(19) |
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EP 0 096 992 A1 |
(12) |
EUROPEAN PATENT APPLICATION |
(43) |
Date of publication: |
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28.12.1983 Bulletin 1983/52 |
(22) |
Date of filing: 25.05.1983 |
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(51) |
International Patent Classification (IPC)3: F02M 35/14 |
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(84) |
Designated Contracting States: |
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BE DE FR IT NL SE |
(30) |
Priority: |
15.06.1982 GB 8217247
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(71) |
Applicant: Fram Europe Limited |
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Pontyclun
Mid Glamorgan CF7 8YU (GB) |
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(72) |
Inventor: |
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- Azzopardi, Spiridion
Glamorgan (GB)
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(74) |
Representative: Turner, Alan Reginald |
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c/o Bendix Limited
Douglas Road Kingswood, Bristol BS15 2NL Kingswood, Bristol BS15 2NL (GB) |
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(54) |
Air filter assemblies for reciprocating machines |
(57) An air filter assembly primarily for Air I.C. engine is provided with an air streamlining
and sound energy absorbing baffle (12) arranged to substantially obstruct the direct
noise transmission path from the air outlet port (5) through the filter element (9)
to the input air duct (4).
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[0001] This invention relates to air filter assemblies for reciprocating machines and relates
especially to noise reduction in air filter assemblies for internal combustion engines.
[0002] Air filter assemblies for internal combustion engines are known in which an air filter
housing is provided for mounting immediately above an engine air intake (typically
the choke of a carburettor), whereby in operation air is drawn radially inwards through
a generally cylindrical pleated paper filter element for cleaning air from a surrounding
chamber connected to an inlet tube or duct. It is found that such apparatus is prone
to transmit appreciable engine induction noise.
[0003] The principle object of the present invention is to provide inexpensive and efficient
means for reducing such noise.
[0004] According to the present invention there is provided an air filter assembly for a
reciprocating machine including a housing having a chamber for a filter element providing
a filtering barrier surrounding an air outlet port and an inlet duct communicating
with a region of said chamber outside the filter element, characterised by noise attenuating
means located in the air stream from said duct for streamlining and generally directing
the air flow in two directions around the filter element but substantially obstructing
the direct noise transmission path between the outlet port and said duct.
[0005] The attenuating means may have thin walls to form a sound absorbing enclosure which
may preferably be filled with a sound absorbing material such as expanded polystyrene.
[0006] In order that the invention may be more clearly understood and readily carried into
effect the same will be further described by way of example with reference to the
accompanying drawing in wich:
Fig. 1 illustrates in diagramatic form a perspective view of a typical air filter
assembly for a motor vehicle petrol engine and,
Fig. 2 illustrates a part-cut-away view of such an assembly incorporating a noise
absorbing baffle in accordance with the present invention.
[0007] Referring to Fig. 1, a generally flat cylindrical filter housing 1 is provided with
a removeable upper end-cover 2 for providing access to the interior in known manner
for replacement of a generally cylindrical impregnated pleated paper air filter 9
as seen in Fig. 2. The main air inlet to the filter housing is at 3 via a tube or
duct 4 providing access via a tapered portion 17 of the housing to a generally annular
region 6 around the outside of the filter element and the outlet to the carburettor
is via a port 5 which communicates with a region 7 on the inside of the filter element.
It will be understood that in the complete assembly the respective ends of the pleats
of the paper filter 9 are effectively sealed between the cover 2 and the floor of
the housing against the passage of airborne material from 6 to 7.
[0008] In order to provide some control over the temperature of air reaching the carburettor
and especially to prevent excessively colder air reaching it a temperature controlled
vacuum operated motor 10 is incorporated in the tube or'duct 4 to control the opening
and closing of a flap valve (not shown) to permit the entry of warm air at a further
port 11, derived from an enclosure (not shown) around the exhaust manifold of the
engine. If required the apparatus may also incorporate means as described in the Specification
of copending E. P. O. Patent Application No.82300731.5for preventing problems arising
from loss of vacuum at full throttle settings.
[0009] The apparatus as thus described is prone to transmit noise levels from the housing
and the port 3 whereas the current desire of vehicle builders is to reduce noise levels
even lower than hitherto. Accordingly, by virtue of one example of the invention it
is proposed to introduce into the tapered portion 17 of the housing which opens into
the chamber 6, a noise attenuating means in the form of a generally triangular baffle
12. This is of hollow form filled with a noise absorbent material 13 such as expanded
polystyrene. The dimensions of the baffle are so chosen that it streamlines and generally
directs the air flow in two directions around the filter element as indicated by the
arrows. The baffle 12 introduces negligible reduction of cross-sectional flow area
for access of air to the chamber 6 and port 5 but at the same time it substantially
obstructs the direct noise transmission path between the outlet port 5 and the duct
4.
[0010] In the example shown in Fig. 2 the face 14 of the baffle 12 which faces the filter
element is curved to conform generally with the curvature of the housing 1 whereas
the walls 15 and 16 are substantially flat to conform with the adjacent walls of the
tube or duct. With such an arrangement it is found that appreciable noise level reduction
is achieved and it is believed that such reduction results in part from internal reflection
and surface absorbtion especially at surface 14 of the baffle.
[0011] It will be appreciated that dependent upon the shape of the filter housing and duct
or tube, the precise shape of the baffle may be varied. For example in some applications,
the sides such as 15 and 16 may require to be curved to correspond with curved adjacent
walls of the tube or duct. Moreover, the face 14 and even the walls 15 and 1'6 may
be acoustically formed to improve the sound attenuating quality of the assembly. For
example these faces may be perforated, or given a small sawtooth or corrugated form
which does not appreciably detract from the streamline flow of air.
[0012] In an alternative embodiment the tube or duct 4 may be of generally circular or oval
cross-section.
[0013] In such an example the baffle may preferably be designed to be of generally conical
shape. Whilst still streamlining and generally directing air flow in two directions
around the filter element 9. In this case the baffle shape although not having vertical
sides extending between upper and lower faces of the duct would be provided with means
for supporting it in the desired position in the flow path and again such as to substantially
obstruct the direct noise transmission path between the outlet port 5 and the duct
4.
[0014] In yet a further alternative the baffle may be of generally 'V' section. That is
it may be provided with walls such as 15 and 16 or a circular conical or elliptical
conical surface but having no base surface such as 14. In such a case noise attenuation
will occur as a result of internal absorption and reflection within the baffle.
[0015] By virtue of the way in which such a baffle can be positioned to influence noise
transmission and the air flow around the filter element in addition to an attenuated
level of noise improved filter efficiency and dust capacity may usefully and advantageously
be achieved with consequent longer filter element life.
1. An air filter assembly for a reciprocating machine including a housing (1) having
a chamber for a filter element (9) providing a filtering barrier surrounding an air
outlet port (5) and an inlet duct (4) communicating with a region (6) of said chamber
outside the filter element, characterised by noise attentuating means (12) located
in the air stream from said duct (4) for streamlining and generally directing the
air flow in two directions around the filter element (9') but substantially obstructing
the direct noise transmission path between the outlet port (5) and said duct (4).
2. An air filter assembly as claimed in claim 1 characterised by said noise attenuating
means (12) comprising a generally tapered baffle located in a similarly tapered portion
(17) of the housing.
3. An air filter assembly as claimed in claim 2 characterised by said baffle having
a base surface facing the filter element.
4. An air filter assembly as claimed in claim.1, 2 or 3 the surfaces of the baffle
which are impinged by an incoming air stream being generally flat surfaces (15, 16).
5. An air filter assembly as claimed in claim 1, 2 or 3, said baffle having a generally
conical surface presented to the incoming air stream.
6. An air filter assembly as claimed in claims 1, 2, 3,4 or 5 said baffle comprising
an outer shell filled with sound absorbent material (13).
7. An air filter assembly as claimed in claim 6, said sound absorbent material (13)
being expanded polystyrene.
8. An air filter assembly as claimed in claim 1, 2, 3, 4, 5, 6 or 7 the surface of
the baffle being provided with acoustically designed perforations corrugations or
sawtooth shape to enhance the resultant noise attenuation.
9. An air filter assembly substaatially as described herein with reference to Fig.
1 and Fig. 2 of the accompanying drawing.
