The invention relates to a silencer for a motor vehicle exhaust system, and also to its method of mounting.
BACKGROUND OF THE INVENTION
In the prior art, an exhaust system comprises in succession, going away from the exhaust manifold of the power unit: a decoupling hose, a catalytic converter, and/or a particle filter, and often two silencers. An exhaust system silencer is of large volume (h=150 millimeters (mm)×L=400 mm×w=200 mm, for example) and it is fixed to the vehicle body by resilient straps, thereby leading to considerable size constraints.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the invention is to devise an exhaust system having a novel type of silencer making it possible to reduce weight, cost, and size in order to mitigate the drawbacks of a conventional exhaust system.
To this end, the invention provides a silencer for a vehicle engine exhaust system, wherein the silencer is constituted by at least one duct which acts as a guide for exhaust gas and as an acoustic attenuator for exhaust noise, and which comprises at least one porous internal metal tubular element, intermediate thermal and acoustic lagging, and a leaktight outer covering of polymer material, and wherein the outer covering is connected in leaktight manner to two tubular metal connection devices via two metal caps.
The internal metal tubular element may be constituted by a flat spring with overlapping turns, by a sheet metal tube with single or double seam joints, or by a flexible or rigid metal tube, each of which elements may be pierced with openings for acoustic reasons.
Advantageously, the internal tubular element may be coated in a refractory fabric possessing a certain degree of porosity, the refractory fabric possibly being made of ceramic, basalt, or glass fibers.
The duct, which may be flexible, may also include leaktight annular volumes arranged longitudinally in the thermal and acoustic lagging, each leaktight intermediate volume being defined by two compression rings, each compression ring being resilient and made of silicone, for example.
The duct may also include acoustic baffles interposed in the internal tubular element.
In general, in order to reduce the temperature of exhaust gases, a tubular metal connection device can be placed at the entrance to the duct, the device presenting external and/or internal cooling fins, and/or a diffuser-forming device may be placed at the exit from the duct.
In an embodiment of the silencer in accordance with the invention, the outer covering of the duct may form a box having the internal metal element passing therethrough, the thermal and acoustic lagging filling said box in which the internal metal element may form at least one bend.
Advantageously, the wall of the box presents at least one resonance surface in the form of a membrane, for example, having resonant frequency(ies) corresponding to certain frequencies of the frequency spectrum that is to be attenuated.
The invention also provides a method of mounting a silencer of the invention in a motor vehicle exhaust system, the method consisting in manufacturing, storing, and transporting the silencer in rectilinear shape, and in deforming it to comply with a given geometrical shape at its mounting site using the corrugations formed by the outer covering of the duct.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages, characteristics, and details of the invention appear from the additional description below made with reference to the accompanying drawings, given purely by way of example, and in which:
FIG. 1 is a perspective view of a prior art exhaust system, mentioned in the introduction;
FIG. 2 is a perspective view of an exhaust system including a silencer in accordance with the invention;
FIG. 3 is a fragmentary longitudinal section view of an embodiment of the FIG. 2 silencer with a flexible duct comprising at least one internal tubular element, thermal and acoustic lagging, and an outer covering;
FIGS. 4
a to 4e are diagrams showing variant embodiments of the internal tubular element of the flexible duct of FIG. 3;
FIG. 5 is a section view of an embodiment of the external covering of the duct;
FIG. 6 is a fragmentary longitudinal section view showing compression rings mounted in the thermal and acoustic lagging of the duct of FIG. 3;
FIG. 7 is a fragmentary longitudinal section view showing acoustic baffles interposed in the internal tubular element of the duct of FIG. 3;
FIG. 8 is a fragmentary longitudinal section view of a device enabling exhaust gas to enter into the FIG. 3 duct;
FIG. 8
a is a view seen looking along arrow VIIIa of FIG. 8;
FIG. 9 is a longitudinal section view of a device enabling exhaust gas to exit from the duct of FIG. 3;
FIG. 10 shows a variant embodiment of FIG. 9;
FIG. 10
a is a section view on line Xa-Xa of FIG. 10;
FIG. 11 is a diagram showing another embodiment of the duct of the invention;
FIG. 12 is a perspective view of FIG. 11; and
FIGS. 13 and 14 are perspective views for showing the method of mounting a silencer of the invention.
MORE DETAILED DESCRIPTION
The exhaust system 1 shown in FIG. 1 shows the state of the art mentioned in the introduction, the system 1 comprising in succession, from a multitube exhaust manifold 3 at the outlet from a power unit 4: a decoupling hose 5; a catalytic converter 6; and two rigid silencers 7 secured to the vehicle body by resilient straps 8; and interconnected by tubes 9 of stainless steel.
In the exhaust system 10 of the invention and as shown in FIG. 2, the two silencers 7 have been eliminated and replaced by at least one silencer 12 constituted by a duct 14 which is fastened by rigid fastening tabs 15 to the body of the vehicle and which acts as a guide for exhaust gas and as an acoustic attenuator for exhaust noise, as described below with reference to FIGS. 2 to 9.
In an embodiment of the invention shown in FIG. 3, the duct 14 is constituted by at least one internal tubular element 16 which is porous, thermal and acoustic lagging 18, and a flexible and leakproof external covering 20 of elastomer material that withstands high temperature, the covering 20 possibly being made out of a thermoplastic material such as PA 66, or an elastomer material such as Vamac®, or silicone, for example.
In general, the duct 14 is constituted by at least one internal tubular element 16 of flexible or rigid type which is preferably made of metal so as to be capable of withstanding the temperature of exhaust gas, and which is porous, in particular for acoustic reasons. The internal tubular element 16 is made to be porous by piercing openings through it over substantially its entire length.
As an example shown in FIG. 4a, the internal tubular element 16 is constituted by a metal tube 25 pierced by openings 27. Advantageously, the openings 27 can be formed by a plurality of series of openings, e.g. three series 27a, 27b, and 27c which are of flow sections or diameters that increase going in the flow direction of the exhaust gas, in particular to avoid any risk of the exhaust gas flowing in the reverse direction through the lagging 18, and as shown in FIG. 4b. These three series of openings 27a, 27b, and 27c may have diameters of 1 mm, 2 mm, and 3 mm respectively, for example. In a first variant embodiment shown in FIG. 4c, the internal tubular element 16 is constituted by two concentric tubes, an inner tube 25a and an outer tube 25b, the inner tube 25a extending over a fraction only of the length of the silencer, for example, e.g. over 5% to 30%, so as to create interference suitable for canceling the soundwaves from the flow of exhaust gases. In a second variant embodiment of the invention, the internal tubular element 16 is made of sheet metal with single or double seam joints (FIG. 4d, FIG. 4e) or by a spring having overlapping turns (FIG. 3), all of which elements present communication passages independently of any additional openings that may be pierced in the same manner as for the metal tubes of FIGS. 4a or 4b.
In the embodiment of a silencer of the invention that is shown in FIG. 3, the internal tubular element 16 is made in the form of a flat spring 29 having overlapping turns, however the element 16 could be replaced by an element as shown in any of the embodiments of FIGS. 4a to 4e. Advantageously, a refractory fabric 30 can be wound around all or part of the internal tubular element 16, said fabric presenting sufficient porosity to enable the lagging 18 to damp acoustic waves, while limiting any direct passage of exhaust gas through the lagging 18 so as to avoid damaging the outer covering 20. The fabric 30 may be made of ceramic, basalt, or glass fibers, for example.
In the embodiment shown in FIG. 5, the duct 14 may present at least one outwardly-extending projection 32 formed in its outer covering 20 to create an additional volume 33 that is filled with the material constituting the lagging 18. Advantageously, an absorbent lining 34 having a very low index of reflection can be received against the inside wall of the projection 32 so as to obtain better noise absorption. This is made possible by the low temperature level in the vicinity of the projection 32, and would be impossible to do with a metal silencer of the prior art. The lining 34 may be made of a cellular silicone foam, for example.
In the embodiment shown in FIG. 6, compression rings 40 are provided in the lagging 18 to compress it, thereby defining a plurality of volumes V that are matched to the frequencies that are to be countered. These rings 40 are resilient, being spaced apart regularly from one another, e.g. being made of silicone, and they bear against the outer covering 20. Thus, compressing the insulating material on one side and pressing against the outer covering 30 on the other side, they serve to define a leaktight volume V which acts as an acoustic resonant volume. Such rings 40 thus create an incompressible zone suitable for supporting the weight of the internal tubular element 16 without any risk of the insulating material suffering creep.
In the embodiment shown in FIG. 7, acoustic baffles 45 are interposed inside the internal tubular element 16 of the duct 14. A baffle 45 may be constituted by an assembly of three metal disks, two end disks comprising an upstream disk 47 and a downstream disk 49, and a middle disk 51, all three disks being disposed perpendicularly to the flow direction of the exhaust gases, and two connecting metal tubes 53 and 55 pierced by holes 52 and mounted coaxially inside the internal tubular element 16, being of smaller diameter. More precisely, the upstream end disk 47 presents a central opening 57 having the diameter of the two connection tubes 53 and 55, and openings 59 distributed around the central opening, while the downstream end disk 49 has only one central opening 57 of the diameter of the two connection tubes 53 and 55. The middle disk 51 is solid in its central portion so as to prevent direct communication between the two connection tubes 53 and 55, however it does present openings 61 in its periphery. This defines a first volume V1 inside the connection tube 53, a second volume V2 that is annular around the connection tube 53, a third volume V3 that is annular around the connection tube 55, and a fourth volume V4 inside the connection tube 55. Thus, the exhaust gas penetrates directly firstly into the first volume V1 via the central opening 57 in the upstream disk 47, and then into the second volume V2 through the holes 52 in the connection tube 53, and secondly into the volume V2 through the holes 59 in the upstream disk 47. The exhaust gas passes from the second volume V2 to the third volume V3 through the openings 61 in the middle disk 51, and then penetrates into the fourth volume V4 through the openings 52 in the connection tube 55 prior to escaping from the baffle 45 via the central opening 57 in the downstream disk 49. A plurality of baffles 45 may be interposed inside the internal tubular element 16 of the duct 14.
FIG. 8 shows an embodiment of a connection device 70 mounted at the entrance to the duct 14. In general, the exit from the catalytic converter 6 is provided by a metal tubular element 72, e.g. made of stainless steel, whose downstream end 72a is flared so as to connect to the duct 14 which is of diameter greater than that of the tubular element 72. The internal tubular element 16 is welded to the flared end 72a of the tubular element 72, while the outer covering 20 of the duct 12 is connected by means of a long and thin-walled metal cap 75 that serves to protect the outer covering 20 against high temperatures. Advantageously, external and/or internal cooling fins 77 can be provided on or in the tubular element 72 in order to cool the exhaust gas prior to entry into the duct 14 of the silencer 12, and the outer covering 20 may be corrugated. To further encourage heat exchange and to reduce the temperature of the exhaust gas penetrating into the duct 14, the tubular element 72 can be flattened, giving it an undulating or corrugated shape, as can be seen in FIG. 8a.
In general, the exhaust gas must be rejected to the atmosphere at a temperature of less than 200° C., for example, whereas on the entry to the duct 14 it may be at a temperature of about 500° C. When the cooling fins 77 of the connection device 70 at the entrance of the duct 14 (FIG. 8) are found to be insufficient, it is possible to mount a diffuser-forming exit device 80 made of metal at the outlet from the duct 14. This exit device 80, as shown in FIG. 9, may comprise at least one element 82 of generally conical shape that is pierced by holes 84, and a tubular exit element 86 which surrounds and extends the element 82. Thus, the exhaust gas leaves via the holes 84 to penetrate into the tubular exit element 86 which presents at least one opening 88 in its wall so as to allow ambient air to enter, thereby encouraging the expulsion of exhaust gases at moderate temperature.
FIG. 10 shows another embodiment of the exit device 80 of FIG. 9. This exit device 80 also has an element 82, but this time it is star-shaped, and it has an exit element 86 which surrounds and extends the element 82, having at least one opening 88 in its wall so as to allow air to enter.
In a variant embodiment of the invention as shown in FIG. 11, the outer covering 20 of the duct 14 can be made over at least a portion of the duct in the form of a leaktight box 90 having the internal metal tubular element 16 passing therethrough coated in its refractory fabric 30. The box 90 is made of two portions that are assembled together after the internal metal element 16 has been inserted, the box 90 being filled with the thermal and acoustic lagging 18. The internal metal element 16 may form at least one C-shaped bend inside the box 90 so as to increase the acoustic insulation of the duct 14.
Advantageously, and as shown in FIG. 12, the wall of the box 90 may include at least one resonant surface 92 in the form of a diaphragm, for example, having one or more resonant frequencies corresponding to certain frequencies in the frequency spectrum that is to be attenuated. Such a surface 92, on being excited, is set into vibration, thereby dissipating energy in such a manner as to contribute effectively to acoustically insulating the duct 14.
FIGS. 13 and 14 show a method of mounting a silencer 12 of the invention in an exhaust system of a motor vehicle. In general, a silencer 12 is manufactured, stored, and transported in a rectilinear shape. Then, on the site where the silencers 12 are mounted, each silencer is deformed into the geometrical configuration it is to occupy prior to being fastened to the vehicle body via its rigid fastening tabs 15. In the example shown, the silencer 12 presents at least two series of corrugations 14a and 14b, and it is via these corrugations 14a and 14b that is it possible to bend the silencer 12.
In the examples described above, the duct 14 presents a porous internal metal element 16 extending over substantially its entire length, however the duct 14 could also be made as a plurality of portions assembled together in pairs by substantially smooth tubular metal elements connected to two adjacent porous metal elements 16, where a smooth element is suitable for being bent and is optionally covered in a refractory fabric 30, in lagging 18, and in the outer covering 20.
Patent Application
20050167192
