ALUMINIUM HEAT EXCHANGER FOR AN "EGR" SYSTEM

Field of the Invention

The present invention relates to a heat exchanger for a system of exhaust gas recirculation (EGR) of an internal combustion engine and, more particularly, to a heat exchanger with a central aluminium body. Background of the Invention

In the current art, various systems of exhaust gas recirculation in internal combustion engines are known, these being called EGR systems.

These systems recirculate exhaust gases from the exhaust manifold to the intake manifold after subjecting them to a cooling process, with the aim of reducing the amount of NOx emissions.

In most heat exchangers of the known art, this cooling process is carried out in cooling chambers housing a duct assembly through which the gas passes, the ducts being surrounded by a coolant in permanent recirculation. Various designs of these exchangers are known with a single or multiple passage of gas which, in whatever case, require welding of inner ducts to the plates and casings.

In turn, designs of exchangers with cylindrical corrugated ducts, ducts of rectangular section or oval ducts and also designs using plates instead of ducts are known.

All these designs have in common two independent circuits which use stainless steel as the manufacturing material due to its properties of resistance to corrosion and resistance to high temperatures and which require welding during the assembly. Proposals are also known for heat exchangers with one- piece bodies formed with internal pipes for the passage of hot gas and a cooling circuit external to the one-piece body and/or integrated in the same. In this sense the proposals described in patents GB 2 280 256, US 4 986 349 and FR 2 825 456 should be cited.

The car industry demands improvements in the known EGR systems for meeting various needs. One of these is motivated by

the growing requirements of administrative regulations regarding the acceptable limits of NOx emissions. Another need to be satisfied is facilitating the assembly of automobile engines by simplifying the design of its components to improve its capacity of integration.

The present invention is aimed at meeting these demands. Summary of the Invention

The present invention has the object of providing, as an integrating element of an EGR system, a heat exchanger for recirculated exhaust gases of an internal combustion engine which, like the exchangers known, comprises a casing housing a plurality of pipes for the passage of the gas to be cooled, means for its cooling, several heads on its ends coupled to the inlet pipe of gas from the exhaust manifold and from the gas outlet pipe connected to the inlet manifold of the engine, and in which, unlike them, said pipes for the passage of gas to be cooled are configured inside a body formed by means of at least two extruded aluminium profiles, at least one of these being inserted inside an outer profile, and delimiting the pipes between said profiles for the passage of gas to be cooled.

The gas circulating through these pipes enters into contact with the inner walls of the aluminium body, transferring part of its heat to the inner wall . In order to increase the transfer of heat the aluminium profiles are configured such that the surface of the pipes provides a large area of heat transfer and causes turbulences in its surroundings.

The coolant circulates through the outside of this aluminium body, wetting it and withdrawing the heat from the inner surface by heat conduction (a marked property of aluminium) .

The central aluminium body is housed inside a casing and a cooling chamber is formed between both of them through which the coolant circulates. The casing can be made of different materials because there is no need it to be welded to the aluminium body.

The forming of said body by means of at least two extruded aluminium profiles facilitates its manufacture which is carried

out by assembling at least one inner profile inside an outer profile such that they enter into contact. In this sense, when the exchanger is active the inner profile will be in contact with the hot gases and will have a higher temperature than the outer profile which will be in contact with the coolant. The difference in temperature between the two makes the inner profile expand to a greater extent then the outer profile, favoring the contact between them.

Among the advantages of the exchanger according to the present invention the following must be pointed out:

- A reduction in the costs of the product by substituting the manufacture of corrugated ducts in stainless steel and the welding processes required for extruded aluminium profiles. Aluminium is a much cheaper material and the number of operations to be performed is much lower and much simpler.

- A reduction in the industrialization times both due to the simplification of the manufacturing process and to being able to have homologated profiles for different heat specifications wherein the desired heat capacity can be achieved by modifying only the length of the aluminium body.

- A reduction in the weight of the heat exchanger due to being able to use aluminium or plastic materials for the outer casing.

The possibility of using various anti-deposition products which cannot be used at present on current designs, given that they go through the welding furnace and destroy the finishing at high temperatures.

Other features and advantages of the present invention are included in the following detailed description of an illustrative and in no sense limiting embodiment, of its object in relation with the accompanying drawings. Description of the Drawings

Figure 1 shows a perspective view of the extruded aluminium body of a heat exchanger for exhaust gases according to a first embodiment of the present invention.

Figures 2a and 2b show cross-sectional views of the two profiles used for forming the extruded aluminium body of Figure

1.

Figure 3 shows a cross-sectional view of the extruded aluminium body of a heat exchanger for exhaust gases according to a second embodiment of the present invention. Figures 4a and 4b show cross-sectional views of the two profiles used for forming the extruded aluminium body of Figure 3.

Figures 5a and 5b show side section and cross-sectional views of a heat exchanger for exhaust gases with the extruded aluminium body of Figure 3.

Figure 6 shows a cross-sectional view of the extruded aluminium body of a heat exchanger for exhaust gases according to a third embodiment of the present invention.

Figure 7 shows a side section view of a heat exchanger for exhaust gases with the extruded aluminium body of Figure 6.

Figure 8 shows a cross-sectional view of the extruded aluminium body of a heat exchanger for exhaust gases according to a fourth embodiment of the present invention.

Figures 9a and 9b show two sectional views of a heat exchanger for exhaust gases with the extruded aluminium body of Figure 8.

Figures 10a, 10b, 10c and 1Od show schematic cross- sectional views of a heat exchanger for exhaust gases according to the present invention with different casings. Detailed Description of the Invention

In an EGR system, a part of the exhaust gases of the engine comes outside through the exhaust pipe and another part is recirculated. The amount to be recirculated is controlled by the EGR valve which in certain circumstances, for example, in a maximum power situation, can even be closed and not recirculate anything. The recirculated gases are mixed with the clean air and return to the engine through the intake manifold.

In a first embodiment of the invention, shown in Figures 1 and 2, the aluminium central body 21 is formed by inserting the inner profile 23 inside the outer profile 25.

The outer profile 25 is formed by a profile of annular section 27 from which a plurality of inner radial flanges 29

project .

The inner profile 23 is formed by a profile of annular section 31 from which a plurality of outer radial flanges 33 project . Both profiles are configured such that when the inner profile 23 is inserted in the outer profile 35 the radial flanges 33 of the inner profile are located between two radial flanges 29 of the outer profile 25 delimiting the pipes 35 between them for the passage of the gas. In turn, the flanges 33 of the profile 23 must be sized to enter into contact with the annular part 27 of the profile 25 and the flanges 29 of the profile 25 must be sized to enter into contact with the annular part 31 of the profile 23 to maximize the heat exchange. A central body 21 with this configuration can be used for a heat exchanger of single passage with or without a by-pass pipe, using for that purpose a central duct 37 formed inside the profile 23, having poor exchange efficiency because it is not in direct contact with the cooling water. In the event that a by-pass pipe is not required, the central duct 37 can be used to pass the coolant through it and improve the performance of the heat exchange of the device or close it with a plug to avoid the passage of gas inside it. A configuration equivalent to the latter would be a profile 23 with a central core of compact circular section instead of the annular section 31.

In a second embodiment of the invention, shown in Figures 3, 4a, 4b, 5a and 5b, the aluminium central body 41 is formed by inserting the inner profile 43 inside the outer profile 45. The outer profile 45 is formed by a profile of annular section 47 with widened areas 46 from which a plurality of inner parallel flanges 49 project.

The outer profile 43 is formed by a T-shaped profile 51 from which a plurality of parallel flanges 53 project. Both profiles are configured such that when the inner profile 43 is inserted in the outer profile 45 the flanges 53 of the inner profile are located between two flanges 49 of the

outer profile 45 delimiting the pipes 55 between them for the passage of the gas. In turn, the pipes 57 used as by-pass pipes are formed between both profiles 43 and 45.

Figure 3 shows an embodiment of the invention with two by- pass pipes 57 in the form of circular semi-segments but the invention also comprises an embodiment with only one by-pass pipe 57.

The flanges 53 of the profile 43 must be sized to enter into contact with the annular part 47 of the profile 45 and the flanges 49 of the profile 45 must be sized to enter into contact with the section 51 of the profile 43 to maximize the heat exchange .

A central body 41 with this configuration can be used for a heat exchanger 59 of a single passage of gas the general structure of which includes a casing 11, an inlet head 13 with a by-pass valve 15, an outlet head 17 and a cooling chamber 19 with pipes 12, 14 for the inlet and outlet of the coolant.

In a third embodiment of the invention, shown in Figures 6 and 7, the aluminium central body 61 is formed by inserting the inner profile 63 inside the outer profile 65.

The outer profile 65 is formed by a profile of annular section 67 from which a plurality of inner parallel flanges 69 project .

The inner profile 63 is formed by a straight section 71 from which a plurality of parallel flanges 73 project towards each one of its sides.

Both profiles 63, 65 are configured such that when the inner profile 63 is inserted in the outer profile 65, the straight section 71 separates the pipe delimited by the annular profile 67 into two halves and the flanges 73 of the inner profile 63 are located between two flanges 69 of the outer profile 65 delimiting the pipes 75 between them for the passage of the gas.

The flanges 73 of the profile 63 must be sized to enter into contact with the annular part 67 of the profile 65 and the flanges 69 of the profile 65 must be sized to enter into contact with the section 71 of the profile 63 to maximize the heat

exchange .

A central body 61 with this configuration can be used for a heat exchanger 79 of two passages of gas the general structure of which includes a casing 11, an inlet-outlet head 13 with a by-pass valve 85, a manifold 16 and a cooling chamber 19 with pipes 12, 14 for the inlet and outlet of the coolant.

Although Figure 6 shows a central body 61 with symmetrical configurations for the two areas of passage of gas, in a preferred embodiment and as is shown schematically in Figure 7, the circuit 81 of the first passage must have a section of passage greater than the one of the second circuit 83 so that when the gas is cooler and there is greater tendency towards dirtying, the speed of the gas is increased and the deposition of soot in the walls of the central body is reduced. In a fourth embodiment of the invention, shown in Figures 8 and 9 which can be considered to be a variant of the third embodiment, the exchanger includes a cooling circuit inside the inner profile 63 and through the body of the by-pass valve 85.

The section 71 separating the circuit 81 of the first passage of gas from the circuit 83 of the second passage of gas includes a central orifice in which a central plate 90 is inserted delimiting the pipes 87, 89 of said inner cooling circuit closed in its rear part with a plug assembled on the inner profile 63 in a leak-tight manner. The inlet passage 93 and outlet passage 94 of this circuit are incorporated in the by-pass valve 85.

The central plate can be included in the profile 63 itself or be an independent plate placed to that effect and which can be made of different materials, both plastic and metallic materials, because it is perfectly cooled.

The direct cooling of both the outer profile 65 and the inner profile 63 introduce significant improvements compared to previous embodiments such as:

- Increasing the power of heat exchange of the exchanger, allowing making exchangers of a smaller size in order to obtain determined thermal features .

- Obtaining a cooling of the by-pass valve which allows

using aluminium for the manufacture of the body of the by-pass valve with the subsequent cost reductions.

As indicated previously, using the extruded aluminium bodies 21, 41, 61 of the embodiments which have just been described, aluminum casings 11a or plastic casings lib can be used because welds between both elements are not necessary. In the assembly of the heat exchanger, different closing means of the joints between the body 21, 41, 61 and the casings 11a, lib can be used, like the ones shown in Figures 10a, 10b, 10c and 1Od using Oring seals 95, straps 97, metal rings 98 and screws 99.

Flanges with cogged edges have been used in all the embodiments described but the person skilled in the art will understand that the invention also comprises edges with other suitable shapes to favor the heat exchange.

The present invention provides a heat exchanger for EGR systems which can be easily adapted to different requirements by modifying some of the design parameters such as the length of the central body (by lengthening it, a greater area of heat exchange, and therefore a greater heat efficiency, is obtained for a same cross-section) and the wet perimeter of the cross- section (in order to have a greater or smaller area of exchange for a same length) .

In all the embodiments of the invention which have been described, the central body is formed with two profiles to facilitate the manufacture and the person skilled in the art will easily understand that the present invention also comprises a body formed with more than two profiles.

The assembly of the different profiles must be carried out such that the different pieces enter into contact well in order to minimize losses by contact resistance to heat transmission by conduction. For the most demanding assemblies, the possibility of assembling the different profiles at different temperatures is considered so that the inner profiles have lower temperatures than the outer profiles with the purpose of obtaining expansion degrees between the inner and outer pieces and favoring the assembly. Once the temperatures of the two bodies of the

profiles are equal, the interferences or contacts between the different parts are favored by the contraction of the outer profile with respect to the inner profile.

If it were necessary to improve the heat transmission between the inner profile and the outer profile (if two profiles are used) , the use of welds between the different profiles can be considered with the purpose of facilitating heat transmission between them in those applications in which the requirements of heat or product exchange are so demanding that the simple contact of metal with metal cannot satisfy the needs demanded from the product and the cost increase that this entails is justified.

The preferred outer shape of the outer profile is cylindrical in order to simplify the closing system of the cooling circuit by means of seals like the ones shown in Figures 10a, 10b, 10c and 1Od that are better adapted to cylindrical shapes. Nevertheless, the invention can also comprise different shapes because the extrusion process of aluminium allows making irregular shapes which may be convenient. With respect to the embodiments described in the invention, those modifications comprised within the scope defined by the following claims can be introduced.