Centrifugal separator for cleaning gas

Abstract

The present invention relates to a centrifugal separator (1) for cleaning gas containing contaminants The centrifugal separator (1) comprises: a stationary casing (2), enclosing a separation space (3) through which a gas flow is permitted, the casing having a longitudinal centre axis (I), a gas inlet pipe module (180) comprising a gas inlet pipe (18, 18r) permitting supply of the gas to be cleaned to the stationary casing (2), and a fitting (200) connecting the gas inlet pipe module (180) to the stationary casing (2), a rotating member (7) comprising a plurality of separation members (9) arranged in the separation space (3) and being arranged to rotate around an axis (X) of rotation, a gas outlet (28) configured to permit discharge of cleaned gas out from the stationary casing (2), a drainage outlet (25) configured to permit discharge from the centrifugal separator (1) of liquid contaminants that have been separated from the gas, a drive member (22) for rotating the rotating member (7), wherein the centrifugal separator (1) is provided with a heat shield (60) attached to and at least partially covering the gas inlet pipe module (180).

Description

[0001] CENTRIFUGAL SEPARATOR FOR CLEANING GAS

[0002] Field of the Invention

[0003] The present invention relates to the field of centrifugal separators for cleaning a gas containing liquid contaminants. In particular, the present invention relates to a separator for cleaning crankcase gases of an internal combustion engine from oil particles.

[0004] Background of the Invention

[0005] It is well known that a mixture of fluids having different densities may be separated from one another through use of a centrifugal separator. One specific use of such a separator is in the separation of oil from gas vented from a crankcase forming part of an internal combustion engine.

[0006] Regarding this specific use of separators, there can be a tendency for the high-pressure gas found in the combustion chambers of an internal combustion engine to leak past the associated piston rings and into the crankcase of the engine. This continuous leaking of gas into the crankcase can lead to an undesirable increase of pressure within the crankcase and, consequently, to a need to vent gas from the casing. Such gas vented from the crankcase typically carries a quantity of engine oil (as droplets or a fine mist), which is picked up from the reservoir of oil held in the crankcase.

[0007] To allow vented gas to be introduced into the inlet system without also introducing unwanted oil (particularly into a turbocharging system wherein the efficiency of the compressor can be adversely affected by the presence of oil), it is necessary to clean the vented gas (i.e. to remove the oil carried by the gas) prior to the gas being introduced into the inlet system. This cleaning process may be undertaken by a centrifugal separator, which is mounted on or adjacent the crankcase and which directs cleaned gas to the inlet system and directs separated oil back to the crankcase. An example of such a separator is disclosed e.g. in US 8,657,908.

[0008] A centrifugal separator for cleaning crankcase gas is usually fastened to the engine or engine block. The environment by the engine is however rather harsh for the centrifugal separator for example in terms of e.g. heat and vibrations. Therefore, there is a need to improve centrifugal separators so that they may better withstand such harsh conditions.Summary

[0009] It is an object of the invention to at least partly overcome one or more limitations of the prior art. In particular, it is an object to provide a centrifugal separator which withstands harsh conditions in terms of heat and vibrations by engines and which can be adapted to different engines or engine blocks in a flexible way.

[0010] As a first aspect of the invention and as defined in the appended claims, there is provided a centrifugal separator for cleaning gas containing contaminants, said centrifugal separator comprising

[0011] a stationary casing, enclosing a separation space through which a gas flow is permitted, the casing having a longitudinal centre axis and an opening for receiving a gas flow,

[0012] a gas inlet pipe module comprising a gas inlet pipe permitting supply of the gas to be cleaned to the stationary casing, and a fitting connecting the module to the stationary casing onto the opening,

[0013] a rotating member comprising a plurality of separation members arranged in said separation space and being arranged to rotate around an axis (X) of rotation, a gas outlet configured to permit discharge of cleaned gas out from the stationary casing,

[0014] a drainage outlet configured to permit discharge from the centrifugal separator of liquid contaminants that have been separated from the gas,

[0015] a drive member for rotating the rotating member,

[0016] wherein the centrifugal separator is provided with a heat shield attached to and at least partially covering the gas inlet pipe module.

[0017] The heat shield is used to protect the centrifugal separator from heat. By attaching the heat shield to the gas inlet pipe module including the gas inlet pipe, it is possible to adapt the position of the heat shield when adapting the position of the gas inlet pipe. Thus, when the gas inlet module is turned and adapted to different engine designs and / or actual available space around the engine, also the heat shield is moved, since it is attached to the gas inlet pipe module. In contrast, if the heat shield were attached to the stationary casing at a beforehand designed position and the gas inlet pipe position were changed, re-design of the heat shield attachment means would be needed in order to fit the gas inlet pipe at a desired position. By the attachment of the heat shield to the gas inlet pipe module, it can be ensured that the heat shield is always in correct position in respect to the gas inlet Pipe.By the gas inlet pipe module is in this context meant a module comprising a gas inlet pipe that is arranged to be fluidly connected to a crankcase of an internal combustion engine. The gas inlet pipe may comprise a radial portion directed towards and in fluid connection with the crankcase. The gas inlet pipe module may further comprise a portion for guiding the gas to be cleaned from the gas inlet pipe into the stationary casing. The stationary casing may thus comprise on the top portion an opening onto which the gas inlet module may be mounted. The gas inlet pipe module further comprises a fitting, which is aimed for the attachment of the gas inlet pipe module to the stationary casing. The fitting is thus a portion of the gas inlet pipe module and comprises an attachment portion to the stationary casing, for example via a rim that is welded or mechanically fastened to an opening of the stationary casing. The gas inlet pipe module may comprise or consist of a polymeric material and can be molded to its shape. The gas inlet pipe module may be formed as a single unit that is attached to the stationary casing. A non-limiting example of suitable polymeric material includes polyamide / nylon and composite materials thereof.

[0018] The heat shield may be removably attached to the fitting of the gas inlet pipe module. This may facilitate the mounting of the centrifugal separator and maintenance and service of the centrifugal separator.

[0019] The fitting may comprise one or more mounting recesses, such as screw bosses, to which heat shield fastening means are removably fastened. There is thus no need to design new mounting recesses, such as screw bosses, for the attachment of the heat shield in different engine designs, since the mounting recesses are comprised in the gas inlet pipe module.

[0020] The fitting may be connectable to the stationary casing at a chosen mutual angular position in respect to the longitudinal centre axis (I) which coincides with the axis of rotation (X). Thus, it is possible to adapt the gas inlet pipe of the centrifugal separator with the heat shield to different engine designs. This can be obtained by arranging the fitting to comprise a first rim portion and the stationary casing comprise a second rim portion which receives the first rim portion of the fitting, whereby a robust connection can be obtained. The first rim portion and the second rim portion may be fastened to each other by welding / rotary welding. Thereby the number of components in the manufacturing of the centrifugal separator can be decreased. However, in some variants, mechanical means may be used. The firstrim portion may comprise a polymeric material that at least partially melts during rotary welding. Thus, a firm connection can be provided.

[0021] The gas inlet pipe module may comprise a first polymeric material and the stationary casing may comprise a second polymeric material. In this way the different parts of the centrifugal separator can be provided with different characteristics.

[0022] The heat shield may have a shape adapted to the outer contour of the gas inlet pipe module. Thus, the shape may follow the outer contour of the gas inlet pipe both in the axial direction and radial direction. For example, the heat shield may comprise a section having semi-circular shape, while the remaining parts can comprise partial circular sections and / or sections adapted to the outer shape of the gas inlet pipe and / or attachment points of the heat shield.

[0023] The heat shield may be attached to the gas inlet pipe module at a distance from 2-30 mm, or 3 to 25 mm. In this way it can be ensured that the parts of the gas inlet pipe module can be protected against heat, which may be up to about 150°C at the heat shield.

[0024] The heat shield may comprise a heat resisting material having a melting point of 500°C or more and a density of 3000 kg / m3or less. According to an example, the heat shield comprises or is made of aluminium. The heat shield may be made of an aluminium sheet, which may have a thickness of from 0.5 to 3 mm, such as about 1mm. Thereby, the overall weight of the centrifugal separator can be kept low, while sufficient heat protection is obtained. Additionally, by using a lightweight material in the heat shield, it may be possible to decrease the negative effects of the vibrations on the centrifugal separator.

[0025] Aluminium is a lightweight metal with good heat resisting properties and stiffness properties, i.e. it is not easily bent. The stiffness and mass of the centrifugal separator result in a certain eigenfrequency of the centrifugal separator. Mass far away from the moving center affects the eigenfrequency more negatively than mass at the moving center. The heat shield is relatively far away from the moving center and therefore has a more negative effect in eigenfrequency. However, since aluminium has a reduced mass compared to for example steel, the eigenfrequency can be affected positively, and there is no need to add material to other parts of the centrifugal separator to balance for the weight of the heat shield. A target eigenfrequency of the centrifugal separator may be for example more than 250 Hz, for example 300 Hz. Therefore, the lightweight heat shield can further improve thedesign of the centrifugal separator and decrease the negative effects of vibrations on the centrifugal separator.

[0026] The invention also relates to a method for assembling a centrifugal separator for cleaning gas as defined in the appended claims and in the detailed description below.

[0027] As used herein, the term “axially” denotes a direction which is parallel to the rotational axis (X). Accordingly, relative terms such as “above”, “upper”, “top”, “below”, “lower”, and “bottom” refer to relative positions along the rotational axis (X). Correspondingly, the term “radially” denotes a direction extending radially from the rotational axis (X). A “radially inner position” thus refers to a position closer to the rotational axis (X) compared to “a radially outer position”. A radial plane is a plane having its normal parallel to the axis of rotation (X). An axial plane is a plane having its normal perpendicular to the axis of rotation (X).

[0028] The contaminants in the gas may comprise liquid contaminants, such as oil, and soot.

[0029] Consequently, the centrifugal separator may be for separating liquid contaminants, such as oil, from gas. The gas may be crankcase gas of a combustion engine. However, the centrifugal separator may also be suitable for cleaning gases from other sources, for instance the environment of machine tools which frequently contains large amounts of liquid contaminants in the form of oil droplets or oil mist.

[0030] The stationary casing of the centrifugal separator may comprise a surrounding side wall, and first and second end walls, which enclose the separation space. The stationary casing may have a cylindrical shape with circular cross-section having a radius R from the axis (X) of rotation to the surrounding side wall. This radius R may be constant at least with respect to a major part of the circumference of the surrounding side wall. The first and second end walls may thus form an upper end wall and a lower end wall of the cylindrical shaped casing. The stationary casing may also be slightly conical.

[0031] The gas inlet of the centrifugal separator may be arranged through the first end wall or through the surrounding side wall close to the first end wall, thus at the top of the separator, such that gas entering through the gas inlet is directed to the separation space. The downstream portion of the gas inlet may be centred around the axis of rotation (X). The gas inlet may further comprise an upstream portion in the form of a gas inlet pipe or conduit. At least a portion of the gas inlet pipe isaccording to the present disclosure comprised in a separate gas inlet pipe module that is attached to the stationary casing. The gas inlet pipe may extend radially and / or axially from the axis of rotation of the centrifugal separator, or in any other direction therebetween.

[0032] The rotating member is arranged for rotation during operation by means of the drive member. The rotating member comprises a plurality of separation members arranged in the separation space. The separation members of the rotating member are examples of surface-enlarging inserts that promote separation of contaminants from the gas. The separation members may be a stack of separation discs or alternatively one or more filter elements, which are rotatable.

[0033] The plurality of the separation members can be a stack of separation discs, such as a stack of frustoconical separation discs. Such discs may have an outer radius and an inner radius, thus forming a central opening in the disc. The frustoconical separation discs may comprise a flat portion that extend perpendicularly to the axis of rotation (X), and a conical portion that extend outwardly and downwardly or upwardly from the flat portion. The flat portion may be closer to the rotational axis than the frustoconical portion.

[0034] Openings in the flat portion may form part of a central space within the centrifugal separator into which gas to be cleaned is guided from the gas inlet. Thus, gas to be cleaned may be guided into the central space and then to the interspaces formed between the discs in the disc stack. As a complement, or alternative, the central space may also be formed radially within the inner radius of the discs.

[0035] Further, the discs of the stack may be radial discs, in which substantially the whole disc extends in a plane that is perpendicular to the axis of rotation.

[0036] It is also to be understood that the separation members, such as separation discs, not necessarily have to be arranged in a stack. The separation space may for example comprise axial discs, or plates that extend around the axis of rotation. The axial discs or plates may be planar, i.e. extending in planes that are parallel to the axis of rotation. The axial discs or plates may also have a slightly or significantly curved shape, such as an arcuate or spiral shape, as seen in a radial plane.

[0037] In embodiments of the first aspect, the rotating member comprises an axial shaft that is supported by the at least one bearing. The axial shaft may thus be centred at the axis of rotation (X). The separation members may be arranged around such axial shaft.The rotating member may be journaled within the stationary casing via at least one bearing, such as via an upper and lower bearing arranged axially above and below the stack of separation members, respectively.

[0038] The drainage outlet may be arranged in the lower portion of the stationary casing, such as arranged in the second end wall, e.g. at the bottom of the separator.

[0039] Separated contaminants may first be led from the separation space internally to e.g. a drive chamber in which the drive member is arranged. Such drainage may be via internal drainage members formed by several spot shaped through holes of the stationary casing or by a single drainage passage. The drainage from the separation space may also be in an annular collection groove at the inner end wall of the stationary casing. The internal drainage may be arranged such that contaminants, such as oil, are drained though a bearing arranged for journaling the rotating member. If the drive member comprises a turbine wheel driven by an oil jet, the separated contaminants may be drained together with the oil used for driving the oil jet. Then, the drainage outlet of the centrifugal separator may be connected to the drive chamber.

[0040] Thus, the drainage outlet may be arranged axially at and end of the centrifugal separator that is opposite the end through which, or at which, the inlet is arranged. The drainage outlet may be arranged at the axis of rotation or centred around the axis of rotation.

[0041] The outlet for cleaned gas extends through a wall of the stationary casing, such as through a lower portion of the surrounding side wall of the stationary casing. The gas outlet may thus be a conduit for the clean gas having a gas inlet inside the stationary casing and a gas outlet outside of the stationary casing. Such conduit may extend through the stationary casing to a radial position that is larger than the radial position of outer wall of the stationary casing, or to a radial position that is the same as the radial position of the outer wall of the stationary casing. The gas outlet may be connected to a valve, such as a membrane valve, through which clean gas is transported before leaving the centrifugal separator.

[0042] During operation, gas to be cleaned may be directed centrally through the plurality of separation members, such as centrally through the stack of separation discs. In such a set-up, the rotating member may further define a central space formed by at least one through hole in the separation members. This central space is connected to the gas inlet and configured to convey the gas to be cleaned from the gas inlet to the interspaces between the separation members, such as betweenthe interspaces between the discs of a stack of separation discs. A separation disc that may be used as separation member may comprise a central, essentially flat portion perpendicular to the axis of rotation. This portion may comprise the through holes that form part of the central space.

[0043] Thus, the centrifugal separator may be configured to convey gas to be cleaned, such as crankcase gases, from the gas inlet into a central portion of the rotating member. In this manner the crankcase gases may be "pumped" from the central portion of the rotating member into the interspaces between the separation discs in the stack of separation discs by the rotation of the rotating member. Thus, the centrifugal separator may work according to the concurrent flow principle, in which the gas flows in the disc stack from a radial inner part to a radial outer part, which is opposite to a separator operating according to the counter-current flow principle, in which the gas is conducted into the separation space at the periphery and conveyed towards a central part of the separation space.

[0044] The drive member may for example comprise a turbine wheel, rotated by means of an oil jet from the lubrication oil system of the combustion engine or a free jet wheel comprising a blow-back disk. However, the drive member may also be independent of the combustion engine and comprise an electrical motor, a hydraulic motor or a pneumatic motor.

[0045] Brief description of the Drawings

[0046] The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.

[0047] Fig. 1 shows a schematic drawing of the cross-section of an embodiment of a centrifugal separator for cleaning gas.

[0048] Fig. 2a shows a schematic perspective view of an embodiment of a centrifugal separator.

[0049] Fig. 2b shows how the gas inlet pipe module and the stationary casing may be engaged in different angular positions around the longitudinal axis (I) of the stationary casing, which coincides with the axis of rotation (X) shown in Fig. 1.Fig. 3 shows a partially cut schematic perspective view of an embodiment of a centrifugal separator with the gas inlet pipe module attached to the opening of the centrifugal separator.

[0050] Fig. 4 shows a schematic view from above of an embodiment of a centrifugal separator with heat shield attached to the centrifugal separator.

[0051] Fig. 5 shows steps of a method for manufacturing the centrifugal separator shown in Fig. 2a.

[0052] Detailed description

[0053] The centrifugal separator according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.

[0054] Fig. 1 shows schematically a cross-section of a centrifugal separator 1 according to the present disclosure. The centrifugal separator 1 comprises a stationary casing 2, which is configured to be mounted to an internal combustion engine (not shown), such as a diesel engine, at a suitable position, such as on top or at the side of the internal combustion engine or to the engine block of the internal combustion engine.

[0055] The centrifugal separator 1 as disclosed herein may also be suitable for cleaning gases from other sources than internal combustion engines, for instance the environment of machine tools which frequently contains large amounts of liquid contaminants in the form of oil droplets or oil mist.

[0056] The stationary casing 2 encloses a separation space 3 through which a gas flow is permitted. The stationary casing 2 comprises, or is formed by, a surrounding side wall 4, an upper end wall 5 and a lower end wall 6.

[0057] The centrifugal separator 1 comprises a rotating member 7, which is arranged to rotate around a longitudinal axis (X) of rotation. It should be noted that the stationary casing 2 is stationary in relation to the rotating member 7, and preferably in relation to the internal combustion engine to which it may be mounted.

[0058] The stationary casing 2 has a radius from the axis (X) of rotation to the surrounding side wall 4 that is constant at least with respect to a major part of the circumference of the surrounding side wall 4. The surrounding side wall 4 thus has a circular, or substantially, circular cross-section in a radial plane.

[0059] The rotating member 7 comprises a rotatable shaft, i.e., spindle 8 and a separation unit 16 attached to the spindle 8. The separation unit 16 comprises a plurality of separation members 9’, which in the illustrated example are separationdiscs 9’ arranged in a stack 9. The separation discs 9’ of the stack 9 are provided between a top disc 10 and a lower end plate 11. The spindle 8, and thus the rotating member 7, is rotatably supported in the stationary casing 2 by means of an upper bearing 12 and a lower bearing 13, the bearings being arranged one on each axial side of the stack 9 of separation discs 9’, only one of which is provided with a reference sign. However, the bearings 12, 13 could for example both be arranged axially below or above the stack 9 of separation discs 9’.

[0060] The separation discs 9’ of the disc stack 9 are frustoconical and extend outwardly from the direction of the axis of rotation and upwardly from the spindle 8. The separation discs thus comprise a flat portion 9a, which extends perpendicularly to the axis of rotation (X), and a conical portion 9b, that extends outwardly and upwardly, in this case towards a gas inlet 20, which may be a part of a gas inlet pipe module 180 described more in detail below, from the flat portion 9a. As an alternative, the separation discs could also extend outwardly and downwardly, and / or even radially.

[0061] The separation discs of the stack 9 are provided at a distance from each other by means of distance members (not shown) to form interspaces 14 between adjacent separation discs 9, i.e. , an interspace 14 between each pair of adjacent separation discs 9. The axial thickness of each interspace 14 may e.g., be in the order of 0.5-2 mm, such as 1-2 mm.

[0062] The separation discs 9’ of the stack 9 may comprise or be made of plastic or metal. The number of separation discs in the stack 9 is normally higher than indicated in Fig. 1 and may be for instance 50 to 100 separation discs 9 depending on the size of the centrifugal separator 1.

[0063] In the illustrated example, the centrifugal separator 1 comprises an oil nozzle 24 arranged for being connected to an engine oil circuit of an internal combustion engine. During running of the internal combustion engine, oil is pumped through the oil nozzle 24 onto a turbine wheel 22, which is arranged in turbine housing 26. Since turbine wheel 22 is connected to the spindle 8, the rotating member 7, and thus the stack 9 of separation discs 9’, also rotate upon rotation of wheel 22. As an alternative, the centrifugal separator 1 may comprise an electric motor arranged to rotate the spindle 8 and rotating member 7. As a further alternative, the centrifugal separator 3 may comprise a turbine wheel connected to the spindle 8, where the turbine wheel is arranged to be driven by exhaust gases from the internal combustion engine to rotate the spindle 8 and the rotating member 7. The rotatingmember 7 may also be arranged for being rotated by a mechanical drive unit. Thus, the centrifugal separator may comprise a mechanical drive unit for rotating the rotating member 7.

[0064] The rotating member 7 defines a central space 15. The central space 15 is in this example formed by a through hole 150 in each of the separation discs 9. In the embodiments of Fig. 1, the central space 15 is formed by a plurality of through holes 150 (only two of which are depicted by a reference sign), each extending through the top disc 10 and through each of the separation discs 9’, but not through the lower end plate 11. The through holes 150 are arranged in at least partially in the flat portions 9a of the separation discs 9’. The through holes 150 may extend to the conical portion of the separation discs, but the peripheral portion of the discs is solid.

[0065] The gas inlet, or gas inlet 20 extends through the stationary casing 2, and more precisely through upper end wall 5, and is arranged for supplying gas to be cleaned to the separation space 3. The gas inlet 20 is formed by the axially extending gas inlet pipe or conduit 18, which forms an upstream portion, and by through channels 21 that form a downstream portion of the inlet 20.

[0066] The through channels 21 are in fluid connection with the central space 15 and are arranged radially outside the upper bearing 12. Thus, the gas inlet 20 communicates with the central space 15 so that the gas to be cleaned is conveyed from the inlet 20 via the central space 15 to the interspaces 14 of the stack of separation discs 9. The gas inlet 20 is configured to communicate with the crankcase of the combustion engine, or any other source, via the inlet pipe or conduit 18 permitting the supply of crankcase gas from the crankcase to the gas inlet 20 and further to the central space 15 and the interspaces 14 as explained above.

[0067] The centrifugal separator 1 comprises a drainage outlet 29, which is arranged in the lower portion of the stationary casing 2 and configured to permit discharge of liquid contaminants separated from the gas. The drainage outlet 29 is in this embodiment in the form of through holes 150 arranged in the lower end wall 6 so that separated liquid contaminants flow through the lower bearing 13 as they are drained from the separation space 3 to the turbine housing 26. The separated oil, and other particles and / or substances, is led to an oil outlet 25 of the centrifugal separator 1 , which together with oil from the oil nozzle 24 used to drive the wheel 22, may be led back to the engine oil circuit of an internal combustion engine. The drainage outlet 29 in this embodiment is placed centrally on the lower end wall 6. Inalternative embodiments, the drainage outlet 29 may be placed elsewhere on the lower end wall 6.

[0068] The gas outlet tube 28 of the centrifugal separator 1 is arranged through the stationary casing 2 and is configured to permit discharge of cleaned gas.

[0069] During operation of the centrifugal separator as shown in Fig. 1, the rotating member 7 is kept in rotation by the oil nozzle 24 supplying oil against the wheel 22. As an example, the rotational speed may be in the range of 7.500-12.000 rpm.

[0070] Contaminated gas, e.g., crankcase gas from the crankcase of an internal combustion engine, is supplied to the gas inlet 20 via the pipe or conduit 18. This gas is conducted further into the central space 15 and from there into and through the interspaces 14 between the separation discs of the stack 9. Because of the rotation of the rotating member 7 the gas is brought to rotate, whereby it is pumped further on radially outwardly through gaps or interspaces 14.

[0071] During the rotation of the gas in the interspaces 14, solid or liquid particles such as oil suspended in the gas are separated therefrom. The particles settle on the insides of the conical portions 9b of the separation discs and slide or run after that radially outwardly thereon. When the particles and / or liquid drops have reached out to the radial outer edges of the separation discs of the stack 9, they are thrown away from the rotating member 7 and hit the inner surface 40 of the surrounding side wall 4. Separated oil particles may form a film on the inner surface of the stationary casing 2. From there, oil may be pulled by gravity downwardly to bottom end wall 6 and then leave the separation space 3 through the drainage outlet 29. For this purpose, the inner wall of the bottom end wall 6 may be tilted radially inwards, so that oil leaving the surrounding inner wall of the stationary casing 2 may be pulled by gravity towards drainage outlet 29. The path of the contaminants in the gas is schematically illustrated by arrows “D” in Fig. 1.

[0072] Cleaned gas freed from particles and exiting from the stack of separation discs 9 leaves the stationary casing 2 through the gas outlet tube 28. The path of the gas through the centrifugal separator 1 is schematically shown by arrows “C” in Fig. 1.

[0073] The centrifugal separator of Fig. 1 may also comprise a stationary insert 50, which is arranged in a lower portion of the stationary casing 2, and more precisely axially below the stack 9 of separation discs. The stationary insert 50 may be fastened to the surrounding side wall 4 of the stationary casing, and or / to lower end wall 6 via supporting legs (not shown). The stationary insert 50 comprises an outer annular wall member 51 and a central frustoconical cup member 53 with conicallyextending sidewalls. The lower part of the end plate 11 is arranged within the central cup member 53. The annular wall member 51 extends axially downwards from the outer edge of the cup member 53.

[0074] The stationary insert 50 forms a physical barrier between cleaned gas and separated contaminants prior to the cleaned gas and separated contaminants exit the stationary casing 2. For this purpose, the stationary insert 50 is arranged in the stationary housing 2 to form an annular vertical channel 52 for the separated contaminants between the inner surface 40 of the stationary casing 2 and the annular wall member 51 and a flow path for clean gas within the central cup member 53 towards the gas outlet 28. Thus, the annular vertical channel 52 may form an annular slit and, during use of the separator 1, may collect separated oil droplets that run downwards on the inner surface 40 of the surrounding side wall 4 under the action of gravity. Also, the action of a downwards spiralling gas flow may force the oil on the inner surface 40 downwards. The annular vertical channel 52 thus shields the separated liquid particles flowing down on inner wall 40 from the rotating gas, to decrease the risk of separated oil being pulled from the inner wall 40 on its way down to drainage outlet 29. The stationary insert 50 may be a moulded unit, preferably of a polymer or a plastic material.

[0075] As an alternative, the annular wall member 51 could also be left out, so that the stationary insert 50 is mainly defined by the conical cup member which could be sufficient to direct the gas flow in connection to the gas outlet.

[0076] Reference is now made to Fig. 2a, which schematically shows a centrifugal separator 1 for cleaning gas containing contaminants according to an example. The centrifugal separator 1 comprises a substantially circular cylindrical stationary casing 2, as described above. The casing has a longitudinal centre axis (I), which coincides with the axis of rotation (X) shown and explained in connection with the Fig. 1.

[0077] Further, the centrifugal separator 1 comprises a gas inlet pipe module 180, which is attached to the centrifugal separator 1 to the top or upper end wall 5 of the stationary casing 2. The gas inlet pipe module 180 comprises the gas inlet pipe 18, 18r and a fitting 200 which connects the module 180 to the stationary casing 2, more precisely via an opening 500 on the top 5 of the stationary casing 2 (See Fig. 3). The fitting 200 is thus a portion of the gas inlet pipe module that comprises an attachment portion to the stationary casing 2, for example via a rim that is welded to the opening of the stationary casing and as explained more in detail in connectionwith Fig. 3. Alternatively, the fitting 200 comprises sections adapted for mechanical connection to the stationary casing, such as via screws or similar.

[0078] The gas G from an engine (not shown) enters the centrifugal separator 1 in a radial direction via the gas inlet pipe 18 in the gas inlet pipe module 180. Therefore, the gas inlet pipe comprises a gas inlet pipe portion 18r, which extends radially outwards from the longitudinal centre axis (I) and from the fitting 200 to receive the gas from an engine. The gas inlet pipe 18 further comprises the axially extending inlet pipe or conduit portion 18 (Fig. 1), which forms the gas inlet 20 extending through the stationary casing 2, and more precisely through the upper end wall 5 (see Fig. 1).

[0079] Further, according to the invention, the centrifugal separator is provided with a heat shield 60 attached to and at least partially covering the gas inlet pipe module 180. The heat shield is made of a heat-resistant sheet material, such as aluminium sheet. The aluminium sheet may have a thickness of about 0.5 to 3 mm, such as 1 mm. It can be cut and pressed to a suitable shape, which can be principally circular and thus comprise circular sections and sections adapted at least partially to the outer contour of the gas inlet pipe module 180. The heat shield 60 is removably attached to the fitting 200 of the gas inlet pipe module 180. The distance of the heat shield 60 from the gas inlet pipe module and / or the outer contour of the gas inlet pipe module can be from 2-30 mm, such as 3-25mm. In Fig. 2 the heat shield 60 is attached by means of three screws 62 through respective through holes in the heat shield 60. The fitting 200 comprises a corresponding number of mounting recesses, such as screw bosses 64, to which the screws 62 are respectively and removably fastened. The bosses 64 can be attached or integrated in the fitting 200. By bosses in this context are meant protrusions with holes that can accommodate threaded inserts, screws and other mechanical fasteners. The bosses may be cylindrical parts. The bosses may further improve the strength on the part of the fitting 200 when added thereto.

[0080] The fitting 200 with the bosses 64 may comprise or consist of a polymeric material and may be formed by molding, such as injection molding or any other suitable molding technique known in the art. When the heat shield 60 is attached to the gas inlet pipe module 180 and / or the fitting 200 via screws 62 attached to the bosses 64 included therein, the position of the heat shield is constant in respect of the gas inlet pipe 18 and the radial portion 18r thereof. Therefore, there is no need to design new bosses or recesses when the inlet position is turned around thelongitudinal axis (I), as indicated by the arrow “A” in Fig. 2a, when installed to different engine installations. By rotating the gas inlet pipe module 180 around rotational axis (I), as indicated by rotational angle a in Fig. 2b, the heat shield 60 follows with the rotation of the gas inlet pipe module 180 to the variety of positions. Thus, a more flexible design which can be adapted to several engine types is provided.

[0081] The gas inlet pipe module 180 may be a single unit comprising at least a portion of the gas inlet pipe 18. The radial portion 18r may be an integrated part of the gas inlet pipe module 180, and may be connected thereto. The gas inlet pipe module 180 opens to the interior of the stationary casing via the opening 500 on the top 5 of the stationary casing 2. The fitting 200 connects the gas inlet pipe module 180 to the opening 500 on top of the stationary casing, as further illustrated in Fig. 3. The fitting 200 is arranged centrally around the longitudinal axis (I) and the axis of rotation (X). Since the fitting 200 is arranged on top of the stationary casing, it may function as a cover for the inlet 20 of the centrifugal separator 1.

[0082] The fitting 200 may be attached to the stationary casing 2, and the top 5 thereof, at a chosen mutual angular position in respect to the longitudinal centre axis (I) which coincides with the axis of rotation (X), as illustrated and described in connection with Fig. 2b.

[0083] In the shown embodiment in Fig. 3, which is a partial schematic cross-sectional side view of a centrifugal separator 1 comprising the fitting 200. The fitting 200 comprises a first rim portion 601, and the stationary casing 2 and the opening 500 on the top 5 thereof comprises a second rim portion 501. The second rim portion 501 is adapted so that it receives the first rim portion 601 of the fitting 200. The first and second rim portions 601 , 501 are at least partially mating, so that a tight connection between the two parts can be obtained. For example, as shown in Fig. 3, the first rim portion 601 of the fitting 200 is male-shaped and the second rim portion 501 is female-shaped.

[0084] The first rim portion 601 and the second rim portion 501 can be fastened to each other by welding / rotary welding. In rotary welding or rotary friction welding (RFW) one workpiece is rotated relative to another under a compressive axial force, whereby the parts are joined together. This can be a solid-state joining process. Thus, in this process the first rim portion 601 may be rotated at high speed and pressed against the second rim portion 501, which is stationary. The friction generates heat, and the parts are therefore forged together seamlessly and firmly.However, other joining methods could be conceivable, for example rotational molding in which heat is used soften or melt material, which then sticks to another workpiece under rotation. The first rim portion 601 of the fitting 200 may comprise a first polymeric material that melts during rotary welding and thereby sticks to the second rim portion 501 and provides a firm seal.

[0085] The gas inlet pipe module 20 may comprise a first polymeric material and the stationary casing 2 may comprise a second polymeric material. The first polymeric material may be included in the first rim portion 601 of the fitting 200 and may be adapted to soften or at least partially melt during the joining of the fitting 200 to the stationary casing 2. The second polymeric material of the stationary casing 2, which may be comprised in the second rim portion 501, may have a higher melting point and will thus not melt equally as much as the first polymeric material. Alternatively, the first and second materials are vice-versa, i.e. that the second polymeric material in the second rim portion 601 has a lower melting point than the first polymeric material of the first rim portion 501. In a further embodiment, the gas inlet pipe module 20 may comprise and the stationary casing 2 may be comprised of the same polymeric material.

[0086] With reference to Fig. 4, which is a top view of the centrifugal separator 1 when the heat shield 60 is attached to the centrifugal separator, it is shown that the heat shield may have has a shape adapted to the outer contour of the gas inlet pipe module. Therefore, in the top view the gas inlet pipe module is nearly not visible, except for the radially extending pipe portion 18r. Thus, the heat shield 60 can protect the gas inlet pipe module from the heat from the engine. The heat shield can be made of a heat resisting material having a melting point of 500°C or more and a density of 3000 kg / m3or less. The heat shield may comprise or be made of an aluminium sheet having a thickness from 0.5 to 3 mm, such as 1 mm. By choosing a low-density material with high melting point, the weight of the centrifugal separator can be minimized, while sufficient protection towards the heat is obtained. Further, the heat shield 60 may be attached to the gas inlet pipe module 180 at a distance from 2-30 mm, or 3 to 25 mm.

[0087] According to an example, the heat shield may comprise or be made of aluminium, which is a light-weight stiff material. The eigenfrequency of the centrifugal separator can be in this way improved, and weight increasing material needs not to be added to the centrifugal separator. In the know arrangements, the heat shield has often been a steel plate, which is a heavy material compared to forexample aluminium, and therefore material has been added to other parts of the centrifugal separator to balance the separator. It is a goal to obtain an eigenfrequency of the centrifugal separator of more than 250 Hz, or more than 300 Hz. To obtain eigenfrequency of more than 300 Hz with a steel heat shield would require that additional weight increasing material is added to the centrifugal separator, for example to the stationary casing. However, when using a lightweight material for the heat shield according to the invention, there is no need to add weight to the centrifugal separator. Therefore, the construction of the centrifugal separator can be made more streamlined with fewer parts, while the eigenfrequency can be increased towards the target, i.e. 250 to 300 Hz or more. Thereby a more robust and simplified structure is obtained.

[0088] According to a further aspect of the invention, and with reference to Fig. 5, a method 100 for assembling a centrifugal separator 1 for cleaning gas is provided. The method comprises the steps of:

[0089] • S101: providing a stationary casing 2 enclosing a separation space 3 through which a gas flow is permitted, the casing 2 having a longitudinal centre axis (I) and comprising an inlet opening 20 for receiving the gas flow;

[0090] • S102: providing a gas inlet pipe module 180 comprising a gas inlet pipe 18, 18r permitting supply of the gas to be cleaned to the stationary casing 2 and a fitting 200 configured to connect the gas inlet pipe module 180 to the opening of the stationary casing,

[0091] • S103: connecting the gas inlet pipe module 180 to the stationary casing at a chosen mutual angular position in respect of the longitudinal centre axis (I) of the stationary casing,

[0092] • S104: permanently attaching the gas inlet pipe module 180 to the opening 20 of the stationary casing 2; and

[0093] • S105: removably attaching a heat shield 60 to the gas inlet pipe module 180.

[0094] The permanent attachment in the step S104 may be performed by:

[0095] - connecting a first rim portion of the fitting in the gas inlet pipe module to a second rim portion of the opening in the stationary casing, the first rim portion comprising a polymeric material,- rotating the gas inlet pipe module in respect of the stationary casing under axial pressure so that the first rim portion of the fitting at least partially melts.

[0096] The permanent attachment of the gas inlet pipe module to the opening of the stationary casing may be performed by rotary- welding or rotary friction welding as described above in connection with Fig. 3.

[0097] The centrifugal separator 1 that is assembled according to the above-mentioned method may be the centrifugal separator 1 as described in the detailed description above.

[0098] The invention is not limited to the embodiment disclosed but may be varied and modified within the scope of the claims set out below. The invention is not limited to the orientation of the axis of rotation (X) disclosed in the figures. The term “centrifugal separator” also comprises centrifugal separators with a substantially horizontally oriented axis of rotation. In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.

Claims

CLAIMS1. A centrifugal separator (1) for cleaning gas containing contaminants, said centrifugal separator (1) comprisinga stationary casing (2), enclosing a separation space (3) through which a gas flow is permitted, the casing having a longitudinal centre axis (I) and an opening for receiving a gas flow,a gas inlet pipe module (180) comprising a gas inlet pipe (18, 18r) permitting supply of the gas to be cleaned to the stationary casing (2), and a fitting (200) connecting the gas inlet pipe module (180) to the stationary casing (2) onto said opening,a rotating member (7) comprising a plurality of separation members (9) arranged in the separation space (3) and being arranged to rotate around an axis (X) of rotation,a gas outlet (28) configured to permit discharge of cleaned gas out from the stationary casing (2),a drainage outlet (25) configured to permit discharge from the centrifugal separator (1) of liquid contaminants that have been separated from the gas,a drive member (22) for rotating the rotating member (7),wherein the centrifugal separator (1) is provided with a heat shield (60) attached to and at least partially covering the gas inlet pipe module (180).

2. The centrifugal separator (1) of claim 1, wherein the heat shield (60) is removably attached to the fitting (200) of the gas inlet pipe module (180).

3. The centrifugal separator (1) of claim 2, wherein the fitting (200) comprises one or more mounting recesses (64), such as screw bosses, to which heat shield fastening means (62) are removably fastened.

4. The centrifugal separator (1) of any one of the preceding claims, wherein the fitting (200) is connectable to the stationary casing (2) at a chosen mutual angular position in respect to the longitudinal centre axis (I) which coincides with the axis of rotation (X).

5. The centrifugal separator (1) of claim 4, wherein the fitting (200) comprises a first rim portion (601), and the stationary casing (2) comprises a second rim portion (501) which receives the first rim (601) portion of the fitting.

6. The centrifugal separator (1) according to claim 5, wherein the first rim portion (601) and the second rim portion (501) are fastened to each other by welding / rotary welding.

7. The centrifugal separator (1) according to claim 5 or 6, wherein the first rim portion (501) comprises a polymeric material that at least partially melts during rotary welding.

8. The centrifugal separator (1) according to any one of the previous claims, wherein the gas inlet pipe module (180) comprises a first polymeric material and the stationary casing (2) comprises a second polymeric material.

9. The centrifugal separator according to any one of the preceding claims, wherein the heat shield (60) has a shape adapted to the outer contour of the gas inlet pipe module (180).

10. The centrifugal separator (1) according to any one of the preceding claims, wherein the heat shield (60) is attached to the gas inlet pipe module (180) at a distance from 2-30 mm, such as 3 to 25 mm.

11. The centrifugal separator (1) according to any one of the preceding claims, wherein the heat shield (60) comprises a heat resisting material having a melting point of 500°C or more and a density of 3000 kg / m3or less.

12. The centrifugal separator (1) according to any one of the preceding claims, wherein the heat shield (60) comprises or is made of an aluminium sheet having a thickness from 0.5 to 3 mm.

13. A method (100) for assembling a centrifugal separator (1) for cleaning gas, comprising the steps of• S101: providing a stationary casing (2) enclosing a separation space (3) through which a gas flow is permitted, the casing (2) having a longitudinal centre axis (I) and comprising an opening (500) for receiving the gas flow,• S 102: providing a gas inlet pipe module (180) comprising a gas inlet pipe (18, 18r) permitting supply of the gas to be cleaned to the stationary casing (2) and a fitting (200) configured to connect the gas inlet pipe module (180) to the opening (500) of the stationary casing, • S103: connecting the gas inlet pipe module (180) to the stationary casing at a chosen mutual angular position in respect of the longitudinal centre axis (I) of the stationary casing,• S104: permanently attaching the gas inlet pipe module (180) to the opening (500) of the stationary casing (2), and• S 105: attaching a heat shield (60) to the gas inlet pipe module (180).

14. A method (100) according to claim 13, wherein permanent attachment in the step S104 is performed by:- connecting a first rim portion (601) of the fitting (200) of the gas inlet pipe module (180) to a second rim portion (501) of the opening (500) in the stationary casing (2), the first rim portion (601) comprising a polymeric material,- rotating the gas inlet pipe module (180) in respect of the stationary casing (2) under axial pressure so that the first rim portion (601) of the fitting at least partially melts.

15. A method (100) according to any one of claims 13-14, wherein the centrifugal separator (1) being assembled is a centrifugal separator (1) according to any one of claims 1-12.

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