ES2573937T3 - Gas heat exchanger, especially for engine exhaust - Google Patents

Abstract

Heat exchanger (1) for gases, especially for the exhaust gases of an engine, comprising a metal body (3, 7) disposed inside a plastic housing (2), said metal body incorporating a circuit ( 3) intended for the circulation of gases with heat exchange with a cooling fluid and at least one gas tank (7), or support flange, coupled to at least one end of said circuit (3), and joining means for fixing at least one of the ends of the metal body (3, 7) to the plastic housing (2), characterized in that said joining means comprise a plurality of support points (11) of small contact surface, integral with the plastic housing (2), capable of being housed in respective recesses (12) belonging to said at least one gas tank (7) or support flange.

Description

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DESCRIPTION

Gas heat exchanger, especially for engine exhaust

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

Very particularly, the invention is applicable in the exhaust recirculation exchangers of an engine (EGRC).

Background of the invention

In certain heat exchangers used to cool gases, for example those used in exhaust gas recirculation systems towards the admission of an explosion engine, the two heat exchange means are separated by a wall.

The heat exchanger itself can have several different configurations: by way of example, it can consist of a tubular housing inside which a series of parallel conduits for the passage of gases are arranged, the refrigerant circulating through the housing on the outside of the ducts; In another embodiment, the exchanger has a series of parallel plates determining the heat exchange surfaces, then circulating the exhaust gases and the refrigerant between two plates, in alternating layers.

In the case of duct beam heat exchangers, the joint between the ducts and the housing can be of different types. In general, the ducts are fixed at their ends between two support plates coupled to each end of the housing, both support plates having a plurality of holes in which the respective ducts are housed. Said support plates, in turn, are fixed to means of connection with the recirculation line.

Said link means may consist of a V-fitting or a perimeter link flange or a flange, depending on the design of the recirculation line to which the exchanger is attached. The perimeter flange may be assembled together with a gas tank, the gas tank then constituting an intermediate piece between the housing and the flange. The flange can also be mounted directly on the housing.

The gas circuit may also be of the linear type, in which the inlet and outlet of the gases are arranged at opposite ends; or, it may be of the "U" type, in which the inlet and outlet of the gases occupy adjacent positions in correspondence with the same open end, the opposite end being closed and defining a one-way and one-step step back. In the latter case, the closed end for the return of the gases is generally constituted from a closed gas tank.

EGR heat exchangers are usually metallic and generally made of stainless steel or aluminum. All the components of the duct beam exchangers, like those of the stacked plate exchangers, are metallic, so that the exchangers are assembled by mechanical means, with subsequent welding to ensure a level of tightness suitable for this application.

One means of reducing the cost of the EGR heat exchanger is to replace the stainless steel housing with another material, with the proviso that it is less expensive and allows other functions to be integrated, such as the incorporation of the cooling fluid conduits or supports of fixation to a surface of the surroundings of the engine that will serve to fix the exchanger.

Duct beam heat exchangers are known which comprise a plastic housing. Plastic housings offer the advantage of reducing the cost of the final product, since they allow the integration of the coolant circuit ducts and the fixing brackets to a surface around the engine.

In this case, the plastic housing houses the metal core or body of the exchanger constituted from the tube bundle and, at least, a support plate and a gas tank. The metal body must be fixed to the plastic housing without emerging from it, in order to assume the mechanical resistance of the heat exchanger against motor vibrations.

Patents are known for the purpose of plastic housing EGR exchangers, which describe the union between the metal and plastic parts, ensuring the tightness of the cooling fluid to prevent any leakage.

A key aspect of the heat exchanger design lies in the union 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 joints, namely a union that has the function of fixing the different materials, in other words, plastic and metal, and taking care of the tightness, and a union that has a single and unique support function.

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In this "U" shaped configuration, the joint of the open side generally incorporates a sealing gasket that serves to prevent any possible leakage of the cooling fluid to the outside, not requiring the joint function of the closed side, by how much this side only serves to support the metal body inside the plastic housing. WO 2007/048603 discloses a heat exchanger of this type, in which the joining means of the closed side comprise a support integral to the plastic housing, which is provided with a groove intended to receive a projection integral with the tank closed gas.

However, known heat exchangers of this type have a number of drawbacks, since the fixing of the metal body of the exchanger to the plastic housing is particularly problematic, and due to the fact that it is important to take into account the following criteria of design:

1) The contact surface:

The working temperatures associated with the plastic housing and the exchanger body are different. The metal body can reach high temperatures, due to the fact of being in contact with the gas, whose temperature varies from 750 ° C at the entrance to 500 ° C at the exit. The plastic housing, meanwhile, is subjected to relatively low temperatures, due to the fact that it is immersed in the cooling fluid, whose temperature ranges between 70 ° C and 90 ° C.

The contact surface between the body of the heat exchanger and the plastic housing must be strongly cooled by the cooling fluid.

This means that, on the one hand, the flow of the refrigerant fluid in correspondence with this surface has to be sufficiently abundant, and favored its passage and, on the other, the contact surface has to be very small in order to maintain the temperature in the area of contact of the plastic material in values close to the temperature of the refrigerant fluid. On the other hand, the contact surface has to be large enough to support the metal body.

2) Thermal expansion:

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

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

3) Distance between the metal body and the housing:

As indicated, the contact surface between the plastic housing and the metal body, generally the gas tank, has to be cooled sharply by the refrigerant fluid, which means that it is of interest to favor the passage of the refrigerant fluid in correspondence with this surface. Therefore, design requirements play an essential role in improving the flow of the cooling fluid in correspondence with this surface.

In this sense, the definition of the distance between the metal body and the plastic housing is of singular importance. The choice of this value depends on the minimum cross section of the refrigerant fluid inside the heat exchanger. As an 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 the two opposite sides, between the gas tank and the plastic shell.

4) Position of the coolant inlet fitting:

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

5) Position of the fixing brackets to a surface of the motor environment:

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

6) Design of the means of joining the metal body to the housing:

Proper design of the union of the metal body to the plastic housing 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 heat exchanger for gases, especially for the gases of

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Exhaust of an engine, designed to overcome the inconveniences of the exchangers known in the art thanks to an optimized union between the plastic housing and the metal body of the exchanger.

The heat exchanger for gases, especially for the exhaust gases of an engine, object of the present invention, is of the type comprising a metal body disposed inside a plastic housing, said metal body incorporating a circuit intended for the circulation of the gases with heat exchange with a cooling fluid and at least one gas tank, or support flange, coupled to at least one end of said circuit, and joining means for fixing at least one of the ends of the body metallic to the plastic housing, and characterized in that said joining means comprise a plurality of support points of small contact surface, integral with the plastic housing, capable of being housed in respective recesses belonging to said at least one gas tank or support flange.

Since the joining means are constituted from a plurality of support points of small contact surface, it is possible to obtain a compromise solution that offers a sufficiently small surface, which allows to maintain the temperature in the contact area of the plastic material in values close to the temperature of the coolant fluid, but large enough, to support the metal body.

This solution also allows to improve the distribution of the flow of refrigerant fluid and, therefore, the cooling of the contact surface subjected to a high temperature.

Additionally, it facilitates the positioning of the heat exchanger body in the plastic housing during the assembly operation.

The support points are preferably formed from longitudinal ribs.

The support points, advantageously, are distributed radially and in a substantially equidistant manner in an internal area of the plastic housing.

In this way a correct distribution of the weight of the metal body on the plastic housing is obtained, which ensures a good stability of the assembly.

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

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

According to another embodiment of the invention, also in the case of a rectangular cross-sectional housing, the joining means comprise two support points distributed symmetrically, so that each major side of said rectangular cross-section has a point of support for.

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

The support points advantageously comprise a minimum longitudinal dimension that allows the displacements caused by the different thermal expansion between the metal body and the plastic housing.

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

Likewise, it is advantageously provided, between the metal body and the plastic housing, a minimum distance, function of the minimum cross section of the flow of refrigerant fluid inside the exchanger.

Thus, this ensures an adequate distance between the metal body, generally the gas tank, and the plastic housing, and consequently obtain an abundant flow of cooling fluid.

Preferably, in the case of a gas circuit that incorporates a plurality of parallel ducts, the minimum distance between the metal body and the plastic housing, measured on each of the opposite sides of the metal body, corresponds to twice the distance between the gas ducts.

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

Advantageously, given that the exchanger comprises an inlet and an outlet for the cooling fluid integrated in the plastic housing, the inlet or outlet of the cooling fluid is located near said contact surface of the points of support, which ensures a minimum flow of

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coolant

Also advantageously, given that the exchanger comprises fixing brackets to a surface around the motor, at least one fixing bracket is located near said contact surface of the support points, in order to improve the strength of the metal body to the vibrations coming from the engine.

Also advantageously, the support points have an adequate configuration that allows the absorption of space due to the tolerances of the metal body and the plastic housing.

In this way, improved joining means are obtained which offer a long useful life and an easy assembly operation between the body of the exchanger and the plastic housing. The shape of the support points will allow a lower deformation of the constituent plastic material in the case where the mounting socket between the two components exceeds the allowable fit, in other words, if the gas tank has the highest allowable tolerance and the lowest distance between support points.

The support points preferably have a branched configuration.

According to an embodiment of the invention, the support points have two divergent branches that form 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 assembly effort.

According to another embodiment of the invention, the support points have three divergent branches incorporated. In this case, the incorporation of a supplementary central branch makes it possible to strengthen stability.

Preferably, the support points, on its outer surface, have a plurality of small protrusions incorporated that allow the volume of plastic to be deformed to be reduced in the case of a mounting socket and, therefore, to facilitate the assembly procedure.

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

The gas inlet is preferably located near the outlet of the cooling fluid.

According to an embodiment of the invention, the heat exchanger is of the "U" type, in which the entry and exit of the gases occupy adjacent positions in correspondence with the same open end of the metal body, the opposite end being closed, and defining a one-way and one-way step, and characterized in that the support points are constituted from longitudinal ribs integrated in an internal surface of the plastic housing, said respective ribs being susceptible of staying in corresponding recesses practiced on the external surface of the gas tank located in correspondence with said closed end.

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

Brief description of the drawings

With the purpose of facilitating the description of what has been stated above, some drawings are attached in which, schematically and only by way of non-limiting example, some practical cases of embodiments of the heat exchanger for gases of the invention. In these drawings:

Figure 1 is an exploded perspective view of a heat exchanger for gases of the invention;

Figure 2 is a longitudinal sectional view of the armed exchanger of Figure 1;

Figures 3, 4 and 5 are cross-sectional views of the exchanger, according to the NI-NI Line of Figure 2, showing the joining means with six, four and two ribs, respectively, according to different embodiments of the invention ;

Figure 6 is a partial perspective view of a longitudinal section showing two longitudinal ribs;

Figures 7 and 8 are cross-sectional views of the exchanger showing the joining means with two branched ribs that respectively have two and three branches incorporated, according to different embodiments of the invention;

Figures 9 and 10 are cross-sectional views of the exchanger, showing the joining means with six ribs of two branches with different angles respectively, according to different embodiments of the invention; Y

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Figure 11 is a cross-sectional view of the exchanger, showing an enlarged view of a longitudinal rib provided with a plurality of protuberances.

Description of preferred embodiments

Referring to Figures 1 and 2, the heat exchanger 1 is constituted from a plastic housing 2 containing a metal body comprising a bundle of parallel ducts 3, intended for the passage of the gases to be cooled. Inside the casing 2 and outside the ducts 3 circulates a cooling fluid, from an inlet 4 to an outlet 5. Said metal body also incorporates a support plate 6 and a gas tank 7, as will be explained hereafter.

In this example, the housing 2 has a substantially rectangular section, and is closed at one of its ends, to allow the duct beam 3 to be accommodated there, which, in this case, is of the "U" type, in other In other words, the inlet 8 and the outlet 9 of said ducts 3 are arranged on the same side in correspondence with the open end of the housing 2, defining a passage and return passage of the gases to be cooled.

It is convenient to arrange the inlet 8 of the gases near the passage of the cooling fluid, regardless of its inlet or outlet. In the embodiment illustrated in Figure 1, the inlet 8 of the gases is located near the outlet 5 of the cooling fluid.

The bundle of conduits 3 is fixed, at its free end, to said metal support plate 6, which has a plurality of holes in which the respective conduits 3 and, at its closed end, to the metal gas tank 7.

Said support plate 6 is fixed to the open end of the plastic housing 2 by screw means. It is further provided to place, between said open end of the housing 2 and the support plate 6, a plastic gasket 10 for the purpose of taking care of the sealing of the cooling fluid.

The plastic housing 2 is fixed, at its closed end, to said metal gas tank 7 by means of joining which incorporate a plurality of longitudinal ribs 11 of small contact surface, integral with the plastic housing 2 and capable of being accommodated. in corresponding recesses 12 belonging to the gas tank 7.

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

The longitudinal ribs 11 allow to obtain a compromise solution that offers a sufficiently small surface, which allows to maintain the temperature in the contact area of the plastic material at values close to that of the temperature of the cooling fluid, but sufficiently large, which allows the body to support metal.

This solution also allows to obtain an abundant flow of cooling fluid to ensure the cooling of the contact surface subjected to an elevated temperature.

Additionally, it facilitates the positioning of the heat exchanger body in the plastic housing during the assembly operation.

Generally, between two and eight longitudinal ribs 11 distributed in a substantially equidistant manner are used, in order to obtain a correct distribution of the weight of the metal body on the plastic housing that ensures a good stability of the assembly.

According to an embodiment of the invention illustrated in Figure 3, the joining means comprise six longitudinal ribs 11 symmetrically distributed, so that each major side of said rectangular cross section has two ribs and each minor side of said cross section rectangular presents a nerve.

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

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

The longitudinal ribs 11 comprise a minimum longitudinal dimension that allows the displacements caused by the different thermal expansion between the metal body 7 and the plastic housing 2, thus ensuring correct operation of the exchanger. The direction of said longitudinal displacements is illustrated in Figure 6 by a double-headed arrow.

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Likewise, a minimum distance between the gas tank 7 and the plastic housing 2 is advantageously provided as a function of the minimum cross section of the flow of refrigerant fluid inside the exchanger 1. This minimum distance allows an abundant flow of refrigerant fluid to be obtained .

Said minimum distance between the gas tank 7 and the plastic housing 2, measured on each of the opposite sides of the gas tank 7, corresponds to twice the distance between the gas lines 3. Also, a distance is provided of safety between 1.5 and 2.5 times the minimum cross section of the flow of refrigerant fluid.

The inlet fitting 4 of the refrigerant fluid is located near said contact surface of the joint between the housing 2 and the gas tank 7, as shown in Figures 2 and 6, which ensures a minimum flow of refrigerant fluid.

The exchanger 1 comprises fixing brackets 13 to a surface around the engine, which are located near said contact surface of the joint between the housing 2 and the gas tank 7, as shown in Figure 1, in order to improve the resistance of the metal body to vibrations from the engine.

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

The shape of the longitudinal ribs 11 will admit a lower deformation of the constitutive plastic material in the case where the fitting between the two components exceeds the allowable fit, in other words, if the gas tank has the highest allowable tolerance and the lowest distance between longitudinal nerves. In this case, the longitudinal ribs 11 may have a branched configuration, as can be seen in Figures 7 to 10.

According to an embodiment of the invention illustrated in Figure 7, the longitudinal ribs 11 incorporate two divergent branches that form a suitable angle, chosen according to the plastic material used.

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

According to another embodiment of the invention illustrated in Figure 8, the longitudinal ribs 11 have three divergent branches incorporated. In this case, the incorporation of a supplementary central branch makes it possible to strengthen stability.

The longitudinal ribs 11, on its outer surface, can incorporate a plurality of small protuberances 14, as shown in Figure 11, which allow reducing the volume of plastic to be deformed in the case of a mounting socket and, therefore, facilitating The assembly procedure.

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

Claims (15)

5 10 fifteen twenty 25 30 35 40 Four. Five 1. Heat exchanger (1) for gases, especially for the exhaust gases of an engine, comprising a metal body (3, 7) disposed inside a plastic housing (2), said metal body incorporating a circuit (3) intended for the circulation of gases with heat exchange with a cooling fluid and at least one gas tank (7), or support flange, coupled to at least one end of said circuit (3), and means of connection to fix at least one of the ends of the metal body (3, 7) to the plastic housing (2), characterized in that said joining means comprise a plurality of support points (11) of small contact surface, solidary of the plastic housing (2), capable of being housed in respective recesses (12) belonging to said at least one gas tank (7) or support flange. 2. Exchanger (1) according to claim 1, characterized in that the support points (11) are constituted from longitudinal ribs. 3. Exchanger (1) according to claim 1, characterized in that the support points (11) are distributed radially and substantially equidistant in an internal area of the plastic housing (2). 4. Exchanger (1) according to claim 1, characterized in that the joining means comprise between two and eight support points (11). 5. Exchanger (1) according to claim 1, characterized in that the support points (11) comprise a minimum longitudinal dimension that allows the displacements caused by the different thermal expansion between the metal body (7) and the plastic housing (2 ). 6. Exchanger (1) according to claim 1, characterized in that it is provided, between the metal body (7) and the plastic housing (2), a minimum distance, function of the minimum cross-section of the flow of cooling fluid in the inside of the exchanger (1). 7. Exchanger (1) according to claim 1, of the type comprising an inlet fitting (4) and an outlet fitting (5) of the cooling fluid integrated in the plastic housing (2), characterized in that the inlet fitting (4) or outlet (5) of the refrigerant fluid is located near said contact surface of the support points (11). 8. Exchanger (1) according to claim 1, of the type comprising fixing brackets (13) to a surface around the motor, characterized in that at least one fixing bracket (13) is located near said contact surface of the support points (11). 9. Exchanger (1) according to claim 1, characterized in that the support points (11) have a suitable configuration that allows the absorption of space due to the tolerances of the body (7) of the exchanger and the plastic housing (2 ). 10. Exchanger (1) according to claim 9, characterized in that the support points (11) have a branched configuration. 11. Exchanger (1) according to claim 10, characterized in that the support points (11) incorporate two divergent branches that form a suitable angle, chosen according to the plastic material used. 12. Exchanger (1) according to claim 10, characterized in that the support points (11) have three divergent branches incorporated. 13. Exchanger (1) according to claim 1, characterized in that the support points (11), on its outer surface, have a plurality of small protuberances (14) incorporated. 14. Exchanger (1) according to claim 1, characterized in that the inlet (8) of the gases is located near the passage of the refrigerant fluid, regardless of its inlet or outlet. 15. Exchanger (1) according to claim 1, of the "U" type, wherein the inlet (8) and the outlet (9) of the gases occupy adjacent positions corresponding to the same open end of the metal body (3), the opposite end being closed, and defining a one-way and one-way step, characterized in that the support points are constituted from longitudinal ribs (11) integrated in an internal surface of the plastic housing (2), said ribs (11) being capable of being housed in corresponding recesses (12) made in the external surface of the gas tank (7) located in correspondence with said closed end.