WO2018050952A1

WO2018050952A1 - A method of and an arrangement for fastening a hot article to a cold article

Info

Publication number: WO2018050952A1
Application number: PCT/FI2016/050642
Authority: WO
Inventors: Michele CERNIGOJ; Leonardo GAMBINI; Francesco SALIERNO; Odorico Contento
Original assignee: Wärtsilä Finland Oy
Priority date: 2016-09-16
Filing date: 2016-09-16
Publication date: 2018-03-22
Also published as: KR102134108B1; KR20190039720A; CN109642486B; EP3516185A1; CN109642486A; EP3516185B1

Abstract

The present invention relates to a method of and a means for fastening an exhaust module (14) of a multi-cylinder internal combustion engine to its support (26) such that the mechanical stresses caused by the thermal expansion of the exhaust module to its feet (24) and the support (26) are avoided by arranging the feet (24) of the exhaust 5 module (14) slide on the support surface (28).

Description

A method of and an arrangement for fastening a hot article to a cold article

Technical field of the invention

(001 ) The present invention relates to a method of fastening a first article on a second article in accordance with the preamble of claim 1 . The invention also relates to an arrangement for fastening an exhaust module of an internal combustion engine to a support arranged in connection with the internal combustion engine in accordance with the preamble of claim 8. More specifically the present invention discusses the method of and the arrangement for fastening an exhaust module on its support in an internal combustion engine. The present invention also relates to the novel exhaust module and the novel support as well as the internal combustion engine.

Background of the invention

(002) The engine rooms of marine vessels are usually kept as small as possible to save space for more profitable use. Therefore it is desirable to fit the engines and the auxiliaries, such as turbochargers, in as compact manner as possible. In V- type engines, each bank of the engine is often provided with a turbocharger of its own, and positioning of the turbochargers may therefore be problematic. Turbochargers that are normally used in connection with marine engines have their turbine inlet in radial direction, whereby, to make the installation simple, the turbochargers are arranged such that their axis is in a plane at right angles to the plane of the axis of the engine, whereby the exhaust gases may be brought from the engine banks by means of straight exhaust manifolds to the exhaust inlets of the turbochargers. This kind of an installation means that the turbochargers are positioned with their shafts one after another at an end of the engine transverse to the vertical axial plane of the engine. However, now that the combined axial length of two turbochargers is more than the width of the V- engine, such a turbocharger installation takes additional space at the sides of the engine.

(003) To correct the above problem, an exhaust module has been designed. The exhaust module is a device between the exhaust manifolds arranged in the longitudinal direction of the engine and the turbine inlets of the turbochargers. By means of the exhaust module the flow directions of the exhaust gases are turned from the longitudinal direction of the engine to a transverse direction such that the turbochargers may be positioned with their axes parallel with the axis of the engine. Thus by means of the exhaust module the turbochargers may be fitted side by side within the width dimension of the V- type engine. The exhaust module has been discussed in more detail in WO-A2- 2013/030445, which is incorporated herein by reference.

(004) However, now that the exhaust module is working merely with high temperature exhaust gases, the fixing of the exhaust module to its support is challenging due, mostly, to thermal expansion of the exhaust module itself. Naturally, also external loads, like thermal expansion of the members coupled to the exhaust module, are subjected to the exhaust module but such may be absorbed by flexible bellows- type pipe joints.

(005) The thermal expansion of the exhaust module could be, in a way, fought, by means of fixing the exhaust module on its support by means of standard fastening bolts, whereby high stress would be subjected to all members of the connection, i.e. the exhaust module, the fastening bolts and the support. Such a high stress could result in fatigue of one or more fastening bolts, for instance, whereby there is a risk of loosening of the exhaust module that would easily get even worse due to the vibrations of the engine. Another way of taking into account the thermal expansion of the exhaust module would be to leave the exhaust module for the bellows- type pipe joints to carry, but such is, in practice, an impossible choice as the bellows- type pipe joints are, by nature, flexible and not designed to carry any load.

(006) In view of the above, an object of the present invention is to provide an improved way of fastening the exhaust module of a multi-cylinder internal combustion engine, where the cylinders are arranged in a V-configuration, on its support.

(007) Another object of the present invention is to provide such an improved way of fastening the exhaust module on its support that the exhaust module may both freely expand thermally and the exhaust module be still securely fastened on its support.

(008) Yet another object of the present invention is to provide such an improved way of fastening the exhaust module on its support that the free thermal expansion of the exhaust module is based on a sliding connection between the exhaust module and its support.

(009) A further object of the present invention is to provide such an improved way of fastening the exhaust module on its support that the arrangement used for fastening the exhaust module on its support has a specific design for allowing thermal movements of the exhaust module. Disclosure of the invention

(010) The objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

(01 1 ) In accordance with an embodiment of the present invention a method of fastening a first article on a second article, the first article being at a temperature higher than the second article, the first article being provided with a plurality of feet, each foot having a hole for a fastening bolt and a first surface facing the second article, the second article being provided with threaded holes for the fastening bolts and second surfaces facing the feet of the first article, the method comprising by the steps of

1 . providing both the first article and the second article with means for positioning the first article on the second article,

2. providing low-friction means between the feet and the second article,

3. mounting the first article on the second article such that the positioning means match one another, and

4. tightening the fastening bolts such that the feet of the first article are allowed to slide on second surfaces with the assistance of the low-friction means, while the first article is heated.

(012) In accordance with an embodiment of the present invention an arrangement for fastening an exhaust module of an internal combustion engine to a support arranged in connection with the internal combustion engine, the exhaust module having feet adapted to rest on the support, the feet having holes for fastening bolts and foot surfaces, when in use, facing the support; the support having threaded holes for the fastening bolts and support surfaces, when in use, facing the foot surfaces, wherein a low-friction surface is provided between the support and at least all but one of the feet of the exhaust module.

(013) In accordance with an embodiment of the present invention an exhaust module for a multi-cylinder internal combustion engine, in which engine the cylinders are arranged in a V-configuration, the exhaust module comprising a first exhaust duct for connecting a first exhaust manifold of the engine to the turbine inlet of a first turbocharger, a second exhaust duct for connecting a second exhaust manifold of the engine to the turbine inlet of a second turbocharger, and feet for fastening the exhaust module on a support, the feet having holes for fastening bolts and foot surfaces facing, when in use, the support, wherein at least all but one of the foot surfaces is machined or coated to have low-friction properties. (014) In accordance with an embodiment of the present invention a support for an exhaust module for a multi-cylinder internal combustion engine, in which engine the cylinders are arranged in a V-configuration, the support having threaded holes for fastening bolts, wherein the support has surfaces round the threaded holes, at least all but one of the surfaces round the threaded holes being machined or coated to have low- friction properties.

Brief description of the drawings

(015) In the following the present invention will be explained in more detail with reference to the accompanying schematic drawings of which

Figure 1 illustrates a prior art internal combustion engine in accordance with WO-A2- 2013/030445,

Figure 2 illustrates a prior art exhaust module in accordance with WO-A2-2013/030445,

Figure 3 illustrates a partial cross section of a front view of the exhaust module - support combination in accordance with a first preferred embodiment of the present invention,

Figure 4 illustrates a partial cross section of a front view of the exhaust module - support combination in accordance with a second preferred embodiment of the present invention,

Figure 5 illustrates a top view of a partial section of the support in accordance with a first preferred embodiment of the present invention, and

Figure 6 illustrates a cross sectional view of the arrangement for fastening the exhaust module on its support.

Detailed description of the invention

(016) Figure 1 illustrates a prior art internal combustion engine 2 having its cylinders 4 in V- configuration, i.e. arranged in two banks, a first bank 6 and a second bank 8. The exhaust gases of the first and the second banks 6 and 8 are collected in a first exhaust manifold 10 and in a second exhaust manifold 12. The first and the second exhaust manifolds 10 and 12 take the exhaust gases to an exhaust module 14 (discussed in more detail in Figure 2) used for connecting the first and the second exhaust manifolds 10 and 12 to a first turbocharger 16 and a second turbocharger 18. The internal combustion engine may be, for instance, a main or an auxiliary engine of a ship, or an engine that is used for producing electricity at a power plant. (017) Figure 2 illustrates an exemplary exhaust module 14, which may be provided with the improvements in accordance with the various embodiments or variations of the present invention. The exhaust module 14 comprises two exhaust ducts 20 and 22, the connection for air by pass system and the connection for exhaust waste gate system that are integrated into the same module 14. The exhaust module 14 is, preferably, made as a single-piece casting. The material of the exhaust module 14 may be, for example, cast iron. The first exhaust duct 20 is provided for connecting a first exhaust manifold (10 in Fig. 1 ) of a first bank of an engine to a first turbocharger. The second exhaust duct 22 is provided for connecting a second exhaust manifold (12 in Fig. 1 ) of a second bank of the engine to a second turbocharger. The first exhaust duct 20 crosses the second exhaust duct 22, both the ducts (20 and 22) are connected internally with the connection for air by-pass and exhaust waste gate. The exhaust module 14 may be located at one end of the engine (as shown in Figure 1 ) and fastened, for example, to a suitable support, for instance a turbocharger bracket (shown in Figures 3, 4 and 5) by means of a plurality of (normally four) feet 24.

(018) The first exhaust duct 20 of the exhaust module 14 is arranged to receive hot exhaust gases from the first exhaust manifold through an inlet 20a. The inlet 20a may be connected to the first exhaust manifold either directly or via an intermediate duct, for instance a bellows- type duct section. The second exhaust duct 22 of the exhaust module 14 is arranged to receive hot exhaust gases from the second exhaust manifold through an inlet 22a. The inlet 22a may be connected to the second exhaust manifold either directly or via an intermediate duct, for instance a bellows- type duct section. The other end of the first exhaust duct 20 is arranged to introduce the hot exhaust gases into the turbine of the first turbocharger via an outlet 20b. The other end of the second exhaust duct 22 is arranged to introduce hot exhaust gases into the turbine of the second turbocharger via an outlet 22b. The outlet 20b of the first exhaust duct 20 is preferably at an angle of 70 - 1 10 degrees in relation to the inlet 20a of the first exhaust duct 20, and the outlet 22b of the second exhaust duct 6 is at an angle of 70 - 1 10 degrees in relation to the inlet 22a of the second exhaust duct 22 in the horizontal plane.

(019) The problem the present invention is solving relates to the fact that, as hot exhaust gases pass the exhaust module, the exhaust module is running hot, the temperature thereof may be as high as 550 - 600°C in the upper part and 300 - 350°C in the lower part, and, since the exhaust module has to be fastened to a support, which is, by no means, subjected to corresponding high temperatures, but is, most probably, close to the engine block temperature of 80 - 90°C, the differences in thermal expansion of the two elements require that the fastening of the exhaust module, i.e. a hot article, to a support, i.e. a cold article, has to be considered in detail in order to avoid stresses subjected to the two elements. As the engine may be run in different load conditions, it should be understood that the temperature of the exhaust gases fluctuate in direct proportion to the load, whereby also the thermal expansion of the exhaust module changes in direct proportion to the engine load.

(020) Figure 3 illustrates as a partial cross section the front view of the exhaust module - support combination (i.e. a hot article - a cold article combination) of the first preferred embodiment of the present invention from the direction the hot exhaust gases enter the inlets of the exhaust ducts. The feet 24 of the exhaust module 14 are resting on a suitable support 26, the support being, preferably, but not necessarily, the turbocharger bracket. In accordance with a first preferred embodiment of the present invention the support 26 is a planar member having a surface 28 on which the feet 24 of the exhaust module 14 are arranged to rest. The feet 24 are provided with holes 30 (here shown by their centerlines) for the fastening bolts (shown and discussed in more detail in Figure 6). The support 26 is provided with threaded holes (shown in Fig. 6) for fastening bolts and a first means 32 for positioning (from now on referred as 'the first positioning means') the exhaust module on the support 26, which, in this variation of the first preferred embodiment of the present invention, is a pin-like member extending upwardly from the surface 28 of the support 26 and, preferably but not necessarily, arranged, in this cross section, half-way between the threaded holes. For cooperating with the first positioning means 32, there is a second means 34 for positioning (from now on referred as 'the second positioning means') the exhaust module on the support 26, i.e. a blind opening matching the cross sectional shape of the first positioning means, provided at the bottom of the exhaust module 14, preferably in a protrusion 36 extending to a level of such surfaces 38 of the feet 24 that rest on the surface 28 of the support 26. In accordance with another variation of the first preferred embodiment of the present invention, the first positioning means is a blind opening in the surface 28 of the support 26, whereby the second positioning means is a pin-like member having a cross sectional shape matching to that of the first positioning means and extending from the protrusion arranged to the bottom of the exhaust module. In accordance with yet another variation of the first preferred embodiment of the present invention, the first positioning means is a blind opening in the surface 28 of the support 26, whereby the second positioning means is a pin-like member having a cross sectional shape matching to that of the first positioning means and extending (without protrusion) from the bottom of the exhaust module. (021 ) The purpose of the first and the second positioning means 32 and 34 is to prevent unexpected movements and sliding of the exhaust module due to thermal expansion and external loads. In other words, their purpose is to maintain the overall position of the exhaust module 14 in relation to the support and on the support 26 such that, in accordance with the present invention, the thermal expansion of the exhaust module 14 makes the feet 24 of the exhaust module 14 slide on the surface 28 of the support 26 in predetermined directions away of or towards the positioning means, depending on the direction of the change in the temperature of the exhaust module 14.

(022) The sliding of the exhaust module 14 on the support 26 is, when prior art constructions are used, cumbersome, as both the exhaust module 14 and the support 26 are normally made of cast iron. In such circumstances, the coefficient of friction between the two machine elements is of the order of 0.5, which means, in practice, that the fastening bolts have to be left rather loose to allow any sliding movement between the surfaces 38 of the feet 24 and the support 26. If tightened to a higher torque, the bolts press the high-friction surfaces of the exhaust module and the support so tightly together that the surfaces cannot slide at all, but subject both the exhaust module, especially the feet thereof, and the support to a considerable stress. To be able to tighten the fastening bolts to a torque sufficient for reliable fastening, and still allowing the counter surfaces 38 and 28 of the exhaust module and the support slide in relation to one another, the coefficient of friction between the surfaces has to be reduced. There is a number of ways the frictional properties between the surfaces may be reduced, i.e. at least one of the counter surfaces is provided to have low-friction properties such that the coefficient of friction between the counter surfaces is 0.2 or less.

1 . To machine at least one of the counter surfaces of the exhaust module and the support to have a low-friction surface.

2. To provide at least one of the counter surfaces of the exhaust module and the support with a low-friction coating. For an applicable low-friction coating various metal and ceramic materials may be used. An optional treatment is, for example, phosphating the surface with manganese (Fe/Mnph/g/5/T4 in accordance with EN-12476).

3. To provide at least one shim with at least one low-friction surface between the counter surfaces of the exhaust module and the support. The at least one shim may be either manufactured of or coated with a material having an appropriate low-friction surface. Preferred options for the shim material are stainless steel and ceramics. The thickness of the shim is of the order of 2 to 10 mm. In accordance with an exemplary embodiment a standard AISI 304 steel sheet (in accordance with EN 10028) that is cold rolled to have hardness of -170HV1 and bright surface is used. However, the mechanical properties of the shim are less relevant due to the lower contact pressure. The main thing in lowering the friction is to avoid the contact of two identical materials, because they have a higher coefficient of friction compared with two different materials.

4. To provide the low-friction surface with hardness equal or higher than that of cast iron to prevent the irregular surface of the counter surface penetrating the low-friction surface.

As to the low friction surfaces, performed tests have shown that a coefficient of friction of the order of 0.2 or less is sufficient for allowing both the relative movement between the counter surfaces and high enough tightening torque for the fastening bolts.

(023) Figure 4 illustrates as a partial cross section the front view of the exhaust module - support combination (i.e. a hot article - a cold article combination) of the second preferred embodiment of the present invention from the direction the hot exhaust gases enter the inlets of the exhaust ducts. The feet 24 of the exhaust module 14 are resting on a suitable support 26, the support 26 being, preferably, but not necessarily, the turbocharger bracket. In accordance with a second preferred embodiment of the present invention the support 26 has protrusions or beds 40 raised above its planar surface 28, for simplifying and reducing the possible machining operation (no need to machine the entire top surface of the support), such that the feet 24 of the exhaust module 14 are arranged to rest on the surfaces 42 of the beds 40. The feet 24 are provided with holes 30 (here shown by their centerlines) for the fastening bolts (shown and discussed in more detail in Figure 6) and the beds 40 (and support) with corresponding threaded holes (shown in Fig. 6) for the fastening bolts. The support 26 is provided, in addition to the beds 40 and the threaded holes, also with a protrusion or bed 44 for a first positioning means 32, which, in this variation of the present invention, is a pin-like member extending upwardly from the surface of the protrusion or bed 44 and, preferably but not necessarily, arranged, in this cross section, half-way between the threaded holes (the positioning means is discussed in more detail in connection with Figure 5). For the first positioning means 32, there is a second positioning means 34, i.e. a blind opening having a cross sectional shape matching to that of the first positioning means 32, provided at the bottom of the exhaust module 14, preferably in a protrusion 36 extending to a level of such surfaces 38 of the feet that rest on the bed surfaces 42 of the support 26. In accordance with another variation of the present invention, the first positioning means is a blind opening in the surface of the support 26, whereby the second positioning means is a pinlike member having a cross sectional shape matching to that of the first positioning means and extending from the protrusion arranged to the bottom of the exhaust module. In accordance with yet another variation of the present invention, the first positioning means is a blind opening in the surface of the support 26, whereby the second positioning means is a pin-like member having a cross sectional shape matching to that of the first positioning means and extending (without protrusion) from the bottom of the exhaust module.

(024) Figure 5 illustrates a partial section of the support 26 from above showing all four threaded holes 46 for the fastening bolts and the first positioning means 32. In accordance with Figure 5, the positioning means 32 is positioned to a point where the diagonals of a rectangle drawn via the centers of the threaded holes 46 intersect one another. This is the optimal location for the positioning means, as the positioning means maintain the exhaust module and its support in place irrespective of thermal cycles, and now that the first positioning means 32 is at the center of the threaded holes 46, the effect of the thermal expansion of the exhaust module is equal at each threaded hole 46, whereby each foot of the exhaust module moves the same distance away of or towards the first positioning means 32. This kind of an arrangement is the best in view of the stress subjected to the members of the fastening arrangement, but if there is no need for taking into account such a stress, the positioning means may be located in any suitable location between the exhaust module and its support.

(025) An option is to use one of the fastening bolts and a threaded hole in the support in which the fastening bolt in question is threaded into as the first positioning means and the hole in the foot as the second positioning means. The hole functioning as the second positioning means has a diameter smaller than that in the rest of the feet. When the hole functions as the second positioning means its diameter, preferably, but not necessarily, matches to that of the fastening bolt functioning as the first positioning means. When one of the fastening bolts functions as the first positioning means, the bolt may be shorter than the rest of the fastening bolts, as there is no need for the bolt to bend and to allow any lateral movement. When one of the fastening bolts is used as the first positioning means, at least the foot surfaces 38 (see Figure 3) and/or their counter surfaces 40 on the support 26 at a distance from the positioning means are provided with low-friction properties for allowing the feet to slide on the support. Therefore, there is a need to machine or coat at least all but one of the foot surfaces and/or of their counter surfaces to have proper low-friction properties between the exhaust module and its support. Naturally, it is also possible that the foot surface and/or its counter surface on the support immediately round the positioning means is coated or machined, though there is, in practice, no noticeable sliding between the surfaces.

(026) The numeral 40 referring to an area defined by a broken circle may be considered to represent, in case of the first preferred embodiment of Figure 3, a low-friction surface machined and/or coated to the support surface 28 for allowing the foot to slide easier on the support 28, or in case of the second preferred embodiment of Figure 4, a protrusion or bed raised from the surface 28 of the support 26 and/or the low-friction surface machined and/or coated on the bed. The numeral 44 referring to yet another broken circle may be considered to represent a protrusion or bed raised from the surface 28 of the support 26 for the first positioning means 32 as shown also in Figure 4.

(027) Figure 6 illustrates the fastening arrangement used for attaching the exhaust module 14 on the support 26. The same principle may be applied in both the first and the second embodiments of the present invention. In accordance with Figure 6, for fastening the exhaust module 14 on the support 26 a fastening bolt 48 is first provided with a lengthy sleeve 50, secondly (after the exhaust module is placed on the support such that the positioning means are matched to one another and the holes 30 of the feet 24 are aligned with the threaded holes 46 of the support 26) the bolt is inserted in the hole 30 in the foot 24 of the exhaust module 14, thirdly the bolt 48 is threaded in the threaded blind hole 46 in the support 26 (either in the bed of the support or in the planar support) and tightened to a predetermined torque to secure the exhaust module on the support firmly, but also such that the foot 24 of the module 14 may slide along the surface 28 or 40 of the support 26.

(028) Another option for fastening the exhaust module on the support is a set of headless bolts threaded first in the threaded blind holes 46 in the support 26. In such a case, the shims 54 may be inserted next, if needed, on the bolts, whereafter the exhaust module is installed with its feet round the headless bolts, then sleeves are inserted on the bolts and finally nuts are threaded on the threaded end of the headless bolts down against the sleeves. The positioning means will, in this case, be matched more or less automatically.

(029) As to the bolts used in fastening the exhaust module on the support, in accordance with an example, bolts of 8.8 Grade are used. The bolts are tightened with a medium force such that the tensile stress on the bolt sections having the smallest diameter equals to about ½ of the yield stress. Such a stress level results in that the exhaust module is secured with reasonable safety against sliding due to longitudinal force and in that there is enough safety margin in view of the bending stress subjected to the bolt by thermal displacement. As to the sleeves, they may, for example, be made of standard (S355) steel, as their cross sectional area is larger than that of the bolts and thus they are not subjected to any particular stress.

(030) Figure 6 shows, with dashed lines, an insulation cap 56 provided on the bolt for insulating the bolt and the sleeve from the hot environment of exhaust area for preventing material properties decay. Figure 6 also shows that the diameter d of the bolt 48, or, preferably, but not necessarily, of an enlarged section thereof, is smaller than that D of the hole 30 in the foot 24. By arranging the gap between the bolt and the wall of the hole equaling to (D-d)/2 wider than the maximal thermal expansion at the distance of the hole 30 from the positioning means it is ensured that the foot 24 may slide along the surface 28 or 40 of the support 26 without the hole wall and the bolt getting into contact with each other. In other words, the gap absorbs the thermal expansion. As, in any case, there is relative movement between the hole 30 and the bolt 48, the bolt 48 is clearly longer than would be needed in traditional bolt fastening. The bolt 48 is provided with a sleeve 50 that extends between the head 52 of the bolt 48 and the foot 24, pressing the foot 24 against the support 26. By arranging the sleeve 50 on the bolt 48 the length of the bolt is increased to allow the relative movement between the bolt 48 and the foot 24 to be spread over the length of the bolt 48, as it is the head 52 of the bolt 48 that is moved by means of the sleeve 50 supported on the foot 24 and, thus, tending to move therewith. Thus, such a relative movement is absorbed by the bolt 48, and possibly by the sleeve 50, by bending slightly. Preferably, but not necessarily, at about a distance of one half of the length of the sleeve measured from the head of the bolt, the bolt is provided with an enlarged section the diameter of which corresponds to the inner diameter of the sleeve. Such a design forces both the bolt and the sleeve to bend together. The longer the bolt and the sleeve are, the less the bolt or they both need to bend to allow a certain amount of movement in the foot.

(031 ) Figure 6 also illustrates a shim 54 between the foot 24 and the support 26. As was already discussed above, the shim has at least one low-friction surface whereby the surface facing the low-friction surface of the shim slides easily along the shim surface. The shim may be made of stainless steel or ceramics, the frictional properties of which are good for low-friction purposes. Another option is to arrange two shims one above the other, whereby it is the shim surfaces that slide in relation to one another. (032) As a further embodiment of the present invention an optional construction for the sleeve may be mentioned. The sleeve may be replaced with a vertical hollow extension of the foot having a height corresponding to that of the sleeve. Such an extension may be a unitary part of the exhaust module casting or a sleeve-like element fastened, for example, welded on the foot. The diameter of the extension is somewhat longer than that of the bolt whereby the bolt may bend inside the extension.

(033) It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims.

Claims

1 . A method of fastening a first article (14) on a second article (26), the first article (14) being at a temperature higher than the second article (26), the first article (14) being provided with a plurality of feet (24), each foot (24) having a hole (30) for a fastening bolt (48) and a first surface (38) facing the second article (26), the second article (26) being provided with threaded holes (46) for the fastening bolts (48) and second surfaces (28) facing the feet (24) of the first article (14), the method being characterized by the steps of

a) providing both the first article (14) and the second article (26) with means for positioning the first article (14) on the second article (26), b) providing low-friction means (54) between the feet (24) and the second article (26),

c) mounting the first article (14) on the second article (26) such that the positioning means match one another,

d) tightening the fastening bolts (48) such that the feet (24) of the first article (14) are allowed to slide on second surfaces (28) with the assistance of the low-friction means, while the first article (14) is heated.

2. The method as recited in claim 1 , characterized by, after step c),

i. inserting fastening bolts (48) to the holes (30) in the feet (24), and ii. threading the fastening bolts (48) to the threaded holes (46) in the second article (26).

3. The method as recited in claim 1 , characterized by, before step c),

i. inserting the fastening bolts to the threaded holes (46) in the second article (26), and

ii. threading the fastening bolts to the threaded holes (46), whereby the fastening bolts are headless bolts.

4. The method as recited in claim 2 or 3, characterized by, prior to step i., inserting a sleeve (50) on each fastening bolt (48).

5. The method as recited in claim 1 , characterized by, in step b) positioning a shim (54) with at least one low-friction surface between the feet (24) of the first article (14) and the second article (26).

6. The method as recited in claim 1 , characterized by, in step b), machining or coating at least one of the first surface (38) and the second surface (28) for reducing its frictional properties.

7. The method as recited in claim 1 , characterized in that the first article is an exhaust module and that the second article is a support (26) for the exhaust module (14).

8. An arrangement for fastening an exhaust module of an internal combustion engine to a support arranged in connection with the internal combustion engine, the exhaust module (14) having feet (24) adapted to rest on the support (26), the feet (24) having holes (30) for fastening bolts (48) and foot surfaces (38), when in use, facing the support (26); the support (26) having threaded holes (46) for the fastening bolts (48) and support surfaces (28), when in use, facing the foot surfaces (38), characterized in a low-friction surface provided between the support (26) and at least all but one of the feet (24) of the exhaust module (14).

9. The arrangement as recited in claim 8, characterized in that the low-friction surface is a machined or coated foot surface (38) and/or a machined or coated support surface (28).

10. The arrangement as recited in claim 8, characterized in shims (54) arranged between the support (26) and at least all but one of the feet (24) of the exhaust module (14), the shims (54) being provided with the low-friction surface.

1 1 . The arrangement as recited in any one of the preceding claims 8 - 10, characterized in that the support (26) is provided with a first positioning means (32) and the exhaust module (14) is provided with a second positioning means (34), the first and the second positioning means (32, 34) being matched, when the exhaust module (14) is installed on the support (26), to one another.

12. The arrangement as recited in claim 1 1 , characterized in that the first positioning means is a pin-like member (32) or a blind opening.

13. The arrangement as recited in claim 1 1 , characterized in that the second positioning means is a pin-like member or a blind opening (34).

14. The arrangement as recited in claim 1 1 , characterized in that the first positioning means is one of the fastening bolts (48) threaded in one of the threaded holes (46), and the second positioning means is a hole in one of the feet (24).

15. The arrangement as recited in any one of the preceding claims 8 - 14, characterized in that at least all but one of the fastening bolts (48) has a diameter smaller than that of the holes (30) in the feet (24), whereby a gap is left between the fastening bolt (48) and the hole (30), the gap absorbing the thermal expansion of the exhaust module (14).

16. The arrangement as recited in any one of the preceding claims 8 - 15, characterized in that at least all but one of the fastening bolts (48) are provided with a sleeve (50) adapted to be positioned on the foot (24) when installing the fastening bolt (48) in the hole (30) in the foot (24).

17. The arrangement as recited in any one of the preceding claims 8 - 15, characterized in that at least all but one of the fastening bolts (48)are provided with a sleeve (50) adapted to be positioned on the foot (24) after the exhaust module (14) is installed on the support (26).

18. An exhaust module (14) for a multi-cylinder internal combustion engine (2), in which engine (2) the cylinders (4) are arranged in a V-configuration, the exhaust module (14) comprising a first exhaust duct (20) for connecting a first exhaust manifold (10) of the engine (2) to the turbine inlet of a first turbocharger (16), a second exhaust duct (22) for connecting a second exhaust manifold (12) of the engine (2) to the turbine inlet of a second turbocharger (18), and feet (24) for fastening the exhaust module (14) on a support (26), the feet (24) having holes (30) for fastening bolts (48) and foot surfaces (38) facing, when in use, the support (26), characterized in that at least all but one of the foot surfaces (38) is machined or coated to have low-friction properties.

19. The exhaust module as recited in claim 18, characterized in that the exhaust module (14) is provided with a positioning means (34) defining the position of the exhaust module (14) on the support (26).

20. The exhaust module as recited in claim 19, characterized in that the positioning means (34) is a pin-like member or a blind opening.

21 . The exhaust module as recited in claim 19, characterized in that the positioning means (34) is a hole in one of the feet (24).

22. A support for an exhaust module (14) for a multi-cylinder internal combustion engine (2), in which engine (2) the cylinders (4) are arranged in a V-configuration, the support (14) having threaded holes (46) for fastening bolts, characterized in that the support (26) has surfaces (40) round the threaded holes (46), at least all but one of the surfaces (40) round the threaded holes (46) being machined or coated to have low-friction properties.

23. The support as recited in claim 22, characterized in that the support (26) is provided with a first positioning means (32) defining the position of the exhaust module (14), when in use, (14) on the support (26).

24. The support as recited in claim 23, characterized in that the first positioning means (32) is a pin-like member or a blind opening.

25. The support as recited in claim 23, characterized in that the first positioning means is one of the threaded holes (46).

26. An internal combustion engine (2) comprising a plurality of cylinders (4) that are arranged in a first bank (6) and a second bank (8), a first exhaust manifold (10) for receiving exhaust gases from the cylinders (4) of the first bank (6), a second exhaust manifold (12) for receiving exhaust gases from the cylinders of the second bank (8), a first turbocharger (16) that is operated on the exhaust gases from the cylinders (4) of the first bank (6) of the engine (2), and a second turbocharger (18) that is operated on the exhaust gases from the cylinders of the second bank (8) of the engine (2), characterized in that the engine (2) comprises at least one of an arrangement in accordance with any one of claims 8 - 17, an exhaust module (14) in accordance with any one of claims 18 - 20, and a support (26) in accordance with any one of claims 21 - 25.