contact shield (42) may be secured to the outer race (38) by a spring or snap-fit. Alternatively, the first non-contact shield (42) may be integrally formed with the outer race (38) as a single unitary component.

[129] The rolling bearing may comprise a second non-contact shield (43). The second non-contact shield (43) may be positioned at a second axial end (B) of the rolling bearing. Preferably, the second non-contact shield (43) may extend between the outer race (38) and inner race (37).

[130] The second non-contact shield (43) may be substantially annular. Preferably, the second non-contact shield (43) may have substantially identical dimensions as the first non-contact shield (42). The second non-contact shield (43) may be coupled to the outer race (38), preferably about the inner circumference of said outer race (38). Typically, the second non-contact shield (43) may extend substantially radially inwardly from the inner circumference of the outer race (38). Typically, the second non-contact shield (43) will not operatively engage the inner race (37).

[131] Typically, the second non-contact shield (43) may be secured to the outer race (38) by a spring or snap-fit. Alternatively, the second non-contact shield (43) may be integrally formed with the outer race (38) as a single unitary component.

[132] Typically, the first (42) and second (43) non-contact shields may be arranged such that the rolling elements (39,40) may be positioned between said first (42) and second (43) non-contact shields in an axial direction.

[133] Typically, the first non-contact shield (42) may comprise a metallic or polymeric material, preferably a metallic material. Preferably, the second non-contact shield (43) may comprise the same material as the first non-contact shield (42).

[134] The first (42) and second (43) non-contact shields may be configured to reduce ingress of contaminants into the rolling bearing. Contaminants may include particulates whose presence may cause wear. Such wear may be detrimental to the rolling efficiency of the rolling bearing, and may even lead to premature failure of one or more components, for example the rolling elements (39,40), the inner race (37), and/or the outer race (38).

[135] Additionally, or alternatively, the first (42) and second (43) non-contact shields may be configured to reduce lubricant egress from within the rolling bearing. Lubricant may be employed to enable more efficient rolling of the rolling elements (39,40) within the rolling bearing.

[136] However, the first (42) and/or second (43) non-contact shields may not substantially reduce fluid flow, especially gaseous flow, between the first (A) and second (B) axial ends of the rolling bearing. Therefore, the first (42) and/or second (43) non-contact shields may not maintain an appreciable pressure difference between said first (A) and second (B) axial ends of the rolling bearing.

[137] Accordingly, in use, fluid may flow between the first axial end (A) and the second axial end (B) of the rolling bearing relatively unimpeded. Thus, when such a rolling bearing is positioned within a vacuum pump, for example a scroll pump, an additional seal may be required to maintain a pressure difference between a region within a pump chamber and a region exterior to said pump chamber.

[138] Figure 3a provides a cross-section of a rolling according to the present invention.

[139] The rolling bearing is substantially similar to that described above in Figure 2.

[140] The rolling bearing may exhibit, at a first axial end (A), a non-contact shield (28). Alternatively, the non-contact shield (28) may instead be at a second axial end (B). Preferably, the non-contact shield (28) may extend between the outer race (22) and inner race (21) of the rolling bearing.

[141] The non-contact shield (28) may be substantially annular. The non-contact shield (28) may be coupled to the outer race (22), preferably at or towards an innermost surface (26) of said outer race (22). Typically, the non-contact shield (28) may extend substantially radially inwardly from the outer race (22). Preferably, the non-contact shield (28) extends substantially radially inwardly towards an outermost surface (27) of the inner race (21). Typically, the non-contact shield (28) may not operatively engage the inner race (21).

[142] Typically, the non-contact shield (28) may be secured to the outer race (22) by a spring clip or snap fit. Alternatively, the non-contact shield (28) may be integrally formed with the outer race (22) as a single unitary component.

[143] The rolling bearing may further comprise a selectively sealable shield (29) at an opposite axial end of the rolling bearing to the non-contact shield (28). For example, the selectively sealable shield (29) may be at a second axial end (B) of the rolling bearing. Conversely, if the non-contact shield (28) were positioned at the second axial end (B) of the rolling bearing, then the selectively sealable shield (29) may be positioned at the first axial end (A) of the rolling bearing.

[144] Typically, the selectively sealable shield (29) may be substantially annular.

Preferably, the selectively sealable shield (29) may be fixedly attached to the outer race (22). Preferably, the selectively sealable shield (29) may extend substantially radially inwardly from the outer race (22).

[145] Typically, the selectively sealable shield (29) operatively engages the inner race (21) to form a seal. In this embodiment, the selectively sealable shield (29) is operatively engaged with an axially extending face of the inner race (21).

[146] Typically, the selectively sealable shield (29) may be fixedly attached to the outer race (22). Preferably, the selectively sealable shield (29) may be fixedly attached to the outer race (22) by means of a spring clip or a snap fit. Alternatively, the selectively sealable shield (29) and the outer race (22) may be integrally formed as a single, unitary component.

[147] The selectively sealable shield (29) may comprise a single component, or alternatively, may comprise two or more parts. For example, the selectively sealable shield (29) may comprise a relatively rigid structural portion (not shown) comprising a polymeric or metallic material, and a relatively flexible sealing portion (not shown) comprising an elastomeric material. Preferably, the structural portion may comprise steel, and/or the sealing portion may comprise nitrile.

[148] In use, the selectively sealable shield (29) may substantially limit the ingress of contaminants into the rolling bearing. Furthermore, the selectively sealable shield (29) may substantially prevent fluid flow from a second axial end (B) of the rolling bearing to a first axial end (A) of the rolling bearing. Said seal may be achieved by the engagement between the selectively sealable shield (29) and the inner race (21). Preferably, said seal may be achieved by the engagement of a sealing lip of the selectively sealable shield (29) with the inner race (21). Preferably, the selectively sealable shield (29) may be biased into engagement with the inner race (21).

[149] In the embodiment of Figure 3a, the selectively sealable shield (29) is shown in engagement with a substantially axially extending surface of the inner race (21).

[150] Figure 3b shows a portion of a cross-sectional view of an alternative embodiment of a rolling bearing according to the present invention, wherein the inner race (21) comprises a step (30). The step comprises a substantially radially extending surface (31) against which the selectively sealable shield (29) may be configured to engage. The step (30) may preferably extend about the entire circumference of the inner race (21).

[151] Beneficially, the engagement of the selectively sealable shield (29) with the substantially radially extending surface (31) may provide improved sealing.

[152] The prevention of fluid flow of the selectively sealable shield (29) is described in further detail in relation to Figure 5 below.

[153] Figure 4 illustrates a cross-sectional view of an alternative embodiment of a rolling bearing according to the present invention.

[154] The rolling bearing is substantially the same as the rolling bearing of Figure 3, but differs in that the rolling bearing of Figure 4 has a selectively sealable shield (32) at both the first axial end (A) and the second axial end (B) of the rolling bearing. In this embodiment, the rolling bearing has a first selectively sealable shield (29) at a second axial end (B), and a second selectively sealable shield (32) substantially opposite the first selectively sealable shield (29) at the first axial end (A) of the rolling bearing.

[155] Typically, the first (29) and second (32) selectively sealable shields may be substantially annular. Preferably, the first (29) and second (32) selectively sealable shields may be fixedly attached to the outer race (22). Preferably, the first (29) and second (32) selectively sealable shields may extend substantially radially inwardly from the outer race (22).

[156] Typically, the first (29) and second (32) selectively sealable shields may operatively engage the inner race (21). Preferably, the first (29) and second (32) selectively sealable shields may operatively engage the inner race (21) about the outer circumference of the inner race (21).

[157] Alternatively, the skilled person will appreciate that the inner race (21) may comprise one or more steps as shown in Figure 3b such that the first (29) and/or second (32) selectively sealable shield may engage will respective radially extending surfaces of steps.

[158] Typically, the first (29) and/or second (32) selectively sealable shields may be fixedly attached to the outer race (22) by means of a spring clip or snap fit. Additionally, or alternatively, the first (29) and/or second (32) selectively sealable shields and the outer race (22) may be integrally formed as a single, unitary component.

[159] The first (29) and second (32) selectively sealable shields may each comprise a single component, or alternatively, may comprise two or more parts.

[160] In use, the first (29) and second (32) selectively sealable shields may substantially prevent ingress of contaminants into the rolling bearing. Furthermore, the first (29) and second (32) selectively sealable shields may substantially prevent fluid flow between the first (A) and second (B) axial ends of the rolling bearing, in either direction.

[161] Figure 5 shows a cross-sectional view of a rolling bearing in a vacuum pump according to the present invention. The vacuum pump may a pump as shown in Figure 1.

[162] The rolling bearing is identical to that defined above in relation to Figure 3a.

[163] The inner race (21) may be coupled to a drive shaft (33) of the vacuum pump. Preferably, the inner race (21) may be coupled to the drive shaft (33) by a press fit. The inner race (21) may be coupled to an outer surface of the drive shaft (33) such that, in use, the inner race (21) may rotate with the rotation of the drive shaft (33).

[164] Preferably, the rolling bearing may be mounted onto the drive shaft (33) such that the central axis (X) of the rolling bearing is substantially coaxial with a central axis of the drive shaft (33) or portion of the drive shaft with which it is attached.

[165] The outer race (22) may be coupled to a pump housing (34) of the vacuum pump. Preferably, the outer race (22) may be coupled to a surface of the pump housing (34) by an interference fit.

[166] The rolling elements (23,24) may operatively engage the inner race (21) and outer race (22). Preferably, in use, when the drive shaft (33) is rotating, the inner race (21) may rotate with the drive shaft (33), and the rolling elements (23,24) may rotate and/or travel about the rolling bearing. The outer race (22) may remain substantially stationary in relation to the pump housing (34).

[167] In alternative embodiments, the outer race (22) may rotate whilst the inner race (21) remains substantially stationary.

[168] The rolling bearing may be arranged within the vacuum pump to selectively seal first cavity of relatively low pressure from a second cavity of relatively high pressure.

[169] Thus, a first axial end (A) of the rolling bearing may be proximal the first cavity and may be fluidly exposed to said first cavity (35) within the vacuum pump. Preferably, the first cavity (35) may a pump chamber of the vacuum pump. In use, the first cavity (35) may comprise fluid at a first pressure.

[170] The second axial end (B) of the rolling bearing may be distal to the first chamber and may be fluidly exposed to a second cavity (36). Said second cavity (36) may be within the vacuum pump, but selectively sealed from the first cavity (35) by the rolling bearing. For example, the second cavity (36) may be defined by the motor housing of the vacuum pump. In use, the second cavity (36) may comprise fluid at a second pressure, typically a higher pressure than the first pressure.

[171] The rolling bearing may comprise a non-contact shield (28) at a first axial end (A). The rolling bearing may further comprise a selectively sealable shield (29) at a second axial end (B).

[172] The rolling bearing may have a sealed configuration and an over-pressure configuration.

[173] The sealed configuration may be defined as when the fluid within the first cavity (35) is at a relatively low pressure, and the fluid within the second cavity (36) is at a relatively high pressure.

[174] Typically, when the rolling bearing is in the sealed configuration, and the pump is in use, the pressure of the fluid in the first cavity (35) may be from about 10-2 mbar to about 20 mbar. When the vacuum pump is pumping, the pressure of the fluid within the first cavity (35) may vary.

[175] Typically, when the rolling bearing is in the sealed configuration, the pressure of the fluid in the second cavity (36) may be about atmospheric pressure (e.g. 1.013 bar).

[176] As described in previous embodiments, the selectively sealable shield (29) may be coupled to the outer race (22), and preferably may extend substantially radially inwardly therefrom. The selectively sealable shield (29) may operatively engage the inner race (21), preferably an outer surface of the inner race (21).

[177] In the sealed configuration, the selectively sealable shield (29) may operatively engage the inner race (21) to form a seal. Preferably, a sealing lip of the selectively sealable shield (29) may operatively engage the inner race (21) to form a seal.

[178] The selectively sealable shield (29) is pivotally mounted so that it can move between the sealed configuration and the over-pressure configuration. Preferably, the selectively sealable shield (29) may be biased towards the sealed configuration, e.g. into engagement with the inner race (21).

[179] The sealing surface of the selectively sealable shield (29) may be configured so as to engage a substantially axially extending surface of the inner race (21), or, preferably, a substantially radially extending surface of the inner race.

[180] Said sealed configuration may ensure that substantially no fluid flow may occur across the bearing from the cavity having a relatively high pressure, to the cavity having a relatively low pressure. In this instance, there may be substantially no fluid flow from the second cavity (36) to the first cavity (35).

[181] There may also be substantially no fluid flow from the first cavity (35) to the second cavity (36) in the sealed configuration.

[182] Typically, the fluid may be gas. Preferably air or nitrogen.

[183] Typically, the selectively sealable shield (29) may operatively engage the inner race (21) to substantially prevent fluid flow even when the pump is in operation, i.e. when the inner race (21) is rotating relative to the selectively sealable shield (29).

[184] The over-pressure configuration may occur when the fluid within the first cavity (35) is at a relatively high pressure, and the fluid within the second cavity (36) is at a relatively low pressure.

[185] Typically, when the rolling bearing is in the over-pressure configuration, the pressure of the fluid within the first cavity may be from about 1.3 bar or greater. If the first cavity is the pump chamber, such a relatively high pressure may result from a blockage of the pump outlet of the pump chamber.

[186] Typically, when the rolling bearing is in the over-pressure configuration, the pressure of the fluid within the second cavity may be about atmospheric pressure (e.g. 1.013 bar).

[187] In the over-pressure configuration, the selectively sealable shield (29) may move, preferably pivot or deflect, to an over-pressure position such that the selectively sealable shield (29) is no longer sealed against the inner race (21). At this point, fluid may flow from a first cavity (35) to the second cavity (36).

[188] Preferably, in the over-pressure configuration, although the selectively sealable shield may allow fluid to flow from the first cavity (35) to the second cavity (36). The selectively sealable shield (29) and/or non-contact shield (28) may substantially prevent ingress of contaminants into the bearing, and/or egress of lubricant from within the bearing Reference Numeral Key 1. Scroll pump 2. Pump housing 3. Drive shaft a. First portion b. Second portion 4. Motor 5. Orbiting scroll 6. Fixed scroll 7. Pump inlet 8. Pump outlet 9. Orbiting scroll wall 10. Orbiting base plate 11. Fixed scroll wall 12. Fixed base plate 13. Pumping chamber 14. Motor housing 15. First bearing 16. First shaft seal 17. Second bearing 18. Second shaft seal 19. Counterweight 20. Anti-rotation device 21. Inner race 22. Outer race 23. Rolling element 24. Rolling element 25. Bearing cage 26. Surface 27. Surface 28. Non-sealable shield 29. Selectively sealable shield 30. Step 31. Radially extending surface 32. Selectively sealable shield 33. Drive shaft 34. Pump housing 35. First volume 36. Second volume 37. Inner race 38. Outer race 39. Rolling element 40. Rolling element 41. Bearing cage 42. Non-contact shield 43. Non-contact shield

Claims

Claims 1 A vacuum pump comprising a pump mechanism including a pump chamber and a rolling bearing; wherein the rolling bearing comprises an inner race, an outer race, a plurality of rolling elements operatively engaged between said inner race and outer race, wherein the rolling bearing is in fluid communication with the pump chamber and arranged such that a first end of the rolling bearing is proximal to the pump chamber, and a second end of the rolling bearing is distal to the pump chamber; and wherein the bearing further comprises a single selectively sealable shield positioned at either the first end or the second end of the rolling bearing configured to selectively seal the outer race to the inner race.
2. The vacuum pump according to claim 1, wherein the selectively sealable shield is positioned at the second end of the rolling bearing.
3 The vacuum pump according to claim 2, wherein the rolling bearing has a sealed configuration and/or an over-pressure configuration; wherein, in the sealed configuration, fluid within the pump chamber is at a relatively low pressure, and fluid at a non-pump side of the bearing is at a relatively high pressure, and wherein the selectively sealable shield substantially prevents fluid flow from second end to the first end; and/or wherein, in the over-pressure configuration, fluid within the pump chamber is at a relatively high pressure, and fluid at the non-pump side is at a relatively low pressure, and wherein the selectively sealable shield permits fluid flow from the first end to the second end.
4. The vacuum pump according to either of claims 2 or 3, wherein the bearing further comprises a non-contact seal at the first end.
5. The vacuum pump according to either of claims 3 or 4, wherein the selectively sealable shield is pivotally mounted the inner race or outer race.
6 The vacuum pump according to claim 3 or 4 or 5, wherein, in the over-pressure configuration, the selectively sealable shield is at least partially disengaged from the inner race and/or outer race, preferably the inner race.
7 The vacuum pump according to any of claims 3 to 6, wherein the pump chamber comprises an exhaust valve, wherein the exhaust valve is configured to open at or above a threshold pressure difference between fluid in the pump chamber and fluid on an exhaust egress side of the valve, and wherein the selectively sealable shield is configured such that transition from the sealed configuration to the over-pressure configuration occurs when the pressure difference between fluid at the first end of the bearing and fluid at the second end of the bearing is greater than the threshold pressure difference of the exhaust valve of the pump.
8. The vacuum pump according to any preceding claim, wherein the selectively sealable shield is substantially annular.
9 The vacuum pump according to claim 1, wherein the rolling bearing further comprises a second selectively sealable shield, the second selectively sealable shield being positioned on the other end of the rolling bearing from the first selectively sealable shield.
10. The vacuum pump according to claim 9, wherein the rolling bearing is configured to substantially prevent fluid flow from both the first end of the bearing to the second end of the bearing and the second end of the bearing to the first end of the bearing.
11. The vacuum pump according to any preceding claim, wherein, in use, the inner race is configured to rotate about the central axis of the rolling bearing and the outer race is configured to remain substantially stationary; preferably wherein the selectively sealable shield is configured to remain substantially stationary relative to said axis.
12. The vacuum pump according to any preceding claim wherein the selectively sealable shield comprises a first relatively flexible sealing portion and a second relatively rigid support portion.
13. The vacuum pump according to any preceding claim, wherein the vacuum pump is a scroll pump.
14. The vacuum pump according to any preceding claim, wherein the rolling elements are balls.A method of assembling a vacuum pump comprising providing a vacuum pump with a rotor shaft and attaching a rolling bearing to the vacuum pump rotor shaft, the rolling bearing comprising an inner race, an outer race, a plurality of rolling elements operatively engaged between said inner race and outer race, wherein the rolling bearing is in fluid communication with the pump chamber and arranged such that a first end of the rolling bearing is proximal the pump chamber, and a second end of the rolling bearing is distal to the pump chamber; and wherein the bearing further comprises a shield positioned at the first end or the second end of the rolling bearing configured to selectively seal the outer race to the inner race.