DE102011002629B4 - Component of an exhaust system with at least one heat exchanger - Google Patents

Abstract

Component of an exhaust system for an internal combustion engine, in particular a motor vehicle, - with an inner wall (2) which delimits an interior (5) of the component (1) which is used for exhaust gas routing or to accommodate at least one exhaust gas treatment element, - with an outer wall (3) which is arranged on a side of the inner wall (2) facing away from the interior (5) at a distance from the inner wall (2), - with at least one heat exchanger (8), which is arranged between the inner wall (2) and the outer wall (3), which Inner wall (2) connects to the outer wall (3) in a heat-transferring manner, characterized in that the respective heat exchanger (8) is a heat pipe, the evaporator section (9) of which is connected to the inner wall (2) in a heat-transferring manner and the condenser section (10) of which is connected to the outer wall (3) is connected to transfer heat.

Description

The present invention relates to a component of an exhaust system for an internal combustion engine, in particular of a motor vehicle, having the features of the preamble of claim 1.

Components of exhaust systems, such as pipes and exhaust gas ducts and housings for receiving exhaust gas treatment devices, such as catalytic converters, particulate filters and mufflers, usually have an inner wall which delimits an interior of the component and which serves for exhaust gas routing or for receiving at least one exhaust gas treatment element. In order to reduce the heat emission to an environment of the respective component of the exhaust system, it is fundamentally possible to provide an outer wall at a distance from the inner wall, whereby an air gap insulation can be realized. Optionally, in principle, a thermally insulating insulation between the inner wall and the outer wall may be arranged in order to improve the insulating effect on the environment.

The highest possible thermal insulation is of particular interest for a cold start of an internal combustion engine, since a high-quality insulation means that the components of the exhaust system can be heated comparatively quickly to a predetermined operating temperature. This is important for maintaining low pollutant emission levels. However, the good thermal insulation is for the normal operation of the internal combustion engine, so after reaching the usual operating temperatures disadvantageous because the individual components can overheat or are exposed at elevated temperatures of greater risk of corrosion. For the normal operation of the internal combustion engine therefore a reduced thermal insulation would be advantageous.

From the WO 2010/015 940 A2 is a catalyst of an exhaust system for an internal combustion engine, in particular of a motor vehicle, known comprising an inner wall defining an interior of the catalyst, which serves to receive at least one catalyst element, and an outer wall which is spaced on a side facing away from the interior side of the inner wall to the inner wall is arranged. Between the inner wall and outer wall, a cavity is formed, which can be flowed through by a liquid heat transfer medium to heat-transfer the inner wall to the outer wall.

From the DE 10 2009 057 367 A1 An exhaust gas heat recovery device is known which operates in the manner of a cyclic process in which a working medium is vaporized by means of an evaporator, expanded by means of an expansion machine, condensed by means of a condenser and driven by means of a conveyor and pressurized. The evaporator is formed by a through-flow of the working fluid jacket of a component of an exhaust system of an internal combustion engine.

From the JP 2005-226892 A It is known to envelop a exhaust pipe of an exhaust system of an internal combustion engine, which can be penetrated by exhaust gas, with a cooling jacket, through which a coolant can flow. Between exhaust pipe and cooling jacket thermoelectric Genartoren are arranged, which convert a heat flow into an electric current.

From the JP 58-013144 A It is known, for heat-transmitting coupling of an exhaust gas leading exhaust pipe of an internal combustion engine with a cooling circuit in which a coolant circulates a heat exchanger arranged in the exhaust pipe primary heat exchanger by means of several heat pipes with a arranged in the cooling circuit secondary heat exchanger kopeckeln.

The JP 2002-317629 A proposes to dissipate heat from an exhaust pipe leading exhaust gas of an internal combustion engine to heat transfer via a plurality of heat conductive wires to the exhaust pipe by connecting the wires at one end touching the exhaust pipe and the other end are secured by a bracket to the discharge device.

The present invention is concerned with the problem of providing an improved embodiment for a component of the type mentioned at the beginning or for an exhaust system equipped therewith, which is characterized in particular by the fact that rapid heating in the course of a cold start is possible on the one hand and excessive heating on the other hand can be avoided during normal operation.

This problem is solved according to the invention by the subject matter of the independent claim. Advantageous embodiments are the subject of the dependent claims.

The invention is based on the general idea to arrange at least one heat exchanger in a double-walled component between the inner wall and the outer wall, which connects the inner wall with the outer wall to transmit heat. Such a passive heat exchanger allows heat transfer from the inner wall to the outer wall despite the thermally insulating effect of the gap between the inner wall and the outer wall. Thus, can sufficient heat is transported to the outer wall especially for higher temperatures and radiated from the outer wall into the environment. In this way, the thermal management for the respective component can be improved because overheating or an elevated temperature level for the component can be avoided.

In an advantageous embodiment, a thermally insulating insulation is arranged between the inner wall and the outer wall, ie in the gap. The respective heat exchanger can be embedded in this insulation or penetrate the insulation. In any case, the heat exchanger can selectively transfer heat from the inner wall to the outer wall despite this isolation.

According to a particularly advantageous embodiment, the at least one heat exchanger may be designed such that its heat transfer performance increases abruptly when the temperature exceeds a predetermined activation temperature of the heat exchanger. In particular, the temperature on the inner wall is relevant. Under a "sudden" increase in heat transfer performance is to understand a disproportionate relationship between heat transfer performance and temperature, which is significantly different from a usually z. B. sets in a solid material existing proportional relationship between heat transfer performance and temperature. By skillful specification of the activation temperature, it is particularly easy to leave the respective heat exchanger below the activation temperature largely inactive, so that it can transport only comparatively little heat from the inner wall to the outer wall. In this lower temperature range, the thermal insulation between the inner wall and the outer wall is effective and in particular not weakened by the respective heat exchanger. However, as soon as the activation temperature is exceeded, the respective heat exchanger can transfer comparatively much heat from the inner wall to the outer wall, whereby the insulation effect is significantly impaired. In other words, above the activation temperature there is less good thermal insulation. Thus, it is possible to switch between a cold start operation in which the temperatures of the component are in the lower temperature range and a normal operation in which the temperatures of the component are in an upper temperature range which adjoins the activation temperature. Thus, during the warm-up operation or cold start operation, the desired high thermal insulation can be ensured in order to shorten the warm-up phase in time. At the same time, the thermal insulation can be weakened for normal operation in order to avoid overheating or an excessive temperature level for the respective component.

According to the invention, the respective heat exchanger is a heat pipe. Such heat pipes are also referred to as "heat pipe" and have an evaporator section and a condenser section. In a heat exchanger designed as a heat exchanger, the evaporator section is expediently connected to transmit heat to the inner wall, while the condenser section is expediently connected in a heat-transmitting manner to the outer wall. Thus, a working medium of the heat pipe in the evaporator section can be vaporized, taking up comparatively much heat energy, and condensing in the condenser section, giving off comparatively much heat. The heat transfer in conjunction with a phase change is greater by several orders of magnitude than a heat exchanger of the same size, which is made for example of a heat conducting material, such as aluminum or copper. Evaporator section and condenser section are interconnected, for example, by means of an adiabatic transport section, which contains, for example, a capillary structure to transport the condensate from the condenser section to the evaporator section. However, this intensive heat transfer only occurs from a temperature at which the working medium can evaporate. This corresponds to the aforementioned activation temperature, which in the present context can also be referred to as the first activation temperature.

Particularly advantageous is an embodiment in which the respective heat pipe is designed as a sintered heat pipe. In a sintered heat pipe, extremely large capillary forces can be generated in the capillary structure in order to transport the condensate from the condenser section to the evaporator section. In particular, it does not matter for a sintering heat pipe how the transport direction of the condensate is oriented with respect to the direction of gravity. In particular, the condensate can also be transported against gravity. In other words, the heat can also be transported in the direction of gravity.

In a further advantageous embodiment can be provided to design the heat pipe as a heat pipe with variable conductivity. Such heat pipes are known in the literature as VCHP, where VCHP stands for Variable Conductance Heat Pipe. Such variable conductivity heat pipes differ from conventional heat pipes, inter alia, by a non-condensing gas storage, which is present only in the variable conductivity heat pipes. While at a normal Heat pipe has a proportional, in particular linear relationship between the heat transfer performance and the evaporation temperature at the evaporator section, in a heat pipe with variable conductivity, a sudden increase in heat transfer performance can be achieved upon reaching an activation temperature. This activation temperature can be specifically determined by the selection of the respective non-condensing gas in the heat pipe and can be referred to in the present context as the second activation temperature.

Apart from this second activation temperature of the variable conductivity heat pipe, the aforementioned first activation temperature for heat transfer can also be adjusted in conjunction with the phase change of the working medium, regardless of whether it is a heat pipe with or without variable conductivity. This first activation temperature for the phase change of the working medium can be adjusted comparatively accurately by the targeted selection of the working medium used and by the pressure in the heat pipe or by the pressure prevailing in the heat pipe. In the heat pipe there is a more or less strong vacuum, so compared to the atmospheric environment, a more or less pronounced negative pressure.

In another embodiment, the heat pipe may extend in its condenser section parallel to the outer wall. As a result, a comparatively large contact area can be achieved, which favors the heat transfer between the heat pipe and the outer wall. Additionally or alternatively, the heat pipe may extend in its evaporator section parallel to the inner wall. Again, a relatively large contact surface can be realized, which favors an intense heat transfer from the inner wall to the heat pipe. The heat pipe can be soldered or welded to the inner wall and / or to the outer wall.

The respective heat exchanger can be embedded in the insulating material of the insulation, so apart from the contact surfaces to the inner wall or to the outer wall of the insulating material to be wrapped.

Inner wall and outer wall may in another embodiment form a double-walled tube enclosing the interior of the component in the circumferential direction. In particular, the respective component can then be an exhaust gas guide tube or a tubular housing for receiving an exhaust gas treatment element, such as a catalytic converter or a particulate filter or a silencer or any combination thereof.

The first and / or second activation temperature of the heat exchanger is expediently chosen so that it is above a minimum operating temperature of at least one exhaust gas treatment device of the exhaust system. The activation temperature must prevail on the inner wall. As mentioned, various exhaust treatment devices, such as oxidation catalysts, NOX storage catalysts, SCR catalysts, and three-way catalysts typically each have a minimum operating temperature that they must have in order to properly fulfill their respective emission control function. Until reaching this minimum operating temperature intensive thermal insulation of the respective component or the entire exhaust system is desired. As soon as this minimum operating temperature is reached, however, a reduced thermal insulation is sufficient to avoid excessive heating or overheating of the respective exhaust gas treatment device. By positioning the activation temperature between the minimum operating temperature and the excessive temperature range to be avoided, the desired switching function results for the insulation effect.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

It show, each schematically

1 a greatly simplified, fundamental longitudinal section through a component,

2 a schematic representation of a heat pipe without variable conductivity,

3 a schematic diagram of a heat pipe with variable conductivity.

Corresponding 1 includes a component 1 an exhaust system for an internal combustion engine, in particular a motor vehicle, an inner wall 2 and an outer wall 3 spaced from the inner wall 2 is arranged and accordingly a gap 4 between inner wall 2 and outer wall 3 generated. At the component 1 it may be an exhaust pipe or a housing of an exhaust gas treatment device. A Exhaust system can have several such components 1 have, in particular at least one housing for an exhaust gas treatment device and at least one exhaust pipe. Basically limits the inner wall 2 an interior 5 the component, this interior 5 for exhaust system or for receiving at least one exhaust gas treatment element is used. In the example of 1 is the component 1 tube-shaped, so that the inner wall 2 the interior 5 with respect to a longitudinal central axis 6 encloses in the circumferential direction. The outer wall 3 then encloses the inner wall 2 also in the circumferential direction. The gap 4 is then an annular gap. inner wall 2 and outer wall 3 then form a double-walled pipe, which is the interior 5 encloses in the circumferential direction.

In the gap 4 can be an isolation 7 be arranged, which acts thermally insulating. It is located between the inner wall 2 and the outer wall 3 and causes a thermal decoupling between the inner wall 2 and outer wall 3 ,

In the case of the component presented here 1 is between inner wall 2 and outer wall 3 at least one heat exchanger 8th arranged. The example shows a large number of such heat exchangers 8th in the gap 4 arranged. The respective heat exchanger 8th creates a heat transfer coupling between the inner wall 2 and the outer wall 3 , so the isolation works 7 opposite.

In 1 it can be seen that the heat exchanger 8th in the insulation material of the insulation 7 are embedded. Accordingly, preferably all gaps are within the gap 4 that exist between adjacent heat exchangers 8th exist, through the insulation material 7 filled.

The respective heat exchanger 8th is in the preferred embodiment of the component presented here 1 each formed by a heat pipe or heat pipe. According to the 1 - 3 has such a heat pipe (heat exchanger 8th ) each have an evaporator section 9 that with the inner wall 2 is heat transfer connected, and a capacitor section 10 up, with the outside wall 3 heat transfer connected. Furthermore, such a heat pipe (heat exchanger 8th ) usually with an adiabatic transport section 11 equipped, which is the evaporator section 9 with the condenser section 10 connects and thereby the distance between the inner wall 2 and outer wall 3 bridged.

According to 2 is inside the heat pipe (heat exchanger 8th ) on the one hand a steam path 12 formed by a vaporized working medium or working medium vapor through the transport section 11 from the evaporator section 9 to the condenser section 10 arrives. Furthermore, the heat pipe contains (heat exchanger 8th ) a condensate path 13 , by the condensed or liquid working medium from the condenser section 10 over the transport section 11 to the evaporator section 9 arrives. To the condensate in the condensate path 13 to drive, contains the heat pipe (heat exchanger 8th ) suitably a capillary structure 14 , which causes the transport of the liquid working medium.

During evaporation in the evaporator section 9 takes the working medium by the phase change comparatively much heat, especially latent heat, which is indicated by arrows 15 is indicated. The gaseous working fluid passes through the vapor path via the vapor path 12 to the condenser section 10 where it condenses. In this case, comparatively much heat, in particular latent heat is released again by the phase change, which is indicated by arrows 16 is indicated. The condensed working medium then passes again via the condensate path 13 to the evaporator section 9 back. Within the respective heat pipe (heat exchanger 8th ), therefore, a cyclic process occurs during operation.

As long as the temperature at the evaporator section 9 So on the inside wall 2 However, below a temperature required for the evaporation of the working medium remains, said cycle can not adjust, so that the intense heat transfer from the evaporator section 9 to the condenser section 10 omitted. This evaporation temperature or light-off temperature is hereinafter also referred to as the activation temperature and in particular as the first activation temperature of the heat pipe (heat exchanger 8th ) designated. This first activation temperature has the consequence that the heat pipe or the heat exchanger 8th shows a sudden increase in its heat transfer performance as soon as the temperature on the inner wall 2 exceeds the first activation temperature.

Appropriately, the heat pipe (heat exchanger 8th ) be designed as a sintered heat pipe. In this case, the capillary structure 14 sintered, whereby the transport of the liquid working medium can easily be done against gravity. Accordingly, then also heat from the evaporator section 9 in the direction of gravity to the condenser section 10 be transported.

In 3 is a special embodiment of such a heat pipe (heat exchanger 8th ). This is a heat pipe (heat exchanger 8th ) with variable conductivity. The variable conductivity is achieved by means of a non-condensing gas in addition to the working medium 17 realized, wherein the variable conductivity equipped heat pipe (heat exchanger 8th ) For this purpose, a corresponding memory 18 can have. The gas pressure of the non-condensing gas 17 counteracts the spread of the vaporized working medium. At low temperatures, the adiabatic transport section expands in the direction of the evaporator section 9 out. The non-condensing gas 17 prevents the transport of the working medium vapor to the condenser section 10 , Accordingly, the heat pipe (heat exchanger 8th ) also have only a reduced heat transfer performance above the aforementioned first activation temperature. As the temperature increases, the vapor pressure in the vaporous working medium increases, causing the non-condensing gas 17 more and more in the store 18 is displaced. As a result, the adiabatic transport section 11 more and more direction capacitor section 10 expand. When a further or second activation temperature is reached, the vaporous working medium can now reach the condenser section 10 penetrate and condense there, whereby the cycle of the heat pipe (heat exchanger 8th ) gets underway. Also, this second activation temperature, the only one heat pipe (heat exchanger 8th ) occurs with variable conductivity, there is a sudden increase in heat transfer performance.

The first activation temperature can be determined by the selection of the respective working medium and by the heat pipe (heat exchanger 8th ) in the steam path 12 or in the condensate path 13 Set the adjusted pressure. When pressure in the steam path 12 or in the condensate path 13 It is a more or less pronounced vacuum, so compared to the atmospheric environment to a vacuum.

At the heat pipe (heat exchanger 8th ) with variable conductivity can also the second activation temperature by selecting the respective non-condensing gas 17 be set.

At the heat pipes (heat exchanger 8th ) are the capacitor sections 10 and the evaporator sections 9 to realize the most effective heat transfer to the respective wall 2 . 3 according to 1 as large as possible with the respective wall 2 . 3 connected, for example by means of soldered joints or welded joints. For this purpose, the heat pipes (heat exchangers 8th ) in their respective condenser section 10 parallel to the outer wall 3 extend and / or in their respective evaporator section 9 parallel to the inner wall 2 extend. Unless the walls 2 . 3 form cylindrical pipes, the heat pipes (heat exchangers 8th ) also deviating from the in 1 shown axial orientation in the circumferential direction or have an orientation with axial component and peripheral component. The capacitor sections 10 or the evaporator sections 9 then extend correspondingly with the respective curvature of the respective wall 2 . 3 in order to realize the desired large-area contacting.

For a heat pipe (heat exchanger 8th ) with or without variable conductivity, the first activation temperature is expediently chosen such that it is above a minimum operating temperature at least one exhaust gas treatment device of the exhaust system, which is, for example, an oxidation catalyst or an NOX storage catalyst or an SCR catalyst or a three Way catalyst can act. If a plurality of such exhaust gas treatment devices are provided in the exhaust system, different first activation temperatures can also be achieved by the respective component 1 be selected, depending on the type of exhaust treatment device.

If the heat pipe (heat exchanger 8th ) is configured as a heat pipe with variable conductivity, the second activation temperature above the minimum operating temperature of the respective exhaust gas treatment device or in the range of a maximum operating temperature of the respective exhaust gas treatment device can be selected.

It is also conceivable to combine heat pipes with and without variable conductivity at one component, in particular with different first and / or second activation temperatures.

Since the heat transfer within the heat pipe (heat exchanger 8th ) except for the temperature difference between evaporator section 9 and capacitor section 10 works without external energy, this is a passive or passive heat exchanger 8th ,

Claims (11)

Component of an exhaust system for an internal combustion engine, in particular of a motor vehicle, - with an inner wall ( 2 ), which has an interior ( 5 ) of the component ( 1 ), which serves for the exhaust system or for receiving at least one exhaust gas treatment element, - with an outer wall ( 3 ) at one of the interior ( 5 ) facing away from the inner wall ( 2 ) spaced from the inner wall ( 2 ), - with at least one heat exchanger ( 8th ), which between inner wall ( 2 ) and outer wall ( 3 ) is arranged, which the inner wall ( 2 ) with the outer wall ( 3 ) heat-transferingly connecting, characterized that the respective heat exchanger ( 8th ) is a heat pipe whose evaporator section ( 9 ) with the inner wall ( 2 ) is heat-transmitting connected and whose capacitor section ( 10 ) with the outer wall ( 3 ) is heat transfer connected. Component according to claim 1, characterized in that the at least one heat exchanger ( 8th ) is configured so that its heat transfer performance increases abruptly when the temperature reaches a predetermined activation temperature of the heat exchanger ( 8th ) exceeds. Component according to claim 1 or 2, characterized in that the heat pipe is designed as a sintered heat pipe. Component according to one of claims 1 to 3, characterized in that the heat pipe is designed as a heat pipe with variable conductivity. Component according to one of claims 1 to 4, characterized in that the heat pipe in its evaporator section ( 9 ) parallel to the inner wall ( 2 ). Component according to one of claims 1 to 5, characterized in that the heat pipe in its condenser section ( 10 ) parallel to the outer wall ( 3 ). Component according to one of claims 1 to 6, characterized in that between inner wall ( 2 ) and outer wall ( 3 ) a thermally insulating insulation ( 7 ) is arranged. Component according to claim 7, characterized in that the respective heat exchanger ( 8th ) in an insulating material of the insulation ( 7 ) is embedded. Component according to one of claims 1 to 8, characterized in that the inner wall ( 2 ) and outer wall ( 3 ) form a double-walled tube, the interior ( 5 ) encloses in the circumferential direction. Component according to one of claims 1 to 9, characterized in that the component ( 1 ) is an exhaust pipe or a housing of an exhaust gas treatment device. Component according to at least claim 2, characterized in that the activation temperature is above a minimum operating temperature of at least one exhaust gas treatment device of the exhaust system.

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