EP0158013B1 - Reflection muffler for combustion engines - Google Patents

Description

The invention relates to a reflection muffler for internal combustion engines, consisting of a closed housing provided on its opposite end walls with an inlet or an outlet connection, in which two tubes are arranged at least partially juxtaposed in the axial direction, one of which is connected to the inlet connection and has on its periphery a passage area through which the exhaust gases pass from the inlet port into the interior of the housing, and of which the other is connected to the outlet port and has a passage area on its periphery through which the exhaust gases pass from the housing to the drain port .

The principle of sound insulation with the aid of reflection is that a reflective obstacle is arranged in the sound line channel in such a way that the largest possible proportion of the sound wave is extinguished by interference between the reflected and the incident sound wave. It should be noted that walls arranged in the propagation path as well as changes in the cross-section of the sound-conducting channel represent an obstacle for sound waves. Therefore, the simplest version of a reflection silencer consists of a closed housing of relatively large diameter, to which an inlet connector and an outlet connector of smaller diameter are connected.

Mufflers for internal combustion engines also serve to smooth out the loud, pulsating gas flow that the internal combustion engine generates through its exhaust system and to reduce the muzzle noise, which primarily results from the ignition noise. The sound insulation for internal combustion engines is so difficult because the critical noise spectrum is very broadband, namely in a range from about 50 to 1000 Hz, which is the reason why silencers for internal combustion engines are relatively complicated structures, or that several silencers in series have to be switched in order to cover the noise spectrum as completely as possible.

The damping effect of reflection mufflers can be further improved by controlling the exhaust gas flow leading to throttling effects.

A reflection silencer of the type specified is known from US-A-3 191 715. In this known reflection silencer, the tubes connected to the inlet and the outlet run transversely to the housing axis. This is intended to ensure that the inflowing exhaust gases pass through approximately three times the length of the housing before they leave the housing again. The main flow of the exhaust gas runs along the pipe connected to the inlet, leaves it at its open end approximately in the middle of the housing, is reflected on the housing wall, between the pipes and the housing wall is directed back towards the entrance, whereupon it is reversed in the direction of the input open, near the middle of the housing end of the pipe connected to the outlet is introduced. A much smaller part of the exhaust gas flow passes through a plurality of slots provided on the pipes from the housing inlet to the housing outlet in order to enable the pulsating exhaust gas flow to expand and the flow resistance to be reduced.

This known reflection silencer is sound-absorbing only in a relatively small, medium frequency range. In addition, the smoothing of the pulsating exhaust gas flow is only incompletely guaranteed. The inclusion of the entire housing wall has a detrimental effect on the insulation value of this silencer, since in this way a very considerable part of the exhaust noise is emitted to the surroundings via the housing wall.

Another reflection silencer for internal combustion engines is known from DE-C-617 831. The housing of this muffler has sloping boundary surfaces and is divided into a plurality of chambers connected to one another by pipes of different diameters, each of which insulates a different, relatively narrow limit range of the noise spectrum. The arrangement of the pipes slightly improves the individual insulation area of each chamber above the chamber cut-off frequency, but a step-by-step course of the insulation also remains. This silencer also emits a significant proportion of the exhaust gas noise to the surroundings via the housing wall.

A subdivision into subchambers also characterizes the additional device for silencers known from DE-C-626 321, in which two transversely extending pipes of different lengths are inserted in the single partition, one of which has one end at the level of the housing inlet in the partition is inserted. With increasing speed of the internal combustion engine, the pipe opposite the inlet should be sufficient to a lesser extent for a smooth passage of the exhaust gases, as a result of which the exhaust gases are forced to make a detour via the pipe arranged offset to the inlet opening, which is intended to make the sound insulation more uniform. A disadvantage is the increasing flow resistance of this additional device for a muffler with increasing speed, which has unfavorable repercussions on the internal combustion engine itself. In addition, the sound-absorbing effect of this additional device is limited to a very narrow frequency range.

The silencer known from US Pat. No. 3,469,652 is used primarily to smooth the pulsating exhaust gas flow. The damper housing itself is tuned to the low-frequency part of the noise spectrum and acoustically coupled to a pair of curved pipes running between the inlet and the outlet, which in turn are subsequently connected to the inlet and the outlet with a curved pipe connecting the inlet and the outlet, the relatively good Smoothing of the pulsating exhaust gas flow is opposed to narrow-band noise damping in this silencer, with a considerable part of the noise spectrum being emitted to the outside via the damper housing.

The object of the present invention is to provide a reflection muffler of the type specified, which broadly attenuates the critical noise spectrum of the exhaust gases and at the same time smoothes the pulsating exhaust gas flow sufficiently, the structure being compact, the manufacture economically possible and the number of components required should be simple, should be as small as possible. In addition, the risk of corrosion and / or burnout of the housing is to be counteracted by the design according to the invention.

This object is achieved in accordance with the characterizing part of the main claim in that the ends of the tubes facing away from the inlet and outlet connections are closed, that the passage areas are provided only on the opposite sides of the respective other tube, that the passage areas are opposite first reflection shells , and that the first reflection shells on the side of the tubes facing away from the passages are opposite second reflection shells. As a result, the noise component of the exhaust gas flow is reflected in a variety of ways in the smallest space, with each reflection confronting it with a different obstacle or a different channel cross section, which leads to broadband damping of the noise components. Direct exposure to the hot exhaust gases on the housing walls is effectively avoided.

The exhaust gas flow which is subsequently divided onto the two tubes by means of the reflection shells at the housing inlet is brought together again in the region of the housing outlet, as a result of which the different-frequency noise waves are exposed to a further path difference and thus further extinctions which contribute to damping.

Since the exhaust gas flow is essentially guided between the reflection shells of the two pipes, the radiation of noise through the housing wall is considerably reduced.

The long path through which the pulsating exhaust gas flow has to travel results in a largely smoothing of the vibrations of the exhaust gas flow. All of these advantageous effects are achieved with an extremely compact and thus space-saving structure and with at least tube-like components which are available at low cost and permit economical production.

The passage areas are preferably formed essentially over the entire length of the tubes and have the shape of rectangular windows. As a result, the noise waves and the exhaust gas flow are reflected or conducted over the entire length of the pipe between the pipes and the reflection shells and between the two pipe reflection bowl systems, which further improves the damping effect and the smoothing of the exhaust gas flow. The pipes, which are open over a wide range, provide practically no flow resistance to the exhaust gas flow, so that unfavorable repercussions due to a build-up of the exhaust gases in the muffler on the internal combustion engine are avoided.

The tubes are arranged substantially along the entire length between the housing end walls, which are preferably arranged parallel to one another, which ensures that the sound waves, even when largely open tubes are used, are conducted exclusively between the two tube reflection shell systems, so that none Sound is emitted through the housing wall.

In order to emit the exhaust noise through the housing end walls, with which the pipes each with their from the inlet nozzle or outlet. connecting end facing away tightly to avoid, it is advisable to provide the pipes with circumferentially closed end regions, which are preferably relatively short.

A development which is particularly important in practice is characterized in that the tube axes run at an acute angle to one another, the angle enclosed by the tube axes being between 3 and 45 °, preferably approximately 30 °, and the apex of the angle on the inlet side lies, d. H. that the pipes diverge from the inlet to the outlet side, so that the path that the exhaust gas flow travels from one pipe reflection shell system to the other from the inlet to the outlet side continuously increases and the critical noise spectrum is not only broadband but also very evenly attenuated becomes.

The first reflection shells are preferably tubular and have on the side facing away from the passage areas of the tubes an approximately the entire shell length of the reflection window, which has a rectangular shape in plan view and whose opening angle with respect to the shell axis between 45 ° and 90 °, in particular approximately Is 60 °.

The ends of the first reflection shells are expediently tightly connected to the housing end walls and have relatively short, circumferentially closed end regions, the length of which is preferably equal to the length of the end regions of the tubes.

An essential feature of the invention be is that both the first and the second reflection shells are at an acute angle to one another, the angle included by the first reflection shells being smaller than the angle included by the tubes, while the angle included by the second reflection shells is smaller than that of angles included in the first reflection shells. The axes of the first reflection shell preferably coincide with the tube axes on the inlet side, while the axes of the second reflection shells essentially coincide with the axes of the first reflection shells on the outlet side.

The tubes are preferably located essentially within the first reflection shells.

The second reflection shells which are tightly connected at the end to the housing end walls have opening areas which are advantageously provided on their sides facing away from the assigned reflection shell windows, the opening angles of the second reflection shells with respect to their axes being less than 180 ° and in particular being about 90 °.

The first reflection shells are expediently only partially arranged within the second reflection shells and in such a way that between the first. Reflective shells and the longitudinal edges of the second reflection shells delimiting the opening areas, each with two separate opening areas.

• . Fig. 1 einen Längsschnitt durch den er^findungs- gemäßen Reflexionsschalldämpfer und
• Fig. 2 einen Schnitt entlang der Linie li-li in Figur 1.

The invention is explained in more detail with reference to the drawing; in the drawing shows:

• . Fig. 1 shows a longitudinal section through the ^f he proper reflection silencer indungs- and
• 2 shows a section along the line li-li in FIG. 1.

The flow path of the exhaust gases is indicated by arrows in FIG. From the exhaust system of the engine, the exhaust gases pass through an inlet connection 6 inserted in the upper region of a flat inlet end wall 8 of the damper housing 10 into the interior of the reflection muffler, which they essentially have via an arranged in the lower region at a distance from the inlet end wall 6 parallel thereto leave the same design, flat outlet end wall 9 used outlet port 7 again. Between the two end walls 8, 9, the damper housing 10 consists of two cylinder half-shells 10 ′, 10 ″ with their open sides opposite one another, between which flat and parallel housing side walls 4, 5 extend.

A pipe 15 connected to the inlet connector 6 extends obliquely upward from the inlet end wall 8 through the damper housing 10 to the outlet end wall 9, with which it is tightly connected. Another tube 16 is connected to the outlet nozzle 7 and also extends obliquely upwards from the outlet wall 9 to the inlet end wall 8, with which it is tightly connected. The two pipes 15 and 16 thus run completely next to one another and parallel to the housing side walls 4 and 5. The pipe axes 15 'and 16' intersect to the left of the inlet wall 8 at an acute angle α, which is approximately 30 °. The distance between the tubes 15, 16 on the inlet end wall 8 is selected such that the first reflection shells 13, 14, which will be described below, can be accommodated.

Rectangular windows 11, 12 are provided on mutually facing sides of the tubes 15 and 16, which extend approximately over the entire tube length and have an opening angle 8 of approximately 60 ° with respect to the tube axes 15 ', 16'. The tubes 15, 16, however, have a short, circumferentially closed end region.

Each of the two tubes 15 and 16 is surrounded at an increasing distance by a first reflection shell 13 and 14 and by a second reflection shell 21 and 22, which are tightly connected to the end walls 8, 9 on the end face.

The first reflection shells 13, 14 are tubular and surround the associated tube 15 or 16. They have rectangular windows 17, 18 on the side facing away from the windows 11, 12 of the tubes 15, 16, which extend almost over the entire length of the housing 10 extend and have an opening angle with respect to the shell axis 13 ', 14' of approximately 90 °. The second reflection shells 21, 22 extend over an angle of approximately 270 ° and lie with their closed side radially opposite the windows 17, 18. The first reflection shells 13, 14 extend through the open side of the second reflection shells 21, 22 at a distance from the longitudinal edges 21 ', 22' of the second reflection shells 21, 22. This creates axially continuous opening areas 19, 19 'and 20, 20' .

The axes of the first and second reflection shells 13, 14 and 21, 22 lie essentially in the same plane as the axes 15 ', 16' of the two pipes 15 and 16 and intersect to the left of the inlet end wall 8. The axis 13 ' , 14 'of the first reflection shells 13, 14 included angle β is smaller than the angle a enclosed by the tube axes 15', 16 'and is approximately 25 °. In contrast, the second reflection shells 21, 22 run at an acute angle y to one another, which in turn is smaller than the angle β enclosed by the first reflection shells 13, 14 and is approximately 10 °.

The flow pattern of the exhaust gases within the reflection silencer according to the invention will be described below with reference to FIGS. 1 and 2.

The exhaust gas stream entering the inlet connection 6 of the damper housing 10 flows into the pipe 1 and exits the window 11. It is partially reflected back and forth between the tube 15 and the first reflection shell 13, while at the same time moving towards the outlet end wall 9, and partially directed through the first reflection shell 13 to the window 17 through which it points to the second reflection shell 21 arrives, where it is reflected or redirected to the opening areas 19, 19 '. Through the opening areas 19, 19 ', the exhaust gases flow through the housing 10 into the open areas 20, 20' of the second reflection shell 22. After reflection or deflection at the second reflection shell 22, the exhaust gas flow passes through the window 18 and after deflection at the first Reflection bowl 14 through the window 12 into the ring 16, whereby multiple reflections occur again. The exhaust gas flow then finally reaches the outlet connection 7 along the pipe 16.

Due to the design according to the invention, the various interferences occurring within each pipe shell system and from pipe shell system to pipe shell system have the effect that formation of standing waves within the muffler housing is prevented. The very different paths through which different amounts of the exhaust gas flow pass within the damper housing lead to a large number of extinguishments, with the result that the critical noise spectrum of the exhaust gas flow is damped effectively and uniformly.

Claims (28)

1. Baffle silencer for internal combustion engines, consisting of a closed housing (10) which is provided at its opposed end walls (8, 9) with inlet and outlet sockets (6 and 7 respectively) and in which are disposed two tubes (15, 16) extending in the axial direction at least partially adjacent to each other, one (15) of which is connected to the inlet socket (6) and comprises at its circumference a throughflow zone (11) through which the exhaust gases flow from the inlet socket (8) into the interior of the housing (10), while the other (16) is connected to the outlet socket (7) and comprises at its circumference a throughflow zone (12) through which the exhaust gases flow out of the housing (10) to the outlet socket (7), characterised in that the ends of the tubes (15 and 16) remote from the inlet and outlet sockets (6 and 7) are sealed, the throughflow zones (11, 12) are provided only on the sides opposite the respective other tube (15, 16), first baffle shells (13, 14) are located opposite the throughflow zones (11, 12), and second baffle shells (21, 22) are located opposite the first baffle shells (13, 14) on the sides of the tubes (15, 16) remote from the throughflow zones (11, 12).

2. Baffle silencer according to claim 1, characterised in that the throughflow zones (11, 12) extend essentially over the full length of the tubes (15, 16).

3. Baffle silencer according to claim 1 or 2, characterised in that the throughflow zones (11, 12) are in the form of rectangular apertures.

4. Baffle silencer according to any of the preceding claims, characterised in that the aperture angle (8) of the throughflow apertures (11, 12) relative to the tube axes (15', 16') is between 40 and 60°, preferably about 50°.

5. Baffle silencer according to any of the preceding claims, characterised in that the tubes (15, 16) extend adjacent to each other essentially over the full length between the housing end walls (8, 9), which are preferably arranged parallel to each other.

6. Baffle silencer according to any of the preceding claims, characterised in that the tubes (15, 16) are connected in sealing tight relationship to the housing end walls (8, 9), in each case by their end remote from the inlet socket (6) or outlet socket (7).

7. Baffle silencer according to any of the preceding claims, characterised in that the tubes (15, 16) comprise circumferentially closed end zones which are preferably relatively short.

8. Baffle silencer according to any of the preceding claims, characterised in that the tube axes (15', 16') are at an acute angle (α) to each other.

9. Baffle silencer according to claim 8, characterised in that the angle (a) formed by the tube axes (15', 16') is between 3 and 45°, preferably about 30°.

10. Baffle silencer according to claim 8 or 9, characterised in that the vertex of the angle (a) is located on the inlet side.

11. Baffle silencer according to claim 1, characterised in that the first baffle shells (13, 14) are of tubular construction and comprise, on the side remote from the throughflow zones (11, 12) of the tubes (15, 16), a baffle shell aperture (17, 18) extending almost over the full length of the shell.

12. Baffle silencer according to claim 11, characterised in that the baffle shell apertures (17, 18) have a rectangular shape in plan view.

13. Baffle silencer according to claim 11 or 12, characterised in that the aperture angles of the baffle shell apertures (17, 18) relative to the shell axis (13, 14) are between 60° and 90°, preferably about 80°.

14. Baffle silencer according to claim 11, characterised in that the ends of the first baffle shells (13, 14) are connected to the housing end walls (8, 9) in sealing tight relationship.

15. Baffle silencer according to any of claims 11 to 14, characterised in that the first baffle shells (13, 14) comprise relatively short, circumferentially closed end zones whose length is preferably approximately equal to the length of the end zones of the tubes (15, 16).

- 16. Baffle silencer according to any of claims 11 to 15, characterised in that the first baffle shells (13, 14) are at an acute angle (p) to each other, which is preferably between 15° and 35° and in particular about 25°.

17. Baffle silencer according to claim 16, characterised in that the angle (p) formed by the first baffle shells (13, 14) is smaller than the angle (a) formed by the tubes (15, 16).

18. Baffle silencer according to any of the preceding claims, characterised in that the tube axes (15', 16') and the axes of the first baffle shells (17', 18') essentially coincide on the inlet side.

19. Baffle silencer according to any of the preceding claims, characterised in that the tubes (15, 16) are located essentially inside the first baffle shells (13, 14).

20. Baffle silencer according to any of the preceding claims, characterised in that the opening zones (19', 20') of the second baffle shells (21,

22) are provided on their sides remote from the associated baffle shell apertures (17, 18).

21. Baffle silencer according to claim 20, characterised in that the aperture angles of the second baffle shells (21, 22) relative to their axes are smaller than 180° and preferably about 90°.

22. Baffle silencer according to claim 20 or 21, characterised in that the ends of the second baffle shells (21, 22) are connected to the housing end walls (8, 9) in sealing tight relationship.

23. Baffle silencer according to any of claims 20 to 22, characterised in that the second baffle shells (21, 22) are at an acute angle (y) to each other.

24. Baffle silencer according to any of the preceding claims, characterised in that the angle (y) formed by the second baffle shells (21, 22) is smaller than the angle (β) formed by the first baffle shells (13, 14).

25. Baffle silencer according to any of the preceding claims, characterised in that the axes (17', 18' ; 23', 24') of the first and second baffle shells (13,14; 21, 22) essentially coincide on the outlet side.

26. Baffle silencer according to any of the preceding claims, characterised in that the first baffle shells (13, 14) are only partially arranged inside the second baffle shells (21, 22), in such a way that between the first baffle shells (13, 14) and the longitudinal edges (21', 22') of the second baffle shells (21, 22), which define the opening zones, in each case there are two separate opening zones (19, 19' ; 20, 20').

27. Baffle silencer according to any of the preceding claims, characterised in that the second baffle shells (21 ; 22) are surrounded at a distance by cylinder halfshells (10', 10") of the silencer housing (10), which are connected to each other by planar housing side walls (4, 5) parallel to each other.

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