Abstract:
An active carbon filter intended for the fuel supply system of the internal combustion engine of a vehicle consists of a housing ( 1 ), inside of which flow paths for the different operating states of the filter are established between the ports ( 10, 11, 12 ) for connection with the top space of a tank, the ambient atmosphere and the intake manifold of the internal combustion engine. Proceeding from the port ( 11 ), these flow paths are characterized by chambers situated one in back of the other for pre-warming the air, an adjacent chamber ( 22 ) equipped with a first heating unit, an adjacent chamber ( 23 ) that accommodates active carbon particles, and another, adjacent chamber ( 28 ) that accommodates active carbon particles, is equipped with a second heating unit ( 34 ), and is provided with the ports ( 10, 12 ). This yields the establishment of optimal, in particular thermal conditions for the regeneration of the active carbon particles.

Description:
BACKGROUND OF THE INVENTION 
     This application claims foreign priority to German Patent Application 10 2009 020 703.1, filed May 11, 2009, which is hereby incorporated by reference herein. 
     The invention relates to an active carbon filter intended for the fuel supply system of the internal combustion engine of a vehicle and consists of a housing with ports for connection with the top space of a tank, for connection with the ambient atmosphere, and for connection with an intake manifold of the internal combustion engine, wherein the inside of the housing accommodates flow paths for the different operating states of the active carbon filter between these ports, and wherein at least one chamber containing a filler comprised of active carbon is arranged along the progression of these flow paths. 
     When using a hybrid drive characterized by an internal combustion engine and an electric engine for a motor vehicle, the time for which the internal combustion engine is in operation is reduced by the time for which the electric engine is in operation. Among other things, this fact is also important for an active carbon filter connected with a fuel tank that supplies the internal combustion engine, since its regeneration is limited to the times for which the internal combustion engine is in operation. 
     The fuel tank is usually in contact with the ambient atmosphere by way of a line, which prevents both a pressure buildup and a partial vacuum in the top space of the tank, which can arise during refueling, the removal of fuel, or an evaporation of fuel due to temperature conditions. An active carbon filter conventionally placed in this line is intended to prevent hydrocarbons from being uncontrollably released into the environment in this way. 
     Such an active carbon filter globally consists of an apparatus designed to accommodate active carbon particles, with ports for establishing a connection with the fuel tank, ambient atmosphere, and intake manifold of the internal combustion engine. 
     In order to reduce the amount of active carbon to be used, the port connected with the mentioned intake manifold routes ambient air through the active carbon filling of the filter during the scavenging phase, which takes up hydrocarbons adsorptively bound through desorption and introduces the latter into the combustion chamber of the engine, so that the active carbon is regenerated as a result. However, this process presupposes that the internal combustion is in operation. Since the amount of hydrocarbons exiting the top space due to evaporation and to be absorbed in the active carbon filling is independent of the operating time of the vehicle, the regeneration process must be concluded in a shorter time in a hybrid drive. 
     It is generally known that the conditions for regeneration in terms of acceleration can be improved via the thermal conditions of this conversion by heating the air used for regeneration and/or the active carbon. 
     Known from Document DE 102 95 967 T5 is an active carbon filter of this type in which the active carbon filling can be heated. In this case, use is made of plate-shaped or tubular, electrically operated heating elements with PTC characteristics that project into the active carbon filling from below, thereby setting up a temperature limit in an easy manner. 
     Known from Document US 2006/0174857 A1 is an apparatus for heating the air intended for regenerating an active carbon filter, which consists of component that is equipped with several channels running parallel to each other and carrying the air to be heated and made out of an active, heat-insulating material, wherein the air is heated by electrical resistor elements that extend inside the channels in their longitudinal direction. 
     Within the framework of the specific structural configuration, these known techniques for pre-warming the air used to regenerate the active carbon filling of such a filter under certain conditions have only a limited suitability for setting up a regeneration process that is sufficiently quick even for a hybrid drive, given the inadequate heat transfer. 
     Known at the company of the applicant for heating the air for regeneration purposes is to use an electrical conductor made of carbon, around which the air to be heated streams. Comparable hereto is a monolithic molding made of an active material that absorbs hydrocarbons, which is provided with boreholes extending in its longitudinal direction, and is simultaneously used as an electrical conductor to heat the air streaming through it. 
     The problem with regard to the two aforementioned technical solutions is the requirement for an exact and especially reliable temperature controller, since it is necessary that the ignition temperature of the hydrocarbons not be reached, and in particular that any sparking be prevented. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to improve an active carbon filter of the kind mentioned at the outset with respect to the conditions of the regeneration process while preventing the disadvantages inherent in the prior art introduced at the outset. This improvement is to relate in particular, but not exclusively, to the suitability for use in hybrid drives. The object is achieved in such an active carbon filter as described herein. 
     Based on the above, it is essential with respect to the invention that the ambient air streaming into the active carbon filter be subjected to heating immediately, meaning already before entering the mentioned filling comprised of active carbon. As a result, the filling can be regenerated under conditions that are implemented by a rapid temperature control within the framework of the desired rate of desorption of the hydrocarbons adsorptively bound in the filling. This makes an active carbon filter conceived in this way especially suitable for use in hybrid drives, among other applications. 
     According to an aspect of at least one embodiment of the invention, the chamber containing a filling comprised of active carbon is additionally equipped with an electrically operable heater. 
     Aspects of at least one embodiment of the invention are geared toward a configuration of the path taken by the flowing air in conjunction with the port connected with the ambient atmosphere. Based on the above, this flow path is characterized by at least two chambers situated one in back of the other in the throughput direction, which are set up to pre-warm the entering air before the latter is exposed to a heating unit. These chambers carrying the flowing, heated air are also thermally connected with the chamber containing a filling comprised of active carbon, so that optimal conditions can be established for regenerating the active carbon or any other adsorptively active substances, in particular by heating the filling even without the necessity of a heating unit projecting directly into this filling, in that the air streaming into the active carbon filter is effectively heated, specifically using at least one heating unit arranged within the housing of the active carbon filter. 
     According to an aspect of at least one embodiment of the invention, a monolithic absorption unit intended to carry a flow is placed downstream from the chamber set up with a heating unit intended for heating the air in the direction of the inflowing atmospheric air. This absorption unit consists of a material that is absorptively active for hydrocarbons, and enhances the absorptive effect of the fillings that are present as a bulk material consisting of active carbon particles, accommodated in special chambers, and intended for carrying a flow. Because this adsorption unit is allocated almost directly to the atmospheric port of the housing, residual hydrocarbons that were not absorbed in the upstream filling are held back in a particularly reliable manner. Since this absorption unit can be oppositely subjected to heating, i.e., viewed in the direction of air flowing into the housing prior to entry into the absorption chamber, especially favorable preconditions for desorption are already established at this juncture during a rinsing operation of the active carbon filter. 
     Aspects of at least one embodiment of the invention are geared toward a more precise configuration of the used heating units. The critical aspect is that an electrical heating element is connected in a thermally conductive manner with a system of metallic, and hence highly heat conductive, wall elements, wherein the wall elements are configures and arranged to establish contact over a large area with either the air flowing through the heating unit or the active carbon particles present at the latter. Because the electrical heating element is designed as PTC thermistor or PTC element (positive temperature coefficient), it becomes especially easy to produce a temperature limitation that at least prevents the ignition temperature of the hydrocarbons from being reached. 
     Aspects of at least one embodiment of the invention are targeted at a more precise configuration of the heating unit intended for heating the air. Based on the above, the latter consists of a hollow structure, for example a tubular cylinder, which is used in the same way as the wall element rigidly connected thereto for purposes of heat transfer. 
     Aspects of at least one embodiment of the invention are geared toward the configuration of the chambers for the air entering the housing, which are situated upstream from the at least one heating unit, and can be used for pre-heating the air. The crucial aspect has to do with the fact that the flowing path traversing both chambers is characterized by a reversal of direction, so that the space inside the housing is utilized in an especially effective way, and heat transfer surfaces adequate in particular for purposes of pre-warming can be made available. 
     Aspects of at least one embodiment of the invention are geared toward the at least one heating unit intended for heating the filler comprised of active carbon. This is characterized by numerous wall elements that each form heat transfer surfaces, and in their entirety comprise a structure preferably shaped like a star in cross section. 
     Aspects of at least one embodiment of the invention are geared toward additional configurations of the absorption unit, as well as of the chambers intended for accommodating active carbon particles. 
     An aspect of at least one embodiment of the invention relates to the electrical configuration of the used heating units. It is here especially advantageous that the wall elements of several heating units be actively connected with only a single heating element. As a result, this heating element acts as a heat source, the heat from which is relayed due to the thermal conduction properties of the interconnected wall elements of several heating units. 
     According to an aspect of at least one embodiment of the invention, the heating units are connected with a controller in order to activate the heating unit as a function of the operating state of the active carbon filter as well as the vehicle, in particular the current absorption capacity. This controller, which can be connected with a hydrocarbon sensor that acquires the current absorption capacity, can be set up in such a way that the heating units are already activated prior to a regeneration process. 
     Let it be noted at this juncture that the active carbon particles used for absorption can also be replaced by any other adsorptively active particles known and suitable to the expert for this purpose. 
     The chambers containing the active carbon particles, in particular their inlet and outlet openings, are occupied by a filter layer according to the features in claim  18 , e.g., a mat. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in greater detail below drawing reference to the exemplary embodiments depicted in the attached drawings. Shown on: 
         FIG. 1  is a perspective view of an active carbon filter according to the invention; 
         FIG. 2  is a depiction of the active carbon filter according to cutting plane II-II on  FIG. 1 ; 
         FIG. 3  is a depiction of the active carbon filter according to a cutting plane III-III on  FIG. 1 ; 
         FIG. 4  is a bottom view of the active carbon filter in a cutting plane IV-IV on  FIG. 1 ; 
         FIG. 5  is an isolated, perspective overall view of a first exemplary embodiment of a heater used in the active carbon filter; 
         FIG. 6  is an isolated, perspective view of a first section of the heater shown on  FIG. 5 ; 
         FIG. 7  is an isolated, perspective view of a second section of the heater shown on  FIG. 5 ; 
         FIG. 8  is a second exemplary embodiment of a heater used in the active carbon filter, viewed in a vertical cutting plane of the latter; 
         FIG. 9  is an isolated, perspective view of the heater according to  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     The housing of an active carbon filter with approximately a rectangular cross section marked  1  on  FIG. 1  is provided at location  2  on its vertical wall  3  with a mounting device  4  intended for fixation in a vehicle, which is not described in any greater detail below. 
     The rest of housing  1  consists of the vertical walls  5 ,  6  and  7 , a floor section  8  and a cover  9 , which is detachably connected with the facing edges of walls  5  to  7 . The floor section  8  is connected with a port  10  intended for connection to a tank, a port  11  intended for connection to the ambient atmosphere, and a port  12  intended for connection with the intake manifold of an internal combustion engine. Finally, an electrical port is marked  13 , and just as port  11 , is arranged in the front side of a cylindrical housing section  14  that protrudes from the plane of the floor section  8 . The ports  10  to  12  are each depicted by tubular supports, which are set up for attaching line elements (not graphically depicted), while the electrical port is shown by example as a plug-and-socket connection. 
     Functional elements that correspond with those on  FIG. 1  are numbered appropriately on  FIG. 2 to 9 , thus eliminating any need for repeated descriptions in this respect. 
     As evident based on  FIGS. 2 and 3 , the housing section  14  externally covers a circular recess  15  in the floor section  8 , in which a cylindrical tubular element  16  is inserted within the housing  1 , extending coaxially to the housing section  14 , and secured therein in a manner not shown. A deflection cover  17  to be described in greater detail below that extends approximately in the plane of the recess  15  closes the tubular element  16  in its front side facing the housing section  14 . 
     The end of the tubular element  16  facing away from the housing section  14  is connected by a constriction  18  with an also cylindrical tubular element  19  with a large diameter that extends coaxially to the housing section  14 , wherein a conical transition section  20  is arranged between the tubular elements  16 ,  17 . The end of the tubular element  19  facing away from the housing section  14  is supported on the cover  9 . 
     The interior space of the insert comprised of the tubular elements  16 ,  19  along with the transition section  20  is divided by an intermediate floor  21  into a chamber  22  essentially formed by the tubular element  16  and a chamber  23  essentially formed by the transition section  20  and the tubular element  19 , which are interconnected by openings (not graphically depicted) in the intermediate floor  21 . 
     The end of the chamber  23  facing the cover  9  is formed by a pressure plate  25  that is adjusted to its cross section and resiliently supported against the cover by a pressure spring  24 , and is to be provided with at least one central opening  26 . Openings  27  are also situated in the wall section of the tubular element  19  that extends between the cover  9  and pressure plate  25 , and whose function will be explained below. 
     The chamber  28  definable by the interior side of the housing  1  on the one hand and the exterior side of the insert described above on the other is bordered on its end facing away from the housing section  14  by pressure plates  29 , which are supported against the interior side of the cover  9  in the same way as the pressure plate  25  via pressure springs  30 . Each of the pressure plates  29  is characterized by at least one opening  31 , which establishes a connection between the chamber  28  and the space between the cover  9  and the pressure plate  27 . 
     As evident, the chambers  23 ,  28  are continuously interconnected via the openings  26 ,  27 ,  31 . 
     Situated within the chambers  22 ,  28  is a heating device  32  depicted in isolation on  FIGS. 5 and 7 , which consists of a first  33  heating unit inserted in chamber  22  and a second heating unit  34  inserted in chamber  28 . 
     The heating unit  33  shown on  FIG. 6  consists of a metal tubular cylinder  35 , the exterior side of which has secured to it diametrically opposed, equally dimensioned, flat wall elements  36 . The interior space of this tubular cylinder  35  is characterized by two parallel wall elements  37 ,  38 , the intermediate space between which accommodates an electrical heating element  39 . Extending perpendicular to the wall elements  37 ,  38  and flush with the wall elements  36  mentioned at the outset are two additional, equally dimensioned wall elements  40 , which divide the mentioned interior space into four equally dimensioned chambers  41  broken up into circular sectors in cross section. 
     As evident from a combined examination of  FIGS. 2 ,  3  and  6 , the interior space of the tubular element  16  is divided by the wall elements  36  into two chambers  42 ,  43  shaped like half-rings in cross section with the heating device  32  built in. 
     As evident from  FIG. 3 ,  5 , the deflection cover  17  is semi-circular in design, and on the end of the tubular element  16  facing the housing section  14  forms an opening  44  for the chamber  42  and a closed wall for the chamber  43 . In particular, the deflection cover  17  is provided with connecting wall elements  45 , which attach to the wall elements  36  of the heating unit  33 , and separate the chambers  42 ,  43  from each other at this location. 
     As a result of the connecting wall elements  45 , which abut the facing front side of the tubular cylinder  35 , an opening  46  is set up between this front side and the facing bottom side of the deflection cover  17 , which establishes a connection between the chambers  42 ,  43 . 
     The front side of a deflection ring marked  47  supports the end of the heating unit  33  facing away from the housing section  14 . Molded onto this deflection ring  47  comprised of a tubular element  51  is a ring flange  48 , which forms the lower termination of the chambers  42 ,  43 , meaning the one that lies opposite the deflection cover  17 . After the wall elements  36  end at a distance above the ring flange  48 , the chambers  42 ,  43  are interconnected at this location. The ring flange  48  is also designed in such a way as to establish a bottom termination for the chambers  42 ,  43 . 
     An absorption unit marked  49  is supported against the intermediate floor  21  via a sealing ring  50 . The monolithic absorption unit  49  is also fixed within the tubular element  51 , and intended to carry a stream of air. The function of the absorption unit will be explained in the following. 
     Line elements marked  52  start from the heating unit  33  and extend through the chamber  23  until into the chamber  28 , and are here connected with the second heating unit  34 . The heating unit  34  consists of a centrally arranged, slotted receptacle  54  for an electrical heating element  53 , wherein radially uniformly distributed, star-shaped wall elements  55  are molded onto the walls of the receptacle. 
     Within the housing  1 , the chamber  28  bordered on the inside by the tubular element  16 , transition section  20  and tubular element  19  is filled with active carbon particles, wherein a mat  56  is provided as the filter layer in front of the outlet opening of the ports  10 ,  12  as well as overlapping the openings  31  of the pressure plates  29 . 
     In like manner, the chamber  23  is filled with active carbon particles, wherein the outlet openings in the intermediate floor  21  and the openings  26  of the pressure plate  25  are overlapped by a mat  57  as the filter layer. 
     The heating unit  34  is held within the chamber  28  adjacent to the port  4  in a manner not graphically depicted in any greater detail, so that the wall elements  55  are integrated into the filling comprised of active carbon particles, imparting an intensive heat exchange with the latter. 
     When installed, the active carbon filter is incorporated via its ports  10  to  12  into a line system, which connects it with the intake manifold of the internal combustion engine, the top space of a tank and the ambient atmosphere, wherein the respective lines integrate valves with a position adjusted to the operating phase of the active carbon filter. In addition to equalizing pressure within the tank taking into account varying fill levels, temperature fluctuations, and evaporations, the key here is to at least limit the escape of hydrocarbon shares for reasons of environmental protection. These hydrocarbon shares are to be retained with the engine idling through adsorption in the filter, and routed to the combustion chamber of the engine together with the combustion air within the framework of a purging operation as a result of desorption. 
     In the following, the path taken by the air starting from the ambient atmosphere, passing thorough the active carbon filter, and ending at the port  12  with the engine running will be described, drawing reference to  FIG. 1 ,  3 . 
     During exposure to the vacuum present in the intake manifold of the engine and conveyed to the port  12 , ambient air is aspirated via the port  11  in the direction of the arrow  58 , and enters into the chamber  42  via the housing section  14  and opening  44 . A deflection takes place at the deflection ring  47 , the ring flange  48  of which seals this chamber on its side facing away form the housing section  14 , in the direction of arrow  59  toward the chamber  43 , wherein an additional deflection point is set up in the chamber  22  after the stream has passed through this chamber  43  in the direction of arrow  60  on the deflection cover  17  that covers this chamber on its end facing the housing section  14  via the opening  46  according to arrow  61 . Inside the chamber  22 , the air flows through the heating units  33  placed therein, in particular its chambers  41 , to subsequently pass into the chamber  23  via the absorption units  49  and openings in the intermediate floor  21  according to arrow  62 . The air exits the chamber  23 , and passes through its opening  26  in the floor and the openings  31  also situated in the floor, into the chamber  28  and to the port  12 . 
     Because the air is guided on the inlet side through the absorption unit  49  and the active carbon fillings of the chambers  23 ,  28 , the hydrocarbon shares introduced into the combustion chamber of the engine together with the air and retained therein undergo desorption. 
     The heating unit  34  mentioned at the outset heats the active carbon filling in the chamber  28 . The heating unit  33  also mentioned at the outset heats the air directly, so that the air entering the chambers  42 ,  43  is pre-heated, in particular as the result of contacting the tubular element  16  and tubular cylinder  35 . 
     This makes it possible to effectively counter a cooling of the active carbon particles triggered by desorption, so that optimal thermal conditions can be established for regenerating the active carbon and absorption unit  49 , despite the fact that combustion engine operation is diminished by a hybrid engine, for example. 
     The second exemplary embodiment of an active carbon filter shown on  FIG. 8  differs from the one on  FIG. 1 to 7  only in that a uniform heating device  63  is used here, depicted in isolation on  FIG. 8 , which exerts a heating effect both inside the chamber  28  and inside the chamber  22 . 
     As evident from  FIG. 9 , the heating device  63  consists of a centrally located heating unit  33 ′ that structurally corresponds to the heating unit  33 , whose tubular cylinder  35  accommodates two diametrically opposed, equally dimensioned heating units  64  on the outside and peripherally. Each heating unit  64  consists of two equally dimensioned wall elements  65 ,  66  that extend perpendicularly to each other, one of which is rigidly connected with the tubular cylinder  35 . 
     The entire structure of the heating unit  63  comprised of the heating units  33 ′,  64  consists of a metal, so that the heat generated via thermal conduction via the electrical heating element  39  is conveyed over the wall elements  37 ,  38 ,  40  and  65 ,  66  to the air streaming through the chambers  41  as well as to the active carbon particles, into which the wall elements  65 ,  66  are embedded in the installed state. 
     As evident from  FIG. 8 , the heating units  64  extend within the chamber  28  and therein perform the same function as the heating units  34  in the exemplary embodiment according to  FIG. 1 to 7 . 
     The used electrical heating elements  39 ,  53  are preferably designed as resistor elements with PTC characteristics, thereby setting up a simple and functionally reliable thermal cutout. 
     REFERENCE LIST 
     
         
         
           
               1 . Housing 
               2 . Location 
               3 . Wall 
               4 . Holding device 
               5 . Wall 
               6 . Wall 
               7 . Wall 
               8 . Floor section 
               9 . Cover 
               10 . Port 
               11 . Port 
               12 . Port 
               13 . Electrical port 
               14 . Housing section 
               15 . Recess 
               16 . Tubular element 
               17 . Deflection cover 
               18 . Constriction 
               19 . Tubular element 
               20 . Transition section 
               21 . Intermediate floor 
               22 . Chamber 
               23 . Chamber 
               24 . Pressure spring 
               25 . Pressure plate 
               26 . Opening 
               27 . Opening 
               28 . Chamber 
               29 . Pressure plate 
               30 . Pressure spring 
               31 . Opening 
               32 . Heating device 
               33 . Heating unit 
               33 ″. Heating unit 
               34 . Heating unit 
               35 . Tubular cylinder 
               36 . Wall element 
               37 . Wall element 
               38 . Wall element 
               39 . Heating element 
               40 . Wall element 
               41 . Chamber 
               42 . Chamber 
               43 . Chamber 
               44 . Opening 
               45 . Connecting wall element 
               46 . Opening 
               47 . Deflection ring 
               48 . Ring flange 
               49 . Absorption unit 
               50 . Sealing ring 
               51 . Tubular element 
               52 . Line elements 
               53 . Heating element 
               54 . Receptacle 
               55 . Wall element 
               56 . Mat 
               57 . Mat 
               58 . Arrow 
               59 . Arrow 
               60 . Arrow 
               61 . Arrow 
               62 . Arrow 
               63 . Heating device 
               64 . Wall element 
               65 . Wall element