WO2002052142A1

WO2002052142A1 - Heat-exchanger module, specially designed for an exhaust gas recycling system

Info

Publication number: WO2002052142A1
Application number: PCT/EP2001/015411
Authority: WO
Inventors: Carlos Perez Caseiras; David Paja Burgoa; José Luis GARCIA BERNARD; José Luis LAZARO
Original assignee: Valeo Termico Sa
Priority date: 2000-12-19
Filing date: 2001-12-17
Publication date: 2002-07-04
Also published as: ATE391844T1; EP1343963A1; EP1343963B1

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

HEAT EXCHANGER MODULE, SPECIFICALLY DESIGNED FOR AN EXHAUST GAS RECYCLING SYSTEM

The present invention relates to a heat exchanger module for an exhaust gas recycling system, which can in particular be applied to systems for recycling the exhaust gases from the engine of a vehicle to the intake. The other applications of this exchanger module can be the heating of the intake air as well as the refrigeration of the exhaust gases which are led to the catalytic converter for petrol engines.

There is a well-established use in the automotive field which consists in providing a system for recycling the exhaust gases of a diesel engine, known under the name EGR or "Exhaust Gas Recycling", so as to mix these gases with intake air, since the presence of exhaust gases 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, in order to improve the efficiency of the system. Inside the loop, there is also a valve (EGR valve) which controls the passage of exhaust gas through the exchanger.

The actual heat exchanger 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.

In all cases, the current EGR systems which are cooled have a drawback because the exhaust gases circulate via the exchanger whatever the operating mode of the engine from the moment the EGR valve opens: the gases are cooled as long as the engine is running at stable speed and their temperature is high, as during a cold start, when the gas temperature is significantly lower.

This operation of cooling the gases when their temperature is not high represents a drawback from an ecological point of view since it increases the level of CO and hydrocarbon emissions, accompanied in addition by 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 recycling system making it possible to maintain a minimum level of gas emission. pollutants in the exhaust gases, regardless of the engine's operating condition.

The heat exchange module of this invention is of the heat exchanger type equipped with circuits allowing the flow of exhaust gases, the latter comprising among these means the conduits reserved for the flow of gases with heat exchange with a cooling; its peculiarity lies in the fact that the circuits serving for the flow of the exhaust gases comprise at least one by-pass duct, integrated into 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 a "bypass", makes it possible to avoid cooling of the exhaust gases according to the different operating modes of the engine, for example in the event of a cold start, for which its temperature n is not high and cooling it would be dangerous because of the emission of polluting gases 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 is very important for vehicles whose available space is always limited.

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

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

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 assemble.

In accordance with one application, the exhaust gas path selection circuits include a three-way valve; this valve can be placed at the inlet of the exchanger, but it can either located at the exit of the exchanger.

Even if it is possible to mount this valve at the outlet of the exchanger for manufacturing-related reasons, the pressure difference ensures the transmission of gases to the appropriate conduits, depending on the position of the valve.

In accordance with an application for replacing this three-way valve, the means for selecting the path of the exhaust gases comprise a two-position valve which is associated with the bypass pipe mentioned above, which opens or closes the pipe at when the exhaust gases pass.

This valve makes it possible to direct the exhaust gases to the conduits with heat exchange 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 outlet of said bypass. When the valve closes the outlet of this conduit, the gases must pass through the tubes of the exchanger, while when the valve leaves the passage through the bypass open, the gases preferably take this path, because they lose less dump; it is possible to install either the valve at the inlet of the bypass.

In accordance with a chosen application of this invention, the valve associated with the bypass is linear drive, since this mode makes it possible to ensure sealing of the assembly more easily; in this case it is possible to choose between a flat seat valve, a needle valve, a gate valve or a piston valve.

The valve can be either rotatable, and a choice should be made between 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 coolant.

The thermostatic control removes any external control, which avoids any problem of tightness as well as the need to exercise an external control.

In accordance with a particularly practical manufacturing approach, 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 should 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 slight modifications.

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

In addition, the exchanger preferably consists of means for selecting the path of the exhaust gases, thus allowing these selection means to allow the circulation of gases via the pipes 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 above, plans are attached hereto, which present schematically and only by way of non-exhaustive example, a practical case of the application.

In these plans, FIG. 1 schematically represents a heat exchanger module according to the present invention, in the operating position; Figure 2 shows the module of Figure 1 in another operating condition; Figure 3 is a sectional view of the heat exchanger; FIGS. 4 and 5 are views in longitudinal section of an exchanger according to an application of the present invention, in which a valve with planar seat is mounted, respectively in the closed and open position; finally Figures 6 and 7 are views similar to Figures 4 and 5, for an exchanger provided with a butterfly valve.

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

At the inlet of the exchanger 1 is the 3-way valve 2, through which the exhaust gases enter by a line indicated by the arrow A, and through which they are led, according to the position of the valve, to the bundle of tubes 11 via the line indicated by arrow B, as shown in figure 1, or to bypass 12 via the line indicated by arrow C, as shown in figure 2.

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

As shown in Figure 3, which shows in more detail the 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 by- pass 12. The exhaust gases from the engine cylinders pass, through the valve shown in FIG. 1, from valve 2 to the tubes 11, through the inlet manifold 13, while in FIG. 2 the gases pass from valve 2 to line 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 module EGRC described also includes circuits making it possible to detect the temperature of the gases leaving the cylinders, as well as means for controlling the valve 2.

The operation of the module described is simple: during normal engine operation, the valve 2 remains in the position in FIG. 1, and the exhaust gases are cooled in the exchanger, in the traditional way, since they circulate in the tube bundle 11. However, when the temperature of the exhaust gases is low, for example in the case of a cold start or under low load or when the engine is at low speed, it is not advisable to cool them more, since this would cause an increase in CO and hydrocarbon emissions; the means to control then change the state of the valve to that of FIG. 2, so 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 gas flow 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 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 approximately 500 mm ² and 1000 mm ² , this section consisting of a large number of tubes with a hydraulic diameter between 5 mm and 12 mm, inside a flange whose internal diameter is approximately 43 mm to 52 mm.

In this case, the hydraulic diameter of the tubular bypass can be between approximately 10 mm and 40 mm. The characteristic values of the temperatures of the gases circulating in a traditional exchanger, when the engine has a normal speed, are 300 ° C at the inlet and 150 ° C at the outlet; in the event of a cold start, the gases entering the exchanger are between 100 and 150 ° C and the exchanger cools them down to 50 ° C. With this invention, thanks to the bypass, the gases leaving the exchanger have practically the same temperature as at the inlet.

It is possible to install valve 2 either at the inlet of the exchanger, as presented, or at the outlet; in this case, the pressure difference between the inlet and the outlet passes the exhaust gases through the tube bundle or through the bypass 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 in a single module in connection with the exchanger, or to arrange it as an external component.

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

In Figure 4 we can consider an exchanger with an inlet manifold 13, a flange 10 with a bundle of heat exchange tubes 11, a bypass or bypass 12, as well as an outlet manifold 14.

In this case, it passes from a module fitted with a single three-way valve, which has the dual function of controlling the flow of gas via the EGR and of opening or closing its access by means of the by-pass of the 'exchanger, to an exchanger module fitted 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 TOR valve, integrated in the exchanger.

This is why, in accordance with the application shown in FIGS. 4 and 5, a valve 20 is associated with the bypass duct 12 - in the present case it is a plane seat valve - located on the manifold of exit 14.

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

At the location of the valve 20 shown in 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 which circulates inside the flange 10 (although its inputs and outputs are not shown in the figures).

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

The other linear drive valves which could replace the butterfly valve 20 are needle valves, gate valves of different sections or piston valves.

Figures 6 and 7 show a variant of the application of the exchanger, in which a butterfly valve 20 'has been integrated instead of a plane seat valve 20 as proposed in the previous figures.

In this case, the drive axis 21 'of the rotary valve, and the valve 21 can pass from the closed position of the bypass duct 12 (Figure 6) to 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 house 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 conduit passing through them, or rotary valves, composed of a plate articulated from a point of its periphery to a hinge pin located on the periphery of the conduit 12 to be closed.

A rotary drive valve could be installed, such as the butterfly valve 20 ′, by equipping it with a connecting rod-crank system or the like, inside the exchanger, so that the drive mode goes linear. . The bypass valve can be either pneumatic, electric or thermostatic.

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

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

Indeed, the tests carried out at medium and low speed (2250 rpm and 1250 rpm) and when the engine is at low load (PME = 1 bar), demonstrate that the emissions of hydrocarbons and carbon monoxide are reduced by significantly when the bypass duct is completely open; the characteristic increase in NOx relating to the reduction in hydrocarbons and carbon monoxide is almost nonexistent at low load. In transient conditions, improvement is also important.

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

It is important to insist on the fact that the invention has so far been described as applied to an exchanger, the type of which has a bundle of tubes in which the exhaust gases circulate, this exchanger being integrated in a flange in which circulates a coolant; however, this invention is not limited to this concrete type of exchanger. It would be possible to apply to other types of exchanger a similar branch conduit or passage, for example a parallel plate exchanger, in which the gas and coolant flows 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 bundle exchanger, the scheduling shown in the figures is entirely suitable since it does not require any significant modification of the exchanger production lines. For a plate heat exchanger, it would be possible to have a duct with a completely different geometry. For all these cases, what is important lies in the fact that the bypass is integrated in the body of the exchanger.

Finally, although a concrete representation of this invention has been made and represented, it is obvious that the authority in the matter may introduce variants as well as modifications, or even replace certain details with others of the same technical equivalence, without departing from the protective field defined by the appended claims.

Claims

1. Module ^' heat exchanger, specially designed for an exhaust gas recycling system, which comprises a heat exchanger (1) provided with means serving for the flow of these exhaust gases, comprising among said means, certain conduits (11) intended for the flow of gases with heat exchange with a cooling fluid, characterized in that the means serving for the flow of exhaust gases further comprise at least one bypass (12), integrated in the exchanger (1), adapted so that the exhaust gases circulate there without them undergoing real cooling.

2. Heat exchanger module as described in claim 1, the characteristic of which resides in the fact that it further comprises means (2; 20; 20 ') for selecting the path of the exhaust gases, thus allowing these selection means to let the gases circulate -by the conduits (11) intended for the flow with heat exchange or else by the by-pass conduit (12) without there being any real cooling.

3. Heat exchanger module as described in claim 2, the characteristic of which lies in the fact that said means (2; 20; 20 ') for selecting the path of the exhaust gases comprise a temperature detector of said gases. . Heat exchanger module as described in claims 2 or 3, whose characteristic resides in the fact that said means (2; 20; 20 ') for selecting the exhaust gas path are at least partly integrated in the exchanger module heat.

5. Heat exchanger module as described in claims 2 to 4, the characteristic of which lies in the fact that said means for selecting the path of the exhaust gases are provided with a three-way valve. (2).

6. heat exchanger module as described in claim 5, the characteristic of which is that said three-way valve (2) is located at the inlet of the exchanger (1).

7. Heat exchanger module as described in claim 5, the characteristic of which is that said three-way valve (2) is located at the outlet of the exchanger (1). 8. Exchanger module as described in claims 2 to 4, the characteristic of which resides in the fact that said means for selecting the path of the exhaust gases comprise a valve (20, 20 ′) with two positions, associated with the bypass duct. -pass (12), which opens or closes said conduit during the passage of exhaust gases.

9. Exchanger module as described in claim 8, whose characteristic resides in the fact that the valve (20,20 ') is mounted at the outlet of said by-pass (12).

10. Exchanger module as described in claim 8, the characteristic of which is that the valve (20,20 ') is mounted at the inlet of said bypass (12). 11. Exchanger module as described in claims 8 to 10, the characteristic of which lies in the fact that said valve (20) has a linear drive mode.

12. Exchanger module as described in claim 11, the characteristic of which lies in the fact that said valve (20) is chosen from a plane seat valve, a needle valve, a gate valve or a piston valve.

13. Exchanger module as described in claims 8 to 10, the characteristic of which is the fact that said valve (20 ') has a rotary drive mode.

14. Exchanger module as described in claim 13, whose characteristic resides in the fact that said valve (20 ') is chosen between a butterfly valve, a ball valve or a rotary valve.

15. Exchanger module as described in claims 8 to 14, whose characteristic lies in the fact that the control of said valve (20,20 ') is thermostatic.

16. Heat exchanger module as described in the preceding claims, the characteristic of which resides in the fact that it has the general configuration of an exchanger (1) with a bundle of parallel tubes (11) to allow the passage of gases from 'exhaust, and by the fact that the bypass consists of a single tube (12).

17. Exchanger module as described in claim 16, whose characteristic resides in the fact that said single tube (12) has a section almost equivalent to that of the above-mentioned bundle of tubes (11).

18. heat exchanger module as described in claims 16 or 17, the characteristic of which lies in the fact that said tube (12) is positioned on the longitudinal axis of the exchanger (1). 19. Heat exchanger (1), specially designed for an exhaust gas recycling system, which comprises means necessary for the flow of exhaust gases, comprising among said means, certain conduits (11) intended for the flow of gases with heat exchange with a cooling fluid, the characteristic of which resides in the fact that the circuits serving for the flow of the exhaust gases further comprise at least one bypass (12), mounted in the exchanger

(1), suitable for the circulation of exhaust gases without these being subjected to real cooling. 1 S

20. Heat exchanger (1) as described in claim 19, the characteristic of which resides in the fact that it further comprises means (2; 20; 20 ') for selecting the path of the exhaust gases, allowing thus to these distribution circuits to let the gases circulate in the conduits (11) intended for their flow with heat exchange or else by the by-pass conduit (12) without there being any real cooling.