Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02406284 2007-06-05
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A METHOD OF CLEANING CRANKCASE GAS
This application is a divisional application of co-pending Canadian Patent
Application No. 2,390,944, filed May 9, 2002.
The present invention relates to a method of cleaning crankcase gas, by means
of centrifugal force, from solid or liquid particles suspended in the gas and
having a larger density than the gas. Crankcase gas is a gas generated in a
combustion engine, and containing particles in the form of oil and/or soot.
More closely the invention concerns cleaning of crankcase gas in a way such
that the gas is conducted through a chamber, which is delimited by a
stationary
housing, and is caused to rotate in the chamber by means of a rotor kept in
rotation around a rotational axis, the particles by upcoming centrifugal force
being separated from the gas and thrown towards the stationary housing.
An apparatus for cleaning of crankcase gas in this way is known for instance
through each one of the patents DE 35 41 204 Al and DE 43 11906 AI.
Thus, DE 35 41 204 Al shows an apparatus of this kind, in which the rotor is
formed as a turbine or pump wheel, which is adapted to be brought into
rotation
by gas to be cleaned entering from below into said chamber. The gas to be
cleaned is caused to flow through the turbine or pump wheel from its centre to
its periphery, where it leaves the turbine or pump wheel, rotating at the same
speed as this wheel. Particles are separated from the gas rotating in the
chamber by centrifugal force, and cleaned gas leaves the chamber through an
outlet at the upper part thereof. Particles separated from the gas deposit
onto
the surrounding wall of the chamber, liquid particles coalescing on the
surrounding wall and liquid, thereafter, running down it and further out
through
an outlet situated at the bottom of the chamber.
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DE 43 11 906 Al shows a similar apparatus for cleaning of crankcase gas, in
which the rotor is adapted to be driven by means of pressurized lubricating
oil
coming from the combustion engine, the crankcase gas of which is to be
cleaned in the apparatus. The driving lubricating oil is supplied to the rotor
at its
centre and leaves the rotor through tangentially directed outlets situated at
a
distance from the rotational axis of the rotor. The rotor constitutes in
itself, in this
case, a device for cleaning of the driving lubricating oil. The cleaned
lubricating
oil is released in the lower part of the chamber, through which the crankcase
gas
shall pass in order to be cleaned, and is returned therefrom to the
lubricating oil
system of the combustion engine. The crankcase gas is caused to pass axially
through a narrow space delimited in the chamber between the rotor and the
surrounding stationary housing. Gas rotating in the space is freed from
particles
suspended therein, which particles deposit onto the inside of the stationary
housing, where liquid particles coalesce and liquid thus formed, thereafter,
flows
towards an outlet.
The two above described known apparatuses for cleaning of crankcase gas
have rather a poor efficiency when it comes to separation of particles from a
through flowing gas.
The object of the present invention primarily is to accomplish a method of
cleaning crankcase gas, which is substantially more effective than the above
described gas cleaning methods. It is suggested that a technique previously
proposed for separating dust particles from air is utilised and improved.
Thus, the invention provides a method of cleaning crankcase gas, characterized
in that
- a rotor is kept rotating around a rotational axis in a chamber delimited
by a stationary surrounding wall, which rotor comprises a stack of conical
separation discs arranged coaxially with each other and concentrically with
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said rotational axis, the separation discs being provided with radially outer
surrounding edges,
- the crankcase gas to be cleaned is conducted through interspaces
formed between the separation discs from gas inlets to gas outlets situated at
differently large distances from the rotational axis of the rotor, so that the
crankcase gas is caused to rotate with the rotor and the particles, as a
consequence of upcoming centrifugal force, are brought into contact with the
insides of the separation discs, and
- separated particles by the rotation of the rotor are caused first to move
a distance in contact with the separation discs substantially along the
generatrices thereof towards said surrounding edge and then are thrown from
the separation discs towards said surrounding wall.
US-A-2,104,683 and US-A-3,234,716 describe apparatus for cleaning of dust-
laden air, operating according to similar principles. In each one of these
patent
specifications it is described how particles are separated from air flowing
inwardly, towards the axis, between the conical separation discs and, having
been brought into contact with the insides of the separation discs, are moved
by
means of centrifugal force towards the surrounding edges of the separation
discs.
US-A-2,104,683 describes (with reference to figure 2) that particles in the
areas
of the radially outermost parts of the separation discs are influenced
substantially only by centrifugal forces and move substantially along the
generatrices of the separation discs, i.e. in straight paths along radii drawn
from
the rotational axis of the rotor, whereas particles in the areas of the
radially inner
parts of the separation discs also and to a very large degree are influenced
by
flowing gas and, thereby, move in a direction forming an angle with these
generatrices. The flowing gas may move substantially freely between the
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separation discs and may adopt a flow direction determined by among other
things the speed by which the gas enters the interspaces between the
separation discs and the degree of influence from the rotating separation
discs.
US-A-3,234,716 describes (with reference to the figures 3 and 4) how particles
are separated in the interspaces between conical separation discs. After
having
got into contact with the insides of the separation discs the separated
particles
move substantially radially outwardly from the rotational axis of the rotor
towards
the surrounding edges of the separation discs.
For improvement of the separation efficiency in a preferred method according
to
the invention
- separated particles moving in contact with the separation discs
substantially along the generatrices thereof are caught and conducted,
together
with other particles caught in a similar way, further towards the said
surrounding
edges of the separation discs along paths forming an angle with said
generatrices and
- separated particles are caused to leave said paths and are thrown from
the separation discs substantially only in limited areas spaced from each
other
along the surrounding edges of the respective separation discs.
The improvement hereby obtainable is that particles which have once
been separated from the gas have increased possibilities in comparison with
use of the previously known technology to remain separated from the gas and,
thus, not to be entrained again by gas flowing at a large velocity through the
space through which the particles have to pass on their way from the rotor to
the
surrounding stationary surrounding wall. Thus, the particles are collected by
means of guiding or conducting members, after which they are conducted
further on by means of the centrifugal force towards the surrounding edges of
the separation discs while being agglomerated or coalesced to larger
particles.
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In an agglomerated form or as relatively large drops the separated particles
are
then thrown towards the stationary surrounding wall in limited areas
distributed
along the surrounding edges of the separation discs, whereas between such
areas spaces are left for gas flow into or out of the interspaces between the
separation discs.
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The crankcase gas to be cleaned may be brought to flow between the
separation discs either in a direction from or in a direction towards the
rotational
axis of the rotor. It is preferred that the flow is taking place in the
direction from
the rotational axis, as the flow will then be assisted by a pumping effect of
the
rotor on the gas. Thereby, no auxiliary means are needed to get the gas to
flow
through the interspaces between the rotating separation discs. The gas to be
cleaned preferably is conducted into the interspaces through an inlet space
delimited centrally in the stack of separation discs, whereas cleaned gas is
conducted out of the interspaces to an outlet space in said chamber, which
surrounds the stack of separation discs.
The separation discs may have the form of either complete or frustums of
cones,
each separation disc having either one large or several small holes in its
central
portion for through flow of gas to be cleaned or gas having been cleaned. Such
holes in the separation discs form together with the interspaces between the
separation discs central parts of one or more inlet or outlet spaces centrally
in
the stack of separation discs. For reasons having been given before it is
preferred that the flow space centrally in the stack of separation discs
communicates with the inlet and that the flow space surrounding the separation
discs communicates with the gas outlet, so that gas to be cleaned is caused to
flow in a direction from the rotational axis of the rotor through the
interspaces
between the separation discs.
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In a cleaning operation according to the invention by means of separation
discs,
which are provided with guiding or conducting members of the aforementioned
kind, liquid particles depositing on the surfaces of the separation discs will
coalesce to larger drops, which when they reach said conducting members and
move along these will coalesce to even larger drops. The liquid drops leaving
the separation discs are, therefore, substantially larger than the liquid
particles
contained in the not yet cleaned gas. Even solid particles depositing on the
surfaces of the separation discs will accumulate or be agglomerated to
substantially larger units, before they are thrown away from the surrounding
edges of the separation discs.
Since particles having got into contact with a separation disc will then move
substantially along the generatrices thereof, it is suitable that said
conducting
members are distributed around the rotational axis of the rotor and have an
extension such that two adjacent conducting members cross one and the same
generatrix of the separation disc at points situated at different distances
from the
rotational axis of the rotor. Hereby, it can be assured that substantially all
particles having got into contact with the separation disc are caught by the
conducting members and may agglomerate or coalesce with other particles to
larger units on or at these conducting members on their way towards the
surrounding edge of the separation disc.
The conducting members advantageously are formed such that they can also
serve as spacing members between adjacent separation discs. Then, each
conducting member along the whole or parts of its extension may bridge the
whole distance between two adjacent separation discs. More or less the
conducting members will then also determine the flow direction of the gas
flowing between the separation discs. Nothing prevents, however, that all or
some of the conducting members extend only across part of the axial distance
between adjacent separation discs. Preferably, a conducting member is firmly
connected with a separation disc.
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The stationary housing surrounding the rotor preferably has an outlet at the
lower part of the chamber for liquid or sludge having been separated from the
contaminated gas and having deposited on the surrounding wall of the chamber.
In an apparatus operable according to the invention the rotor may be driven by
means of any suitable kind of driving device, e.g. an electrically,
hydraulically or
pneumatically driven motor.
The invention is further described in the following with reference to the
accompanying drawing, which in figure 1 shows a longitudinal section through
an apparatus formed for performing the method according to the invention and
in figure 2 shows a section along the line II-II in figure 1.
In the drawing, figure 1 shows a sectional view of an apparatus formed for
cleaning of crankcase gas from particles suspended therein and having a larger
density than the gas. The apparatus includes a stationary housing 1 delimiting
a
chamber 2. The housing forms a gas inlet 3 to the chamber 2 for gas to be
cleaned and a gas outlet 4 from the chamber 2 for cleaned gas. The housing
further forms a particle outlet 5 from the chamber 2 for particles having been
separated from the gas.
The housing 1 includes two parts, which are kept together by means of a
number of screws 6. These screws 6 also are adapted to keep the housing
fastened to suspension members 7 of an elastic material of some kind, through
which the housing may be supported on a support (not shown).
Within the chamber 2 there is arranged a rotor 8 rotatable around a vertical
rotational axis R. A motor 9, e.g. an electric motor, is arranged for rotation
of the
rotor 8. The rotor 8 includes a vertically extending central spindle 10, which
at its
upper end is journalled in the housing 1 through a bearing 11 and a bearing
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holder 12 and at its lower end is journalled in the housing I through a
bearing 13
and a bearing holder 14. The bearing holder 14 is situated in the gas inlet 3
of
the housing and, therefore, is provided with through holes 15 for incoming gas
to
be cleaned in the chamber 2.
The rotor 8 further includes an upper end wall 16 and a lower end wall 17,
which
two end walls are connected with the central spindle 10. The lower end wall 17
in a central portion is provided with through holes 18, so that the interior
of the
rotor may communicate with the gas inlet 3. Furthermore, the lower end wall 17
is provided with an annular flange 19, which is adapted to co-operate with a
similar annular flange 20 of the bearing holder 14, so that gas entering
through
the gas inlet 3 is conducted into the interior of the rotor 8 through the
aforementioned holes 18. The flanges 19 and 20 may be adapted to completely
seal against each other, but a complete sealing between them is not necessary.
The reason for this shall be explained later.
The lower end wall 17 is formed in one piece with a hollow column 21 extending
axially upwardly from the end wall 17 and sealingly surrounding the central
spindle 10. The column extends all the way up to the upper end wall 16. In the
area of the column 21 the central spindle 10 is cylindrical, preferably for
cost
reasons circular cylindrical, and the inside of the column 21 is formed in the
same way as the outside of the spindle. The outside of the column 21 has a
non-circular cross sectional form, as can be seen from figure 2.
A stack of conical separation discs 22 is arranged between the end walls 16
and
17. Each one of the separation discs has a frustoconical portion and in one
piece therewith a plane portion 23 closest to the column 21. The plane
portion,
as can be seen in figure 2, is formed so that it may engage the non-circular
column 21 such that the separation disc shall not be able to rotate relative
to
the column 21. Furthermore, the plane portion 23 is provided with several
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through holes 24. Irrespective of whether the holes in the various separation
discs 22 are aligned axially with each other or not they form together with
the
interspaces between the central portions of the separation discs 22 a central
inlet space 25 within the rotor 8 (see figure 1), which communicates with the
gas
inlet 3.
For the sake of clarity the drawing shows only a few separation discs 22
having
large axial interspaces. In practice several more separation discs should be
arranged between the end walls 16 and 17, so that relatively thin interspaces
are formed between the discs.
Figure 2 shows the side of a separation disc 22 facing upwardly in figure 1.
In
the following this side is called the inside of the separation disc, since it
faces in
a direction inwardly towards the rotational axis of the rotor. As can be seen
the
separation disc on its inside is provided with several elongated ribs 26
forming
spacing members between the separation disc and the adjacent separation disc
situated above it in the disc stack. Between the adjacent ribs 26 in an
interspace
between two separation discs flow passages 27 are formed for gas to be
cleaned. The ribs 26 extend, as shown in figure 2, along curved paths and form
at least at the radially outer surrounding portions of the separation discs an
angle with the generatrices of the separation discs. As a consequence of the
curved form of the ribs 26 also the flow passages 27 for gas to be cleaned
extend along paths which are curved in a corresponding way. The ribs 26
extend preferably across substantially the whole of the conical portion of
every
separation disc and end up in the vicinity of the radially outer surrounding
edge
of the separation disc.
An annular space 28 surrounds the rotor 8 in the housing 1 and forms a part of
the chamber 2.
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The apparatus described above and shown in the drawing operates in the
following manner when cleaning crankcase gas from particles suspended
therein and having a larger density than the gas. It is assumed in this case
that
the particles are of two kinds, namely solids in the form of soot particles
and
liquid particles in the form of oil particles.
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By means of the motor 9 the rotor 8 is kept in rotation. Gas contaminated by
particles is introduced into the housing 1 from below through the inlet 3 and
is
conducted further on into the central inlet space 25. From here gas flows into
and radially outwardly through the interspaces between the separation discs
22.
While the gas flows between the separation discs 22 it is brought into
rotation as
a consequence of the rotation of the rotor. Thereby, the particles suspended
in
the gas are forced by the centrifugal force to move towards and into contact
with
the insides of the separation discs, i.e. the sides of the separation discs
facing
upwardly in figure 1. Upon contact with the separation discs the particles
will be
entrained thereby and, thereafter, be influenced mainly by centrifugal forces
causing the particles to move radially outwardly along the generatrices of the
separation discs. The movement of the particles along these generatrices is
illustrated by means of arrows in figure 2.
Owing to the ribs 26 forming an angle with the generatrices of the separation
discs the ribs will catch particles moving in contact with the separation
discs
towards the surrounding edges thereof. The particles caught will be conducted
further along the ribs 26 which, thus, will serve as guiding members for the
particles.
As to separated liquid particles, these coalesce to larger particles while
moving
in contact with the separation discs 22. Further such coalescense occurs when
the liquid particles move further on along the ribs 26 towards the surrounding
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edges of the separation discs. This latter movement also occurs by influence
of
centrifugal force. When the liquid particles reach the surrounding edges of
the
separation discs the coalescense has proceeded so far that the liquid is
thrown
out of the rotor in the form of relatively large liquid drops. These liquid
drops hit
the surrounding wall of the housing 1, after which the liquid thus formed runs
downwardly along this surrounding wall and out through the particle outlet 5.
Said liquid drops will leave the separation discs in limited areas situated at
a
distance from each other along the surrounding edges of the respective
separation discs, i.e. in the areas of the radially outer ends of the ribs 26.
As to separated solids, also these move in contact with the separation discs
22
towards said ribs 26 and further in contact with these ribs towards the
radially
outermost edges of the separation discs. Together with the liquid drops the
particles are thrown from the rotor against the surrounding wall of the
housing 1,
where they are entrained by down running liquid to and out through the
particle
outlet 5.
As can be seen from figure 2, the ribs 26 have a location and an extension
such
that two adjacent ribs on the same separation disc cross one and the same
generatrix of the separation disc at different distances from the rotational
axis of
the rotor. In other words the ribs 26 distributed around the rotational axis
partly
overlap each other, if they are seen from the rotational axis. Such
overlapping
may be to a larger or smaller extent, so that substantially all particles
being
brought into contact with the underside of the separation disc can be caught
by
means of curved ribs of this kind and by the ribs be conducted further towards
the surrounding edge of the separation disc.
The above described function of the curved ribs 26 is obtained independently
of
the chosen rotational direction for the rotor. The ribs need not necessarily
be
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curved as shown in figure 2. The main thing is that they form an angle with
the
generatrices of the separation discs and that this angle is such that
particles
having been caught by the ribs may be guided along these ribs towards the
surrounding edges of the separation discs. As to solid particles, the angle of
repose of the particles has to be considered in each particular case.
The gas which in each interspace between adjacent separation discs has been
freed from particles leaves the interspace through spaces situated between the
aforementioned areas, at which separated particles are thrown away from the
separation discs towards the stationary housing. The cleaned gas leaves the
chamber 2 through the gas outlet 4. As a consequence of the rotor rotation the
gas flowing through the interspaces between the separation discs 22 will get
an
increased pressure. Thus, a higher pressure prevails in the space 28 around
the
rotor 1 and in the area of the gas outlet 4 than in the central space 25 and
in the
gas inlet 3. This means that a possible leak between the flanges 19 and 20
does
not have any substantial importance. Uncleaned gas, thus, may not flow
between the flanges 19 and 20 directly from the gas inlet 3 to the gas outlet
4
but, instead, some cleaned gas will flow back into the central space 25.
Thanks to the above described concentration or agglomeration of particles on
the surfaces of the separation discs, particularly close to the spacing
members
26, solid or liquid material having been separated from the gas wiil leave the
separation discs in particle aggregates or drops so large that these will not
to a
substantial degree be entrained out of the housing 1 by the gas flowing
through
the space 28.
The described and shown apparatus has a large separation efficiency and may
be produced very cheaply upon a suitable choice of material for the different
parts of the apparatus. Thus, most of the apparatus parts may be made of
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plastics. Apart from screws and bearings only the central spindle 10 should
preferably be made of metal.
As already mentioned the lower end wall 17 of the rotor and the column 21 may
be made in one piece, suitably out of plastics. A part of the rotor formed in
this
way may form a basis for an automatized mounting of the separation discs 22,
which also suitably are made of plastics. The whole rotor mounted in this way,
with or without a spindle 10, may form an inexpensive unit for the finished
apparatus, which is easily exchangeable.
