FR3081919A1 - EXHAUST SYSTEM AND ASSEMBLY WITH A HEAT-PROTECTED ACTUATOR, MANUFACTURING METHOD AND USE THEREOF - Google Patents

Abstract

The assembly (1) comprises: - a member (29) comprising a circulation channel (30) of a heat transfer fluid, having an external surface (41) cooled by thermal contact with the heat transfer fluid; - an actuator (25); - a cover (55) defining with the cooled external surface (41) a closed volume (57) in which the actuator (25) is housed; - a foamed material (59), at least partially filling the closed volume (57) around the actuator (25).

Description

Assembly and exhaust line with an actuator protected from heat, manufacturing process and corresponding use

The present invention generally relates to the protection of electric actuators against heat.

Certain motor vehicle exhaust lines are equipped with an assembly comprising a heat recovery exchanger. A valve directs the exhaust gases either to the heat exchanger or to a bypass duct. It is possible to use an electric motor directly mounted at the end of the drive shaft to move the valve flap. In this case, it is advantageous to provide a member called a "water box", between the actuator and the valve of the heat recovery device. This member includes a circulation channel for a heat transfer fluid, and protects the actuator from the temperature of the exhaust thanks to the passage of the heat transfer fluid. Since the fluid always has a temperature below the maximum temperature of the actuator, it is no longer sensitive to the temperature of the exhaust.

When the assembly is placed in a tunnel in the floor of the vehicle, the temperature of the air surrounding the actuator is generally that of the tunnel. This temperature is usually below 120 ° C, which is not a problem for the actuator.

On the other hand, in certain extreme cases, the temperature of the tunnel can reach 200 ° C temporarily. Exposure to this temperature is short enough, on the order of 2 minutes, but long enough for the actuator to be damaged. In fact, the electronic equipment inside the actuator cannot withstand temperatures exceeding 140 to 160 ° C. Certain plastic components cannot withstand temperatures exceeding 140 ° C, or even 120 ° C for certain versions having inexpensive material compositions.

In this context, the invention aims to provide an assembly equipped with an actuator, which can be placed in the tunnel of a motor vehicle without the actuator being damaged.

To this end, the invention relates according to a first aspect to a set comprising:

- a member comprising a circulation channel for a heat transfer fluid, having an external surface cooled by thermal contact with the heat transfer fluid;

- an actuator;

- a cover defining with the cooled external surface a closed volume in which the actuator is housed;

- a foamed material, filling at least partially the closed volume around the actuator.

The cover and the foamed material increase the thermal inertia of the assembly relative to the outside temperature.

Furthermore, it is possible to play on the thermal conduction characteristics of the foamed material to take advantage of the presence of a cooled surface and / or to thermally isolate the actuator from the surrounding atmosphere.

It is possible to provide that at least part of the foamed material has good thermal conduction and creates thermal contact between the actuator and the cooled external surface of the member.

In addition or instead, it is possible to provide that at least part of the foamed material has poor thermal conduction and thermally isolates the actuator from the outside atmosphere.

The properties of the foamed material can thus be easily adapted according to the application case to be treated, to favor thermal transfers to the cooled external surface or thermal insulation.

The use of a foamed material is particularly advantageous since it can be injected into a mold having the desired shape, and thus adapt to the complex shapes of the actuator and of the cooled external surface. In particular, the cooled external surface generally has reliefs and concavities. The foamed material can be injected with a shape which is the negative of the shape of the cooled outer surface, thus filling the hollows in which the dirt is likely to accumulate.

Simple insulation, using a conventional fiberglass commonly used in exhaust, would not be suitable because its formatting is complex and expensive. It is only suitable for use with a small thickness variation.

In addition, the hull creates protection against external aggressions such as tree branches, stones, etc.

The set may also have one or more of the characteristics below, individually or in any technically possible combination:

- an external part of the foamed material is in contact with the cover and has a thermal conductivity of less than 0.2 W / m. ° K;

- an internal part of the foamed material is in contact with the cooled external surface and has a thermal conductivity greater than 0.8 W / m. ° K;

- The internal part of the foamed material comprises a foam and an additive of high thermal conductivity dispersed in the foam;

- the actuator comprises an external envelope in direct contact with the cooled external surface;

- The cooled external surface has concave zones towards said closed volume, the foamed material filling at least some of the concave zones;

- the set includes:

* a heat exchanger having an exhaust gas circulation side and a circulation side of the heat transfer fluid;

* a bypass duct of the heat exchanger;

* a valve configured to selectively direct the exhaust gases either to the heat exchanger or to the bypass duct, the valve having a shutter and a shutter drive shaft extending in an axial direction, the actuator being configured by driving the drive shaft;

* the circulation channel of the organ fluidly communicating with the circulation side of the heat transfer fluid, the organ being arranged to cool the drive shaft;

- the member forms a screen interposed axially between the heat exchanger and the actuator.

According to a second aspect, the invention relates to a motor vehicle comprising a floor in which a tunnel is formed, and an exhaust line partially housed in the tunnel, the exhaust line comprising an assembly having the above characteristics, at least the actuator and the cover being housed in the tunnel.

According to a third aspect, the invention relates to a method for manufacturing an assembly having the above characteristics, comprising a step during which at least part of the foamed material is injected into the cover.

According to a fourth aspect, the invention relates to the use of the hood and of the foamed material in the assembly of a vehicle having the above characteristics, to prevent the actuator from reaching a temperature higher than 110 ° C., when the vehicle undergoes the following life situation:

- driving at a speed greater than 100 km / h on average for at least 15 minutes;

- immediately after, complete stop of the vehicle.

Other characteristics and advantages will emerge from the detailed description which is given below, for information and in no way limitative, with reference to the appended figures, among which:

- Figure 1 is a is a simplified schematic representation of an exhaust line equipped with an assembly according to the invention;

- Figure 2 is a perspective view of the assembly of Figure 1;

- Figure 3 is a perspective view similar to that of Figure 2, the cover not being shown and the actuator appearing transparently through the foamed material;

- Figure 4 is a perspective view similar to that of Figure 2, the cover and the foamed material not being shown;

- Figure 5 is an axial sectional view showing the flap, the drive shaft, the actuator and the water box cooling the drive shaft;

- Figure 6 is a simplified schematic representation, in axial section, of the actuator, the foamed material, the shell and the upper half of the water box of all of Figures 2 to 4;

- Figure 7 is an exploded perspective view of the cover and the foamed material of all of Figures 2 to 4; and

- Figure 8 is a simplified schematic representation, from the side, of all of Figures 2 to 4 housed in the tunnel of the floor of a motor vehicle.

The assembly 1, in the example shown in FIGS. 1 to 8, is intended to be integrated into an exhaust line 2 of a vehicle, in particular of a motor vehicle such as a car or a truck, as shown in Figure 1.

The assembly 1 in this case has at least one exhaust gas inlet 3 and an exhaust gas outlet 5.

The exhaust gas inlet 3 is fluidly connected to a manifold C, collecting the exhaust gases leaving the combustion chambers of the vehicle engine M. Typically, other equipment such as a turbo-compressor and one or more pollution control devices are interposed between the manifold C and the exhaust gas inlet 3.

The exhaust gas outlet 5 communicates fluidly with a cannula A through which the clean-up exhaust gases are released into the atmosphere. Typically, other equipment such as one or more silencers and one or more pollution control devices are interposed between the cannula A and the exhaust gas outlet 5.

Furthermore, the assembly 1 comprises a heat exchanger 7, having a side G for circulation of the exhaust gases and a side F for circulation of a heat transfer fluid (FIG. 1).

The exhaust gases and the heat transfer fluid are in thermal contact with each other in the heat exchanger 7, the exhaust gases yielding part of their heat energy to the heat transfer fluid.

The heat transfer fluid is of any suitable type. For example, the heat transfer fluid is water, possibly containing additives such as antifreeze products, in particular antifreeze products typically comprising glycol.

The side G of the exhaust gas circulation has an EG exchanger inlet connected to the exhaust gas inlet 3 and an SG exchanger outlet connected to the exhaust gas outlet 5 (FIG. 1).

The side F of circulation of the coolant has a coolant inlet 9 and a coolant outlet 11 (Figure 1).

The assembly 1 also includes a bypass duct 13 of the heat exchanger 7.

The bypass duct 13 defines a passage path for the exhaust gases from the exhaust gas inlet 3 to the exhaust gas outlet 5 by bypassing the heat exchanger 7. This is understood to mean that the exhaust gases passing through the bypass duct 13 flow directly from the inlet 3 to the outlet 5 without passing through the heat exchanger 7.

The assembly 1 also includes a valve 15 configured to selectively direct the exhaust gases either to the heat exchanger 7 or to the bypass duct 13.

The valve 15 regulates the quantities of exhaust gas flowing respectively through the heat exchanger 7 and through the bypass duct 13 (Figure 1).

In the example shown, the valve 15 is placed at the outlet 5 of the exhaust gas.

In this case, the assembly 1 typically comprises a cone 17 fluidly connecting the exhaust gas inlet 3 to the exchanger inlet EG and to an upstream end of the bypass duct 13.

Furthermore, the valve 15 comprises a valve body 19 internally traversed by the exhaust gases.

The valve 15 also includes a flap 21 and a shaft 23 for driving the flap 21 (Figures 1 and 5).

The flap 21 is disposed inside the valve body 19 and is movable relative to the valve body 19.

The valve body 19 fluidly connects the exhaust gas outlet 5 to the exchanger outlet SG and also to the downstream end of the bypass duct 13.

Alternatively, the valve 15 it placed at the level of the exhaust gas inlet

3.

In this alternative embodiment, the positions of the cone 17 and of the valve body 19 are reversed.

The assembly 1 also includes an actuator 25 configured to drive the drive shaft 23 of the flap 21. The actuator 25 is typically an electric actuator, for example an electric gear motor.

The actuator 25 drives the drive shaft 23, either directly as shown in FIG. 5, or via a kinematic chain.

The shutter 21 typically rotates relative to the valve body 19.

The valve 15 is for example a regulating valve. In this case, the flap 21 can be placed at a plurality of positions relative to the valve body 19. This makes it possible to vary the passage sections offered to the exhaust gas circulating respectively from the exchanger outlet SG to the exhaust gas outlet 5 and from the downstream end of the bypass duct 13 to the exhaust gas outlet 5.

Alternatively, the valve 15 is an all-or-nothing valve. In this case, the flap 21 is capable of adopting either a heat exchange position in which the flap 21 prevents the circulation of exhaust gas in the bypass duct 13, or a bypass position in which the flap 21 prevents the circulation of exhaust gases in the heat exchanger 7.

The assembly 1 also comprises a member 29 comprising a channel 30 for circulation of a heat transfer fluid (FIG. 5).

The drive shaft 23 is in thermal contact with the heat transfer fluid passing through the circulation channel 30, which makes it possible to cool this drive shaft 23 of the flap 21.

In the example shown, the member 29 is in the form of a hollow fluid box, communicating fluidically with the side F of circulation of the heat transfer fluid, arranged around the drive shaft 23 so as to cool said drive shaft 23 (Figure 5).

The member 29 can be any member internally delimiting a circulation channel traversed by the heat transfer fluid.

The member 29 has a channel inlet and a channel outlet, not shown, opening into the circulation channel 30. The heat transfer fluid flows from the channel inlet to the channel outlet along the traffic 30.

Typically, the channel inlet is fluidly connected to the heat transfer fluid outlet 11, by means not shown. In this case, the channel outlet is designed to be connected to a heat recovery circuit, not shown. The assembly 1 then typically comprises an inlet duct 35 (FIG. 2) connected to the heat transfer fluid inlet 9 through the member 29. It also includes an outlet duct 37 (FIG. 2) connected to the outlet of channel.

The heat recovery circuit is intended to recover part of the heat energy from the exhaust gases and transfer it to another circuit or another component of the vehicle. Typically, it transfers this heat energy to the engine coolant.

The heat transfer fluid circulates in a loop in the heat recovery circuit, the heat exchanger 7 and the member 29.

The valve 15 includes a bearing 39 for guiding the drive shaft 23 (FIG. 5). Typically, this bearing 39 is rigidly fixed inside the circulation channel 30 of the member 29, on the valve body 19.

The member 29 has an external surface 41 (FIGS. 4 and 6) cooled by thermal contact with the heat transfer fluid circulating in the circulation channel 30.

The member 29 advantageously comprises a lower half-shell 43 and an upper half-shell 45 attached in leaktight manner to the lower half-shell 43 (FIGS. 2 to 5).

The lower half-shell 43 is typically made of a metallic material.

The upper half-shell 45 is typically made of a plastic material. It defines the cooled external surface 41 of the member 29.

The actuator 25 is fixed to member 29, outside of member 29.

The actuator 25 is fixed to the upper half-shell 45, for example by means of screws 47 referred to in the upper half-shell 45, visible in FIG. 4.

The upper half-shell 45 has an opening 49 (FIGS. 5 and 6) for the passage of the drive shaft 23.

One end 51 of the drive shaft 23 comes out of the guide bearing 39 and projects outside the member 29. The end 51 is connected to the actuator 25.

The actuator 25 is of any suitable type.

For example, the actuator 25 is an electric motor, provided with a rotary output shaft 53 (see FIG. 5).

Advantageously, the assembly 1 also comprises:

- A cover 55 defining with the external surface 41 a closed volume 57 in which is housed the actuator 25 (Figures 2, 6 and 7);

- a foamed material 59, at least partially filling the closed volume 57 around the actuator 25 (Figures 3, 6 and 7).

The cover 55 has the shape of a half-shell, concave towards the member 29.

The cooled external surface 41 of the member 29 is substantially planar. It carries a rib 61 with a closed or partially closed contour, visible in FIGS. 3, 4 and 6. The free edge 63 of the cover 55 comes to fit around the rib 61. It is rigidly fixed to this free edge, using clips or screws in a leaktight manner.

The cover 55 is made of a plastic resistant to high temperatures, typically PA 6.6, PA 6.6 reinforced with glass fibers from 15 to 40%, for example PA 6.6 GF30, PPA, PPE, PPS, PI or others. . As a variant, the cover 55 is made of metal, for example aluminum or of a steel sheet coated with aluminum of the Aluminié AS 120 type.

In addition to the actuator 25, part of the inlet duct 35 and part of the outlet duct 37 are housed in the closed volume 57. The free edge 63 has interruptions for the passage of the inlet and outlet ducts 35, 37 of set 1.

The term foamed material is understood here to mean a material comprising, by volume, mainly foam, typically one or more foams of a plastic material.

As visible in FIG. 6, an external part 65 of the foamed material 59 is in contact with the cover 55 and has a thermal conductivity less than 0.2 W / m. ° K. Preferably, the external part 65 has a thermal conductivity of between 0.2 and 0.02 W / m. ° K, more preferably between 0.1 and 0.04 W / m. ° K.

The external part 65 of the foamed material 59 is typically a polyurethane foam. Alternatively, it is a phenolic foam, a polyamide foam, a polyethylene foam, any other polymeric foam, a perfluorinated or chlorofluorinated foam, vermiculite or any other suitable type of foam.

It typically has a low density, for example between 15 and 110 g / L, and preferably between 40 and 100 g / L.

The external part 65 of the foamed material 59 covers the entire internal surface of the cover 55, with the exception of the free edge 63 pressed against the rib 61.

The outer part 65 of the foamed material 59 has a thickness of about 5 mm. This thickness must be large enough to thermally isolate the actuator 25 from the external atmosphere. It cannot be too large for reasons of space.

An internal part 67 of the foamed material 59 is in contact with the cooled external surface 41 and has a thermal conductivity greater than 0.8 W / m. ° K.

Preferably, the internal part 67 has a thermal conductivity of between 0.8 and 3 W / m. ° K, more preferably between 1 and 1.5 W / m. ° K.

The internal part 67 of the foamed material 59 comprises for this purpose a foam and an additive of high thermal conductivity dispersed in the foam.

The foam is typically a polyurethane foam. Alternatively, it is a phenolic foam, a polyamide foam, a polyethylene foam, any other polymeric foam, a perfluorinated or chlorofluorinated foam, vermiculite or any other suitable type of foam.

Preferably, the foam is a polyurethane foam, a phenolic foam or a polyamide foam. Preferably, the foam is a polyamide foam.

It typically has a high density, for example between 70 and 500 g / L.

The additive is chosen from metallic fibers, glass fibers, graphite balls or any other material which can increase the thermal conductivity of the foam. The additive concentration is typically 25 to 70%, and preferably 30 to 50% by volume.

The internal part 67 has a lower surface 69 in contact with the cooled external surface 41. It is thus in direct contact with the member 29, and more precisely with the upper half-shell 45. The thickness of the wall of the half - upper shell 45 is approximately 2.5 mm and this half-shell is typically made of PPA, PPS or PA6.6. Its temperature is very close to the temperature of the heat transfer fluid.

The internal part 67 has a first lateral surface 71 in contact with the actuator 25.

The actuator 25 comprises an outer casing 73, having a peripheral surface 75 with a closed contour around the axial direction. The lateral surface 71 is in direct contact with at least 50% of the peripheral surface 75, preferably at least 75% of the peripheral surface 75.

The internal part 67 has second and third lateral surfaces 77 and 79 in contact with the inlet and outlet conduits 35 and 37.

The foamed material 59 occupies at least 75%, preferably at least 90% of the free part of the closed volume 57, that is to say the part of the closed volume 57 not occupied by the actuator 25 and the various accessories which are housed there.

The cooled external surface 41 has concave zones 81 towards the closed volume 57. These concave zones 81 are for example delimited by ribs 83 formed on the cooled external surface 41, as visible in FIG. 6. The ribs 83 are typically provided for structurally reinforce the cooled external wall 41.

Advantageously, the foamed material 59 fills at least some of these concave areas 81. Dirt cannot accumulate in these concave areas 81.

It should be noted that the external casing 73 of the actuator 25 is in direct contact with the cooled external surface 41. More specifically, it comprises a zone surrounding the rotary output shaft 53, pressed directly against the cooled external surface 41 .

Furthermore, the member 29 forms a screen interposed axially between the heat exchanger 7 and the actuator 25, which contributes to limiting the heating of the actuator 25. The member 29 also forms a screen interposed axially between the actuator 25 on the one hand and on the other hand the valve 15 and the bypass duct 13.

The invention also relates to a manufacturing process for assembly 1 having the above characteristics.

The method advantageously comprises a step during which at least part of the foamed material 59 is injected into the cover 55.

Indeed, the foamed material 59 is typically formed by a foaming operation. This foaming takes place in a cavity or mold. The cover 55 is arranged in the mold. The foaming operation takes place directly in the inner part of the cover 55. A single piece is obtained, the foam material 59 adhering strongly to the cover 55. This makes it possible to give the foam material 59 a complex shape, determined by the mold.

When the foamed material 59 comprises two parts in different materials, such as the external and internal parts 65 and 67, the mold comprises at least two foam injection zones, in order to have the right characteristics in the right places.

As a variant, the external part 65 is injected into the cover 55 in a first mold. Then, the internal part 67 is formed on the external part 65 in a second mold.

According to yet another variant, the foamed material 59 is produced separately from the cover 55, then added to the cover 55.

As illustrated in FIG. 8, the invention also relates to a motor vehicle 85 comprising a floor 87 in which a tunnel 89 is formed. The tunnel 89 is open towards the running surface. It extends in the longitudinal running direction of the vehicle 85.

The exhaust line 2 is partially housed in the tunnel 89. The exhaust line 2 comprises an assembly 1 as described above, at least the actuator and the cover 55 being housed in the tunnel 89. Typically, everything assembly 1 is housed in tunnel 89.

The invention also relates to the use of the cover 55 and of the foamed material 59 in the assembly 1 of this vehicle, to prevent the actuator 25 from reaching a temperature higher than 110 ° C., when the vehicle undergoes the life situation. next :

- driving at a speed greater than 100 km / h on average for at least 15 minutes;

- immediately after, complete stop of the vehicle.

The cover 55 and the foamed material 59 can be used to prevent the actuator 25 from reaching a temperature above 120 ° C, or even 140 ° C.

The life situation considered can be, for the first phase, taxiing at a speed greater than 110 km / h for 20 minutes, or even taxiing at a speed greater than 130 km / h for 30 minutes.

This use is particularly advantageous, as described below.

During the first phase, vehicle 85 runs at full load and at high speed for a significant period of time. The engine is hot and the valve 15 of the heat recovery system is typically in the open position, letting the exhaust gases pass directly into the bypass duct 13.

The temperature of the heat transfer fluid is "cold", that is to say around 85 ° C-90 ° C. In fact, at this speed, the air flow through the front exchanger of the vehicle 85 is very sufficient to maintain the engine at the above temperature. In the tunnel 89 where the assembly 1 is housed, convection is strong, with a minimum of 100 W / m ^2. ° K. The air is strongly circulated, and at a fairly low temperature, which depends very much on the outside temperature. In the worst conditions, the air in tunnel 89 is at 60 ° C.

In the second phase, the vehicle 85 stops suddenly. Convection in tunnel 89 becomes almost zero, as it is limited to natural convection. This is of a value close to 15 W / m ² . ° K. During the first phase, the exhaust line 2 is substantially at a temperature approximately 100 ° C lower than that of the exhaust gases, that is to say 750 ° C. Just after stopping the vehicle 85, the exhaust line 2 will therefore heat the air contained in the tunnel 89, which can reach a temperature of 200 ° C. This value is reached a few minutes after stopping, for a period of up to 2 minutes. Then the temperature slowly decreases.

The outer part 65 of the foamed material 59 thermally isolates the actuator 25 from the high temperature atmosphere of the tunnel 89.

The internal part 67 of the foamed material 59 is in contact both with the cooled external surface 41 and with the actuator 23. The cooled external surface 41 is substantially at the temperature of the heat transfer fluid. This remains at a moderate level during the second phase, even if it increases a little (110 ° C maximum). Due to its thermal conductivity, the internal part 67 of the foamed material 59 helps to cool the actuator 25.

When the cover 55 is made of a plastic material, it behaves like a black body with an emissivity of the order of 0.9. It will therefore substantially absorb thermal radiation from surrounding equipment when the ambient temperature is high. On the other hand, it radiates on its environment, which causes a decrease in its skin temperature.

When the cover 55 is made of metal, in particular aluminum, its emissivity will be of the order of 0.2, which makes it not very sensitive to external radiation. It does not heat up under the influence of outdoor equipment, but cannot dissipate radiant heat into the environment.

Thus, one chooses to produce the cover 55 in a plastic material if the surrounding surfaces are weakly emitting, and in metal otherwise.

The assembly 1 described above can have multiple variants.

According to an alternative embodiment, the foamed material 59 can be entirely made of a material with high thermal conductivity, such as a foam loaded with additive of high thermal conductivity. It then only has the internal part 67, and does not have an external part 65. In this case, the external part 65 is advantageously replaced by a layer of air, ensuring thermal insulation between the shell and the actuator 25 As a variant, the foamed material 59 comprises both the external part 65 and the internal part 67, these two parts being made of the same material with high thermal conductivity.

According to another alternative embodiment, the foamed material 59 is entirely made of a material with low thermal conductivity, such as polyurethane foam. It then only comprises the external part 65, and does not comprise an internal part 67. As a variant, it comprises both the external part 65 and the internal part 67, these two parts being made of the same material with low thermal conductivity.

According to yet another alternative embodiment, the foamed material 59 is made of a material having an intermediate thermal conductivity, between 0.2 and 1 W / m. ° K.

Thus, it is possible to adapt the characteristics of the external and internal parts 65, 67 of the foamed material 59 as a function of the stresses undergone by the assembly 1, in particular the temperature inside the tunnel 89 during the second phase, the duration exposure of the assembly 1 to a high temperature, and the maximum temperature to be guaranteed for the components of the actuator 25.

The foamed material 59 does not necessarily have only two parts made of different materials. It can be made entirely of the same material as described above. It alternatively comprises three parts in different materials from one another, or more than three parts.

The invention has been described for an assembly 1 integrated in a device for recovering heat from a motor vehicle exhaust line. It applies to other cases.

The member 29 may not be a fluid box intended to cool the drive shaft 23 of a valve flap 21. The member 29 is alternately any other structure in which a heat transfer fluid circulates: heat exchanger , fluid distribution circuit, etc.

The actuator 25 is not necessarily an electric motor. This actuator alternatively is a solenoid valve, a pump, or any other actuator comprising components sensitive to temperature.

The assembly 1 can be integrated into another circuit of the vehicle, different from the exhaust line. It may also not be integrated into a vehicle, but rather into any other static installation.

Claims (11)

1, - Set (1) comprising: - A member (29) comprising a circulation channel (30) of a heat transfer fluid, having an external surface (41) cooled by thermal contact with the heat transfer fluid; - an actuator (25); - A cover (55) defining with the cooled external surface (41) a closed volume (57) in which is housed the actuator (25); - a foamed material (59), at least partially filling the closed volume (57) around the actuator (25). 2, - assembly according to claim 1, wherein an outer part (65) of the foamed material (59) is in contact with the cover (55) and has a thermal conductivity less than 0.2 W / m. ° K. 3, - An assembly according to claim 1 or 2, wherein an internal part (67) of the foamed material (59) is in contact with the cooled external surface (41) and has a thermal conductivity greater than 0.8 W / m. ° K. 4, - assembly according to claim 3, wherein the internal part (67) of the foamed material (59) comprises a foam and an additive of high thermal conductivity dispersed in the foam. 5, - An assembly according to any one of claims 1 to 4, wherein the actuator (25) comprises an outer casing (73) in direct contact with the cooled outer surface (41). 6, - assembly according to any one of claims 1 to 5, wherein the cooled external surface (41) has concave zones (81) towards said closed volume (57), the foamed material (59) filling at least some of the concave areas (81). 7, - assembly according to any one of claims 1 to 6, in which the assembly (1) comprises: - A heat exchanger (7) having a side (G) for circulation of the exhaust gas and a side (F) for circulation of the heat transfer fluid; - a duct (13) bypass of the heat exchanger (7); - a valve (15) configured to selectively direct the exhaust gases either to the heat exchanger (7) or to the bypass duct (13), the valve (15) having a flap (21) and a shaft ( 23) for driving the shutter (21) extending in an axial direction, the actuator (25) being configured by driving the drive shaft (23); - The circulation channel (30) of the member (29) fluidly communicating with the side (F) of circulation of heat transfer fluid, the member (29) being arranged to cool the drive shaft (23). 8. - The assembly of claim 7, wherein the member (29) forms a screen interposed axially between the heat exchanger (7) and the actuator (25). 9. - Motor vehicle (85) comprising a floor (87) in which a tunnel (89) is formed, and an exhaust line (2) partially housed in the tunnel (89), the exhaust line (2) comprising an assembly (1) according to any one of the preceding claims, at least the actuator (25) and the cover (55) being housed in the tunnel (89). 10. - A method of manufacturing an assembly (1) according to any one of claims 1 to 8, the method comprising a step during which at least a portion of the foamed material (59) is injected into the cover (55 ). 11. - Use of the cover (55) and of the foamed material (59) in the assembly (1) of the vehicle (85) of claim 9, to prevent the actuator (25) from reaching a temperature greater than 110 ° C , when the vehicle (85) undergoes the following life situation: - driving at a speed greater than 100 km / h on average for at least 15 minutes; - immediately after, complete stopping of the vehicle (85).