TECHNICAL FIELD The invention relates to a sound absorptive exhaust-gas conduit, particularly an exhaust-gas conduit which extends from an internal combuβion engine in an automotive vehicle, the exhaust-gas conduit including a chamber which is through- passed by exhaust gases and which has a gas-permeable wall, a sound absorbent surrounding the wall, and a substantially impervious casing surrounding the sound absorbent.

BACKGROUND ART

The invention relates particularly to automotive vehic¬ les driven by internal combustion engines, particularly auto- mobiles, and then especially private automobiles having a forwardlγ mounted engine and a rearwardly located exhaust-gas outlet. It will be readily understood by those skilled in this art that the inventive sound-dampening or silencing device can be used, in addition to automotive vehicles, also in apparatus with which exhausts gases are to be conducted away from an exhausts-gas emitting device to a location at a pronounced distance therefrom, and in which the exhaust-gas flow is to be muffled prior to being released. By "exhauβtβ- -gaseβ" is also meant waste-gas flows other than those deri- ving from internal combustion engines, for example general waste-gas flows which may be contaminated and which would generate noise if released directly from their source to their surroundings.

The invention will be described hereinafter, however, with reference to the exhaust systems of private automobiles. The exhaust system of an automobile having a forwardly mounted engine conventionally comprises a simple exhaust con¬ duit which includes one or more silencers, normally two silencer assemblies. The exhaust system must be capable of affording an exhaust-pressure drop which is well adapated to

the engine and which is conventionally determined by the silencer cans. The silencers must also be able to dampen sound in a practical manner. Moreover, the exhaust-gas system must be well adapted to the respective vehicle with respect to the size of the silencers and their position in relation to the vehicle. The conduit must have a given extension in order to fit the vehicle in question, and the design and positioning of the silencer cans is also determined by the design of the vehicle in question, the engine etc. In addition hereto, the exhaust-gas conduit and the silencer cans incorporated therewith also vary with vehicles of dif¬ ferent make, model and year, and it will be perceived that the manufacture and retail of such exhaust-gas systems becomes expensive, especially for the consumer who needs to replace the entire vehicle exhaust system or parts thereof. An object of the invention is to provide a sound— absorptive exhaust-gas conduit with which the aforementioned disadvantages are eliminated or reduced while, at the same time, fulfilling the requirements placed on the conduit with respect to the gas-pressure drop and sound damping. A parti¬ cular object of the invention is to provide a sound-absorp¬ tive exhaust-gas conduit which can be bent to a desired shape with the aid of simple means while retaining its original internal, free cross-section and its sound-absorbing or sound-moderating ability.

A further object is to provide a sound-absorptive exhauβt-gaβ conduit which can be readily bent and therefore readily adapted to the vehicle in question, thereby requiring only a few types of sound-absorptive exhaust-gas conduits to be kept in stock in order to satisfy market demands.

Another object of the invention is to provide a method for manufacturing a sound-absorptive or sound-moderating exhaust-gas conduit of the aforedeβcribed kind.

DISCLOSURE OF THE INVENTION sound-absorptive or sound-moderating exhaust-gas conduit, preferably an exhaust-gas conduit extending from an internal combustion engine in an automotive vehicle, compri-

see a chamber through which exhaust gas passes and which has a gas-permeable wall; a sound absorbent surrounding the wall; and an impervious casing surrounding the sound absorbent, the exhauβt-gaβ conduit being characterized in that the chamber wall iβ of circular cross-section, said cross-section being constant along the length of the chamber; in that the wall is composed of a helically wound metal wire and a net sleeve arranged externally on the wire helix; and in that the sleeve is made of a bendable material. The length of the chamber iβ preferably substantially equal to the length of the conduit. Consequently, an exhauβt-gaβ conduit according to the inven¬ tion can entail the length of the entire exhaust system down¬ stream of the engine manifold.

The chamber wall may optionally include a second heli- cally wound metal wire arranged on top of the net sleeve, such as to clamp the net sleeve between the two wire helices. The metal wireβ are suitably such as. to be readily bendable, thuβ not spring-wire, so that the conduit retains its shape subsequent to being bent. The metal wire or metal wires, ensures, or ensure, that the croββ-βection of the chamber remains conβtant along itβ length even after having bent the conduit. The sound absorbent, may comprise a relatively firmly compacted mineral fibre sljβeve, which may optionally comprise mutually joined pipe insulation sheathing, so called pipe cups.

The casing may comprise a thin-walled metal pipe or tube which iβ preferably resistant to corrosion or rust protected, for example an externally galvanized sheet-iron tube. A method for manufacturing a sound-absorptive or sound- moderating exhaust-gas conduit, particularly for use in auto¬ motive vehicles driven by internal combustion engineβ, iβ characterized by

- winding a metal wire to form a cylindrical helix; - placing a net sleeve on the wire helix;

- embracing the net caβing with a sound absorbent; and

- embracing the sound absorbent with a bendable caβing.

A βecond metal wire may optionally be wound helically around the net sleeve to form a cylindrical helix, in which case the sound absorbent can be placed around the tubular core formed by the two metal wires and the net sleeve. The resultant tubular silencer or muffler can be bent so aβ to adapt the same to a required extension without changing the free gas through-flow area.

When bending the inventive exhaust-gas conduit, defor- mations can occur in the caβing. The βound abβorbent iβ com¬ pressible and iβ thuβ able to yield in order to accommodate folds in the caβing. Consequently, the free cross-sec ion of the exhauβt-gaβ conduit will remain conβtant and will not be affected by any folds in the casing. The pressure drop through the inventive exhauβt-gaβ conduit primarily depends upon the free gas through-flow area and the length of the conduit. The βound moderating ability of the conduit gener¬ ally increaβeβ with the length of the exhaust-gas conduit, but iβ already βatiβfactory at a length, for example, of one meter, particularly, when the conduit exhibits a change in direction, βuch aβ a bend, when fitted to the vehicle. In the caβe of automobileβ having a forwardly mounted engine and a rearwardly located exhaust .outlet, the length of the conduit iβ substantially the same for different vehicles and models thereof, and hence the pressure drop iβ only affected relati¬ vely slightly by the length of the exhaust system.

Consequently, the exhauβt-gaβ conduit according to the invention can be used relatively generally for engineβ within a given power range and the exhauβt-gaβ conduit need genera- llγ be produced in a few diameters corresponding to given engine power rangeβ . The length of the conduit can be select¬ ed to provide a sound absorbing or moderating effect of an at least acceptable level even when the conduit iβ substantially straight when fitted to the vehicle. The inventive conduit can be advantageously manufactured in βuch lengthβ that they constitute substan ially the whole of the exhaust-gas passage

between the engine outlet manifold and the exhaust outlet. In this way it iβ only necessary to manufacture the exhaust-gas conduit in a few standard lengths in order to βatiβfy requi¬ rements. It should be particularly noted in this reβpect that the bendability of the inventive exhauβt-gaβ conduit renders it possible to decrease the length of the exhaust-gas system between the outlet end and the end which connects to the engine or the engine manifold.

A retailer of replacement exhaust βyβtemβ need then only keep a few types of the inventive sound-absorptive exhauβt-gaβ conduit in βtock and iβ readily able to bend a conduit of βuitable diameter and length to a configuration and length suitable for a respective vehicle, this bend having no βubβtantial influence on the reduction of silencer exhauβt-gaβ pressure. Alternatively, βuch bending of the exhaust-gas conduit can be readily effected by the manufact¬ urer, therewith again affording the advantage that only a email number of conduit modelβ need be manufactured, together with the simplicity in which the straight inventive conduit can be bent.

Aβ will be understood, a relatively short tubular con¬ duit can be connected to the rear end of the inventive con¬ duit in a manner to ensure, that the outlet end of the exhaust conduit iβ suitably located. If desired, a complete automo- bile exhaust-gas conduit can be. conβtructed downβtream of the engine manifold by two conduitβ according to the invention connected in βerieβ. The advantage afforded hereby iβ that exhauβt-gaβ condensate will normally form in the downstream part of the exhauβt-gaβ system, this down-βtream part con- βequenly often being subjected to greater corroβion and therewith needing to be changed more often.

The invention will now be described in more detail with reference to an embodiment thereof illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 illustrates schematically an axial section

through a sound-absorptive exhaust-gas conduit according to the invention.

Figure 2 iβ a schematic croββ-βectional view of a con¬ duit according to the invention.

Figure 3 illustrates schematically a method of manu- facturing the tubular core of a conduit according to the in¬ vention.

EMBODIMENT

Figureβ 1 and 2 illustrate a βound-abβorptive or βound moderating exhaust-gas conduit comprising a gaβ permeable cylindrical core generally referenced 1, a sleeve 2 made of a βound absorbent material and encircling the core 1, and a caβing 3 which encircles the sleeve. Located at one end of the conduit is a socket end 4 while a simple pipe socket 5 iβ mounted on the other end of the conduit. Thiβ enables βimple cylindrical exhauβt-conduits of predetermined free croββ- βectional area to be ^' connected in a conventional manner with¬ out forming cσnβtrictionβ at the joint locations.

The core 1 compriβeβ galvanized iron wire 10 which iβ openly wound to form a cylindrical helix. A net sleeve 12 iβ threaded over the wire 11. A further galvanized iron wire 13 iβ wound over the net sleeve 12 to form a further cylindrical helix, thiβ further helix clamping the net βleeve 12 againβt the firstmentioned wire helix 11. The two wire helices 11,13 preferably have the same pitch, with the turnβ of the wire heliceβ mutually displaced. The inner diameter of the outer wire helix 13 iβ preferably smaller than the outer diameter of the inner wire helix 11. The wires 11 and 13 may comprise galvanized iron wire having a diameter of 2 mm. The net sleeve may comprise a woven net of filaments having a diame- ter of approximately 0.3 mm and a spacing of 2 mm. The tubu¬ lar core haβ a diameter of approximately 40 mm. The sound absorbent may comprise glasβ-fibre pipe cups having a wall

thickness of approximately 10 mm. The metal sheet casing may have a thickneββ of approximately 0.5 mm.

Fig. 3 illustrates a cylindrical mandril 7 on which there are temporarily mounted a socket end 4 and a pipe βock- et 5. The mandril 7 iβ arranged for movement in itβ axial direction and for rotation aβ indicated by the arrowβ in Fig. 3. Three βtorage units 111,112,113 for storing the wire 11, a web of net 12 and the wire 13 are arranged to enable the wireβ 11 and 13 and the net web 12 to be fed to the mandril 7 at an angle to the longitudinal axiβ thereof corresponding to the pitch angle of the helical movement of the mandril 7. The tubular core 1 with associated socket end 5 and pipe socket 4 can be readily conβtructed by firsts connecting the wire 11 to the pipe socket 5, whereupon the mandril 7 iβ driven in the manner indicated with co-rotation of the pipe socket 5 and the socket end 4, whereafter the net web 12 is connected to the pipe socket 5, and then the wire 13 iβ connected to the pipe s'ocket 5. Winding is then continued along ^* the man¬ dril 7 until the wire 11, the net web 12 and the wire 13 are connected to the socket end 4. The tubular core 1, together with the pipe socket 5 and the βocket end 4 can then be removed from the mandril and provided with the sound-absorb¬ ent sleeve 2 and an outer caβing.

Aβ beforementioned, the sound-absorbent sleeve 2 may comprise so-called pipe cups made of mineral fibre or some other porous material capable of withstanding the presence of exhauβt gaβeβ and the relatively high temperatures of said gases .

The cylinder 3 may comprise a thin walled sheet metal tube whose end portions are formed and downwardly bent in a suitable manner into substantially tight abutment with and optional connection to the pipe socket 5 and the βocket end 4 respectively.

The caβing 3 can thuβ be readily placed over the ab- βorbent sleeve 2 on the core 1 as a result of the radial re¬ silience or suppleness of the sleeve 2, and iβ then shaped

and/or deformed at the endβ thereof for connection to the pipe socket 5 and the 4 socket end 4 respectively.

The material from which the caβing 3 iβ made and the thickness of said material iβ βuitably βuch aβ to enable the caβing to be bent to the deβired curvature of the inventive exhauβt-gaβ conduit. Any radially inwardly directed foldβ in the caβing 3 will be accommodated by the sleeve 2, so that the free inner cross-section of the core 1 remains constant even after bending or curving the conduit. Any reβidual de- formations in the sleeve 2 will have no appreciable affect on the sound-abβorbing performance of the exhauβt-gaβ conduit.

The primary purpose of the casing 3 iβ to provide a gaβ seal which prevents the exhaust gases from departing through the porous sleeve 2. It will be understood in this reβpect that the caβing 3 can be formed by winding metal foil heli¬ cally around the sleeve 2 in a manner βuch that mutually adjacent turns overlap one another, the foil strip advantage- ouβly presenting on the side thereof facing the sleeve 2 a heat-adhesive and exhaust-gas reβiβtant composition, partly for anchoring the casing to the sleeve and partly for secur¬ ing adjacent turns one to the other. The casing can be readi¬ ly connected to the pipe βocket 5 and the βocket end 4 by meanβ of any conventional technique.

The components of the tubular core 1 are preferably hard-soldered or welded to the socket end 4 and the pipe socket 5 respectively.

Although there has been described in the aforegoing a method of producing a tubular core 1 with associated pipe socket 5 and βocket end 4 piecewiβe, it will be obvious that the tubular core 1 can be made in continuous lengths, with the aid of conventional techniques, and that these lentghβ can be cut into suitable sections, to which the pipe section 5, the socket end 4 and the absorbent sleeve 2 and the caβing 3 are subsequently fitted. The sound-absorptive exhaust-gaβ conduit according to the invention has nowhere along the length thereof an exter¬ nal dimension which significantly deviates from the external

dimension of conventional exhaust conduits, and hence there iβ afforded a high degree of freedom with reβpect to bending and extending the conduit between its connection to the engine manifold of an automobile having a forwardly mounted engine to the outlet of the exhaust conduit at the rear end of the automobile. Thiβ freedom alβo enables further curves or bends to be made in the conduit in order to adapt its effective length in the longitudinal direction of the vehic¬ le, βo that the end of the exhaust conduit discharges at a desired location adjacent the rear end of the vehicle. If the exhausts conduit iβ too short, it iβ a βimple matter to join thereto a shorter, βimple conduit which places the exhausts outlet in the desired location, since the βound absorbing requirements have been well fulfilled in the inventive exhaust-conduit section.

When the caβing 3 iβ formed by an overlap of helically wound foil it may be βuitable to stabilize the casing and alβo to protect the same mechanically by means of a metal wire, corresponding to the wire 11, wound helically over the foil.

It should be understood that the wires 11 and 13 are chosen βo as not to afford any appreciable springiness, but instead comprise a material which can be deformed βo that the inventive exhaust-gas conduit retainβ the bent or curved shape imparted thereto.

The exhauβt-gaβ conduit can be readily fitted to the chassis of a motor vehicle at desired locations thereon with the aid of conventional fittings, it being poββible to select the anchoring locations substantially arbitrarily due to the fact that the external dimensions of the conduit are constant along the length thereo .