EP1343963B1 - Heat-exchanger module, specially designed for an exhaust gas recycling system - Google Patents

Abstract

The invention concerns a heat-exchanger module specially designed for an exhaust gas recycling system comprising a heat exchanger (1) provided with ducts (11) for heat exchanging gas flow with a coolant. The invention is characterised in that it further comprises at least a bypass (12) integrated in the exchanger (1), adapted to circulate exhaust gases without the latter being actually cooled. The module can further comprise means (2, 20, 20') for selecting the path of the exhaust gases, which preferably comprise a valve (20, 20') having two positions associated with said bypass (12), which opens or closes said duct to allow through exhaust gases or a three-way valve (2). As a result of its minimum space requirement and its simple construction mode, it enables to cool exhaust gases selectively while maintaining a minimum level of polluting gases.

Description

The present invention relates to a heat exchanger module for an exhaust gas recirculation system, which can in particular be applied to the exhaust gas recirculation systems of the engine of a vehicle to the intake. Other applications of this exchanger module may be the heating of the intake air and the refrigeration of the exhaust gases which are led to the catalytic converter for the gasoline engines.

There is a well-established use in the automotive field of providing a diesel engine exhaust gas recirculation system, known as EGR or Exhaust Gas Recycling, so as to mix these gases with one another. intake air, since the presence of the exhaust gas in said mixture decreases the production of NOx.

Before being mixed with the intake air, the exhaust gases are cooled in a heat exchanger (EGRC or "Exhaust Gas Recycling Cooler") mounted on the loop of the EGR system, so as to improve the efficiency of the system.

Inside the loop, there is also a valve (EGR valve) which controls the passage of the exhaust gas in the exchanger.

The heat exchanger itself can have different configurations: for example, it can consist of a tubular flange inside which is arranged a series of parallel tubes in which the gases circulate, the refrigerant spreading in the flange, outside the tubes; in another application, the exchanger is composed of a series of parallel panels which constitute the exchange surfaces heat, so that the exhaust gases and the refrigerant circulate between two panels in alternating layers (see for example DE-A-914 450 ).

In any case, the current EGR systems which are cooled have a disadvantage because the exhaust gases circulate via the exchanger whatever the mode of operation of the engine from the moment the EGR valve opens: the gases are cooled as long as the engine is operating at steady state and its temperature is high, such as during a cold start, when the temperature of the gases is much lower.

This operation of cooling the gases when their temperature is not high represents a disadvantage from an ecological point of view since it increases the level of CO and hydrocarbon emissions, accompanied by additional noise pollution. .

The object of the present invention is to provide a solution to the drawbacks mentioned above by developing a heat exchanger module designed specifically for an exhaust gas recirculation system for maintaining a minimum level of gas emission. pollutants in the exhaust, irrespective of the engine operating condition.

The heat exchange module of this invention is of the heat exchanger type equipped with circuits allowing the flow of the exhaust gases, the latter comprising among these means the ducts reserved for the flow of gases with heat exchange with a fluid of cooling; its particularity lies in the fact that the circuits used for the flow of the exhaust gases comprise at least one bypass duct, integrated in the exchanger, which is suitable for the circulation of the exhaust gases without these being subjected to a real cooling.

The bypass duct, which can simply be called "bypass", makes it possible to avoid the cooling of the exhaust gases according to the different modes of operation of the engine, for example in the case of a cold start, for which its temperature does not vary. is not high and its cooling would be dangerous because of the emission of gaseous pollutants that it would generate.

The integration of the bypass inside the exchanger is very advantageous, since it makes it possible to reduce the space required for this assembly; this element is very important for vehicles whose available space is always limited.

Among a selected application of this invention, the exchanger module further comprises circuits for selecting the path of the exhaust gas, thus enabling these selection means to let the gases circulate through the ducts intended for their flow with heat exchange or well by the bypass duct without there being any real cooling.

These means for selecting the path of the exhaust gases are preferably equipped with a temperature detector of these gases; it is thus possible to ensure that, whatever the mode of operation of the engine, the gases will be led to the most appropriate conduit, maintaining a minimum threshold emission of gaseous pollutants.

In a more advantageous application, the means for selecting the path of the exhaust gases are incorporated at least in part in the heat exchanger module. This feature allows the device to be compact and simple to mount.

According to one application, the exhaust path selection circuits comprise a three-way valve; this valve can be placed at the entrance of the exchanger, but it can indifferently be at the exit of the exchanger.

Although it is possible to mount this valve at the outlet of the exchanger for manufacturing reasons, the pressure difference ensures the transmission of gases to the appropriate ducts, depending on the position of the valve.

In accordance with a replacement application of this three-way valve, the exhaust path selection means comprise a two-position valve which is associated with the aforementioned bypass conduit, which opens or closes the conduit at moment of the passage of the exhaust gases.

This valve allows to direct the exhaust gases to the heat exchange ducts or to the bypass, depending on the nature of these gases, in a simple manner and without complicating the structure of the exchanger.

In a variant of the application, this valve is mounted at the output of said bypass. When the valve closes the outlet of this conduit, the gases must necessarily pass through the tubes of the exchanger, whereas when the valve leaves the passage through the bypass open, the gases preferably take this path, because they lose less charge; it is possible to install indifferently the valve at the input of the bypass.

According to a chosen application of this invention, the valve associated with the bypass is linearly driven, since this mode makes it possible to seal the assembly more easily; in this case, it is possible to choose between a plane seat valve, a needle valve, a gate valve or a piston valve.

The valve may be rotatable, and a choice must be made between a butterfly valve, ball valve or rotary valve.

The control of the thermostatic valve is more advantageous; its opening and closing are directly controlled by the temperature of the refrigerating liquid.

The thermostatic control eliminates any external control, which makes it possible to avoid any problem of tightness as well as the need to exert an external control.

According to a particularly practical manufacturing procedure, the exchanger has the general structure of an exchanger equipped with a bundle of parallel tubes in which the exhaust gases circulate, the bypass being composed of a single tube, section roughly equivalent to the total section of this bundle of tubes; this tube will preferably be installed on the longitudinal axis of the exchanger.

This solution simplifies the manufacture of the heat exchanger, since it can be manufactured on a traditional line with only a few minor modifications.

This invention also relates to any heat exchanger, in particular for an exhaust gas recirculation system, which includes exhaust gas flow circuits, including the aforementioned circuits which serve for the flow of gases with heat exchange with a cooling fluid, and which is distinguished by the fact that the circuits used for exhaust gas flow further comprise at least one bypass, incorporated in the exchanger, suitable for the circulation of the gases of exhaust without these undergoing a real cooling.

In addition, the exchanger preferably consists of means for selecting the path of the exhaust gas, thus enabling these selection means to allow the flow of gas via the ducts intended for their flow. with heat exchange or via the bypass duct without any real cooling.

In order to allow a better understanding of what has been explained before, plans are attached hereto, which show schematically and only by way of non-exhaustive example, a practical case of the application.

• la figure 1 représente schématiquement un module échangeur de chaleur conforme à la présente invention, en position de fonctionnement;
• la figure 2 représente le module de la figure 1 dans une autre condition de fonctionnement;
• la figure 3 est une vue en coupe de l'échangeur de chaleur;
• les figures 4 et 5 sont des vues en coupe longitudinale d'un échangeur conformément à une application de la présente invention, dans lequel est montée une soupape à siège plan, respectivement en position fermée et ouverte; enfin
• les figures 6 et 7 sont des vues semblables aux figures 4 et 5, pour un échangeur muni d'une vanne papillon.

On these plans,

• the figure 1 schematically represents a heat exchanger module according to the present invention, in the operating position;
• the figure 2 represents the module of the figure 1 in another operating condition;
• the figure 3 is a sectional view of the heat exchanger;
• the Figures 4 and 5 are longitudinal sectional views of an exchanger according to an application of the present invention, wherein is mounted a plane seat valve, respectively in closed and open position; finally
• the Figures 6 and 7 are views similar to Figures 4 and 5 , for an exchanger equipped with a butterfly valve.

As shown in the figures, an EGRC module according to the invention comprises a heat exchanger 1, composed mainly of a flange 10 provided with a bundle of tubes 11 further having inside a bypass duct or by- pass 12, of greater diameter than each of the tubes 11 constituting the beam and which is independent of them.

At the inlet of the exchanger 1 is the valve 2, three-way, through which enter the exhaust gas by a line indicated by the arrow A, and through which they are driven, depending on the position of the valve, to the bundle of tubes 11 via the line indicated by the arrow B, as shown in figure 1 , or to the bypass 12 via the line indicated by the arrow C, as shown in FIG. figure 2 .

In both cases, the gases exit through the other end of the exchanger, through a line D which leads them to the inlet to the cylinders.

As shown in figure 3 , which represents in more detail the heat exchanger 1, the tubes 11 converge at the ends of the flange in two annular collectors, an inlet manifold 13 and an outlet manifold 14, which are arranged around the bypass 12. exhaust from the engine cylinders pass through the valve shown in figure 1 , from the valve 2 to the tubes 11, through the inlet manifold 13, while figure 2 the gases pass from the valve 2 to the conduit 12.

A cooling fluid circulates inside the flange 10, but outside the tubes 11 and the bypass 12, between the fluid inlet 15 and a fluid outlet 16.

Although this is not shown, the EGRC module described also includes circuits for detecting the temperature of the gases at the cylinder outlet, as well as means for controlling the valve 2.

The operation of the module described is simple: during normal operation of the engine, the valve 2 remains in the position of the figure 1 , and the exhaust gases are cooled in the exchanger, in the traditional way, since they circulate in the bundle of tubes 11.

However, when the temperature of the exhaust gas is low, for example in the case of a cold start or low load or when the engine is at low speed, it is not appropriate to cool more, since this cause an increase in CO and hydrocarbon emissions; the means of control then change the state of the valve to that of the figure 2 in such a way that most of the exhaust gases pass through the exchanger 1 via the bypass 12: because of the relatively large diameter of this duct, the heat exchange between the flow rate of the gases and the cooling fluid is thus reduced, and the gases are not cooled during their passage through the exchanger.

For use on passenger vehicles, the flow rate of gas recycled by the exchanger is usually between 5 g / s and 15 g / s, for a flow section with a heat exchange of between about 500 mm ² and 1000 mm ² , this section consisting of a large number of tubes with a hydraulic diameter of between 5 mm and 12 mm, inside a flange whose inner diameter is about 43 mm to 52 mm.

In this case, the hydraulic diameter of the tubular by-pass may be between 10 mm and 40 mm approximately.

The characteristic values of the temperatures of the gases flowing in a conventional exchanger, when the engine is at a normal speed, are 300 ° C at the inlet and 150 ° C at the outlet; in case of cold start, the gases at the inlet of the exchanger are between 100 and 150 ° C and the exchanger cools them to 50 ° C. With this invention, thanks to the by-pass, the gases leaving the exchanger have almost the same temperature as at the inlet.

It is possible to install the valve 2 either at the inlet of the exchanger, as shown, or at the outlet; in this case, the pressure difference between the inlet and the outlet causes the exhaust gases to pass through the tube bundle or by-pass depending on the location of the valve.

The modeling technique applied to the valve can take any form suitable for the design of the exchanger and its bypass; he is possible to integrate it into a single module in connection with the exchanger, or to have it as an external component.

With reference to 4 to 7, an exchanger module will then be defined for different applications of the gas path selection means.

On the figure 4 it is possible to consider an exchanger equipped with an inlet manifold 13, a flange 10 with a bundle of heat exchange tubes 11, a bypass or bypass duct 12, and an outlet manifold 14.

In this case it passes from a module equipped with a single three-way valve, which has the dual function of controlling the flow of gas via the EGR and opening or closing its access through the bypass of the exchanger, to an exchanger module provided with a traditional EGR valve, located outside the exchanger (not shown in the figures), and a second valve associated with the bypass duct, the latter being a digital valve, integrated into the exchanger.

Therefore, according to the application shown on the Figures 4 and 5 a valve 20 is associated with the bypass duct 12 - in this case it is a plane seat valve - located on the outlet manifold 14.

The drive of the valve 20 (linear drive) is effected via an axis 21, and the outlet manifold 14 is suitably modified, the outlet 22 of the gases being effected perpendicular to the axis of the exchanger, for allow to house the valve 20 and its drive devices.

At the location of the valve 20 shown on the figure 4 the bypass duct 12 remains in the closed position, since the gases must necessarily pass through the tubes 11, as shown by the arrows; they are then cooled by the coolant circulating inside the flange 10 (although its inputs and outputs are not shown in the figures).

If the valve 20 opens, as shown in figure 5 most of the gases pass through the bypass duct 12, since they encounter only insignificant resistance and they are not cooled by their passage through the exchanger.

Other linear drive valves that could replace the butterfly valve 20 are needle valves, gate valves of different sections or piston valves.

The Figures 6 and 7 show a variant of the application of the exchanger, in which a throttle valve 20 'has been incorporated instead of a plane seat valve 20 as proposed in the preceding figures.

In this case, the drive shaft 21 'of the rotary valve, and the valve 21 can pass from the closed position of the bypass duct 12 ( figure 6 ) at an open position of the duct 12 ( figure 7 ).

For this application, the modification of the outlet manifold 14 is limited to its elongation which allows it to accommodate the valve 20 '.

The other rotary drive valves which may also be suitable for the application described may be two-way ball valves, which are provided with a duct passing therethrough, or rotary valves, composed of a plate articulated from a point of contact. its periphery to an axis of articulation located at the periphery of the duct 12 to be closed.

It would be possible to install a rotary drive valve, such as the butterfly valve 20 ', by equipping it with a crank-rod system or the like, inside the exchanger, so that the drive mode goes into linear mode. .

The bypass duct valve can be either pneumatically, electrically or thermostatically driven.

In the latter case, the control of the valve is carried out from the temperature of the gases themselves or the cooling fluid, so that the bypass duct opens, for example during the cold start of the engine, avoiding as well as the exhaust gases do not cool too much. This thermostatic drive mode is placed inside the exchanger, in order to avoid sealing problems related to the passage of a drive shaft in the flange.

The results of the tests carried out demonstrate that the solution of the digital valve with respect to the bypass duct is satisfactory in addition to its simple installation and its reasonable cost.

Indeed, the tests carried out at medium and low revs (2250 rpm and 1250 rpm) and when the engine is in low load (PME = 1 bar), demonstrate that the emissions of hydrocarbons and carbon monoxide are reduced by significantly when the bypass duct is fully open; the characteristic increase in NOx related to the reduction of hydrocarbons and carbon monoxide is practically non-existent at low load. Under transient conditions, improvement is also important.

It would be possible to incorporate the bypass valve into the outlet manifold (or into the inlet manifold) in one piece, which would have the effect of improving the tightness of the assembly. The pump body itself will include the connection to the gas circuit.

It is important to stress that up to now the invention has been described applied to an exchanger whose type has a bundle of tubes in which the exhaust gas circulates, this exchanger being integrated into a flange in which circulates a coolant; nevertheless, this invention is not limited to this concrete type of exchanger. It would be possible to apply to another type of exchanger a conduit or passage analogous bypass, for example a parallel plate heat exchanger, in which the flow of gas and refrigerant would be superimposed in alternating layers.

The actual location of the bypass inside the exchanger, as well as its final geometry, may vary from one case to another depending on the type of exchanger: for the tube-beam heat exchanger, the The scheduling shown in the figures is entirely appropriate since it does not require any major modification of the manufacturing lines of the exchangers. For a plate heat exchanger, it would be possible to have a conduit with a completely different geometry. For all these cases, what is important is that the bypass is integrated in the body of the exchanger.

Finally, although a concrete representation of this invention has been made and shown, it is obvious that the authority in the field may introduce variants and modifications, or replace some details with others of the same technical equivalence, without departing from the scope of protection defined by the appended claims.

Claims (19)

1. Heat exchanger module, specially designed for an exhaust gas recycling system, comprising a heat exchanger (1) provided with means of allowing the flow of these exhaust gases, comprising, among said means, certain ducts (11) designed for heat-exchanging gas flow with a coolant, presenting the general configuration of an exchanger (1) with a parallel tube bundle (11) to allow the passage of the exhaust gases, and having a bypass comprising a single tube (12), characterized in that the means used for the flow of exhaust gases further comprise at least the bypass (12), integrated in the exchanger (1), designed to circulate the exhaust gases therein without the latter being actually cooled and having a cross section virtually equivalent to that of the parallel tube bundle (11).
2. Heat exchanger module according to Claim 1, characterized in that it further comprises means (2; 20; 20') of selecting the path of the exhaust gases, thus enabling these selection means to allow the gases to circulate via the ducts (11) designed for the heat-exchanging flow or even via the bypass duct (12) without there being any actual cooling.
3. Heat exchanger module according to Claim 2, characterized in that said means (2; 20; 20') of selecting the path of the exhaust gases comprise a detector for sensing the temperature of said gases.
4. Heat exchanger module according to either of Claims 2 and 3, characterized in that said means (2; 20; 20') of selecting the path of the exhaust gases are at least partly integrated in the heat exchanger module.
5. Heat exchanger module according to Claims 2 to 4, characterized in that said means of selecting the path of the exhaust gases are provided with a three-way valve (2).
6. Heat exchanger module according to Claim 5, characterized in that said three-way valve (2) is located at the inlet of the exchanger (1).
7. Heat exchanger module according to Claim 5, characterized in that said three-way valve (2) is located at the outlet of the exchanger (1).
8. Exchanger module according to Claims 2 to 4, characterized in that said means of selecting the path of the exhaust gases comprise a two-position valve (20, 20'), associated with the bypass duct (12), which opens or closes said duct when the exhaust gases pass through.
9. Exchanger module according to Claim 8, characterized in that the valve (20, 20') is mounted at the outlet of said bypass (12).
10. Exchanger module according to Claim 8, characterized in that the valve (20, 20') is mounted at the inlet of said bypass (12).
11. Exchanger module according to Claims 8 to 10, characterized in that said valve (20) has a linear drive mode.
12. Exchanger module according to Claim 11, characterized in that said valve (20) is chosen between a flat-seat valve, a needle valve, a gate valve or a piston valve.
13. Exchanger module according to Claims 8 to 10, characterized in that said valve (20') has a rotary drive mode.
14. Exchanger module according to Claim 13, characterized in that said valve (20') is chosen between a butterfly valve, a ball valve or a rotary valve.
15. Exchanger module according to Claims 8 to 14, characterized in that the control of said valve (20, 20') is thermostatic.
16. Heat exchanger module according to any one of the preceding claims, characterized in that said tube (12) is positioned on the longitudinal axis of the exchanger (1).
17. Heat exchanger (1), specially designed for an exhaust gas recycling system, which comprises means required for the flow of exhaust gases, comprising among said means, certain ducts (11) designed for heat-exchanging gas flow with a coolant, presenting the general configuration of an exchanger (1) with a parallel tube bundle (11) to allow the passage of the exhaust gases, and having a bypass comprising a single tube (12), characterized in that the circuits used for the flow of exhaust gases further comprise at least one bypass (12), mounted in the exchanger (1), designed to circulate the exhaust gases without the latter being actually cooled and having a cross section virtually equivalent to that of the parallel tube bundle (11).
18. Heat exchanger (1) according to Claim 17, characterized in that it further comprises means (2; 20; 20') of selecting the path of the exhaust gases, thus enabling these distribution circuits to allow the gases to circulate in the ducts (11) designed for their heat-exchanging flow or even via the bypass duct (12) without there being any actual cooling.
19. Heat exchanger (1) according to Claim 17 or 18, characterized in that the tube (12) is positioned on the longitudinal axis of the exchanger (1).

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