FR2938321A1 - Heat exchanger for exhaust gas recirculation circuit of heat engine of motor vehicle, has inlet and exhaust ducts with end longitudinally separated from reference plane by distance that is less than another distance measured along near axis - Google Patents

Abstract

The exchanger (21) has fluid inlet and exhaust ducts (31, 32) that are extended parallel to a longitudinal axis (AX). Each duct has an end (42) opened in a return chamber (34) closed by a base. A fluid circulation circuit (33) transfers heat between two fluids by an intermediate of the ducts. The end of the ducts is longitudinally separated from a reference plane (PR), normal to the longitudinal axis, by a distance, where the distance is less than another distance measured along a near axis of a separation plane (PS).

Description

1 Heat exchanger with parallel pipes

The invention relates to a heat exchanger for cooling exhaust gases of a recirculation circuit of these gases equipping a heat engine, also known under the acronym EGR meaning "Exhaust Gas Recirculation". BACKGROUND OF THE INVENTION Such a known exchanger, shown diagrammatically in FIG. 1 by being marked with 1, comprises a generally cylindrical casing 2 provided with a curved bottom 3 closing one of its ends, a collector 4 of FIG. connection to the exhaust gas recirculation circuit closing the other end of this envelope, and a main body 6 surrounded by the enclosure defined by the casing 2 and the collector 4. The collector is provided with a first mouth 7 intake of the exhaust gas to be cooled, and a second mouth 8 for discharging the cooled exhaust gas, and a movable valve 9. This valve 9 is movable between a first so-called cooling position, that it occupies in Figure 1, and a second position not shown, called bypass. When the valve is in the first position, it directs the gas admitted by the first mouth 7 to the main body 6 to be cooled before being discharged by the second mouth 8. When it occupies the second position, the gas admitted is directly transferred to the second mouth without being cooled.

As shown in Figure 1, the main body 6 comprises said intake pipes identified by 11, and said discharge pipes marked by 12, extending parallel to the longitudinal direction AX, between the bottom 3 and the collector 4 .

This main body also includes a cooling water passage circuit, marked by 13, and in which circulates the water that cools the main body. In operation, the gas is cooled when it runs through the so-called intake and discharge pipes of the main body, the latter being itself cooled by the cooling water. The gas admitted by the first mouth 7 engages in the intake ducts 11, via their ends located opposite the collector 4, it traverses these ducts 11 until reaching their other ends located in screws. 3 to the bottom of the casing 2, to open into a return chamber 14. The gas passing through the chamber 14 then enters the ends of the discharge pipes 12 which are also located opposite each other. of the bottom 3 and communicate with the chamber 14, then it traverses these pipes 12 to reach their other ends located opposite the collector 4, before being discharged via the second mouth 8. This general structure of exchanger, that is to say comprising inlet and outlet pipes communicating with each other by a return chamber is adapted for integration into a recirculation circuit of the combustion gases. Indeed, thanks to this general structure, the inlet mouth and the gas discharge mouth are contiguous, which facilitates the integration with an existing gas circuit because the connection requires to modify a very short section of this circuit. However, it is also expected from such an exchanger that it offers the best compromise between space and thermal efficiency because it is integrated in the compact environment of a vehicle powertrain, between different members of this group shown schematically. In fact, the specifications of such an exchanger limit its size by giving a maximum height, a maximum length and a maximum width. OBJECT OF THE INVENTION The object of the invention is to propose an exchanger architecture whose general structure offers an improved efficiency with respect to its bulk.

SUMMARY OF THE INVENTION To this end, the subject of the invention is a heat exchanger, for transferring heat between a first fluid and a second fluid, comprising a series of inlet and outlet pipes of the first fluid, the pipes intake and discharge lines extending parallel to a longitudinal axis being located respectively on either side of a longitudinal separation plane, each pipe having an end opening into a return chamber closed by a bottom and in which the first fluid passes to be transferred from the intake pipes to the discharge pipes, and a circulation circuit of the second fluid for transferring heat between the two fluids, in particular via the pipes, characterized in that the distance longitudinally separating a pipe end from a normal reference plane to the longitudinal axis intercepting all intake and / or discharge, is of -tower than it is measured along an axis close to the plane of separation. With this solution, the return chamber has a hollow face which is delimited by the ends of the pipes, so that the other face of this return chamber can be delimited by a bottom having a low curvature shape, even flat, this which makes it possible to increase the internal volume of the exchanger without modifying its length. The invention also relates to an exchanger as defined above, comprising a plurality of intake and discharge pipes, and in which each pipe has its end all the closer to the reference plane intercepting all the inlet and outlet pipes. repression that it is close to the plane of separation.

The invention also relates to an exchanger as defined above, comprising at least one pipe end having a section oriented obliquely with respect to the longitudinal direction, the distance separating longitudinally this section of the reference plane intercepting all the intake and discharge pipes, being all the weaker as it is measured along an axis close to the plane of separation. The invention also relates to an exchanger as defined above, comprising an extruded section comprising the intake and discharge pipes, a flat-bottomed shell enclosing one end of this section to delimit the return chamber, and which end enclosed by the shell is cut to have a hollow shape.

The invention also relates to an exchanger as defined above, wherein the end is cut to present, in a longitudinal plane normal to the separation plane, a V-shaped profile. The invention also relates to an exchanger as defined above, comprising an extruded profile comprising the intake and discharge pipes, a flat-bottomed hull enclosing one end of this section to define the return chamber, and in which the the end enclosed by the shell is bevelled, so that the distance separating a pipe end of an intercepting reference plane is all the intake ducts or all the discharge pipes is even lower than it is measured along an axis close to the plane of separation.

BRIEF DESCRIPTION OF THE FIGURES - FIG. 1 is a schematic representation of a prior art exchanger; FIG. 2 is a schematic representation of the exchanger according to the invention; FIG. 3 shows an exemplary embodiment of a first variant of the exchanger according to the invention; FIG. 4 is a schematic side view of a second variant of the exchanger according to the invention; FIG. 5 is a schematic side view of a third variant of the exchanger according to the invention; FIG. 6 is a schematic side view of a fourth variant of the exchanger according to the invention. DETAILED DESCRIPTION OF THE INVENTION The idea underlying the invention is to design a geometry of the gas return function optimizing the heat exchange and the available space. The exchanger according to the invention, identified by 21 in FIG. 2, comprises a cylindrical envelope 22 having a rectangular base, provided with a bottom 23 closing one of its ends, a manifold 24 connecting to the closing gas circuit. the other end of this envelope, and a main body 26 surrounded by the enclosure that jointly delimit the envelope 22 and the manifold 24. The manifold 24 has a first inlet mouth 27 of the exhaust gas, and a second mouth 28 through which this gas is discharged. It also includes a valve 29 movable between a first position, which it occupies in Figure 2, and a second position not shown. In the first position, the valve 29 orients the gas admitted by the first mouth 27 to the main body 26 to cool before it is discharged by the second mouth 28. When in the second position, the gas admitted is directly transferred to the second mouth 28, without being cooled.

The main body 26 comprises intake ducts 31, and discharge ducts 32, extending parallel to the longitudinal direction AX between the bottom 23 and the manifold 24. The intake ducts 31 are located on one side of the duct. a longitudinal separation plane, noted PS, and the discharge pipes 32 are located on the other side of this separation plane PS. The exchanger further comprises a circuit for circulating the cooling water, marked by 33. The gas admitted by the first mouthpiece 27 engages in the intake ducts 31, via their ends situated opposite the collector 24, it traverses these pipes 31 until reaching their other ends located opposite the bottom 23, to open into the return chamber 34.

After having passed through the chamber 34, the gas enters the ends of the discharge pipes 32, which are located opposite the bottom 23 and communicate with the chamber 34, and it traverses these pipes 32 until reaching their other the ends facing the collector 24, before being discharged via the second mouth 28. As can be seen in FIG. 2, the bottom 23 of the envelope 22 is a flat bottom which extends along a Normal rection to the axis AX, and the intake and delivery pipes have lengths that differ from each other instead of being identical. These pipes 31 and 32 have first ends, marked 41, opening towards the collector 24, being located at the same level with respect to the longitudinal direction AX, ie in the same plane normal to this axis. . But their second ends, marked 42, and which open towards the flat bottom 23 are located at different levels along the axis AX. In other words, each pipe 31, 32 has its second end 42 which is separated from a reference plane PR normal to the axis AX, by a distance that depends on the considered pipe.

This reference plane PR is one of the planes normal to the axis AX intercepting all the intake ducts and all the delivery pipes, and the distance separating longitudinally one end 42 of the plane PR is even lower than the considered driving is close to the separation plane PS. Thus, the ends 42 of the central pipes, ie those which are closest to the separation plane PS are closest to the reference plane PR. The pipes which are distant from this separation plane PS, ie those which are the closest to the upper face and the lower face of the envelope, have their ends 42 which are distant from the reference plane PR. These ends jointly delimit an inner hollow face of the return chamber 34, the latter being further delimited by the flat bottom 23, which makes it possible to increase the total length of these pipes without increasing the length of the exchanger . Thus, for the same length of exchanger, noted L, and for the same length of the return chamber, note 1, the total length of the inlet and discharge pipes that the gas must go is increased. In the case of the known exchanger of FIG. 1, the length of the inlet and discharge pipes is (L-1), whereas in the case of the invention, the average length of these pipes is (L-1). 1/2), which results in a gain in efficiency or efficiency of the exchanger, since the cooling length of the gas is increased, with identical dimensions.

In the present example, the length L is eighty millimeters and the length 1 is twenty millimeters, so that the gain obtained in terms of increasing the length of pipe is of the order of fifteen percent.

In the case of FIG. 2, the invention is applied to an exchanger whose main body 22 comprises, on the one hand, gas circulation lines to be cooled, and, on the other hand, cooling water circulation ducts. of this gas.

However, the invention also applies to another type of heat exchanger, which is shown in FIG. 3 by being identified by 43. This other heat exchanger also comprises an outer shell 44 which has a generally cylindrical shape with a rectangular base, of which one end is closed by an attached bottom 46, and the other end is closed by a manifold which is not shown. The enclosure delimited by the casing 44 with its bottom 46 encloses a main body 47 comprising an extruded aluminum profile 48 having a cross section with a rectangular contour, surrounded by a stainless steel shell 49 having a cylindrical side wall with a rectangular base. 51 closed by a flat bottom 52. The extruded section 48 comprises gas inlet and discharge pipes, the ends opening towards the bottom 52 are marked by 53 and 54, respectively. The intake ducts are located on one side of a longitudinal separation plane PS, containing the longitudinal axis AX of the exchanger, and the discharge lines are located on the other side of this plane. The cooling water, instead of circulating within the extruded aluminum profile, bathes it to cool it by circulating between the outer shell 44 and the stainless steel shell 49 which is significantly smaller. Each intake or discharge line here has a generally rectangular section, oriented obliquely to the separation plane PS which is itself parallel to two opposite outer faces of the body. Each section of the end of a pipe extends from an area near the separation plane PS to another region which is close to an outer planar face of the profile. As can be seen in FIG. 3, the end of the section 48 is V-shaped. It has a first planar face oblique with respect to a reference plane PR normal to the axis AX, and intercepting all the inlet and outlet ducts. discharge, the ends of the intake ducts being distributed in this first face. It comprises a second flat face oriented obliquely relative to the reference plane PS, and in which are distributed the ends 54 of the discharge pipes. These two oblique faces meet at an edge inscribed in the separation plane PS, they delimit the end of the section 48 to which they give a hollow shape which delimits the return chamber 56, together with the bottom 52 .

The end of each intake or discharge pipe thus has a section of relatively large dimensions vis-à-vis the exchanger, and which is oriented obliquely, so that the distance that separates longitudinally from the reference plane PR depends on the measurement axis considered. Concretely, the portions of such an end section near the separation plane PS are closer to the plane PR than the portions remote from this reference plane which are very far from the plane PR. As in the example of Figure 2, the invention provides here a gain on the length of the pipes to go through the gas to be cooled, the average length of each pipe being in practice increased by fifteen percent. In the example of FIG. 3, the two oblique faces of the end of the profile 48 have rectangular contours of the same dimensions, and they are oriented symmetrically with respect to the separation plane PS. These faces may also have different dimensions and orientations to optimize the gas flow. In the example of FIG. 4, the exchanger comprises a profile 57 which is provided with a face 58 wedging with the ends of the intake ducts whose dimensions are larger than those of the face 59 coinciding with the ducts. of repression. With this solution, the intake pipes have a larger average section than the discharge pipes, to take into account the fact that the mass volume of the gas is conditioned by its temperature. This greater mass volume when the gas is hot, ie when it circulates in the intake ducts, than when it is cold, ie when it circulates in the discharge pipes .

The assembly can then be enclosed by a stainless steel shell 61 flat bottom, as in the case of Figure 4, or by a hull whose bottom is curved, as in the example of Figure 5.

In the examples of Figures 1 to 5, the ends of the inlet and discharge pipes jointly define a hollow shape corresponding to one of the internal faces of the return chamber. The pipe ends are then separated from a reference plane PR by a distance that is smaller as it is measured along an axis close to this separation plane PS, the reference plane PR then intercepting all the pipes . Other geometries are possible, as in the example of FIG. 6, where the end of the profile simply has a beveled shape, defined by a single face oriented obliquely with respect to the longitudinal axis, the end being enclosed in a shell having a flat bottom normal to the axis AX.

The chosen reference plane PR then intercepts only the intake pipes or only the discharge pipes. The distance separating longitudinally a pipe end of the reference plane PR, is also lower than it is measured along an axis close to the separation plane PS. As in the other cases, the longitudinal separation plane PS is the one on each side of which are respectively the intake pipes and the discharge pipes.

Claims (6)

REVENDICATIONS1. A heat exchanger (21; 43) for transferring heat between a first fluid and a second fluid, comprising a series of intake (31) and discharge (32) conduits of the first fluid, the inlet ducts (31) ) and the discharge pipes (32) extending parallel to a longitudinal axis (AX) being located respectively on either side of a longitudinal separation plane (PS), each pipe having one end (42) 53, 54) opening into a return chamber (34; 56) closed by a bottom and into which the first fluid passes to be transferred from the intake lines (31) to the discharge lines (32), and a circuit (33) for circulating the second fluid for transferring heat between the two fluids, in particular via the lines (31, 32), characterized in that the distance separating a pipe end (42; 53, 54) a reference plane (PR) normal to the longitudinal axis (PR) intercepting all the intake (31) and / or discharge (32) pipes, is even lower than it is measured along an axis close to the separation plane (PS). 2. Exchanger (21) according to claim 1, comprising a plurality of inlet and outlet pipes, and wherein each pipe (31, 32) has its end all the closer to the reference plane (PR) intercepting all the intake and discharge lines are close to the separation plane (PS). 3. Exchanger (43) according to claim 1, comprising at least one pipe end (54) having a section oriented obliquely with respect to the longitudinal direction (AX), the distance longitudinally separating this section from the reference plane. (PR) inter-ceptant all intake and discharge pipes, being all the lower as it is measured along an axis close to the separation plane (PS). 4. Exchanger (43) according to one of the preceding claims, comprising an extruded section (48; 57) comprising the inlet and discharge pipes, a flat-bottomed shell (49; 61) enclosing an end of this profile (48; 57) for delimiting the return chamber (56), and wherein the end gripped by the body (48; 57) is cut to have a hollow shape. 5. Exchanger (43) according to claim 4, wherein the end is cut to present, in a longitudinal plane normal to the separation plane (PS), a V-shaped profile. 6. Exchanger according to one of claims 1 to 3, comprising an extruded section (57) comprising the intake and discharge pipes, a shell (61) with a flat bottom enclosing an end of this section to de-limit the chamber back, and wherein the end enclosed by the shell (61) is bevelled, so that the distance separating a pipe end of a reference plane (PR) intercepting all or all inlet ducts the discharge pipes are all the smaller as they are measured along an axis close to the separation plane (PS).