Abstract:
A carbon canister adapted for use in an automotive vehicle is disclosed. The system has a carbon canister housing defining a cavity adapted for holding carbon pellets with the housing including: a port and a strainer disposed between the port and the cavity with a portion of a surface of the strainer being convex with respect to the cavity wherein the strainer has a plurality of orifices. The integral strainer obviates the need for a foam filter to prevent the carbon pellets from escaping from the carbon canister housing through the port. In some applications, the carbon canister system has three ports: one to the engine, one to atmosphere, and one to a vent of the fuel tank, each having a strainer disposed in the port.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a carbon canister as part of a fuel vapor management system on an automotive vehicle. 
         [0003]    2. Background 
         [0004]    For many years, carbon canisters containing activated carbon pellets have been used on automotive vehicles to reduce or prevent fuel vapors from a vehicle fuel tank escaping to atmosphere. In a typical application, the vapor storage canister is coupled to the vehicle fuel tank as well as the vehicle engine with a vent valve to atmosphere. The activated carbon pellets in the canister absorb fuel vapors from the fuel tank during a storage mode, such as when the fuel tank is being filled. The stored fuel vapors are periodically purged from the carbon pellets during a purge mode by passing air from atmosphere over the pellets to desorb the fuel, with the fuel vapor inducted by the engine and combusted during engine operation. The carbon pellets are added to the canister during assembly. Typically, a permanent filter, such as a foam filter, is installed at each entry/exit port to retain the pellets and any small particles that may break off of the pellets during assembly or subsequent operation. The size of each port is determined in conjunction with the filter characteristics to maintain a desired flow rate through the filter/port while accommodating some reduction in flow rate due to anticipated filter clogging. A decreased filter/port flow rate may result in incomplete purging of the stored fuel vapors during certain, regulated driving events. It is known in the prior art to provide a filter at each entry/exit port of the carbon canister to prevent the activated carbon pellets from migrating out of the carbon canister. It is also known in the prior art to affix tubes to the carbon canister housing to provide entry/exit ports. The resulting carbon canister is assembled of many parts. It is desirable to reduce the number of parts to be assembled to reduce cost and parts complexity and to increase robustness of the carbon canister. 
       SUMMARY 
       [0005]    To overcome at least one problem in the prior art, a carbon canister is disclosed in which a strainer and a tube for making connections to the carbon canister are molded integrally with the carbon canister housing. The strainer has orifices with a width less than a width of the average carbon pellet to prevent carbon pellets from exiting the carbon canister. By molding the tube and strainer integrally with the carbon canister, the need for affixing separate tube and filters is obviated. According to one embodiment of the present disclosure, the strainer extends into the carbon canister cavity in 3 dimensions to provide a large surface area with orifices so that pressure drop across the strainer is minimized. 
         [0006]    An advantage of the present disclosure is that by integrally molding in the tube and the strainer with the carbon canister housing, the number of individual parts to assembly a carbon canister is reduced. This makes assembly simpler, less prone to assembly mistakes, and cheaper. The carbon canister is more robust by having the parts integrally molded with the carbon canister housing. Any one tube, such as the tube coupled to the fuel tank, can be integrally molded with the canister housing. Alternatively, any combination of the strainers and tubes can be integrally molded. 
         [0007]    Yet another advantage of the present disclosure is that because the strainer extends into 3 dimensions, the surface area of the strainer is greater than it would be if the strainer surface was planar. A planar strainer configuration is able to accommodate fewer orifices than a strainer with a more convoluted surface. Because the 3-dimensional strainer has more orifices, it can accommodate more occlusion of orifices by carbon pellets without suffering such a large pressure drop across the strainer as compared to a filter or a planar strainer configuration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic of a fuel recovery system operating in a vapor recovery mode; 
           [0009]      FIG. 2  is a schematic of a fuel recovery system operating in a purge mode; 
           [0010]      FIGS. 3 and 4  are cutaways of a carbon canister according to embodiments of the present disclosure; 
           [0011]      FIGS. 5 through 8  are perspective drawings of strainers according to embodiments of the present disclosure; and 
           [0012]      FIG. 9  is a sketch of a carbon pellet. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0014]    When an automotive fuel tank is filled, fuel vapor laden air is displaced by fuel. To prevent those fuel vapors from entering the atmosphere, fuel tank  10  is provided with a fuel vent  12  communicating to a carbon canister  14  filled with activated carbon pellets via port  16 , as shown schematically in  FIG. 1 . As the gases containing fuel vapor pass through the bed of carbon pellets, the fuel vapor is absorbed by the carbon pellets. Carbon canister  14  also has a port  18  communicating to the atmosphere. When such gases exit carbon canister  14 , all, or substantially all, of the fuel has been stripped from the gases displaced from the fuel tank by virtue of contact with the carbon pellets. Such operation as shown in  FIG. 1  is sometimes referred to as vapor recovery mode. 
         [0015]    The activated carbon pellets have a limited ability to store fuel and, therefore, must be purged so that they can once again absorb fuel vapor displaced from fuel tank  10 . This is accomplished by pulling fresh air through the carbon pellet bed within carbon canister  14  and inducting that air, which contains desorbed fuel, through port  22  into an operating internal combustion engine  20 , as shown in  FIG. 2 . The fuel vapors that are desorbed into the incoming air are combusted in engine  20  largely forming carbon dioxide and water before being exhausted from engine  20 . A valve  24  located upstream of engine  20  is adjusted by electronic control unit  26  to control the flow of gases through carbon canister  14 . The gases introduced through purge valve  24  are mixed with air entering an engine intake through throttle valve  27 , which is also controlled by electronic control unit  26 . Such operation as shown in  FIG. 2  is sometimes referred to as purge mode. 
         [0016]    In  FIG. 3 , a carbon canister  14  is shown having a housing  27 , which defines a cavity  28  within. In use, cavity  28  is filled with activated carbon pellets. However for illustration purposes in  FIG. 3 , a portion of a carbon pellet bed  31  is shown in a corner of cavity  28 . Carbon canister  14 , as shown in  FIG. 3 , is a two-pass canister, with divider  29  diverting the flow so that it does not short circuit directly from port  16  to port  18 . In vapor recovery mode, gases flow from the fuel tank  10  through port  12  through port  16  into cavity  28  of carbon canister  14  and exit through port  18  to atmosphere. Carbon pellets  31  provided in cavity  28  remove fuel vapors from the gases entering carbon canister  14  so that the gases exiting to the atmosphere contain substantially no fuel vapor. Between port  12  and cavity  28 , a strainer  30  is provided. Strainer  30  substantially prevents carbon pellets from migrating out of cavity  28 . A strainer  32  is also provided between cavity  28  and port  18 . Not shown in  FIG. 3  is a compression plate that is typically included at the bottom of carbon canister  14 . The spring-loaded compression plate compacts the carbon pellets, which would force pellets through ports  12  and  18  if strainers  30  and  32  were not provided. In the embodiment shown in  FIG. 3 , port  16  is provided in a tube  33  continuing into a strainer  34 , shown in cross-section. Tube  33  has a cylindrical section extending away from canister housing  27  providing a sealing surface to connect to fuel tank  10 . In the embodiment shown in  FIG. 3 , tube  33  has a circumferential raised portion providing an annular ridge for securing a connecting tube. Strainer  34  forms a conical section at one end. There is a hole of diameter, D, in the end. There are slits  35  of width, W, formed in the conical section and continuing into the cylindrical portion of strainer  33 . Tube  33  and strainer  34  are integrally molded with canister housing  27 . In the prior art, tube  33  and strainer  34  were molded separately and then attached to canister housing  27 . However, by using modern simulation techniques, the molding process can be optimized, without resort to trial and error, to avoid non-uniform mold temperatures and pressures during the molding process. By careful iteration on the gates, runner, and cavity layouts, features, such as  33  and  34 , can be molded integrally with housing  27  without incurring excessive tool wear and within dimensional tolerance for the features. 
         [0017]    In  FIG. 4 , a view of carbon canister  14  is provided which shows a port  22  leading to engine  20  (not shown). When carbon canister  14  is purging, air from the atmosphere is inducted through port  18  into cavity  28  and exits port  22  to be introduced into engine  20 . The flowing air strips off absorbed fuel from the carbon pellets (not shown in  FIG. 3 ) and delivers that fuel to engine  20  where it is combusted. Port  22  is formed in tube  36  and continues through strainer  37 . Strainer  37  has an orifice of diameter, D, at one end. Strainer  37  also has slits of width, W, in a conical section and continuing in the cylindrical portion. Strainer  32 ′ is provided in between port  18  and cavity  28  to ensure that the carbon pellets remain within cavity  28 . 
         [0018]    In  FIGS. 1-4 , ports  16 ,  18 , and  22  are in the top of carbon canister  14  and carbon canister  14  has a two-pass arrangement. This is a non-limiting example. Carbon canister  14  can have any number of passes. When the number of passes is an odd number, port  18  is disposed in an opposite end of carbon canister  14  from ports  16  and  22 . In  FIG. 3 , port  16  is shown in cross-section and in  FIG. 4 , port  22  is shown in cross-section. In one embodiment this is due to the two ports being in line with each other and visible only by virtue the cross-sectional view being different in the two Figures. 
         [0019]    According to one embodiment, strainer  32  of  FIG. 3  is integrally molded with housing  27 . Strainer  32  extends into cavity  28 . Referring to  FIG. 5 , strainer  32  has multiple orifices, one of which is designated  38 . In a non-limiting example, the orifices are slots having a width, W. The slots are parallel along the distal surface of strainer  32 . The slots extend down the cylindrical surface of strainer  32 . Strainer  32  has a 3-dimensional shape with the distal end substantially being a part of a sphere connected to the cylindrical sides. The shape of the surface of strainer  32  is overall convex as viewed from cavity  28 . 
         [0020]    Referring to  FIG. 6 , strainer  39  is substantially square in cross-section having circular orifices of diameter D (one of which is designated  42 ) on the planar, distal end and slots having a width, W, (one of which is designated  40 ) along sloping sides of strainer  39 . 
         [0021]    In  FIG. 7 , strainer  37  has a cylindrical portion with a conical tip and having slots  44  with width, W. In  FIG. 8 , strainer  32 ′ is shown having both circular orifices  46  and slots  48 . 
         [0022]    Surfaces of strainers  32 ,  32 ′,  34 ,  37 , and  39  are 3-dimensional. Each of these embodiments is generally convex as viewed from cavity  28 . However, these are non-limiting examples. A strainer having a surface with a concave portion as viewed from cavity  28  is a further alternative. 
         [0023]    In  FIG. 9 , a typical carbon pellet is shown having a diameter of S (or span). W of the slots or D of the circular orifices are smaller than S of the pellet to prevent the pellets from migrating through the strainers. The diameters for individual pellets of a batch of carbon pellets have a distribution in size. The W and D dimensions of the orifices are selected so that substantially even the smallest pellet does not slide through the strainer&#39;s orifices. 
         [0024]    As such, the present disclosure provides a tube for attachment and a strainer integrally molded with the carbon canister housing to obviate the need for a separate filter element or a separately attached tube, thereby reducing system complexity and cost. Because the strainer extends into 3 dimensions, the surface area is increased and can accommodate more openings to provide a desired flow rate while tolerating some blockage by pellets or particles such that purge times are not adversely impacted due to strainer blockage. 
         [0025]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.