DE69607229T2 - Mineral wool absorbent element for noise reduction in an exhaust silencer, component therefor, its use and method of manufacture - Google Patents

Abstract

An absorption member (40) is formed as a board-type shaped article, particularly a punched member, which is made up of bound mineral wool and comprises at least one recess (46) for passage of an inner pipe (22) of a muffler (2). For the case that it is not possible to slip it onto the inner pipe (22) in an axial direction, a parting slit (47) is introduced at the periphery of the recess (46) at which the recess (46) may be bent open to receive the inner pipe. It was surprisingly found that the quite considerable deformation required for this purpose nevertheless does not result in disadvantageous destructions of the material structure, apparently because the deformation distributes more or less homogeneously over the entire inner periphery of the recess (46), whereby great deformation paths may be obtained at low stress peaks. The board-type design of the absorption members comprising opposite parallel major surfaces (52) as well as its design as a punched member further contribute to good, non-destructive deformability, as its formation from a mineral wool board as a punched member ensures the overwhelming majority of fibers being oriented transversely with respect to the bending axis and thus counteracts gaping fissures. It is thereby sufficiently ensured that following its closing around the inner pipe (22), a resilient return movement of the material takes place whereby the parting slit is closed, such that any subsequent work for entirely filling the inner cavity of the muffler (2) with mineral wool is avoided. <IMAGE>

Description

The invention relates to an absorption part made of bonded mineral wool for soundproofing in an exhaust silencer, in particular of a passenger car, according to the preamble of claim 1, a part for this according to claim 10, and a method for its production according to claim 11.

Exhaust silencers, such as those found in every car, are often filled with mineral wool as a sound absorption material. To this end, the inner pipe that carries the exhaust gas flow is perforated around its circumference in order to direct the pressure pulsations of the exhaust gas flow into the sound-absorbing mineral wool material. The mineral wool material is often covered with a layer of metal wool around the circumference of the inner pipe in order to prevent mineral fibers from being significantly torn loose under the force of the pulsations and blown out into the environment, which would of course impair the sound absorption.

Depending on the specifications of the automobile manufacturer, the exhaust pipe simply runs straight through the silencer, or it branches out into a number of inner pipes, it expands into an inner pipe in the form of an inner shell, or it runs with a curved axis, for example with two bends over 180º. This variety of required shapes places correspondingly diverse requirements on the properties of the silencer filling.

In the simplest case, loose wool is stuffed into the muffler. However, this requires considerable manual work and additional effort for quality control by the manufacturer of the exhaust system. Therefore, people have started to look for ways to prefabricate the mineral wool filling as a hardened molded part by the mineral wool manufacturer, which is delivered in consistent quality and only needs to be assembled by the manufacturer of the exhaust system.

Such molded parts can be prefabricated in several parts, whereby the parts are then put together accordingly during assembly to form the entire absorption part. Such a construction of the absorption part from parts is necessary if, due to the structural design of the exhaust muffler, it is not possible to slide the absorption part axially onto the inner pipe system, be it This is due to curvatures of the inner pipe, be it due to webs or partitions running between the inner pipe system and the housing of the exhaust muffler.

A particular difficulty in assembling the absorption part, which is designed as a molded body, from opposing sections arises when the inner pipe system of the silencer consists of three or more inner pipes that are not in the same plane. Such a situation is also the basis of the state of the art in this category, which can be seen in DE 90 12 260 U. In such a case, it is only possible to completely fill the interior between the inner pipes by plugging with loose wool, but not by using prefabricated molded parts, as is required for acoustic reasons. The reason why the sections cannot completely enclose the inner pipes and fill the entire interior is that the areas of the sections that engage behind the inner pipes would have to be compressed too much during assembly in order to fit through the gap between adjacent pipes. This not only results in an unreasonable hindrance to assembly, but also, in particular, in a destruction of the fiber structure in the compressed area of the hardened molded part. As a result of the resulting permanent deformation or even sheared-off material parts, complete filling of the interior space between the inner tubes would not be guaranteed in practice. Just as with a shape of the parts that avoids compression in accordance with the teaching of DE 90 12 260 U, hollow spaces would also be unavoidable with a rear-engaging shape, which would have to be laboriously filled with loose wool.

In contrast, the invention is based on the object of creating an absorption part which, in a structure made up of parts that can be mounted from the side, i.e. transversely to the axis of the silencer, also in the case of a silencer with three parallel inner tubes that are not in a common plane, allows the space between the inner tubes to be completely filled with hardened mineral wool material without having to resort to laborious re-packing work or the like.

This problem is solved by the characterizing features of claim 1.

This makes it possible to open the closed passage opening in the section at the separating slot by bending the mineral wool material in the plate plane, so that the edges of the separating slot can grip around the associated inner pipe, whereby the edges of the separating slot spring back into a position that grips behind the inner pipe after gripping over the circumference of the pipe. It has surprisingly been shown that such a relatively strong deformation is possible without damaging the section. This is probably due to the fact that the deformation is distributed over the entire material on the circumference of the passage opening, thus avoiding concentration of the required considerable deformation path on only a small area of mineral wool. The plate-shaped design of the absorption part or each section avoids local stress peaks and promotes such a relatively even distribution of the deformation over the circumference of the passage opening without any additional measures. In addition, the limited thickness of each section enables easy manipulation during assembly even by inexperienced workers without special tools, without any fear of damage.

The section is particularly preferably obtained from a conventional mineral fiber board, which is produced by placing mineral fibers provided with a binding agent on a production belt, compacting them to the desired bulk density and curing them in this compressed form, as defined in claim 11. In a conventional mineral fiber board produced in this way, the fibers lie predominantly in planes parallel to the plane of the production belt. If the section is produced by cuts perpendicular to the large surfaces of a board produced in this way, the mineral wool material on the circumference of the passage opening is particularly strong when the separating slot is bent around a bending axis perpendicular to the plane of the board to protect it from functionally detrimental damage. The alignment of the fibers in the board perpendicular to the bending axis reduces the risk of local destruction of the fiber composite and ensures that good resilience is maintained.

The assembly of an absorption part according to the invention is further facilitated by the fact that each section is snapped onto one of the inner tubes and is secured in this position by the elastic grip behind the inner tube until the muffler is closed. This prevents sections that have already been attached to the inner tube system from falling off again during further manipulation. The construction of the entire absorption part from a large number of sections that are adjacent on the circumference and in particular axially does not cause any assembly problems.

The preferred design of the absorption part or section as a stamped part enables simple and low-dust production compared to a sawn or even milled part.

It is already known to use plate-shaped molded parts with through-openings for inner pipes as absorption parts for exhaust silencers. The through-openings are closed at their periphery and the plate-shaped molded part is pushed axially onto the inner pipe system like a pair of glasses. The introduction of a separating slot between the through-opening and the outer contour is not planned, nor is any other deformation during assembly.

If the material thickness between the side of the passage opening opposite the separating slot and the adjacent outside of the section is very large, so that only a small amount of deformation occurs when the separating slot is bent open due to the very high strength, the deformability at this point can be specifically supported by an expansion slot in the peripheral wall of the passage opening opposite the separating slot. Depending on the depth of the expansion slot, the material on the opposite side of the separating slot is then used to a greater or lesser extent to participate in the deformation, and the required pre-forming path along the remaining peripheral edge of the passage opening is specifically reduced.

Molded parts in which the mineral wool provided with a binding agent and not yet hardened is brought into the desired three-dimensional shape and hardened in this shape typically have binding agent contents of significantly more than 2% by weight (dry). This ensures that even exposed areas of the molded part have sufficient strength. According to claim 3, an absorption part according to the invention is, however, produced with a lower binding agent content of 2% by weight (dry) or less, as is also usual in the production of mineral wool panels for building purposes or the like. Due to the panel-shaped design or, in the preferred case, by producing the absorption part from a conventional panel, stress peaks at exposed areas are avoided in view of the more two-dimensional design, so that lower binding agent contents can be used.

In case of a short axial length of the silencer or one of its chambers to be filled with mineral wool material, complete filling with a plate-shaped absorption part that is undivided in the axial direction. However, in view of the plate-shaped design of the absorption part, it is also possible without any problem to construct the absorption part according to claim 4 from a plurality of plate-shaped sections arranged side by side. Due to the snap connection between the sections and the associated inner tube, a structure made up of a large number of sections does not pose any assembly problems.

The use of plate-like sections with a limited thickness, according to claim 5 in particular with a thickness of less than 10 cm, preferably less than 8 cm and in particular less than 6 cm, on the one hand enables easy handling during assembly by bending at the separating slot, and on the other hand enables the sections to be produced by punching, which is preferred over material-giving processing.

In the case of three inner tubes, according to claim 6, two sections are preferably formed, the dividing line of which runs between two inner tubes. In this way, each section is assigned an inner tube to which it can be attached by snapping it on.

According to claim 7, the dividing line cuts the third inner tube, preferably along its axis. This makes it possible to simply attach the sections to the third inner tube on the circumference without any undercuts occurring.

In a particularly preferred development of the invention, according to claim 8, the sections are prefabricated in a connected manner and separated from one another by a dividing line. This ensures that the correct and appropriate sections are available at the time of assembly without the risk of confusion and can be safely assembled without errors. If, according to claim 9, the dividing line is formed by a punched cut interrupted in the manner of a perforation, the connected sections can be broken apart with one hand and assembled individually without any increased manufacturing effort being required.

Alternatively, however, the parts can also be manufactured separately and made available as independently marketable products, as claimed in claim 10.

Such sections can be used according to the invention to form absorption parts for silencers with at least three inner tubes that are not located in a common plane.

Further details, features and advantages of the invention emerge from the following description of embodiments based on the drawing. It shows:

Fig. 1 is a perspective exploded view of a silencer with absorption parts according to the invention made up of sections which, in a first example, extend over the entire width of the installation space and which, in a second example, are constructed from a plurality of partial plates arranged side by side;

Fig. 2 is a perspective view of an absorption part according to the invention or a partial plate thereof;

Fig. 3 shows a partial view of the absorption part according to Fig. 2;

Fig. 4 the part according to Fig. 3 in its deformed position for installation before its mounting on the silencer;

Fig. 5 is a schematic representation of the process for producing an absorbent part or section according to the invention; and

Fig. 6 is a schematic partial representation of a punching knife for producing an interrupted cut.

Fig. 1 shows an example of a silencer 2 to be dampened with absorption parts according to the invention. The silencer 2 has a silencer housing 4, which in turn consists of peripheral wall parts 6 and 8, which are welded or flanged together at their edges to form a peripherally closed housing shell, as well as of associated end wall parts 10 and 12, which have an exhaust gas inlet nozzle 14 and an exhaust gas outlet nozzle 16, respectively. Exhaust gas from an internal combustion engine (not shown in detail), in particular the engine of a passenger car, is fed via the exhaust gas inlet nozzle 14 into the space enclosed by the peripheral wall made up of the peripheral wall parts 6 and 8. and discharged again from the silencer 2 by means of the exhaust gas discharge nozzle 16 on the opposite side.

In the interior of the silencer housing 4, an inner tube arrangement, designated overall by 18, is provided, which in the example consists of three inner tubes 20, 22 and 24 in a parallel arrangement, which are secured in position in the interior of the silencer housing 4 by means of three intermediate walls 26, 28 and 30. The outer circumference of the intermediate walls 26, 28 and 30 has a contour corresponding to the circumference of the silencer housing 4, so that the intermediate walls 26, 28 and 30 divide the interior of the silencer housing 4 into chambers 32, 34, 36 and 38 that are sealed against one another on the circumference.

The exhaust gas is first introduced from the exhaust gas inlet nozzle 14 of the front wall part 10 into the inner pipe 24, which is closed on the circumference in the area of the chamber 32 (hidden in the drawing) and is provided with a circumferential perforation 25 in the area of the chambers 34 and 36. The exhaust gas passes through the perforation 25 in the chambers 34 and 36, which act as absorption chambers, in a manner known per se, interacting with absorption parts 40 and 42 and thus losing part of its sound or pulsation energy. The exhaust gas passes from the inner pipe 24 into the chamber 38 opposite the inlet side, which is designed as a reflection chamber. In this process, a further part of the sound energy is destroyed by reflection phenomena. From the reflection chamber 38, the exhaust gas then enters the inner pipe 22, which is provided with a perforation 23 on the outer circumference, through which sound energy is again destroyed in the absorption chambers 34 and 36. From the inner pipe 22, the exhaust gas then enters the reflection chamber 32 opposite the reflection chamber 38, where sound energy is again destroyed by reflection. From the reflection chamber 32, the exhaust gas flow finally reaches the inner pipe 20, which is completely closed on the circumference and is extended downstream of the last intermediate wall 26 and opens into the exhaust gas discharge nozzle 16 of the silencer housing 4.

The absorption chambers 34 and 36 are filled with the absorption parts 40 and 42 made of bonded mineral wool, which must therefore accommodate the inner pipe arrangement 18 in the area of the absorption chamber 34 and 36. The outer contour of the absorption parts 40 and 42 corresponds to that of the circumference of the silencer housing 4, while the inner pipes 20, 22 and 24 are accommodated in associated recesses 44, 46 and 48 of the absorption parts 40 and 42. To protect the Mineral wool can be used to protect against the strong pressure pulsations and to improve the blow-out behavior, a mechanically resistant but acoustically permeable protective layer, for example made of metal wool, can be arranged in a known manner on the inner circumference of the recesses 46 and 48. In the area of the recesses 44, this is not necessary in the example case, since these accommodate the non-perforated inner pipe 20 and are therefore not exposed to any stress from the exhaust gas flowing in the inner pipe 20.

Due to the arrangement of the intermediate walls 26, 28 and 30, the absorption parts 40 and 42 cannot be pushed on axially in the example case. Assembly on the inner tube arrangement 18 from the side, i.e. radially rather than axially, is therefore necessary.

For assembly, the absorption parts 40 and 42 are constructed from sections 40a and 40b or 42a and 42b, which in the assembled position lie against one another at their dividing lines or cutting surfaces 50. The recess 44 for the inner tube 20 is cut through in the middle by the dividing line or cutting surface 50, so that two semicircular troughs associated with the respective sections 40a and 40b and 42a and 42b are formed, which surround the inner tube 20 from both sides. The recesses 46 and 48, on the other hand, are designed as circumferentially closed passage openings, which accommodate the inner tubes 22 and 24 completely inside each section 40a and 40b and 42a and 42b. To enable the assembly explained in more detail below, the recesses 46 and 48 are provided with a separating slot 47 or 49 running to the outside of the associated sections 40a or 40b and 42a or 42b, through which the inner tubes 22 or 24 can pass when the sections 40a or 40b and 42a or 42b are assembled.

The sections 40a or 40b and 42a or 42b or the absorption parts 40 and 42 have large surfaces 52 perpendicular to the cut surfaces 50 that are parallel to one another, and thus have a basic plate-like shape. In order to enable the advantageous production by punching from a mineral wool plate, as will be explained in more detail below, the plate thickness, i.e. the width of the absorption parts 40 and 42, is limited. If an installation space in an absorption chamber 34 or 36 with a width greater than 6 to 10 cm is to be filled by the absorption body 40 or 42, it is advantageous to build the individual absorption parts, as is illustrated in the case of the absorption part 40 or the sections 40a and 40b, from plate-like shaped sections 41 that have a small width of, in the example, 4 cm. By means of such a multiple arrangement of plate-like sections 41, any desired construction width can be achieved without the mineral wool plate used to produce the absorption parts 40 and 42 having to have an undesirably large thickness.

In Fig. 2, the absorption part 40 or a plate-like section 41 thereof is shown with further details. As can be seen from this, each absorption part 40 or each plate-like section 41 in the example shown is prefabricated in the complete contour of the absorption part 40, whereby the outer contour can be produced by a punch cut. Likewise, the recess 44 for the non-perforated inner tube 20, composed of semicircular depressions in the individual sections 40a and 40b, is produced using appropriate punching knives. Furthermore, the recesses 46 and 48, designed as circumferentially closed passage openings within each section 40a and 40b, together with the separating slots 49 and the cutting surface or separating line 50, are produced in one go using an appropriate punching knife. The dividing line 50 has a section 51 in which only an interrupted punch cut is produced, so that the sections 40a and 40b initially remain connected to one another after they have been produced. Only during assembly are the material webs shown at 51a in the area of section 51 of the dividing line or cutting surface 50 destroyed by hand by bending the dividing line 50 between the sections 40a and 40b, so that the sections 40a and 40b are present individually, as shown in Fig. 1.

In this way, the section 40a shown again in view in Fig. 3 is obtained. The assembly of the section 40a is shown in more detail in Fig. 4. The material on the circumference of the recess 46 is bent at the separating slot 49. This causes a deformation which is more or less evenly distributed over the entire circumference of the recess 46, i.e. it includes all of the material there without excessive stress peaks. In this way, despite the relatively large deformation path, the deformation is successful without excessive stress peaks and therefore largely without destroying the structure of the bound mineral wool, so that the edges of the separating slot 49 spring back again after the section 40a has been pushed onto the inner tube 22 in the illustration according to Fig. 4 and thus result in a final assembly position which would essentially also exist if the section 40a could have been mounted by pushing it onto the inner tube 22. The plate-shaped nature of the partial plates 41 and the absorption parts 40 and 42 also contributes to the avoidance of stress peaks that significantly impair the structure. This avoids irregularities in shape and the resulting unavoidable stress peaks. The design of the absorption part as a punched part from a conventional mineral fiber board also contributes to this, since in this case the fibers of the mineral wool lie essentially transversely to the bending axis, i.e. to the axis of the recess 46, and thus have good resistance to gaping of the structure.

Fig. 5 shows a schematic illustration of the production of absorption parts 40 and 42 or of plate-like sections 41 for this purpose. A conventional fiberizing unit (not shown in detail), such as a fiberizing rotor, in conjunction with suitable gas flows, produces a cooling gas stream 202 containing fibers, which is led into a chute 204 and is sprayed with binding agent via nozzles 206. The fibers thus provided with uncured binding agent reach a production belt 208 on the underside of the chute 204, where they are deposited under the influence of negative pressure and form a fleece 212 towards the exit 210 from the chute 204. As a result of the described type of fiber deposition, a very high percentage of the fibers are aligned in planes parallel to the production belt 208, with a largely random alignment within this plane. Only a relatively small proportion of the fibers are aligned in the direction of the thickness of the fleece 212.

In a tunnel oven 214, the fleece 212 is compressed to the desired final thickness and the binding agent is simultaneously hardened, so that the material leaves the tunnel oven 214 in the form of a continuous plate 216 with a desired height and density. The continuous plate 216 is then fed to a punching device 218, in which the punching knife 220 produces, in a manner known per se, for example, the partial plate 41 shown in Fig. 2 or, if the installation space is narrow, an entire absorption part 40 with all cuts lying perpendicular to the large surfaces 52.

As is illustrated in more detail in Fig. 6, the punching knife used 220 is provided with interruptions 222 in the area of the section 51 of the cutting surface 50, so that corresponding material webs 51a remain between the cutting surface elements, which hold the parts 40a and 40b together until the moment of assembly. This ensures that no confusion occurs during assembly and that the necessary assembly parts are always to hand.

Claims (12)

1. Absorption part (40, 42) made of bonded mineral wool for sound attenuation in an exhaust silencer (2), in particular of a passenger car, with at least three inner tubes (20, 22, 24) running parallel to one another and not lying in a common plane, with an outer contour corresponding to the circumference of the silencer housing (4) and with recesses (44, 46, 48) corresponding to the inner tubes (20, 22, 24) to be accommodated, and with a structure of the absorption part from parts (40a, 40b, 42a, 42b) which can be mounted from the side on the inner tubes (20, 22, 24) so that together they form the absorption part (40, 42) which accommodates the inner tubes (20, 22, 24) in the recesses, marked by its design as a plate-shaped molded part, in particular a stamped part, with large surfaces parallel to one another (52), by forming at least one of the recesses (46, 48) in at least one of the sections (40a, 40b, 42a, 42b) as a central passage that is at least approximately completely closed on the circumference and has a contour that is adapted to the circumference of an associated inner tube (22, 24), and through a separating slot (47, 49) in the material of the section running from the recess (46, 48) designed as a central passage to the outside of the section (40a, 40b, 42a, 42b). 2. Absorption part according to claim 1, characterized in that the edge of the central passage has an expansion slot on the side opposite the separating slot (47, 49). 3. Absorption part according to claim 1 or 2, characterized by a binder content of 2 dry weight % or less. 4. Absorption part according to one of claims 1 to 3, characterized by its structure from a plurality of plate-shaped mold sections (41) arranged side by side. 5. Absorption part according to claim 4, characterized in that each of the plate-shaped mold sections (41) has a thickness of less than 10 cm, preferably less than 8 cm, and in particular less than 6 cm. 6. Absorption part according to one of claims 1 to 5, characterized in that in the case of three inner tubes (20, 22, 24) two sections (40a, 40b or 42a, 42b) are formed, the dividing line (50) of which runs between two inner tubes (22, 24). 7. Absorption part according to claim 6, characterized in that the dividing line (50) preferably intersects the third inner tube (20) in its axis. 8. Absorption part according to one of claims 1 to 7, characterized in that the sections (40a, 40b or 42a, 42b) are prefabricated in a continuous manner and are separated from one another by a dividing line (50). 9. Absorption part according to claim 8, characterized in that at least one section (50 or 51) of the dividing line is formed by a punch cut interrupted in the manner of a perforation. 10. Part (40a, 40b, 42a, 42b) for the absorption part (40, 42) according to claim 1, wherein the part has at least one recess (46, 48) as an at least approximately completely closed central passage with a contour adapted to the circumference of an associated inner tube (22, 24), and wherein the part further has a recess (46, 48) formed as a central passage Recess (46, 48) extending towards the outside of the section (40a, 40b, 42a, 42b) and having a separating slot (47, 49) in the material of the section. 11. Method for producing an absorption part (40, 42) according to claim 1 or a part (40a, 40b, 42a, 42b) according to claim 10, characterized by the steps Depositing mineral fibers (202) provided with a binding agent on a production belt (208) and subsequent compaction and curing of the thus formed fiber fleece (212) to produce a mineral wool board (216), and Punching out the absorption parts (40, 42) or the sections (40a, 40b, 42a, 42b) including the recesses (44, 46, 48) and the slots (47, 49) from the mineral fiber board (216). 12. Method according to claim 11, characterized in that an interrupted punching knife (220) is used to produce a perforation section (51) in the region of the dividing line (50) between sections (40a, 40b or 42a, 42b) belonging to an absorption part (40, 42).