Abstract:
A heat shield configuration having a heat shield for shielding an object from heat and/or noise having an internal surface facing toward the object and an external surface facing away from the object as well as an opening, which goes through the heat shield having internal surface and external surface. The heat shield has a closure for at least regionally closing the opening. In addition, an actuating device is provided, which is implemented to open and close the closure as a function of a controlled variable relevant for the function of the object.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims benefit from EP 06020255.3 filed on Sep. 27, 2006 which is incorporated by reference in its entirety.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a heat shield configuration having a heat shield for shielding an object against heat and/or noise having an internal surface facing toward the object and an external surface facing away from the object as well as at least one opening, which goes through the heat shield having internal and external surfaces.  
       BACKGROUND OF THE INVENTION  
       [0003]     Heat shields of this type are used, for example, in engine compartments of motor vehicles, in particular in the area of the exhaust system, to protect neighboring temperature-sensitive components and assemblies from impermissible heating. The heat shields are often used simultaneously as a noise protector. Concretely, such heat shields may be used, for example, for shielding a catalytic converter or pre-catalytic converter, a particulate filter, or other components in the area of the exhaust system or of a turbocharger. In regard to continuous operation, it is often not only important for these components to be protected from too strong a temperature strain, but rather the operating temperature is to be subjected to strong oscillations during the entire operating life as little as possible.  
         [0004]     The most possible constant operating temperature is advantageous, for example, for the components used for exhaust treatment, because in this way a more uniform exhaust treatment effect may be achieved. Simultaneously, the service life of the components, neighboring housing parts, and gas-conducting components may also be lengthened. Rapid heating and keeping the operating temperature constant are of special significance in regard to maintaining the future EU exhaust gas standard Euro  5 . In addition to the exhaust gas limiting values in the normal operating phase of an engine, exhaust gas limiting values of the cold starting phase are also incorporated here. The efficiency of the exhaust treatment catalytic converters for the pollutants contained in the exhaust gas is known to differ as a function of the temperature. Thus, for example, the discharge of hydrocarbons and carbon monoxide is particularly high at the beginning of the cold start phase. This is primarily to be attributed to the fact that the catalytic converter has not yet reached its operating temperature. To reduce these pollutants, it is therefore necessary to increase the operating temperature of the catalytic converter as rapidly as possible. On the other hand, the operating temperature cannot rise too much, however, because this results on the one hand in the increase of other pollutants such as nitrogen oxides in the exhaust gas, and on the other hand, too high a temperature may damage the catalytic converter itself.  
         [0005]     In other cases, it may be desirable, for example, to be able to set a higher or lower temperature during a specific operating phase than in other operating phases. Thus, for example, a particulate filter may pass through an operating phase of higher temperature in which accumulated particles in the particulate filter are removed by oxidation. Up to this point, reaching this elevated temperature by engine measures or by additional injection of fuels was typical. After completed particle removal, the measures were returned to normal operation again. However, this procedure is very complex and requires additional energy.  
         [0006]     In consideration of the problems described above, it is the object of the present invention to specify a heat shield configuration which is capable of setting the operating temperature of an object shielded thereby to a predefined range. The heat shield configuration is on the one hand to allow the temperature to be kept as constant as possible and simultaneously ensure the most rapid possible achievement of the operating temperature. On the other hand, the heat shield configuration is also to allow selective operation at various predefined temperatures.  
         [0007]     This object is achieved by the heat shield configuration according to claim  1 . Preferred embodiments are specified in the subclaims.  
       SUMMARY OF THE INVENTION  
       [0008]     The heat shield configuration according to the present invention comprises a heat shield for shielding an object against heat and/or noise having an internal surface facing toward the object and an external surface facing away from the object. An opening is provided in the heat shield, which goes through the internal and external surfaces. According to the present invention, this opening is at least regionally closable by a closure, which may be opened and closed using an actuating device as a function of a controlled variable relevant for the function of the object.  
         [0009]     The opening implemented in the heat shield is exposed by opening the closure, so that better temperature regulation is made possible by the passage thus resulting. For example, hot air accumulated between the object to be shielded, which is situated neighboring the internal surface of the heat shield, and the heat shield may escape through the exposed opening and thus the temperature in the area around the object to be shielded may be reduced. Vice versa, it is just as possible, for example, to introduce colder air in the direction toward the object to be shielded through the exposed opening and thus reduce the temperature in its environment. It is also possible to feed hot air in the direction toward the object to be shielded through the opened opening or discharge cold air if its temperature increase is desired. In addition, the opening may be at least partially closed in an operating phase of increased temperature, while it is at least partially exposed in an operating phase of lower temperature, so that accumulated heat may escape through the opening. More than two operating phases of different temperatures are also fundamentally settable as a function of the opening size of the opening.  
         [0010]     At least one of the following measured variables comes into consideration as a controlled variable which the closure is opened or closed as a function of:  
         [0011]     a temperature,  
         [0012]     a pressure,  
         [0013]     a velocity,  
         [0014]     an acoustic signal,  
         [0015]     an exhaust gas value,  
         [0016]     a volume flow, and  
         [0017]     an operating time.  
         [0018]     In the preferred application of the present invention in the area of internal combustion engines, very generally, those measured variables which may be measured in the area of the internal combustion engine come into consideration.  
         [0019]     The temperature is expediently a temperature in the environment of the object to be shielded or the component temperature of the object or another component, if this temperature has effects on the function of the object to be shielded. By measuring the temperature, it may be established directly whether the object to be shielded is threatened with overheating. If so, the actuating device may counteract this by opening the closure in the heat shield. Vice versa, in the event of too strong cooling, the closure may be closed again using the actuating device.  
         [0020]     The internal pressure of the object to be shielded may particularly be measured as the pressure. A possible application is in particulate filters, in which the internal pressure rises with increasing charging by particles. The throughput correspondingly worsens, and the particulate filter must be freed of the deposited particles to obtain the desired filtering action. This may be performed by raising the temperature in the interior of the particulate filter so strongly that the particles oxidize and are blown out of the filter. The required temperature increase may be performed or at least supported by closing the closure, by which heat accumulates in the area of the heat shield around the particulate filter. After passage of a predefined time or alternatively upon reaching a lower internal pressure, which allows regular operation of the particulate filter, the closure may be opened again, so that the operation runs at the desired filter operating temperature.  
         [0021]     To be able to operate the object to be shielded at a desired operating temperature—as noted—the temperature of the object itself may be measured directly or in its environment. Instead of the temperature, however, other measured variables may also be measured, which have effects on the operating temperature of the object. Such a parameter is, for example, a flow which may result in cooling if it flows along the object to be shielded. The closure may thus be closed more in the event of stronger flow and opened more in the event of lesser flow as a function of the flow velocity to set a desired operating temperature. If the object is moved during operation, the travel velocity may also be measured instead of a flow velocity.  
         [0022]     Acoustic signals may be ascertained if the object, which produces noise itself, is to be shielded to the environment. In the event of stronger noise development, the closure is expediently closed. The noise pressure is preferably measured.  
         [0023]     Exhaust gas values may also be used as measured variables. For example, concentrations of one or more gases in the exhaust gas may be determined in a way known per se. As noted at the beginning, the effectiveness of the catalytic converter for the various pollutants changes as a function of the temperature. The measurement of the exhaust gas value for these pollutants thus allows conclusions as to whether the temperature is in the desired range. If the measured exhaust gas values deviate from predefined setpoint values, the exhaust treatment action may be brought back into the setpoint range by temperature correction. This is performed according to the present invention, for example, by opening or closing the closure and correspondingly regulating the opening cross-section of the opening in the heat shield as a function of one or more measured values of the pollutant concentration in the exhaust gas.  
         [0024]     In addition to the cited measured variables, in principle, all those measured variables come into consideration which may have an influence on the function of the object to be shielded or contain information about the operating state or another property of the object. The actuating device may act as a function of only one measured variable or also as a function of multiple measured variables.  
         [0025]     To measure the measured variable, the heat shield configuration according to the present invention expediently comprises at least one suitable measuring device. The measuring device may fundamentally be a typical device from the prior art for measuring the particular measured variable. For example, a temperature sensor may be used for temperature measurement, which is attached to the object to be shielded, the heat shield, or another point in proximity to the object. Analogously, other sensors (pressure, noise pressure, electrochemical value) may be used, which are already known in the prior art. Ideally, sensors which may be replaced independently of other parts are used. In many cases, measuring devices already present in the overall device which comprises the heat shield configuration according to the present invention, such as measuring devices for measuring exhaust gas values or vehicle velocities, may also be used.  
         [0026]     The heat shield configuration expediently also comprises means for analyzing the measurement results and control means for controlling the actuating device on the basis of the analysis of the measurement result. Both means may be spatially combined in one device and may be situated separately from or integrated in the actuating device. In each case, these are components known per se, which do not have to be described in greater detail here. As already for the measuring device, means present in any case in the overall device may also be used for the analysis and control means.  
         [0027]     The actuating device may, for example, be a pneumatic, hydraulic, or electrical actuating device. Preferably, a servomotor is used as an electrical actuating device or a vacuum unit is used as a pneumatic actuating device. The connection between actuating device and closure is fundamentally arbitrary. For example, a push rod or pull rod may be used.  
         [0028]     The opening may either be a through opening in the heat shield or also an opening in an external edge area of the heat shield. Both variants may also be combined with one another in one heat shield. The possibility which is selected is also a function, inter alia, of the available space on the heat shield. The shape of the opening is fundamentally arbitrary and is also primarily a function of the available space. The size of the opening is selected as a function of the required heat exchange and/or in regard to the desired noise insulation. The required opening cross-section may be implemented using one or more openings.  
         [0029]     The closure may fundamentally have any arbitrary shape which is capable of closing the opening in the heat shield to the required extent. It may be inserted fitting into the opening or may be situated on the heat shield covering the opening. The way in which the closure exposes the opening is also fundamentally arbitrary. For example, the closure may be displaced laterally in relation to the opening and/or pivoted and/or lifted like a flap off the opening. In the two first cases, the closure is preferably displaced and/or pivoted predominantly parallel to the external surface of the heat shield using a slide. In the latter case, the closure may fundamentally open toward any side of the heat shield. However, for space reasons it is frequently expedient for the closure to open toward the side of the external surface of the heat shield, because there is frequently insufficient space on the side of the internal surface between heat shield and object to be shielded. The flap may also comprise multiple lamellae, which may be opened or closed individually or jointly. The material of the closure may be selected arbitrarily. The closure preferably comprises the same material as the heat shield. The closure is fastened to the heat shield depending on the type of actuation, for example, using hinges in the case of a flap closure, a screw or rivet connection, which simultaneously provides the rotation point, in the case of a rotating slide, or using guide rails in the case of a slide. A flap closure may possibly also be fastened to an object in proximity to the heat shield and not to the heat shield itself.  
         [0030]     A preferred application of the heat shield according to the present invention is, as already noted, the shielding of components in the area of an internal combustion engine and in particular in the area of the exhaust system. In these applications, the danger primarily exists that the object to be shielded will overheat as a result of the accumulated heat in the area of the heat shield. To prevent this, the heat shield according to the present invention is expediently implemented in such a way that the closure is opened if a specific limiting temperature is exceeded, so that the accumulated heat may escape from the area between heat shield and object to be shielded. As long as the components situated in the area of the heat shield have not yet reached their operating temperature, however, the accumulation of heat in the area of the heat shield is completely advisable, so that the components may reach their optimal operating temperature as rapidly as possible. For this reason, the heat shield according to the present invention is preferably designed in this variant in such a way that the closure remains closed until reaching the limiting temperature. The temperature does not have to be measured directly, as noted, but it may be a measured value other than the temperature.  
         [0031]     A further preferred application is the shielding of particulate filters, in particular diesel particulate filters. As described, it may be expedient here to remove the accumulated particles by oxidation at increased temperature in a specific operating phase. Using the heat shield according to the present invention, the required temperature increase may be achieved especially easily and rapidly. In contrast to the prior art, it is frequently no longer necessary to increase the exhaust gas temperature by additional engine measures, although this still remains possible. Rather, the opening in the heat shield may be closed by closing the closure using the actuating device. The temperature then rises in the area of the heat shield and thus also in the particulate filter. If this temperature increase alone is insufficient to begin the oxidative cleaning, in addition, the fuel/air mixture of the engine may be adapted or fuel may be injected directly, as usual. After completed cleaning, the closure is opened again, the additional altered injection is ended if necessary, and the temperature in the area of the heat shield falls again, so that the particulate filter may operate further in the regular operating state.  
         [0032]     In the case of the heat shield for a particulate filter or a similar device, the closure is expediently opened at lower temperature and closed at increased temperature. This is preferably reversed for the heat shield described for a catalytic converter. The closure is closed with sinking temperature here, while it is opened in the event of temperature increase. Both variants may be implemented corresponding to the requirements in the scope of the present invention. They may also be used jointly in the same heat shield. Moreover, in a heat shield for a particulate filter, an additional higher temperature limit may be defined to make the closure open in order to prevent overheating of the particulate filter.  
         [0033]     It is not absolutely necessary for the closure to open suddenly if the predefined limiting value is exceeded, for example, and expose the opening 100%, while the closure is immediately completely closed and completely covers the opening at a value of less than or equal to the limiting value. Rather, it is also possible that the opening and closing of the closure occurs within a pre-defined limiting measured value interval. For example, it may be advisable for the closure to increasingly expose the opening with increasing deviation from the predefined limiting value, so that, for example, with increasing temperature (with more strongly deviating measured value), an increasing temperature exchange with the environment is possible. Vice versa, the opened closure may be increasingly closed again if the increased temperature (or another measured value) falls in the direction toward the limiting value again. In this way, a continuous temperature control adapted to the ambient temperature (or the relevant measured value) is possible, which allows the object to be shielded by the heat shield to be kept at an essentially constant operating temperature which is optimal for this object. Closing the opening does not have to result in a hermetic seal of the opening. A significantly reduced temperature exchange in relation to the opened state is generally sufficient. The above statements also apply for the case of opening upon sinking (temperature) measured value and closing upon higher (temperature) measured value.  
         [0034]     The range in which the limiting measured value is set, in which the closure in the heat shield configuration according to the present invention opens or closes, is mainly a function of the temperature at which the object which is to be shielded using the heat shield according to the present invention is to be kept. In the case of catalytic converters, this is expediently the temperature at which the best exhaust gas reduction is possible. For particulate filters, on the one hand the optimal temperature for particle filtration and on the other hand the best temperature for oxidative removal of the particles in the particle removal phase may be set. This particular optimal operating temperature may be achieved very rapidly using the heat shield configuration according to the present invention, because heat may be accumulated in the area around the object to be shielded in the warm-up phase by closing the opening using the closure, so that the object heats rapidly. On the other hand, exceeding an optimal operating temperature too strongly may be pre-vented by setting the limiting measured value appropriately, upon exceeding which the closure in the heat shield is opened and thus exposes the opening entirely or partially depending on the measured value. Heat accumulated between heat shield and object to be shielded may escape through the exposed opening. Additionally or alternatively, it is possible to inject cool air through the opened opening in the direction toward the object to be shielded (such as the catalytic converter, particulate filter, etc.), to cool it.  
         [0035]     Especially good regulation of the temperature in the area between heat shield and object to be shielded is possible if in addition to the first opening having the first closure at least one further opening is provided, which is also closable using a closure to be opened and closed as a function of a measured variable relevant for the function of the object to be shielded. This measured variable may, but does not have to be the same measured variable as for the first closure.  
         [0036]     The further closure may fundamentally be implemented as described above. It may also be opened and closed by an actuating device, as was described above. However, it is also possible to leave out the actuating device and use a closure opening and closing automatically as a function of a measured variable. This is preferably a closure opening and closing as a function of the temperature. The closure therefore expediently has a bimetallic element, which deforms as a function of the temperature. The bimetallic element may be a part of the closure which deforms in relation to the opening, or a separate part which works together with a slide, rotating slide, or flap and displaces it in relation to the opening.  
         [0037]     The presence of at least one further closure and an opening closable thereby has the advantage that the temperature in the area between heat shield and object to be shielded may be set even more precisely. For example, it is possible to implement the actuating device(s) and closures in such a way that the latter open in sequence if various limiting measured values are exceeded. This may be achieved by storing various limiting measured values and corresponding differing activation of the closures. The closures may be opened in sequence, for example, in such a way that the exposed total opening cross-section of the openings rises with increasing temperature, so that increasingly more hot air may escape through the exposed opening. Overheating may thus be prevented even in the event of very strongly rising temperatures.  
         [0038]     A further advantage which may be achieved by providing multiple openings closable using a closure is that targeted flow guiding is possible in the space between heat shield and object to be shielded. For example, cooler air may be introduced in the direction toward the object through one or more of the exposed openings if the closure is opened, while heated air flows out through the remaining openings. The openings and closures on the heat shield are expediently oriented in such a way that the hot air flowing out is not directed toward temperature-sensitive parts situated in the surroundings of the heat shield. Ideally, the hot exhaust air is directed in such a way that it is fed to an external flow existing in the area around the heat shield and is conveyed thereby. It is also advantageous if the cooler air introduced into the area between heat shield and object to be heated is fed from this external flow existing in the area around the heat shield.  
         [0039]     As already described above, it is also possible in the case of feeding cooler air into the area between heat shield and object to be shielded that various closures open for the feeding of cooler air at different temperatures. This is also fundamentally true for the closures through which the heated air flows out. In this way, a very constant temperature may be ensured in the area between heat shield and object to be shielded over a large temperature range. Additionally or alternatively to these measures, it is also possible that the closures for the feeding of cooler air open at a different temperature than the closures for the exhaust of heated air. In the latter case, it is preferable for the feed closures to open at a somewhat higher temperature than the closures for the exhaust of hot air.  
         [0040]     The heat shield according to the present invention is not restricted to special shapes or sizes. For example, it may be a planar heat shield, which is attached above the object to be shielded, so that hot air accumulates below the heat shield. The present invention is especially suitable for a heat shield which essentially encloses the object to be shielded on all sides. A comparable effect may also be achieved if a heat shield open on one side is closed by an adjoining component. The object to be shielded is thus largely encapsulated by the heat shield and possibly other components. This typically does not represent a hermetic enclosure, because hermetically terminated passages for supply lines and drain lines are typically not provided in the heat shield. Nonetheless, the heat exchange with the environment is relatively restricted in these cases, so that overheating of the components encapsulated in the heat shield may occur very rapidly. On the other hand, the cold start phase is relatively short, because the desired operating temperature is achieved rapidly by the heat retention inside the heat shield. This optimal operating temperature may be kept constant in a desired range easily using the heat shield configuration according to the present invention by the provision according to the present invention of at least one opening which is closable by a flap opening and closing as a function of a measured variable. The at least one heat shield, which essentially completely encloses the object to be shielded, additionally ensures especially good noise insulation.  
         [0041]     The measures suggested according to the present invention may be implemented easily and cost-effectively without additional complicated measures or components in typical heat shields. The main bodies of the heat shield according to the present invention may thus fundamentally correspond in their implementation to those which are already known from the prior art. Size, shaping, and materials thus correspond to the prior art. Heat shields in sandwich construction, which comprise two outer layers typically made of metallic material and an insulating layer embedded between them, are preferred. The surfaces may be smooth, textured, or perforated. Heat shields of this type are described, for example, in DE 3834054 A1 and EP 1775437 A1 (European Patent Application 05022095.3) of the applicant. Furthermore, reference may be made to GB 2270555 A and US 2004/0142152 A1.  
         [0042]     The present invention may fundamentally be applied to all heat shields of the prior art. The present invention is especially suitable for those heat shields which are used in the area of high temperature development and for shielding those objects which may be damaged by excess temperature. A preferred use of the heat shields according to the present invention is therefore in the area of internal combustion engines and particularly in the area of the exhaust system here. Examples of preferred heat shields are those for catalytic converters, pre-catalytic converters, diesel particulate filters, or also turbochargers. The present invention may additionally be applied in particular to metallic subfloors or their components in the area of an exhaust system.  
         [0043]     The present invention is explained in greater detail in the following on the basis of drawings. These drawings are exclusively used to illustrate preferred exemplary embodiments of the present invention, without the present invention being restricted thereto. Identical parts are provided with identical reference numerals in the drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which:  
         [0045]      FIG. 1 ( a ): schematically shows a cross-section through a first exemplary embodiment of a heat shield configuration according to the present invention for shielding a catalytic converter having closed closure;  
         [0046]      FIG. 1 ( b ): schematically shows the heat shield configuration from  FIG. 1 ( a ) having opened closure;  
         [0047]      FIG. 2 ( a ): schematically shows a cross-section through a second exemplary embodiment of a heat shield configuration according to the present invention for shielding a catalytic converter having two closed closures;  
         [0048]      FIG. 2 ( b ): schematically shows the heat shield configuration from  FIG. 2 ( a ) having one open and one closed closure;  
         [0049]      FIG. 2 ( c ): schematically shows the heat shield configuration from  FIG. 2 ( a ) having two open closures;  
         [0050]      FIG. 3 ( a ): schematically shows a cross-section through a third exemplary embodiment of a heat shield configuration according to the present invention for shielding a catalytic converter having one closed closure, the heat shield being open on one side;  
         [0051]      FIG. 3 ( b ): schematically shows the heat shield configuration from  FIG. 3 ( a ) having open closure;  
         [0052]      FIG. 4 : schematically shows a block diagram to explain the activation of an actuating device:  
         [0053]      FIG. 5 : schematically shows a partial cross-section through a further exemplary embodiment of a heat shield configuration according to the present invention in the area of a closure;  
         [0054]      FIG. 6 : schematically shows a top view of a further exemplary embodiment of a heat shield configuration according to the present invention and a catalytic converter thus shielded, and  
         [0055]      FIG. 7 : schematically shows a top view of still a further exemplary embodiment of the heat shield configuration according to the present invention and a catalytic converter thus shielded. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0056]     It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless the claims expressly state otherwise.  
         [0057]     FIGS.  1 ( a ) and  1 ( b ) show a first exemplary embodiment of a heat shield configuration according to the present invention having a heat shield  1 , which is used for shielding a catalytic converter  2  situated in the interior of the heat shield  1 . The catalytic converter  2  may be, for example, a catalytic converter for treating exhaust gases of an internal combustion engine of a motor vehicle. The exhaust treatment action of the catalytic converter  2  is best within a specific temperature range. This temperature range is to be reached as rapidly as possible, but is not to be exceeded. The catalytic converter  2  is enclosed essentially completely and on all sides by the heat shield  1 . In this way, the catalytic converter  2  and its environment are insulated especially well from one another in regard to temperature influences and noise. In addition, the encapsulation is used so that the catalytic converter  2  reaches the operating temperature required for optimal exhaust treatment rapidly. The cold start phase may thus be shortened by rapid temperature increase in the interior of the heat shield  1 , which is a significant advantage in regard to the expected exhaust gas standard Euro  5 .  
         [0058]      FIG. 1 ( a ) shows the heat shield  1  having the catalytic converter situated in its interior during the warm-up phase to the optimal operating temperature of the catalytic converter  2 . In this phase, the closure  6 , which is located on the top side of the heat shield and encloses an opening present there in the form of a through opening in the heat shield, is completely closed. The heat generated during operation of the internal combustion engine therefore remains in the interior of the heat shield  1  and heats the catalytic converter rapidly to the desired operating temperature.  
         [0059]     In the case shown, the closure  6  completely comprises a flap  13 . The flap is expediently manufactured from the same material as the heat shield  1  and is fastened thereto using at least one hinge. Above a specific limiting temperature (or another measured variable representative for the temperature in the environment of the catalytic converter), the flap  13  is opened using an actuating device  7  in the form of a positioning motor. To be able to establish reaching the limiting temperature, a temperature sensor  8  is fastened to the inside  3  of the heat shield  1 . After an analysis described later in connection with  FIG. 4 , the actuating device  7  comes into action if exceeding the fixed limiting temperature is established and opens the flap  13 , which is connected to the rod  14 , via a push and pull rod  14 . This is shown in  FIG. 1 ( b ).  
         [0060]     With rising temperature in the interior of the heat shield  1  and correspondingly increasing opening by the actuating device  7 , the closure  6  exposes an increasingly larger opening cross-section of the through opening  5 . The opening of the closure  6  and the exposure of the through opening  5  upon exceeding the predefined limiting temperature ensure that heat accumulated in the interior of the heat shield  1  may escape through the through opening, as illustrated by the arrows. Overheating of the catalytic converter  2  in the interior of the heat shield  1  is thus avoided. If the temperature in the interior of the heat shield  1  sinks again, the actuating device  7  closes the closure back in the direction toward the starting situation shown in  FIG. 1 ( a ). The through opening  5  is closed by the closure  6  again. In this way, too strong reduction of the temperature in the interior of the heat shield  1  is prevented. Another cold start of the engine would again occur with closed closure  6 , so that the catalytic converter  2  in the interior of the heat shield  1  may again be brought rapidly to the required operating temperature. These procedures are repeatable arbitrarily often with good reproducibility, so that optimum operating conditions of the catalytic converter may be ensured with very good noise protection simultaneously.  
         [0061]     FIGS.  2 ( a ) through  2 ( c ) show a refinement of the heat shield configuration from FIGS.  1 ( a ) and  1 ( b ). In addition to the first closure  6 , a further closure  6   a  is provided in the heat shield  1 , which may close a further through opening  5   a  in the top area of the heat shield  1 . The functional principle of both closures corresponds to that of the preceding exemplary embodiment. For simplification, the measuring device  8  is no longer shown.  
         [0062]      FIG. 2 ( a ) shows the state of the heat shield  1  in the warm-up phase. Both closures  6  and  6   a  are closed, so that the heat remains in the interior of the heat shield  1  and contributes to rapidly reaching the operating temperature of the catalytic converter  2 . Above a first limiting temperature, which may result in overheating of the catalytic converter  2  especially in full load operation, the first closure  6  is opened in the way described above and exposes the through opening  5  on the top right side of the heat shield  1 , so that the hot air indicated by the arrows may escape from the interior of the heat shield  1 . The second closure  6   a  is still closed in this phase. It is first opened by the second actuating device  7   a  upon further temperature increase in the interior of the heat shield  1 . This is shown in  FIG. 2 ( c ). To achieve the opening of the closures  6  and  6   a  at different limiting temperatures, the actuating devices  7 ,  7   a  are activated in such a way that they open at different limiting temperatures. Cooler air may enter through this through opening into the interior of the heat shield  1  due to the exposure of the through opening  5   a . The colder air flows along the top side of the catalytic converter  2 , cools it, and entrains hot air through the through opening  5  on the top right side of the heat shield out of its interior. In this way, effective cooling of the catalytic converter is possible even at very high exhaust gas temperature. The exemplary embodiment described thus allows the catalytic converter to operate under essentially constant temperature conditions even in the event of relatively strongly oscillating exhaust gas temperature.  
         [0063]     FIGS.  3 ( a ) and  3 ( b ) show an alternative heat shield configuration, in which the heat shield  1  does not completely enclose the catalytic converter  2 , but rather is open on its bottom side. The lower edge only has a small distance to the neighboring component  15 , which radiates heat in operation of the engine. The measuring device  8  is again not illustrated. As in the exemplary embodiment from FIGS.  1 ( a ) through  1 ( c ), the heat shield only has one closure  6 . The small distance between heat shield  1  and neighboring component  15  accelerates the achievement of the operating temperature of the catalytic converter  2  with closed closure  6 . Upon reaching the limiting temperature, the closure  6  is opened by the actuating device  7 , as shown in  FIG. 3 ( b ). The hot air from the interior of the heat shield may escape through the opening  5 . The suction thus arising causes cooler air to flow behind through the space between heat shield  1  and neighboring component  15 , so that an optimal operating temperature of the catalytic converter  2  is ensured in spite of the heat radiated by the component  15 . The space between heat shield  1  and neighboring component  15  may be tailored—insofar as this is possible in the existing space—to this operating temperature of the catalytic converter  2  and the radiation of the component  15 .  
         [0064]      FIG. 4  illustrates the sequence upon actuation of the closure  6  using the actuating device  7  in the form of a block diagram. A measuring device  8  ascertains measurement data for a measured variable relevant for the function of the object  2  to be shielded continuously or at fixed intervals. This may be the temperature in the environment of the catalytic converter, for example. The ascertained measured data is transmitted in a way known per se to an analysis unit  9  and analyzed there. The analysis unit compares the measured data to a previously established limiting value, such as a limiting temperature. If the analysis unit  9  establishes that the limiting value has been exceeded, it transmits the result to the control unit  10 . In turn, this transmits a control signal to the actuating device  7 , because of which it opens the closure  6  to the predefined extent. The closing procedure runs correspondingly, if it is established the temperature falls below the limiting temperature. Analysis and control units may also be unified in a shared device and installed in the heat shield configuration separately from or jointly with the measuring device  8 .  
         [0065]     In the case of a particulate filter, a measuring apparatus  8  may be for the pressure in the interior of the particulate filter. The ascertained measured data is compared to a previously established base pressure by the analysis unit  9  in this example. If this pressure is exceeded, this is relayed via the control unit  10  to the actuating device  7 , on the basis of which it closes the closure  6  in the predefined procedure. This opening procedure runs correspondingly if the pressure falls below the limiting pressure after oxidative regeneration of the particulate filter, for example. A second limiting pressure may also be established, which is below the first limiting pressure for the closing. The sequence for other measured signals runs comparably.  
         [0066]      FIG. 5  shows a partial section of a further embodiment of the present invention in the area of the closure  6 , which may be opened and closed by an actuating device  7 . The mode of operation corresponds to those of the preceding figures. The curves of the heat shield  1  and the closure  6  are adapted to the external contour of the object to be shielded, whose external outline is illustrated by the line  16 . By tailoring the curves, the heat shield having closure  6  may be brought very close to the object to be shielded. The solid line at  6  illustrates the open position of the closure, and the dashed line lying underneath illustrates the closed position of the closure.  
         [0067]      FIGS. 6 and 7  show alternative embodiments of the closure  6 .  FIG. 6  shows an embodiment in which the opening  5  in the heat shield  1  is a recess in the external edge area. The opening  5  is closable using a slide  11  as the closure  6 . The closure  6  may be displaced in the direction of the arrow using the actuating device  7 . A situation having almost completely open closure and nearly completely exposed opening  5  is shown.  
         [0068]      FIG. 7  shows an embodiment similar to  FIG. 6 , but having a rotating slide  12  as the closure  6 . The rotating slide is fastened to the heat shield  1  at a point  17  using screw or rivet connections and is mounted at this point so it is rotatable. By actuating the actuating device  7 , namely by extending the rod  14 , which is fastened to the rotating slide  12  so it is rotatable at the point  18 , more or less, the rotating slide may be pivoted around the point  17 , as is illustrated by the double arrow. The through opening  5  in the heat shield is correspondingly covered more or less by the rotating slide  12 .  
         [0069]     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.