Centrifugal separator having a particle guide trough

Abstract

A centrifugal separator for separating non-gaseous particles from a gas flow having a separator housing enclosing a rotor with a raw gas inlet, a clean gas outlet, and a particle outlet. A circumferential wall encloses the rotor. A raw gas flow is guided axially into the rotor. A clean gas flow is guided out of the rotor and then between the rotor and the circumferential wall to the clean gas outlet. The rotor comprises particle separation elements so that particles separated from the gas flow are centrifuged onto the circumferential wall. The circumferential wall particles are guided to the particle outlet via at least one particle guide trough running diagonal to the rotor axial direction on the interior of the circumferential wall. A radius of each trough as well as the distance between the rotor and the circumferential wall decreases in the direction of the clean gas flow.

Claims

1. A centrifugal separator for separating liquid particles from a gas flow, comprising: a separator housing having a rotor rotatable about an axis arranged therein, the separator housing having a raw gas inlet, a clean gas outlet and a liquid outlet as well as an imperforate circumferential wall which radially encloses an outer circumference of the rotor at a distance therefrom, the raw gas inlet axially guiding a raw gas flow into the rotor where the gas flow is set into rotation by the rotating rotor, a clean gas flow being guided away radially out of the rotor and then between the outer circumference of the rotor and an inner circumference of the circumferential wall to the clean gas outlet, the rotor having particle separation elements comprising a disc stack separator, by means of which liquid which has been separated from the gas flow is thrown off onto the inner circumference of the circumferential wall by centrifugal force when the rotor is rotating, the liquid on the circumferential wall being fed to the liquid outlet via at least one liquid guide trough in the form of an inverted groove which runs at an angle to the axis direction of the rotor and which is arranged on the inner circumference of the imperforate circumferential wall, each liquid guide trough forming a section of a conical spatial spiral defining a liquid flow path and being configured to guide the liquid along said liquid flow path of the conical spatial spiral, wherein a progression of each liquid guide trough has a radius from the axis which decreases towards the clean gas outlet in the direction of the clean gas flow, and a distance between the outer circumference of the rotor and the inner circumference of the circumferential wall becoming smaller towards the clean gas outlet in the direction of the clean gas flow.

2. The centrifugal separator as claimed in claim 1, wherein a measure of the reduction in the radius is sized depending on a width of each liquid guide trough and on the number of liquid guide troughs, so that the circumferential wall with the separator housing which has at least one liquid guide trough, can be removed from a mold axially without undercuts when manufactured as an injection molded or diecast part.

3. The centrifugal separator as claimed in claim 1, wherein each liquid guide trough extends over less than a total height of a part of the rotor which throws off liquid.

4. The centrifugal separator as claimed in claim 3, wherein the clean gas outlet is arranged above the rotor in the separator housing, the clean gas flow being guided away between the outer circumference of the rotor and the inner circumference of the circumferential wall upwards to the clean gas outlet, and each liquid guide trough beginning at the same height or above a top end of the part of the rotor which throws off liquid and extending downwards therefrom.

5. The centrifugal separator as claimed in claim 4, wherein each liquid guide trough is continued downwards into a vertical liquid discharge trough which runs axially further downwards.

6. The centrifugal separator as claimed in claim 5, wherein the distance between the outer circumference of the rotor and the inner circumference of the circumferential wall is constant over the range of height taken up by the axially running liquid discharge trough.

7. The centrifugal separator as claimed in claim 5, wherein each liquid guide trough and liquid discharge trough is undercut when viewed in cross section and is open in an opposite direction to a direction of rotation of the rotor and is formed steplessly and continuously with the inner circumference of the circumferential wall in the direction of rotation of the rotor.

8. The centrifugal separator as claimed in claim 1, wherein the circumferential wall with the at least one liquid guide trough is an integral part of the separator housing.

9. The centrifugal separator as claimed in claim 8, wherein the part of the separator housing having the at least one liquid guide trough is a housing cover which can be removed from the remaining separator housing.

10. The centrifugal separator as claimed in claim 1, wherein the circumferential wall with the at least one liquid guide trough is a sleeve which is inserted in the separator housing.

11. The centrifugal separator as claimed in claim 1, wherein a single liquid guide trough, which extends over 360° in the circumferential direction, is arranged on the inner circumference of the circumferential wall.

12. The centrifugal separator as claimed in claim 1, wherein n liquid guide troughs, each extending over 360°/n and not overlapping one another, are arranged on the inner circumference of the circumferential wall, wherein n≧2.

13. The centrifugal separator as claimed in claim 1, wherein a circumferential liquid collection trough which is connected to the liquid outlet is arranged in the separator housing below an axial bottom end of each liquid guide trough.

14. The centrifugal separator as claimed in claim 5, wherein a circumferential liquid collection trough which is connected to the liquid outlet is arranged in the separator housing below an axial bottom end of each liquid discharge trough.

15. The centrifugal separator as claimed in claim 1, wherein the centrifugal separator is an oil mist separator for the crankcase exhaust gas of an internal combustion engine.

16. The centrifugal separator as claimed in claim 15, wherein the internal combustion engine is in a motor vehicle.

17. A centrifugal separator for separating liquid particles from a gas flow, comprising: a separator housing having a rotor rotatable about an axis arranged therein, the separator housing having a raw gas inlet, a clean gas outlet and a liquid outlet as well as a circumferential wall which radially encloses an outer circumference of the rotor at a distance therefrom, the raw gas inlet axially guiding a raw gas flow into the rotor where the gas flow is set into rotation by the rotating rotor, a clean gas flow being guided away radially out of the rotor and then between the outer circumference of the rotor and an inner circumference of the circumferential wall to the clean gas outlet, the rotor having particle separation elements comprising a disc stack separator, by means of which liquid which has been separated from the gas flow is thrown off onto the inner circumference of the circumferential wall by centrifugal force when the rotor is rotating, the liquid on the circumferential wall being fed to the liquid outlet via at least one liquid guide trough which runs at an angle to the axis direction of the rotor and which is arranged on the inner circumference of the imperforate circumferential wall, each liquid guide trough forming a section of a conical spatial spiral, wherein a progression of each liquid guide trough has a radius from the axis which decreases towards the clean gas outlet in the direction of the clean gas flow, and the outer circumference of the rotor having a cylindrical shape and the inner circumferential wall having a conical shape, narrowing in the direction towards the clean gas outlet, such that a distance between the outer circumference of the rotor and the inner circumference of the circumferential wall becomes smaller towards the clean gas outlet in the direction of the clean gas flow.

18. A centrifugal separator for separating liquid particles from a gas flow, comprising: a separator housing having a rotor rotatable about an axis arranged therein, the separator housing having a raw gas inlet, a clean gas outlet and a liquid outlet as well as a circumferential wall which radially encloses an outer circumference of the rotor at a distance therefrom, the raw gas inlet axially guiding a raw gas flow into the rotor where the gas flow is set into rotation by the rotating rotor, a clean gas flow being guided away radially out of the rotor and then between the outer circumference of the rotor and an inner circumference of the circumferential wall to the clean gas outlet, the rotor having particle separation elements comprising a disc stack separator, by means of which liquid which has been separated from the gas flow is thrown off onto the inner circumference of the circumferential wall by centrifugal force when the rotor is rotating, the liquid on the circumferential wall being fed to the liquid outlet via at least one liquid guide trough which runs at an angle to the axis direction of the rotor and which is arranged on the inner circumference of the circumferential wall, each liquid guide trough being in the form of an elongated groove formed by two side walls and a bottom wall along the inner circumference of the circumferential wall, wherein an inner surface of one of the side walls is flush with the circumferential wall and an outer surface of the other of the side walls is flush with the circumferential wall, each liquid guide trough forming a section of a conical spatial spiral, wherein the progression of each liquid guide trough has a radius which decreases towards the clean gas outlet in the direction of the clean gas flow, and a distance between the outer circumference of the rotor and the inner circumference of the circumferential wall becoming smaller towards the clean gas outlet in the direction of the clean gas flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are explained below with reference to a drawing. The figures of the drawing show:

(2) FIG. 1 a centrifugal separator in a longitudinal section,

(3) FIG. 2 a housing cover of the separator from FIG. 1 in a longitudinal section,

(4) FIG. 3 the housing cover from FIG. 2 in a view at an angle from below,

(5) FIG. 4 the housing cover from FIG. 3 in a view from below,

(6) FIG. 5 the housing cover in a modified design in a view at an angle from below,

(7) FIG. 6 the housing cover from FIG. 5 in a view from below,

(8) FIG. 7 a sleeve as part of the centrifugal separator in front view,

(9) FIG. 8 the sleeve from FIG. 7 in a view at an angle from below,

(10) FIG. 9 the geometric progression of a guide trough in the form of a conical spatial spiral in cylindrical coordinates,

(11) FIG. 10 a geometric development of a guide trough,

(12) FIG. 11 a schematic front view of the separator housing with four guide troughs connected to one another in the circumferential direction,

(13) FIG. 12 the separator housing from FIG. 11 in longitudinal section, and

(14) FIG. 13 a schematic front view of the separator housing with four guide troughs overlapping one another in the circumferential direction,

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(15) FIG. 1 of the drawing shows a centrifugal separator 1 in a schematic diagram in a longitudinal section. The centrifugal separator 1 has a separator housing 10 which is only partially shown here. An upper part of the separator housing 10 is formed by a housing cover 11 which is releasable and connected to the remaining separator housing 10 while interposing a sealing ring 11′. A rotor 3, which for example is formed by a disc stack 3′ as is known per se, is arranged inside the separator housing 10, here inside the housing cover 11. The rotor 3 can be set into rotation about an axis of rotation 31 with the direction of rotation 32 by means of a drive 33 arranged in the separator housing below the rotor 3.

(16) A raw gas flow 13 carrying particles to be separated, for example the crankcase exhaust gas of an internal combustion engine containing oil mist, is fed axially into the rotor 3 from below. The gas flow is deflected outwards in a radial direction within the rotor 3 and then leaves the rotor 3 at its outer circumference 30 in the height range A. Particles fed into the raw gas flow 13 are first separated from the gas flow by deflecting the flow at surfaces present within the rotor 3 and then thrown off outwards by centrifugal force, as a result of which the particles are deposited on the inner circumference 20 of the circumferential wall 2 of the housing cover 11. The gas which has been freed from particles flows upwards as clean gas 14 through the annular gap between the outer circumference 30 of the rotor 3 and the inner circumference 20 of the circumferential wall 2 to a clean gas outlet 14′, which here is arranged in the center of the cover 11.

(17) One or more, four in the example according to FIG. 1, particle guide troughs 21 are provided on the inner circumference 20 of the circumferential wall 2, in this case molded on in one piece. The particle guide troughs 21 each run spirally from top to bottom viewed in the direction of rotation 32 of the rotor 3, wherein the diameter of the circumferential wall 2 and therefore also the radius of the particle guide troughs 21 arranged thereon at the same time increases from top to bottom. The gas flow in the annular gap between circumferential wall 2 and rotor 3 which is set into rotation by the rotating rotor 3 ensures that the particles deposited on the inner circumference 20 of the circumferential wall 2 are fed along the inner circumference 20 to the particle guide troughs 21 and then guided downwards at an angle along the particle guide troughs 21. In the downwards direction, each particle guide trough 21 merges into an axially running particle discharge trough 22 which in each case finally opens out into a particle collection trough 15 running around the separator housing 10 in the circumferential direction.

(18) The distance a between the inner circumference 20 of the circumferential wall 2 and the outer circumference 30 of the rotor 3 is not constant viewed over the height A of the outer circumference 30 of the rotor 3 which throws off particles but becomes smaller in the flow direction of the clean gas flow 14, here seen from bottom to top. With the dimension a2, the said distance is greater in a lower region of the outer circumference 30 of the rotor 3 than in an upper region of the outer circumference 30 of the rotor 3 where the distance has the smaller dimension a1. As a result, a larger flow cross section is provided for the clean gas escaping from the rotor 3 in the lower region of the outer circumference 30 of the rotor 3, which ensures a lower gas flow speed in this region. This in turn makes it easier for the separated particles to be guided away downwards without the risk of particles deposited on the inner circumference 20 of the circumferential wall 2 ever finding their way unwanted into the clean gas flow 14 once more. The relatively large distance a2 is not a problem here, as predominantly large particles which have a large inertia, with which they can also overcome the relatively larger distance a2 without being picked up by the relatively slow clean gas flow 14 here, are thrown off in this lower region of the rotor 3.

(19) Predominantly smaller and lighter particles are thrown off in the upper region of the outer circumference 30 of the rotor 3, for which it is of advantage that, with the dimension a1, the distance from the outer circumference 30 of the rotor 3 to the inner circumference 20 of the circumferential wall 2 is smaller here. As a result of this small distance a1, smaller and lighter particles also reliably reach the inner circumference 20 of the circumferential wall 2 in spite of their lower inertia and are thus likewise reliably separated from the gas flow.

(20) FIG. 2 of the drawing shows the housing cover 11 of the centrifugal separator 1 from FIG. 1 as a single part in longitudinal section. As a result of this, the particle guide troughs 21 arranged on the inner circumference 20 of the circumferential wall 2 and the particle discharge troughs 22 which continue them downwards now become visible. Each particle guide trough 21 has a beginning 21.1 at the top and an end 21.2 in the downwards direction after a height A1. Each particle discharge trough 22 extends over a height A2. The ratio of the heights A1 and A2 to one another can be changed as required and optimized by testing.

(21) As FIG. 2 further shows, viewed in the circumferential direction, each particle guide trough 21 extends over somewhat less than 90° so that in each case two adjacent particle guide troughs 21 do not overlap one another in the circumferential direction, which enables a particularly compact design to be achieved.

(22) Furthermore, FIG. 2 illustrates that each particle guide trough 21 at its side which points upwards at an angle and each particle discharge trough 22 at its side which points in the direction of rotation of the rotor is formed continuously and steplessly with the inner circumference 20 of the circumferential wall 2, as a result of which troublesome gas eddies are prevented or at least reduced.

(23) The lower diameter of the inner circumference 20 of the circumferential wall 2 is greater than the diameter in the upper region of the circumferential wall 2. At the same time, expediently, the lower diameter is greater than the upper diameter to such an extent that the particle guide troughs 21 can be removed axially downwards and without undercuts from the mold when the housing cover 11 is manufactured as an injection molded part.

(24) The lower diameter is the diameter up to which the particle guide troughs 21 are present in a downwards direction. No further tapering is required in the region below this where the spiral particle guide troughs 21 are no longer present but only the particle discharge troughs 22 which continue these axially in a straight line.

(25) FIG. 3 of the drawing shows the housing cover 11 from FIGS. 1 and 2 in a view at an angle from below. Here, two of the four particle guide troughs 21 with their axial particle discharge troughs 22 which are connected to the bottom of each are visible on the inner circumference 20 of the circumferential wall 2. Here too it can be seen that each particle guide trough 21 has a beginning 21.1 at the top and an end 21.2 at the bottom. At the same time, the particle guide troughs 21 do not overlap one another viewed in the circumferential direction as each of the four particle guide troughs 21 in each case extends over somewhat less than 90° viewed in the circumferential direction. Likewise, it can be clearly seen in FIG. 3 that each particle guide trough 21 and particle discharge trough 22 is formed continuously and steplessly with the inner circumference 20 of the circumferential wall 2 viewed in the direction of rotation of the rotor.

(26) FIG. 4 of the drawing shows the housing cover 11 from FIG. 3 in a view from below. The circumferential wall 2 with its inwardly facing inner circumference 20 runs radially outwards. The four particle guide troughs 21, which in each case extend over somewhat less than 90° viewed in the circumferential direction, run on the inner circumference 20. The number of particle guide troughs 21 can of course also be less than four or greater than four.

(27) An example of an embodiment of the centrifugal separator or its housing 11 with a single particle guide trough 21 on the inner circumference 20 of the circumferential wall 2 is shown in FIGS. 5 and 6. The particle guide trough 21 thus has a relatively small pitch which, although it extends the path for the separated particles along the particle guide trough 21, overall makes for a smoother surface of the inner circumference 20 of the circumferential wall 2 and thus reduces troublesome gas eddies to a minimum.

(28) The view from below of the housing cover 11 in FIG. 6 illustrates that, also in the case of the embodiment with only a single particle guide trough 21, its beginning 21.1 and its end 21.2 are spaced slightly apart in the circumferential direction in order to guarantee simple removal from the mold in an axial direction when the housing cover 11 is manufactured. Here too, the inside diameter of the inner circumference 20 of the circumferential wall 2 with the particle guide trough 21 becomes smaller from bottom to top, that is to say in the gas flow direction towards the clean gas outlet, in order to make the annular gap between the inner circumference 20 of the circumferential wall 2 and the outer circumference of the rotor narrower in the direction of the clean gas outlet when the centrifugal separator is assembled.

(29) An exemplary embodiment, for which it is characteristic that the circumferential wall 2 with particle guide troughs 21 has the form of a separate sleeve 12 which is made as a single part and then inserted in the separator housing, is shown in FIGS. 7 and 8.

(30) The front view in FIG. 7 shows the circumferential wall 2 radially outwards with its inner circumference 20 which faces radially inwards, on which here too four particle guide troughs 21 distributed in the circumferential direction are molded on in one piece.

(31) The view in FIG. 8 shows the progression of the particle guide troughs 21 on the inner circumference 20 of the circumferential wall 2, wherein here each particle guide trough 21 again has a beginning 21.1 at the top and a lower end 21.2. From the bottom end 21.2 of each particle guide trough 21, an axially running particle discharge trough 22 leads down further to a bottom front end of the sleeve 12. At the same time, the inside diameter of the sleeve 12 above the particle guide troughs 21 is in each case less than below the particle guide troughs 21. This ensures that, even with the sleeve 12, the distance between the inner circumference 20 of the circumferential wall 2 and the outer circumference of the rotor becomes smaller towards the clean gas outlet in the gas flow direction in the assembled state of a centrifugal separator with the sleeve 12.

(32) The sleeve 12 can likewise be manufactured in one piece as an injection molded part and in doing so can likewise easily be removed from the mold in an axial direction, as even with the sleeve 12 the particle guide troughs 21 do not overlap one another in the circumferential direction.

(33) Here too, the transition of each particle guide trough 21 and each particle discharge trough 22 in the direction of rotation of the rotor is stepless and continuous in order to prevent troublesome gas eddies.

(34) When the sleeve 12 is inserted into a separator housing, expediently a particle collection trough 15, as shown by way of example in FIG. 1, lies below the bottom front end of the sleeve 12.

(35) FIG. 9 of the drawing shows the progression of a guide trough geometrically as a conical spatial spiral in cylindrical coordinates and FIG. 10 shows a development of a guide trough geometrically. Here: R=Start radius (=maximum radius) D=Change in radius H=Overall height of guide trough Ω=Total angle of guide trough [rad] S=Pitch of guide trough, and α=Helix angle of guide trough.

(36) Under the assumption that R>>D, the following is approximately true:

(37) $S=\frac{H}{\Omega *R}$

(38) In practice, the value for the pitch S advantageously lies between 0.5 and 1, and the value for the helix angle α between 30° and 45°.

(39) Also in FIG. 9:

(40) h=Height of a point on the guide trough

(41) r=Radius of a point on the guide trough, and

(42) ω=Angle of a point on the guide trough [rad].

(43) The angle ω and the radius r can then be expressed as a function of h as follows:

(44) $\omega \left(h\right)=\frac{h}{H}*\Omega \mathrm{and}r\left(h\right)=R-\frac{h}{H}*D$

(45) The demolding chamfers are small and are ignored in the following considerations; normal values are 0.5°-1° for plastic and 1°-3° for aluminum diecasting.

(46) The progression of the guide trough(s) shown in FIG. 9 and described above has a radius R (=distance from central axis) which decreases in the clean gas flow direction. This change D in the radius can advantageously be chosen so that the component of the separator which has the guide trough or troughs, i.e. its housing or cover or also the sleeve, can be removed from the mold without undercuts in the opposite direction to the clean gas flow.

(47) For this purpose, the quantities B (=width of the guide troughs) and n (=number of guide troughs) are also considered with reference to FIGS. 11 to 13 which show appropriate examples in a purely geometric form, wherein the width B is shown greatly enlarged for better clarity.

(48) FIG. 11 shows schematically an example with four non-overlapping guide troughs 21 in a front view; FIG. 12 shows the same example in a longitudinal section.

(49) FIG. 13 shows an embodiment which, in contrast to the embodiments shown in the remaining figures, differs by way of guide troughs 21 which overlap one another in the circumferential direction. Such an embodiment is likewise possible and can be manufactured without increased effort using the injection molding or diecasting method, but has the disadvantage of an increased spatial requirement.

(50) However, it is only necessary for a guide trough to be present on the main part of the circumference in order to guarantee the function; the embodiments with non-overlapping guide troughs are therefore to be seen as particularly advantageous.

(51) In order to guarantee that the component of the separator which has the guide trough or troughs can be removed from the mold without undercuts, the following must apply for the maximum width Bmax of the guide trough:

(52) $B_{\mathrm{ma}x}=D*\frac{2*\pi }{n*\Omega }$
for demoldability; B is always D;

(53) and simultaneously

(54) $n\ge \frac{\Omega }{2*\pi }$

(55) which means that at least one guide trough is always present on the complete circumference. For some practical examples, this then results in the following relationships for the maximum permissible width Bmax of the guide trough as a function of the radius change D which enables removal from the mold in an axial direction:

Example 1

(56) For Ω=2*π (=360°) and n=1 (without overlap):

(57) Bmax=D

Example 2

(58) For Ω=π/2 (=90°) and n=4 (without overlap):

(59) Bmax=D

Example 3

(60) For Ω=π (=180°) and n=4 (with overlap):

(61) Bmax=D/2

Example 4

(62) For Ω=2*π (=360°) and n=2 (with overlap):

(63) Bmax=D/2

(64) This clearly shows that, with particle guide troughs which do not overlap one another in the circumferential direction, these can have a greater width than particle guide troughs which overlap one another in the circumferential direction. Embodiments other than those stated in the examples are of course possible.

(65) As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

(66) TABLE-US-00001 List of references: Symbol Designation  1 Centrifugal separator 10 Separator housing 11 Housing cover 11′ Sealing ring 12 Sleeve 13 Raw gas flow 14 Clean gas flow 14′ Clean gas outlet 15 Particle collection trough  2 Circumferential wall 20 Inner circumference 21 Particle guide trough 21.1 Beginning of 21 (top) 21.2 End of 21 (bottom) 22 Axial particle discharge trough  3 Rotor 30 Outer circumference 31 Axis of rotation 32 Direction of rotation 33 Drive a, a.sub.1, a.sub.2 Distances between 20 and 30 A Height of the part of 3 which throws off particles A.sub.1 Extent of height of 21 A.sub.2 Extent of height of 22