EP1192339A2

EP1192339A2 - Device for catalytic treatment of a motor vehicle engine exhaust gases

Info

Publication number: EP1192339A2
Application number: EP00946021A
Authority: EP
Inventors: Said Boutrif; Frédéric NOVEL-CATTIN; André Walder; Brigitte Martin
Original assignee: Office National dEtudes et de Recherches Aerospatiales ONERA; IFP Energies Nouvelles IFPEN; Imphy Ugine Precision SA; Renault SAS; Gervois SA; Arvin Exhaust SA
Current assignee: Renault SAS; Gervois SA; Arvin Exhaust SA; Aperam Stainless Precision SAS
Priority date: 1999-06-29
Filing date: 2000-06-27
Publication date: 2002-04-03
Also published as: JP2003503621A; FR2795768B1; WO2001000970A3; WO2001000970A2; AU5992300A; FR2795768A1

Abstract

The invention concerns a device (10) for catalytic treatment of a motor vehicle exhaust gases (G), comprising an upstream tube (12) for exhaust gas (G) intake and a downstream tube (14) for exhaust gas (G) evacuation between which is interposed a longitudinal gas (G) treating chamber comprising catalytic treatment means based on metal fibres (24) traversed by the gases (G). The invention is characterised in that the catalytic treatment means is a block (18) of metal fibres (24) impregnated with a catalytic compound arranged inside the treatment chamber (16) and comprising at least an upstream conical or tapering intake cavity (26), directly fed by the gas (G) intake tube (12) which emerges opposite the cavity (26) base and whereof the concave housing (34) forms the entry surface of the gases (G) to be treated in the fibre block.

Description

"Device for catalytic treatment of exhaust gases from a motor vehicle engine"

The invention relates to a device for catalytic treatment of exhaust gases from a motor vehicle engine.

The invention relates more particularly to a device for catalytic treatment of the exhaust gases of a motor vehicle engine, of the type which comprises an upstream tube for the arrival of exhaust gases and a downstream tube for discharging the exhaust gases. exhaust between which is interposed a substantially longitudinal gas treatment chamber which comprises a catalytic treatment means based on metallic fibers crossed by the gases.

Many examples of gas treatment devices are known which allow the reduction of polluting emissions by catalytic treatment of the gases.

These exhaust gas treatment devices are commonly used in all types of automobiles to comply with the existing pollution control standards. Conventionally, these are devices in which the gas treatment means are formed by a block of a material having catalytic properties, more commonly known under the name of "monolith".

The exhaust gases are conveyed in the gas treatment chamber via the inlet tube, pass through the monolith and are discharged out of the gas treatment chamber by the discharge tube.

Monoliths of a first type are known which are produced in the form of blocks of alveolate ceramic substrate called "honeycomb", containing several thousand cells in the form of fine channels. The ceramic substrate is made from a paste containing silicon, aluminum, and magnesium, in particular a ceramic compound such as a magnesium aluminosilicate, also called "cordierite", which is matrix then dried and annealed. The ceramic walls are impregnated with a layer of aluminum oxide, or "washcoat", strongly cracked, which multiplies the surfaces of exchange with the exhaust gases, and which is covered with the catalytic material which allows the conversion of pollutants.

These monoliths have the disadvantage of opposing a significant back pressure to the flow of exhaust gases.

Furthermore, their calorific capacity is significant, so that they are generally long in reaching an operating temperature capable of causing efficient catalysis of the exhaust gases.

Finally, they are vulnerable to high temperatures and gas pulsations, either because of their sensitivity to thermal shock, or because of their relatively low melting point, of the order of 1350 ° C against 1450 ° C for ferritic stainless steels (Fe-Cr-AI). As such, they must be kept in the gas treatment enclosure by a heat-expandable mattress, generally made from ceramic fibers or steel wool.

To remedy these drawbacks, monoliths of a second type have been proposed, which comprise a honeycombed "honeycomb" metal frame which replaces the ceramic substrate described above.

These monoliths are lighter, more resistant to thermal and mechanical shock, and quicker to reach the catalysis temperature, but they are more expensive.

To remedy this drawback, it has been proposed to produce monoliths of the type described above, it is to say monoliths which are made from metal fibers which have the advantage, compared to honeycomb honeycomb substrates, of causing a turbulent flow of exhaust gases in the gas treatment enclosure, which has as a consequence of increasing the mixing of gases and the conversion of pollutants.

However, it has been found that the fibers made from metal wires make it possible to obtain a gas treatment block which, whatever allowing a turbulent flow of the exhaust gases to be obtained inside the treatment chamber gas favorable to the conversion of pollutants, has the disadvantage of opposing a high back pressure to the flow of exhaust gases, which affects the proper functioning of the vehicle engine. To overcome this drawback, the invention proposes to use an arrangement of fibers which only slightly disturbs the flow of exhaust gases insofar as its geometry allows the gases to pass entirely through the block of fibers, which makes it possible to use only a small volume of fibers for treating the exhaust gases and, therefore, not to oppose significant back pressure to the flow of the exhaust gases.

To this end, the invention provides a device for treating the exhaust gases of a motor vehicle engine, of the type described above, characterized in that the catalytic treatment means is a block of metallic fibers impregnated with a compound catalytic which is arranged inside the treatment enclosure and which comprises at least one upstream inlet cavity of conical or frustoconical shape, supplied directly by the gas inlet tube which opens facing the base of the cavity, and of which the concave envelope constitutes the inlet surface of the gases to be treated in the block of fibers.

According to other characteristics of the invention:

the block of fibers is received transversely with clearance in the longitudinal treatment enclosure so that the peripheral surface of the block constitutes a first outlet surface for the gases treated by the block,

a transverse upstream end face of the block of fibers is attached to an upstream annular flank of entry of the enclosure,

a transverse downstream end face of the block constitutes a second outlet surface for the gases treated by the block,

a transverse downstream end face of the block is closed and impermeable to the gases treated by the block, in order to diffuse the gases only towards the peripheral wall of the treatment enclosure,

- the conical cavity extends axially only over part of the length of the block of fibers, - the conical cavity extends axially over the entire length of the block of fibers,

the treatment enclosure is substantially cylindrical and coaxial with the gas inlet and outlet tubes, and the fiber block is cylindrical and mounted coaxially inside the treatment enclosure, the axial length of the fibers being less than that of the enclosure,

- the cylindrical block of fibers is mounted coaxially in the treatment enclosure by means of a complementary cylindrical holding box which is fixed inside the treatment enclosure by an upstream edge and by at least three tabs centering radials interposed between the outer wall of the housing and the inner wall of the enclosure, - the peripheral wall of the holding box is pierced to allow the passage of the gases treated by the block,

the holding box comprises a downstream transverse grid adjacent to the transverse downstream end face of the block constituting the second outlet surface for the treated gases,

- The enclosure is of a frustoconical shape u u downstream to form a convergent which opens into the exhaust gas discharge tube and promote the flow of treated gases. Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

- Figure 1 is a view in axial longitudinal section of a block of fibers according to a first embodiment of a treatment device according to the invention;

- Figure 2 is a view in axial longitudinal section of a first embodiment of the processing device according to the invention; - Figure 3 a cross section through the plane 3-3 of Figure 2 of the first embodiment of the treatment device according to the invention;

- Figure 4 is a view in axial longitudinal section of a block of fibers according to a second embodiment of a treatment device according to the invention;

- Figure 5 is a view in axial longitudinal section of a second embodiment of the processing device according to the invention; and

- Figure 6 is a cross section through the plane 6-6 of Figure 5 of the second embodiment of the processing device according to the invention. In the following description, identical reference numerals designate identical parts or having similar functions.

FIGS. 2 and 5 show the assembly of a device 10 for catalytic treatment of the exhaust gases G of a motor vehicle engine produced in accordance with the invention. Figure 2 illustrates a first embodiment of the invention and Figure 5 illustrates a second embodiment of the invention. In known manner, the device 10 comprises an upstream tube 12 for the arrival of the exhaust gases G and a downstream tube 14 for discharging the exhaust gases G between which is interposed an enclosure 16 for treating gases comprising a means 18 for catalytic treatment of the gases G. In known manner, the means 18 for catalytic treatment of the fibers is a block 18 of metallic fibers which is arranged inside the treatment enclosure 16 and which is interposed between an orifice 20 opening out inside the enclosure 16 belonging to the gas inlet tube 12 G and a similar opening 22 belonging to the gas discharge tube 14 G.

The block of fibers 18 corresponding to the first embodiment illustrated by FIG. 2 is represented in FIG. 1 while the block of fibers 18 corresponding to the second embodiment illustrated by FIG. 5 is represented in FIG. 4.

As can be seen in these FIGS. 1 and 4, the block 18 is, in known manner, preferably made up of metallic fibers 24 which are obtained for example by a direct casting foundry process, also known by the name of the "Melt overflow process"". However, another method can also be used. The fibers 24 are made from an alloy based on iron, chromium and aluminum, the proportion of aluminum being, by weight, greater than or equal to 5%, and low concentrations of Yttrium, of rare earths, or mixtures of rare earths also called "Mischmetall". These fibers 24 are collected in a mold corresponding to the block 18, then welded by an electric discharge. Finally, the fibers 24 can be covered with a porous binder or "washcoat" which forms large attachment surfaces on the surface of the fibers 24 and which is then impregnated with a catalytic compound intended to ensure the treatment of G gases.

This arrangement is of course not restrictive of the invention, and any means of obtaining the fibers 24 and, more generally, of the block 18 of metallic fibers, can be used for the implementation of the present invention.

In the preferred embodiment of the invention, and without limitation of the invention, the enclosure 16 for treating the exhaust gases G has a substantially cylindrical shape and the block 1 8 of metallic fibers also has a cylindrical shape with a diameter less than that of the treatment enclosure 16 so as to be received there coaxially with play in the radial direction.

According to the invention, and as shown in Figures 1, 2, 4, and 5, the block 1 8 of metal fibers comprises at least one cavity 26 for admission of the exhaust gas G.

As can be seen in FIGS. 1 and 4, this cavity 26 is preferably of conical shape but can also, without limitation of the invention and as a variant (not shown), be of frustoconical shape. The base of the conical shape of the cavity 26 faces the upstream inlet tube 12 and the top of the conical shape of the cavity 26 faces the downstream tube 14 for evacuating the exhaust gases. The cavity 26 extends axially inside the cylindrical block 18 of metallic fibers 24. As illustrated more precisely in FIGS. 2 and 5, this cavity 26 is intended to be supplied directly by the inlet tube 12 of the gases G, the orifice 20 of which opens into an annular blank 28 upstream of the inlet of the enclosure 16, also opens opposite a base 30 of the cone or truncated cone of the cavity 26.

To this end, a transverse face 32 of upstream end of the block 18 of fibers is attached to the annular blank 28 upstream of the inlet of the enclosure 16.

In this way, the block 1 8 of fibers comes to "close" the orifice 20 of the inlet tube 12 and a concave surface 34 of the cavity 26 of the block 18 of metallic fibers constitutes the inlet surface of the gases G to be treated in the fiber block. The gases G to be treated therefore penetrate into the cavity 26, pass through the fibers 24 of the block 18 and leave the block 18 through at least one peripheral surface 36 of said block 18.

Furthermore, the cylindrical block 1 8 of fibers is mounted coaxially in the treatment enclosure 16 by means of a support housing 38, a complementary riq ue, which is fixed inside the enclosure 16 by an upstream edge 40 of the holding housing 38 and by at least three radial tabs 42 for centering which are interposed between the external wall of the housing 38 and an internal cylindrical wall 44 of the enclosure 16.

The holding box 38 is hollow, with an inside diameter substantially equal to the outside diameter of the block of fibers 1 8, so that the block of fibers 1 8 is perfectly held inside the holding box 38. A peripheral surface 50 of the holding housing 38, which is pierced, constitutes a first outlet surface for the treated gases G. Figures 2 and 5 show this peripheral surface 50 shaped as a grid, but it may alternatively be an initially full surface, which when made, is pierced with multiple holes.

In the first embodiment of the invention shown with reference to FIGS. 1 to 3, the conical cavity 26 extends axially only over part of the length of the block 18 of fibers and the housing 38 for cylindrical holding comprises a face transverse downstream end 46 which is adjacent to a transverse downstream end face 48 of the block 18 and which is shaped as a grid so as to form a second outlet surface for the treated gases G. This arrangement is not limitative of the invention and any means of constituting a second outlet surface for the treated gases G, in particular a wall pierced with multiple holes, can be used. In this way, the exhaust gases G pass through the block

18 of fibers and escape therefrom on the one hand by the peripheral wall 50 of the holding box 38 forming the first gas outlet surface G, and on the other hand by the grid of the transverse face 46 of downstream end of the holding box 38 forming the second gas outlet surface.

In addition, the holding box 38 is of a lower length than that of the treatment enclosure 16 so as to constitute, beyond the transverse face 46 of downstream end of the holding box 38 and upstream of the tube gas evacuation 14, an expansion chamber 52 which allows satisfactory soundproofing of the gas treatment device 1 0.

Advantageously, the soundproofing of the treatment enclosure 16 is further improved by the fact that the diameter of this treatment enclosure 16 is greater than that of the holding housing 38. The exhaust gases G are in fact emitted according to a determined pulsation which depends on the operating speed of the engine, and they escape through the wall. perforated peripheral 50 of the holding box 38. The inner peripheral wall 44 of the enclosure 16 causes multiple reflections to the wave trains associated with the gases G, and these reflections interfere with each other, which contributes to further improving the soundproofing of the treatment enclosure 16.

Furthermore, to promote the flow of the treated gases G, the enclosure 16 is of a frustoconical shape on the downstream side so as to form a convergent 54, the smallest diameter of which coincides with the orifice 22 of the discharge tube. 14 of the gases G treated.

Advantageously, the enclosure 16 can be designed so that the gas expansion chamber 52 is arranged axially at the level of the convergent 54, which then makes it possible to have a particularly compact treatment enclosure 16.

Figures 4 to 6 illustrate a second embodiment of the invention in which the conical cavity 26 extends axially over the entire length of the block 18 of fibers.

In this configuration, the block 18 of fibers is arranged in the holding box 38 in a manner substantially similar to the first embodiment described with reference to Figures 1 to 3, except that the transverse face 46 of downstream end of the housing 38 is a solid face which is impermeable to exhaust gases G.

In this way, the exhaust gases G q ui penetrate into the conical cavity 26 of the block 18 of fibers all escape therefrom through the pierced peripheral side wall 50 of the holding housing 38 by diffusing towards the inner peripheral wall 44 of the processing enclosure 16.

We then fully benefit from the interference effect caused by the multiple reflections of the waves, which contributes adequate soundproofing of the treatment device 16, while saving on a grid on the transverse face 46 of downstream end, which contributes to reducing the production costs of such a treatment device 1 0. In a similar manner to the first embodiment of the invention, the exhaust gases G are then conveyed, due to the pressure prevailing inside the treatment enclosure 16, towards the expansion chamber 52 gases, then they are evacuated from the enclosure 16 by means of the gas evacuation tube 14.

These two embodiments are not restrictive of the invention, and it is understood that any shape of the section of the treatment enclosure 16 and / or of the section of the holding box 38, or even of the block 1 8 of fibers may be accepted, provided that the block 18 is received with clearance in the treatment enclosure 16 and that it comprises a conical or frustoconical cavity 26.

In particular, it would also be possible to envisage at least a third embodiment, not shown, in which the frustoconical cavity 26 extends axially over the entire length of the block of fibers 18 and in which the transverse face 46 of downstream end is g-shaped, and a fourth embodiment, not shown, in which the conical cavity 26 extends axially only over part of the length of the block of fibers 18 and in which the transverse face 46 of the downstream end of the holding case 38 is impermeable to exhaust gases G.

Thus, the device 10 comprises an arrangement of a block 18 of metallic fibers which is traversed in its entirety by the exhaust gases G coming from the engine of the vehicle, so that there is no need to have a block 18 of fibers of a large volume to achieve so effective catalytic treatment of said gases G, which allows, compared to a conventional treatment device, to significantly reduce the size, weight and manufacturing cost of such a treatment device 10. Finally, such an arrangement of the block 1 8 of fibers within the treatment enclosure 16 particularly favors the flow of the exhaust gases G insofar as their path is carried out generally globally along the axial direction, and it therefore opposes only a low back pressure at the exhaust, which represents a definite advantage compared to conventional treatment devices which require the use of arrangements which may, in order to cause multiple turbulences for favor the treatment of gases, disturb the flow of G gases and set up a considerable back pressure on the exhaust.

Claims

RESELL ICATIONS

1. Device (1 0) for catalytic treatment of the exhaust gases (G) of a motor vehicle engine, of the type which comprises an upstream inlet gas tube (G) and a downstream tube (G) 14) for evacuating the exhaust gases (G) between which is interposed a substantially longitudinal enclosure (16) for treating gases (G) which comprises a catalytic treatment means based on metallic fibers (24) traversed by the gases (G), characterized in that the catalytic treatment means is a block (18) of metal fibers (24) impregnated with a catalytic compound which is arranged inside the treatment enclosure (16) and which comprises at least one inlet cavity (26) of conical or frustoconical shape, fed directly by the gas inlet tube (12) (G) which opens out opposite the base of the cavity (26), and the concave envelope (34) of which constitutes the gas inlet surface (G) to be treated in the block of fibers.

2. Device (10) for treatment according to the preceding claim, characterized in that the block (1 8) of fibers is received transversely with clearance in the longitudinal inal enclosure (16) of treatment so that the peripheral surface (36) of the block constitutes a first outlet surface for the gases (G) treated by the block (18).

3. Treatment device (10) according to one of claims 1 or 2, characterized in that a transverse face (32) of upstream end of the block of fibers is attached to an annular flank (28) upstream of entry of the enclosure (16).

4. Device (10) for treatment according to one of claims 2 or 3, characterized in that a face transverse (48) downstream end of the block (18) constitutes a second outlet surface of the gases (G) treated by the block (1 8).

5. Device (10) for treatment according to one of claims 2 or 3, characterized in that a transverse face (48) of downstream end of the block is closed and impermeable to the gases treated by the block, for diffusing the gases (G) only towards the peripheral wall (44) of the treatment enclosure (16).

6. Device (10) according to one of the preceding claims, characterized in that the cavity

(26) conical extends axially only over part of the length of the block (1 8) of fibers.

7. Device (10) according to any one of claims 1 to 5, characterized in that the conical cavity (26) extends axially over the entire length of the block (18) of fibers.

8. Device (10) according to any one of the preceding claims, characterized in that the treatment enclosure (16) is substantially cylindrical and coaxial with the tubes (12) of inlet and (14) of gas discharge ( G), and in that the block (18) of fibers is cylindrical and mounted coaxially inside the treatment enclosure (16), the axial length of the block (18) of fibers being less than that of the enclosure (16).

9. Device (1 0) for treatment according to the preceding claim, characterized in that the block (18) of cylindrical fibers is mounted coaxially in the enclosure (16) for treatment by means of a housing (38) of additional cylindrical support which is fixed inside the treatment enclosure (16) by an upstream edge (40) and by at least three radial centering tabs (42) interposed between the outer wall (50) of the housing (38 ) and the inner wall (44) of the enclosure (16).

10. Device (10) according to claim 9, characterized in that the peripheral wall (50) of the holding box is pierced to allow the passage of gases (G) treated by the block (18).

1 1. Device (10) according to one of the claims 9 or

1 0 taken in combination with claim 4, characterized in that the housing (38) for holding comprises a downstream transverse grid adjacent to the transverse face (48) of the downstream end of the block (18) constituting the second outlet surface gases (G) treated.

12. Device (10) according to any one of claims 8 to 1 1, characterized in that the enclosure (16) is of a frustoconical shape on the downstream side to form a convergent which opens into the tube (14) d 'evacuation of exhaust gases (G) and promote the flow of treated gases (G).