U.S. patent application number 16/812675 was filed with the patent office on 2020-09-17 for exhaust system for an internal combustion engine of a motor vehicle as well as motor vehicle.
The applicant listed for this patent is Faurecia Emissions Control Technologies, Germany GmbH. Invention is credited to Lin Strobio Chen.
Application Number | 20200291837 16/812675 |
Document ID | / |
Family ID | 1000004719170 |
Filed Date | 2020-09-17 |
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United States Patent
Application |
20200291837 |
Kind Code |
A1 |
Chen; Lin Strobio |
September 17, 2020 |
EXHAUST SYSTEM FOR AN INTERNAL COMBUSTION ENGINE OF A MOTOR VEHICLE
AS WELL AS MOTOR VEHICLE
Abstract
An exhaust system for an internal combustion engine of a motor
vehicle includes an exhaust-gas line and an associated active
silencing device. A sound coupling-in line of the silencing device
substantially concentrically surrounds the exhaust-gas line on the
outside. A first perforation is provided in an axial portion facing
away from a sound line in an area of the exhaust-gas line enclosed
by the sound coupling-in line. An axial portion facing the sound
line is designed perforation-free at least in a portion.
Furthermore, a motor vehicle with such an exhaust system is
explained.
Inventors: |
Chen; Lin Strobio;
(Augsburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Faurecia Emissions Control Technologies, Germany GmbH |
Augsburg |
|
DE |
|
|
Family ID: |
1000004719170 |
Appl. No.: |
16/812675 |
Filed: |
March 9, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01N 1/065 20130101;
F01N 2470/02 20130101 |
International
Class: |
F01N 1/06 20060101
F01N001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2019 |
DE |
10 2019 106 159.8 |
Claims
1. An exhaust system for an internal combustion engine of a motor
vehicle comprising: an exhaust-gas line routing exhaust gas; an
active silencing device that comprises a sound-generating unit
which is acoustically coupled to the exhaust-gas line via a sound
line and a sound coupling-in line connected downstream thereto,
such that sound generated by the sound-generating unit can be
introduced into an exhaust gas flow present inside the exhaust-gas
line; wherein the sound coupling-in line substantially
concentrically surrounds the exhaust-gas line on an outside and an
area of the exhaust-gas line enclosed by the sound coupling-in line
has an axial portion facing the sound line and an axial portion
connected downstream thereto facing away from the sound line; and
wherein a first perforation is provided in the axial portion facing
away from the sound line and the axial portion facing the sound
line is designed perforation-free at least in a portion.
2. The exhaust system of claim 1 wherein the first perforation runs
around a whole periphery of the axial portion of the exhaust-gas
line facing away from the sound line.
3. The exhaust system of claim 1 wherein openings comprised by the
first perforation each have a substantially round cross
section.
4. The exhaust system of claim 1 wherein, in the area enclosed by
the sound coupling-in line upstream of the first perforation, the
exhaust-gas line has a second perforation in a peripheral portion
facing away from the sound line, wherein a peripheral portion
facing the sound line is designed perforation-free.
5. The exhaust system of claim 4 wherein at least one radial rib is
provided on an outer surface of the exhaust-gas line between the
peripheral portion facing away from the sound line and the
peripheral portion facing the sound line.
6. The exhaust system of claim 4 wherein at least one radial rib is
provided on an inner surface of the sound coupling-in line between
the peripheral portion facing away from the sound line and the
peripheral portion facing the sound line.
7. The exhaust system of claim 5 wherein the at least one radial
rib comprises a plurality of ribs with one radial rib being
provided in each of two border areas between the peripheral portion
facing away from the sound line and the peripheral portion facing
the sound line.
8. The exhaust system of claim 5 wherein the at least one radial
rib is shorter in an axial direction of the exhaust-gas line than
the sound coupling-in line.
9. The exhaust system of claim 4 wherein openings comprised by the
second perforation each have a substantially rectangular cross
section.
10. The exhaust system of claim 5 wherein a radial outer end of the
at least one radial rib or radial ribs provided on the outer
surface of the exhaust-gas line is or are at a radial distance from
the sound coupling-in line, wherein each radial rib radiating from
the exhaust-gas line is complemented by a radial rib, pointing
radially inwards radiating from the sound coupling-in line, which
is at only a small peripheral distance from an associated radial
rib radiating from the exhaust-gas line or touches the periphery of
same, and the radial inside end of which is at a radial distance
from the exhaust-gas line.
11. The exhaust system of claim 1 wherein, in an area upstream of
the sound coupling-in line, the exhaust-gas line has an axial bend
or an axial kink.
12. The exhaust system of claim 11 wherein, in the area enclosed by
the sound coupling-in line upstream of the first perforation, the
exhaust-gas line has a second perforation in a peripheral portion
facing away from the sound line, wherein a peripheral portion
facing the sound line is designed perforation-free, and wherein the
second perforation is arranged downstream of a convex area of the
axial bend or of the axial kink.
13. The exhaust system of claim 1 wherein a center axis of the
sound line runs substantially along a radial direction of the sound
coupling-in line.
14. The exhaust system of claim 5 wherein the at least one radial
rib extends up to the sound coupling-in line.
15. The exhaust system of claim 6 wherein the at least one radial
rib extends up to the sound coupling-in line.
16. The exhaust system of claim 9 wherein a short side of the
rectangle is oriented in a peripheral direction and a long side of
the rectangle is oriented in an axial direction of the exhaust-gas
line.
17. The exhaust system of claim 11 wherein the axial bend or axial
kink is substantially 90.degree..
18. A motor vehicle with an exhaust system of claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. non-provisional application
claiming the benefit of German Application No. 10 2019 106 159.8,
filed on Mar. 11, 2019, which is incorporated herein by its
entirety.
TECHNICAL FIELD
[0002] The disclosure relates to an exhaust system for an internal
combustion engine of a motor vehicle, with an exhaust-gas line
routing exhaust gas and an active silencing device, wherein the
active silencing device comprises a sound-generating unit which is
acoustically coupled to the exhaust-gas line via a sound line and a
sound coupling-in line connected downstream thereto, with the
result that sound generated by the sound-generating unit can be
introduced into an exhaust gas flow present inside the exhaust-gas
line.
[0003] Furthermore, the disclosure relates to a motor vehicle with
such an exhaust system.
BACKGROUND
[0004] Such exhaust systems are known from the state of the art.
Via the active silencing device, sound can be generated which is
superposed with a sound carried by the exhaust gas flow. Here, the
superposition is at least partly destructive in nature, with the
result that the sound carried by the exhaust gas flow is muffled or
cancelled by the active silencing device.
[0005] As a rule, loudspeakers which can function only within a
specific temperature range are used as sound-generating units of
such silencing devices.
[0006] In exhaust systems, the situation often arises that a
temperature of the exhaust gas flow, which carries the sound to be
muffled or cancelled, lies outside the temperature window in which
loudspeakers or other sound-generating units function reliably. For
this reason, such components of active silencing devices must be
protected against the high temperatures of the exhaust gas flow.
However, thermal protection must not take place at the expense of
the acoustic effectiveness of the silencing device. In other words,
in exhaust systems with active silencing devices, a compromise
between acoustic effectiveness and reliability must always be
chosen.
[0007] An exhaust system is to be provided that has an active
silencing device, which is acoustically particularly effective and
at the same time functions reliably. In particular, the active
silencing device is to be reliably protected against the thermal
influences of the exhaust gas flow.
SUMMARY
[0008] An exhaust system has a sound coupling-in line that
substantially concentrically surrounds an exhaust-gas line on an
outside, and an area of the exhaust-gas line enclosed by the sound
coupling-in line has an axial portion facing a sound line and an
axial portion connected downstream thereto facing away from the
sound line. A first perforation is provided in the axial portion
facing away from the sound line and the axial portion facing the
sound line is designed perforation-free at least in a portion. A
sound generated by the sound-generating unit therefore firstly runs
through the sound line and thus passes into the sound coupling-in
line, to be more precise into an annular space between the sound
coupling-in line and the exhaust-gas line. From here, the sound
passes into the inside of the exhaust-gas line via the first
perforation and can thus interact with the sound carried by the
exhaust gas flow. By a perforation is meant in this connection a
group of openings which are arranged with a degree of regularity.
An axial portion designed perforation-free at least in a portion is
here either designed wholly without perforation or has a
perforation merely in one portion. Compared with the axial portion
facing away from the sound line, the portion facing the sound line
is thus less markedly perforated. This can be effected, for
example, in that a total cross section of the perforation openings
in the axial portion facing the sound line is lower than a total
cross section of the perforation openings in the axial portion
facing away from the sound line. Because the axial portion facing
the sound line is designed perforation-free at least in a portion,
i.e. has no openings at least in a portion, a flow, coming from
this axial portion, of a possibly hot exhaust gas flow into the
sound line is reduced or wholly prevented. Consequently, a flow of
hot exhaust gas to the sound-generating unit is thus also reduced
or prevented. A flow of hot exhaust gas in the direction of the
sound-generating unit can thus substantially only take place via
the axial portion facing away from the sound line and the first
perforation provided there. The sound-generating unit is thus
protected against a direct inflow by a hot exhaust gas flow because
such an inflow is wholly or partly prevented. An exhaust gas flow
exiting the exhaust-gas line via the first perforation can reach
the sound-generating unit only via several deviations. This means
that the exhaust gas flow cools significantly on its way to the
sound-generating unit. Thus, the sound-generating unit is
effectively protected against the temperature influences of the
exhaust gas flow. As a result, it functions reliably and is
durable. At the same time, the sound-generating unit can be
arranged relatively close to the exhaust-gas line, as a result of
which the latter can be operated efficiently and effectively from
an acoustic point of view. Moreover, an exhaust system designed in
this way can be constructed comparatively compact. In other words,
it requires only a comparatively small installation space on a
motor vehicle which is fitted with such an exhaust system. It can
also be flexibly integrated into available installation spaces.
[0009] The idea underlying the disclosure is to perforate that area
of the exhaust-gas line which is surrounded by the sound
coupling-in line but lies in the region of the sound line as little
as possible or not at all. The region of the sound line is to be
understood as an axial portion of the exhaust-gas line which lies
opposite a mouth of the sound line into the sound coupling-in line.
The perforation, which is necessary for the acoustic coupling of
the sound-generating unit to the inside of the exhaust-gas line, is
arranged as far as possible outside the abovementioned region, thus
in an axial portion of the exhaust-gas line facing away from the
sound line. Here, the axial portion facing away from the sound line
can directly adjoin the portion, facing the sound line, that is
perforation-free at least in a portion or be arranged at a
particular distance from the portion that is perforation-free at
least in a portion.
[0010] Consequently, such an exhaust system is close to ideal in
that the sound-generating unit is coupled resistance-free from an
acoustic point of view to the inside of the exhaust-gas line, but
at the same time exhaust gas cannot flow out of the inside of the
exhaust-gas line to the sound-generating unit.
[0011] A further thermal decoupling of the sound-generating device
from the exhaust gas flow can be achieved by lengthening the sound
line. The geometric distance of the sound-generating unit from the
exhaust-gas line is thereby increased.
[0012] The first perforation advantageously runs around the whole
periphery of the axial portion of the exhaust-gas line facing away
from the sound line. This results in an effective coupling of the
sound generated by the sound-generating unit into the inside of the
exhaust-gas line.
[0013] The openings comprised by the first perforation preferably
each have a substantially round cross section. It has become
apparent that such a first perforation is particularly suitable for
coupling the active silencing unit to the inside of the exhaust-gas
line and at the same time limiting an outflow of exhaust gas via
the first perforation.
[0014] In an embodiment, the exhaust-gas line has a second
perforation in the area enclosed by the sound coupling-in line
upstream of the first perforation in a peripheral portion facing
away from the sound line, wherein a peripheral portion facing the
sound line is designed perforation-free. The peripheral portion
facing away from the sound line and the peripheral portion facing
the sound line are preferably complementary to each other to form
the whole periphery of the exhaust-gas line, i.e. there are no
further peripheral portions. This second perforation serves to
acoustically couple the sound-generating unit to the inside of the
exhaust-gas line. A sound generated by the sound-generating unit
therefore firstly runs through the sound line and thus passes into
the sound coupling-in line, to be more precise into an annular
space between the sound coupling-in line and the exhaust-gas line.
From here, the sound passes into the inside of the exhaust-gas line
via the second perforation and can thus interact with the sound
carried by the exhaust gas flow. By a perforation is again meant a
group of openings which are arranged with a degree of regularity.
Because the peripheral portion facing the sound line is designed
perforation-free, thus has no openings, a possibly hot exhaust gas
flow coming from the inside of the exhaust-gas line is prevented
from flowing directly into the sound line and in this way reaching
the sound-generating unit. A flow of hot exhaust gas in the
direction of the sound-generating unit is instead possible only via
the peripheral portion facing away from the sound line and the
second perforation provided there. The sound-generating unit is
thus protected against a direct inflow by a hot exhaust gas flow.
An exhaust gas flow exiting the exhaust-gas line via the second
perforation can reach the sound-generating unit only via several
deviations. This means that the exhaust gas flow cools
significantly on its way to the sound-generating unit. Thus, the
sound-generating unit is particularly effectively protected against
the temperature influences of the exhaust gas flow. Moreover, an
exhaust system designed in this way can be constructed
comparatively compact.
[0015] For the case where both a first and a second perforation are
provided, it can happen that exhaust gases exit the inside of the
exhaust-gas line via the second perforation. They can then be
returned into the exhaust-gas line again via the first perforation.
This is possible due to the downstream arrangement of the first
perforation relative to the second perforation. The static pressure
prevailing within the exhaust-gas line namely decreases along the
flow direction of the exhaust gas. An exhaust gas flow which has
exited the exhaust-gas line via the second perforation at
comparatively high pressure can thus re-enter the inside of the
exhaust-gas line along the pressure gradient via the first
perforation. The pressure ratios are reversed in the gap between
the exhaust-gas line and the sound coupling-in line. Here, the
highest static pressure is reached at the downstream end of the
gap, thus in the area of the first perforation. Because of these
pressure ratios, hot exhaust gases are consequently prevented from
flowing in the direction of the active silencing unit.
[0016] A radial rib, which preferably extends up to the sound
coupling-in line, can be provided on an outer surface of the
exhaust-gas line between the peripheral portion facing away from
the sound line and the peripheral portion facing the sound line.
Such a radial rib represents a flow obstacle for an exhaust gas
flow which flows out of the inside of the exhaust-gas line in the
direction of the sound-generating unit. Thus, the inflow of hot
exhaust gas into the active silencing device is further prevented.
In addition, the radial rib can be formed as cooling fin for the
exhaust-gas line. Thus, the exhaust gas flow present inside the
exhaust-gas line is cooled by via the radial rib.
[0017] The radial rib can either be attached to the exhaust-gas
line on the outside and extend in the direction of the sound
coupling-in line or be attached to the sound coupling-in line on
the inside and extend in the direction of the exhaust-gas line. It
is likewise possible for the radial rib to be connected both to the
outside of the exhaust-gas line and to the inside of the sound
coupling-in line. For example, the radial rib can be welded to the
exhaust-gas line and/or the sound coupling-in line. It is likewise
possible to manufacture the radial rib integral with the
exhaust-gas line and/or the sound coupling-in line.
[0018] According to an embodiment, a radial rib is provided in each
of the two border areas between the peripheral portion facing away
from the sound line and the peripheral portion facing the sound
line. Thus, a total of two radial ribs are provided. They each
represent a flow obstacle at the transition point between the
peripheral portion facing away from the sound line and the
peripheral portion facing the sound line, with the result that, as
already described above, the inflow of hot exhaust gas into the
sound line is impeded or prevented. The two radial ribs are
arranged, for example, radially opposite, thus they are offset
relative to each other by an angle of 180.degree. on the periphery
of the exhaust-gas line. Naturally, it is also possible to choose a
different angle here. Thus, for example, the peripheral portion
facing away from the sound line can merely cover an angle of
90.degree. and the peripheral portion facing the sound line can
cover an angle of 270.degree.. Intermediate values are also
possible. As a result of the second radial rib, the protection of
the active silencing unit against hot exhaust gases is particularly
effective.
[0019] The radial rib is preferably shorter in axial direction of
the exhaust-gas line than the sound coupling-in line. Thus, at an
axial end of the annular space formed by the exhaust-gas line and
the sound coupling-in line, an acoustic coupling channel results
via which sound generated by the sound-generating unit can flow
around the radial rib or the radial ribs on the periphery of the
exhaust-gas line. Only as it progresses further can the sound pass
into the inside of the exhaust-gas line via the second perforation.
An effective acoustic coupling of the silencing device to the
inside of the exhaust-gas line is thereby guaranteed.
[0020] An exhaust system in which the radial ribs merely extend to
an axial length which corresponds to the axial length of the second
perforation is particularly preferred. Thus, no radial ribs are
provided in the area of the first perforation.
[0021] In a variant, the openings comprised by the second
perforation each have a substantially rectangular cross section,
wherein preferably a short side of the rectangle is oriented in
peripheral direction and a long side of the rectangle is oriented
in axial direction of the exhaust-gas line. It has become apparent
that a second perforation designed in such a way effects a good
compromise between a thermal decoupling of the inside of the
exhaust-gas line from the active silencing device and an effective
acoustic coupling of these components.
[0022] An alternative design provides that a radial outer end of
the radial rib or radial ribs provided on the outer surface of the
exhaust-gas line is or are at a radial distance from the sound
coupling-in line, wherein each radial rib radiating from the
exhaust-gas line is complemented by a radial rib, pointing radially
inwards radiating from the sound coupling-in line, which is at only
a small peripheral distance from the associated radial rib
radiating from the exhaust-gas line or touches the periphery of
same, and the radial inside end of which is at a radial distance
from the exhaust-gas line. Each radial rib provided on the outer
surface of the exhaust-gas line forms a so-called radial rib pair
together with the radial rib allocated to it provided on the sound
coupling-in line. An alternative term for this is double rib. Such
a radial rib pair represents an effective flow obstacle for hot
exhaust gases, with the result that the active sound-generating
unit is protected against high temperatures. The fact that the
radial rib radiating from the outer surface of the exhaust-gas line
is not connected to the sound coupling-in line and the radial rib
radiating from the sound coupling-in line is not connected to the
exhaust-gas line is advantageous in terms of production technology.
Namely, the necessity of attaching a radial rib both to the
exhaust-gas line and to the sound coupling-in line, which is
complex, is avoided. Moreover, the omission of such connections
results in a particularly long service life of the exhaust system
as the connection points are often exposed to comparatively high
stresses.
[0023] The small peripheral distance between the radial ribs
forming the radial rib pair is to be seen in comparison with the
line diameter of the exhaust-gas line and means that the distance
is at most 10%, preferably at most 5%, of the line diameter. In
this way, it is achieved that hot exhaust gas, given a flow in the
direction of the active silencing device, is effectively countered
by a flow resistance.
[0024] In an area upstream of the sound coupling-in line, the
exhaust-gas line can have an axial bend or an axial kink, in
particular wherein an axial bend of substantially 90.degree. is
present. The sound coupling-in line is preferably arranged directly
adjacent to the axial bend or the axial kink. A compact
construction of the exhaust system thus results. As a result of an
axial kink or an axial bend, the pressure ratios inside the
exhaust-gas line can be influenced in a targeted manner in an area
downstream of the axial kink or of the axial bend. In particular, a
pressure level is thereby increased in a convex area of the axial
bend or of the axial kink. The pressure level decreases
correspondingly in a concave area.
[0025] In this case, the second perforation is preferably arranged
downstream of a convex area of the axial bend or of the axial kink.
As already explained, the second perforation is arranged in a
peripheral portion facing away from the sound line. Because the
axial bend or the axial kink causes the pressure in the exhaust gas
flow to be higher on the convex side than on the concave side, an
exhaust gas flow in the direction of the sound-generating unit is
thus effectively prevented.
[0026] A center axis of the sound line can run substantially along
a radial direction of the sound coupling-in line. By this is meant
that a predominant proportion of the direction of the center axis
of the sound line is oriented in radial direction of the sound
coupling-in line. A smaller proportion can also run in axial
direction and/or in peripheral direction of the sound coupling-in
line. The center axis of the sound line can thus impinge obliquely
on the sound coupling-in line, wherein the radial component is
always the largest. However, it is preferred that the sound line
runs along the radial direction of the sound coupling-in line. This
effects a high-quality acoustic coupling of the sound-generating
unit to the inside of the exhaust-gas line. Moreover, a compact
construction of the exhaust system can thus be achieved.
[0027] In addition, a motor vehicle of the type mentioned at the
beginning is provided which comprises an exhaust system according
to the disclosure. Such a motor vehicle emits only little or no
sound at all via an exhaust gas flow conducted into the
surroundings by the exhaust system. Thus, the motor vehicle can be
operated comparatively quietly. At the same time, the motor vehicle
is particularly reliable and durable because the
temperature-sensitive components of the exhaust system are
protected against hot exhaust gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The disclosure is explained below with reference to various
embodiment examples which are shown in the attached drawings. There
are shown in:
[0029] FIG. 1 shows a schematic view of a motor vehicle according
to the disclosure with an exhaust system according to the
disclosure,
[0030] FIG. 2 shows the exhaust system according to the disclosure
in a view from above,
[0031] FIG. 3 shows a perspective view of the exhaust system from
FIG. 2, wherein a sound line and a sound coupling-in line are
represented transparent,
[0032] FIG. 4 shows the exhaust system from FIG. 2 in a view from
above, wherein the sound line and the sound coupling-in line are
omitted,
[0033] FIG. 5 shows a perspective view of the exhaust system from
FIG. 2, wherein, as in FIG. 4, the sound line and the sound
coupling-in line are omitted,
[0034] FIG. 6 shows a schematic detail view of a radial rib of the
exhaust system from FIG. 2,
[0035] FIG. 7 shows a schematic detail view of a radial rib of the
exhaust system from FIG. 2 according to an alternative design
and
[0036] FIG. 8 shows a schematic detail view of a radial rib of the
exhaust system from FIG. 2 according to a further alternative
design.
DETAILED DESCRIPTION
[0037] FIG. 1 shows a motor vehicle 10 with an internal combustion
engine 12 which is coupled to an exhaust system 14. Thus, the
exhaust gas produced by the internal combustion engine 12 is
conducted into the surroundings 16 via the exhaust system 14.
[0038] The exhaust system comprises an exhaust-gas line 18 routing
the exhaust gas and an active silencing device 20.
[0039] The active silencing device 20 has a sound-generating unit
22 which comprises, for example, a loudspeaker and a sound line 24.
A sound coupling-in line 26 is connected to the sound line 24
downstream.
[0040] A center axis of the sound line 24 runs substantially along
a radial direction of the sound coupling-in line 26. The center
axes of the sound line 24 and the sound coupling-in line 26 are
thus substantially perpendicular to each other.
[0041] Furthermore, the sound coupling-in line 26 surrounds the
exhaust-gas line 18 substantially concentrically on the outside.
The center axes of the sound coupling-in line 26 and the
exhaust-gas line 18 are thus substantially coincident.
[0042] The active silencing device 20, more precisely the
sound-generating unit 22, is acoustically coupled to an exhaust gas
flow present inside the exhaust-gas line 18. Here, sound generated
by the sound-generating unit 22 is conducted into the sound
coupling-in line 26 via the sound line 24 and thus passes into an
annular space which is formed by the sound coupling-in line 26 and
the exhaust-gas line 18.
[0043] The portion of the exhaust-gas line 18 running inside this
annular space can be subdivided into an axial portion facing the
sound line 24 and an axial portion, connected downstream thereto,
facing away from the sound line 24.
[0044] In the embodiment represented, the axial portion facing the
sound line 24 and the axial portion facing away from the sound line
24 are directly adjacent to each other.
[0045] Here, a first perforation 38 is provided in the axial
portion facing away from the sound line 24. The axial portion
facing the sound line 24 is designed perforation-free in a portion,
as will be explained later.
[0046] The first perforation 38 runs around the whole periphery of
the axial portion facing away from the sound line 24.
[0047] Here, the openings of the first perforation 38 have a
substantially round cross section. Within the axial portion facing
the sound line 24, the exhaust-gas line 18 furthermore comprises a
peripheral portion 28a facing the sound line 24 and a peripheral
portion 28b facing away from the sound line 24. In the embodiment
example represented, the two peripheral portions 28a, 28b are
complementary to each other to form the whole periphery of the
exhaust-gas line 18.
[0048] A second perforation 30 is provided in the peripheral
portion 28b facing away from the sound line 24. The peripheral
portion 28a facing the sound line 24 is designed
perforation-free.
[0049] The sound generated by the sound-generating unit 22 which
has already reached the abovementioned annular space, can thus
interact with the exhaust gas flow present inside the exhaust-gas
line 18 via the first perforation 38 and/or the second perforation
30.
[0050] Here, the openings comprised by the second perforation 30
each have a substantially rectangular cross section, wherein the
short sides of the rectangle are each oriented in peripheral
direction and the long sides of the rectangle are each oriented in
axial direction of the exhaust-gas line 18.
[0051] Furthermore, the exhaust-gas line 18 has an axial bend 32 in
an area upstream of the sound coupling-in line 26 which is designed
as a 90.degree. bend in the embodiment example represented.
[0052] The second perforation 30 and the axial bend 32 are arranged
relative to each other such that the second perforation 30 is
positioned downstream of a convex area of the axial bend 32.
[0053] Moreover, the exhaust system 14 represented comprises a
radial rib 34 in each of the border areas between the peripheral
portion 28b facing away from the sound line 24 and the peripheral
portion 28a facing the sound line 24.
[0054] These can be designed in different ways.
[0055] In the variant according to FIG. 6, the radial rib 34 is
attached to an inner surface of the sound coupling-in line 26 and
extends in the direction of the exhaust-gas line 18. Here, a radial
distance 36 can be provided between the end of the radial rib 34
lying inside and the exhaust-gas line 18. Equally, the radial rib
34 can touch the exhaust-gas line 18 or be connected thereto.
[0056] Alternatively, according to FIG. 7, the radial rib 34 can be
attached to the exhaust-gas line 18 and extend in the direction of
the sound coupling-in line 26. A radial distance 36 can again be
provided which results between the outer end of the radial rib 34
and the sound coupling-in line 26. It is equally conceivable that
the radial rib 34 touches the sound coupling-in line 26 with its
outer end or is connected to same.
[0057] Instead of a single radial rib 34 in each border area
between the peripheral portion 28a facing the sound line 24 and the
peripheral portion 28b facing away from the sound line 24, a radial
rib pair can also be provided which comprises radial ribs 34a, 34b.
In this connection, the radial rib 34a is attached to the sound
coupling-in line 26 and extends in the direction of the exhaust-gas
line 18. In contrast, the radial rib 34b is attached to the
exhaust-gas line 18 and extends in the direction of the sound
coupling-in line 26.
[0058] In peripheral direction, the radial ribs 34a, 34b are only
slightly spaced apart from each other or touch each other.
[0059] In radial direction, the radial rib 34a radiating from the
sound coupling-in line 26 has a radial distance 36a from the
exhaust-gas line 18 at its inner end. The radial rib 34b radiating
from the exhaust-gas line 18 leaves a radial distance 36b free
between its outer end and the sound coupling-in line 26.
[0060] In all variants, the radial ribs 34, 34a, 34b are shorter in
an axial direction of the exhaust-gas line 18 and of the sound
coupling-in line 26 arranged concentric thereto than the sound
coupling-in line 26. Thus, there is an axial portion of the sound
coupling-in line 26 in which there can be flow around the radial
ribs 34, 34a, 34b in peripheral direction of the exhaust-gas line
18. To be more precise, the radial ribs 34, 34a, 34b extend merely
in the area of the second perforation 30.
[0061] The mode of operation of the exhaust system 14 is as
follows.
[0062] The sound generated by the sound-generating unit 22 flows
via the sound line 24 into the sound coupling-in line 26. There, it
enters into the inside of the exhaust-gas line 18 via the openings
of the first perforation 38. Furthermore, after the sound has
flowed around the radial ribs 34, 34a, 34b in the area of the first
perforation 38, it also passes into the inside of the exhaust-gas
line 18 via the openings of the second perforation 30. In this way,
a sound carried by the exhaust gas flow inside the exhaust-gas line
18 is actively muffled.
[0063] However, hot exhaust gas can also flow via the openings of
the first perforation 38 and the second perforation 30 from the
inside of the exhaust-gas line 18 into the annular space formed by
the exhaust-gas line 18 and the sound coupling-in line 26. The
active silencing device 20 and in particular the sound-generating
unit 22 are to be protected against these hot exhaust gases.
[0064] Exhaust gas exiting via the openings of the second
perforation 30 must first flow around the radial ribs 34, 34a, 34b
on its path in the direction of the sound-generating unit 22. Here,
the radial ribs 34, 34a, 34b represent a flow obstacle on the one
hand and cool the exhaust gas on the other.
[0065] In addition, because of the flow ratios inside the
exhaust-gas line 18, a large part of the exhaust gas which has
exited via the openings of the second perforation 30 is conducted
back inside the exhaust-gas line 18 via the openings of the first
perforation 38. This is due to the fact that inside the exhaust-gas
line 18 a higher pressure prevails in the area of the second
perforation 30 than in the area of the first perforation 38. In the
annular space, the pressure ratios are reversed, with the result
that a higher static pressure prevails in the area of the first
perforation 38. This also serves to protect the sound-generating
unit 22 against high temperatures.
[0066] A direct flow of hot exhaust gas into the sound-generating
unit 22 is also prevented in that the peripheral portion 28a facing
the sound line 24 is designed perforation-free.
[0067] Although various embodiments have been disclosed, a worker
of ordinary skill in this art would recognize that certain
modifications would come within the scope of this disclosure. For
that reason, the following claims should be studied to determine
the true scope and content of this disclosure.
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