VEHICLE EXHAUST SYSTEM

Abstract: First (2) and second (3) exhaust pipe portions are in substantial axial alignment and displaceable axially relative to one an other. A seal (5) extends between the first and second exhaust pipe portions, the seal (5) being expandable or contractible in the axial direction dependent upon relative displacement of the first and second pipe portions. A spring (8) secures the first and second pipe portions in a predetermined axial orientation, the spring (8) exerting a biassing force in opposed axial directions depending upon the displacement relationship between the first and second portions.

Description: Vehicle Exhaust System The present invention relates to a vehicle exhaust system, and in particular to such a system incorporating a connection known in the art as a flexible coupling. Exhaust systems incorporating flexible couplings for connecting axially adjacent exhaust pipe portions are known and disclosed, for example in EP-A-0861974 and DE-A- 29708669. Such flexible couplings typically include a spring bellows seal extending between the adjacent exhaust pipe portions, permitting the pipe portions to displace in both directions. The bellows perform the functions of: i) providing a gas seal preventing leakage of exhaust gas from the exhaust system; and, ii) acting as a spring damper to prevent transmission of vibration from the engine to items downstream in the exhaust system such as catalytic converters. As described in EP-A-0861974, conventional flexible connections have usually employed an outer wire mesh or wire rope sheath to prevent over-stretching/collapsing of the bellows and also acting to an extent as a vibration damper. Particularly in load bearing situations (for example where the axis of the coupling is arranged vertically, and the coupling consequently supports a significant portion of the exhaust system weight) the wire mesh or rope sheath is not well suited to counteract forces acting to expand the coupling (expanding the bellows) . In such circumstances, excess expanding (load) force may cause damage to the joint. An improved exhaust system flexible coupling has now been devised. According to the present invention, there is provided a vehicle exhaust system comprising: a first exhaust pipe portion; a second exhaust pipe portion in substantial axial alignment with the first exhaust pipe portion and displaceable axially relative to the first exhaust pipe portion; a seal element extending between the first and second exhaust pipe portions, the seal being expandable or contractible in the axial direction dependant upon relative displacement of the first and second pipe portions; and, securing means securing the first and second pipe portions in a predetermined axial orientation, the securing means comprising spring means arranged to exert a biassing force in opposed axial directions depending upon the displacement relationship between the first and second pipe portions. The spring securing means ensures that the axial forces in both directions are primarily taken up in the spring securing means rather than the expandable/contractible seal . By selecting the appropriate spring characteristics for a particular situation, the degree of stiffness or flexibility of the coupling can be selectively determined. Furthermore, in view of trends to include increasing numbers of components (such as catalytic converters and mufflers) in the exhaust system it is desirable to provide the flexible coupling as close as possible to the engine exhaust outlet manifold. This is particularly the case in view of improved catalytic converter performance achievable by situating the catalytic converter as close as possible to the engine. It is therefore advantageous to include the flexible coupling in a portion of the exhaust system extending substantially vertically from the engine exhaust outlet manifold. To do this means that a proportion of the weight of the exhaust system is transmitted to the flexible coupling. The present invention ameliorates the possibility of damage to the expandable/contractible seal that might otherwise occur, because the weight is transmitted via the spring securing means. When the spring securing means is in equilibrium supporting the proportion of the weight of the exhaust system it remains able to permit the upstream and downstream portions of the exhaust pipe to displace in either axial direction whilst exerting a spring force tending to return the arrangement to the equilibrium position. The securing means preferably comprises a spring clip arrangement having a respective limb acting on a respective one of the first and second exhaust pipe portions, the respective limbs desirably extending adjacent one another and preferably being connected proximate respective proximal portions at a spring connection. The respective distal ends of respective limbs are preferably spaced from one another and have respective terminal portions. The spring clip arrangement preferably includes a central void portion for accommodating the exhaust pipe permitting the spring clip arrangement to straddle the exhaust pipe. The provision of the securing means in the form of a spring clip aids in ease of assembly and construction of the exhaust system. The securing means beneficially acts on respective ones of the first and second exhaust pipe portions at circumferentially spaced positions about the axis of the first and second pipe portions. Desirably, one (or more preferably both) of the first and second pipe portions is provided with a respective connection collar, the securing means preferably acting on the respective connection collars. The connection collars preferably extend substantially about the exhaust pipe axis substantially enclosing the expandable or contractible seal. A seal may be provided between the respective connection collars . The respective connection collars beneficially have overlapping portions overlapping in the axial direction of the exhaust pipe. A circumferential seal is preferably provided between the respective overlapping portions, the circumferential seal preferably being effectively fixed relative to one of the connection collars and slidable relative to the other. The connection collars are beneficially provided with respective engagement formations upon which the securing means acts. Each connection collar is preferably provided with respective engagement formations spaced in the axial direction of the exhaust pipe upon which respective formations the securing means acts in opposed axial directions. The engagement formations may comprise respective depressions, or projections, preferably running circumferentially about the outer surface of the respective connection collars. The expandable or contractible seal advantageously comprises a bellows seal connected to the first and second exhaust pipe portions respectively. Desirably, each of the first and second pipe portions is provided with a respective connection collar over laying the respective pipe portion, the bellows seal having portions sandwiched between respective exhaust pipe portions and overlaying collars. A tubular shield preferably extends adjacent at least a portion of the expandable or contractible seal on the axial side of the seal . The tubular shield preferably comprises a portion of one of the first and second exhaust pipe portions. The invention will now be further described in a specific embodiment by way of example only, and with reference to the accompanying drawings in which: Figure 1, is a schematic part sectional view of an exhaust system according to the invention. Figure 2, is a schematic front view of a spring clip comprising a system according to the invention; and Figure 3, is a schematic side view of the spring clip of figure 1. Referring to the drawings, there is shown a portion of a vehicle exhaust system 1, including an upstream exhaust pipe portion 2 and downstream exhaust pipe portion 3 which are axially co-aligned along axis 4. Pipe portions 2, 3 are arranged end to end and coupled by an arrangement including a flexible metallic bellows seal 5 extending between pipe portions 2,3 providing a flexible gas sealed connection between the adjacent ends of pipe portions 2, 3. Respective connection collars 6, 7 are fixed to respective pipe portions 2, 3, the collars being coupled together secured in the arrangement shown in Figure 1 by a securing spring clip 8. The opposed ends of bellows seal 5 are spot welded to respective outer collars 6, 7 which are themselves welded to respective pipe portions 2, 3. Collars 6, 7 overlap m the axial direction, and a wire mesh seal 9 is spot welded to the internal circumference of the outer collar 7, and extends angularly around the circumference of the collars 6, 7 to provide an annular sliding seal as the connection expands and contracts (as a result of pipe portions 2, 3 being axially displaced) . The wire mesh seal 9 carried by outer collar 7 slides m the axial direction m sealing abutment w th the annular outer surface of collar 6. Annular collar 6 includes a pair of upstanding circumferentially running ridges 10, 11 defining a circumferentially running slot 13 configured to receive securing tabs 17a, 17b carried by a first pair of arms (12a, 12b) of spring clip 8. Collar 7 includes an upstanding ridge 14 and spaced shoulder 15, defining a circumferentially running slot 16 for receiving tabs 17c, 17d carried by arms 12c, 12d of spring clip 8. As shown m Figure 2, spring clip 8 includes a central void portion 19 arranged to accommodate the diameter of the collar 6, 7. The clip snaps m position around the connection and thereafter remains m the clipped position. The spring connection between the arms 12 at the proximal end 20 of the clip 8 enables the respective pairs of arms 12a, 12d and 12b, 12c to be deflected against a biassing spring force m the direction shown by the arrows m figure 3. In use, the arrangement permits pipe portions 2, 3 to displace relative to one another axially (as a result of forces acting in operation) . The engagement tabs 17a, 17b of spring clip 8 acts on ridges 10, 11, 14 or shoulder 15 of the respective collar 6, 7 tending to restore the pipes 2, 3 to an equilibrium orientation against forces acting to displace pipe portions 2, 3 from the equilibrium position. The use of spring clip 8 therefore ensures that the arrangement acts more than as simply a "stop" mechanism limiting the extent to which the connection may be expanded/contracted, by rather the restoring force provided by the spring increases with deflection of the spring arms (and consequently the pipe portions 2, 3) away from the equilibrium position. The spring force acting on pipe portions 2, 3 via the respective collars 6, 7 provides that forces are taken up via the spring clip 8 rather than the flexible metallic bellows 5. This results in improved life of the bellow seal 5 and therefore of the connection. A further advantageous feature is that pipe portion 2 includes a narrowed diameter terminal portion 2a which extends adjacent the majority of the length of the bellows seal shielding the bellow seal 5, to a degree, from the hot exhaust gasses passing along the exhaust system. The arrangement is believed to be particularly useful where the connection is arranged with its axis in a vertical orientation (not horizontal as shown in Figure 1) because in such an orientation a portion of the weight of the exhaust system will be transmitted via the connection. The arrangement according to the invention ensures that exhaust system weight transmitted via the connection is taken up in the spring clip 8 (acting on collars 6, 7) rather than through the bellows seal 5. An arrangement in which the connection is orientated with its axis extending vertically (rather than horizontally) is believed to be beneficial because it enables the catalytic convertor (situated downstream of the flexible connection 1) to be positioned more closely to the engine exhaust outlet manifold which improves performance of the catalytic convertor. Such an arrangement further provides increased facility downstream for inclusion in the exhaust system of further systems (such as mufflers and further catalytic convertors) .

Claims: Claims : 1. A vehicle exhaust system comprising: a first exhaust pipe portion; a second exhaust pipe portion in substantial axial alignment with the first exhaust pipe portion and displaceable axially relative to the first exhaust pipe portion; a seal element extending between the first and second exhaust pipe portions, the seal being expandable or contractible in the axial direction dependant upon relative displacement of the first and second pipe portions ; and, securing means securing the first and second pipe portions in a predetermined axial orientation, the securing means comprising spring means arranged to exert a biassing force in opposed axial directions depending upon the displacement relationship between the first and second pipe portions. 2. A vehicle exhaust system according to claim 1, wherein the securing means comprises a spring clip arrangement having a respective limb acting on a respective one of the first and second exhaust pipe portions. A vehicle exhaust system according to claim 2 , wherein the respective limbs extend adjacent one another . A vehicle exhaust system according to claim 3, wherein the respective limbs extend adjacent one another and are connected proximate respective proximal portions at a spring connection. 5. A vehicle exhaust system according to claim 4, wherein the respective limbs extend adjacent one another, respective distal ends of respective limbs being spaced from one another and having respective terminal portions. 6. A vehicle exhaust system according to any preceding claim, wherein the securing means comprises a spring clip arrangement having respective limbs acting on respective ones of the first and second exhaust pipe portions at circumferentially spaced positions about the axis of the first and second pipe portions. 7. A vehicle exhaust system according to any preceding claim, wherein the securing means comprises a spring clip arrangement having respective limbs acting on respective ones of the first and second exhaust pipe portions, and a central void portion for accommodating the exhaust pipe permitting the spring clip arrangement to straddle the exhaust pipe. 8. A vehicle exhaust system according to any preceding claim, wherein each of the first and second pipe portions is provided with a respective connection collar. 9. A vehicle exhaust system according to claim 8, wherein the respective connection collars extend circumferentially about the exhaust p pe axis substantially enclosing the expandable or contractible seal. 10. A vehicle exhaust system according to claim 9, wherein a seal is provided between the respective connection collars. 11. A vehicle exhaust system according to any of claims 8 to 10, wherein the respective connection collars have overlapping portions. 12. A vehicle exhaust system according to any of claims 8 to 11, wherein the respective connection collars have overlapping portions a circumferential seal being provided between the respective overlapping portions. 13. A vehicle exhaust system according to claim 12, wherein the circumferential seal is effectively fixed relative to one of the connection collars and slidable relative to the other. 14. A vehicle exhaust system according to any of claims 8 to 13 , wherein the securing means acts on the respective connection collars. 15. A vehicle exhaust system according to claim 14, wherein the connection collars are provided with respective engagement formations upon which the securing means acts . 16. A vehicle exhaust system according to claim 15, wherein each connection collar is provided with respective engagement formations spaced m the axial direction of the exhaust pipe upon which respective formations the securing means acts m opposed axial directions . 17. A vehicle exhaust system according to claim 15 or 16, wherein the engagement formations comprise respective depressions, or projections. 18. A vehicle exhaust system according to any of claims 15 to 17, wherein the engagement formations comprise respective formations running circumferentially about the outer surface of the respective connection collars . 19. A vehicle exhaust system according to any preceding claim, wherein the expandable or contractible seal comprises a bellows seal connected to the first and second exhaust pipe portions respectively. 20. A vehicle exhaust system according to claim 19, wherein each of the first and second pipe portions is provided with a respective connection collar over laying the respective pipe portion, the bellows seal having portions sandwiched between respective exhaust pipe portions and overlaying collars. 21. A vehicle exhaust system according to any preceding claim, wherein a tubular shield extends adjacent at least a portion of the expandable or contractible seal . 22. A vehicle exhaust system according to claim 21, wherein the tubular shield comprises a portion of one of the first and second exhaust pipe portions extending adjacent at least a portion of the expandable or contractible seal. 23. A vehicle exhaust system substantially as herein described with reference to the accompanying drawings .

Inventors: SPRASON MALCOLM, SPRASON, MALCOLM
Applicants: LLANELLI RADIATORS LTD, SPRASON MALCOLM, LLANELLI RADIATORS LIMITED, SPRASON, MALCOLM
Application year: 2000
Main classification: F01N7
IPC codes: F01N7, F16L27