Patent Publication Number: US-2017350301-A1

Title: Air Gap-Insulated Muffler

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT International Application No. PCT/EP2016/051480, filed Jan. 26, 2016, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2015 205 318.0, filed Mar. 24, 2015, the entire disclosures of which are herein expressly incorporated by reference. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to a muffler, in particular an end muffler, for an exhaust gas system of a vehicle. 
     In conventional passenger motor vehicles, the vehicle body usually consists of steel or lightweight materials, such as aluminum. New developments in lightweight engineering make larger amounts of weight saving possible by use of carbon fiber-reinforced plastics. These materials are composite materials, the individual material segments of which have been connected by way of resin adhesives. 
     Although plastics have considerable weight advantages in comparison with conventional metal materials, they can be used only to a restricted extent with regard to their thermal operating range. Depending on the resin which is used, carbon fiber-reinforced plastic components already have to be protected at temperatures between 80° C. and 120° C. In particular, components in the immediate vicinity of internal combustion engines or other components which heat up to a pronounced extent (for example, exhaust gas system, catalytic converter, end muffler, pipelines, etc.) have to be designed sufficiently in thermal terms. 
     It is an object of the invention to provide a muffler, in particular an end muffler, which is designed in such a way that it can be arranged relatively close to thermally sensitive components. 
     This and other objects are achieved by a muffler, in particular an end muffler for an exhaust gas system of a vehicle, having a muffler housing which has an exhaust gas inlet pipe, via which exhaust gas flows into the muffler housing, and an exhaust gas outlet pipe, via which exhaust gas flows out of the muffler housing. At least part of the muffler housing or the entire muffler housing is surrounded by a casing housing. An air gap is provided between the muffler housing and the casing housing. 
     A starting point of the invention is a muffler, in particular an end muffler, for an exhaust gas system of a vehicle. The muffler has a muffler housing. An exhaust gas inlet pipe opens into the muffler housing, via which exhaust gas inlet pipe exhaust gas can flow into the muffler housing. Exhaust gas can flow out of the muffler housing via an exhaust gas outlet pipe of the muffler. 
     A central concept of the invention consists in that at least part of the muffler housing or the entire muffler housing is surrounded by a casing housing, an air gap being provided between the muffler housing and the casing housing. The air gap produces a thermal insulation layer, as a consequence of which the surface temperature of the casing housing is considerably lower than the temperature of the muffler housing. As a result, the muffler can be positioned substantially closer to temperature-sensitive components, such as fiber-reinforced plastic components of a vehicle. 
     The muffler housing and/or the casing housing can be manufactured from steel, in particular from stainless high-grade steel, from a titanium alloy or from another temperature-resistant metal material. 
     According to the invention, the casing housing is held spaced apart from the muffler housing by way of spacer elements. The spacer elements ensure that an air gap remains between the muffler housing and the casing housing. It can be provided, for example, that the casing housing is spaced apart from the muffler housing by between 0.3 cm and 2.0 cm. However, the range, in which the air gap lies, can also be smaller and can lie, for example, in the range between 0.8 cm and 1.2 cm. 
     According to one development of the invention, the casing housing has an inlet for fresh air. Via the inlet, cool surrounding air can flow into the casing housing. The inlet is preferably designed in such a way that as much fresh air as possible is caught or collected and flows into the casing housing. The inlet can be designed, for example, in a funnel-like or fan-like manner or in the manner of an air guide blade, which ensures that a sufficiently great fresh air volumetric flow is guided into the air gap while the vehicle is driving. 
     In order to ensure that a sufficiently great air volumetric flow flows into the casing housing even in the case of a stationary vehicle, a blower can be provided which delivers or blows fresh air from the surroundings via the inlet for fresh air into the casing housing. 
     In order to achieve air circulation which is as satisfactory as possible and therefore a cooling action which is as satisfactory as possible, the casing housing can have an air outlet, via which air which is heated by the muffler housing can flow out of the casing housing into the surroundings. 
     It can be provided according to the invention that the exhaust gas outlet pipe of the muffler ends at least a certain extent in front of the air outlet of the casing housing, that is to say within the casing housing. The exhaust gas which flows out of the muffler via the exhaust gas outlet pipe results in a suction jet pump effect which delivers heated air from the air gap between the muffler housing and the casing housing via the air outlet of the casing housing into the surroundings. The suction jet pump effect achieves a comparatively great cooling air volumetric flow, with the result that relatively high thermal outputs of the muffler housing can be discharged into the surroundings, to be precise largely independently of the speed of the vehicle. The suction jet pump effect is namely dependent primarily only on the exhaust gas volumetric flow, but not directly on the speed of the vehicle. 
     The casing housing can be of tubular design in the region of the exhaust gas outlet pipe and can be arranged coaxially with respect to the exhaust gas outlet pipe. As has already been indicated above, the exhaust gas outlet pipe ends within the tubular section of the casing housing, which results in the suction jet pump effect which is typical for the invention. 
     It goes without saying that the subject matter of the invention is not only a muffler or an end muffler, but rather also a vehicle having an exhaust gas system which has a muffler of this type. 
     In order to ensure that the muffler which is still hot is cooled sufficiently even in the case of a stationary vehicle or after the (hot) internal combustion engine has been switched off, a fan device can be provided which delivers or blows fresh air from the surroundings via the inlet for fresh air into the casing housing. It goes without saying that the fan device or the blower can be controlled or regulated in accordance with requirements. To this end, the temperature of the muffler housing, the temperature of the air in the air gap and/or the temperature of the casing housing can be measured or determined in some other way. If a predefined temperature of the muffler housing, the air which is situated in the air gap and/or the casing housing is exceeded, the fan device can be switched on and/or regulated to a sufficient rotational speed. 
     A muffler according to the invention can be installed in the vehicle transversely or longitudinally. In the case of a transverse installation, a longitudinal direction of the muffler extends parallel to a transverse direction of the vehicle or perpendicularly with respect to a longitudinal direction of the vehicle. In the case of a longitudinal installation, a longitudinal direction of the muffler extends parallel to a longitudinal direction of the vehicle. 
     In a test vehicle, the muffler has been installed in a front car region of the vehicle. In principle, however, the muffler can also be arranged in an underbody region or in a rear car region of the vehicle. 
     The abovementioned test vehicle has an internal combustion engine which is likewise arranged in the front car region. The entire exhaust gas system of the test vehicle is likewise arranged in the front car region, and the muffler is therefore also arranged in the front car region. The air outlet of the casing housing is situated in front of a front wheel of the test vehicle. The exhaust gas therefore likewise exits in front of the front wheel laterally out of the casing housing and therefore transversely with respect to the front wheel out of the casing housing or out of the muffler. 
     A muffler according to the invention can be arranged very close, that is to say at a spacing of only a few centimeters, for example less than 10 cm, in particular less than 5 cm, in particular less than 4 cm, in particular less than 3 cm, in particular less than 2 cm, in particular less than 1 cm away from “temperature-sensitive components”, such as carbon fiber-reinforced plastic components. 
     In the abovementioned test vehicle, the muffler according to the invention is arranged below a bulkhead which is manufactured from carbon fiber-reinforced plastic and is arranged substantially horizontally in the front car region, that is to say the muffler is arranged below an upper front car region. In the test vehicle, the muffler is arranged in the region of the front wheels or just in front of the front wheels. 
     In the test vehicle, as viewed in the driving direction of the vehicle, an air delivery device is arranged in front of the muffler housing, which air delivery device can be formed by way of one or more fans. 
     In the test vehicle, furthermore, an air/refrigerant heat exchanger of a refrigerant circuit of the vehicle is arranged in front of the muffler housing and/or in front of the air delivery device as viewed in the driving direction of the vehicle, via which air/refrigerant heat exchanger heat from the refrigerant circuit can be discharged to the ambient air. The air/refrigerant heat exchanger can be, for example, what is known as a low temperature heat exchanger which outputs waste heat of an electric machine of the vehicle, for example of an electric drive motor of the vehicle, or waste heat of power electronics. 
     As an alternative or in addition to an air/refrigerant heat exchanger, a (high temperature) cooler can be provided in this region, that is to say in front of the muffler housing and/or in front of the air delivery device as viewed in the driving direction of the vehicle, which cooler is connected to a coolant circuit of an internal combustion engine of the vehicle. 
     According to one development of the invention, the casing housing is encapsulated with an insulating material, as a result of which the surface temperature can again be lowered considerably. Furthermore, the insulating material can be encapsulated with a metal foil, which leads to a further considerable reduction of the radiant heat and therefore of the surface temperature. 
     Tests have shown that it is possible by way of the muffler according to the invention to reduce the “thermal effects” of the exhaust gas system on its surrounding components by up to 500° C. It is therefore possible to arrange a complete exhaust gas system in the front car region of a vehicle and, at the same time, to keep the temperatures of components which surround the exhaust gas system within the respectively permissible operating temperature ranges. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a fundamental principle of the invention in a diagrammatic illustration. 
         FIG. 2  also illustrates a fundamental principle of the invention in a diagrammatic illustration. 
         FIG. 3  is a section view through a front car region of a vehicle, in which an end muffler according to an embodiment of the invention is arranged. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an end muffler  1  which is arranged transversely in a vehicle (not shown in greater detail here). “Transversely” means that a longitudinal direction  2  of the end muffler  1  extends transversely or substantially perpendicularly with respect to a driving direction of the vehicle, which driving direction is indicated by way of an arrow  3 . The arrow  3  is therefore substantially parallel to the longitudinal direction of the vehicle. 
     The muffler  1  has an exhaust gas inlet pipe  4 , via which exhaust gas can flow into a housing  1   a  of the muffler  1 . Furthermore, the “muffler housing”  1   a  has an exhaust gas outlet pipe  5 , via which exhaust gas can flow out of the muffler  1 . 
     As can be seen from  FIG. 1 , the entire muffler housing  1   a  is surrounded by a casing (outer) housing  6 . The casing housing  6  is arranged at a spacing from the muffler housing  1   a , which results in an air gap  7  between the casing housing  6  and the muffler housing  1   a . The air gap can lie, for example, in the range between 0.3 cm and 2.0 cm, in particular in the range between 0.8 cm and 1.2 cm. The air gap results in thermal insulation. The surface temperature of the casing housing  6  is therefore considerably lower than the surface temperature of the end muffler housing  1   a.    
     The end muffler housing  1   a  and/or the casing housing  6  can consist, for example, of a metal material, such as steel, an aluminum alloy or another sufficiently temperature-resistant material. 
     The casing housing  6  is of tubular design in the region of the exhaust gas outlet pipe  5 . A tubular section  6   a  of the casing housing extends substantially coaxially with respect to the exhaust gas outlet pipe  5  of the muffler  1 . As can be seen from  FIG. 1 , however, the exhaust gas outlet pipe  5  ends “within the casing housing  6  or within the tubular section  6   a  of the casing housing  6 ”. In other words, the tubular section  6   a  of the casing housing projects beyond the exhaust gas outlet pipe  5 . 
     Furthermore, the casing housing  6  has a funnel-like or fan-like inlet  8  for fresh air. As viewed in the driving direction  3  of the vehicle, the inlet  8  is arranged on a front side or in the region of a front side  9  of the muffler  1 . Furthermore, two blowers  10   a ,  10   b  which blow fresh air from the surroundings in the direction of the inlet  8  are provided in the region of the front side  9 . 
     The muffler housing  1   a  is cooled by way of the fresh air which flows into the casing housing  6  via the inlet  8 . The air which is heated by the muffler housing  1   a  exits laterally again via the air outlet  6   a.    
     A suction jet pump effect results on account of the exhaust gas which flows through the muffler  1  and the fact that the air outlet  6   a  projects beyond the exhaust gas outlet pipe  5 . This suction jet pump effect improves the air circulation from the surroundings via the inlet  8 , through the gap of the casing housing  6  to the air outlet  6   a . This circulation is additionally assisted by way of the airflow which is produced by the two blowers  10   a ,  10   b.    
       FIG. 2  shows one variant, in which the end muffler  1  is installed longitudinally in the vehicle, that is to say a longitudinal axis  2  of the end muffler  1  is parallel here to the driving direction  3  or to the vehicle longitudinal direction. 
       FIG. 3  shows an installation situation, in which the muffler  1  is accommodated in a front underbody region of a vehicle. A blower  10   a  is arranged in front of the end muffler  1  in the driving direction  3 . A high temperature cooler  11  is provided in front of the blower, which high temperature cooler can be, for example, a liquid/air heat exchanger, the liquid circuit of which is connected to the cooling circuit of an internal combustion engine of the vehicle. A low temperature cooler  12  is arranged in front of the high temperature cooler  11 , which low temperature cooler can be, for example, a refrigerant/air heat exchanger. The low temperature cooler can be coupled thermally, for example, to an electric motor of the vehicle or power electronics of the vehicle, with heat from the electric motor or the power electronics being discharged via the refrigerant circuit to the low temperature cooler  12 , and heat being discharged by said low temperature cooler  12  to the surroundings. A condenser  13  of a refrigerant circuit is arranged in front of the low temperature cooler  12 . 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.