FR2935475A1 - Heat exchanger i.e. cooler, for cooling re-circulated exhaust gas, in cooling circuit of heat engine of motor vehicle, has fluid inlets for inletting fractions of coolant, and fluid outlet for evacuating fractions of coolant at same time - Google Patents

Abstract

The exchanger (10) has a case provided with a fluid inlet (14) to inlet a coolant to be cooled, and a fluid outlet (16) to outlet the coolant. A fluid circulation unit circulates the fluid between the fluid inlet and the fluid outlet. Another fluid inlet (18) inlets fraction (F1) of the coolant at temperature, and a third fluid inlet (20) inlets another fraction (F2) of the coolant at another temperature that is higher than the former temperature. Another fluid outlet (22) evacuates the fractions of the coolant at the same time. An independent claim is also included for a cooling circuit comprising a main line.

Description

BACKGROUND OF THE INVENTION The invention relates to the field of heat exchangers, in particular for motor vehicles. It relates more particularly to a heat exchanger for cooling a fluid such as, for example, the recirculated exhaust gas of a heat engine. Heat exchangers of this type are already known which comprise a housing provided with a fluid inlet for the fluid to be cooled, a fluid outlet for the cooled fluid and means for circulating fluid between the inlet of the fluid and the fluid outlet, as well as circulation means for a cooling fluid which exchanges heat with the fluid to be cooled inside the housing. In order to cool and increase the charge air density of an internal combustion engine, it is known to use a charge air cooler in which a liquid such as water is used as the charge air cooler. coolant.

Furthermore, to reduce the pollutant emissions of an internal combustion engine, it is known to take a portion of the exhaust gas for reinjection into the air 30 admission fees. To ensure correct filling of the engine cylinders and to protect the elements of the intake line, these gases are then cooled by water exchangers, called recirculated exhaust gas coolers. In order to reinject hot exhaust gases with a sufficient flow rate, while limiting the circulation ducts, it is known to take high-pressure exhaust gases from the engine exhaust manifold, to cool them at the same time. using a water exchanger called high pressure exhaust gas cooler, and reinject them into the intake manifold of the engine. It is also known to bypass this heat exchanger to warm up the engine faster at startup.

In addition, to reinject clean and cold exhaust gases, it is known to remove low pressure exhaust gases after a particulate filter, to cool them with a water exchanger called a gas cooler. exhaust at low pressure, and reinject them upstream of the turbo-compressor that provides the charge air. It is known to cool these different heat exchangers with a cooling circuit independent of the engine cooling circuit. This independent circuit is commonly called low temperature circuit (or LV circuit) with reference to a coolant temperature lower than that of the high temperature circuit (or HT circuit). It is known to cool all the heat exchangers in parallel or all the heat exchangers in series.

Furthermore, it is known from publication WO 2005/073535 to cool the exhaust gas recirculated by two different fluids. The beginning of the heat exchange is ensured by the high temperature liquid coming from the engine block, while the end of the heat exchange is ensured by the low temperature liquid coming from the low temperature loop (LV loop). . The recirculated exhaust gas is then cooled by two separate heat exchangers.

It is further known to provide the heat exchangers for cooling the recirculated exhaust gas according to different techniques, in particular according to a technique with plates and spacers, and according to a tube technique.

A heat exchanger of the type mentioned above must have high thermal performance. It must be able, especially in the case of cooling the recirculated exhaust gas, to cool gases which enter the housing at a temperature of up to 900 ° C, for example.

In conventional cooling circuits, the coolant flowing through the radiator also passes through the various heat exchangers mentioned above.

If the heat exchangers are cooled in parallel, it requires a very large total flow of the coolant, and the efficiency of the radiator is reduced accordingly. On the other hand, if the heat exchangers are in series, this creates significant losses in the coolant, and therefore significant compression requirements at the circuit pump. In addition, the heat exchange at each exchanger will be reduced, the coolant heating up after each exchanger.

Usually, the heat exchangers of the type mentioned in the introduction comprise a single inlet and a single outlet for the cooling fluid. As a result, these heat exchangers, in particular in the case of the cooling of the recirculated exhaust gas, have a good heat exchange in a first part of the exchanger, then this exchange deteriorates as the difference temperature decreases between the gases and the coolant.

Cooling recirculated exhaust gases with two different fluids, as taught by WO 2005/073535, requires a complex circuit with many different connections and two exchangers, which increases the complexity and therefore the cost.

The object of the invention is in particular to overcome the aforementioned drawbacks.

It proposes for this purpose a heat exchanger of the type defined in the introduction, which comprises a first fluid inlet for admitting a first fraction of the cooling fluid, at a first temperature, a second fluid inlet for admitting a second fraction of the same fluid. cooling, at a second temperature above the first temperature, and a common fluid outlet for discharging at the same time the first fraction and the second fraction of the cooling fluid.

Advantageously, the fluid inlet and the fluid outlet are provided for or concern a gas, and they thus constitute respectively a gas inlet and a gas outlet. In the remainder of the description, the fluid entering and leaving will be considered to be a gas.

The cooling of the gas is thus effected by the flow rates of the first fraction and the second fraction within the same heat exchanger, therefore by a higher flow rate, which allows better thermal performance.

Since the cooling fluid is generally a liquid, such as water, this higher flow rate makes it possible to prevent the liquid from boiling and thus the creation of gas bubbles within the liquid. These gas bubbles are detrimental to good cooling and they are more likely to create a number of problems, including hot spots on the cylinder head of the engine, when the liquid is also used for cooling such an engine.

The fact of being able to cool the incoming gases by the flow rates of the two fractions of the cooling fluid is particularly advantageous in the case of recirculated exhaust gases which penetrate into the housing at an elevated temperature, as mentioned above.

In addition, the structure of the heat exchanger is simplified because it has only two inlets and a single outlet for the coolant.

In a first general embodiment of the invention, the housing has an elongated configuration, the gas inlet and the gas outlet being respectively located at two opposite ends of the housing so that the gases follow a substantially straight path between the gas inlet and the gas outlet.

In a second general embodiment of the invention, the housing has an elongated configuration, the gas inlet and the gas outlet being located at the same end of the housing, a return being provided at another end of the housing for that the gases follow a substantially U-shaped path between the gas inlet 35 and the gas outlet.

In a first variant, the first fluid inlet is located in a first zone of the housing located on the gas outlet side, the second fluid inlet is located in a second zone of the housing located between the gas inlet and the first zone, and the common fluid outlet is located in a third zone of the housing located on the side of the gas inlet.

This allows to benefit from a cumulative flow of the first fraction and the second fraction of cooling fluid in the third zone of the housing where the gases are at a higher temperature.

As a result, the incoming gases are first cooled by the cumulative flow rate of the first and second fractions, that is, precisely where the gases to be cooled are the hottest.

This cooling of the incoming gases is carried out by a mixture of the first and the second fraction, that is to say at a temperature intermediate between the first temperature and the second temperature mentioned above. Then, the gases which have been cooled in this third zone are cooled in a second zone by the second fraction of the cooling fluid and finally in the first zone by the first fraction of the cooling fluid which is at the lowest temperature.

In a second variant, the first zone of the housing is located on the side of the gas outlet, the second zone of the housing is located on the gas inlet side, and the third zone of the housing is located between the first zone and the second zone.35 This variant makes it possible to use the respective flow rates of the two fluid fractions, but without cumulation of these flows as in the previous variant.

The heat exchanger of the invention can be made by techniques known per se, in particular according to the tube technique, or according to the technique with plates and spacers.

The heat exchanger of the invention is advantageously made in the form of a cooler for the recirculated exhaust gas of a heat engine, but it can also be used in other applications that require the cooling of a fluid (the same principle can be used for oil, refrigerant, etc.).

In the invention, the cooling fluid is preferably the coolant of a motor vehicle thermal engine.

In another aspect, the invention relates to a cooling circuit traversed by a cooling fluid, and comprising a heat exchanger as defined above.

In the description which follows, made only by way of example, reference is made to the appended drawings, in which:

FIG. 1 is a schematic diagram of a heat exchanger according to the invention, illustrating the different cooling zones;

FIG. 2 is a perspective view of a heat exchanger comprising an elongated housing and made in a tube technique; - Figure 3 is a schematic longitudinal sectional view of the heat exchanger of Figure 2;

FIG. 4 is a perspective view of an upper plate capable of forming part of a stack of plates in a heat exchanger according to the invention;

Figure 5 is a perspective view of a lower plate adapted to be assembled with the top plate of Figure 4;

- Figure 6 shows the assembly of the upper plate of Figure 4 and the lower plate of Figure 5;

FIG. 7 is a schematic view of a heat exchanger according to the invention made according to a U-circulation technique of the gases;

FIG. 8 schematically represents part of a cooling circuit of a motor vehicle engine incorporating a heat exchanger according to the invention;

Figure 9 is a schematic view of a heat exchanger similar to that of Figure 7;

- Figure 10 is a view similar to Figure 9 showing the circulation of the cooling fluid;

Figure 11 is a view similar to Figure 9 showing the circulation of the gas to be cooled; and

FIG. 12 illustrates an exemplary embodiment of the heat exchanger of FIG. 9 in the form of a tube exchanger.

Figure 1 schematically shows a heat exchanger 10 for gas cooling, comprising a housing 12 provided with a gas inlet 14 at one end and a gas outlet 16 at another end. Between the inlet and the outlet, the gases pass through the housing along its entire length, as indicated by the arrows G.

In the example, the gases pass through the housing in a linear path and are cooled in the housing by a cooling fluid.

The housing comprises a first fluid inlet 18 for admitting a first fraction F1 of the cooling fluid at a first temperature T1 in a first zone Z1 of the housing located on the gas outlet side 16. The exchanger further comprises a second fluid inlet 20 for admitting a second fraction F2 of the same cooling fluid, at a temperature T2 greater than the first temperature T1, in a second zone Z2 of the housing located between the gas inlet 14 and the first zone Z1.

The housing further comprises a common fluid outlet 22 located in a third zone Z3 of the housing located on the side of the gas inlet 14, between this gas inlet and the second zone Z2 to evacuate at the same time the first fraction F , and the second fraction F2 of the cooling fluid.

This makes it possible to benefit from a cumulative flow rate of the first fraction F and the second fraction F2 of the cooling fluid in the third zone Z3 of the housing where the incoming gases are at a higher temperature.

The cooling fluid is advantageously constituted by the coolant of a motor vehicle engine.

In the particular application to a chiller recirculated exhaust gas of a heat engine, the gases enter the inlet 14 at a temperature of the order of 900 ° C. By way of example, the temperatures T1 and T2 may be respectively of the order of 50 ° C. and 80 ° C., these values being given for information only. The word temperature also applies to intervals or ranges of temperature.

Under these conditions, the gases are cooled in the first place by the cumulative flow of the fractions F1 and F2, and therefore by a higher flow rate, which makes it possible to avoid the boiling of the cooling fluid when the latter is a liquid such as the water. Then, the gases are further cooled in the zone Z2 by the fraction F2 at the temperature T2 and finally in the zone Z1 by the fraction F1 at the temperature T1, which is the lowest, which allows to further cool the gases that leave then the heat exchanger 10.

In the embodiment of FIG. 2, the housing 12 has an elongated configuration, the gas inlet 14 and the gas outlet 16 being located respectively at two opposite ends of the housing, in the same direction, so that the gases follow. a substantially straight path between the gas inlet and the gas outlet. The inlet 14 and the outlet 16 are respectively connected to an inlet manifold 24 and to an outlet manifold 26 of substantially rectangular section (any other shape or type of sections may of course be envisaged), between which a wall is mounted. housing 28 of parallelepiped general shape which defines an enclosure for the circulation of the cooling fluid.

On one of its longitudinal sides, the wall 28 has three bosses 30, 32 and 34 respectively carrying the fluid inlets 18 and 20 and the common fluid outlet 22. On another longitudinal side of the wall 28 are formed two bosses 35 and 36, which are connected by a transfer conduit 38 which runs outside the housing.

As seen in the schematic sectional view of FIG. 3, the housing 12 houses a bundle of straight and parallel tubes 40 which open at one end into the gas inlet 14 and at another end into the gas outlet 16 to be traversed by the gases as indicated by the arrows and be scanned externally by the first fraction F1 and the second fraction F2 of the cooling fluid. The tubes 40 open on the one hand into a tube plate 42 of the collector 24 and on the other hand into a tube plate 44 of the collector 26.

The housing 12 delimits internally a first chamber corresponding to the first zone Z1 and in which opens the first inlet 18 of cooling fluid and a second chamber 48 separated from the first chamber 46 by a transverse partition 50. The second chamber 48 corresponds to the second zone Z2 and the third zone Z3. In the second chamber 48 open the second fluid inlet 20 and the common fluid outlet 22. The transfer conduit 38 connects the first chamber 46 and the second chamber 48 to evacuate the first fraction F1 of the cooling fluid from the first zone Z1 to the third zone Z3.

As seen in Figure 3, the first fluid inlet 18 opens into the first chamber 46 on the gas outlet side 16, while the second fluid inlet 20 opens into the second chamber 48 on the side of the partition 50 The transfer duct 38 opens into the first chamber 46 on the side of the partition 50 and into the second chamber 48 on the side of the gas inlet 14. The chamber 46 is delimited at its two ends by the partition 50 and the plate 44, while the chamber 48 is delimited at its two ends by the partition 50 and by the tube plate 42.

The heat exchanger of FIGS. 2 and 3 makes it possible to obtain a cooling of the gases by countercurrent circulation of the coolant, with a cumulative flow of the two fractions F1 and F2 in the first zone Z3 which is located immediately after the tube plate 42 and which receives the hottest gases.

The body of the heat exchanger can be made by other techniques, for example by a technique with plates and spacers.

Figure 4 shows an example of an upper plate 52 made by stamping and bending and which comprises a substantially flat bottom 54 of rectangular contour, surrounded by a peripheral edge 56 projecting, that is to say a raised edge. On the two long sides of the rectangle of the plate are formed two longitudinal edges 58 folded U and two transverse edges 60 unfolded. The plate 52 comprises a first partition 62 formed in excess thickness and having a branch 64 parallel to the transverse edges 60 and a branch 66 parallel to one of the longitudinal edges 58 The branch 64 is connected to one of the longitudinal edges 58, while the branch 66 ends at a distance from one of the transverse edges 60. In addition, the plate 52 comprises a second partition 68 formed in extra thickness and parallel to the transverse edges 60, which is located at a short distance from one of these. The partition 68 extends towards the branch 66, without reaching the latter.

The edge 56 and the partitions 62 and 68 are formed in an extra thickness on the same side of the bottom 54, that is to say upwards in FIG. 4, while the longitudinal edges 58 are folded on the opposite side, c that is, towards the bottom of FIG. 4. Furthermore, the plate comprises three bosses 70, 72 and 74 which respectively correspond to the first fluid inlet 18, the second fluid inlet 20 and the common fluid outlet. 22. These bosses are hollow and extend downwards of FIG.

The upper plate 52 is intended to cooperate with a lower plate 76 homologous, as shown in Figure 5, which has the same shape, but in which the edge 56 and the partitions 62 and 68 are formed in the opposite thickness, so downward in Figure 5, while the longitudinal edges 58 protrude upwards.

The plates 58 and 76 once assembled, as shown in Figure 6, delimit between them a passage 78 for the circulation of the gases to be cooled. Inside this passage, may be provided if necessary a corrugated insert (not shown).

The upper plate 58 is also intended to receive, above it, a lower plate 76. When two plates are thus assembled, their respective peripheral edges 56 are contiguous, as are their respective partitions 62 and 68, which allows to define a circulation blade which can receive the first fraction F1 of the cooling fluid by the boss 70, the second fraction F2 of the cooling fluid by the boss 72 and which can then evacuate the common flow of the two fractions by the boss 74.

Thus, the stacking of plates 52 and 76 of elongate form, grouped in pairs, makes it possible to define circulation plates for the first fraction F1 and the second fraction F2 of the circulation fluid, while each communicating with the first fluid inlet. 18 (through the boss 70) and with the second fluid inlet 20 (through the boss 72). These blades alternate with the circulation passages 78 which open at one end into the gas inlet 14 and at another end into the gas outlet 16.

Each pair of plates thus delimits a first chamber 80 (FIG. 6) corresponding to the first zone Z1 and into which the first cooling fluid inlet 18 (via the boss 70) opens, and a second chamber 82 separated from the first chamber and corresponding to the second zone Z2 and the third zone Z3.

In this second chamber 82 open the second fluid inlet 20 (via the boss 72) and the common fluid outlet 22 (via the boss 74). A transfer conduit 84 extends between the first chamber and the second chamber to evacuate the first fraction F1 of the cooling fluid from the first zone Z1 to the third zone Z3. Here, the first chamber 80 and the second chamber 82 are separated by the partition 62 which contributes to defining the transfer conduit 84. The second partition 68 is housed in the second chamber 82 and contributes to delimiting the second zone Z2 and the third zone Z3. The circulation of the cooling fluid is symbolized by arrows in FIG.

The first fluid inlet 18 opens into the first chamber 80 on the gas outlet side, while the second fluid inlet 20 opens into the second chamber 82 on the side of the first partition 62, while the common fluid outlet 22 opens out between the second partition 68 and the gas inlet.

Referring now to Figure 7 wherein the housing 12 has an elongated configuration, the gas inlet 14 and the gas outlet 16 being located at the same end 86, a return 88 being provided at another end 90 of the housing for the gases to follow a substantially U-shaped path between the gas inlet and the gas outlet.

The housing defines a first chamber 92 located on the side of the gas outlet 16, that is to say extending between the return 88 and the gas outlet 16. This first chamber 92 corresponds to the first zone Z1 and in this first chamber opens the first coolant inlet 18 for fraction F1.

The housing further defines a second chamber 94 separated from the first chamber 92 and parallel to the latter. The chamber 94 is located on the gas inlet side 14, that is to say it extends between the gas inlet and the return 88. This second chamber 94 corresponds to the second zone Z2 and in the third zone Z3. In this second chamber 94 open the second fluid inlet 20 for the fraction F2 and the common fluid outlet 22. Moreover, and by analogy to the previous embodiments, a transfer conduit 96 connects the first chamber 92 and the second chamber 94 to evacuate the first fraction F1 of the cooling fluid from the first zone Z1 to the third zone Z3.

The first fluid inlet 18 opens into the first chamber 92 on the gas outlet side 16, the second fluid inlet 20 opens into the second chamber 94 on the return side 88, while the communication conduit 96 opens into the first chamber 92 on the return side 88 and in the second chamber 94 on the gas inlet side 14.

The U-shaped heat exchanger of FIG. 7 can be made according to known techniques, for example tubes, or plates and spacers. The heat exchanger shown in the preceding figures advantageously constitutes a cooler for the recirculated exhaust gas of a motor vehicle engine.

Figure 8 shows a part of a cooling circuit 100 of a motor vehicle engine. The circuit 100 comprises a main line 102 traversed by a cooling fluid, here the engine coolant, under the action of a pump 104.

Upstream of the pump 104 is placed a radiator 106 conventionally used for cooling the engine. The main line 102, which forms a closed loop, divides downstream of the pump 104 into a first secondary line 108 containing a heat exchanger 110 and a second secondary line 112 containing another heat exchanger 114. The first line 108 delivers, at its outlet, a first fraction F1 of the cooling fluid at a first temperature T1r while the second secondary line 112 delivers at its outlet a second fraction F2 of the same cooling fluid, but at a second temperature T2 greater than the first T1 temperature. The secondary lines 108 and 112 are respectively connected to the first inlet 18 and to the second inlet 20 of a heat exchanger 110 according to the invention. These two fractions then leave the exchanger via a common outlet 22 of the heat exchanger 10 which is connected to the main line 102 upstream of the radiator 106.

The heat exchanger 10 of the circuit 100 is advantageously a recirculated exhaust gas cooler. The heat exchanger of Figures 9 to 12 is similar to that of Figure 7 and the common elements are designated by the same reference numerals. The housing 12 delimits a first chamber 116 located on the gas outlet side 16 and corresponding to a first zone Z1 of the housing and in which opens the first inlet 18 of cooling fluid. The housing further defines a second chamber 118 separated from the first chamber 116 and located on the gas inlet side 14, corresponding to a second zone Z2 and a third zone Z3 of the housing, and into which the second inlet 20 and the common fluid outlet 22. A partition wall 120 provided with a communication opening 122 (FIG. 12) is provided between the first chamber 116 and the second chamber 118. In the embodiment of FIG. The exchanger comprises a plurality of tubes 124 which are traversed by the gas G to be cooled.

As seen more particularly in FIG. 9, the first fluid inlet 18 opens into the first chamber 116 on the gas outlet side 16, the second fluid inlet 20 opens into the second chamber 118 on the side of the gas inlet 14, while the common outlet pipe 22 opens into the second chamber 118 of the return side 88. Therefore, and contrary to the embodiment of Figure 7, the gas is first cooled by the fraction F2 at the temperature T2 and then by the fraction F1 at the temperature Ti along a U-shaped path (FIG. 11). In this embodiment, the two fractions of the cooling fluid do not mix and are discharged together by the common outlet 22 which is located at the end of the chamber 118 before the return (FIG. 10).

The fraction F1 is advantageously a fraction at low temperature and fraction F2 a fraction at high temperature. These two fractions can come from an exchanger called multi-radiator that delivers a high temperature fluid fraction and a low temperature fluid fraction. An example of such an exchanger will not be described here with respect to an element known from the prior art.

However, the heat exchanger of FIGS. 9 to 12 could also be coupled to a circuit of the type of FIG.

Thus, in the embodiment of FIGS. 9 to 12, the two fluid fractions do not mix in a chamber or a common passage before their exit via the common outlet 22. Unlike the previous embodiments, the gas is not not first cooled by the cumulative flow of the two fluid fractions, but first by the fraction F2 and then by the fraction F1.

In this type of structure of the exchanger, namely a U-shaped structure, in order to perform the nori-mixing / mixing fractions F1 and F2, a conduit, not shown in Figures 9 to 11 but visible schematically in Figure 12 , is provided in the chamber 116 or 118, depending on the location of the common output 22 (placed on the input side 18 of the fraction F1 or on the input side 20 of the fraction F2), so to respectively drive the fraction F1 or F2, directly and without prior mixing with the other fraction F1 or F2, to the common output 22.

It will be understood that the exchanger of the invention can be made according to different variants, with tube-type techniques or plate-and-insert type techniques, or with other techniques. The circulation of the gases to be cooled can be carried out according to a linear course, according to a U-shaped course, or according to other types of course.

The invention finds particular application to heat exchangers for motor vehicles. The main application envisaged is that of the recirculated exhaust gas coolers, but the invention can also be applied to other types of heat exchangers, for example for cooling the charge air of an engine. with turbo-compressor.

Claims (20)

Revendications1. A heat exchanger for cooling a fluid, comprising a housing (12) having a fluid inlet (14) for the fluid to be cooled, a fluid outlet (16) for the cooled fluid, and a cooling means fluid circulation between the fluid inlet and the fluid outlet, as well as circulation means for a cooling fluid which exchanges heat with the fluid to be cooled inside the casing, characterized in that it comprises a first fluid inlet (18) for admitting a first fraction (F1) of the cooling fluid, at a first temperature (Ti), a second fluid inlet (20) for admitting a second fraction (F2) of the same cooling fluid at a second temperature (T2) higher than the first temperature (Ti) and a common fluid outlet (22) for discharging at the same time the first fraction (F1) and the second fraction (F2) of the cooling fluid . 2. Heat exchanger according to claim 1, characterized in that the fluid inlet (14) and the fluid outlet (16) are provided or relate to a gas and respectively constitute a gas inlet and a gas outlet. Heat exchanger according to claim 2, characterized in that the housing (12) has an elongated configuration and that the gas inlet (14) and the gas outlet (16) are respectively located at two opposite ends of the housing. housing (12) so that the gases follow a substantially straight path between the gas inlet and the gas outlet. 4. Heat exchanger according to claim 3, characterized in that the housing (12) houses a bundle of 21 rectilinear tubes (40) which open at one end into the gas inlet (14) and at the other end into the gas outlet (16) to be traversed by the gases and to be externally scanned by the first fraction (F1) and the second fraction (F2) of the cooling fluid. 5. Heat exchanger according to claim 4, characterized in that the housing (12) defines a first chamber (46) corresponding to a first zone (Z1) of the housing and into which opens the first inlet (18) of cooling fluid. and a second chamber (48) separated from the first chamber (46), corresponding to a second zone (Z2) and a third zone (Z3) of the housing, and into which the second fluid inlet (20) and the outlet of common fluid (22), a transfer duct (38) being provided between the first chamber (46) and the second chamber (48) for discharging the first fraction (F1) of the cooling fluid from the first zone (Z1) to the third zone (Z3). 6. Heat exchanger according to claim 5, characterized in that the first chamber (46) and the second chamber (48) are separated by a partition (50), in that the first fluid inlet (18) opens into the first chamber (46) on the gas outlet side (16), in that the second fluid inlet (20) opens into the second chamber (48) on the side of the partition (50), and in that the conduit transfer member (38) opens into the first chamber (46) on the side of the partition (50) and into the second chamber (48) on the gas inlet (14) side. 7. Heat exchanger according to claim 3, characterized in that the housing (12) houses a stack of plates (52, 54) of elongate shape which are grouped in pairs to define the circulation blades for the first fraction (F1) and the second fraction (F2) of the coolant and which each communicate with the first fluid inlet (14), said blades alternating with gas flow passages (78) which open at one end into the gas inlet ( 14) and at the other end into the gas outlet (16). 8. Heat exchanger according to claim 7, characterized in that each pair of plates defines a first chamber (80) corresponding to a first zone (Z1) of the housing and in which opens the first inlet (18) of cooling fluid and a second chamber (82) separated from the first chamber (80), corresponding to a second zone (Z2) and a third zone (Z3) of the housing, and into which the second fluid inlet (20) and the exit of common fluid (22), a transfer line (84) being provided between the first chamber (80) and the second chamber (82) for discharging the first fraction (F1) of the cooling fluid from the first zone (Z1) to the third zone (Z3). 9. Heat exchanger according to claim 8, characterized in that the first chamber (80) and the second chamber (82) are separated by a first partition (62) which contributes to delimit the transfer duct (84), in that the second chamber (82) houses a second partition (68) which contributes to delimiting the second zone (Z2) and the third zone (Z3), in that the first fluid inlet (18) opens into the first chamber (80). ) on the gas outlet (16) side, in that the second fluid inlet (20) opens into the second chamber (82) on the side of the first partition (62), and in that the common fluid outlet (22) opens between the second partition (68) and the gas inlet (14). 10. Heat exchanger according to claim 2, characterized in that the housing (12) has an elongated configuration, and in that the gas inlet (14) and the gas outlet (16) are located at the same end. (86) of the housing, a return (88) being provided at the other end (88) of the housing for the gases to follow a substantially U-shaped path between the gas inlet and the gas outlet. 11. Heat exchanger according to claim 10, characterized in that the housing defines a first chamber (92) located on the side of the gas outlet (16) and corresponding to a first zone (Z1) of the housing and in which opens the first coolant inlet (18) and a second chamber (94) separate from the first chamber (92) and located on the gas inlet side (14), corresponding to a second zone (Z2) and a third zone (Z3) of the housing, and into which the second fluid inlet (20) and the common fluid outlet (22) open, a transfer duct (96) being provided between the first chamber (92) and the second chamber ( 94) for discharging the first fraction (F1) of the cooling fluid from the first zone (Z1) to the third zone (Z3). Heat exchanger according to Claim 11, characterized in that the first fluid inlet (18) opens into the first chamber (92) on the gas outlet (16) side, in that the second fluid inlet ( 20) opens into the second chamber (94) on the return side (88), and in that the transfer conduit (96) opens into the first chamber (92) on the return side (88) and into the second chamber ( 94) on the side of the gas inlet (14). 13. Heat exchanger according to one of claims 5, 8, 9 and 11, characterized in that the first zone (Z1) of the housing is located on the side of the gas outlet (16), the second zone (Z2) of the housing is located between the gas inlet (14) and the first zone (Z1), and the third zone (Z3) of the housing is located on the side of the gas inlet (14), between this gas inlet ( 14) and the second zone (Z2). 14. Heat exchanger according to claim 10, characterized in that the housing defines a first chamber (116) located on the side of the gas outlet (16) and corresponding to a first zone (Z1) of the housing and in which opens the first coolant inlet (18) and a second chamber (118) separate from the first chamber (116) and located on the gas inlet (14) side, corresponding to a second zone (Z2) and a third zone (Z3) of the housing, and into which the second fluid inlet (20) and the common fluid outlet (22) open, a partition wall (120) provided with a communication opening (122) being provided between the first chamber (92) and the second chamber (94) for discharging the first fraction (F1) of the cooling fluid from the first zone (Z1) to the third zone (Z3). 15. Heat exchanger according to claim 14, characterized in that the first zone (Z1) of the housing is located on the side of the gas outlet (16), the second zone (Z2) of the housing is located on the side of the gas inlet (14), and the third zone (Z3) of the housing is located between the first zone (Z1) and the second zone (Z2). 16. Heat exchanger according to one of claims 14 and 15, characterized in that the first fluid inlet (18) opens into the first chamber (116) on the side of the gas outlet (16), in that the second fluid inlet (20) opens into the second chamber (118) on the side of the gas inlet (14), and in that the common outlet pipe (22) opens into the second chamber (118) on the back (88). 17. Heat exchanger according to one of claims 2 to 16, characterized in that it is designed as a cooler for the recirculated exhaust gas of a heat engine. 18. Heat exchanger according to one of claims 2 to 17, characterized in that the cooling fluid is a coolant of a motor vehicle engine. 19. Cooling circuit traversed by a cooling fluid, characterized in that it comprises a heat exchanger (10) according to one of claims 1 to 18. 15 20. The cooling circuit according to claim 19 comprising a main line (102) traversed by the cooling fluid and dividing into a first secondary line (108) delivering a first fraction (F1) 20 of the cooling fluid to a first temperature ( Ti) and a second secondary line (112) delivering a second fraction (F2) of the same cooling fluid to a second temperature (T2) higher than the first temperature (T1), characterized in that the first secondary line ( 108) and the second secondary line (112) are respectively connected to the first fluid inlet (18) and the second fluid inlet (20) of the heat exchanger.