ES2332253A1 - Heat exchanger for gases, in particular for the exhaust gases from an engine - Google Patents

Abstract

The heat exchanger (1) of the present invention comprises a metal body (3, 7) arranged inside a plastic casing (2), said metal body (3, 7) incorporating a circuit through which gases are intended to flow with heat exchange with a coolant, and at least one gas reservoir (7) or support flange coupled to at least one end of said circuit, and junction means for fastening at least one of the ends of the metal body (3, 7) to the plastic casing (2). The heat exchanger is characterized in that said junction means comprise a plurality of bearing points (11) of small contact area which are rigidly connected to the plastic casing (2) and which can be located in respective recesses (12) belonging to said at least one gas reservoir (7) or support flange.

Description

Heat exchanger for gases, especially of the exhaust gases of an engine.

The present invention relates to a heat exchanger for gases, especially gases from engine exhaust

The invention is especially applied in Exhaust gas recirculation exchangers of an engine (EGRC).

Background of the invention

In some heat exchangers for the gas cooling, for example those used in recirculation of the exhaust gases towards the intake of an engine of explosion, the two means that exchange heat are separated by a wall

The heat exchanger itself it can have different configurations: for example, it can consist in a tubular housing inside which a series of parallel conduits for the passage of gases, circulating the refrigerant through the housing, externally to the ducts; in other embodiment, the exchanger consists of a series of plates parallel that constitute the heat exchange surfaces, so that the exhaust gases and the refrigerant circulate between two plates, in alternating layers.

In the case of beam heat exchangers of ducts, the junction between the ducts and the housing can be of different kinds. Generally, the ducts are fixed by its ends between two support plates coupled at each end of the housing, both support plates having a plurality of holes for the placement of the respective ducts. These support plates are fixed in turn to connection means with the recirculation line.

Said connection means may consist of a V connection either on a peripheral connection flange or flange, depending on the design of the recirculation line where The exchanger is assembled. The peripheral flange can be assembled together with a gas tank, so that the gas tank is an intermediate piece between the housing and the flange, or the flange may be assembled directly to the Case.

Also, the gas circuit can be of type linear in which the inlet and outlet of gases are arranged in opposite ends; or it can be in the form of "U" in which the inlet and outlet of gases are arranged adjacent in a same open end, the opposite end being closed, and defining a one-way step and a return step. In this last case, the closed end for the return of gases is usually constituted by a closed gas tank.

Usually, EGR heat exchangers they are metallic, usually made of stainless steel or aluminum. Both the duct beam exchangers and those of stacked plates, have all their metal components, so which are assembled by mechanical means and then welded to ensure a level of tightness required for this application.

An action to reduce the cost of EGR heat exchanger is to replace the steel housing stainless by another material, whether this material has a cost low as if it allows integrating other functions, such as the integration of the cooling fluid ducts or mounting brackets to a surface of the motor environment where it will be Fixed the exchanger.

Beam heat exchangers are known of conduits comprising a plastic housing. The plastic housings have the advantage that the cost of final product since it allows to integrate the conduits of the circuit of the cooling fluid and fixing brackets to a surface of the motor environment.

In this case, the plastic housing houses in inside the core or metal body of the exchanger constituted by the tube bundle, and at least one support plate and a gas tank The metal body must be fixed to the housing of plastic preventing it from being cantilevered, and thus guarantee the mechanical resistance of the heat exchanger against Engine vibration

Patents are known regarding EGR exchangers with plastic housing describing the joint between the metal and plastic parts, ensuring a sealing of the cooling fluid to avoid any leakage.

A key point of the design of the exchanger of heat is the union between the plastic components and the metal components, such as aluminum or stainless steel. At case of "U" shaped heat exchangers, there are two types of unions, a union whose function is to fix the different materials, plastic and metal, as well as guarantee the tightness, and another union with a single support function.

In this "U" shaped configuration, the joint on the open side generally includes a gasket tightness to avoid any possible leakage of the fluid from outward cooling while joining on the side closed does not require the sealing function since on that side it is only necessary to support the metal body inside the housing of plastic. WO 2007/048603 describes a heat exchanger heat of this type, in which the joining means on the side closed comprises a support integral to the plastic housing, which is provided with a slit intended to receive a highlight of the closed gas tank.

However, the known exchangers of This type has a series of drawbacks as the fixation From the metal body of the exchanger to the plastic housing is very conflictive and it is necessary to take into account the following design considerations:

1) The contact area :

Working temperatures for the housing of Plastic and exchanger body are different. The body metallic can reach high temperatures since it is in contact with the gas, which varies its temperature from 750ºC in the input up to 500 ° C at the exit; while the housing of plastic withstands relatively low temperatures because it is bathed by the cooling fluid that is at a temperature of between 70ºC and 90ºC.

The contact area between the body of the exchanger and plastic housing should be very well cooled by the cooling fluid.

This means that, on the one hand, the flow of cooling fluid in this area must be sufficiently abundant, therefore the passage of cooling fluid preferred, and that, on the other hand, the contact area must be very small to maintain the temperature in the contact area of the plastic material at values close to the temperature of the cooling fluid Also, the contact area must be large enough to support the metal body.

2) Thermal expansion :

Due to the temperature difference between the metal body and plastic housing, thermal expansion for the two components it will be different, also depending on the coefficient of thermal dilation.

This has the disadvantage that they occur unwanted movements preferably longitudinally between the components due to its own expansion.

3) Distance between the metal body and the housing :

As mentioned, the contact area between the plastic housing and the metal body, usually the gas tank, must be very well cooled by the fluid of cooling, which means that the cooling fluid in This area should be preferential. To improve the fluid flow of refrigeration in this area the requirements are very important of design.

In this sense, it is very important to define the distance between the metal body and the plastic housing. The Choice of this value depends on the minimum cross section of cooling fluid inside the heat exchanger. By example, if a tubular heat exchanger has a distance between the 1.3 mm gas pipes, the recommendation is have a distance of 2.6 mm, on both opposite sides, between the gas tank and plastic housing.

4) Position of the cooling fluid inlet connection :

It is very important to locate the input connection of the cooling fluid near said contact area, with the in order to guarantee a minimum cooling fluid flow.

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

It is advisable to place at least one support of fixing to the motor in the support area of the conduit beam to the exchanger housing in order to have better resistance to the vibrations of the metal body motor.

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

A good design of the union of the metal body with plastic housing to absorb the space due to component tolerances.

Description of the invention

The purpose of the heat exchanger for gases, especially the exhaust gases of an engine of the present  invention is to solve the drawbacks of exchangers known in the art, providing a joint optimized between the plastic housing and the metal body of the exchanger

The heat exchanger for gases, in special exhaust gas of an engine, object of the present invention, is of the type comprising a metal body arranged in the inside of a plastic housing, including said body metallic a circuit intended for the circulation of 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 metal body to the plastic housing, and it characterized by the fact that said joining means comprise a plurality of support points of small contact area solidary of the plastic housing, capable of being fitted in both incoming ones belonging to the at least one gas tank or support flange.

Thanks to the means of joining constituted by a plurality of small area support points contact is able to resolve the commitment to have an area Small enough to maintain the temperature in the area of plastic material contact at values close to the temperature of the cooling fluid, and in turn have an area contact large enough to support the body metal.

In addition, this solution allows to improve the cooling fluid flow distribution also improving  the cooling of the contact area that is high temperature.

Moreover, positioning is facilitated of the heat exchanger body inside the housing plastic during assembly operation.

Preferably, the support points are constituted by longitudinal nerves.

Advantageously, the support points are distributed radially in an internal area of the housing plastic in a substantially equidistant way.

In this way, you get a correct distribution of the weight of the metal body on the housing of plastic guaranteeing a good stability of the set.

Preferably, the joining means comprise between two and eight support points.

According to an embodiment of the invention, in the case of a rectangular cross section housing, the means of union include six distributed support points symmetrically, so that there are two points of support on each side major and a fulcrum on each minor side of that section rectangular cross.

According to another embodiment of the invention, also in the case of a rectangular cross section housing, the joining means comprise two distributed support points symmetrically, so that there is a foothold on each side greater of said rectangular cross section.

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

Advantageously, the support points comprise a minimum longitudinal dimension to allow displacements caused by the different thermal expansion between the body Metallic and plastic housing.

In this way, a correct one is guaranteed exchanger operation despite unwanted longitudinal movements generated by the dilation of the metal body and plastic housing to different temperatures

Also advantageously, a distance is provided minimum between the metal body and the plastic housing that is depending on the minimum cross section of the fluid flow of cooling inside the exchanger.

Therefore, an appropriate distance is guaranteed between the metal body, usually the gas tank, and the plastic housing, in order to obtain an abundant flow of cooling fluid

Preferably, in the case of a circuit of gases that includes a plurality of parallel ducts, the minimum distance between the metal body and the plastic housing, measured on each opposite side of the metal body, it is twice the distance between the gas ducts.

Also preferably, a distance is provided of security between 1.5 and 2.5 times the minimum section Transverse cooling fluid flow.

Advantageously, taking into account that the exchanger comprises an input connection and a connection of cooling fluid outlet integrated into the housing plastic, the fluid inlet or outlet connection of cooling is located near said contact area of the Support points. This ensures a fluid flow of minimum cooling

Also advantageously, considering that the exchanger comprises surface fixing brackets of the motor environment, at least one fixing bracket is located near said contact area of the support points. This way, you get better vibration resistance coming from the motor on the metal body.

Also advantageously, the points of support comprise a suitable configuration to absorb space due to the tolerances of the exchanger body and the housing of plastic.

Therefore, joining means are obtained enhanced with longer life, and more assembly operation simple between the body of the exchanger and the housing of plastic. The shape of the support points will admit a deformation less than its plastic material in case the interference of assembly between the two components is greater than the allowable, it is that is, a gas tank with the highest allowable tolerance and the Shortest distance between support points.

Preferably, the support points comprise a branched configuration.

According to an embodiment of the invention, the Support points include two divergent branches that form an angle suitable chosen according to the plastic material used. Fits emphasize that the greater the defined angle between the branches, The lower the assembly effort.

According to another embodiment of the invention, the Support points include three divergent branches. In this case, the incorporation of an additional central branch allows to improve the stability.

Preferably, the support points include a plurality of small bumps on its surface external Thus, the volume of plastic to be deformed is smaller, in the case of mounting interference, and therefore the Assembly procedure is simpler.

Advantageously, the gas inlet is located near the cooling fluid passage, either in its entry or exit

Preferably, the gas inlet is located near the outlet of the cooling fluid.

According to an embodiment of the invention, The heat exchanger is of the "U" type in the which the entry and exit of the gases are arranged adjacent in the same open end of the metal body, the end being opposite closed, and defining a one-way and one-return step, and It is characterized by the fact that the footholds are constituted by longitudinal nerves integrated in a surface  internal of the plastic housing, said ribs being liable to fit in corresponding starters formed on the external surface of the gas tank located at said closed end.

Generally, the gas tank is manufactured by stamping and fixing areas in the form of recesses They provide the gas tank itself with additional rigidity.

Brief description of the drawings

In order to facilitate the description of how much It has been exposed above are attached some drawings in which, schematically and only by way of non-limiting example, they represent some practical cases of realizations of gas heat exchanger of the invention, in the which:

Figure 1 is a perspective view and in explosion of a heat exchanger for gases from the invention;

Figure 2 is a longitudinal section view of the mounted exchanger of Figure 1;

Figures 3, 4 and 5 are sectional views transverse of the exchanger, according to the line III-III of Figure 2, showing the means of union with six, four and two nerves respectively, according to different embodiments of the invention;

Figure 6 is a partial perspective view of a longitudinal section, showing the nerves longitudinal;

Figures 7 and 8 are sectional views cross section of the exchanger, showing the joining means with two branched nerves including two and three branches respectively, 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;
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Figure 11 is a cross-sectional view. of the exchanger, showing an enlarged view of a nerve longitudinally provided with a plurality of protuberances.

Description of preferred embodiments

Referring to figures 1 and 2, the heat exchanger 1 is constituted by a housing of plastic 2 that contains inside a metal body that comprises a bundle of parallel ducts 3, intended for the passage of the gases to cool. Inside housing 2, externally to the ducts 3, a cooling fluid circulates, from an inlet 4 to an outlet 5. Said metal body also includes a plate of support 6 and a gas tank 7 as will be explained hereafter.

In this example, housing 2 is sectional substantially rectangular and is closed by one of its ends, to accommodate inside the bundle of ducts 3 which, in this case is of the "U" type, that is, entry 8 and outlet 9 of said ducts 3 are arranged on the same side in the open end of the housing 2, and defining a one-way step and a return step of the gases to cool.

It is convenient that the inlet 8 of the gases is arranged near the passage of cooling fluid, either in Your entry or exit. In the embodiment illustrated in Figure 1, the gas inlet 8 is located near outlet 5 of the fluid of refrigeration.

The beam of conduits 3 is fixed at its end free to said metal support plate 6, which has a plurality of holes for the placement of the respective ducts 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 means of screws. In addition, between said open end of the housing 2 and the support plate 6 provides for the placement of a gasket 10 plastic to ensure the level of tightness.

The plastic housing 2 is fixed by its closed end to said metal gas tank 7 by means of binding means that include a plurality of ribs longitudinal 11 of small contact area integral with the plastic housing 2, and capable of being fitted in some corresponding incoming 12 belonging to the gas tank 7.

In this example, the entrees 12 are formed in said gas tank manufactured by stamping

Longitudinal nerves 11 allow to solve the commitment to have an area small enough to maintain the temperature in the contact area of the plastic material at values close to the fluid temperature of cooling, and in turn have a contact area sufficiently Great to support the metal body.

In addition, this solution allows to provide a abundant flow of cooling fluid to cool the area of contact that is at high temperature.

Moreover, positioning is facilitated of the heat exchanger body inside the housing plastic during assembly operation.

Generally, they are used between two and eight longitudinal nerves 11 distributed substantially equidistant to obtain a correct distribution of the weight of the metal body on the plastic housing, thus guaranteeing a Good set stability.

According to an embodiment of the invention illustrated in figure 3, the joining means comprise six ribs longitudinal 11 distributed symmetrically, so that there are two nerves on each major side and one nerve on each minor side of said rectangular cross section.

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

According to another embodiment of the invention, illustrated in figure 5, the joining means comprise two ribs  longitudinally distributed symmetrically, so that there is a nerve on each major side of said cross section rectangular.

Also, the longitudinal nerves 11 they comprise a minimum longitudinal dimension to allow displacements caused by the different thermal expansion between the metal gas tank 7 and the plastic housing 2, ensuring proper operation of the exchanger. In the Figure 6 is illustrated by a double pointed arrow the direction of said longitudinal displacements.

A minimum distance between the gas tank 7 and plastic housing 2 which is a function of the minimum cross section of the cooling fluid flow inside the exchanger 1. This ensures a Abundant flow of cooling fluid.

This minimum distance between the gas tank 7 and the plastic housing 2, measured on each opposite side of the gas tank 7, is twice the distance between the ducts of gas 3. A safety distance included is also provided between 1.5 and 2.5 times the minimum cross section of the flow of cooling fluid

The inlet connection 4 of the fluid cooling is located near the contact area of the joint between the housing 2 and the gas tank 7, as can be seen in Figures 2 and 6. This ensures a fluid flow of minimum cooling

The exchanger 1 comprises supports of fixing 13 to a surface of the motor environment, which are located near said contact area of the junction between the housing 2 and the gas tank 7, as can be seen in the Figure 1. In this way, a better resistance of the vibrations from the motor on the metal body.

The longitudinal ribs 11 comprise a adequate configuration to absorb space due to tolerances of the gas tank 7 and the plastic housing 2.

The shape of the longitudinal nerves 11 will admit a minor deformation of its plastic material in case the mounting interference between the two components is greater than the admissible, that is, a gas tank with the highest tolerance admissible and the shortest distance between longitudinal nerves. In this case, the longitudinal ribs 11 may comprise a branched configuration, as can be seen in figures 7 to 10.

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

In figures 9 and 10 you can see respectively different values of the angle formed by the branches of the longitudinal nerves 11. The larger the angle defined between the branches, the lower the assembly effort.

According to another embodiment of the invention shown in figure 8, the longitudinal ribs 11 include three branches divergent In this case, the incorporation of a central branch Additional improves stability.

Longitudinal nerves 11 may include a plurality of small bumps 14 on its surface external, as can be seen in Figure 11. Thus, the plastic volume to be deformed is smaller, in the case of mounting interference, and therefore the mounting procedure is more easy.

Although in this example a parallel tube beam exchanger, the invention can also  apply to stacked plate exchangers. Also, in both cases, the gas circuit may be of the "U" type (the entry and exit of gases arranged at the same end) or it can be of linear type (the entrance and exit of arranged gases at opposite ends).

Claims (21)

1. Heat exchanger (1) for gases, especially the exhaust gases of an engine, comprising a metal body (3.7) disposed inside a plastic housing (2), said metal body including 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 area of contact solidary of the plastic housing (2), capable of being fitted in two incoming (12) belonging to the 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 by longitudinal ribs. 3. Exchanger (1) according to claim 1, characterized in that the support points (11) are distributed radially in an internal area of the plastic housing (2) in a substantially equidistant manner. 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 4, of the type that the housing (2) is of rectangular cross-section, characterized in that the joining means comprise six support points (11) distributed symmetrically, so that there are two support points on each major side and one support point on each minor side of said rectangular cross section. 6. Exchanger (1) according to claim 4, of the type that the housing (2) is of rectangular cross-section, characterized in that the joining means comprise two support points (11) distributed symmetrically, so that there is a fulcrum on each major side of said rectangular cross section. 7. Exchanger (1) according to claim 4, of the type that the housing (2) is of rectangular cross section, characterized in that the attachment means comprises four support points (11) distributed symmetrically, so that there are two support points on each major side of said rectangular cross section. 8. Exchanger (1) according to claim 1, characterized in that the support points (11) comprise a minimum longitudinal dimension to allow displacements caused by the different thermal expansion between the metal body (7) and the housing plastic (2). 9. Exchanger (1) according to claim 1, characterized in that a minimum distance between the metal body (7) and the plastic housing (2) is provided which is a function of the minimum cross-section of the flow of cooling fluid inside the exchanger (1). 10. Exchanger (1), according to claim 9, of the type that the gas circuit (3) includes a plurality of parallel ducts, characterized in that the minimum distance between the metal body (7) and the plastic housing (2), measured on each opposite side of the metal body (7), is twice the distance between the gas conduits (3). 11. Exchanger (1) according to claim 9 or 10, characterized in that a safety distance between 1.5 and 2.5 times the minimum cross section of the cooling fluid flow is provided. 12. Exchanger (1) according to claim 1, of the type comprising an inlet connection (4) and an outlet connection (5) of the cooling fluid integrated in the plastic housing (2), characterized by the fact that the inlet (4) or outlet (5) connection of the cooling fluid is located near said contact area of the support points (11). 13. Exchanger (1), according to claim 1, of the type comprising fixing brackets (13) to a surface of the motor environment, characterized in that at least one fixing bracket (13) is located near said area of contact of the support points (11). 14. Exchanger (1) according to claim 1, characterized in that the support points (11) comprise a suitable configuration to absorb space due to the tolerances of the exchanger body (7) and the plastic housing ( 2). 15. Exchanger (1) according to claim 14, characterized in that the support points (11) comprise a branched configuration. 16. Exchanger (1) according to claim 15, characterized in that the support points (11) include two divergent branches that form a suitable angle chosen according to the plastic material used. 17. Exchanger (1) according to claim 15, characterized in that the support points (11) include three divergent branches. 18. Exchanger (1) according to claim 1, characterized in that the support points (11) include a plurality of small protuberances (14) on their outer surface. 19. Exchanger (1) according to claim 1, characterized in that the inlet (8) of the gases is located near the passage of cooling fluid, either at its inlet or outlet. 20. Exchanger (1) according to claim 19, characterized in that the inlet (8) of the gases is located near the outlet (5) of the cooling fluid. 21. Exchanger (1), according to claim 1, of the "U" type in which the inlet (8) and outlet (9) of the gases are arranged adjacent to the same open end of the metal body (3) , the opposite end being closed, and defining a forward passage and a return passage, characterized by the fact that the support points are constituted by longitudinal ribs (11) integrated in an internal surface of the plastic housing (2) , said ribs (11) being able to fit into corresponding recesses (12) formed on the external surface of the gas tank (7) located at said closed end.