DOUBLE HEAT EXCHANGER WITH ORTHOGONAL GAS FLOW

Description

Domaine technique de l'invention

[0001] The present invention relates to a high temperature gas cooling system.

[0002] The present invention relates more particularly to the field of cooling systems for internal combustion engines, in particular the cooling of the intake gases of a motor vehicle thermal engine.

[0003] It relates more particularly to a cooling system for an internal combustion engine, said cooling system comprising a heat exchanger connected to two high-temperature gas circulation circuits, in particular compressed air and burnt gases, and in which a heat transfer fluid circulates. State of the art

[0004] As is known, a motor vehicle equipped with a thermal engine includes an air intake circuit to bring fresh air, generally captured at the front of the vehicle and then filtered using an air filter, to the thermal engine.

[0005] As is known, a heat engine may include a supercharging system to increase the performance of said engine. The supercharging system includes an air compression stage before it is admitted into the engine to be mixed with fuel. This compression stage may be associated with a turbine stage to together form a turbocharger or be an electric compression module.

[0006] To improve the efficiency of the said heat engine, the fresh air is compressed as it passes through the compression stage, which causes its temperature to increase, which is likely to reduce the efficiency of the engine.

[0007] It is therefore known to pass the compressed air after the compression stage and upstream of the engine into a cooling stage commonly called a "precooler" which is formed by an air-water exchanger. In said exchanger, the air circulates in contact, for example, in tubes housed in a chamber in which circulates cooling water from an engine cooling circuit. The cooling circuit can, for example, pass through the engine to also cool parts of the engine that are brought to high temperatures, such as the cylinder block and the cylinder head, the cooling water then taking on calories, and then through a radiator to allow said calories to be removed and evacuated. The circulation of the cooling water is carried out using a water pump driven by the heat engine or by an electric water pump.

[0008] To reduce the emission of pollutants generated by combustion, burnt gases can be returned from the exhaust, i.e. downstream of combustion in the cylinders, to the engine's intake ducts. The gases are called recirculated gases. There are different types of recirculated burnt gases: high pressure recirculated gases taken from the exhaust system upstream according to the direction of flow of the gases from pollution control devices such as a catalyst or nitrogen oxide (NOx) trap. Generally, the high pressure recirculated burnt gases are taken directly from an exhaust manifold attached to an exhaust face of the cylinder head, on the lateral side opposite the intake face and are then sent to the intake ducts or into the intake manifold. low pressure recirculated burnt gases taken from the exhaust system and in a known manner after a pollution control device. The low pressure recirculated burnt gases are therefore taken downstream of an exhaust device and returned to the engine intake blow-by gases or oil vapors taken from a decanter generally attached to the cylinder head.

[0009] As is known, the recirculated gases are cooled before being mixed with fresh or compressed air.

[0010] The invention relates to the cooling of compressed air and the cooling of recirculated gases at the thermal intake.

[0011] Document US 2011 / 0139133 describes an internal combustion engine that is equipped with a special cooling system. During a cold start of the engine, this "cooling" system is used to warm the engine using the heat released by the burnt gases.

[0012] To achieve this, the cooling system includes a heat exchanger that circulates a heat transfer fluid around the recirculated gas circuit, allowing the heat transfer fluid to recover some of the heat from the burnt gases. The heat transfer fluid then circulates around the cylinders and transfers some of the recovered heat to them.

[0013] Document FR3079880-A1 proposes a casing capable of housing a heat exchanger for cooling high-pressure recirculated gases and a heat exchanger for cooling compressed air upstream of the intake ducts of the thermal engine.

[0014] DE-A-102011013029 discloses a cooling system according to the preamble of claim 1.

[0015] The document proposes that the recirculated gas and mixed air inlets are both turned towards the exhaust side of the engine, which allows for a compact but less efficient cooling device. In addition, since the gas temperatures are very high, the crankcase temperature can be significantly increased in certain locations, particularly near the gas inlets, which can generate significant expansions. The subject of the invention is a device for cooling compressed gas and air circuits having high temperatures upstream of the engine intake which overcomes the problems mentioned. Subject of the invention

[0016] For this purpose, the present invention proposes a system for cooling gas and compressed air whose temperatures are different, comprising a double-flow heat exchanger crossed by the gases along a first axis and the compressed air along a second axis,

[0017] Characterized in that the exchanger comprises a cooling chamber for the gases attached to and communicating with a cooling chamber for the compressed air in which the axis of the gas flow is substantially orthogonal to the axis of the compressed air flow.

[0018] Advantageously, the axes of the gas and compressed air in the exchanger of the cooling system are substantially orthogonal, which makes it possible on the one hand not to accumulate at the same locations in the exchanger casing, in particular near the gas and compressed air inlets, and on the other hand to allow expansions of the exchanger, in particular of the exchanger casing, in different directions.

[0019] According to other characteristics of the invention: The heat exchanger includes a coolant circuit that passes consecutively through the cooling chambers.

[0020] Advantageously, the cooling circuit is capable of consecutively cooling the air and gases by passing through one chamber and then into the second chamber, which makes it possible to obtain graduated cooling of the gases and the compressed air. The coolant circuit has a circulation branch in each of the two chambers with parallel axes.

[0021] Advantageously, the coolant circuit has in each of the chambers a coolant circulation branch substantially along an axis, the two being parallel, which has a coolant path length that is substantially identical in the two chambers and therefore a cooling efficiency that is substantially equal in the two chambers. The inlet and outlet of the liquid circuit are arranged in different chambers.

[0022] Advantageously, the inlet and outlet of the casing, of the liquid circuit are arranged in different chambers to avoid heating of the gases or air at the end of the liquid circuit. the inlet of the liquid circuit opens into the compressed air cooling chamber.

[0023] Advantageously, the coolant passes into the crankcase first through an inlet which opens into the compressed air cooling chamber to cool the compressed air as much as possible for improved engine efficiency, and to avoid too great a temperature difference between the coolant and the recirculated gases, which is likely to produce condensates or aggregates at the crankcase inlet. the coolant circuit follows a U-shaped path.

[0024] Advantageously, the coolant circuit has a path with a U-shaped profile to properly direct the liquid and reduce pressure losses. the liquid circulation axis is orthogonal to the compressed air circulation axis.

[0025] Advantageously, the cooling fluid circulation axis is orthogonal to the compressed air circulation axis to achieve high heat exchange efficiency. the circulation axis of the liquid is parallel to the circulation axis of the recirculated gases.

[0026] Advantageously, the cooling fluid circulation axis is parallel to the recirculated gas circulation axis to avoid liquid boiling phenomena. The coolant circuit passes through a wall separating the two chambers through an opening.

[0027] Advantageously, the casing comprises a wall capable of separating the two cooling chambers. The cooling circuit passes through said wall through an opening pierced in this wall. The liquid can thus pass from the first chamber into the second chamber. the opening is arranged substantially diametrically opposite the fluid inlet into the exchanger.

[0028] Advantageously, the opening in the partition wall is arranged substantially diametrically opposite the coolant inlet to allow maximum length of the heat exchange zone. The opening in the partition wall is arranged substantially diametrically opposite the coolant outlet to allow maximum length of the heat exchange area.

[0029] Advantageously, the opening in the partition wall is arranged substantially diametrically opposite the coolant outlet to allow maximum length of the heat exchange zone. the recirculated gases and compressed air pass through the exchanger through oblong tubular conduits.

[0030] Advantageously, the recirculated gases and the compressed air pass through the casing and in particular the exchanger via cooling ducts which extend from an inlet wall to an outlet wall of the casing, the cross-section of each cooling duct is oblong to present a large exchange surface.

[0031] The cooling pipes are immersed in the coolant. The invention also relates to a heat engine comprising a heat exchanger with two gas flows according to the characteristics presented. Brief description of the figures

[0032] Other characteristics and advantages of the invention will appear on reading the following description of particular embodiments of the invention given as non-limiting examples and represented in the appended drawings, in which: [ Fig. 1 ] is a schematic view of a double gas flow heat exchanger body. [ Fig. 2 ] is a schematic view of the heat exchanger. [ Fig. 3 ] is a schematic longitudinal sectional view of the exchanger. Detailed description of the figures

[0033] In the following description, like reference numerals designate like parts or parts having similar functions.

[0034] To facilitate understanding, the following description concerns the cooling of recirculated burnt gases and compressed air upstream of the intake ducts of a thermal engine, here a motor vehicle.

[0035] A thermal or internal combustion engine (not shown) of a motor vehicle comprises a so-called fresh air intake circuit generally captured from the front face of the vehicle capable of conveying this fresh air to the engine, in particular to an intake distributor capable of distributing the intake air to intake ducts hollowed out in a cylinder head and connected to combustion chambers.

[0036] To improve engine efficiency, it is known to increase air density. The fresh air passes through a compression stage, which may be the compressor stage of an engine turbocharger. It is also known to have an electric compressor.

[0037] At the outlet of the compression stage, the air temperature has also increased, by around 200°C, which reduces the efficiency of the engine. The air downstream of the compression stage, depending on the direction of air flow, must be cooled before being admitted into the engine.

[0038] The air then has to go through a cooling stage which is generally formed by a gas-liquid coolant heat exchanger. Said exchanger is known under the English name "Precooler" for upstream cooler. The coolant is based on water which circulates in an engine cooling circuit thanks to a coolant pump.

[0039] At the same time, to reduce pollutant emissions, it is known to return burnt gases to the engine intake. These burnt gases come from combustion in the engine's combustion chamber. They are captured in an exhaust system and routed to the engine intake, particularly to the engine's intake ducts, via a burnt gas recirculation system.

[0040] The gases here are high-pressure recirculated gases captured at an exhaust gas collection device. These gases are known as "EGR" gases in English. These EGR gases will subsequently be referred to as recirculated gases.

[0041] The recirculated gases are at a high temperature, around 700°C. They need to be cooled before being admitted to the engine. The recirculated gas circuit also passes through a gas / coolant heat exchanger.

[0042] To reduce the size of the assembly comprising the engine with the engine operating devices including the heat exchangers, the heat exchanger for the compressed fresh air can be assembled with the heat exchanger for the recirculated gases. A gas cooling system 100 at the engine intake is obtained comprising a double-flow exchanger 10. The compressed air and recirculated gas inlets are for example arranged on a wall of the housing of the double-flow exchanger facing the exhaust face of the engine while the outlets are facing the intake face of the engine.

[0043] However, the respective temperatures of the compressed air and the recirculated gases are very different, which leads to differential expansion problems between the two assembled exchangers and, more clearly, to the walls of the double-flow exchanger casing. Indeed, the significant temperature difference between the recirculated gases and the intake air can lead to strong thermomechanical stresses that endanger the strength of the exchanger and in particular the exchanger casing. Subsequently, the walls of the exchanger are the walls of the exchanger casing.

[0044] According to the figure 1 , the double-flow exchanger 10 comprises an inlet for compressed air 11 arranged on a first gas inlet wall 12 and an inlet for recirculated gases 21 arranged on a second inlet wall 22 for the inlet of recirculated gases. According to the invention, the first inlet wall 12 is distinct from the second inlet wall 22 and more precisely the first inlet wall is adjacent and orthogonal to the second inlet wall 22.

[0045] The compressed air flow passes through the exchanger along a rectilinear axis Xa between the first air inlet wall 12 and the first air outlet wall 14 of the air-coolant exchanger. The first air inlet 12 and outlet 14 walls are symmetrical with respect to a median plane orthogonal to the axis Xa.

[0046] Similarly, the flow of recirculated gases passes through the exchanger along a rectilinear axis Xg between the second inlet wall 22 and the second outlet wall 24 of the recirculated gas-coolant exchanger. The second inlet 22 and outlet 24 walls are symmetrical with respect to a median plane orthogonal to the axis Xg.

[0047] According to the invention and preferably, the compressed air flow axes Xa and recirculated gas Xg are substantially orthogonal to have a smaller footprint with ease of assembly with other components of the engine. However, the compressed air flow axis may be at an angle relative to the recirculated gas flow axis to facilitate the attachment of the exchanger to the engine and reduce the overall size of the assembly.

[0048] As represented by the figure 2 , the air intake circuit is connected by an inlet horn 13 fixed to the first inlet wall 12 of the casing and by an outlet horn 15 to the first outlet wall 14. The first outlet wall 14 is parallel and opposite the first inlet wall 12.

[0049] The downstream passage section, in the direction of air flow, of the fixed horn 13 is substantially equal to the passage section of the air-water heat exchanger. In fact, the downstream passage section of the inlet horn 13 is the largest possible. It is substantially equal to or even slightly greater than the passage section of the compressed air-coolant exchanger.

[0050] The exchanger passage section is understood to be the cross-section of the exchanger chamber, orthogonal to the axis of the direction of the flow Xa of compressed air.

[0051] The outlet horn 15 is substantially identical to the inlet horn. The upstream passage section of the outlet horn 15 is therefore equal to the passage section of the compressed air-coolant heat exchanger.

[0052] Preferably, the burnt gas recirculation circuit is also connected by a second inlet horn 23 fixed to the second inlet wall 22 of the exchanger and by an outlet horn 25 to a second outlet wall 24 opposite the second inlet wall 22. The second inlet wall 22 is parallel to the second outlet wall 24. The second inlet 22 and outlet 24 walls are therefore orthogonal to the first inlet 12 and outlet 14 walls.

[0053] The downstream passage section of the second inlet horn 23 fixed to the exchanger is substantially equal to the passage section of the recirculated gas-coolant heat exchanger. The downstream passage section of the second inlet horn 23 is as large as possible. It is substantially equal to the passage section of the recirculated gas-coolant exchanger, or even slightly larger. The passage section of the exchanger is understood to mean the cross-section relative to the direction of flow of the gases or air, of the heat exchange chamber, here the heat exchange chamber between the recirculated gases and the coolant, orthogonal to the axis Xg of the direction of flow of the recirculated gases.

[0054] The coolant circuit is connected to the exchanger by coolant inlet 32 ​​and outlet 33 nozzles which extend respectively from a water inlet wall 31 and a water outlet wall 34 of the exchanger. The liquid inlet 30 and the liquid outlet 35 defined by said nozzles are arranged at one end of the inlet 31 and outlet 34 walls to obtain the greatest possible coolant path length.

[0055] Preferably, the water inlet wall 31 is separate from the water outlet wall 34. In fact, the path of the water in the exchanger does not return backwards at the risk of altering the efficiency of the exchanger, as represented by the figure 3 .

[0056] The coolant circuit follows a path in the exchanger 10 according to two parallel cooling branches 38, 39 and substantially symmetrical with respect to a flat central separation wall 36 parallel to the water inlet 31 and outlet 34 walls. The exchanger 10 thus comprises two water chambers 41 and 42 for individually cooling the compressed air and the recirculated gases.

[0057] In the two water chambers 41,42 are housed tubular conduits 43,44 of oblong cross-section to conduct respectively the compressed air and the recirculated gases between the inlet 12,22 and outlet 14,24 walls.

[0058] The tubes guiding the air and the recirculated gases are placed perpendicularly. Thus, their respective expansions under the effect of heat do not occur in the same direction. The casing can therefore deform independently to adapt to the variation in length of the tubes in each direction.

[0059] Preferably, the volumes of the two chambers 41, 42 of the exchanger are substantially equal.

[0060] Preferably, the two branches 38, 39 for cooling and circulating the coolant inside the exchanger are separated by the central separating wall 36.

[0061] The separating wall 36 comprises an opening 37 allowing communication between the two chambers 41, 42. Said opening 37 is pierced in the separating wall diametrically opposite the liquid inlet 30 to allow an optimal exchange length, the longest possible. Said opening 37 is also arranged substantially diametrically opposite the fluid outlet 35.

[0062] Preferably, the coolant inlet 30 opens into the first cooling chamber 41 dedicated to heat exchanges with the compressed air. According to the figures 2 And 3 , the axis of the tubular air ducts 43 is orthogonal to the direction of circulation of the water in the first chamber 41. The axes of circulation of the compressed air and the coolant are orthogonal or “cross-flow in English” to improve the efficiency of the heat exchanges.

[0063] The coolant first passes into the compressed air cooling chamber 41, is charged with heat and its temperature increases before joining the second cooling chamber 42 to cool the recirculated gases.

[0064] Heat exchanges between the liquid and the compressed air and recirculated gases take place in series to promote cooling of the compressed air at the intake.

[0065] In addition, the temperature difference between the coolant and the recirculated gases is smaller and can prevent the formation of condensate in the tubes.

[0066] The path of the coolant in the chambers 41, 42 is directed along an axis substantially parallel to the central separating wall 36 in a first direction from the water inlet 30 towards the opening 37, then in a second opposite direction from the opening 37 towards the water outlet 35 forming a path with a U-shaped profile inside the exchanger 10 as shown in figure 3 .

[0067] The axis of the recirculated gas tubular conduits is parallel to the central separating wall and to the water circulation axis in the second chamber 42. The circulation axis of the coolant substantially parallel to the axis Xg of the recirculated gas circulation tubular conduits makes it possible to avoid water boiling phenomena.

[0068] The objective is achieved: The double-flow exchanger 10 for cooling the compressed air and the recirculated gases is compact due to the assembly of the two exchangers, ensuring the thermomechanical constraints linked to the temperature differences between the two air and gas flows, by a clever assembly having orthogonal flow circulation axes. Thus, the respective expansions of the walls of the exchanger under the effect of heat do not take place in the same direction. The casing of the exchanger can therefore deform independently to adapt to the variation in length of the tubular conduits of compressed air 43 and recirculated gas 44 in each of the two directions.

[0069] As goes without saying, the invention is not limited to the embodiments of this socket described above as examples; on the contrary, it encompasses all variants thereof.

[0070] For example, the flow of recirculated gases can be in the same direction as that of the coolant or in the opposite direction.

[0071] The heat exchanger according to the invention may relate to a field other than the automobile, to cool two gas flows at different temperatures.

Claims

1. Cooling system (100) for gas and air, comprising a double-flow heat exchanger (10) through which the gases flow along a first axis and the compressed air flows along a second axis, and comprising a cooling chamber for the gases (42) adjoining each other and communicating with a cooling chamber for the compressed air (41) in which the axis of the gas flow (Xg) is substantially orthogonal to the axis of the compressed air flow (Xa) and a coolant circuit which passes consecutively through the two cooling chambers (41, 42), characterized in that the two chambers (41, 42) are adjoined and separated from each other by a median separating wall (36) comprising an opening (37) allowing liquid communication between the two chambers (41,42) and in that the coolant circuit inside the exchanger (10) has two parallel circulation branches (38,39) and follows a U-shaped path inside the exchanger from an inlet (30) to an outlet (35) arranged in different chambers (41,42).

2. Cooling system (100) according to claim 2, characterized in that the coolant circuit comprises an inlet (30) and an outlet (35) in the exchanger, arranged in different chambers (41,42).

3. Cooling system (100) according to either claim 1 or claim 2, characterized in that the liquid inlet (30) opens into the compressed air cooling chamber (41).

4. Cooling system (100) according to any of claims 1 to 3, characterized in that the liquid circulation axis is orthogonal to the compressed air circulation axis.

5. Cooling system (100) according to any of claims 1 to 4, characterized in that the liquid circulation axis is parallel to the recirculated gas circulation axis.

6. Cooling system (100) according to any of claims 1 to 5, characterized in that the opening (37) is arranged substantially diametrically opposite the fluid inlet (30) in the exchanger.

7. Cooling system (100) according to any of claims 1 to 6, characterized in that the opening (37) pierced in the separating wall (36) is arranged so as to be substantially diametrically opposite the coolant outlet (35) to allow maximum length of the heat exchange zone.

8. Cooling system (100) according to any of claims 1 to 7, characterized in that the recirculated gases and compressed air pass through the exchanger via tubular ducts (43,44) of oblong cross-section.

9. Heat engine comprising an air intake circuit and a recirculated gas circuit which pass through a cooling system according to any of claims 1 to 8.

10. Motor vehicle comprising a heat engine according to claim 9.