FIELD OF THE INVENTION

This invention relates to an improved hollow pivotable coupling, and in particular to an improved hollow pivotable coupling for use in an engine exhaust system.

It is conventional practice in a vehicle powered by an internal combustion engine, firstly to mount the engine on flexible supports to permit the engine some vibration and lunge during vehicle movement, and secondly to mount a major part of the exhaust system rigidly on the vehicle chassis. It is therefore usual to include a pivotable joint between the engine and the exhaust system, to inhibit fracture of the exhaust system from the stresses arising from the relative (motion-induced) movements of engine and exhaust, and also to alleviate acoustical drumming.

DISCLOSURE OF THE PRIOR ART

A system for absorbing the vibrations of the exhaust lines of motor vehicles is disclosed in European patent application

0,084,589. The use is taught of single or double joints (ball and socket couplings), whose action is integrated "by springs recovering the optimal position of the exhaust line".

In a first embodiment a single helical compression spring is used, mounted on "circular sectors" alongside the ball joint, and so greatly increasing the space envelope reguired to accommodate the disclosed system. The circular sectors inhibit the flow of cooling air to the (exhaust) gas sealing surfaces.

I have realised that the spring pressure of European patent application 0,084,589 acts in the "compression" direction tending to shorten the distance between the line (pipe) sections. Thus the inner bulbous end of the first pipe section extends within the bulbous end of the second pipe section to form one of the sealing surfaces, with the spring pressure urging this surface against the adjacent surface of the bulbous end of the second pipe section. However, if the system is mounted with the exhaust line vertical, there can be created a gap between these two sealing surfaces when the engine moves upwardly under motion-induced vibration i.e. in the "tension" direction between the pipe ends. Thus in my pending international application PCT/GB90/00875 is disclosed mounting the resilient means so as to "co-act" with the tension force i.e. with a first pipe section being urged relative to a second pipe section in the "tension" direction, with therefore the bulbous ends being resiliently urged in a direction to increase the distance between the pipe sections, with therefore the pipe sections being urged apart.

I am aware of British Patent 255,082 in which there is

disclosed a hollow pivotable coupling which includes a first pip section, a first pipe section bulbous end having a firs part-spherical external surface, a second pipe section, a secon pipe section bulbous end having a second part-spherical interna surface, said first external surface being sized as a sliding fi within the secong internal surface, resilient spring means havin first and second ends, the resilient means being located to urge the pipe sections apart. The spring means is however tightl located about the first pipe section, and so its second en cannot move together with the second pipe section bulbous end. Furthermore, the spring is heated throughout its length by conduction from the first pipe section i.e. at each spring coil.

In my earlier proposal disclosed in PCT/GB90/00875, the spring has at least its intermediate coils spaced from the pipe section. In order to support that end of the spring immediately adjacent a ball and socket coupling, usually and as shown in Fig.2 thereof with that spring-end "downstream" of the exhaust flow direction, my earlier proposal of PCT/GB90/00875 teaches an annular pressure ring slidably engagable with the second bulbous end external surface 24.

I have now recognised possible disadvantages of the arrangements disclosed in international application PCT/GB90/00875.

A first possible disadvantage is that the bulbous end of th second pipe section could wear "doubly" i.e. both at its inne surface from the sliding engagement with the external surface of the first pipe section, and at its outer surface from the sliding engagement with the annular pressure ring. The bulbous end of the second pipe section could therefore wear more rapidly than the bulbous end of the first pipe section. Thus I now propose an alternative arrangement wherein one spring-end, usually the "downstream" end of the resilient means e.g. a coil spring, is located relative to the second pipe section bulbous end.

A second possible disadvantage is that the spring was not mounted to provide both a co-acting force in the tension direction and a constraining return force urging the ball and socket towards its optimal "at rest" or normal position. To provide such dual forces was thought to require an extra spring, with increased complexity and cost. I now propose a dual-acting spring, having a rate equivalent to that of those springs combined.

STATEMENT OF THE INVENTION

Thus according to one feature of my invention I propose a hollow pivotable coupling which includes a first pipe section, a first pipe section bulbous end having a first part-spherical external surface, a second pipe section, a second pipe section bulbous end having a second part-spherical internal surface, the

said first external surface being sized as a sliding fit withi the second internal surface, resilient spring means having firs and second ends, the resilient means being located to urge th pipe sections apart, characterised in that the said second end o the resilient spring means is movable together with the secon pipe section bulbous end, and in that the spring means i arranged both to urge the pipe sections apart and to return th pipe sections to their optimal relative position.

Preferably the spring means is an annular coil spring having a first spring-end located in or on an abutment, convenientl formed as a flange or cup rigidly fixed to the first (e.g. upstream) pipe section, but alternatively as an outwardl protruding pipe formation; in an alternative embodiment, the cu can be adjustably fixed to the first pipe section to permit a variable spring loading; the spring has a second spring-end engageable directly or indirectly with the second bulbous end.

The spring-ends can be ground, the better to fit the abutment and second bulbous end.

In an engine exhaust system, usually at least one such coupling would be mounted vertical or substantially vertical, with the exhaust gas flowing downwardly. However, although I prefer the exhaust gas to flow from the first pipe section into the second pipe section, with my modified arrangement of spring means, this relative flow direction can be reversed. Furthermore, I can provide means to avoid direct impingement of the hot exhaust gas

on the sealing surfaces, and which if suitably shaped can provide a gaseous buffer zone adjacent the sealing surfaces containing in use cooler exhaust gas.

The coupling of the invention can be separate from but sealingly attached to adjacent pipe sections, or be made integral therewith. The gas flow can be in either relative direction.

I also propose a method of forming a hollow pivotable coupling having a first pipe section terminating in a bulbous end with a sealing surface, and a second pipe section terminating in a bulbous end with a sealing surface, the said sealing surfaces being part-spherical and concentric, part of the first bulbous end being within and in sliding engagement with the second bulbous end at said sealing surfaces, and with resilient means to urge the sealing surfaces together, the coupling in use being subject to tension forces acting in a direction to separate the pipe sections and compression forces acting in a direction to press the pipe sections together, the resilient means being arranged to co-act with the tension forces, characterised by locating the resilient means both to move together with the second pipe section bulbous end, and to urge the pipe sections towards their optimal relative position.

I have recognised that the pipe sections do not maintain their spatial symmetry during vehicle-induced motions, but that the difference in the spring pressure forces upon and around the

second bulbous end is small (because the angle between th external surface of the second bulbous end and the spring axis i small); thus the possible additional wear at different annula locations from the lack of symmetry is of no or minimal practica consequence.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described by way of example, wit reference to the accompanying schematic drawings, in which:-

Fig.l is a schematic end view of an engine which is transversly and flexibly mounted on the chassis of a vehicle, including part of an exhaust system comprising a composite hollow and universally articulating pipe joint comprising three hollow pivotable couplings made according to the invention;

Fig.2 is an enlarged schematic sectional view of one hollow pivotable coupling according to the invention, with some components including the spring ends shown spaced apart for clarity, with the pipe sections in their optimal relative or at rest position;

Fig.3 is an enlarged schematic sectional view of a second hollow pivotable coupling according to the

invention, with some components including the spring ends again shown spaced apart for clarity;

Fig.4 is a schematic sectional view of yet a further embodiment according to the invention; and

Fig.5 is a schematic sectional view of another alternative embodiment, arranged for reverse exhaust gas flow, and with an internal pipe extension.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As seen in Fig.l, the vehicle engine 2 is transversly mounted, on chassis attachment points 13. Interposed flexible mountings 3 enable the engine 2, and consequently the exhaust manifold 4, to vibrate and lurch relative to exhaust pipe section 8, which is rigidly connected to the vehicle chassis 1. A typical engine movement, about the centre of twist C, during vehicle motion is shown by arrow Cl. A catalytic converter or exhaust silencer (muffler) box 15 is rigidly connected to chassis 1 by arms 17, and thus moves therewith; there may be sonant dampers between silencer box 15 and the chassis attachment points.

Exhaust manifold 4 has its egress directed generally downwards, and has bolted thereto a first pipe section 6 having a bulbous end 16 (Fig.2). It is partly surrounded by a second bulbous end

18 of larger diameter, forming part of second pipe section 12.

The bulbous ends 16,18 are elements of a pivotable coupling 11a;

additional pivotable pipe couplings lib and lie are locate downstream of coupling 11a, and in a substantia horizontally-disposed exhaust run.

In the embodiment disclosed, the first bulbous end of couplin lib is carried by the end of pipe 12 remote from bulbous end 18; similarly pipe section 14 carries at its inlet end the secon bulbous end for coupling lib, as well as the first bulbous en for coupling lie.

Each of the couplings 11a,lib,lie has a limited range universal pivoting. Thus interposed in the exhaust pipeline is a pipe length with three couplings i.e. between engine 2 and pipe 9 is an articulated joint 10, comprising couplings 11a,lib,lie, with, in this embodiment, the couplings being identical in structure and operation, but in an alternative embodiment, with at least the couplings being in accordance with this disclosure.

In this embodiment, pipe section 8 is connected to inlet pipe 9 of silencer box 15. In an alternative embodiment, silencer inlet pipe 9 is formed with the second bulbous end of coupling lie.

As more clearly seen in Fig.2, shown with the coupling 11a in its rest position with pipe sections 6,12 co-axial, and with

exhaust gas flow downwards as viewed in this Figure. The firs bulbous end has a part-spherical mating surface 20 and is locate within the downstream second part-spherical bulbous end 18 whic has an internal concentric part-spherical surface 22. Surface 20,22 are sized to mate, to permit relative rotation, includin pivotting and swivelling, of the bulbous ends 16,18, whils maintaining substantially complete exhaust gas sealin therebetween. Such pivotting and swivelling as may temporaril be required in response to vehicle-induced movements is o restricted range, being shared between couplings 11a,lib,lie, fo instance until the terminal portion 23 of the second bulbous en 18 abuts pipe section 6.

In an alternative embodiment, the couplings are arranged t accept exhaust gas flow in the opposite relative direction i.e. from pipe section 12 (and thus from pipe 9) to pipe section 6 i.e. the couplings can be reversed axially.

Pipe sections 6,12 can be short in length to permit access fo welding internal pipe extensions (such as extension 6a of Fig. .)

It is a feature of my invention that the spring 30 acts both to urge the pipe sections 6,12 apart, and to urge them towards thei optimal relative position, which they naturally occupy "at rest". It is a further feature of my invention that the "downstream" end 31 of spring 30 moves together with bulbous end 18.

In the embodiment of Fig.2, coil spring 30 has sufficien flexibility to be deformed, temporarily, upon pivotting an swivelling of bulbous end 18 relative to bulbous end 16. Thus th wire diameter, the coil diameter, the coil pitch and the sprin length are selected to ensure that the frictional resistanc between end 31 and bulbous end 18 deforms spring 30, rather tha permitting slippage between spring-end 31 and bulbous end 18.

To ensure that the second end of the resilient spring means is movable together with the second pipe section bulbous end, the second spring end engages the second bulbous end at a position such that the included angle "X" (Figs.2,3) between the central axis of spring 30 and the tangent at the contact point of spring end 31 to the second bulbous end 18 is less than 35 degrees, preferably between 5 degrees and 10 degrees when measured in the "at rest" in-line condition of the first and second pipe sections.

In the Fig.2 embodiment, the (upstream) end 29 of spring 30 is located in a flange or cup mounted on pipe section 6, and which forms an abutment 32a for this upstream spring-end, whereby this upstream spring-end is spaced well away from pipe section 6. In the alternative embodiment of Fig.3, an abutment 32b is formed by outward deformation of pipe section 6, either as shown as an annular outward deformation, or in an alternative embodiment as a plurality of separate outward deformations, or a series of welded

pips, which also act to separate the spring end 29 from pipe 6 t inhibit heat transfer.

The longitudinal axis of spring 30 makes only a small angl with the external surface of the second bulbous end at th engagement position of spring-end 31. Thus the radially inward force from spring 30 upon second bulbous end is small, so tha the changes in this inward force component with changing spatial positions of the bulbous ends results in no or minimal differential wear at the mating surfaces.

As seen in the Fig.3 embodiment, pipe section 6 can extend within the first and second bulbous ends, to inhibit direct impingement of the hot exhaust gases with surfaces 20,22. In this embodiment, bulbous end 16 is pre-formed and welded or otherwise secured at 19 to the pipe section 6, and is internally shaped to form a gaseous buffer zone 33 adjacent surfaces 20,22, containing exhaust gas likely to be cooler than the gas in pipe section 6, because of heat lost by convection and radiation from external surface 24 of the second bulbous end. In an alternative but less preferred embodiment, the interior of bulbous end 16 fills buffer zone 33.

Thus the Fig.3 embodiment has a tapered-bore spring with the abutment 32 formed by enlarging the pipe 6 diameter and by abutting the other spring end directly onto bulbbous end 18; in an alternative embodiment this other spring end abuts onto the

pressure ring 26, ^" as shown in Fig.2.

In the embodiment of Fig.4, the downstream end 31 of spring 30 is located in stools 35 spaced apart around bulbous end 18, and rigidly connected thereto as by welding. In an alternative embodiment, the stools can be connected so to provide an annular location for spring-end 31, encircling surface 24. In further embodiments, stools 35 can be formed integrally with bulbous end 18, since the external surface 24 need not be part-spherical. Spring end 31 is thus constrained to move with bulbous end 18.

in the Fig.4 embodiment, hollow pipe extension 6a is secured to the inner surface of pipe section 6 adjacent the widening thereof into bulbous end 16, as by welding, but alternatively by heat resisting adhesive 50. The upstream end of pipe extension 6a is chamfered at 52.

Spring 30 can abut stools which though attached to bulbous end 18 as by welding are nevertheless inhibiting to heat conduction to spring 30. In an alternative embodiment the stools are formed as raised portions of the exterior surface of bulbous end 18.

In the further alternative embodiment of Fig.5, annular stool 135 is not rigidly fixed to bulbous end 18. It is however of a size and shape to be located just upstream (for the flow direction indicated) of the diametral line "A" of bulbous end 18; thus spring 30 exerts a greater but nevertheless equilibrium

radial component force via annular stool 135 in the ratio of the cotangent of the "approximate" angle of contact (9.51 at 6 degrees) from the common central axis of the pipe sections 6,12, to ensure that it grips bulbous end 18 - preferably at an angle of between 5 and 10 degrees. The spring is selected to deform, in preference to inducing slippage between stool 135 and surface

24 of bulbous end 18. If desired, the engagement surface of stool

135 can be roughened or its coefficient of friction otherwise increased. There is thus co-movement of stool 135 and bulbous end 18. In an alternative but less preferred embodiment, stool

135 can either contain axial cuts, or be separated into at least two parts with each part encircling a portion of the second bulbous end.

Spring 30 exerts only a small component of force parallel to the median plane "A", so that small imbalances to diametrically opposite sides of the bulbous end 18 when the spring 30 flexes, result in minimal extra wear at the corresponding diametrically opposed positions on mating engagement surfaces 20,22.

As an optional feature, in this embodiment pipe section 12 can have welded thereto a pipe extension, projecting towards but not reaching the pipe section 6. Thus an annular gap is provided, which with the (upward) mass gas flow indicated, allows gas flow in the "reverse" direction into the buffer zone 33 which has been created, with "double-reverse" flow required if the gas is to penetrate between sealing surfaces 20,22. Since there is little,

if any, escape of gas from between the sealing surfaces 20,22 there is little flow of hot exhaust gas into the buffer zone, the gas in this buffer zone thereby remaining substantially cooler in use (because of the heat lost through convection and radiation) than the exhaust gases in pipes 6,12.

To reduce outward heat flow from the pipe sections to the respective spring-ends, one or both of the abutment 32a,32b, and stool 35,135 can be apertured, corrugated or castellated, both at the support surface for spring end 31 and at the engagement surface with pipe 6 or surface 24 respectively.

The coil spring 30 can be replaced by three or more springs (preferably four) equi-angularly spaced about the coupling, as on a spider or on dedicated arms. Thus the sections will not remain in their offset condition, as might occur with two diametrically-opposed springs in "tumbler-switch" array, but at least one spring will be active to return the pipe sections to their optimal relative position.

To inhibit conductve heat transfer from the bulbous end 18, the second spring end is not circular, and is such that the last coil of at least one spring end provides a three-point engagement, preferably spaced apart by 120 degrees, with either the second pipe section bulbous end 18, or the pipe section 6.

Thus the last coil acts as a gripping ring to the bulbous end;

although this coil is normally "downstream", the gas flow can reversed so that it is upstream.

The invention permits improved sealing aainst exhaust ga escape, with consequent danger to the vehicle driver an passengers, and possible noisy operation. The bulbous ends ar continuously urged towards their sealed condition, to permi continuous gas-tightness.

We have also disclosed a hollow coupling having an abutmen ring 26 sized and positioned to create friction between it contacting (mating) surfaces so as to ensure co-movement wit bulbous end 18.