SE461290B - EXHAUST SYSTEM FOR MOTOR VEHICLE - Google Patents

Description

461 290 2 ӕ0 In recent years, the exhaust system has also been required to eliminate unburned hydrocarbons from the exhaust gases. This has been accomplished using a separate catalytic converter. The converter essentially consists of an additive to the conventional exhaust system and in turn constitutes a relatively bulky container. The exhaust gases containing unburned hydrocarbons flow into the converter and are passed by catalysts taken from the platinum group within the precious metals, including platinum, palladium and rhodium, all coated on alumina. The alumina may be in tablet form or may be present on a sprayed ceramic substrate. The converter causes the hydrocarbons to be oxidized, thereby reducing the pollutants in the atmosphere. Even in this case, the converter's space requirement means that the vehicle's construction is adapted to accommodate the converter. The oxidation of the unburned hydrocarbons generates a lot of heat, and the converter therefore reaches a high temperature. Furthermore, the vehicle must be designed in such a way that no damage occurs as a result of this high temperature.

The conventional muffler, converter, connecting pipes, exhaust pipes and end pipes are connected by means of clamps and mounted on the vehicle by means of holders. The various components must be assembled and placed on the vehicle on the assembly line. The relative complexity of the construction results in an extensive and expensive assembly operation.

A simplified exhaust system is described in US 3,104,732, where an exhaust pipe runs directly from the exhaust manifold to the atmosphere. This exhaust pipe has a constant diameter along its entire length and lacks any form of insert. There is no type of conventional, large muffler. Instead, sound attenuation is achieved by placing the exhaust pipe inside an outer pipe made of larger diameter and having perforations in various places along its length.

At the perforations, sound-absorbing material is applied around the outside of the exhaust pipe, which centers the exhaust pipe in the outer pipe and delimits resonant chambers. These are poorly ventilated and carry a high risk of corrosion. In addition, the double tubes require more space and increase weight. 3 ”461 290 It is known from US 3,746,126 to apply a straight attachment in the rear part of the exhaust pipe to an otherwise conventional exhaust system with a muffler for sound-absorbing purposes. This additive, in the form of a screw-like element, is carefully designed to avoid excessive back pressure in the exhaust system.

There is a need for an improved exhaust system that maintains the sound attenuation and oxidation properties of the conventional muffler and converter, while reducing the size, cost and weight of the system. This would allow increased flexibility in vehicle construction. There is also a need to provide an improved exhaust system which reduces installation time and material cost, but which has equivalent or improved service life during use.

The object of the invention is to achieve such an improved exhaust system.

This object is achieved according to the invention in that a pipe made with a constant diameter in a manner known per se extends all the way from the exhaust manifold to the atmosphere, that the pipe is unperforated and constitutes a flow channel for the exhaust gases, that the diameter of the pipe is at most equal to the diameter of a conventional exhaust pipe, that it is arranged in the pipe. A sound-absorbing means which extends continuously along the entire length of the pipe and in several places has contact with the inside of the pipe and is arranged in the path of the exhaust gases flowing in the pipe, whereby a sound-absorbing effect is obtained along the entire length of the pipe, that the pipe is designed to fit the vehicle without changing its design, this due to conformity in diameter measurements between the pipe and a conventional exhaust pipe, and that the sound-absorbing member consists of a strip provided with openings, which is so placed in the pipe that exhaust gases are forced to pass through openings in the strip.

The sound attenuation means is advantageously folded at predetermined locations along its length to form separate filters between the weeks, with each filter located at a predetermined distance from the adjacent filters. The predetermined distance between adjacent filters may vary along the length of the pipe to improve the sound attenuation of the exhaust system within a frequency range, and the pipe may comprise at least one section which along its length lacks a filter and which is intended to form a mixing chamber where parts of sound shocks that have been divided by previous filters cancel each other out.

The filters can have either a rectangular cross-sectional shape, forming four channels along the tube, between its inner wall and the edges of the filters, which channels contribute to the decomposition of the sound shocks, or an elliptical cross-sectional shape to allow the filters to contact the inner wall of the tube. According to an advantageous embodiment, the strip-shaped sound-absorbing means can be twisted in a spiral shape, the width of the strip being substantially equal to the inner diameter of the tube.

The invention is explained in more detail below with the aid of exemplary embodiments shown in the accompanying drawing, in which Fig. 1 shows a bottom view of a vehicle having a solid embodiment shown in solid lines of an exhaust system according to the invention, while on the other hand a conventional exhaust system Fig. 2 shows a perspective view of an exhaust pipe system, where a part of the pipe wall has been cut away to show the stretched material in the outer pipe, Fig. 2 with a conventional muffler, a conventional catalytic converter and clamps. Fig. 3 shows a vertical cross-section of the exhaust system along the line 3-3 in Fig. 2, in the direction of the arrows, Fig. 3A shows a detail of the cross-section of the stretched material along the line 3A-3A in Fig. 3, in the direction of the arrows Fig. 4 shows a horizontal cross-section of the exhaust system taken along line 4-4 in Fig. 2, in the direction of the arrows, Fig. 5 shows a horizontal cross-section of a first modification of the exhaust system, u Fig. 6A-C shows views of a second modification of the exhaust system, with an element weight less than 1800 between the filter sections, Figs. 7A-C show views of a third modification of the exhaust system, with circular filters, Figs. 8A-C C shows a fourth modification of the exhaust system, with elliptical filter portions folded less than 1800 between the filters, Figs. 9A-C show a fifth modification of the exhaust system, where the filter portions are formed by spirally rotating materials made porous by stretching, weaving or otherwise, Fig. 10 shows an exhaust system according to a second embodiment of the invention, a portion being folded up to show the interior design, when a plurality of baffles extend into the gas flow, Fig. 11 shows a cover for use at the exhaust system according to the second embodiment, Fig. 12 shows a vertical cross-section of the exhaust system according to the second embodiment, along the line 12-12 in Fig. 10, in the direction of the arrows, Fig. 13 v is a cross-section of a wing profile taken along line 13-13 of Fig. 12, in the direction of the arrows; Fig. 14 shows a horizontal cross-section of the exhaust system according to the first embodiment, adapted for attachment to an exhaust manifold and bent to fit the vehicle Fig. 15 shows a section of a fifth modification of the first embodiment, and shows the spiral winding of the stretched material, Fig. 16 shows a design, showing the minor deformation of the element which occurs when the pipe is bent or flanged. vertical cross-section of the fifth modification along the line 16-16 in Fig. 15, in the direction of the arrows, and Fig. 17 shows a view, partly in section, of a third embodiment of the invention, using woven material.

In the drawing, where the same reference numerals refer to the same or corresponding parts in several figures, Fig. 1 shows a vehicle 10, which for propulsion is provided with an internal combustion engine 12. The engine 12 is provided with an exhaust manifold 14, which collects combusted exhaust gases from the engine from one or more cylinders, for transport away to the atmosphere.

The components shown in broken lines represent a conventional muffler 20, a conventional catalytic converter 18 and conventional terminals 21. The converter and muffler are joined by a tube 22. It is clear that the design of the vehicle 10 must be adapted to accommodate the relatively bulky converter. 18 and the muffler 20.

It also appears that the conventional system consists of many parts which must be mounted at the same time as or before the vehicle is mounted on the mounting belt.

The exhaust system 24 shown in Fig. 1 constitutes a first embodiment of the exhaust system according to the invention. As can be clearly seen, the exhaust system comprises a continuous outer diameter pipe 26, which at one end has a flange 28 for connection to the exhaust manifold 14. The opposite end of the pipe 26 has an opening 30 located at the rear of the vehicle for discharging the combust the gases from the engine into the atmosphere.

The tube 26 may have bends 32, 34, 36, 38, 40, 42 and 43 along its length to suit the structure of the vehicle, including the rear axle and other parts. As will be described in more detail, the exhaust system 24 provides attenuation of the exhaust noise from the engine and may also include catalytic conversion elements to oxidize the unburned hydrocarbons to thereby reduce the air pollutants.

The internal details of the exhaust system are best described with reference to Figures 2 - 4. Figs. 2 shows an element 44 of stretched, porous material 46. The element 44 is folded along folds 48 to form separate, spaced apart rectangular filters 50. The rectangular filters can be folded sufficiently to form square filters, as shown. The network 52 at each filter 50 defines a plurality of holes 54 which allow the 4 exhaust gases to pass through the filters. The network breaks up and destroys the shock waves present in the exhaust gases with acoustic frequency generated by the explosive emission of the combusted air / fuel mixture from the engine 12.

The bending angle 56 of the folds 48 is selected to provide an optimal cross-section of the filters 50. In the embodiment of Figures 2-4, the folding angle 56 of the material is approximately 1800 to provide square filters 50 across the exhaust flow represented by the arrow 58. At In a modified form according to Figs. 6A - C, the bending angle 56 is less than 1800 to provide a stretched element with rectangular filters 60 which are not set across the direction of gas flow. The bending angle 56 can be varied along the length of the element to improve the sound attenuation within a frequency range of the exhaust flow. Steel is a preferred material for the stretched material 46.

However, a high temperature plastic, ceramic or other material can also be used. In an exhaust system according to the invention, a number of 54 holes with the dimension 6.4 x 6.4 mm were used, which was found to attenuate the exhaust sound in a satisfactory manner, with acceptable back pressure.

With rectangular filters 50 (including the square filters 50 shown), four curved passages 62, 64, 66 and 68 are formed between the inner wall 70 of the tube 26 and the outer edges 72 of the filters. Parts of the shock waves in the exhaust gases enter the passages. The turbulent imbalances in the gas flow between the passages and gas filtration in the filters 50 facilitate the decomposition of the 461 290 shock waves with acoustic frequency and improve the sound attenuation.

Although the element 44 can fill the entire length of the tube 26, according to the preferred embodiment one or more mixing chambers 74 are arranged along the length of the tube, according to Fig. 5.

The mixing chamber may be formed between two elements 44, or a single continuous element may have a portion 76 extending linearly along the mixing chamber, as shown in Fig. 5. The mixing chambers mix the separated portions of the disintegrating shock waves so as to take each other out, for to further improve the sound attenuation. By having a linear portion 76, the element 44 can extend along the entire length of the tube in a single continuous strip, to facilitate manufacture. Ideally, to attenuate a maximum number of sound frequencies, the exhaust system 24 may have a series of filters and mixing chambers, the filters having varying heel sizes to provide attenuation of the shock paths. The pattern can be repeated along the length of the exhaust system to form several stages of intentional acoustic decay for each frequency. The network 52 can also be designed with different wing profile-like cross-sectional shapes to move the gas inside the pipe, thereby improving the damping.

The exhaust system 24 can also function as a catalytic converter. Conventional catalytic converters are designed in two basic variants. One variant is to use a number of alumina tablets that are coated with a metal in the platinum group.

The platinum group includes platinum, palladium and rhodium. According to the second variant, a ceramic is coated with alumina and then with a catalyst from the platinum group. The catalyst facilitates oxidation of the unburned hydrocarbons in the exhaust gases, thereby reducing hydrocarbon contamination.

The network 52 is coated with alumina 78 and a metal 80 from the platinum group, as best seen in Fig. 3A, to provide the catalytic conversion function of the exhaust system 24. If the stretch material 46 is steel, it is desirable 461 290 to coat the steel with ceramic. before coating with alumina and a metal 80 from the platinum group.

A second modification of the exhaust system 24 is shown in Figs. 7A-C.

The modified exhaust system comprises an element 82 made of stretch material 46 which has circular filters 84. The folds 48 between each filter 84 have been folded about 1800, whereby the circular filters are set substantially across the gas flow.

The edges 86 of the circular filters are in contact with the inner wall 70, whereby each filter extends over the entire inner cross-section of the tube. The curved passages 62 - 68 are thereby eliminated.

According to a fourth modification of the exhaust system 24, an element 88 made of stretched material 46 is used, which defines elliptical filters 90. The material is folded at an angle of less than 1809 at each fold 48 to expand the element. However, the elliptical shape of the filters 90 allows each elliptical filter 90 to be in contact with the inner wall 70 of the tube 26 along an inner circumference positioned obliquely relative to the longitudinal direction of the tube.

The filters are thus not directed across the flow direction. Passengers 62 - 68 have been eliminated, so the entire gas flow must pass through each filter. The distance between the filters 90 can be adjusted as a function of the length of the ellipse.

A fifth modification of the exhaust system 24 is shown in Figs. 9A-C and Figs. 15 and 16. According to this embodiment, an element 94 made of stretched material 46 in the form of a continuous strip of constant width has been rotated in a spiral shape so that the outer the edges 96 of the element are in contact with the inner wall 70 of the tube 26 along helices 98 and 100. The gas flows through each filter 102, defined by the helical member 94, which presents a plurality of porous cross-sections for the flow, which cross-sections extend around the inner wall. whole circumference.

Fig. 15 carefully shows the placement of a portion of the member 94 within the tube 26. Figs. 16 shows an end view of the exhaust system provided 461 290., with a filter 102 formed of a sufficient length of the element 94 to cover the entire circumference of the inner wall.

Many advantages are achieved with the exhaust system 24. The pipe 26 in the system 24 forms a continuous sound-absorbing pipe.

Experiments have shown that a pipe 26 having substantially the same outer diameter as the connecting pipe 22 in a conventional system 16, and extending along the entire length of a conventional exhaust system 16, produces substantially the same sound attenuation effect as the conventional exhaust system 16.

This eliminates the bulky muffler. If the exhaust system 24 comprises a catalytic converter function, the catalytic converter 18 can also be eliminated. The exhaust system 24 therefore reduces the size and weight of the exhaust system, which enables increased flexibility in vehicle construction, leading to a lighter vehicle with a lower profile and better streamlined shape. This can result in fuel savings. The smoother, less bulky profile of the system 24 also means that the system is less exposed to damage from the road.

In addition, the continuous pipe 26 does not require any clamps of the type used in the conventional exhaust system 16. The simplicity of the exhaust system 24 can result in savings in the assembly stage, reduced material costs and can provide a lower back pressure for a desired sound attenuation level. in an embodiment with a catalytic converter function, the exhaust system 24 further has the advantage of spreading the heat generation from the catalytic converter function along the distance of the exhaust system 24 which houses the catalytic converter. This reduces the heat concentration in any special part of the vehicle, which in turn enables greater flexibility in the vehicle construction.

The exhaust system 24 can have three functions on a given distance and within a minimum diameter, while the pipe 22 of similar diameter present in the conventional system 16 only transports gases. The cross section of the pipe 22 not only transports gases away, but also dampens the exhaust noise and removes pollutants. 11 - 461 290 The presence of a passage 52 - 68 can improve the ventilation in the exhaust system when the system is not in operation. This reduces the corrosion level below that which occurs with conventional mufflers, as a result of which the exhaust system 24 has a longer service life. The exhaust system 24 also allows great flexibility in terms of bending to enable adaptation to the construction of the vehicle. For example, Fig. 14 shows the inner cross-section of the exhaust system 24 at bends 40 and 42. Since the sound attenuation occurs along a considerable length of the exhaust system, any limited deformation or breakdown of the filters at a particular bend does not significantly affect the function of the exhaust system. The deformation of the few filters 60 which are compressed at the inner radius of the bend and disassembled at the outer radius of the bend has no practical effect on the function of the exhaust system. A few filters 59 are pressed closer together as the tube is shortened when forming the flange 53, something which hardly has any negative effect.

The material 46 may be sprayed ceramic of varying porosity and shape, and may be made in sizes and shapes to fit in the tube 26 before the tube is formed and welded together with a seam. When the pipe is bent, the ceramic elements can be crushed at the flanges and bends, which does not significantly impair the exhaust system's sound attenuation ability.

The exhaust system 24 can be manufactured in various designs to suit the displacement of the internal combustion engine with which it is to be used, the pipe length to be installed, the desired sound attenuation properties, the degree of back pressure tolerated, and the degree of air pollution control required.

Since the muffler function and the catalytic converter function are separate, the exhaust system 24 can be used only for muffler or only for pollution control. However, both sound attenuation and catalytic conversion can also be combined in the same exhaust system 24.

It may also be desirable to design the exhaust system 24 in more than one section. This may be desirable to facilitate assembly. In addition, this allows the assembly of a section of the exhaust system intended only for sound attenuation with another section intended only as a catalytic converter. The sound attenuation and conversion sections can then be replaced independently. It is also possible that the sound attenuation section and the catalytic conversion section do not occupy the entire length of the pipe 26. The weight of the exhaust system can be reduced by eliminating unnecessary material inside the pipe. It is also possible to use stretched material consisting of more than one substance inside the exhaust system 24. For example, steel can be used in the sound attenuation section while ceramic material is used in the catalytic conversion section. The ideal method of manufacture is to produce the tube for sound attenuation and for catalytic conversion in a sequence and in one piece, or in a continuously repeating series of shapes and designed so that all parts reach the end of their service life at the same time.

Sound level tests were performed to compare the sound attenuation characteristics of a conventional exhaust system with an exhaust system fitted with a silencer according to U.S. Patent No. 3,746,126, issued July 17, 1973 to de Cardenas and with an exhaust system according to the invention. Sound level tests were also performed with a single 1.5 m long piece of empty pipe, completely without silencers.

All tests were performed with a General Motors V8 engine with a cylinder volume of 4640 cm3. A Genrad Model 1983 sound level meter was used in all measurements, set to "fast" response.

All tests were performed under identical conditions in a villa ~ garage. The sound level meter was mounted on a stand about halfway between the car's side and a wall in the garage, about 1.2 m from the open end of the exhaust system. In all cases, the tested exhaust systems were mounted after the Y-junction that joins the exhaust pipe sections from the two exhaust manifolds to a common pipe immediately in front of the conventional muffler.

The muffler made according to de Cardena's patent was 40 13 461 290 gjoni of a piece of galvanized steel plate of the type used for connection plates on roofs, from this plate was cut a strip with a width equal to the inner diameter of an exhaust pipe with a total diameter of 5 cm. The steel plate was wound helically so that it became 1.5 m long and inserted into a pipe piece with a length of 1.5 m and a total diameter of cm.

Table 1 summarizes the sound level readings with a conventional muffler at different engine speeds, with the test vehicle's automatic transmission in parking mode and in driving mode. §Unventional muffler Table 1 Speed dB (A) dB (A) (per min.) In parking mode í_§§ïl§g§ 500 - 68 600 70 71 800 72 73 1000 73 78 1200 77 - 2000 80 - 2500 84 - The sound level readings for a muffler made according to the Cardcna patents are listed in Table 2.

EeÜCardenas muffler Table 2 speed dB (A) ÖB (A) (per min.) In parking mode ¿__§§§l§g§ 500 - 78 600 76 81 800 80 88 1000 82 94 1200 84 - 2000 88 ~ 2500 90 ~ 14 461 290 - The sound level readings with a muffler tube according to the invention are given in Table No. 3.

According to uvgfinninqen Table 3 Speed dB (A) dB (A) (down min.) In Darkerinc mode in driving mode 500 - 71 600 72 74 800 75 78 1000 77 84 1200 78 - 2000 81 - zsoo sé - The sound level measurements with a hollow or blank 1 , 5 m long pipe is given in table no. 4.

Empty pipe with the lance 1.5 m Iaëell 4 Speed dB (A) dB (A) (Calculate min.) In narcotics mode in driving mode 500 - 80 600 77 83 800 80 89 1000 85 95 1200 85 - 2000 89 - 2500 90 - The result of the sound level measurements when there is no pipe or muffler after the Y-joint is stated in table no. "461 290 Without pipe or muffler Table 5 Speed dB (A) dB (A) (gives min.) in marking position in driving position 500 - 79 600 78 84 800 80 90 1000 81 96 1200 83 - 2000 90 ~ 2500 92 ~ The result of sound level measurements at rapid acceleration to a speed of 3000 per minute is given below.

Sound level Conventional Invention de Cardenas Empty pipe Without pipe Electric muffler sound dancer 1.5 m long clay sounder dB (A) 93 96 103 103 106 The exhaust system 110 shown in Figs. 10 - 13 constitutes a second embodiment of the invention. The exhaust system 110 comprises the pipe 26, which has a substantially constant outer diameter along its entire length. Inside the tube 26, however, there is a cladding 112 which has a plurality of wing profile-shaped baffles 114, which from the cladding 112 reach into the gas flow to break up and disintegrate the sound shocks.

The cladding 112 is preferably made of such a metal as steel. The wing profile shaped baffles 114 can be punched out of the continuous liner strip 112 shown in Fig. 11 by cutting the material along the edges 116, 118 and 120 and thereby bending the baffle 114 in one direction so that all the baffles reach out from one side 122. on the dressing 112.

The tube 26 and the liner 112 can then be simultaneously rolled into a tubular shape, as shown in Fig. 10. After rolling, the tube is welded together along the seam 124 to form a gas-tight exhaust system. - 461 290 16 If desired, both the pipe and the cladding can be welded.

The baffles 114 of the rolled casing extend radially inwardly toward the center of the exhaust system, as best seen in Fig. 12. The baffles may extend completely over the inner diameter of the rolled casing or, if desired, any smaller distance.

The individual baffles 114 are formed into a wing profile shape, as best seen in Fig. 13. The wing profile surface disrupts the gas flow to attenuate the acoustic frequencies in the shock wave. The baffles can have varying profile shape, length, thickness and angle of attack 6 against the gas flow and can occur differently close along the exhaust system.

If a catalytic conversion function is desired, the baffles can be coated with alumina and a metal within the platinum group to achieve the conversion function.

The system 110 has the advantages stated in connection with the exhaust system 24. The exhaust system 110 can also be used in substantially the same manner as the exhaust system 24 described above.

In Fig. 17, the exhaust system 130 forms a third embodiment of the invention. In the exhaust system 130, the tube 26 is filled with a woven wire mesh 132. The woven wire mesh provides a damping of the acoustic frequencies in the sound shock in a manner similar to the systems 24 and 110 described above. The warp in the woven mesh may be wire of varying diameter and cross section. The weft in the fabric can also vary in a similar way. The open spaces between the threads in the fabric can vary in size and shape along the fabric to increase the sound attenuation within different frequency ranges. The exhaust system 130 also enables the advantages and uses stated in connection with the systems 24 and 110 above.

Although different embodiments of the invention have been described in the drawing and in the above description, it is obvious that the invention is not limited to the embodiment shown, but can be varied and modified in numerous variants within the scope of the inventive idea.

Claims (15)

17 '461 290 gate requirements Exhaust system for removing exhaust gases from an combustion engine (12) fitted with an exhaust manifold (14) on a vehicle (10), the engine being of the type which can be silenced by conventional means by means of at least one silencer section (20) connected in a conventional exhaust pipe (26) extending from the exhaust manifold to the atmosphere. and where the muffler section (20) has a larger diameter than the exhaust pipe (26) and where the vehicle is designed to be provided with an exhaust pipe of said diameter. characterized in that a tube (26) of constant diameter extends in a manner known per se all the way from the exhaust manifold (14) to the atmosphere, that the tube is unperforated and forms a flow channel for the exhaust gases. that the diameter of the pipe is at most equal to the diameter of a conventional exhaust pipe. that a sound-absorbing means (46) is arranged in the pipe, which extends continuously along the entire length of the pipe (26) and in several places has contact with the inside of the pipe and is arranged in the path of the exhaust gases flowing in the pipe. whereby a sound-absorbing effect is obtained along the entire length of the pipe, that the pipe is designed to fit the vehicle without changing its design, this as a result of a correspondence in diameter dimensions between the pipe and a conventional exhaust pipe. and that the sound-absorbing means (46) consists of a strip provided with openings (54). which is so placed in the pipe that exhaust gases are forced to pass through openings in the strip. Exhaust system according to claim 1, characterized in that the sound-absorbing means is folded at predetermined places (48) along its length to form separate filters (50) between the folds, with each filter located at a predetermined distance from the adjacent filters. 461 290 - 18 Exhaust system according to claim 2, characterized in that the predetermined distance between adjacent filters (50) varies along the length of the pipe to improve the sound attenuation of the exhaust system within a frequency range. Exhaust system according to claim 2 or 3, characterized in that the pipe (26) comprises at least one section which along its length lacks a filter (S0) and which is intended to form a mixing chamber (74) where parts of sound shocks which have divided by previous filters cancel each other out. Exhaust system according to one of Claims 2 to 4, characterized in that the filters (SO) have a rectangular cross-sectional shape, forming four channels (62. 64. 66. 68) along the pipe, between its inner wall (70) and the edges of filters. which channels contribute to the decomposition of the sound shocks. Exhaust system according to one of Claims 2 to 4, characterized in that the filters (S0) have an elliptical cross-sectional shape to allow the filters to be in contact with the inner wall (70) of the pipe along substantially the entire circumference of the filter. Exhaust system according to claim 1, characterized in that the strip-shaped sound-absorbing means (46) is twisted in a spiral shape, the width of the strip being substantially equal to the inner diameter of the pipe. Exhaust system according to one of Claims 1 to 7, characterized in that the size of the openings (S4) varies along the pipe. Exhaust system according to one of the preceding claims. characterized in that the attenuation means (46) is of a material selected from a group comprising metal, ceramics and high temperature plastics. 19 _ 461 290 Exhaust system according to one of the preceding claims. characterized in that the sound-absorbing means (46) is of the expanded metal type, preferably of steel. 11. ll. Exhaust system according to claim 10. characterized in that the openings (S4) have the dimensions approx. 6 x 13 mm. Exhaust system according to one of Claims 1 to 9, characterized in that the sound-absorbing means (46) is of the woven mesh type. Exhaust system according to claim 12. characterized in that the wire in the fabric varies in diameter and cross section to attenuate sound shocks within a frequency range, and that the openings between the wires also vary in size. Exhaust system according to one of the preceding claims. characterized in that the sound attenuation means (46) is at least locally coated with alumina and a metal from the platinum group to form a catalytic converter in the exhaust system. Exhaust system according to claim 14, characterized in that the pipe comprises at least two sections. a first section intended primarily for attenuating the exhaust noise and a second section intended primarily for reducing the hydrocarbons in the exhaust gases.2.