EP2227667B1 - Heat exchanger for gases, in particular for the exhaust gases from an engine - Google Patents

Description

The present invention relates to a heat exchanger for gas, in particular for the exhaust gases of an engine.

The invention is particularly applicable to the exhaust gas recirculation exchangers of an engine (EGRC).

BACKGROUND OF THE INVENTION

In some heat exchangers used to cool gases, for example those used in exhaust gas recirculation systems to the inlet of an internal combustion engine, the two heat exchange media are separated by a wall.

The heat exchanger itself can have several different configurations: for example, it can be composed of a tubular carcass inside which are arranged a series of parallel ducts for the passage of gases, the circulating refrigerant in the carcass outside the ducts; in another embodiment, the exchanger has a series of parallel plates forming the heat exchange surfaces, the exhaust gas and the refrigerant flowing between two plates, in alternating layers.

In the case of ductwork heat exchangers, the junction between the ducts and the casing may be of different types. In general, the ducts are fixed at their ends between two support plates coupled to each end of the carcass, the two support plates having a plurality of orifices in which the respective ducts are housed. Said support plates are they themselves are attached to connecting means to the recirculation line.

Said connecting means may consist of a V-shaped connection or a peripheral connecting flange or a flange, depending on the design of the recirculation line to which the exchanger is connected. The peripheral flange can be mounted together with a gas tank, the gas tank then constituting an intermediate piece between the carcass and the flange. The rim can also be mounted directly on the carcass.

The gas circuit may also be of the linear type, wherein the gas inlet and outlet are disposed at opposite ends; or it may be of the U-shaped type, in which the gas inlet and outlet occupy adjacent positions at the same open end, the opposite end being closed, and defining a forward passage and a return passage. In the latter case, the closed end for the return of gases is generally constituted by a closed gas tank.

EGR heat exchangers are commonly made of metal and usually made of stainless steel or aluminum. All the components of the ductwork heat exchangers, like those of the stacked plate heat exchangers, are made of metal, so that the exchangers are assembled by mechanical means and then welded to ensure an adequate level of sealing for this application.

One way to reduce the cost of the EGR heat exchanger is to replace the stainless steel casing with another material, provided that it is less expensive and allows other functions such as incorporation to be incorporated. coolant conduits or mounting brackets to a surface of the engine environment that will be used to fix the exchanger.

Duct beam heat exchangers comprising a plastic carcass are known. The plastic casings have the advantage of reducing the cost of the final product in that they allow the integration of the refrigerant circuit conduits and the attachment brackets to a surface of the engine environment.

In this case, the plastic carcass houses the core or metal body of the exchanger consisting of the bundle of tubes, and at least one support plate and a gas tank. The metal body must be attached to the plastic casing without protruding from it so as to ensure the mechanical strength of the heat exchanger vis-à-vis the motor vibration.

There are known patents for EGR exchangers with plastic carcass that describe the junction between the metal parts and plastic, sealing the refrigerant to prevent leakage.

A key aspect of heat exchanger design is the juncture between plastic components and metal components, such as aluminum or stainless steel. In the case of "U" shaped heat exchangers, there are two types of junctions, namely a junction whose function is to fix the different materials, in other words the plastic and the metal, and to ensure the tightness , and a junction having a single support function.

In this "U" shaped configuration, the open-side junction generally incorporates a gasket to prevent any possible leakage of refrigerant to the outside, the closed-side junction not requiring the sealing function in the extent to which this side only serves to support the -body metal inside the plastic carcass. The patent WO 2007/048603 discloses a heat exchanger of this type, wherein the junction means of the closed side comprise a support integral with the plastic carcass, which is provided with a slot for receiving a projection secured to the closed gas reservoir.

The known heat exchangers of this type, however, have a number of disadvantages insofar as the fixing of the metal body of the exchanger to the plastic carcass proves particularly problematic and because it is necessary to take into account the following design criteria:

1) The contact surface:

The working temperatures associated with the plastic carcass and the body of the exchanger are different. The metal body can reach high temperatures because it is in contact with the gas, whose temperature varies from 750 ºC at the inlet to 500 ºC at the outlet. The plastic casing is subjected to relatively low temperatures because it is immersed in the refrigerant whose temperature varies between 70 ºC and 90 ºC.

The contact surface between the body of the heat exchanger and the plastic casing must be strongly cooled by the refrigerant.

This means that, on the one hand, the flow of refrigerant at this surface must be sufficiently abundant, and its passage favored, and, secondly, the contact surface must be very small in order to maintain the temperature in the contact zone of the plastics material at values close to the temperature of the coolant. The contact surface must also be large enough to support the metal body.

2) Thermal expansion:

The difference in temperature between the metal body and the plastic carcass causes different thermal expansion of the two components, also a function of the coefficient of thermal expansion.

This has the disadvantage of producing undesirable movements between the components, more particularly in the longitudinal direction, due to their own expansion.

3) Distance between the metal body and the carcass:

As indicated, the contact surface between the plastic casing and the metal body, generally the gas tank, must be cooled substantially by the refrigerant, which means that the passage of the cooling fluid must be favored. at this surface. The design requirements therefore play a key role in improving the flow of refrigerant at this surface.

The definition of the distance between the metal body and the plastic carcass is of particular importance in this respect. The choice of this value depends on the minimum cross section of the coolant inside the heat exchanger. For example, if the distance between the gas tubes of a tubular heat exchanger is 1.3 mm, it is recommended to provide a distance of 2.6 mm, on both opposite sides, between the tank of gas and plastic carcass.

4) Position of the refrigerant inlet connection:

It is very important to place the coolant inlet fitting near said contact surface in order to ensure a minimum flow of fluid refrigerant.

5) Position of the mounting brackets on a surface of the engine environment:

It is advisable to place at least one mounting bracket to the motor in the support zone of the tube bundle on the shell of the exchanger in order to obtain a better resistance of the metal body to the vibrations of the engine.

6) Design of the means for joining the metal body to the carcass:

A good design of the junction of the metal body to the plastic carcass is necessary to allow the absorption of space due to the tolerances of the components.

DESCRIPTION OF THE INVENTION

The subject of the present invention is a gas heat exchanger, in particular for the exhaust gases of an engine, designed to overcome the drawbacks of exchangers known in the art by virtue of an optimized junction between the plastic carcass and the metal body. of the exchanger.

The gas heat exchanger, in particular for the exhaust gas of an engine, object of the present invention, is of the type comprising a metal body disposed inside a plastic carcass, said metal body incorporating a circuit for the circulation of gases with heat exchange with a refrigerant and at least one gas reservoir or support flange coupled to at least one end of said circuit, and connecting means for fixing at least one end of the metal body at the plastic carcass, and characterized in that said joining means comprises a plurality of contact points of small contact area integral with the plastic carcass, capable of being housed in respective recesses belonging to said at least one gas reservoir or support flange.

Since the joining means consist of a plurality of contact points with a small contact surface, it is possible to obtain a compromise that provides a surface that is sufficiently small to maintain the temperature in the contact zone of the plastics material. values close to the coolant temperature, but large enough to support the metal body.

This solution also makes it possible to improve the distribution of the refrigerant flow rate and thus the cooling of the contact surface subjected to a high temperature.

It also facilitates the positioning of the body of the heat exchanger in the plastic casing during the mounting operation.

The support points are preferably constituted by longitudinal ribs.

The bearing points are advantageously distributed radially and substantially equidistantly in an inner zone of the plastic carcass.

This gives a correct distribution of the weight of the metal body on the plastic carcass ensuring good stability of the assembly.

The joining means preferably comprise between two and eight points of support.

According to one embodiment of the invention, in the case of a carcass of rectangular cross-section, the joining means comprise six symmetrically distributed support points, so that each major side of said rectangular cross section has two fulcrums and each small side of said rectangular cross section has a fulcrum.

According to another embodiment of the invention, also in the case of a carcass of rectangular cross section, the joining means comprise two symmetrically distributed support points, so that each large side of said cross section rectangular has a fulcrum.

According to another embodiment of the invention, also in the case of a carcass of rectangular cross section, the joining means comprise four symmetrically distributed support points, so that each long side of said rectangular cross section presents two points of support.

The bearing points advantageously comprise a minimum longitudinal dimension allowing displacements caused by the distinct thermal expansion between the metal body and the plastic carcass.

This ensures proper operation of the heat exchanger despite undesirable movements in the longitudinal direction due to the expansion of the metal body and the plastic carcass at different temperatures.

It is also advantageously provided a minimum distance between the metal body and the plastic carcass function of the minimum cross section of the refrigerant fluid flow inside the exchanger.

This thus makes it possible to guarantee an adequate distance between the metal body, generally the gas tank, and the plastic casing, and consequently to obtain an abundant flow of fluid. refrigerant.

Preferably, in the case of a gas circuit incorporating a plurality of parallel ducts, the minimum distance between the metal body and the plastic casing, measured on each opposite side of the metal body, is twice the distance between the ducts. gas.

Also preferably, there is provided a safety distance of between 1.5 and 2.5 times the minimum cross section of the refrigerant flow.

Advantageously, given that the exchanger comprises an inlet connection and a refrigerant outlet fitting integrated with the plastic carcass, the inlet or outlet connection of the refrigerant fluid is located near said contact surface of the points of support, which guarantees a minimum flow of coolant.

Advantageously also, considering that the exchanger comprises mounting brackets to a surface of the engine environment, at least one mounting bracket is located near said contact surface of the support points, so as to improve the resistance of the metal body to vibration from the engine.

Advantageously also, the bearing points have a suitable configuration allowing the absorption of the space due to the tolerances of the metal body and the plastic carcass. Improved junction means are thus obtained with an extended service life, and a facilitated mounting operation between the exchanger body and the plastic casing. The shape of the points of support will admit a less deformation of the constituent plastic in the case where the fitting nesting between the two components exceeds the interlocking permissible, ie if the gas tank has the largest permissible tolerance and the smallest distance between points of support.

The bearing points preferably have a branched configuration.

According to one embodiment of the invention, the support points incorporate two diverging branches forming a suitable angle chosen according to the plastic material used. It should be noted that the greater the angle defined between the branches, the lower the mounting effort will be.

According to another embodiment of the invention, the support points incorporate three divergent branches. In this case, the incorporation of an additional central branch makes it possible to reinforce the stability.

The bearing points preferably incorporate on their outer surface a plurality of small protuberances to reduce the volume of plastic to be deformed in the case of a fitting, and thus facilitate the mounting process.

The gas inlet is advantageously located near the passage of the refrigerant fluid, regardless of its entry or exit.

The gas inlet is preferably located near the outlet of the refrigerant.

According to one embodiment of the invention, the heat exchanger is of the "U" -shaped type in which the inlet and the outlet of the gases occupy adjacent positions at the same open end of the metal body, the opposite end being closed, and defining a forward passage and a return passage, and characterized in that the bearing points are constituted by longitudinal ribs integrated into an inner surface of the plastic carcass, said respective ribs being capable of to stay in corresponding recesses on the outer surface of the gas reservoir at said closed end.

The gas tank is generally formed by stamping and its recessed mounting surfaces give it increased rigidity.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 est une vue en perspective et éclatée d'un échangeur de chaleur pour gaz de l'invention ;
• la figure 2 est une vue en coupe longitudinale de l'échangeur monté de la figure 1 ;
• les figures 3, 4 et 5 sont des vues en coupe transversale de l'échangeur, selon la ligne III-III de la figure 2, montrant les moyens de jonction respectivement avec six, quatre et deux nervures, selon des modes de réalisation différents de l'invention ;
• la figure 6 est une vue partielle en perspective d'une coupe longitudinale montrant deux nervures longitudinales ;
• les figures 7 et 8 sont des vues en coupe transversale de l'échangeur montrant les moyens de jonction avec deux nervures ramifiées incorporant respectivement deux et trois branches, selon des modes de réalisation différents de l'invention ;
• les figures 9 et 10 sont des vues en coupe transversale de l'échangeur montrant les moyens de jonction avec six nervures à deux branches respectivement avec des angles différents, selon des modes de réalisation différents de l'invention ; et
• la figure 11 est une vue en coupe transversale de l'échangeur, montrant une vue agrandie d'une nervure longitudinale dotée d'une pluralité de protubérances.

In order to facilitate the description of what has been explained above, drawings are enclosed in which are shown, in schematic form and only by way of non-limiting example, practical examples of embodiments of the heat exchanger. for gas of the invention. In these drawings:

• the figure 1 is a perspective and exploded view of a gas heat exchanger of the invention;
• the figure 2 is a longitudinal sectional view of the mounted exchanger of the figure 1 ;
• the Figures 3, 4 and 5 are cross-sectional views of the heat exchanger along line III-III of the figure 2 , showing the junction means respectively with six, four and two ribs, according to different embodiments of the invention;
• the figure 6 is a partial perspective view of a longitudinal section showing two longitudinal ribs;
• the Figures 7 and 8 are cross-sectional views of the exchanger showing the joining means with two branched ribs respectively incorporating two and three branches, according to different embodiments of the invention;
• the Figures 9 and 10 are cross-sectional views of the exchanger showing the junction means with six ribs with two branches respectively with different angles, according to different embodiments of the invention; and
• the figure 11 is a cross-sectional view of the exchanger, showing an enlarged view of a longitudinal rib with a plurality of protuberances.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Figures 1 and 2 , the heat exchanger 1 consists of a plastic casing 2 containing a metal body comprising a bundle of parallel ducts 3 for the passage of the gases to be cooled. Inside the casing 2 and outside the ducts 3, a refrigerant circulates from an inlet 4 to an outlet 5. Said metal body also incorporates a support plate 6 and a gas reservoir 7 as shown in FIG. will explain later.

In this example, the carcass 2 has a substantially rectangular section and is closed at one of its ends to accommodate the duct bundle 3 which is, in this case, the type of "U", otherwise said inlet 8 and the outlet 9 of said ducts 3 are arranged on the same side at the open end of the carcass 2, defining a forward passage and a return passage of the gases to be cooled.

It is convenient to have the inlet 8 of the gases near the passage of the refrigerant fluid, regardless of its entry or exit. In the embodiment illustrated in figure 1 , the gas inlet 8 is located near the outlet 5 of the refrigerant.

The duct bundle 3 is fixed, by its free end, to said metal support plate 6, which has a plurality of orifices in which the respective ducts 3 are housed and, by its closed end, to the metal gas tank 7 .

Said support plate 6 is fixed to the open end of the plastic casing 2 by means of screws. It is further provided to place a plastic seal 10 between said open end of the carcass 2 and the support plate 6 for the purpose of sealing the coolant.

The plastic casing 2 is fixed, by its closed end, to said metal gas reservoir 7 by connecting means incorporating a plurality of longitudinal ribs 11 of small contact area, integral with the plastic casing 2 and able to be housed in corresponding recesses 12 belonging to the gas reservoir 7.

In this example, the recesses 12 are formed in said gas tank formed by stamping.

The longitudinal ribs 11 make it possible to obtain a compromise offering a sufficiently small surface making it possible to maintain the temperature in the zone of contact of the plastics material at values close to the temperature of the refrigerant fluid, but sufficiently large to support the metal body.

This solution also makes it possible to obtain an abundant flow of refrigerant fluid to ensure the cooling of the contact surface subjected to a high temperature.

It also facilitates the positioning of the body of the heat exchanger in the plastic casing during the mounting operation. It is generally used between two and eight longitudinal ribs 11 distributed substantially equidistantly in order to obtain a correct distribution of the weight of the metal body on the plastic carcass ensuring good stability of the assembly.

According to one embodiment of the invention illustrated in figure 3 the joining means comprise six longitudinal ribs 11 distributed symmetrically, so that each large side of said rectangular cross section has two ribs and each small side of said rectangular cross section has a rib.

According to another embodiment of the invention illustrated in figure 4 , the connecting means comprise four symmetrically distributed ribs, so that each large side of said rectangular cross section has two ribs.

According to another embodiment of the invention illustrated in figure 5 , the connecting means comprise two symmetrically distributed ribs, so that each large side of said rectangular cross section has a rib.

The longitudinal ribs 11 comprise a minimum longitudinal dimension allowing displacements caused by the distinct thermal expansion between the metal body 7 and the plastic casing 2, thereby ensuring proper operation of the exchanger. The direction of said longitudinal displacements is illustrated in FIG. figure 6 by an arrow with two points.

It is also advantageously provided a minimum distance between the gas reservoir 7 and the plastic casing 2 function of the minimum cross section of the refrigerant flow inside the exchanger 1. This minimum distance makes it possible to obtain a flow abundant refrigerant.

Said minimum distance between the gas tank 7 and the plastic casing 2, measured on each opposite side of the gas tank 7, is twice the distance between the gas ducts 3. There is also a safety distance of between 1.5 and 2.5 times the minimum cross section of the fluid flow refrigerant.

The inlet connection 4 of the coolant is located near said contact surface of the junction between the carcass 2 and the gas reservoir 7, as shown by the figures 2 and 6 , which ensures a minimum coolant flow.

The exchanger 1 comprises attachment supports 13 to a surface of the engine environment, which are located near said contact surface of the junction between the carcass 2 and the gas reservoir 7, as shown in FIG. figure 1 , so as to improve the resistance of the metal body to vibration from the engine.

The longitudinal ribs 11 have a suitable configuration allowing the absorption of space due to the tolerances of the gas tank 7 and the plastic carcass 2.

The shape of the longitudinal ribs 11 will admit less deformation of the constituent plastic material in the case where the mounting interlocking between the two components exceeds the allowable interlocking, that is to say if the gas reservoir has the largest permissible tolerance and the most small distance between longitudinal ribs. In this case, the longitudinal ribs 11 may have a branched configuration, as can be seen in Figures 7 to 10 .

According to one embodiment of the invention illustrated in figure 7 , the longitudinal ribs 11 incorporate two diverging branches forming a suitable angle chosen depending on the plastic used.

The Figures 9 and 10 respectively illustrate different values of the angle formed by the branches of the longitudinal ribs 11. The greater the angle defined between the branches, the lower the mounting force will be.

According to another embodiment of the invention illustrated in figure 8 the longitudinal ribs 11 incorporate three diverging branches. In this case, the incorporation of an additional central branch makes it possible to reinforce the stability.

The longitudinal ribs 11 may incorporate on their outer surface a plurality of small protuberances 14, as shown in FIG. figure 11 , to reduce the volume of plastic to deform in the case of a mounting interlock and thus facilitate the mounting process.

If this example has described a parallel tube bundle exchanger, the invention can however also find application in stacked plate heat exchangers. In both cases, the gas circuit may also be of the "U" -shaped type (the gas inlet and the outlet being disposed at the same end) or of the linear type (the gas inlet and outlet being arranged at opposite ends).

Claims (15)

1. Heat exchanger (1) for gases, notably for the exhaust gases from an engine, comprising a metallic body (3, 7) placed inside a plastic shell (2), the said metallic body incorporating a circuit (3) intended for the circulation of the gases with exchange of heat with a coolant and at least one gas reservoir (7) or supporting flange coupled to at least one end of the said circuit (3), and connecting means for fixing at least one of the ends of the metallic body (3, 7) to the plastic shell (2), characterized in that the said connecting means comprise a plurality of bearing points (11) with a small contact area which are solid with the plastic shell (2) and capable of being lodged in respective indentations (12) belonging to the said at least one gas reservoir (7) or supporting flange.
2. Exchanger (1) according to Claim 1, characterized in that the bearing points (11) consist of longitudinal ribs.
3. Exchanger (1) according to Claim 1, characterized in that the bearing points (11) are distributed radially and substantially equidistantly in an internal zone of the plastic shell (2).
4. Exchanger (1) according to Claim 1, characterized in that the connecting means comprise between 2 and 8 bearing points (11).
5. Exchanger (1) according to Claim 1, characterized in that the bearing points (11) have a minimal longitudinal dimension that allows for the movement brought about by the different thermal expansions of the metallic body (7) and of the plastic shell (2).
6. Exchanger (1) according to Claim 1, characterized in that there is a minimal distance between the metallic body (7) and the plastic shell (2) dependent on the minimal cross section of the flow of coolant inside the exchanger (1).
7. Exchanger (1) according to Claim 1, of the type comprising an inlet connector (4) and an outlet connector (5) for the coolant which connectors are incorporated into the plastic shell (2), characterized in that the inlet (4) or outlet (5) connector for the coolant is situated near the said contact surface of the bearing points (11).
8. Exchanger (1) according to Claim 1, of the type comprising mountings (13) for fixing to a surface of the engine environment, characterized in that at least one fixing mounting (13) is situated near the said contact surface of the bearing points (11).
9. Exchanger (1) according to Claim 1, characterized in that the bearing points (11) have a configuration suited to absorbing the space caused by the tolerances on the body (7) of the exchanger and on the plastic shell (2).
10. Exchanger (1) according to Claim 9, characterized in that the bearing points (11) have a branched configuration.
11. Exchanger (1) according to Claim 10, characterized in that the bearing points (11) incorporate two divergent branches making a suitable angle chosen according to the plastic used.
12. Exchanger (1) according to Claim 10, characterized in that the bearing points (11) incorporate three divergent branches.
13. Exchanger (1) according to Claim 1, characterized in that the bearing points (11) incorporate a plurality of small protuberances (14) on their external surface.
14. Exchanger (1) according to Claim 1, characterized in that the gas inlet (8) is situated near the coolant passage, either the inlet or the outlet thereof.
15. Exchanger (1) according to Claim 1 of the U-shaped type in which the inlet (8) or the outlet (9) for the gases occupy adjacent positions at one and the same open end of the metallic body (3), the opposite end being closed, and defining an outbound and a return passage, characterized in that the bearing points consist of longitudinal ribs (11) incorporated into an internal surface of the plastic shell (2), said ribs (11) being able to be lodged in corresponding indentations (12) formed on the external surface of the gas reservoir (7) situated in the region of the said closed end.

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