BACKGROUND TO THE INVENTION : Silencers are used to attenuate the noise from a petrol, gas or other internal combustion engine and also to treat the exhaust gases so as to reduce or remove noxious components therefrom. For convenience, the term silencer will be used herein to denote in general generally tubular members through which the exhaust gases from an internal combustion engine are passed prior to discharge into the atmosphere. Typically a silencer comprises a generally tubular housing member within which are located one or more treatment elements to treat the gas stream as it flows through the tubular member, for example one or more filters to remove particulate material from the gas stream, one or more catalysts for oxidising or reducing noxious gases, and sound attenuating elements. The flow of gas into, through and out of the housing is directed by transverse terminal end walls or caps. The gas stream may flow axially through the housing and the treatment elements from an axial or radial inlet at one end of the housing to an axial or radial outlet at the other end of the housing and the inlet and outlet are typically located in the end caps. Alternatively, the treatment elements are nested upon one another to provide two radially separated treatment paths within a single housing. In this case the

inlet and outlet are located at or adjacent one end of the housing, for example both in the transverse wall of the end cap, and the cap at the other end serves to direct and reverse the direction of the flow of gas between the radially inner series of treatment elements and the radially outward series of annular treatment elements. If desired, this end cap may be provided with one or more inlets for urea or other reagents to treat components of the gas stream. Thus, the end caps can be simple transverse end members having an axially directed inlet located in one end cap and an axially directed outlet located in the other end cap, or the inlet and outlet can be radially off set from one another, both in the one end cap and the other end cap can be a simple sheet metal wall or can have an inlet therethrough as well. For convenience, the term end cap as used herein will be used to denote in general any form of transverse end wall to an axially extending tubular housing member of a silencer.

A silencer is typically fabricated by forming a tubular body member from steel, stainless steel or other suitable material. The required treatment elements are inserted into the tubular body member in the desired axial and radial configuration during or after forming the body member and the structure closed by securing the end caps at each end of the tubular body member.

The end caps can be welded to the terminal annular lip of the body member. However, this requires that the peripheries of the body member and the end caps accurately register with one another to provide virtually continuous

contact between the opposing lips of the body member and the end caps so that a gas tight seal can be readily achieved when the welded joint between them is formed.

This may not prove economically feasible to achieve on large scale automated production techniques. Furthermore, welding introduces heat stresses and localised failures of surface layers, for example the zinc or other protective layer, and into the metal being welded, which can lead to localised corrosion or cracking of the welded joint during use.

In the fabrication of metal cans and other containers it has been proposed to form the opposing peripheries of a cylindrical body member and an end cap with axially and/or radially extending portions which provide overlapping portions of the wall material of the body and end cap at the proposed joint between the end cap and the body member. These overlapping portions are then folded over upon one another to form a mechanical key between the body member and the end cap. By forming the key around the entire periphery of the body member, a strong mechanical joint between the end cap and the body member can be achieved. If the overlapping portions are folded over at least once, a gas tight seal can also be achieved at the mechanical joint. Such a technique is known as crimping.

In forming a crimped joint, the folding over of the overlapping portions is achieved by a rolling action in which a suitably contoured roller is used to impart the folding force progressively to a static or rotating assembly. However, such a technique is not easily

applicable to containers that do not have a circular or near circular cross-section, since the rolling action cannot accommodate sharp changes in direction.

We have now devised a method for fabricating a crimped joint for securing the end caps to the tubular body member of a silencer for an internal combustion engine which reduces the above problems and provides a simple and rapid operation for forming the crimped joint using simple and low capital cost equipment.

SUMMARY OF THE INVENTION: Accordingly, the present invention provides a method for forming a crimped joint between opposing overlapping portions of a tubular body member and an end cap to be secured thereto, which method comprises applying folding forces to the overlapping portions so as to form the crimped joint, characterised in that the folding forces are applied by a plurality of formers located circumferentially around the terminal portion of the tubular body member and urged without significant rolling action against the overlapping portions.

The invention is of especial relevance for the construction of silencers for internal combustion engines.

Accordingly, the present invention also provides a method for forming a crimped joint between opposing overlapping portions of a tubular body member of a silencer and end caps to be secured thereto, which method comprises

applying folding forces to the overlapping portions so as to form the crimped joint, characterised in that the folding forces are applied by a plurality of formers located circumferentially around the terminal portion of the tubular body member and urged without significant rolling action against the overlapping portions.

In the method of the invention, the formers act substantially linearly and substantially normally to the plane of the material to be folded with substantially no relative rotation between the material of the overlapping portions and the formers. By operating in this manner, the individual formers can follow paths of action which do not have to be directed radially towards the axis of rotation of the tubular body member as with rotational forming of the crimped joint. Furthermore, the shaped faces of the formers pressing against the overlapping portions (the press faces) do not have to present the same or a uniform configuration to the overlapping portions. Thus, formers having a plurality of differently shaped press faces, which need not follow the curve of an arc of a circle, can be used to form a crimped joint which has a complex radial configuration incorporating sharp angles, which is not possible with a rotational technique.

Furthermore, the use of a plurality of individual formers may accommodate local errors in the size and shape or registration of the opposed peripheries of the tubular member and the end caps. The method of the invention thus permits a crimped joint to be formed for silencers having cross sections which could not be handled by the

conventional roller crimping techniques and accommodates larger manufacturing tolerances than are acceptable for welding techniques. Furthermore, the materials from which the end cap and the tubular body member are made need not be the same as will usually be required where welding is used to form the joint.

By using a plurality of formers distributed circumferentially around the periphery of the terminal portion of the tubular body member the method allows the folding action to be performed substantially simultaneously around the periphery. This may result in a reduced cycle time for crimped joint formation and hence a lower manufacturing cost. Not performing the folding action substantially simultaneously around the periphery of the body member may result in portions adjacent to a section being folded being deformed in an unwanted manner.

Thus the method may be used to form a crimped joint on a tubular body member with a substantially circular cross section and the resulting joint may also be substantially circular, whereas a joint formed by rolling may include unwanted deformations.

The use of a plurality of formers also allows folding of the overlapping portions inwardly or outwardly, whereas with a roller and a fixed mandrel the folding can only be in one direction or the other.

The individual formers act by bearing against the opposing portions of the end caps and tubular body member to fold the opposing portions over to form the mechanical joint

between them. The formers can act radially and/or axially or at any angle in between, so that the joint can be formed in a series of stages. Complex and repeated folding of the overlapping portions can thus be achieved, which enhances the mechanical key and the seal between the end caps and the tubular body member. The use of a former moving diagonally at an angle between radially and axially may create a tighter crimped joint than would otherwise be possible. Furthermore, the overlapping portions can initially be directed radially and/or axially with respect to the longitudinal axis of the tubular body member. This gives the designer flexibility in designing the individual shapes of the end caps and the end portions of the tubular body member so that each component can be formed to the ideal shape for manufacturing ease and gas flow design requirements. However, it will usually be preferred that at least part of the circumference of the opposed peripheries of an end cap and the associated terminal portion of the tubular body member present faces to one another which lie in the same plane so that the formers can act, at least initially, transversely to that plane so as to initiate the folding of the wall material of the end cap and body member. Preferably, the opposed faces extend for substantially the whole of the circumference of the tubular member and end cap.

It should be understood that the use of a plurality of formers located circumferentially around the terminal portion of the tubular body member permits the formation of crimped joints that could not easily be formed by other methods. For example crimped joints that do not pass fully

around the circumference of the body, that have an intentional weak point, or vary according to the circumferential location. These can be achieved by preventing, or restricting the movement of one or more of the formers, or using different formers depending upon the circumferential location. In this way a non-continuous joint may be formed, or the joint may vary around the circumference. A non-continuous joint may be useful, for instance, if the joint was to be interrupted by a pipe entry, or the joint did not require a complete or perfect seal. A joint which varies around the circumference, possibly including radial and axial crimps, may be useful if there is an obstruction, such as a mounting bracket, around which the joint must pass, or'external equipment, such as a pipe, with which the joint must not interfere.

The invention therefore also provides a silencer assembly having a tubular body member housing treatment elements for gases which are to flow through the silencer assembly and end caps at each end thereof, characterised in that at least one of the end caps is secured to the body member by a crimped joint formed by the method of the invention.

The opposed faces of the overlapping portions of the end cap and tubular body member can initially extend radially and/or axially in substantially the same plane. However, it is within the scope of the present invention for one to extend in a different plane to the other and for an initial folding operation to be carried out to bring the two faces into opposing relationship to one another. Thus, for example, the terminal portion of the tubular member

can be formed with a radial flange and the end cap formed with an axial peripheral flange so that the end cap is cup shaped and is a push fit within the end of the tubular member so as to leave the end of the axial flange of the cap exposed beyond the end of the tubular body member as an axially extending portion which is to be folded radially outward to bring it into opposition with the radial flange of the tubular member, or vice versa.

For convenience, the invention will be described hereinafter in terms of overlapping portions of the end cap and the terminal portion of the body member which are in substantially the same plane as one another and are substantially congruent and contiguous to one another.

As stated above, the press faces of the formers need not all be of the same configuration and the formers can travel different radial distances during the folding operation. The end cap and tubular body member therefore need not have circular cross sections, but could be of oval, squared, polygonal or other cross section, preferably with radiussed transition portions between the planar facets of the profile of the end cap and tubular body member. For convenience, the invention will be described hereinafter in terms of body members which have a circular transverse cross section and end caps which have a corresponding circular plan shape.

Since the formers need not all have the same press face, at least one former may be adapted to create some other feature or deformation whilst being moved to form the

crimped joint. Such a feature may include a deformation in the tubular body member to facilitate gas flow.

The end caps can be provided with any suitable inlet, outlet or other features. Thus, the face which is to be internal when the end cap is secured to the body member may carry annular baffles or vanes which are to co-operate with elements within the tubular body member to guide the flow of gas through the silencer. Similarly, the tubular body member may be provided with radially directed inlets and outlets and may be formed as the terminal module of a modular construction in which the overall body of the silencer is formed by connecting a series of components axially, in which case the method of the invention is utilised to secure the end caps to the terminal modules of such an assembly. However, for convenience, the invention will be described hereinafter in terms of securing an end cap to a unitary body shell of a silencer.

The end cap can have any desired cross sectional shape, for example a substantially flat or a convex or concave domed cross section. For convenience, the invention will be described hereinafter in terms of a conventional slightly outwardly domed circular shaped end cap.

As stated above, the end cap and the tubular body member need not be formed from the same material. For example, the tubular body member can be formed from zinc-galvanised steel, and the end cap from stainless steel. For convenience, the invention will be described hereinafter in terms of an end cap and body member formed from

galvanised mild steel as commonly used in the fabrication of silencers.

The opposing portions of the periphery of the end cap and of the terminal portion of the tubular body member can, as stated above, have a wide range of shapes. However, it is preferred that they are configured so that the end cap is easily located and supported upon the body member so that the initial assembly adopts a substantially consistent configuration prior to formation of the crimped joint.

Thus, for example, the terminal lip of the body member is formed with an outwardly directed radial flange and the end cap is formed with a U cross section annular flange into which the radial flange of the body member locates.

Such initial shapes to the engaging peripheries of the body member and end cap can be formed separately using any suitable technique or can be formed as an initial folding operation using the shaped formers of the method of the invention. For convenience, the invention will be described hereinafter in terms of end caps and tubular body members in which the desired configurations of the engaging peripheries have already been formed. If desired, the engaging peripheries can have been cut with axial or radial slits in the wall material to assist forming thereof into complex shapes. However, we have found that this is usually not necessary.

In the method of the invention a plurality of formers apply folding forces to the overlapping portions of the end cap and the body member. Such folding forces can be applied in a series of stages and can be applied axially

or radially or at any angle therebetween. Initially, the folding forces can be applied to only one of the end cap or body member so as to bring what are to be the opposing faces of the joint into congruent and contiguous configuration. The folding pressure can be applied using any suitable mechanism for driving the formers, for example mechanical, pneumatic or hydraulic mechanisms.

However, it is preferred to mount the formers upon one or more manipulating heads and to move the formers using hydraulic rams. In this way a plurality of shaping heads can be provided, each of which is brought into register with the area of the joint to apply the desired folding forces to form one aspect of the overall joint. The method of the invention thus readily leads itself to automation using conventional techniques for controlling the operation of the shaping heads.

As stated above, the formers can present different press faces to the overlapping portions of the end cap and body member so that the joint which is formed can present a complex axial and/or radial shape. Furthermore, the formers do not have to travel the same distance, notably radially, so that crimped joints which do not have radial symmetry can be formed using common shaping heads but employing different travels for the formers carried by those heads.

The wall thicknesses of the end cap and/or the tubular body member may be sufficient for the assembled end cap and body member to be self supporting during the folding operation. However, it will usually be desired to provide

some form of mechanical support to the assembly during the forming operation to reduce deformation of the components during the formation of the crimped joint. This support will typically take the form of a shaped mandrel or other support to the assembly to provide internal and/or external support for the assembly, but may also be formed by a plurality of movable mandrels or formers acting in opposition to the plurality of formers located circumferentially. For example, a mandrel can be inserted into the tubular body member for the formation of the crimped joint at one end of the silencer and can be an external mandrel when the crimped joint is formed at the other end of the silencer. The invention is of especial application to the application of the end cap to one end of the body of a silencer into which the necessary baffle or other treatment element is subsequently inserted through the other end. The treatment elements or an external mandrel may then provide the necessary mechanical support for the application of the end cap to that other end using the crimped joint technique of the present invention. Typically, the mandrel is configured to the desired internal shape of the end of the silencer and is made from steel or other suitable material. If desired, a series of mandrels may be employed where the internal shape is complex and changes during the formation of the crimped joint. Where an internal mandrel is used in the fabrication of the first crimped joint for a silencer, this can be a single upstanding static mandrel upon which the assembled body member and end cap is mounted by any suitable means. The mandrel thus serves to secure the correct registration of the end cap and the tubular body

member to achieve a silencer having the desired axial dimension. The mandrel can be of a specified axial length so that an end cap inserted into the exposed end of a tubular body mounted axially on the mandrel locates upon the exposed end of the mandrel at a specific axial distance from the base of the mandrel and of the body member mounted thereon.

As stated above, the folding of the overlapping portion of the end cap and body member can be carried out in a series of operations. For example, an axial portion of the end cap can be folded radially outwardly or inwardly to lie against a radial flange of the body member and the radial portions of both the end cap and body member then folded together to adopt an axial orientation. as part of the overall folding operation. Such sequential operations can be carried out using conventional inter-linking techniques using a plurality of shaping heads.

The invention has been described above in terms of assembling the end cap and body member with the overlapping portions which are to be incorporated into the crimped joint in direct contact with one another. However, it may be desired to incorporate some form of gasket material between the opposing faces of the end cap and body member so that this is incorporated into the crimped joint and enhances the gas seal and/or assists retention of the gas seal where some relative movement between the components of the crimped joint takes place during use, for example where high operating temperature differences are encountered. Overlapping portions from many components

may be included in the crimped joint, thus forming a multi layer crimped joint.

A method according to the invention is suitable for forming crimped joints for applications other than in silencers, and although it has been described with reference to this preferred embodiment, the invention should not be so limited.

The invention is also directed to apparatus for carrying out the disclosed methods and including apparatus parts for performing each described method step, be it by way of hardware, software, by combination of the two, or any other manner.

DESCRIPTION OF THE DRAWINGS: A preferred embodiment of the invention will now be described by way of illustration with respect to the accompanying drawings which show in diagrammatic transverse cross section various stages in the formation of a crimped joint and in which Figure 1 shows the initial assembly of an end cap upon a body member mounted upon an internal mandrel, Figure 2 shows a similar assembly mounted upon an external mandrel; and Figures 3 to 6 illustrate stages through which the overlapping portions of the end cap and body member pass in the formation of the crimped joint ; Figures 7 to 10 illustrate a form of a pair of formers for use in the formation of the crimped joint and stages in the formation of the crimped joint using such formers ; Figures 11 to 14 illustrate steps in

folding the upstand as in Figure 7 using radial movement only; and Figures 15 to 18 show steps in folding the upstand as in Figure 7 using radial and axial movement of the former.

DESCRIPTION OF THE PREFERRED EMBODIMENT: A silencer tubular body member 1 and end cap 2 are formed by any suitable technique. The end of the body member 1 is formed with an outwardly directed radial flange 3 and the end cap is formed with a peripheral annular U channel 4 into which flange 3 engages to locate the end cap 2 upon the end of the body 1 to form the loosely assembled end cap and body. The end cap 2 is preferably a push fit within the end of the body 1.

The assembly of the end cap 2 and the body 1 is mounted in a mandrel 10. As shown in Figure 1, the open end of the assembly can be mounted upon an upstanding internal mandrel whose length D corresponds to the internal axial length of the silencer so that the end cap 2 adopts the desired axial position with respect to the body 1. Where sufficient accuracy can be achieved in forming the flanges 3 on the tubular body at the desired axial positions, the mandrel 10 can be an external one as shown in Figure 2 which is a close fit within the annular shoulder 5 of the U channel 4.

The overlapping portions 6 and 7 of the end cap and the body are then folded to form the final crimped joint 20 shown in Figure 6 by folding the radially outward upstand

8 of the U channel 4 so that it lies contiguous and congruent to the flange 3-Figure 4. This radial projection is then folded through initially 45°-Figure 5, then through the remaining 45° so that it lies against the outer face of body 1-Figure 6. This folding forms a mechanical keying of the end cap to the body and the double folding of the wall material of both the end cap and the body member achieves a gas tight seal.

The formers 30 and 40 required to achieve this folding are shown in Figures 7 to 10. A first former 30 moves horizontally to fold the upstand 8 radially inward using a suitably shaped recess 31 in the face of the former-see Figure 7. Former 30 is then retracted and moved to the position shown in Figure 8 where its lower face presents a recess 32 to the upper surface of the folded material.

Former 40 mover vertically to engage an angled face 41 thereof with the combined material of the end cap U channel 4 and the flange 3 of body 1 to bend the material to the 45° folded position-see Figure 9, the suitably shaped recess 32 in former 30 acting as the anvil against which former 40 presses the combined material to form the tight folded structure of Figure 5. Formers 30 and 40 are retracted and former 30 moved downward to bring a suitably shaped recess 43 into register with the partially folded combined material. Former 30 then acts radially inwardly against the anvil of the mandrel 10 to complete the folding of the combined material to form the completed crimp joint shown in Figure 6-see Figure 10.

The formers 40 and 30 are constructed as a plurality of

arcuate segments which combine to form a complete ring around the end of the jointed end of the silencer when in position against the wall of the body member and the exterior of the crimped joint respectively. Typically each arcuate segment will extend over from 15 to 60° of the circumference of the joint and are mounted upon radially and axially acting hydraulic rams (not shown) to effect the necessary motion of the formers 30 and 40. The inter- linking of the operation of the rams can be achieved using any suitable electronic or other control so that the formation of the crimped joint can be achieved automatically.

Stages in the folding of the upstand 8 using radial movement only are shown in Figures 11 to 14. Although stages in the folding are shown, it should be understood that all the stages may take place in a continuous action.

A former 130 having an appropriate recess 131 aligned with the overlapping portions 6,7 is moved 50 radially towards a mandrel 10 behind the overlapping portions 6,7-Figure 11. The former 130 makes contact with the upstand 8 and begins to bend it inwards, the mandrel 10 providing the required opposing force to prevent substantial movement of the overlapping portions 6,7-Figure 12. The overlapping portions 6,7 and upstand 8 are forced into the recess 131 and make contact to form the crimp-Figure 13. The former 130 is moved away 52 leaving the crimp of the overlapping portions 6,7 and the upstand 8-Figure 14.

Stages in the folding of the upstand 8 using radial and axial movement are shown in Figures 15 to 18. A former 230

having an appropriate recess 231 aligned with the overlapping portions 6,7 is moved 50 radially towards a mandrel 110 behind the overlapping portions 6,7-Figure 15. The mandrel 110 has a sloping upper surface 54 and the recess 231 has a corresponding sloped upper surface 56 which is in contact with the sloping upper surface 54 of the mandrel 110. The former 230 moves diagonally 58, at an angle between radially inwards and axially upwards, guided by the contact between the sloping upper surface 54 and the upper surface 56 of the recess 231. The former 230 makes contact with the upstand 8 and begins to bend it inwards, the mandrel 110 providing the required opposing force to prevent substantial movement of the overlapping portions 6,7-Figure 12. The overlapping portions 6,7 and upstand 8 are forced into the recess 231 and make contact to form the crimp-Figure 13. Axial movement of the overlapping portions 6,7 is prevented by the mandrel 110.

The axial movement of the former 230 forces the upstand 8 towards the overlapping portions 6,7 and may result in a tighter crimp. The former 230 is moved away 60-Figure 14. It should be understood that the movement of the former 58 may be dictated by the interaction between the surfaces 54,56, or may be controlled by operation of mechanical, hydraulic or pneumatic rams as discussed previously.

The body member 1 can already contain the desired treatment elements (not shown). Where this is not the case, these are inserted into the body after a first end has been closed by an end cap as described above. The silencer assembly can then be inverted so that the open

end can be fitted with an end cap as described above. If desired, a body member fitted with the desired treatment elements and with an end cap located upon each end thereof can be clamped between two opposed mandrels so that the formation of the crimped joint at each end thereof can be carried out simultaneously.

The completed silencer assembly can be used on an internal combustion engine in replacement for a conventionally fabricated silencer. However, the method of the invention offers the designer greater flexibility in the shape of the silencer which he can design for any given application as well as simplicity and economies in fabrication.