MULTIPLE PIPE COMPRISING AN ENVELOPE

Abstract: The invention relates to a multiple pipe comprising at least two inner pipes (2, 3) lying against each other with a wall piece, characterized in that the inner pipes are enclosed over at least a part of their length by an outer pipe (9). A much greater mechanical strength is obtained by arranging the outer pipe, whereby the bendability also increases. In addition, the thermal and mechanical insulation provided by the thus resulting pipe is much greater than of the two pipes according to the prior art. According to a preferred embodiment the outer pipe is separated from the inner pipes by a gap over at least a part of the length of the inner pipes. According to another preferred embodiment, over their part which is not covered by the outer pipe the inner pipes are branched so as to form a manifold.

Description: MULTIPLE PIPE COMPRISING AN ENVELOPE The present invention relates to a multiple pipe comprising at least two inner pipes lying against each other with a wall piece. Such pipes are known. For mutual fixing of the inner pipes a weld is usually applied to the seams visible from outside. Although such multiple pipes are very satisfactory for particular applications, these multiple pipes have the drawback that they are difficult to bend, that they are not exceptionally robust, in particular when the interior is subjected to high pressures, and that they result only in a mediocre thermal and mechanical insulation. The object of the present invention is to provide such a multiple pipe, wherein the above stated drawbacks are obviated. This objective is achieved in that the inner pipes are enclosed over at least a part of their length by an outer pipe . A much greater mechanical strength is obtained by arranging the outer pipe, whereby the bendability also increases. In addition, the thermal and mechanical insulation provided by the thus resulting pipe is much greater than of the two pipes according to the prior art . It is pointed out here that in the multiple pipes known from the prior art a double wall thickness is present precisely between two passages, while only a single wall thickness is present between each of the passages and the environment. This is precisely the reverse of the requirement; the objective should rather be a multiple pipe wherein the separating walls between the separate passages are only moderately thin and wherein the outer wall is thicker. 2 The invention satisfies this requirement by providing a double outer wall. By choosing an outer pipe with a greater wall thickness than that of the inner pipes the total wall thickness of the outer walls can be increased still further. According to a first preferred embodiment at least half the inner surface of the outer pipe is in contact with the outer surface of the inner pipes. A robust pipe then results with a great wall thickness on the outer side. It is important for other applications that a high thermal and mechanical insulation be obtained between the internal passages and the environment . It is then attractive for the outer pipe to be separated from the inner pipes by a gap over at least a part of the length of the inner pipes . It is noted here that it is likewise possible for the gap to extend over only a part of the length of the pipe. This insulation can be further improved if the gap is filled with insulation material. It is pointed out herein that it is of course possible not to fill the gap with a specific material, so that it is simply filled with air. According to another preferred embodiment the periphery of the combination of the inner pipes is substantially round. This will result in minimum space being occupied, while the ratio of surface of the pipe and diameter is moreover as favourable as possible, this being important in respect of thermal and mechanical insulation. According to a further preferred embodiment both inner pipes have in cross-section the form of a D. This also results in an effective use of the available space. It is pointed out here that this embodiment is particularly suitable as pipe connecting onto an exhaust manifold of an engine, wherein it is important that gas 3 flows coming from diverse groups of cylinders are mutually separated over a certain distance in order to prevent short-circuiting. It is of course essential here that the engine has an even number of cylinders. When the engine has five cylinders it is attractive when the two inner pipes have the shape of a C, that the two inner pipes contact each other and that the inner space between these pipes is filled with a substantially round pipe, wherein the cross-section of each of the two C-shaped pipes equals twice the cross- section of the substantially round pipe. The gas flows from pairs of cylinders of which the moments of ignition lie far apart can herein be combined, while the gas flow from the remaining cylinder can be fed to the single round pipe. The invention also applies however to exhaust pipes for engines with other numbers of cylinders. In six-cylinder engines for instance, three pipes are combined which each have the cross-section of 1/3 sector of a circle. In eight-cylinder engines four pipes are for instance combined which each have the cross-section of 1/4 sector of a circle. It will be apparent that it is also possible to apply other configurations. According to yet another preferred embodiment the outer pipe extends over only a part of the length of an inner pipe combination and over their part which is not covered by the outer pipe the inner pipes are branched so as to form a manifold. It will be apparent that this embodiment is also attractive for use in an engine, for instance an engine of a motor vehicle. It is then attractive when the branched ends of the inner pipes are adapted for connection to such an engine . This can take place by mounting flanges on the free ends of the inner pipes for fixing of the pipes to a machine component . 4 A particularly attractive embodiment results when the flanges are combined to form a plate and the plate is connected to an element enclosing the free inner pipes, wherein the element encloses a space between the pipe pieces and the element . Such a combination can for instance be cast. Other attractive preferred embodiments are stated in the remaining sub-claims. The present invention will be elucidated hereinbelow with reference to the annexed drawings, in which: figure la shows a perspective view of a twofold pipe according to the prior art; figure lb shows a perspective view of the pipe depicted in figure la which is enclosed by an outer pipe according to the invention; figure lc shows a variant of the pipe according to the invention shown in figure lb; figures 2a-2c show the three-fold embodiment of the pipes shown in figures la-lc; figures 3a-3c show another variant of the pipes shown in figures la-lc; and figure 4 is a perspective view of an engine block provided with a manifold according to the present invention. Figure la shows a so-called DD pipe 1 which is known in the prior art . This DD pipe comprises two pipes 2,3 which each take the form of a D and which are placed against each other with their flat sides 4,5. Two welds 6 respectively 7 are arranged for fixation purposes . Other fixing means can also be used. Figure lb shows the DD pipe depicted in figure la which is provided with an outer pipe 9. Outer pipe 9 is in contact with inner pipes 2, 3 over its whole inner surface except for the welds . These inner pipes are thus clamped against each other so that welds 6,7 could be omitted, although these latter could be necessary during 5 the production process. It is further possible to have outer pipe 9 extend over only a part of the length of the two inner pipes . Figure lc shows an embodiment wherein both inner pipes 2,3 are separated from outer pipe 9 by an air gap 10. In order to maintain the spacing between the inner pipes and the outer pipe it will be necessary herein for the air gap 10 either to be filled with an insulating material or to be provided with spacers arranged at regular intervals, or for the air gap to be present over only a part of the length of the pipe. Fixation then takes place at parts of the length wherein the outer pipe is in direct contact with the inner pipe, such as is shown in figure lb. If spacers are used, it may be necessary to mutually fix the inner pipes, for instance by means of welds . It is thus possible to make combinations of the embodiments of figure lb and figure lc. Shown in figure 2a is a prior art three-fold pipe 11 which is formed by three identical pipes 12,13,14 which each take a circle segment form in cross-section and which are fixed against each other with their flat sides. It is here also possible to arrange around the thus formed assembled pipe 11 an outer pipe 15 which is in contact with inner pipes 12,13 and 14. It will likewise be apparent that an air gap can also be applied here, as shown in figure 2c. Inner pipes 12,13,14 are here separated from outer pipe 16 by an air gap 17 which, here also, may or may not be filled with spacers or insulation material. Figure 3a shows a third variant comprising two inner pipes 18,19. These latter each have the form of a C in cross-section and lie against each other with the free ends of their cross-section. A weld not shown in the drawing can here also be applied for fixation purposes. 6 It will be apparent that, as in the foregoing variants, an outer pipe 20 can herein be arranged as shown in figure 3b. In figure 3c is shown an embodiment wherein an air gap 22 is arranged between an outer pipe 21 and inner pipes 18,19. The same considerations otherwise apply for this embodiment as for the embodiments elucidated with reference to figure 1. As stated in the preamble, it is possible to have the outer pipe of the diverse embodiments extending over only a part of the inner pipes and to branch the inner pipes. Such a configuration finds particular application in the form of a manifold, for instance an exhaust manifold of an engine as shown in figure 4. Figure 4 therefore shows an engine 23, the exhaust ports 24 of which are connected to pipe pieces 25,26,27 and 28. These pipe pieces form the branched outer ends of a for instance four-fold configuration of a pipe piece according to the present embodiment which leads to a coupling 29. A small part between coupling 29 and the branching is herein embodied as a pipe according to the present invention. A particularly attractive embodiment results when the separate branched ends of the pipe pieces are encased by a collective casing, which can be formed for instance by a casting. There then also exists the option of providing the casting with fixing means for fixing the whole exhaust manifold onto the engine block, this in one operation. it will be apparent that it is possible to vary in diverse ways from the shown embodiments without departing from the invention.

Claims: CLAIMS 1. Multiple pipe comprising at least two inner pipes lying against each other with a wall piece, characterized in that the inner pipes are enclosed over at least a part of their length by an outer pipe. 2. Multiple pipe as claimed in claim 1, characterized in that at least half the inner surface of the outer pipe is in contact with the outer surface of the inner pipes . 3. Multiple pipe as claimed in claim 1, characterized in that over at least a part of the length of the inner pipes the outer pipe is separated from the inner pipes by a gap. 4. Multiple pipe as claimed in claim 3, characterized in that the gap is filled with insulation material . 5. Multiple pipe as claimed in any of the foregoing claims, characterized in that the periphery of the combination of the inner pipes is substantially round . 6. Multiple pipe as claimed in claim 2, 3, 4 or 5, characterized in that the outer pipe has a round cross-section. 7. Multiple pipe as claimed in any of the foregoing claims, characterized in that both inner pipes have in cross-section the form of a D. 8. Multiple pipe as claimed in any of the claims 1-6, characterized in that the two inner pipes have the shape of a C, that the two inner pipes contact each other and that the inner space between these pipes is filled with a substantially round pipe, wherein the cross-section of each of the two C-shaped pipes equals twice the cross-section of the substantially round pipe. 9. Multiple pipe as claimed in any of the foregoing claims, characterized in that the outer pipe 8 extends over only a part of the length of the inner pipe combination. 10. Multiple pipe as claimed in claim 9, characterized in that over their part which is not covered by the outer pipe the inner pipes are branched so as to form a manifold. 11. Multiple pipe as claimed in claim 10, characterized in that the branched ends of the inner pipes are adapted for connection to a machine. 12. Multiple pipe as claimed in claim 11, characterized in that flanges are mounted on the free ends of the inner pipes for fixing of the pipes to a machine component . 13. Multiple pipe as claimed in claim 11, characterized in that the flanges are combined to form a plate and the plate is connected to an element enclosing the free inner pipes, wherein the element is separated from the pipe pieces by a space. 14. Multiple pipe as claimed in claim 13, characterized in that the element is connected to the outer pipe. 15. Multiple pipe as claimed in claim 11, 12 or 13, characterized in that the plate and the element together form a casting. 16. Multiple pipe as claimed in claim 15, characterized in that the plate, the element and the pipe pieces together form a casting. 17. Multiple pipe as claimed in any of the claims 12-16, characterized in that the multiple pipe, the element and the plate together form an exhaust manifold. 18. Method for manufacturing a multiple pipe comprising at least two inner pipes each fixed against each other with a wall piece, and an outer pipe enclosing the inner pipes, wherein the method comprises the following steps of: - fixing the inner pipes against each other; 9 - decreasing the external diameter of the inner pipes or increasing the internal diameter of the outer pipe; and - sliding the outer pipe over the inner pipes. 19. Method as claimed in claim 18, characterized in that the multiple pipe is then placed in a mould, the inner pipes are filled with a mandrel and the space between the outer pipe and the inner pipes is placed under pressure at the position of the connection of the wall parts between the inner pipes and the outer pipe. 20. Method as claimed in claim 19, characterized in that the space between the outer pipe and the inner pipe is subsequently filled with filler material and then subjected to a bending process. 21. Method as claimed in claim 20, characterized in that the filler material is water and that after introducing the water the water is frozen and the bending process subsequently performed.

Inventors: GROBBENHAAR HERMANUS GERHARDUS, GROBBENHAAR, HERMANUS, GERHARDUS
Applicants: GRAND PRIX SILENCERS BV, GROBBENHAAR HERMANUS GERHARDUS, GRAND PRIX SILENCERS B.V., GROBBENHAAR, HERMANUS, GERHARDUS
Application year: 1998
Main classification: F16L9
IPC codes: F01N7, F16L9