GB2236691A

GB2236691A - A catalytic converter

Info

Publication number: GB2236691A
Application number: GB8921957A
Authority: GB
Inventors: William Richard Hutchins
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1989-09-28
Filing date: 1989-09-28
Publication date: 1991-04-17
Also published as: GB8921957D0

Abstract

The catalytic converter comprises a housing 20 for a catalyst section comprising a matrix 22 formed with passageways 23 coated with a catalyst material. An entry section 28 and an exit section 32 for exhaust gas are defined within the housing. The matrix has a face 24 defining inlets to the passageways 23 and the face is oblique to the direction of gas flow through the entry section. <IMAGE>

Description

A CATALyTIC CONVERTER The invention relates to a catalytic converter for use in an exhaust system, particularly but not exclusively for a motor vehicle.

Catalytic converters have been,in use for many years in exhaust systems of motor vehicles to reduce the release of obnoxious by-products of combustion into the atmosphere.

Fig.l of the accompanying drawings is a diagrammatic cross-section through a standard type of catalytic converter in common use on vehicles. The converter comprises a housing 1, defining an entry section 2 for exhaust gases, a catalyst section 3 and an exit section 4. The catalyst section 3 comprises two matrices 4, 5 each of which defines a plurality of longitudinally extending passages 6 coated, e.g., with platinum and which are open at end surfaces 7, 8 of the substrates to define inlets and outlets 7a, 8a respectively.

The housing 1 is provided with a flange 10 at its inlet end for attachment to an exhaust pipe (not shown) and the housing is then widened at 11 to form the entry section 2. A similar arrangement is provided at the opposite end of the housing to enable the housing to be attached by means of a flange 12 to a tail pipe or silencer of the exhaust system.

It has been found that incoming exhaust gases distribute very unevenly over the surface 7 with the Fig.l arrangement. A central core 13 of incoming gases tends to impinge directly on the end surface 7 and enter the inlets 7a near the centre of the matrix 4 efficiently. However, the expansion of the gases due to the divergence of the entry section 2 causes exhaust gases 13a surrounding the core 13 to flow in a somewhat turbulent manner. That not only results in an inefficient entry of the gases into the remaining inlets 8 but also tends to restrict the flow of the central core of gas. Therefore1 with such an arrangement, only the central part of the catalyst section tends to operate efficiently. Also, after the exhaust gas has left the first matrix 4 it tends to expand before entering the second matrix 5 and inefficient entry into the second matrix results.

Catalytic action is dependent upon the length of time which the exhaust gases spend passing through the catalyst section. As the flow is substantially of an in-line type, the gases tend to flow very quickly through the catalyst section and, therefore, it is necessary to provide long passageways to provide a catalytic action. Normally, that is achieved by arranging two matrices in tandem as shown. However that arrangement tends to create a high back pressure which is undesirable. The diameter of the catalyst section 3 can be increased but by doing that, the efficiency of distribution of exhaust gases across the end surface 7 of the matrices is no better than before and the chemical conversion efficiency of the converter is not necessarily improved. Also, the increased diameter could lead to a catalytic converter having an external diameter too large for certain vehicles.

An object of the present invention is to provide an improved catalytic converter in which the above problems are substantially reduced.

According to the present invention there is provided a catalytic converter comprising an entry section for a stream of incoming exhaust gas and a catalyst section having a surface defining inlet means through which gas from the entry section passes, the surface of the catalyst section and the direction of gas flow through the entry section being oblique relative to each other.

By arranging for the gas flow to be oblique to the surface of the catalyst section in that way, it has been found that substantially the entire incoming stream of exhaust gas will enter the catalyst section efficiently and a much more even distribution of gases across the inlet surface of the catalyst section is achieved.

Preferably, the entry section narrows from a gas entry end towards an opposite end. In that way, the incoming gas is constrained towards the catalyst as it moves through the entry section.

The entry section is preferably defined in part between the surface of the catalyst section in which the inlet means is defined and between an opposite surface. The said opposite surface may be a surface of a housing of the converter. The aforesaid two surfaces are preferably inclined relative to each other.

For efficient movement of the gas through the entry section, the inclination of the surfaces relative to each other may vary over the length of the entry section. In such a case, the inclination may be varied by forming the said opposite surface with a first surface portion inclined at one angle and with a second surface portion inclined at a second angle.

The first and second portions may be formed as flat relatively inclined surface portions.

As an alternative, the aforesaid opposite surface may be curved to provide a gradually narrowing entry sect ion.

Preferably, the entry section is, at least in part, of a rectangular cross section transverse to the direction of gas flow through the entry section.

The surface of the catalyst section defining the inlet means is preferably flat.

With an arrangement according to the invention, a very large surface defining the inlet means can be presented to the exhaust gas flowing through the entry section thereby providing efficient entry to a very large number of flow passages in the catalyst section. In that way, flow rate through the passages is reduced and the depth of the catalyst section can be kept to a minimum. A large number of accessible passages coupled with reduced length thereof results in a back pressure which is significantly less than that which occurs with the standard type of catalytic converter shown in Fig.1. Therefore, a catalytic converter in accordance with the present invention will absorb less power from the engine than the catalytic converter of the standard type.Moreover, by arranging the catalyst section in a manner in accordance with the present invention, gas can be arranged to pass therethrough in a direction transverse to the general direction of gas flow through an exhaust system of which the catalytic converter forms a part. Therefore, the width of the catalytic converter can be kept to a minimum which is highly advantageous where installation space is at a premium.

The catalytic converter preferably includes an exit section which receives gas from outlet means defined by a further surface of the catalyst section. The gas flow through the exit section is preferably oblique to the further surface and the exit section may widen towards an exit end thereof.

The exit section may be formed in a similar manner to the entry section and may, therefore, be defined in part between said further surface of the catalyst section in which the outlet means is defined and between an opposite surface. The opposite surface may be a surface of a housing of the catalytic converter. Preferably, the two surfaces are inclined relative to each other.

The inclination of the latter surfaces relative to each other may vary over the length of the exit section. In such a case, the inclination may be varied by forming the said opposite surface with a first surface portion inclined at one angle and a second surface portion inclined at a second angle.

The first and second surface portions may be formed as a flat relatively inclined surface portions.

Alternatively the said opposite surface may be curved to define a gradually narrowing entry section.

Preferably, the exit section is, at least in part, of rectangular cross section transverse to the direction of gas flow therethrough.

The opposite surface of the exit section may be arranged to constrain gas leaving the outlet means towards the exit end of the exit section.

The catalytic converter may be of a kind which has substantially in-line gas entry and gas exit ends.

In that way, a gas entry end for the entry section and a gas exit end for the exit section may be arranged such that gas will flow substantially'in the same direction therethrough. The gas entry end and ,gas exit end may be offset relative to each other in a transverse sense. Such an arrangement may be useful where a projection on the vehicle e.g., a gear selector linkage needs to be accommodated alongside either the inlet or the outlet of the catalytic converter. In such a case, the projection may lie in a space provided by the offset.

In an alternative arrangement, the gas entry end for the entry section and the gas exit end for the exit section may be arranged such that they lie generally side by side so that gas flows in opposite directions therethrough.

In yet another arrangement, the gas entry end for the entry section and the gas exit end for the exit section may be arranged such that the gas flow through the gas entry end is transverse to the gas flow through the gas exit end.

The surface of the catalyst section in which the inlet means is defined may comprise an end surface of a matrix or substrate defining a multiplicity of passages for gas, the passages having open ends defining the gas inlets.

Similarly, the further surface defining the outlet means of the catalyst section preferably comprises an end surface of a matrix or substrate defining a multiplicity of passages for gas, the passages having open ends defining the gas outlets.

The passages may be coated with platinum or other suitable catalyst.

A catalytic converter in accordance with the invention will now be described by way of example with reference to the remaining accompanying drawings in which: Fig.2 is a diagrammatic perspective view of a catalytic converter in accordance with the invention shown partly broken away, Fig.3 is a horizontal cross section through the catalytic converter shown in Fig.2, Fig.3A is a view of part of a catalytic converter in accordance with the invention with a different shaped entry section wall, Fig.4 is an enlarged view of part of the catalyst section of Fig.3 and showing gas flow in detail, Fig.5 is a graph showing back pressure comparisons, Figs.6 and 7 show a catalytic converter in accordance with the invention with alternative gas entry and exit configurations, and Fig.8 shows another embodiment of catalytic converter in accordance with the invention.

With reference to Figs.2 and 3, a catalytic converter comprises a housing 20 which contains a catalyst section comprising a matrix or a substrate 22 (herein called a "matrix") actively coated with a catalyst such as platinum. The matrix is in the form of a rectangular block formed with a multiplicity of passageways 23 extending between inlet and outlet surfaces 24, 25. The passageways 23 form inlets 26 at surface 24 and outlets 27 at surface 25. In Fig.3 only four of the passageways are shown.

An entry section 28 is defined between an outer wall 29 of the housing, upper and lower walls 30 and the inlet surface 24. The entry section 28 is of rectangular cross section transverse to the direction of gas flow therethrough.

An exit section 32 is defined between an outer wall 33 of the housing, upper and lower walls 34 and the outlet surface 25. The outlet section 32 is also rectangular in cross section in the direction transverse to the direction of gas flow therethrough.

The entry section 28 has an entry end 35 which changes from rectangular to circular cross section and is formed with a flange 36 for attachment to an exhaust pipe of diameter X. The exit section 32 similarly has an exit end 37 which changes from rectangular to circular cross section and is formed with a flange 38 for attachment to an exhaust pipe.

As apparent from Figs.2 and 3, the entry section 28 is somewhat wedge shaped and gradually narrows in the direction away from its entry end. The exit section is similarly formed and gradually widens towards its outlet end.

Exhaust gas (indicated by lines 40) passes through the entry end 35 and into entry section 28. The surface of the matrix 22 is inclined relative to the exhaust gas so that the direction of flow of the latter is oblique to the inlet surface 24 of the matrix. It has been found that the gas flow can be constrained to flow in such a manner very effectively by forming the outer wall 29 from a first flat section 29a and a second flat section 29b inclined relative to the section 29a as shown in broken lines.

Alternatively, the wall 29 could be curved as shown at 29c in Fig.3A By providing an oblique angle A (e.g. around 100) between the surface 24 and incoming gas 40, the gas will flow substantially as series of notional substantially parallel gas streams as shown in Figs.3 and 4. If, say, the matrix 22 has a line of 200 one millimetre square inlets one behind the other longitudinally of the entry section and the entry section has a width Z at its inlet end of 20mm, then a notional "slice" of gas measuring 20mm by Imm will provide 200 parallel gas streams 40a - 40i etc. as shown diagrammatically in Fig.4 each measuring Imm by 0.1mum and each of which enters one inlet 26 in the matrix 22. Each gas stream is slowed down slightly as it is constrained to enter the relevant inlet.

Therefore, there is an accompanying increase in pressure which assists flow of the streams through the passageways 23. This particular method of directing gas to the catalyst section provides an extremely efficient distribution of gas over the whole inlet surface 24 of the matrix avoiding turbulence and the uneven gas distribution present in the standard type of catalytic converter shown in Fig.1. Once the gases have entered passageways 23 in the matrix, the streams pass over the catalyst coating C on the matrix surface and leave the matrix 22 through the outlets 27. The outer wall 33 then constrains the streams of exhaust gas to flow in a direction oblique to the surface 25 towards the exit end 37 of the exit section.The outer wall 33 may alternatively be constructed in a similar manner to outer wall 29 with a first flat section 3a and a second flat section 33b inclined to the first section 33a. Alternatively the wall 33 could be curved in a similar manner to wall 29c in Fig.3A.

The present invention permits the use of a matrix having very large inlet surface 24 thereby presenting an extremely large number of inlets 26 to the incoming gas stream, the inlets having a total area very much greater that the cross sectional area of the entry section 28. Therefore, gas flow through the individual passageways 23 can be achieved which is substantially slower than the gas flow through the in-line matrix arrangement shown in Fig.1. As the catalytic action is dependent upon the speed through which the gases flow through the catalyst passageways, the length of the passageways in the present invention can be substantially reduced.With the increased number of passageways and the reduction in passageway length, the back pressure upstream of the catalytic converter will be substantially less than with the Fig.l system. This is highly advantageous as the catalytic converter of the invention will absorb far lessenergy from the engine than the conventional type. That characteristic is illustrated in the graph shown in Fig.5.

In Fig.5, plots of exhaust back pressure P against engine speed are shown.

Graph A shows back pressure against engine speed where no catalytic converter is provided in the exhaust system, Graph B illustrates the back pressure where a standard catalytic converter is used of the kind shown in Fig.1 and Graph C shows back pressure against engine speed when using a catalytic converter in accordance with the invention.

It is most noticeable that up to engine speed S1, the exhaust pressure is substantially the same for cases A and C whereas with a standard catalytic converter, the exhaust back pressure is substantially higher.

As engine speed increases further, Graph C begins to show an increase in back pressure but the increase is still substantially less than that produced when using the standard catalytic converter. During normal driving conditions, it is envisaged that engine speed will mostly be less than S1 and so the catalytic converter in accordance with the invention will produce a back pressure which is little different from that in an exhaust system where no catalytic converter is present.

It will be noted from Figs.2 and 3 that the entry section 28 and exit section 32 are horizontally offset which can be useful where the catalytic converter needs to be located close to a projection such as a gear linkage cover 50. As shown in Fig.3, the cover 50 can conveniently lie adjacent one end of the first section 22 of the housing to one side of the entry section.

Alternatively, the entry and exit sections 28, 32 can be arranged as in Fig.6 so that the exhaust gases flow in opposite directions thereto.

If desired, the flow through the entry and exhaust systems can be transverse to each other as shown in Fig.7.

In Figs.2 to 4, the surface 24 is inclined to the incoming gas. However, if desired, the arrangement could be modified as in Fig.8 so that the incoming gas 40 is deflected by the inclined wall 29 so as to follow a path oblique to surface 24. Such an arrangement again ensures that the notional gas streams enter the inlets 26 evenly over the entire surface 24. The wall 29 could be formed with two relatively inclined sections 29a, 29b or could be curved as in Fig.3A. The wall 33 of the exit section 32 could be similarly formed.

The rate at which the entry and exit section narrow in any of the embodiments of the invention can be varied depending upon the flow characteristic required.

For an exhaust pipe of diameter X, it is envisaged that the depth D of the matrix 22 may be around 2X.

For a width Z of the rectangular entry section 28, it is envisaged that the length Y of the matrix may be between 3Z and 10Z. Typically, however, Y may be around 4Z. Where it is possible to make Y substantially greater than Z, it may be possible to reduce the depth of the matrix to substantially less than 2X thereby reducing back pressure even further.

However, whilst in theory it may be possible to make 2X very small, there are practical limitations which would make it difficult to reduce the thickness of the matrix beyond a certain limit without jeopardising its structural strength.

Claims

1. A catalytic converter comprising an entry section for a stream of incoming exhaust gas and a catalyst section having a surface defining inlet f means through which gas from the entry section passes, the surface of the catalyst section and the direction of gas flow through the entry section being oblique relative to each other.

2. A catalytic converter according to Claim 1 in which the entry section narrows from a gas entry end towards an opposite end.

3. A catalytic converter according to Claim 1 or 2 in which the entry section is defined in part between the surface of the catalyst section in which the inlet means is defined and between an opposite surface, said two surfaces being inclined relative to each other.

4. A catalytic converter according to any preceding Claim in which the opposite surface is arranged to constrain gas flowing through said entry section whereby the gas moves into the inlet means.

5. A catalytic converter according to Claim 3 or 4 in which the inclination varies over the length of the entry section.

6. A catalytic converter according to Claim 3, 4 or 5 in which the angle of inclination is varied by forming said opposite surface with first and second surface portions inclined relative to each other.

7. A catalytic converter according to any of Claims 3 to 6 in which said opposite surface is substantially flat.

8. A catalytic converter according to any preceding claim in which the entry section is, at least in part, of rectangular cross section transverse to the direction of gas flow therethrough.

9. A catalytic converter according to any preceding Claim in which the catalyst section is arranged such that gas passes therethrough in a direction transverse to the general direction of gas flow through an exhaust system of which the catalytic converter forms a part.

10. A catalytic converter according to any preceding Claim in which the length of said surface of the catalyst section in the direction in which gas flows through the entry section is substantially greater than its depth in the direction in which gas flows through the catalyst section.

11. A catalytic converter,according to any preceding Claim including an exit section which receives gas from outlet means defined by a further surface of the catalyst section.

12. A catalytic converter according to Claim 11, in which the gas flow through the exit section oblique to said further surface.

13. A catalytic converter according to Claim 12 in which the exit section widens towards an exit end.

14. A catalytic converter according to Claim 11, 12 or 13 in which the exit section is defined in part between said further surface of the catalyst section in which the outlet means is defined and between an opposite surface, said two surfaces being inclined relative to each other.

15. A catalytic converter according to Claim 14 in which the angle of inclination varies over the length of the exit section.

16. A catalytic converter according to Claim 15 in which the angle of inclination is varied by forming said opposite surface with first and second surface portions inclined relative to each other.

17. A catalytic converter according to Claim 15 or 16 in which the opposite surface portion is substantially flat.

18. A catalytic converter according to any of Claims 11 to 17 in which the exit section is at least in part of rectangular cross-section transverse to the direction of gas flow therethrough.

19. A catalytic converter according to any of Claims 11 to 18 in which the opposite surface of the exit section is arranged to deflect gas leaving the outlet means towards an exit end.

20. A catalytic converter according to any of Claims 11 to 19 in which the entry section and exit section are arranged such that gas flows in substantially the same direction therethrough.

21. A catalytic converter according to any of Claims 11 to 19 in which the entry section and the exit section are arranged such that gas flows in substantially opposite directions therethrough.

22. A catalytic converter according to any of Claims 11 to 19 in which a gas entry end for the entry section and a gas exit end for the exit section are arranged such that the direction of gas flow through one end is transverse to the direction of gas flow through the other end.

23. A catalytic converter according to any preceding Claim in which the surface of the catalyst section in which inlet means is defined comprises an end surface of a matrix or substrate defining a multiplicity of passages for gas, the passages having open ends forming gas inlets.

24. A catalytic converter according to Claim 23 in which the total cr6ss-sectional area of the inlets is greater than the cross sectional area of an entry for gas into the entry section.

25. A catalytic converter according to any preceding Claim and where the catalyst section has a further surface defining outlet means, in which the further surface comprises an end surface of a matrix or substrate defining a multiplicity of passages for gas, the passages having open ends forming gas outlets.

26. A catalytic converter constructed and arranged substantially as described herein with reference to Figs.2 and 3, Fig.v3A, Fig.4, Fig.5, Fig.6, Fig.7 or Fig.8 of the accompanying drawings.