A centrifugal separator for cleaning gas

Abstract

The present invention provides a centrifugal separator (1) for cleaning gas containing contaminants The centrifugal separator is comprising a stationary casing (2), enclosing a separation space (3) through which a gas flow is permitted, a gas inlet chamber (20) for receiving the supply of the gas to be cleaned and in fluid communication with said separation space (3), a gas inlet tube (60) connected to the gas inlet chamber (20) and arranged for supply of the gas to be cleaned, a rotating member (7) comprising a plurality of separation members (9) arranged in said separation space (3) and being arranged to rotate around an axis (X) of rotation, a gas outlet (28) arranged through the stationary casing (2) and configured to permit discharge of cleaned gas out from the stationary casing (2), a drainage outlet (29) arranged in the stationary casing (2) and configured to permit discharge of liquid contaminants that have been separated from the gas out from the stationary casing and a drive member (22) for rotating the rotating member (7). Further, the gas inlet tube (60) has a curved shape for facilitating pre-rotation of the gas to be cleaned in the gas inlet chamber (20).

Description

[0001] A CENTRIFUGAL SEPARATOR FOR CLEANING GAS

[0002] Field of the Invention

[0003] The present invention relates to the field of centrifugal separators for cleaning gas. In particular, the present invention relates to a separator for cleaning crankcase gases of a 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.

[0006] One specific use of such a separator is in the separation of oil droplets from gas vented from a crankcase of an internal combustion engine. High-pressure gas found in the combustion chambers of an internal combustion engine may 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, as a consequence, 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] In order 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 remove as much oil as possible from the gas prior to the gas being introduced into the inlet system. This cleaning process may be undertaken by a centrifugal separator mounted on or adjacent to the crankcase, which directs cleaned gas to the inlet system and separated oil back to the crankcase. An example of such a separator is disclosed e.g. in US 8,657,908.

[0008] Increasing demands in cleaning efficiency and performance of a crankcase gas separator in combination with limited space for a separator when it is positioned on or close to an engine block of a combustion engine makes improvements and development a challenge. Thus, there is a need in the art for crankcase gas separators with improved performance without taking up to much space when mounted.Summary of the Invention

[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 with an enhanced separation efficiency that also provides for use of the separator in applications where the space is limited.

[0010] As a first aspect of the invention, 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,

[0012] a gas inlet chamber for receiving the supply of the gas to be cleaned and in fluid communication with said separation space;

[0013] a gas inlet tube connected to the gas inlet chamber and arranged for supply of the gas to be cleaned;

[0014] 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 arranged through the stationary casing and configured to permit discharge of cleaned gas out from the stationary casing,

[0015] a drainage outlet arranged in the stationary casing and configured to permit discharge of liquid contaminants that have been separated from the gas out from the stationary casing;

[0016] a drive member for rotating the rotating member;

[0017] wherein the gas inlet tube has a curved shape for facilitating pre-rotation of the gas to be cleaned in the gas inlet chamber.

[0018] The first aspect of the invention is based on the insight that a curved gas inlet tube may provide for pre-rotation of the gas to be cleaned, so that the gas has a rotational motion before the gas enters the separation space in which the actual separation takes place. The leads to better separation and less energy needed to rotate the gas. In addition, a rotating gas flow within the gas inlet chamber further increases the capacity of the inlet in providing an even flow distribution of the gas to be cleaned to the separation space. If e.g. the separation member is a stack of separation discs, the curved gas inlet tube aids in distributing the gas evenly to the stack. For example, the separator may have annularly distributed channels around the axis of rotation forming a connection between the gas inlet chamber and the separation space, and a rotating gas flow may thus provide for a more even flow through these channels to the separation space.The curved shape is thus curved in the same direction as the intended rotational direction during use of the centrifugal separator. The shape of the gas inlet tube may thus be curved in a radial plane, i.e. in a plane having its normal parallel to axis of rotation.

[0019] The gas inlet tube and the gas inlet chamber may be arranged such that all gas and contaminants entering the gas inlet tube is guided to the separation space via the gas inlet chamber.

[0020] The curved shape is formed so as to guide the gas to be cleaned in the curved direction.

[0021] In embodiments, the inner cross-sectional area of the curved shape decreases from an upstream portion to a downstream portion of the curved shape. The cross-sectional area is the area having a normal along the direction of the gas flow in the curved shape.

[0022] 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 (X) of rotation. An axial plane is a plane having its normal perpendicular to the axis (X) of rotation.

[0023] The contaminants in the gas may comprise liquid contaminants, such as oil, and soot.

[0024] 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.

[0025] 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 form an upper end walland a lower end wall of the cylindrical shaped casing. The stationary casing may also be slightly conical.

[0026] The gas inlet chamber may be in fluid communication and attached to an end wall of the stationary casing, such that gas entering through the gas inlet chamber may be directed to the separation space. The gas inlet chamber may be arranged above or below the rotating member of the centrifugal separator, i.e. above or below the separation space. Thus, as an example, the gas inlet chamber may comprise no rotatable parts.

[0027] The gas inlet tube is in fluid communication with the gas inlet chamber. The gas inlet tube may be configured for connection to a hose or conduit for transporting gas to be cleaned to the separator. A portion of the gas inlet tube, such as a downstream portion, may form part of the gas inlet chamber.

[0028] The rotating member is arranged for rotation during operation of the separator 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. The separation discs of the stack may be frustoconical. A frustoconical disc may have a planar portion extending in a plane that is perpendicular to the axis of rotation, and a frustoconical portion that may extend upwards or downwards. The planar portion may be closer to the rotational axis than the frustoconical portion. Further, the discs of the stack may be radial discs, in which substantially the whole disc extends in a plane having a normal that is perpendicular to the axis of rotation.

[0029] The separation members may also be one or several filter members, such as a coalescing filter elements and / or fibrous filter elements.

[0030] 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 plurality of separation members, respectively.

[0031] 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 centered at the axis (X) of rotation. The separation members may be arranged around such axial shaft.

[0032] The gas outlet may be in the form of a gas outlet tube extending through a wall of the stationary casing, such as through a lower portion or upper portion of asurrounding side wall of the stationary casing. The gas outlet tube may be a generally cylindrical tube or have another cross-section, such as an oval crosssection.

[0033] The drainage outlet may be arranged in the lower portion of the stationary casing, such as arranged in a lower at the bottom of the separator. The drainage outlet may be arranged centrally in the end wall opposite the end wall through which, or at which, the inlet is arranged. The drainage outlet of the centrifugal separator may further be formed by several spot shaped through holes in the stationary casing or by a single drainage passage. The drainage outlet may be arranged at the axis of rotation or centered around the axis of rotation. The drainage outlet may also be in an annular collection groove at the inner end wall of the stationary casing. The drainage outlet may be arranged such that contaminants, such as oil, are drained though a bearing, or radially outside a bearing, arranged for journaling the rotating member.

[0034] 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.

[0035] 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 chamber and configured to convey the gas to be cleaned from the gas inlet chamber to the separation members, such as between the interspaces between the discs of a stack of separation discs. A separation disc that may be used as a 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.

[0036] Thus, the centrifugal separator may be configured to convey gas to be cleaned, such as crankcase gases, from the gas inlet chamber 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 through the separation members by the rotation of the rotating member. Thus, the centrifugal separator may work according to the concurrent flow principle, in which the gas flows from a radial inner part to aradial outer part of the separation space, 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.

[0037] In embodiments of the first aspect, the gas inlet tube is arranged such that all gas and contaminants entering the gas inlet tube is guided to the separation space via the gas inlet chamber. Thus, the gas inlet tube may have no overall separation effect in itself. Thus, all gas and contaminants - such as oil - entering the gas inlet tube may be guided to the separation space, and possibly also to the separation members, via the gas inlet chamber.

[0038] In embodiments of the first aspect, the gas inlet tube comprises a straight upstream portion and a downstream portion with a curved shape.

[0039] Thus, the whole gas inlet tube does not have to be curved. “Upstream” refers to a position further back in the gas flow as compared to “downstream. The downstream portion may open up in the gas inlet chamber or may in itself form part of the inlet chamber. The straight upstream portion may be configured for attachment to any suitable connection for transporting crankcase gas to the centrifugal separator.

[0040] In examples, the straight upstream portion and the downstream portion with a curved shape are formed as a single unit.

[0041] As discussed herein, a ’’single unit” may be a unitary moulding of plastics material.

[0042] The curved shape may form an upper inner wall of the gas inlet tube.

[0043] In embodiments, the curved shape forms an upper inner wall of the gas inlet tube, whereas the lower wall of the gas inlet tube opens up in the gas inlet chamber. Thus, the gas inlet chamber may have an upper end wall that has the curved shape, thus aiding in rotating the gas to be cleaned.

[0044] In embodiments of the first aspect, the curved shape spirals around the axis (X) of rotation. A spiral shape provides for pre-rotation of the gas to be cleaned. The inlet tube, such as a downstream portion of the inlet tube, may thus have a volute shape spiralling around the axis (X) of rotation. As an example, the curved shape may spiral at least 25 %, such as at least 35 %, such as at least 50 %, such as at least 75% of a full turn around the axis (X) of rotation.Moreover, the curved shape may spiral less than a full turn around the axis (X) of rotation. As an example, the curved shape may spiral between 25 - 85%, such as between 50 - 80%, of a full turn around the axis (X) of rotation.

[0045] Moreover, the curved shape may spiral axially towards the separation space. As an example, the gas inlet chamber may be arranged above the separation space. Furthermore, the curved shape may spiral axially downwards. This may provide for less overall height of the centrifugal separator, since the gas inlet chamber may be formed at least partly within the stationary casing.

[0046] In embodiments of the first aspect, the gas inlet tube has an exit so that gas is supplied to the gas inlet chamber in a direction that is off-center relative the axis (X) of rotation.

[0047] Gas being supplied “off-center” means that the gas in not introduced centrally to the gas inlet chamber, but instead in a direction that does not intersect the axis (X) of rotation. Thus, gas being supplied “off-center” is supplied at a position that is displaced relative the axis (X) of rotation. Such supply of gas allows for pre-rotation of the gas to be cleaned, and together with the curved inlet tube, e.g. with a curved inlet tube that spirals around the axis (X) of rotation, provides for a low overall height of the complete gas inlet of the separator.

[0048] As an example, the straight upstream portion may be arranged so that its center line (A), or an imaginary straight line drawn from its center line (A), does not intersect the axis (X) of rotation. This may thus provide for supply of the gas “off-center”.

[0049] In embodiments of the first aspect, the gas inlet chamber is arranged axially above or below the separation space. Thus, the gas to be cleaned may be fed to the separator from the top or the bottom.

[0050] In embodiments of the first aspect, the gas inlet tube is integrated to the wall of the gas inlet chamber. The gas inlet tube, such as both a straight upstream portion and a curved downstream portion, may be a single unit forming at least one wall, such as an upper wall, of the gas inlet chamber. This facilitates providing a centrifugal separator with a decreased height.

[0051] In embodiments of the first aspect, e.g. when the gas inlet tube comprises a straight upstream portion and a downstream portion with a curved shape, the straight upstream portion may have its axially lowest wall at an axial position that is less than 10 mm from the axial position of an upper end wall of the stationary casing.This thus provides for a low height of the separator, especially in combination with a curved inlet that spirals axially downward around the axis (X) of rotation.

[0052] In embodiments of the first aspect, the gas inlet chamber is connected to the separation space via at least one channel, wherein the at least one channel extends in a direction that is not parallel to the axis (X) of rotation.

[0053] The channels or channels connecting the gas inlet chamber to the separation space may be formed around the axis (X) of rotation. As an example, there may be a bearing for the rotating member or other structure between the inlet chamber and the separation space, and the channel or channels may be formed around such structure. As an example, the channel or channels may be formed between ribs holding a bearing holder, such as the upper bearing such as between ribs holding or forming part of an upper bearing holder.

[0054] The at least one channel may connect the inlet chamber with a central space within the separation space, such as a central space formed within a disc stack arranged in the separation space.

[0055] The at least one channel may be a plurality of channels, such as at least three, such as at least four, such as at least five, channels connecting the gas inlet chamber to the separation space.

[0056] The inventors have realised that having channels that are parallel to the rotational axis (X) - such as in prior art solutions - a turbulent wake may be formed in the channels, thereby reducing rotating flow motion and creating a pressure drop. Having a channel or channels that are not parallel to the axis of rotation may reduce the flow disturbance.

[0057] As an example, the least one channel may have a curved center line.

[0058] The center line may form part of a spiral that turns around an axis, and that axis may be in the direction that is not parallel to the axis of rotation. The axis may deviate less than 60 degrees, such as less than 45 degrees, from the direction of the rotational axis.

[0059] As an example, the direction of the at least one channel is aligned with the rotating flow path of gas from the inlet chamber to the separation space.

[0060] Making the channels aligned with the flow pattern greatly reduces the flow disturbance. This aids in maintaining the rotating flow in the gas inlet chamber to the separation space.

[0061] In embodiments of the first aspect, the separation members are formed as a stack of separation discs, such as a stack of frustoconical separation discs. Suchdiscs 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 (X) of rotation, and a conical portion that extend outwardly and downwardly or upwardly from the flat portion. Openings in the flat portion may form part of a central space within the separation space into which gas to be cleaned is guided from the gas inlet chamber. 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.

[0062] As a second aspect of the invention, there is provided a method for cleaning gas containing contaminants, the method comprising

[0063] guiding gas containing contaminants to a centrifugal separator according to the first aspect above during rotation of the rotating member,

[0064] discharging cleaned gas from the gas outlet, and

[0065] discharging contaminants from the drainage outlet.

[0066] The contaminants in the gas may comprise liquid contaminants, such as oil, and soot.

[0067] This aspect may generally present the same or corresponding advantages as the former aspects. Effects and features of the second aspect are largely analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect.

[0068] Brief description of the Drawings

[0069] 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.

[0070] Figure 1 shows a schematic drawing of the cross-section of an embodiment of a centrifugal separator for cleaning gas.

[0071] Figure 2 shows a perspective view of the inside of an embodiment of a gas inlet tube.

[0072] Figure 3a shows a top view of the separator having a gas inlet tube with a curved shape.Figure 3b shows a cross-section of an embodiment of a gas inlet tube.

[0073] Figure 4 shows a cross-section of the gas inlet chamber along line Y in Fig. 3a. Figure 5 shows a cross-section of an embodiment of the channels between the gas inlet chamber and the separation space.

[0074] Detailed Description

[0075] The centrifugal separator according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.

[0076] Fig. 1 shows 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 a combustion engine (not disclosed), especially a diesel engine, at a suitable position, such as on top or at the side of the combustion engine.

[0077] It is to be noted that the centrifugal separator 1 is also suitable for cleaning gases from other sources than combustion engines, e.g. the environment of machine tools which frequently contains large amounts of liquid contaminants in the form of oil droplets or oil mist.

[0078] 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.

[0079] The centrifugal separator 1 comprises a rotating member 7, which is arranged to rotate around an axis (X) of rotation within the separation chamber 3. The stationary casing 2 is stationary in relation to the rotating member 7, and preferably in relation to the combustion engine to which it may be mounted.

[0080] 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.

[0081] The rotating member 7 comprises a rotatable shaft, i.e. spindle 8, and a plurality of separation members in the form of a stack of separation discs 9 that is mounted on the spindle 8. All the separation discs 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 stackof separation discs 9. However, the bearings could for example both be arranged axially below or above the stack 9 of separation discs.

[0082] The separation discs of the disc stack 9 are frusto-conical and extend outwardly and upwardly from the spindle 8. The separation discs thus comprise a flat portion 9a, which extend perpendicularly to the axis (X) of rotation, and a conical portion 9b, that extend outwardly and upwardly from the flat portion 9a. It should be noted that the separation discs also could extend outwardly and downwardly, or even radially.

[0083] The separation discs of the stack 9 are provided at a distance from each other by means of distance members (not disclosed) in order to form interspaces 14 between adjacent separation discs, i.e. an interspace 14 between each pair of adjacent separation discs. The axial thickness of each interspace 14 may e.g. be in the order of 0.5 -2 mm, such as 1-2 mm.

[0084] The separation discs of the stack 9 may 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.

[0085] The centrifugal separator 1 comprises a drive member 22 in the form of a turbine wheel that is driven by a jet of pressurized oil from an oil nozzle 24. This nozzle 24 is 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 of separation discs 9, also rotate upon rotation of wheel 22. As an alternative, the centrifugal separator 1 may comprise a drive member in the form of an electric motor arranged to rotate the rotating member 7. As a further alternative, the centrifugal separator 1 may comprise a turbine wheel connected to the spindle 8, wherein the turbine wheel is arranged to be driven by exhaust gases from the internal combustion engine. The rotating member 7 may also be arranged for being rotated by a mechanical drive unit. Thus, the centrifugal separator 1 may comprise a mechanical drive unit for rotating the rotating member.

[0086] The rotating member 7 defines a central space 15 within the separation space 3. The central space 15 is formed by through holes evenly spaced around the axis (X) of rotation in each separation disc in the stack 9. In the embodiments of Fig. 1, the central space 15 is formed by a plurality of through holes, each extending through the top disc 10 and through each of the separation discs 9, but not throughthe lower end plate 11. The through holes are arranged in the flat portions 9a of the separation discs.

[0087] The separator 1 further comprises a gas inlet chamber 20 arranged for receiving the gas to be cleaned. The gas inlet chamber 20 is in this example arranged axially above the separation space and also above and in fluid contact with the central space 15 via channels 21. The channels 21 are arranged radially outside the upper bearing 12. Thus, the gas inlet chamber 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 9 of separation discs. The gas inlet chamber 20 is configured to communicate with the crankcase of the combustion engine, or any other source, via a gas inlet tube 60 permitting the supply of gas from the crankcase to the separator 1. The gas inlet tube 60 is arranged so that it has no overall separation effect in itself. Thereby, all gas and contaminants entering the gas inlet tube 60 is guided to the separation space 3 via the gas inlet chamber 20.

[0088] The gas inlet tube 60 comprises a straight upstream portion 61 and a downstream portion 63 having a curved shape, and will be further discussed in relation to Figs. 2 and 3 below. The gas inlet tube 60 is integrated to, or forms part of, a wall 67 defining the volume of the gas inlet chamber 20, which in this example means that the walls of the gas inlet tube also form and defines at least a portion of the volume of the gas inlet chamber. Due to the curved shape of the gas inlet tube 60 - in this case the downstream curved portion 63 - and the gas inlet tube being arranged to supply the gas off-center in the gas inlet chamber 20, the axial height of the separator, especially the portions above the stationary casing 4, may be reduced. As an example, the straight upstream portion 61 of the gas inlet tube 60 may have its axially lowest wall at an axial position that is less than 10 mm from axial position of the upper end wall 5 of the stationary casing 2.

[0089] The centrifugal separator 1 comprises a drainage outlet 29 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 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. Drainage outlet 29 may as an alternative be arranged radially outside the lower bearing 13. The separated oil, and other particles and / or substances, is led to an oil outlet 25 of the centrifugalseparator 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.

[0090] 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.

[0091] The gas outlet tube 28 forms in this example part of a stationary insert 30, which is arranged in a lower portion of the stationary casing 2. The stationary insert 30 is configured to form a sort of 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 30 is arranged in the stationary housing 2 so that an outer annular vertical channel 32 for the separated contaminants is formed between the inner wall 40 of the stationary casing 2 and an annular wall member 31 of the insert 30. The insert 30 further comprises a central frustoconical cup member 33 with conically extending sidewalls. The annular wall member 31 extends axially downwards from the outer edge of the cup member 33. In this example, the lower part of the end plate 11 is arranged within the central cup member 33. With the design of the insert 30, separated liquid particles flowing down on the inner wall 40 of the casing 2 may be shielded from the rotating gas, so as to decrease the risk of separated oil being pulled from the inner wall 40 on its way down to drainage outlet 29.

[0092] 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. Contaminated gas, e.g. crankcase gas from the crankcase of an internal combustion engine, is supplied to the gas inlet chamber 20 via gas inlet tube 60. This gas is led further into the central space 15 and from there into and through the interspaces 14 between the separation discs of the stack 9. As a consequence 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. 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 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 bygravity downwardly to bottom end wall 6 and then and leave the separation space 3 through the drainage outlet 29. For this, the inner wall of the bottom end wall 6 may be tilted radially inwards, so that oil leaving the surrounding inner wall 40 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.

[0093] 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.

[0094] Fig. 2 and Figs. 3a and 3b show some further details of a gas inlet tube 60 according to an embodiment of the present invention. Fig. 2 shows a perspective section view of the gas inlet tube 60, whereas Fig. 3a shows a top view of the separator 1 and the gas inlet tube 60 and Fig. 3b shows section view from the top of the gas inlet tube 60, i.e. a section as seen in a radial plane. The gas inlet tube 60 comprises a straight upstream portion 61 and a downstream portion 63 having a curved shape.

[0095] The gas inlet 65 to the tube 60 is provided in the straight upstream portion. This inlet 65 is configured to mate with e.g. a flexible tube connecting the separator 1 to a ventilation line from a crankcase of a combustion engine. The straight upstream portion and the curved downstream portion are formed as a single unit, such as a molded plastic unit. In Fig. 2, the inner wall 60a of the downstream curved portion is shown as it spirals around the axis (X) of rotation, as indicated by the gas flow that is represented by arrow “C”. Moreover, since the gas inlet tube is arranged above the separation space 3, the curved portion 63 spirals axially downwards towards the separation space and exits in the gas inlet chamber 20 at gas exit 64.

[0096] The top view of Fig. 3a shows the gas inlet tube 60 attached to the upper end wall 5 of the centrifugal separator 1 and ending in the gas inlet chamber 20.

[0097] In the radial section view of Fig. 3b, it is shown that the curved downstream portion spirals around the axis (X) of rotation less than a full turn, such as about 75% of a full turn, before entering the gas inlet chamber 20 via the gas exit 64.

[0098] Moreover, the exit 64 from the gas inlet tube 60 to the into the gas inlet chamber 20 is arranged so that the gas to be cleaned is supplied to the gas inlet chamber 20 in a direction that is off-center relative the axis (X) of rotation. This means that the rotational motion of the gas within the gas curved portion 63 of the gas inlet tube may be maintained within the gas inlet chamber 20, thereby providing for a pre-rotation of the gas before entering the separation space 3 downstream.As also seen in the cross-section of Fig. 3b, the straight upstream portion 61 is arranged off-center to the axis (X) of rotation. More precisely, the straight upstream portion 61 is arranged so that its center line (A), or an imaginary straight line drawn from its center line (A), does not intersect the axis (X) of rotation.

[0099] Fig. 4 shows a cross-section of the gas inlet chamber 20 along line Y in Fig. 3a. As illustrated, the curved shape - in this case the downstream curved portion 63 -forms an upper inner wall of the gas inlet tube 60 and also the upper inner wall of the gas inlet chamber 20, whereas the lower wall of the gas inlet tube 60 opens up in the gas inlet chamber 20. Thus, in this example, the curved shape of the gas inlet tube 60 forms a curved shape of the actual gas inlet chamber 20. This shape of the gas inlet tube 60 and gas inlet chamber 20 thus facilitates pre-rotation of the gas to be cleaned before entering channels 21 connecting the gas inlet chamber with the separation space 3.

[0100] Fig. 5 shows some further details of an embodiment of the channels 21 connecting the gas inlet chamber 20 with the separation space 20, more precisely with the inner volume or central space 15 formed within the stack 9 of separation discs. These channels or passages 21 are distributed around the upper bearing 12, e.g. forming through holes in a bearing holder arranged for holding the upper bearing 12 in place. In prior art solution, such channels or passages 21 are axial channels, but according to the present disclosure, these channels 21 may extend in a direction E that is not parallel to the axis (X) of rotation. Due to the pre-rotation of the gas to be cleaned within the inlet chamber 20, the channels 21 extending in a direction that is generally aligned with the rotating flow path of gas from the inlet chamber 20 to the separation space 3 greatly reduces the flow disturbance. In other words, any pressure drop may be reduced and the channels 21 may to a further extent be filled with a gas flow.

[0101] The channels 21 may be straight channels, extending in a direction E that forms an angle to the axis (X) of rotation that is less than 60 degrees, such as less than 45 degrees, such as less than 30 degrees. As a complement, or alternative, the center line E of the channels 21 may have a slightly curved shape or a curved center line E. The curved center line E may form a spiral, or part of a spiral, in the axial direction from the inlet chamber 20 to the separation space 3. Thus, a channel 21 may spiral thus spiral downwards around an axial axis that is parallel to the axis (X) of rotation. As an example, a channel 21 may spiral less than a full turn around an axial axis.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 (X) of rotation 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 comprisinga stationary casing (2), enclosing a separation space (3) through which a gas flow is permitted;a gas inlet chamber (20) for receiving the supply of the gas to be cleaned and in fluid communication with said separation space (3);a gas inlet tube (60) connected to the gas inlet chamber (20) and arranged for supply of the gas to be cleaned;a rotating member (7) comprising a plurality of separation members (9) arranged in said separation space (3) and being arranged to rotate around an axis (X) of rotation;a gas outlet (28) arranged through the stationary casing (2) and configured to permit discharge of cleaned gas out from the stationary casing (2);a drainage outlet (29) arranged in the stationary casing (2) and configured to permit discharge of liquid contaminants that have been separated from the gas out from the stationary casing;a drive member (22) for rotating the rotating member (7);wherein the gas inlet tube (60) has a curved shape for facilitating pre-rotation of the gas to be cleaned in the gas inlet chamber (20).

2. A centrifugal separator (1) according to claim 1 , wherein the gas inlet tube (60) is arranged such that all gas and contaminants entering the gas inlet tube (60) is guided to the separation space (3) via the gas inlet chamber (20).

3. A centrifugal separator (1) according to claim 1 or 2, wherein the gas inlet tube (60) comprises a straight upstream portion (61) and a downstream portion (63) with a curved shape.

4. A centrifugal separator (1) according to claim 3, wherein the straight upstream portion (61) and the downstream portion (63) with a curved shape are formed as a single unit.

5. A centrifugal separator (1) according to any previous claim, wherein the curved shape forms an upper inner wall of the gas inlet tube (60), whereas the lower wall of the gas inlet tube (60) opens up in the gas inlet chamber (20).

6. A centrifugal separator (1) according to any previous claim, wherein the curved shape spirals around the axis (X) of rotation.

7. A centrifugal separator (1) according to claim 6, the curved shape spirals at least 25 % of a full turn around the axis (X) of rotation.

8. A centrifugal separator (1) according to claim 6 or 7, wherein the curved shape spirals axially towards the separation space (3).

9. A centrifugal separator (1) according to any previous claim, wherein the gas inlet tube (60) has an exit (64) so that gas is supplied to the gas inlet chamber (20) in a direction that is off-center relative the axis (X) of rotation.

10. A centrifugal separator (1) according to claims 3 and 9, wherein the straight upstream portion (61) is arranged so that its center line (A), or an imaginary straight line drawn from its center line (A), does not intersect the axis (X) of rotation.

11. A centrifugal separator (1) according to any previous claim, wherein the gas inlet chamber (20) is arranged axially above or below the separation space (3).

12. A centrifugal separator (1) according to any previous claim, wherein the gas inlet tube (60) is integrated to the wall (67) of the gas inlet chamber (20).

13. A centrifugal separator (1) according to claim 3, wherein the straight upstream portion (61) has its axially lowest wall at an axial position that is less than 10 mm from the axial position of an upper end wall (5) of the stationary casing (2).

14. A centrifugal separator (1) according to any previous claim, wherein the gas inlet chamber (20) is connected to the separation space (3) via at least one channel (21), wherein said at least one channel (21) extends in a direction that is not parallel to the axis (X) of rotation.

15. A centrifugal separator (1) according to claim 14, wherein said at least one channel (21) has a curved center line (E).

16. A centrifugal separator (1) according to claim 14 or 15, wherein the direction of the at least one channel (21) is aligned with the rotating flow path of gas from the inlet chamber (20) to the separation space (3).

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