Separator

Abstract

A separator (1) for separating contaminants from a fluid stream having entrained particulate contaminants, comprises a cylindrical dividing wall (28) concentrically arranged within an impaction surface (35). The cylindrical dividing wall defines a first chamber (42) into which a fluid stream enters and flows axially through. The dividing wall has apertures (29) through which the fluid stream passes towards the impaction surface. As the fluid impacts the impaction surface, the contaminants are separated from the fluid and flow down to an oil outlet (23). A diaphragm (31) moves along an axis to adjust the open cross-sectional area of the apertures in the dividing wall according to a pressure differential between fluid pressure in the first chamber and a pressure reference by moving along the dividing wall to progressively occlude the apertures. The apertures are spaced so that there is no overlap between them along the actuator axis.

Claims

1. A separator for separating contaminants from a fluid stream which includes entrained particulate contaminants, comprising: a first chamber having a cylindrical wall circumscribing a central axis, a first inlet through which a fluid stream enters the first chamber, to flow axially along the first chamber, the cylindrical wall having a plurality of apertures defined by edges, formed in the cylindrical wall through which the fluid stream can pass out of the first chamber, an impaction surface located downstream of the first chamber, separated from an interior of the first chamber by the cylindrical wall, which is arranged to deflect the fluid stream after the fluid stream leaves the first chamber through the apertures, such that contaminants are separated from the fluid stream, and an actuator which is arranged to move along an actuator axis which is parallel to the axis of the first chamber to adjust the open cross-sectional area of the apertures in the cylindrical wall according to a pressure differential between fluid pressure in the first chamber and a pressure reference by moving along the cylindrical wall so as progressively to occlude the apertures, the actuator comprising a diaphragm which separates the first chamber from a pressure reference, and comprises a tubular membrane which is fastened towards one end of the cylindrical wall and is arranged to fold and unfold progressively in response to a change in the differential pressure across the diaphragm so as respectively to uncover and cover the apertures, with the apertures having straight edges which extend perpendicular to the actuator axis in a circumferential direction around the cylindrical wall, in which a first and second ones of the apertures (a) are spaced apart so that there is no axial overlap between them along the actuator axis, and (b) are the closest-spaced to one another along the actuator axis of any pair of the apertures which are spaced apart along the axis, and in which a ratio of the spacing between a closest of the edges of the first and second apertures along the actuator axis to an axial height of a smaller of the first and second apertures is not more than about 1.5, wherein the closest edges of the first and second apertures are straight along their lengths and extend perpendicular to the actuator axis.

2. A separator as claimed in claim 1, in which each of the first and second apertures is approximately rectangular.

3. A separator as claimed in claim 1, in which a ratio of a width of each of the first and second apertures measured transverse to the actuator axis to the axial height of the respective aperture is at least about 1.

4. A separator as claimed in claim 1, in which each aperture has a center, and the center of the second aperture is displaced along the cylindrical wall transversely relative to the center of the first aperture.

5. A separator as claimed in claim 4, in which the first and second apertures are spaced so that there is no transverse overlap between them along a direction perpendicular to the actuator axis.

6. A separator as claimed in claim 1, in which the first and second apertures are located close to one another on one side of the cylindrical wall.

7. A separator as claimed in claim 6, which includes at least a third aperture which is spaced apart from the first and second apertures around the a periphery of the cylindrical wall.

8. A separator as claimed in claim 7, which includes a fourth aperture which is located close to the third aperture, spaced apart around the periphery of the cylindrical wall from the first and second apertures.

9. A separator as claimed in claim 1, in which an internal diameter of a cylinder which is defined by the cylindrical wall is at least about 10 mm.

10. A separator as claimed in claim 1, in which an area of a smaller of the first and second apertures is at least about 0.2 mm.sup.2.

11. A separator as claimed in claim 1, wherein the apertures are formed in the cylindrical wall in a direction that is perpendicular to a tangent to a surface of the cylindrical wall.

12. A separator as claimed in claim 11, wherein the angle between circumferentially spaced apart edge walls of the first aperture or the second aperture and the tangent to the surface of the cylindrical wall at each of the edge walls is not more than about 20.

13. A separator as claimed in claim 1, in which the ratio of the spacing between a closest of the edges of the first and second apertures along the actuator axis to an axial height of a smaller of the first and second apertures is at least about 0.05 and not more than about 0.075.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described, by way of example only, with reference to the accompanying drawings of which:

(2) FIG. 1 schematically illustrates an engine system including a closed crank ventilation (CCV) system;

(3) FIG. 2 illustrates in a cross sectional view a CCV system including an impactor separator in accordance with the invention;

(4) FIG. 3 is an enlarged cross sectional view of part of the impactor separator of FIG. 2;

(5) FIG. 4 is a cut-away perspective view of part of the impactor separator of FIG. 3 for operating at blow-by gas flow rates of between 0 and 250 liters per minute;

(6) FIG. 5 is a plan view of the impactor separator detail of FIG. 4;

(7) FIG. 6 is the plan view of the detail of the impactor separator of FIG. 5 with three side projections showing side views;

(8) FIG. 7 is a cut-away perspective view of part of an alternative embodiment of the impactor separator of the invention for operating at blow-by gas flow rates between 0 and 500 liters per minute;

(9) FIG. 8 is a plan view of the impactor separator detail of FIG. 7;

(10) FIG. 9 is the plan view of the detail of FIG. 8 with four side projections showing side views;

(11) FIG. 10 is an illustration of the flow of blow-by gas within the dividing wall of the impactor of the present invention in the x-z directions, the x-z directions being represented by the perpendicular arrows;

(12) FIG. 11 is an exemplary illustration of the a filled drawing illustrating the flow of blow-by gas within the dividing wall of the impactor of the present invention in the x-y directions, the x-y directions being represented by the perpendicular arrows;

(13) FIG. 12 is a diagram of the dividing wall for the separator of the present invention illustrating aperture dimensions and spacing;

(14) FIGS. 13A to 13G are schematic representations to illustrate examples of the orientations and spacing of the apertures in the dividing wall; and

(15) FIG. 14 corresponds to the views of FIGS. 6 and 9 illustrating the angular transverse offset between adjacent apertures in the direction of the actuator axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(16) The conventional arrangement of an engine blow-by gas/oil separator returning cleaned gas to an engine air intake is commonly referred to as a Closed Crankcase Ventilation (CCV) system.

(17) FIG. 1 illustrates schematically the arrangement of a conventional CCV system 1 coupled to a diesel engine 2. Blow-by gas from the engine crankcase passes to the CCV system 1 along inlet duct 3. The CCV system 1 comprises a regulator 4 coupled to the inlet duct 3 and a contaminant separator 5 in series. The regulator 4 and separator 5 are shown combined in FIG. 1.

(18) A pump 6 is provided within the CCV system 1 to increase the pressure drop across the separator 5, thereby increasing the filtering efficiency. Cleaned blow-by gas exits the CCV system 1 through gas outlet 7 and is returned to the engine air intake system. Specifically, the engine air intake system draws in air from outside of the vehicle through an inlet 8, the air then passing through an inlet air filter and silencer 9, a compressor 10 driven by a turbo charger 11 (in turn driven by the engine exhaust 13) and an after cooler 12 to cool the compressed air before it is supplied to the engine 2. The cleaned blow-by gas passes from the gas outlet 15 to the compressor 10. Oil and other contaminants separated from the blow-by gas are returned to the engine crankcase through an oil drain 16.

(19) Referring now to FIG. 2, this illustrates a cross sectional view of parts of a CCV system 1 including a separator 5 for separating liquid, aerosol and particulate contaminants from a blow-by gas stream. The respective portions comprising a separator 5 and a pump 6 are shown. In the present invention, the function of the regulator can be performed by means of a rolling diaphragm 31 as will be described in further detail below.

(20) The separator 5 and pump 6 are combined in a single unit. The separator 5 has a housing 21 which includes an inlet 22, and an oil drain outlet 23 which returns separated oil to the engine crankcase via the oil drain 16.

(21) The separator 5 includes a cylindrical dividing wall 28 extending lengthways within the separator housing 21, the interior of which forms a first chamber 42.

(22) The housing 21 has a mounting plate 24 provided towards the base section 25 of the housing 21 and above the oil drain outlet 23. The underside of the mounting plate 24 and base section 25 define a lower chamber 26 of the separator 5. The mounting plate 24 has a separator inlet tube 27 which opens into the lower chamber 26 at one open end. The dividing wall 28 is mounted on the other open end of the separator inlet tube 27. The separator inlet tube 27 connects the first chamber 42 to the lower chamber 26 to define a continuous passage for the blow-by gases to flow through from inlet 22 to the first chamber 42 via the lower chamber 26, and separator inlet tube 27. Blow-by gases from the crankcase are directed from the crankcase into the housing 21 via the inlet 22 and through into the separator inlet tube 27 as indicated by the arrow A in FIG. 2.

(23) An arrangement of spaced apertures 29 are provided in the dividing wall 28, towards the upper end of the dividing wall 28 remote from the separator inlet tube 27. This arrangement will be discussed in further detail below.

(24) The upper end of the dividing wall 28 is closed off by means of a flexible diaphragm arrangement.

(25) The flexible diaphragm arrangement comprises a rolling diaphragm 31 which is attached to the upper edge 30 of the dividing wall 28 by means of a sealing arrangement 32 which can be beading or an O-ring seal.

(26) The pump 6 is mounted on the top of the housing 21 to form the single unit with the separator 5. As mentioned above, the pump 6 serves to generate a region of low gas pressure in order increase the velocity of the gases through the apertures 29 and to draw contaminated blow-by gases through separator 5.

(27) A first inlet 17 to the pump 6 receives a source of pressurised gas, referred to herein as boost gas. The boost gas is provided by the turbo charger 11 or any other source of pressurised gas such as exhaust gas. When used on a turbocharged engine the boost gas may be a derived from a source of pressurised gas such as the intake manifold. Alternatively, the pressurised gas could be derived directly from the turbocharger. The first inlet 17 has a nozzle 18, formed as a convergent nozzle, such as a de Laval nozzle, which serves to accelerate the boost gas to a high velocity, for instance between 100 to 500 m.Math.s.sup.1, with the boost gas typically exceeding Mach 1 at least in the region of the convergent nozzle 18.

(28) The first inlet 17 is connected to an upper chamber 19 of the housing 21, which, in turn, is connected to a diffuser tube 20. The diffuser tube 20 is generally formed as a cylinder. The side walls of the diffuser tube 20 are not necessarily straight for the whole of their length, and may taper outwardly towards the end of the tube remote from nozzle. This tapering assists in controlling the direction of flow and mixing of the combined gas flow.

(29) The upper end of the housing 21 has the diffuser tube 20 mounted thereon. The diffuser tube 20 includes a mounting flange 45 for mounting the diffuser tube 20 on the housing 12.

(30) A cylindrical tube 34 extends from the underside of the diffuser tube 20. The upper end of the dividing wall 28, including the rolling diaphragm arrangement is located within the circular tube 34. The internal wall of the cylindrical tube 34 and the outer wall of the dividing wall 28 define an annular space 36. The internal wall of the cylindrical tube 34 provides an impaction surface 35 the function of which will be described in further detail below. The dividing wall 28 separates the first chamber 42 from the impaction surface 35, which in this embodiment is circular.

(31) The space between cylindrical tube 34 and the housing 21 defines a second chamber 43 which is connected to the upper chamber 19 in the pump 6. An annular diffuser plate 46 is provided at the upper part of the housing 21 around the cylindrical tube 34 and separates the upper chamber 19 from the second chamber 43.

(32) The annular diffuser plate 46 has a curved aperture 50 formed therein which connects the second chamber 43 to the upper chamber 19. The curved aperture 50 extends partially around the annulus of the diffuser plate 46. Clean blow-by gas, stripped of contaminants and oil, flows from the annular space 36 through the second chamber 43 and is directed up to the chamber 19 and the pump 6 through the curved aperture 50. Thus, gas flowing from the annular space 36 does not take the direct path into the upper chamber 19, but rather takes a path which is between 90 to 180 from the upper chamber 19. This is shown by the path B in FIG. 2.

(33) An inner circular flange 37 is provided concentrically within the cylindrical tube 34. The rolling diaphragm 31, along with inner circular flange 37, defines an upper reference chamber 38. The reference chamber 38 is at atmospheric pressure by an air inlet 51 which connects to the outside of the CCV system 1.

(34) The rolling diaphragm 31 is supported at a central portion 41 by an actuator 33 which is configured to move up and down in a longitudinal direction within the first chamber 42 to cause the diaphragm 31 to sequentially cover and uncover the apertures 29 provided in the upper portion of the dividing wall 28 as it moves up and down.

(35) The actuator 33 is a closed ended tube which is slidably mounted on a finger-like extension 44 extending from the diffuser tube 20. This arrangement serves to keep the actuator 33 moving in the longitudinal direction.

(36) The diaphragm 31 comprises an annular rolling portion 40, alternatively referred to as a rolling convolute, which is the portion that progressively covers and uncovers the apertures 29 as the central portion 41 moves up and down

(37) A cylindrical support 54 is located concentrically with the dividing wall 28. A biasing component in the form of a regulator spring 39 is located around the cylindrical support. The cylindrical support 54 is attached by means of three circumferentially equidistantly spaced protrusions 49 extending outwardly of the cylindrical support 54 and connected to the internal surface of the dividing wall 28. The regulator spring 39 acts on the actuator 33 to regulate the movement of the actuator 33 as it moves in response to changing pressure differential. The regulator spring 39 is supported by the three protrusions 49 and positioned underneath the actuator 33. The regulator spring 39 allows the range of normal operating pressure within the crankcase to be shifted within a range of values, for example in the range plus or minus 10 mBar.

(38) A baffle 47 is supported on the mounting plate 24. The baffle 47 is located circumferentially around the periphery of the upper portion of the separator inlet tube 27. The baffle 47 serves to direct oil separated from the blow-by gas to the oil outlet 23 via a check valve 51. Oil separated from the gas therefore flows down the baffle 47 into a sump 52 formed in the mounting plate 24, and back to the oil outlet 23 through the check valve 51, which opens when the pressure in the lower chamber 26 is the same or slightly above that in the sump 52. A number of check valves 51 can be provided although only one is shown in FIG. 2.

(39) In the first embodiment of the invention, the arrangement of apertures 29 around the dividing wall 28 is as illustrated in FIGS. 4 to 6.

(40) There are three groups of apertures spaced substantially equidistantly around the circumference of the dividing wall 28. All of the apertures 29 are rectangular in shape and elongate in the circumferential direction with a width, x, and a height, y. They are spaced from each other in both the longitudinal and transverse directions as will be discussed further below.

(41) The values of x and y are selected to provide the required pressure drop for a given flow rate of blow-by gas through the aperture 29.

(42) In this embodiment, each group comprises a pair of apertures 29 spaced apart transversely with a separation of b, such that the centre of the one of the pair of apertures 29 is displaced apart transversely along the dividing wall 28. The first and second apertures 29 of each group are located close to one another on one side of the periphery of the dividing wall 28. The next group of apertures 29 is then spaced apart from the first group of apertures around the periphery of the dividing wall 28.

(43) In the direction of the longitudinal axis, z, of the impactor 5, dividing wall 28, and actuator 33, the separation a, between successive apertures 29 in a group of apertures is called the spill gap. Unnecessary spill causes a reduction in velocity of the blow-by gas through the aperture 29. In order to prevent unnecessary spill, this longitudinal separation, a, should be small, preferably zero with no overlap between the apertures 29 along the actuator axis, z. i.e. the spill gap, a, should be 0 mm or greater. With a small separation a, peak velocity is maintained for a given pressure differential across the impactor 5 and keeps the vector paths for the airflow taking the shortest distance to the impaction surface 35.

(44) Each group of apertures 29 are located at different longitudinal distances, d, from the upper edge of the dividing wall 28, where d is the distance from the upper edge of the dividing wall 28 to the lower edge of the lowest aperture 29 of the group. As such, the apertures follow a helical path around the periphery of the dividing wall 28.

(45) In addition, two larger apertures 29 are provided adjacent the upper edge of the dividing wall 28 and co-located with one of the second or third group of apertures: one of the larger apertures 29 with each group of apertures 29. These apertures 29 are provided for conditions of engine brake or excessive increase in flow rate.

(46) In use, contaminated blow-by gas is actively drawn out of the crankcase and through the separator 5. The pressure drop across the separator 5 generated by the pump 6 overcomes the high pressure differential of the separator 5 without causing an excessively high crankcase pressure. That is, because of the reduction in pressure caused by the pump 6, the blow-by gas may be drawn through a smaller impaction gap causing more efficient separation.

(47) Gas is drawn into the separator inlet tube 27 generally along the path indicated by arrow A in FIG. 2 through the lower chamber 26. This section acts as a cyclonic pre-separator and the separator inlet tube 27 at this point defines the centre of a vortex of the gas. Liquid oil and large particles are separated from the gas at this stage and flow to the oil drain outlet 23. The blow-by gas then passes upwards through the separator inlet tube 27, into the first chamber 42 which is closed at its upper end by diaphragm 31. The blow-by gas passes through one or more of the apertures 29 and is incident upon the annular impaction surface 35. Oil and other contaminants separated from the blow-by gas at the impaction surface 35 flow under gravity to oil drain outlet 23 via the sloping baffle 47, sump 52 and check valve 51. Oil from the oil drain outlet 23 is returned to the crankcase.

(48) High speed boost gas jet from the first inlet 17 passes into chamber 19. The high velocity boost gas jet causes a region of reduced pressure within the chamber 19 in the vicinity of the nozzle 18. Pressure is reduced by up to 250 mBar relative to external atmospheric pressure. This reduction in pressure allows cleaned blow-by gas from the separator 5 to be drawn into chamber 19 generally along the path of arrow B in FIG. 2.

(49) The blow-by gas flow is entrained and accelerated by the boost gas, intermixing with the boost gas and accelerating to approach the speed of the boost gas. A terminal velocity will be reached at the outlet of the diffuser 20 based on total flow rate.

(50) The combined gas stream passes into a diffuser tube 20. In order to achieve satisfactory entrainment and acceleration of the blow-by gas, preferably the diameter of the diffuser tube should be between 2 to 5 times greater, preferably 3 to 4 times greater, than the critical diameter (typically, the smallest diameter) of boost gas nozzle 18. The position of the critical diameter (alternatively referred to as the throat of the nozzle) may vary from the narrowest point of the nozzle due to aerodynamic effects, as is known in the art of nozzle design.

(51) The separator 5 may be considered to be a variable impactor separator as it is intended to respond to differences between the blow-by gas inlet pressure and the outlet pressure to increase the separation efficiency, as will now be described.

(52) As mentioned above, the reference chamber 38 is kept at atmospheric pressure by an air inlet which connects to the outside of the CCV system 1. The first chamber 42 and lower chamber 26 is therefore at substantially the same pressure as the engine crankcase.

(53) The blow-by gas passes into the annular space 36 through one or more apertures of the apertures 29. The number of apertures 29 open will vary as the rolling diaphragm 31 rolls up and down under control of the actuator 33 to cover and uncover the apertures 29.

(54) The size and number of slots 29 determines the minimum differential pressure drop across the separator 5.

(55) There are two embodiments of the invention described herein, both have three groups of two apertures 29, but the sizes and relative dimensions are different.

(56) The relative dimensions of the apertures 29 in the groups of apertures can be described in terms of a ratio, R being the ratio of the spill gap a to the height, y, of whichever of the two apertures in the pair has the smaller height.

(57) So, R=a/y

(58) For a spill gap a of 0 mm, the value of R will be zero. R will always have a value of zero or greater. R should have a value which is not more than 2. It can be preferred that the value of R is less than this, as discussed above.

(59) Values of R for the pairs of apertures 29 in the two embodiments are provided in Tables 1 and 2 below.

(60) A second ratio S, being the ratio of the width, x, to the height, y, for each aperture can also be used as a measure of the relative dimensions of the apertures.

(61) Thus, S=x/y.

(62) Preferably the value of S is at least 1.

(63) The area of each aperture should be greater than 0.2 mm.sup.2 to prevent excessive aerodynamic drag. Areas of 6 mm.sup.2 to 12 mm.sup.2, could be typical values, with an upper limit of 30 mm.sup.2.

(64) As the contaminated blow-by gas travels through the apertures 29, separation of oil particles due to radial acceleration of the particles occurs. The flow of the blow-by gas is through the apertures 29 and impaction and separation of oil particles due to radial acceleration in making a 180 turn occurs both on the diaphragm 31 face and as the blow-by gas hits the impaction surface 35. This is illustrated in FIGS. 10 and 11.

(65) The impaction surface 35 may be covered with a material opposite the apertures 29 to reduce the tendency of oil droplets and other contaminants to bounce off the impaction surface 35. The media covering the impaction surface serves to reduce re-entrainment of the contaminants.

(66) The pump 6 is used to overcome the pressure drop across the separator 5. Under various engine loads, speed or engine breaking conditions both the vacuum generated by the pump 6, and the volume of blow-by gas passing through the separator 5 changes. To maintain an acceptable crankcase pressure according to the variable vacuum conditions generated by the pump 6, the diaphragm 31 moves up and down to cover and uncover the apertures 29.

(67) The pump 6 is powered with air from the engine turbo and thus creates pressure lift. The developed pressure lift is used to enhance the performance of the impactor 5. By subjecting the second chamber 43 to vacuum, the pressure in the first chamber 42 will consequentially be reduced. The rolling diaphragm 31 responds to cover or close the apertures 29, and whilst the rolling diaphragm 31 is reference to atmosphere, the pressure in the first chamber 42 will be stabilised relative to atmosphere. Similarly, if the vacuum is reduced in the second chamber 43, the pressure in the first chamber 42 will increase and the diaphragm 31 will respond to open up the apertures 29. This relationship then maintains near atmospheric pressure in the first chamber 42 and creates a pressure drop across the impactor 5. This pressure drop is directly related to the separation efficiency of the impactor 5. When the velocity of the gas is accelerated above 100 m/s the fractional efficiency of the impactor 5 is improved.

(68) Thus, a low flow rate through the first chamber 42 or a high vacuum in the second chamber 43 tends to close the diaphragm 31 over the apertures 29 thus decreasing the aperture open area/increasing the pressure differential across the separator 5, and thus preventing excess negative pressures in the engine crankcase.

(69) Conversely, a high flow rate through the first chamber 42 or a low vacuum in the second chamber 43 tends to cause the diaphragm to open up more of the apertures 29 thus increasing the aperture open area/decreasing the pressure differential across the separator 5, and preventing excess positive pressures in the engine crankcase.

(70) The pressure differential of the separator 5 is adjusted and crankcase pressure can be regulated precisely according to atmospheric pressure on the opposing side of the rolling diaphragm 31 or with the specification of the regulator spring 39 which is acts on the actuator 33.

(71) The lowest aperture 29 of the dividing wall 28 has a lower edge 48 which is curved or so as to be non-linear. This ensures that there is not a sharp cut off when the flexible diaphragm 31 covers and uncovers the lowest aperture 29. When this occurs a square form pressure change occurs. The pump 6 then reacts and pulls a high vacuum and the pressure on the upstream has to significantly increase to overcome the negative pressure in the downstream. This non-linear cross sectional area is provided to a near closed position of the rolling diaphragm 31 to prevent pump surge.

(72) By providing of an array of apertures 29 which do not overlap axially, the directional control and velocity streamlines of the blow-by gas can be focused towards the impaction surface 35 via the shortest path. The fractional efficiency is raised when the streamline takes the shortest distance from the aperture exit to the impaction surface 35. This in combination with the gas reaching peak velocity for the given pressure differential can reduce the amount of oil and other contaminants that are carried out with the gas as it exits.

(73) The interaction between the apertures 29 and the rolling diaphragm 31 can maintain relative atmospheric pressure control to the upstream of the impaction surface 35. FIGS. 10 and 11 illustrate how the blow-by gas flows through the apertures 29 and towards the impaction surface 35. In FIGS. 10 and 11, the darker the shading, the greater the velocity of the blow-by gas as exemplified by the legend in FIGS. 10 and 11. Actual velocities will depend upon the size and dimensions of the apertures and impactor.

(74) FIGS. 5 and 8 show the circumferentially spaced apart edges of the apertures 29 being formed at an angle to the radius of the dividing wall 28. The angle is preferably not more than 15. The edges of the apertures 29 which are spaced apart along the actuator axis are perpendicular to the surface of the dividing wall 28.

(75) In a second embodiment of the invention, illustrated in FIGS. 7, 8 and 9, the numbers and dimensions of the apertures 29 are different. Specifically, the second embodiment could be used for gas flow rates of up to 500 liters per minute. It has a larger diameter so that the velocity of the gas after impaction on the impaction surface 35 is not above a predetermined value, above which efficiency is reduced.

(76) The second embodiment also illustrates the provision of a plurality of helical inclined surfaces 53 provided around the cylindrical support 38. These serve to direct the flow of gas entering the first chamber 42 into a helical path as it moves through the first chamber 42. This is illustrated schematically by the arrows in FIG. 7.

(77) The dimensions for the two embodiments can be summarised in the following tables:

(78) TABLE-US-00001 TABLE 1 Approximate dimensions (mm or mm.sup.2) Aperture pair Dimensions Aperture 1 Aperture 2 1 x 4.7 4.0 y 2 1.5 S 0.423 0.375 Area 9.4 6 d 15.31 a 0.1 b 2 R 0.067 2 x 4 4 y 1.5 1.5 S 0.375 0.375 Area 6 6 d 11.61 a 0.1 b 2 R 0.067 3 x 4.5 4.5 y 1.5 1.5 S 0.33 0.33 Area 6.75 6.75 d 8.41 a 0.1 b 2 R 0.067

Embodiment 1

(79) The inner diameter of dividing wall 28 is about 33.5 mm. The length of upper apertures 29 are approximately 12 mm.

(80) In this embodiment, the angular offset, a, between adjacent apertures around the actuator axis z can be calculated to be approximately between 20 and 23 when the adjacent apertures are part of an aperture pair, or approximately 98 when the adjacent apertures are in different aperture pairs. See FIG. 14.

(81) TABLE-US-00002 TABLE 2 Approximate dimensions (mm or mm.sup.2) Aperture pair Parameter Aperture Aperture 2 1 x 10 10 y 1.97 1.5 S 0.197 0.15 Area 19.7 15 d 19.97 a 0.1 b 2 R 0.051 2 x 12 12 y 1.5 1.5 S 0.125 0.125 Area 18 18 d 16.3 a 0.1 b 2 R .067 3 x 14 14 y 1.5 1.5 S 0.11 0.11 Area 21 21 d 13.1 a 0.1 b 2 R 0.067

Embodiment 2

(82) The inner diameter of dividing wall 28 is around 53.5 mm. The length of upper apertures 29 are approximately 30 mm.

(83) In this embodiment, the angular offset, a, between adjacent apertures around the actuator axis z can be calculated to be approximately between 25 and 35 when the adjacent apertures are part of an aperture pair, or approximately between 57 and 63 when the adjacent apertures are in different aperture pairs. See FIG. 14.

(84) FIGS. 13A to 13G are schematic representations to illustrate examples of the orientations and spacing of the apertures around the dividing wall 28 which may be utilised in the invention. Different arrangements and spacings can be selected to achieve the required operational and functional capabilities required.

(85) FIGS. 13A to 13G are schematic projections of the cylindrical dividing wall 28 into a two-dimensional space.

(86) In all of the examples given below, the angular separation , .sub.1, .sub.2, .sub.3 between groups A.sub.1, A.sub.2, A.sub.3, A.sub.4 of apertures is measured between the centre of the groups, or aperture when there is only one aperture.

(87) In FIG. 13A, the dividing wall 28 has four apertures 29.sub.a, 29.sub.b, 29.sub.c, 29.sub.d that are arranged into two groups A.sub.1, A.sub.2 of axially aligned apertures.

(88) The two groups A.sub.1, A.sub.2 are offset around the actuator axis z, the angular separation between the groups A.sub.1, A.sub.2, being denoted in FIG. 13A by .

(89) Adjacent apertures in the axial direction are offset in a transverse direction around the actuator axis.

(90) Thus, first aperture 29.sub.a is adjacent second aperture 29.sub.b and transversely offset with the angular separation . The second aperture 29.sub.b is adjacent to third aperture 29.sub.c and the two apertures are also transversely separation from each other with the angular separation of . Similarly, third aperture 29.sub.c is adjacent fourth aperture 29.sub.d with the same angular separation .

(91) In this example, is 180.

(92) In FIG. 13B, the arrangement comprises five apertures arranged in two groups A.sub.1, A.sub.2.

(93) The first aperture 29.sub.a is adjacent to, and transversely offset from, the second aperture 29.sub.b, the third aperture 29.sub.c is adjacent to, and transversely offset from, the second aperture 29.sub.b and so on. In this arrangement, the first and second apertures 29.sub.a, 29.sub.b and the third and fourth apertures 29.sub.c, 29.sub.d, have a transverse separation.

(94) The fifth aperture 29.sub.e is axially aligned with the first and second apertures 29.sub.a, 29.sub.b to form the first group of apertures A.sub.1. The fifth aperture 29.sub.e is of a different width x than the other apertures 29.sub.a, 29.sub.b 29.sub.c, 29.sub.d.

(95) The third and fourth apertures 29.sub.c, 29.sub.d, form the second group of apertures A.sub.2.

(96) The two groups A.sub.1, A.sub.2 are offset around the actuator axis z, with the angular separation between centre the groups A.sub.1, A.sub.2 being denoted in FIG. 13B by . In this example, is 180.

(97) In FIG. 13C, there are four apertures, three arranged in an axially aligned group of apertures. In the first group A.sub.1, the first aperture 29.sub.a is adjacent to, and transversely offset from, the second aperture 29.sub.b.

(98) The single, third aperture 29.sub.c is transversely offset from the first group A.sub.1, around the actuator axis z, with the angular separation between the centre of the axially-aligned group A.sub.1 and the centre of the third aperture 29.sub.c being denoted in FIG. 13C by .

(99) The fourth aperture 29.sub.d is axially aligned with the first and second apertures 29.sub.a, 29.sub.b to form the first group A.sub.1, and is transversely offset around the actuator axis z from the third aperture 29.sub.c with the angular separation . In this example, is 180.

(100) The fourth aperture 29.sub.d is of a different width x than the other apertures 29.sub.a, 29.sub.b 29.sub.c.

(101) In FIG. 13D, five apertures are arranged into two groups A.sub.1, A.sub.2 of apertures and a single aperture 29.sub.c.

(102) In this example, the first group A.sub.1 is transversely offset from the second group A.sub.2 around the actuator axis z, with an angular separation of .sub.1as measured from the centre of each group. The third aperture 29.sub.c is transversely offset from the centre of the second group A.sub.2 by an angular separation .sub.2. In this example, .sub.1 and .sub.2 are 120.

(103) The arrangement illustrated in FIG. 13E also has two groups A.sub.1, A.sub.2 of apertures and a single, first aperture 29.sub.a.

(104) In this example, the first aperture 29.sub.a is transversely offset from the first group A.sub.1 by an angular separation .sub.1, and the second group A.sub.2 is transversely offset from the first group A.sub.2 with an angular separation of .sub.2.

(105) The second and third apertures 29.sub.b, 29.sub.c and the fourth and fifth apertures 29.sub.d, 29.sub.e, have a transverse separation.

(106) In the arrangement illustrated in FIG. 13F, there are six apertures arranged in a two-three-one grouping with different angular separations .sub.1, .sub.2 between the groups A.sub.1, A.sub.2 and the single aperture 29.sub.d. The first and second groups A.sub.1, A.sub.2, of two and three axially-aligned apertures respectively, are transversely offset with an angular separation .sub.1. The first group A.sub.1 includes the first and second apertures 29.sub.a 29.sub.f.

(107) The single, fourth aperture 29.sub.d is transversely offset from the second group A.sub.2 with an angular separation .sub.2.

(108) In the second group A.sub.2, the second and third apertures 29.sub.b 29.sub.c have a transverse separation. The second group includes the fifth aperture 29.sub.e.

(109) The fifth and sixth apertures 29.sub.e 29.sub.f are of a different width x than the other apertures.

(110) In the arrangement illustrated in FIG. 13G, there are nine apertures arranged in a two-three-two-two grouping A.sub.1, A.sub.2, A.sub.3, A.sub.4 of axially-aligned apertures, with angular separations .sub.1, .sub.2 .sub.3 between the groups A.sub.1, A.sub.2, A.sub.3, A.sub.4. As can be seen in FIG. 13G, the sixth aperture 29.sub.f, which is adjacent the fifth aperture 29.sub.e and the seventh aperture 29.sub.g is in the third group A.sub.3, with the adjacent apertures 29.sub.e 29.sub.g being in the fourth group A.sub.4. As such, adjacent apertures in the axial direction can be in either a clockwise or anticlockwise transverse direction of each other.

(111) In the second group A.sub.2, the second and third apertures 29.sub.b 29.sub.c have a transverse separation. The seventh, eighth and ninth apertures 29.sub.g 29.sub.h 29.sub.i are of a different width x than the other apertures.

(112) In the examples described herein, the groups A.sub.1, A.sub.2, A.sub.3, A.sub.4 of axially aligned apertures are substantially equidistantly placed around the circumference of the dividing wall 28.

(113) As such, the values of the angular separations .sub.1 .sub.2 .sub.3 for the arrangements described above are set out in the Table 3 below:

(114) TABLE-US-00003 TABLE 3 FIG. B.sub.1 B.sub.2 B.sub.3 FIG. 13A 180 FIG. 13B 180 FIG. 13C 180 FIG. 13D 120 120 FIG. 13E 120 120 FIG. 13F 120 120 FIG. 13G 90 90 90

(115) In other arrangements the values of the angular separations can be different.

(116) The angular offset between adjacent apertures around the actuator axis z, and as measured between the centres of the apertures will vary depending upon the width of the apertures, the separation b between apertures, and the diameter of the separator. Examples of these values are shown with respect to Tables 1 and 2 and described above. The angular offset can be 180, or can be less than 180.

(117) The illustrated arrangements are provided as examples only and alternative arrangements may be appropriate.

(118) Although the separator is described with reference to a closed or open crankcase ventilator system, the separator can also be applied to a crankcase ventilator with a downstream pump system to increase separation efficiency, or to any system that requires oil aerosol separation.