Abstract:
An exhaust-gas heat recovery appliance having a heat-exchanger line and a bypass line and a heat exchanger being arranged in the region of the heat-exchanger line. At least one valve device, for the purpose of influencing the mass flow of exhaust gas, is provided in the heat-exchanger line and the bypass line. Further, at least the heat-exchanger line has a slope in the direction of flow of the exhaust gas in the installed position.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to an improved exhaust-gas heat recovery appliance.  
           [0003]    2. Description of Related Art  
           [0004]    Exhaust-gas heat recovery appliances are known from the prior art, e.g. U.S. Pat. No. 4,249,375, which proposes a heat exchanger situated before the muffler, in relation to the direction of exhaust-gas flow, of an internal combustion engine. Engine coolant is used to absorb heat from the hot exhaust gases of the internal combustion engine while flowing through the heat exchanger.  
           [0005]    To drain off any condensed water that may have formed from cooling exhaust gas, the exhaust-gas zone of the heat exchanger is connected by a drainage line to a region of the exhaust system that is situated further back, allowing any condensed water that does form to flow out of the heat exchanger.  
           [0006]    U.S. Pat. No. 4,391,235 has disclosed an exhaust-gas heat recovery appliance which is arranged downstream of an exhaust-gas catalyst, in terms of the flow of exhaust gas, and has an exhaust line with a muffler. Running parallel with the muffler is a bypass line, which can be supplied with exhaust gas via a valve device. In the bypass line there is a heat exchanger, via which heat from the exhaust gas can be fed to engine coolant.  
           [0007]    U.S. Pat. No. 4,884,744 is concerned with a heating system for the interior of a motor vehicle with an internal combustion engine. The system has, in addition to a multiplicity of heat exchangers that feed heat from hot engine-operating fluids, e.g. oil or compressed air, to the interior heating system, an exhaust-gas heat exchanger, which is arranged in a bypass line to the main exhaust duct and through which a heating fluid to be warmed flows. Arranged in the bypass line is a throttle valve, which is actuated as a function of the temperature of the heating medium.  
           [0008]    U.S. Pat. No. 3,968,649 discloses an exhaust-gas purification system that operates with heat exchangers in the exhaust duct in order to condense some of the pollutants as a liquid that can be separated off or as solids that can be separated off.  
           [0009]    U.S. Pat. No. 2,087,411 has likewise disclosed an exhaust-gas condensing device with a condensate separator in which a filter for purifying the condensate is arranged. This appliance is intended to recondense unburnt fuel components in the exhaust gas and feed them back to the engine.  
           [0010]    U.S. Pat. No. 5,121,602 has disclosed an exhaust-gas purification appliance that is intended for separating off certain components of the exhaust gas.  
           [0011]    With the exhaust-gas heat recovery appliances described above, there is the problem that water in vapor form contained in the exhaust gas condenses due to the removal of heat and is present as a liquid in the exhaust duct.  
           [0012]    In the cold part of the year, this liquid can lead to icing in the exhaust duct of the exhaust-gas heat exchanger and, in particular, to icing of exhaust-gas valves arranged in the exhaust duct, thus limiting their operation or even preventing them from operating.  
           [0013]    It is the object of the invention to provide an exhaust-gas heat recovery appliance with which the risk of icing is reduced, in particular eliminated. Moreover, the exhaust-gas heat recovery appliance should be of space-saving and economical configuration.  
         SUMMARY OF THE INVENTION  
         [0014]    These objects are achieved in the exhaust-gas heat recovery appliance of this invention.  
           [0015]    An exhaust-gas heat recovery appliance according to the present invention has a heat-exchanger line and a bypass line, a heat exchanger being arranged in the region of the heat-exchanger line, and at least one valve device for the purpose of influencing the mass flow of exhaust gas being provided in the heat-exchanger line and the bypass line, at least the heat-exchanger line having a slope in a direction of flow of the exhaust gas in the installed position.  
           [0016]    In the installed position, the bypass line likewise advantageously has a slope in the direction of flow of the exhaust gas.  
           [0017]    To ensure that condensed water does not run back into the heat-exchanger the engine is switched off and thereby potentially icing up the heat exchanger, the slope of the heat-exchanger line is expediently less than the slope of the bypass line. This difference in the slope has the effect that there is a vertical difference in height between the end of the heat-exchanger line and the end of the bypass line. The condensed water flowing back would have to overcome this height to flow back to the heat exchanger. The vertical difference in height acts as a barrier to the return flow of condensate. To minimize the additional pressure drop of the exhaust gases in the heat-exchanger line, the piece of tube used to overcome this vertical difference in height and is embodied in an S-shape.  
           [0018]    It is particularly advantageous that at least one valve appliance is arranged in the heat-exchanger line upstream of the heat exchanger. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The invention is explained in detail below by way of example with reference to the drawing, in which:  
         [0020]    [0020]FIG. 1 shows in side view an exhaust-gas heat recovery appliance according to the invention; and  
         [0021]    [0021]FIG. 2 shows in a plan view the exhaust-gas heat recovery appliance according to the invention shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0022]    An exhaust-gas heat recovery appliance  1  according to the invention (FIG. 1, FIG. 2) has an exhaust-gas inlet opening  2  arranged upstream in terms of the flow of exhaust gas and an exhaust-gas outlet opening  3  arranged downstream in terms of the flow of exhaust gas.  
         [0023]    Mounted on the exhaust-gas inlet opening  2  and the exhaust-gas outlet opening  3  are respective fastening means  4  for fastening the exhaust-gas heat recovery appliance  1  to components of the exhaust system, e.g. that of a motor vehicle, which are arranged upstream in terms of the flow of exhaust gas and downstream in terms of the flow of exhaust gas.  
         [0024]    An exhaust-gas heat recovery appliance  1  according to the invention is expediently arranged downstream of an exhaust-gas catalyst.  
         [0025]    Arranged following the inlet opening  2  is a first exhaust-pipe fork  5 , which divides the exhaust duct connected to the inlet side of the exhaust-gas heat recovery appliance  1  into a first exhaust line (heat-exchanger line  6 ) and a second exhaust line (bypass line  7 ).  
         [0026]    Arranged between the heat-exchanger line  6  and the exhaust-line fork  5  there is expediently a corrugated tube  8 , which compensates for any differences in expansion that may occur owing to differences in the heating of lines  6  and  7 . To avoid accumulation of condensed water in the inner, lower corrugations of the corrugated tube, the corrugated tube is expediently arranged in the region of the hotter exhaust gas, ahead of the heat exchanger.  
         [0027]    In plan view (FIG. 2), the heat-exchanger line  6  and the bypass line  7  run parallel to one another at a short distance apart.  
         [0028]    At downstream ends  9  and  10  of the heat-exchanger line  6  and of the bypass line  7 , these lines open into a second exhaust-line fork  11 , which reunites the two component lines  6 ,  7  into one exhaust line  12 .  
         [0029]    In an installed position or orientation in a motor vehicle (FIG. 1), the exhaust-gas heat recovery appliance  1  according to the invention is arranged in such a way that both the heat-exchanger line  6  and, expediently, also the bypass line  7  slope, relative to the horizontal  14 , downward in the direction  13  of flow of the exhaust gas.  
         [0030]    The bypass line  7  encloses an angle a with the horizontal  14 . The heat-exchanger line  6  encloses an angle P with the horizontal  14 . The angles α and β are expediently between 5° and 20°.  
         [0031]    The slope chosen for the bypass line  7  is expediently greater than that for the heat-exchanger line  6 , with the result that the angle α is larger than the angle β. This difference in slope has the effect that there is a vertical difference in height Δh between the heat-exchanger line  6  and the bypass line  7  at a point before the ends  9 ,  10 . The difference in slope between the angle α and the angle β is expediently chosen so that the vertical difference in height Δh is between 0.2*d and 0.5*d, d being the diameter of the heat-exchanger line  6 .  
         [0032]    Toward the end  9 , the heat-exchanger line  6  has a line element  15  bent in an s shape which compensates for the vertical difference in height Δh with respect to the bypass line  7  over a distance s that is very short in relation to the length  1  of the heat-exchanger line  6 , the result being that the heat-exchanger line  6  and the bypass line  7  open into the second fork  11  at a common vertical level in the region of the ends  9 ,  10 .  
         [0033]    To ensure that the pressure drop on the exhaust side, which occurs within the line element  15  bent in an S-shape, is limited, the ratio of the distance s to the vertical difference in height Δh is between 3 and 8.  
         [0034]    The steep path of the line element  15  serves as a barrier to the return flow of exhaust-gas condensate, making it impossible for condensate to remain in the region of the heat-exchanger line  6  and flow back when, for example, the vehicle is parked on a slope.  
         [0035]    A tube-bundle heat exchanger  16  is incorporated within the heat-exchanger line  6  over a large part of its length. The significant components are a multiplicity of inner through tubes, through which exhaust gas flows in parallel, which are soldered into two tube plates (not shown) at both ends. The medium to be warmed (e.g. coolant) flows between the outer walls of the through tubes and the inner wall of the jacket tube  16 . Tube connection pieces  18  for connection of, for example, coolant lines, are arranged in the region of the ends  16   b,    16   c  of the heat-exchanger tube  16   a,  which are upstream and downstream in terms of the flow of exhaust gas, by means of a curved piece  17 .  
         [0036]    Arranged above the end  16   b  of the heat-exchanger jacket tube  16 , which is upstream in terms of the flow of exhaust gas, is an exhaust-gas valve  20 . The valve  20  can shut off or expose the internal cross section of the heat exchanger line  6  in the manner of a throttle valve. The exhaust-gas valve  20  can be actuated in an infinitely variable manner via an actuating device  21 , e.g. a vacuum actuating device, via a push rod  22  connected to an actuating lever  23  of the valve  20 .  
         [0037]    In addition, the exhaust-gas valve  20  has a self-regulating exhaust-gas backpressure control function in the closed state. In the closed state of the flap valve, a torque acts on the stem of the valve flap via the actuating lever  23  by means of a spring preload within the vacuum actuating device. Because the valve stem is arranged eccentrically within the valve flap, an exhaust-gas backpressure produces a torque on the stem of the valve flap counter to the above torque. Where the two torques are in equilibrium, this valve arrangement sets a constant exhaust-gas back pressure.  
         [0038]    Arranged in the bypass line  7  there is likewise a valve device  25 , which can shut off and expose the bypass line  7  via a second actuating unit  26  by means of a push rod  27  and a lever  28 .  
         [0039]    The valve device  25  also is arranged as far as possible upstream in the bypass line  7  in terms of the flow of exhaust gas, depending on the installation-space conditions in the motor vehicle.  
         [0040]    The tube-bundle heat exchanger  16  can be operated as a co-current or counter-current heat exchanger depending on the direction of flow of the fluid to be warmed.  
         [0041]    The exhaust-gas heat recovery appliance  1  according to the invention reliably prevents icing of exhaust-gas valves because, on the one hand, these valve devices are arranged as far as possible upstream in terms of the flow of exhaust gas, with the result that the exhaust gas flowing through the valve devices is at as high a temperature as possible.  
         [0042]    Only after it has flowed through the exhaust-gas valve  20  is heat removed from the exhaust gas in the tubular heat exchanger  16 , with the result that condensate can form from the exhaust gas only downstream in terms of the flow of exhaust gas.  
         [0043]    On the other hand, the sloping arrangement of the heat-exchanger line  6  and the bypass line  7  ensures that any exhaust-gas condensate that forms flows away from the valve devices  20 ,  25  owing to gravity and is taken along with the flowing exhaust gas.  
         [0044]    The particularly preferred arrangement of the heat-exchanger line  6 , which is vertically higher than the bypass line  7  by an amount Δh in its end region, and the subsequently steeper line element  15  in the form of an s bend reliably prevent any condensate that forms in the flow of exhaust gas flowing “upward” in the tubular heat exchanger  16 , counter to the direction  13  of flow of the exhaust gas, owing to backpressure or pressure fluctuations in the exhaust system.  
         [0045]    Because of its relatively steep path, the line element  15  in the form of a double s thus represents a barrier to the return flow of condensate which might be taken along upstream by a reversal in the flow of exhaust gas due to pressure fluctuations in the exhaust system, for example. Thus, according to the invention, icing is avoided in a space- and installation-space-saving manner through the appropriate choice of the tube paths, without additional components.