Technical Field

The present invention relates to a motor for a vacuum pump, a can for use in a motor for a vacuum pump, a vacuum pump containing a motor, a method for operating said vacuum pump, and a method for assembling a motor.

Background

Vacuum pumps are typically driven by a motor, which may be coupled to a housing defining a portion of the vacuum pump. Vacuum pumps include primary vacuum pumps and secondary vacuum pumps. Primary vacuum pumps are vacuum pumps that exhaust to atmospheric pressure, and can typically evacuate to pressures of about 0.1 mbar. Primary vacuum pumps include, for example, oil-sealed rotary vane pumps, diaphragm pumps, scroll pumps, multi-stage roots pumps, piston pumps, screw pumps, and liquid-ring pumps.

For applications where lower pressures that can be provided by a primary vacuum pump are required, pump systems including a secondary pump may be used. Secondary vacuum pumps are typically operable to evacuate to much lower pressures than primary vacuum pumps. For example, secondary vacuum pumps may be operable to evacuate to ultra-high vacuum pressures (i.e. less than about 10’ ⁷ mbar).

Secondary pumps typically operate as part of a pump system as they may require initial evacuation by a primary vacuum pump and/or another secondary vacuum pump to a required pressure before operation. Examples of secondary pumps include oil diffusion pumps, turbomolecular pumps, mechanical boosters, molecular drag pumps and regenerative pumps.

Typically, the operational rotational speed of a rotor of the motor (i.e. a motor rotor) driving a secondary pump will be greater than that of a rotor of a motor of a primary vacuum pump. For example, the operational rotational speed of a rotor of the motor of a secondary pump may be from about 50,000 RPM to about 100,000 RPM.

In vacuum pumps, particularly secondary vacuum pumps, it is common that the entire motor (i.e. the motor rotor and motor stator) may be incorporated within the vacuum envelope. Therefore, the motor rotor and the motor stator may be exposed to pressures well below ambient pressure when the vacuum envelope is depressurised during operation. The pump and motor may operate via a common rotor shaft arranged within the vacuum envelope. A housing may be provided around the motor to substantially hermetically seal the motor within the vacuum envelope during operation.

However, there are a number of problems associated with such motors of the prior art. For example, as the motor is located within the vacuum envelope and surrounded by the housing, an electrical feed must be provided through the housing to supply power the motor. This may require a complicated housing design having additional seals to maintain the pressure difference between the vacuum envelope and the ambient pressure outside of the vacuum envelope. Such a design may be complex to manufacture and assemble. The housing may also be arranged such that it structurally supports the motor rotor and/or motor stator, which may further complicate design and assembly thereof. Additionally, the housing may require materials capable of conducting heat away from the motor, to prevent over-heating of the motor during operation.

These constraints, among others, may increase the complexity and costs of providing such motors, and thereby the vacuum pump. There is a desire to provide an improved motor for a vacuum pump, having a simplified design and a relatively low cost to manufacture.

The present invention aims to solve, at least in part, these and other problems associated with motors of the prior art.

Summary In an aspect, the present invention provides a motor for a vacuum pump. The motor comprises a motor stator, a motor rotor configured to rotate within the motor stator, and a can. The can is positioned between the motor rotor and the motor stator such that, in use, the can hermetically separates the motor rotor from the motor stator. The can is configured to structurally support the motor rotor and/or the motor stator and/or a rotor bearing.

The motor, or “canned” motor, may be configured to be coupled to a housing of a vacuum pump. Typically, the motor may provide a rotary drive to a rotor of the vacuum pump when in operation. Preferably, the motor may be configured to be coupled to the housing of a secondary vacuum pump, more preferably a turbomolecular pump or a molecular drag pump. For example, the motor may be configured to be coupled to the housing of a Holweck or Siegbahn drag pump. The motor may be a brushless direct-current (DC) motor.

The motor stator may comprise one or more stator coils. Preferably the motor stator may comprise a plurality of stator coils. For example, the motor stator may comprise 3, 4, 6, or 12 stator coils. Each stator coil may comprise a wire, for example a copper wire. Typically, the wire may be wound around a core comprising a ferromagnetic material, for example an iron core. Typically, the stator coils may be spaced circumferentially about the axis of rotation of the motor rotor.

The motor rotor may comprise one or more magnets connected to a rotor shaft. Preferably, the or each magnet may comprise a permanent magnet. Preferably, the or each magnet may comprise a rare-earth magnet, such as a samarium cobalt magnet. The or each permanent magnet may be a ring magnet located about the rotor shaft. The motor rotor may further comprise a sleeve arranged circumferentially about the one or more magnets configured to retain the position of the or each magnet relative to the rotor shaft.

In use, the rotor shaft of the motor rotor may be coupled to a rotor shaft of the pump rotor. Such coupling may be via mechanical gears. Alternatively, the rotor shaft of the motor rotor may be the same component as the rotor shaft of the pump rotor. The motor rotor may be rotatably mounted on one or more rotor bearings. At least one rotor bearing may be located within the motor. Preferably, at least one rotor bearing may be mounted on the can. Additionally, or alternatively, one or more of the rotor bearings may be mounted on a pump housing to which the motor is connected when in use. In an embodiment, the rotor shaft of the motor rotor and the rotor shaft of the pump rotor are the same component, the rotor shaft may be mounted on one rotor bearing mounted on the pump housing, and on a second rotor bearing mounted on the can.

The can may comprise a generally tubular portion configured to surround an end portion of the motor rotor. The generally tubular portion, or tubular portion, may have a circular cross-section, although it will be appreciated by the skilled person that other shapes of cross-section may be used.

The tubular portion may have an internal surface having a radius that is larger than the radially outermost portion of the motor rotor contained within the tubular portion. The radially outermost portion of the motor rotor contained within the tubular portion may be defined by the radially outermost portion of the magnet(s). There may be a clearance gap between the radially outermost portion of the motor rotor and the internal surface of the tubular portion. The tubular portion may have an external surface having a radius that is smaller than the innermost radius of the motor stator. An external surface of the tubular portion may be in direct contact with the motor stator.

The can may further comprise an end portion, i.e. the floor of the can. The end portion may close a first end of the tubular portion. The end portion and the tubular portion may be a single, unitary component, or alternatively, the end portion and the tubular portion may be separate components configured to be connected when in use.

Typically, the can may further comprise a flange portion. The flange portion may be at a second end of the tubular portion, opposite the first end. The flange portion may be configured to couple the tubular portion to a portion of the vacuum pump housing or to a further component when in use. Preferably, the flange portion may be configured to couple the motor to a portion of the vacuum pump housing or to a further component when in use. Advantageously, this may provide for a simplified design and assembly of the motor.

Preferably, the flange portion and the tubular portion are a single, unitary component. More preferably, the flange portion, the tubular portion, and the end portion are a single, unitary component. Advantageously, this may simplify the manufacture of the can, and may enable easy assembly of the motor.

The can is configured to hermetically separate the motor rotor from the motor stator when connected to a vacuum pump housing. The can may be arranged between the motor rotor and motor stator. When the vacuum pump is in operation, the can may hermetically separate the motor rotor from the motor stator. This may be defined as, when the vacuum pump is in operation, a region “outside” of the can may be at ambient pressure, whilst a region “inside” of the can may be at a pressure less than ambient pressure. For example, when the vacuum pump is in operation, the region inside the can may be at a pressure less than about 0.1 mbar, preferably less than about 10’ ⁷ mbar. Ambient pressure may be atmospheric pressure, for example about 1013 mbar.

The motor rotor may be arranged in the region inside the can, whilst the motor stator may be arranged in the region outside the can. When the vacuum pump is in operation, the region inside the can may be depressurised with the pump envelope of the vacuum pump. Advantageously, this may remove the requirement for an electrical feed that passes through the can to the motor stator, as the motor stator is arranged outside of the can. Additionally, arranging the motor stator outside of the can may allow for improved thermal conduction away from the motor stator.

For the purposes of the present invention, the term “structurally support” may be defined as the can being configured to maintain the position of the motor rotor relative to the motor stator, and vice versa. Preferably, the can may be loaded with the mass of the component(s) that it is structurally supporting. Preferably, the can may be configured to structurally support any combination of the motor rotor, the motor stator, and the rotor bearing. Most preferably, the can may be configured to structurally support the motor rotor, the motor stator, and the rotor bearing. The can may provide at least a portion of the vacuum pump housing. The motor may additionally comprise an outer cover configured to protect the motor from damage, preferably the outer cover may not be configured to structurally support motor rotor and/or the motor stator and/or the rotor bearing.

Advantageously, the present invention may remove the requirement for a frame or a motor housing configured to structurally support the motor rotor, and/or the motor stator, and/or the rotor bearing. The present invention may reduce the design complexity and number of components of the motor. This may allow for easier manufacture and assembly of motors according to the present invention. Additionally, the present invention may allow for the production of a lightweight motor for relatively low cost.

When used to drive a rotor of a vacuum pump, particularly a high-speed vacuum pump such as a secondary vacuum pump or turbomolecular pump, the motor rotor may rotate at speeds of from about 50,000 RPM to about 100,000 RPM. Accordingly, the torque requirements from the motor are relatively low, allowing for a relatively large air-gap between the motor rotor and the motor stator. This may enable the can to be positioned between the motor rotor and motor stator, and for the thickness of the wall defining the tubular portion of the can to be increased.

Typically, the can may comprise a polymeric material. For example, the can may comprise polyphenylene sulfide (PPS). Additionally, or alternatively, the can may comprise a metallic, ceramic, and/or composite material. Preferably, the tubular portion of the can may comprise a polymeric material. Preferably, the can may consist of a polymeric material.

The can may comprise a single unitary component. Preferably, the can may comprise a single, unitary polymeric component. Advantageously, the can comprising a polymeric material enables the can to be produced via relatively low- cost manufacturing techniques. For example, the can may be a moulded polymeric component.

Alternatively, the can may comprise a plurality of interconnecting portions.

Typically, the motor rotor may be rotatably mounted on a rotor bearing, and the rotor bearing may be mounted on the can. Specifically, the rotor shaft of the motor rotor may be rotatably mounted on at least one rotor bearing. The rotor bearing or bearings may be located at or immediate to one or both ends of the rotor shaft. Typically, the rotor bearing(s) may be rolling-element bearings, preferably wherein the rolling-elements are balls, cylinders, or needles. The rolling-elements may be located between an inner race and an outer race of the rotor bearing. The rotor bearing may be mounted between the motor rotor and the can. Preferably the inner race of the rotor bearing may be mounted on the motor rotor and the outer race of the rotor bearing may be mounted on the can. Preferably the rotor bearing may be mounted within the tubular portion of the can. The can may be configured to structurally support the rotor bearing, and thereby to structurally support the motor rotor. Advantageously, by mounting the rotor bearing on the can, the motor rotor may be structurally supported by the can.

During use, the axial position of the or each rotor bearing on the motor rotor may be maintained by a rotor bearing biasing member. The rotor bearing biasing member may comprise a coil spring or a wave spring.

Typically, the can may comprise bearing retaining means configured to maintain the position of the rotor bearing relative to the can during operation of the motor. Preferably, the rotor bearing biasing member may be configured to bias the bearing towards the bearing retaining means. The rotor bearing biasing member may comprise a compression spring. Preferably, the rotor bearing biasing member surrounds a portion of the motor rotor. The rotor bearing biasing member may be compressed between the rotor bearing and the can.

Preferably, the bearing retaining means comprises at least one of a recess and/or a protrusion defined by the can. The rotor bearing may be located in the recess, and/or biased against the protrusion. The bearing retaining means may further comprise an O-ring configured to retain the position of the rotor bearing. The bearing may be biased against the bearing retaining means by the rotor bearing biasing member. Advantageously, providing such bearing retaining means may maintain the position of the bearing during operation. Additionally, this may also reduce the number of components of the motor, and may also allow for cheaper and easier manufacture thereof. Incorporating the bearing retaining means into the can may allow for the weight of the motor to be kept low as no motor frame or motor housing may be required.

In some embodiments, the can may comprise a can body and a can cap, wherein the can cap is separable from the can body. The can body may comprise the tubular portion configured to surround the motor rotor, and the can cap may comprise the end portion, both as defined hereinbefore. The can body may further comprise the flange portion configured to couple to a portion of the vacuum pump housing.

The can body may be connected to the can cap by fixing means. The fixing means may comprise, for example, a screw thread arranged on either the can body or can cap, and a corresponding screw thread on the other of the can cap or can body. There may be sealing means provided at the interface between the can body and the can cap, such as an O-ring. The sealing means may be configured to, in use, maintain the pressure difference between the region inside the can and the region outside the can.

In use, the rotor bearing biasing means may be compressed between the rotor bearing and the can cap. Providing a can cap that is separable from the can body may allow for easier assembly of the motor. For example, the can body may be inserted over the motor rotor and rotor bearing, then the rotor bearing biasing means may be inserted into the can body, then the can cap may be attached to the can body. The attachment of the can cap may compress the rotor bearing biasing means ready for operation of the motor.

The can cap may comprise a skirt arranged to surround and/or be surrounded by an end of the tubular portion. The sealing means and/or the fixing means may couple the skirt to the tubular portion. In an embodiment, a screw thread of the fixing means may be arranged on the skirt. The skirt may aid in preventing radial splay of the can body.

The can body and can cap may comprise the same material. Alternatively, the can body may comprise a different material to the can cap. Preferably, the can body and can cap comprise one or more polymeric materials, such as polyphenylene sulfide (PPS).

Such embodiments may allow for easier maintenance of the motor, as the components positioned inside of the can body can be accessed without having to detach the can body from the vacuum pump housing. For example, a rotor bearing may be replaced by simply removing the can cap, without having to disassemble the entire motor or detach the can body from the vacuum pump housing.

Typically, the tubular portion of the can may have a wall thickness of from about 0.7 mm to about 2.5 mm. Preferably, the tubular portion of the can may have a wall thickness of from about 1 mm to about 2 mm. The tubular portion of the can in any embodiment described herein may have such wall thicknesses.

Typically, the motor stator may be mounted on the can. Preferably, the motor stator may be mounted about an external surface of the can. The motor stator may be mounted about the tubular portion of the can. The motor stator may be connected to the tubular portion of the can by fixing means. Preferably, the motor stator may be bonded to the tubular portion of the can. The can may structurally support the motor stator. Advantageously, the mounting of the motor stator onto the can such that the can structurally supports the motor stator may remove the need for a motor housing or frame configured to structurally support the motor stator. Therefore, the motor of the present invention may have a simpler design and be cheaper to manufacture than those of the prior art.

Typically, the can may comprise a conduit configured to allow the pump exhaust to pass through the can. Preferably, the conduit may be located through a flange portion of the can. Advantageously, routing the pump exhaust through the can may simplify the design of the motor, and may ease manufacturing and assembly. Alternatively, the pump exhaust may not pass through the can.

The motor may be configured to be coupled to a molecular drag pump or a turbomolecular pump. For example, the can may be configured to be coupled to a nEXT turbomolecular pump, as produced by Edwards Vacuum.

In another aspect, the present invention provides a motor for a vacuum pump, the motor comprising: a motor stator; a motor rotor configured to rotate within the motor stator; a rotor bearing supporting the motor rotor for rotation relative to the motor stator, and; a can positioned between the motor rotor and the motor stator such that, in use, the can hermetically separates the motor rotor from the motor stator; wherein the can comprises a tubular portion and an end portion for closing one end of the tubular portion, and wherein the rotor bearing is structurally supported by an inner surface of the tubular portion. Preferably the motor stator is structurally supported by an outer surface of the tubular portion.

In another aspect, the present invention provides a motor for a vacuum pump. The motor comprises a motor stator, a motor rotor configured to rotate within the motor stator, and a can. The can is configured to provide a portion of the vacuum pump housing. The can is positioned between the motor rotor and the motor stator such that, in use, the can hermetically separates the motor rotor from the motor stator.

For the avoidance of doubt, the motor according to this aspect may include any feature of the motors described in the preceding aspect.

The can is configured to provide a portion of the vacuum pump housing. Advantageously, the can providing a portion of the vacuum pump housing may reduce the requirement for seals between the vacuum pump housing and the motor. The can may provide a conduit configured to allow the exhaust of the vacuum pump to pass through the can.

In use, the can may be directly connected to a further portion of the vacuum pump housing. Sealing means may be provided between the can and the further vacuum pump housing portion.

Advantageously, by arranging the can to provide a portion of the vacuum pump housing, the motor may be better integrated with the vacuum pump, providing a system (i.e. vacuum pump and motor) with a reduced number of parts. This may also allow for easier manufacture. Furthermore, the present invention may allow for straightforward assembly of the system as the can may be directly connected to the vacuum pump housing.

Typically, the can may be configured to structurally support the motor rotor and/or the motor stator and/or a rotor bearing, as described in the preceding aspect.

The motor may be configured to be coupled to a molecular drag pump or a turbomolecular pump. For example, the can may be configured to be coupled to a nEXT turbomolecular pump, as produced by Edwards Vacuum.

In another aspect, the present invention provides a can for use in a motor for a vacuum pump according to any of preceding aspect or embodiment. The can is configured to be positioned between a motor rotor and a motor stator such that, in use, the can hermetically separates the motor rotor from the motor stator. The can may be as described in any preceding aspect or embodiment.

The can may be produced by one or more injection moulding, machining, additive manufacturing, and/or casting steps. Preferably, the can may be produced as a single, unitary component via a moulding process.

In another aspect, the present invention provides a vacuum pump comprising one or more pump rotors, one or more pump stators, and a motor according to one of the preceding aspects or embodiments. The motor is configured to provide rotary drive to the one or more pump rotors.

The pump rotor(s) and pump stator(s) may be arranged such that, upon rotation of the pump rotor(s) during operation, fluid is conveyed through the vacuum pump from a pump inlet to a pump outlet.

Preferably, the vacuum pump may be a secondary vacuum pump. More preferably, the vacuum pump may be a turbomolecular vacuum pump or a molecular drag vacuum pump. For example, the vacuum pump may be an nEXT turbomolecular pump, as produced by Edwards Vacuum. As discussed previously herein, the torque requirements for the motor of a secondary vacuum pump are relatively low due to the high rotational speeds of the rotor. This may allow for the can to be designed as a structurally supportive component, as the air gap between the motor rotor and motor stator can be larger.

In a further aspect, the present invention provides a method for operating the vacuum pump according to the preceding aspect. The method comprises driving the rotation of the one or more pump rotors with the motor, wherein during operation, the motor stator remains at substantially ambient pressure whilst the motor rotor is exposed to a pressure below ambient pressure, preferably less than about 0.1 mbar, more preferably less than about 0.005 mbar, most preferably less than about 10’ ⁷ mbar.

In a further aspect, the present invention provides a method for assembling a motor according to the aspects and embodiments described herein. The method comprises the steps of: a) providing a motor rotor and a motor stator; b) providing a can; c) arranging the can between the motor rotor and the motor stator, such that the can structurally supports the motor rotor and/or the motor stator and/or the rotor bearing. The method may further comprise the step of loading a rotor bearing into the can such that the rotor bearing is mounted between the motor rotor and the can. Preferably this may involve the rotor bearing being located in or against a recess or protrusion defined by the can. The method may further comprise the step of arranging a rotor bearing biasing member within the can to maintain the axial position of the rotor bearing relative to the motor rotor and the can.

The method may further comprise the step of attaching the can to a vacuum pump housing. Preferably, this may involve attaching a flange of the can to the vacuum pump housing via fixing means. This may further include arranging a seal between the can and the vacuum pump housing to reduce pressure loss at their interface during operation.

In embodiments wherein the can comprises a tubular portion and a cap portion as described previously herein, step (c) may comprise positioning the tubular portion about the motor rotor, optionally inserting a bearing biasing member into the tubular portion such that it abuts against the bearing, and securing the cap portion to the tubular portion.

The method may comprise the step of mounting the motor stator on the can. Preferably this may involve mounting the motor stator to an external surface of the can, more preferably mounting the motor stator about the tubular portion of the can. Preferably, this may involve bonding the motor stator to the can. The motor stator may abut against the flange portion of the can.

Advantageously, the method according to the present invention may allow for more straightforward assembly of the motor.

In another aspect the present invention provides a method for assembling a motor for a vacuum pump, comprising the steps of: a) providing a motor rotor, a motor stator and a rotor bearing; b) providing a can comprising a tubular portion and an end portion; c) arranging the can between the motor rotor and the motor stator such that the can hermetically separates the motor rotor from the motor stator and the rotor bearing is structurally supported by an inner surface of the tubular portion. The motor stator is preferably structurally supported by an outer surface of the tubular portion.

For the avoidance of doubt, all aspects and embodiments described herein may be combined mutatis mutandis.

Brief Description of Figures

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 motor in accordance with an embodiment of the present invention;

Figure 2 shows a cross-sectional view of a vacuum pump including a motor in accordance with an embodiment of the present invention;

Figure 3 shows a cross-sectional view of a can for a motor in accordance with an embodiment of the present invention;

Figure 4 shows a cross-sectional view of a can for a motor in accordance with an alternative embodiment of the present invention;

Detailed Description

Figure 1 shows a cross-sectional view of a motor (1 ) for a vacuum pump in accordance with an embodiment of the present invention. The motor (1 ) comprises a motor stator (2), and a motor rotor (3) configured to rotate within the motor stator (3). The motor (1 ) further comprises a can (4). The can (4) is positioned between the motor rotor (3) and the motor stator (2) such that, when the motor (1 ) is in use, the can (4) hermetically separates the motor rotor (3) from the motor stator (2). In this embodiment, the motor rotor (3) comprises a rotor shaft (5). Mounted upon the rotor shaft (5) is a permanent magnet (6). The permanent magnet (6) is a ring- shaped magnet that circumferentially surrounds the rotor shaft (5). The motor rotor (3) is rotatably mounted on a rotor bearing (7). The rotor bearing (7) is a rolling bearing, having an inner race coupled to the rotor shaft (5) and an outer race coupled to the can (4). An O-ring (8) is arranged within a recess (9) in the can (4), and may aid in retaining the position of the rotor bearing (7) relative to the can (4).

A rotor bearing biasing member (10) is arranged between the rotor bearing (7) and an end portion (11 ) of the can (4). The rotor bearing biasing member (10) is a compression spring configured to load the rotor bearing (7) and to prevent axial movement thereof within the can (4) during operation of the motor.

The rotor bearing (7) enables the motor rotor (3) to rotate relative to the can (4) and the motor stator (2) when in use. The can maintains the position of the motor rotor (3) relative to the motor stator (2) when in use. Therefore, the can (4) structurally supports the motor rotor (3), via the rotor bearing (7). The can (4) also bears the mass of the motor rotor (3) and the motor stator (2) when in use.

The motor stator (2) is directly mounted to the can (4). Specifically, the motor stator

(2) is directly mounted to an outer surface of a tubular portion (12) of the can (4). The can (4) retains the position of the motor stator (2) relative to the motor rotor

(3). Therefore, the can (4) structurally supports the motor stator (2).

The can (4) structurally supports the motor rotor (3), the motor stator (2) and the rotor bearing (7).

The can (4) comprises an end portion (11 ), a tubular portion (12), and a flange portion (13). The flange portion (13) is a radially extending flange, and is configured to couple the can (4), and thereby the motor (1 ), to a vacuum pump when in use. The flange portion (13) comprises a conduit (14) to allow an exhaust of the vacuum pump to pass through the can (4). The can (4) comprises a single, unitary component. Preferably, the can (4) may comprise a polymeric material, for example polyphenylene sulfide (PPS). The can (4) may be produced by injection moulding.

Figure 2 illustrates a cross-sectional view of a vacuum pump (15) including a motor (1 ) in accordance with an embodiment of the present invention. The motor (1 ) is that shown in Figure 1 , so its features will not be restated, and corresponding reference numerals will be used.

The vacuum pump (15) comprises a pump rotor (16) arranged within a pump stator

(17). The pump stator (17) provides the housing of the vacuum pump (15). The pump rotor (16) and pump stator (17) may define therebetween a pump chamber

(18). The vacuum pump (15) further comprises a pump inlet (19) configured to be coupled to a chamber to be evacuated. In use, fluid (e.g. gas) may enter the pump chamber (18) via the pump inlet (19). The vacuum pump (15) further comprises a pump outlet (20), through which the pump exhaust may exit the pump chamber (18).

The rotor shaft (5) of the motor rotor (3) is also the rotor shaft of the pump rotor (16). The rotor shaft (5) is mounted within the vacuum pump (15) on a rotor bearing (21 ). The rotor shaft (5) is also mounted within the can (4) on a rotor bearing (7).

The can (4) is connected to the pump stator (17). Specifically, the flange portion (13) of the can (4) is connected to the pump stator (17). The flange portion (13) is connected to the pump stator (17) via fixing means (not shown). The pump outlet (20) aligns with the conduit (14) in the flange portion (13) of the can (4), such that the pump exhaust passes through the flange portion (13) of the can (4).

In use, the motor rotor (3) rotates and drives the rotation of the pump rotor (16). Thereby, fluid (e.g. gas) is conveyed from the pump inlet (19) through the pump chamber (18) to the pump outlet (20). The can (4) hermetically separates the motor stator (2) from the motor rotor (3). Therefore, the interior of the can (4), containing the motor rotor (3) is depressurised with the pump chamber (18), whilst the exterior of the can (4) remains at ambient pressure. Figure 3 illustrates a cross-sectional view of a can (22) in accordance with an embodiment of the present invention. The can (22) has many similar features to the can (4) as shown in Figures 1 and 2.

The can (22) comprises a tubular portion (23), an end portion (24) and a flange portion (25). The end portion (24) is configured to seal an end of the tubular portion (23). The end portion (24) is located at the opposite end of the tubular portion (23) to the flange portion (25). The flange portion (25) is configured to be connected to a portion of the vacuum pump housing (not shown). Thereby, in use, the interior of the can (22) is hermetically separated from the exterior of the can (22).

The tubular portion (23) comprises a narrowed-wall portion (26), wherein the thickness of the wall defining the can (22) is reduced in comparison to the remainder of the tubular portion (23). Specifically, the thickness of the tubular portion (23) in the narrowed-wall portion (26) is from about 0.7 mm to about 2.5 mm, preferably from about 1 mm to about 2 mm.

In use, the motor stator (not shown) may be mounted on the can about the narrowed-wall portion (26). Due to the positioning of the can (22) between the motor stator and motor rotor (not shown), in use, the can (22) is positioned in the magnetic field generated between the motor rotor and motor stator. Therefore, eddy currents may be generated within the can (22), which can disrupt the magnetic field. The reduction in the thickness of the can (22) at the narrowed-wall portion (26) may reduce the formation of eddy currents and therefore may reduce the disruption of the magnetic field.

In this embodiment, the can (22) is a single, unitary component. Preferably, the can comprises a polymeric material, such as polyphenylene sulfide (PPS).

Figure 4 illustrates a cross-sectional view of a can (27) in accordance with an embodiment of the present invention. In this embodiment, the can (27) comprises a can body (28) and a can cap (29). The can body (28) comprises a tubular portion (30) coupled to a flange portion (31 ). The tubular portion (30) is open at both ends. The tubular portion (30) comprises a recess (31 ) configured to retain the position of a rotor bearing (not shown). The flange portion (31 ) comprises a conduit (32) configured to allow the vacuum pump exhaust to pass through.

The can cap (29) is configured to fit to the end of the can body (28) opposite the flange portion (31 ). Sealing means (33), specifically an 0-ring, are provided at the interface between the can body (28) and the can cap (29). The can cap (29) comprises a skirt (34) arranged to surround the end of the tubular portion (30).

The can body (28) and can cap (29) may comprise the same material, or they may comprise different materials.

For the avoidance of doubt, features of any aspects or embodiments recited herein may be combined mutatis mutandis. It will be appreciated that various modifications may be made to the embodiments shown without departing from the spirit and scope of the invention as defined by the accompanying claims as interpreted under patent law.

Reference Key

1. Motor

2. Motor stator

3. Motor rotor

4. Can

5. Rotor shaft

6. Permanent magnet

7. Rotor bearing

8. O-ring

9. Recess

10. Rotor bearing biasing member

11 . End portion

12. Tubular portion

13. Flange portion

14. Conduit

15. Vacuum pump

16. Pump rotor

17. Pump stator

18. Pump chamber

19. Pump inlet

20. Pump outlet

21 . Rotor bearing

22. Can

23. Tubular portion

24. End portion

25. Flange portion

26. Narrowed-wall portion

27. Can

28. Can body

29. Can cap

30. Tubular portion

31 . Flange portion

32. Conduit

33. Sealing means 34. Skirt