Patent Description:
Vacuum pumps, such as turbomolecular pumps, comprise a rotor comprising a plurality of discs mounted on a rotor shaft for rotation relative to a plurality of stator discs disposed in interleaving relationship with the rotor discs. The rotor shaft is supported by a bearing arrangement that may comprise two bearings located at or intermediate respective ends of the shaft. The upper bearing may be in the form of a magnetic bearing and the lower bearing is typically a rolling bearing.

A typical rolling bearing comprises an inner race fixed relative to the rotor shaft, an outer race and a plurality of rolling elements located between the races for allowing relative rotation of the inner race and the outer race. To prevent mutual contact between the rolling elements they are often guided and evenly spaced by a cage. Adequate lubrication is important to ensure accurate and reliable operation of rolling bearings. The main purpose of the lubricant is to establish a load-carrying film to separate the bearing components in rolling and sliding contact in order to minimise friction and wear. Other purposes include the prevention of oxidation or corrosion of the bearing components, the formation of a barrier to contaminants and the transfer of heat away from the bearing components. The lubricant is generally in the form of either oil or grease (a mixture of oil and a thickening agent).

Vacuum pumps using oil-lubricated bearings require an oil feed system to feed oil between the contact areas of the bearing. This enables the oil to perform cooling as well as lubrication and thereby permits the bearings to run at a faster speed. Turbomolecular vacuum pumps have traditionally used a wicking system for supplying oil to a rolling bearing. In such a system, one or more felt wicks are supplied by an oil reservoir and feed oil via one or more stacked felts in a felt stack to a conical "oil feed" nut mounted on the shaft. The felt wicks may lay against respective major surfaces of the staked felts in the felt stack so that the felt wick is sandwiched between stacked felts in the felt stack. This enables oil to wick from the reservoir, via the felt wicks, to the stacked felts and feed that oil to the nut mounted on the shaft. When the shaft rotates, oil travels along the conical surface of the nut to the bearing. The oil then passes through the bearing and is returned to the reservoir under the influence of gravity to be recirculated.

Documents <CIT>, <CIT> and <CIT> disclose oil feed assemblies known from the prior art.

It is desired to provide an improved oil feel system.

According to the invention defined by claim <NUM>, there is provided an oil feed assembly for a vacuum pump, comprising: an oil feeder located for feeding oil to one side of a bearing of the vacuum pump; an oil sump located on the one side of the bearing and configured to receive excess oil from the oil feeder; and a venting bypass conduit fluidly coupled with the oil sump and with another side of the bearing, the venting bypass conduit having an inlet located at an elevated position above each face of the oil sump and configured to convey gas from the oil sump to the another side of the bearing.

The invention recognises that a problem with existing oil feed assemblies is that when the vacuum pump pumps down, gas trapped within the oil feed system can cause oil to be lost. This loss occurs because the gas flowing out of the oil feed system can remove oil with it, which prevents the oil from being captured for recirculation. In time, this leads to insufficient oil being present in the oil feed system, which dries out and results in damage to the pump bearings.

Accordingly, an oil feed assembly is provided. The oil feed assembly is for a vacuum pump. The oil feed assembly comprises an oil feeder which is located or configured to feed oil to a first side of a bearing of the vacuum pump. The oil feed assembly comprises an oil sump, chamber or pot. The oil sump is located or positioned on the first side of the bearing. The oil sump is configured or arranged to receive or hold excess or unretained oil which escapes from the oil feeder. The oil feed assembly comprises a venting bypass conduit which is in fluid communication with the oil sump. The venting bypass conduit is also in fluid communication with a second side of the bearing. The venting bypass conduit has an inlet which is located or arranged at an elevated, raised or offset position from each floor, wall or face of the oil sump. The venting bypass conduit is configured or arranged to convey or communicate gas from the oil sump to the second side of the bearing. In this way, the venting bypass conduit provides an alternative path which allows gas within the oil sump to escape during pump-down. The location of the inlet to that venting bypass conduit helps to prevent oil within the oil sump from escaping with the gas travelling through the venting bypass conduit. This helps to prevent loss of oil from the oil feeder and prolongs the life of the bearings.

In one embodiment which is not claimed, the elevated position is higher than an expected depth of the excess oil. Accordingly, the inlet may be positioned at a height or location which is above the expected height of any excess oil within the oil sump. This helps to ensure that any oil is prevented from being drawn into the venting bypass conduit.

In one embodiment, the inlet is elevated in an axial direction with respect an axis of the bearing. Accordingly, the inlet may be positioned further along the axial direction of the bearing than the floor of the oil sump.

In one embodiment, the inlet is orientated in the axial direction with respect an axis of the bearing.

In one embodiment, the inlet is elevated in a radial direction with respect an axis of the bearing.

In one embodiment, the inlet is orientated in the radial direction.

According to the invention, the inlet is located at the elevated position above each floor of the oil sump. Accordingly, the inlet may be positioned above every floor, wall or face of the oil sump. This helps to ensure that oil is prevented from escaping the oil sump irrespective of the orientation of the oil feed assembly.

In one embodiment which is not claimed, the inlet comprises drip edges configured to direct oil away from the inlet. Providing drip edges helps to prevent any oil in the vicinity of the inlet escaping through the venting bypass conduit.

According to the invention, the venting bypass conduit has a sump section defining the inlet, the sump section extending from at least one face of the oil sump.

Accordingly, the venting bypass conduit may have a first portion which provides the inlet and which extends from a floor of the oil sump.

In one embodiment which is not claimed, the sump section extends further than the expected depth of the excess oil. Accordingly, the sump section may have height and/or length which is greater than the expected depth of the excess oil.

In one embodiment, wherein the sump section extends in an axial direction with respect to an axis of the bearing.

In one embodiment, the sump section extends in a radial direction with respect to an axis of the bearing.

In one embodiment, the sump section is rounded to resist gathering of oil. Accordingly, the sump section may be shaped to prevent oil from gathering.

In one embodiment, the venting bypass conduit comprises a gallery section fluidly coupled with the sump section, extending around the oil feed cap. Accordingly, the sump section may be connected with the gallery section which surrounds the oil sump.

In one embodiment, the gallery section comprises an annulus extending circumferentially, concentric with the bearing. Accordingly, the gallery section may be ring-shaped and surround the oil sump.

In one embodiment, the oil feed assembly may comprise a plurality of sump sections, each defining one the inlet, each sump section being fluidly coupled with the gallery section. Accordingly, more than one sump section may be provided feed a common gallery section. This increases the volume of the venting bypass conduit within the oil sump and reduces the flow rate of gas from the oil sump through the inlets during pump-down.

In one embodiment, the venting bypass conduit comprises a coupling section fluidly coupled with the gallery section.

In one embodiment, the coupling section fluidly couples with the other side of the bearing.

In one embodiment which is not claimed, the coupling section extends axially with respect to an axis of the bearing.

In one embodiment which is not claimed, the coupling section is circumferentially offset from the sump section.

In one embodiment, the sump section and one part of the gallery section are formed as a first unitary part, and the coupling section and another part of the gallery section are formed as a second unitary part. Accordingly, the gallery section may be formed from at least two parts which couple together to form the gallery section. This simplifies manufacture of the gallery section.

In one embodiment, the oil sump defines at least one recess to facilitate flow of gas past the oil feeder. Providing recesses helps to facilitate the flow of gas out of the sump section.

There is also provided a vacuum pump comprising a bearing and the oil feed assembly of the invention.

Features of the dependent claims may be combined with features of the independent claim explicitly set out in the claims.

Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide an oil feed assembly used to feed and recirculate oil to a bearing of a rotating machine such as a vacuum pump. Typically, the assembly is provided within a cap which is fitted to the vacuum pump. The cap has a number of wicks which extend in to a reservoir holding oil used to lubricate the bearing of the vacuum pump. As mentioned above, the oil flows up the wicks and into a series of stacked felts. The stacked felts provide oil to the bearing. When the cap is attached to the vacuum pump, a void, chamber or oil sump holding the felts is sealed by the vacuum pump. When the vacuum pump pumps down, the gas within the void is evacuated by the vacuum pump. Conventionally, such evacuation would occur through the bearing being lubricated by the oil feeder system. However, embodiments provide a bypass conduit which fluidly couples the void with the vacuum pump. This provides an alternative path for gas within the void to be evacuated. The bypass conduit is provided with an inlet within the void which is located so as to help prevent any oil within the void from being removed with the gas during pump-down.

According to the invention, the inlet is located at a position above any face, wall or floor of the void sump on which oil may gather. It will be appreciated that the oil may gather on different faces, depending on the orientation of the vacuum pump. This helps to prevent loss of the oil, which prolongs the life of the bearing and the vacuum pump.

<FIG> shows an oil feed cap <NUM> which feeds oil to a bearing of a vacuum pump (not shown). The oil feed cap <NUM> has a number of wick holders <NUM> which extend into an oil feed reservoir within the vacuum pump.

As can be seen in <FIG>, the wick holders <NUM> retain a wick <NUM> which conveys oil from the reservoir within the vacuum pump to a bearing aperture <NUM> which receives the conical surface of the nut of the bearing, thereby feeding oil to the bearing. A number of coupling section conduits <NUM> are formed in the oil feed cap <NUM>, which are in fluid communication with the vacuum pump.

As can be seen in <FIG>, the wicks <NUM> are received by a stack of felts <NUM> which are stacked within a sump region <NUM> within the oil feed cap <NUM>. A gallery section <NUM> extends around the sump region <NUM>.

As can be seen in <FIG> (which has the wick holders <NUM> and associated structure removed to improve clarity), the sump region <NUM> contains a sump section <NUM> (which forms the first part of the bypass conduit) which extends radially inwards, towards the centre of the sump region <NUM> and which intersects the stack of felts <NUM>. The sump section <NUM> defines an inlet <NUM>. The inlet <NUM> is elevated above a first face <NUM> of the sump region <NUM> (defined by a circular plate), elevated above a second face (not shown - defined by an opposing circular plate supporting the wick holders <NUM>) and elevated above a third face <NUM> (defined by a tubular wall extending between the first face <NUM> and the third face). Hence, as can be seen in <FIG> and <FIG>, should oil from the stack of felts <NUM> gather on the first face <NUM>, the second face (not shown) or the third face <NUM>, then the location of the inlet <NUM>, which is raised off each of these faces, will impair or even prevent the flow of oil into the sump section <NUM>. This helps to prevent loss of oil from the oil feed. The surface of the sump section <NUM> is rounded to help prevent the collection of oil. Also, the sump section <NUM> in the vicinity of the inlet <NUM> may be provided with drip edges to help prevent oil gathered on the sump section <NUM> from entering the inlet <NUM>.

As can be seen in <FIG>, the bypass conduit defined by the sump section <NUM> fluidly couples with a gallery section <NUM> (which forms the second part of the bypass conduit) which comprises an annular chamber which concentrically surrounds the sump region <NUM>. The coupling section conduits <NUM> (which forms the third part of the bypass conduit) are fluidly coupled with the gallery section <NUM>. Although in this embodiment one of the coupling section conduits <NUM> is radially aligned with the sump section <NUM>, in other embodiments the coupling section conduit <NUM> is not radially aligned with the sump section <NUM>. That is to say that the coupling section conduit <NUM> may be circumferentially offset from the sump section <NUM>.

In operation, when the vacuum pump is activated, gas within the sump region <NUM> is evacuated and flows primarily through the inlet <NUM>, along the sump section <NUM>, into the gallery section <NUM> and through the coupling section conduits <NUM> into the vacuum pump. As mentioned above, even when the gas flow out of the sump region <NUM> is high, the location of the inlet <NUM> helps to prevent the flow of oil together with the evacuating gas during pump-down.

The exact positioning of the inlet <NUM>, and in particular the depth of the end portion of the sump section <NUM> which defines the inlet <NUM>, is selected based on the expected depth of any excess oil which gathers in the sump region <NUM>. Also, the dimensioning of the inlet <NUM> and the sump section <NUM> is set to control the velocity of the gas being pumped out of the sump region <NUM>.

<FIG> shows an oil feed cap 10A which feeds oil to a bearing of a vacuum pump (not shown). The oil feed cap 10A has a number of wick holders 20A which each receive a wick 30A.

As can be seen in <FIG>, the wicks 30A feed a stack of felts 60A which provide oil to a bearing aperture 40A.

As can be seen in <FIG> (in which the wicks 30A and the stack of felts 60A have been omitted to improve clarity), sump sections 80A (which form the first part of the bypass conduit) are provided, each of which have an inlet 90A. The inlet 90A is orientated in an axial direction with respect to a rotation axis of the bearing. The inlet 90A is located in an elevated position with respect to the first face 100A, the opposing second face (not shown) and the third face 110A.

As can be seen in <FIG>, the sump section <NUM> forms an axially extending conduit section 95A which bends to form a radially extending conduit 97A. Each inlet 90A is in fluid communication with a gallery section 120A (which forms the second part of the bypass conduit) which is an annular chamber which concentrically surrounds the sump region 70A. The gallery section 120A is enclosed by a further structure (not shown) which provides the coupling section conduits (which form the third part of the bypass conduit) in a similar manner to that described above.

A series of recesses 130A are formed in the first face 100A. Recesses 140A extend axially along each side of the sump section 80A.

In operation, when pump-down occurs, gas is evacuated from the sump region 70A, assisted by flowing along the recesses 130A and 140A. The gas flows through the inlet 90A, along the axial section 95A and into the radial section 97A. The gas is then received within the gallery section 120A, flows through the coupling conduits and into the vacuum pump.

As mentioned above, even when the gas flow out of the sump region 70A is high, the location of the inlet 90A helps to prevent the flow of oil together with the evacuating gas during pump-down. It can be seen that due to the location of the inlets <NUM>, irrespective of the orientation of the oil feed cap 10A, the inlets 90A are positioned above the likely level of any excess oil on any face within the sump region 70A, thereby helping to prevent loss of the oil during pump-down.

The exact positioning of the inlets 90A is selected based on the expected depth of any excess oil which gathers in the sump region 70A. Also, the dimensioning of the inlet 90A and the sump section 80A is set to control the velocity of the gas being pumped out of the sump region 70A.

Embodiments according to the invention provide a preferable gas path during pump down of a Turbo pump to prevent the oil in the oil sump reservoir or oil pot being drawn through the bearing and being lost into the pump. Embodiments according to the invention are functional in any orientation and not allow oil to drain out of the oil sump reservoir Unlike in some inverted-running pumping systems where it has been found during harsh pump down some of the oil is migrating through the bearing and being loss into the pump as this is the only exit for the gas from this area of the pump this starves the reservoir of volume of oil, embodiments according to the invention create a preferential gas path to remove the gas trapped in the oil cavity during harsh venting activities. This has been achieved by connection to the gas cavity with the backing line via a complex path to avoid loss of oil for the reservoir.

One embodiment involves slotting the lower oil felt and introducing a square tunnel section into the centre of the pot. A small gas inlet slot is created in the end of the tunnel to accept gas and the end is rounded so any oil that falls on the surface runs around and away from this inlet. The inlet is then connected via an annulus to the base cap and is vented to the wire cavity which in turn is connected to the backing-line.

Another embodiment is an integrated moulded solution that involves intricate channelling. The gas firstly passes along the slots in the base of the oil pot and reaches the inner wall where is passes up the slotted inner wall and joins any gas drawn across the top face of the upper most felt. From this point it is drawn into the four slots, equispaced around the diameter, once drawn into these it is vented to the wire cavity via an external moulded slot formed on a sliding core. This embodiment also includes moulded sealing edges against vacuum loss.

Embodiments seek to avoid the loss of oil through either being drawn directly into the outlet or oil that has pooled running directly into the outlet when stored or run in a non-inverted orientation.

Embodiments save height in the pumping system by cutting the gas exhaust path into the current oil pot constraints i.e. the pump height stays the same.

Claim 1:
An oil feed assembly for a vacuum pump, comprising:
an oil feeder located for feeding oil to one side of a bearing of the vacuum pump;
an oil sump (<NUM>, 70A) located on said one side of said bearing and configured to receive excess oil from said oil feeder; and
a venting bypass conduit (<NUM>, <NUM>, <NUM>, 80A, 120A) fluidly coupled with said oil sump (<NUM>, 70A) and with another side of said bearing, said venting bypass conduit having an inlet (<NUM>, 90A) located at an elevated position above each face (<NUM>, <NUM>, 100A, 110A) of said oil sump and configured to convey gas from said oil sump (<NUM>, 70A) to said another side of said bearing, such that said venting bypass conduit (<NUM>, <NUM>, <NUM>, 80A, 120A) allows gas within said oil sump (<NUM>, 70A) to be evacuated during pump-down,
characterised in that said venting bypass conduit (<NUM>, <NUM>, <NUM>, 80A, 120A) has a sump section (<NUM>, 80A) defining said inlet (<NUM>, 90A), said sump section (<NUM>, 80A) extending from at least one face (<NUM>, <NUM>, 100A, 110A) of said oil sump (<NUM>, 70A).