Abstract:
A vehicle tank pressurization device has a valve seat establishing an opening for fuel vapours and/or air; such opening has a vertical axis coincident with the direction of application of an opening force, that is directed upwards and is produced, in use, by the pressure in an internal upper region of the tank; the device also has a movable shutter, placed on the valve seat, to open/close the valve seat, and having a weight set by design in such a way as to define the magnitude of a closing force directed downwards and with a center of gravity positioned eccentrically with respect to the vertical axis of the opening.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority from European Patent Application No. 16161287.4 filed on Mar. 18, 2016, the disclosure of which is incorporated herein by reference in its entirety. 
       FIELD OF THE DISCLOSURE 
       [0002]    The present invention relates to a vehicle tank pressurization device, to contain liquid fuel or chemical reducing agents such as AUS32 (aqueous urea solution 32.5%), required for the operation of selective catalytic reduction devices in Diesel cycle engines. 
       BACKGROUND 
       [0003]    A pressurization device is fitted to vehicle tanks in order to maintain a given level of pressure inside the tank itself. Such a device is usually characterised by having a unidirectional valve which is normally closed and is configured to open when the pressure inside the tank reaches a specified threshold. When the valve opens, it allows the outflow of a certain volume of air and/or fuel vapours to the atmosphere, optionally passing through a canister to recover the vapours. 
         [0004]    The valve has a valve seat and a shutter which can move towards and away from the valve seat and, in some solutions, has a weight whose magnitude determines the operation of closure and, therefore, the aforesaid pressure threshold. It may also be provided with a set point spring with a relatively low preload, in order to keep the shutter closed against the valve seat despite the vehicle&#39;s jolts and vibrations in normal driving condition, and/or in order to increase the value of the threshold pressure required to move the shutter. 
         [0005]    In known solutions, the shutter has difficulty in fully lifting from the valve seat and in quickly bringing the internal conditions of the tank below the established threshold pressure, especially when the pressure in the tank slightly exceeds this threshold. 
       SUMMARY OF THE INVENTION 
       [0006]    The purpose of the present invention is to provide a vehicle tank pressurization device, designed to provide a straightforward, low-cost solution to the abovementioned problem. 
         [0007]    The present invention provides a vehicle tank pressurization device, as defined in claim  1 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For a better understanding of the present invention a preferred embodiment is now described, purely as a non-limiting example, with reference to the accompanying drawings, wherein: 
           [0009]      FIG. 1  shows a vehicle tank pressurization device according to the present invention, in simplified perspective view, with parts removed for clarity; 
           [0010]      FIG. 2 a    is a schematic sectional view of the pressurization device of  FIG. 1 , shown in enlarged scale and in a closed state; 
           [0011]      FIGS. 2 b  and 2 c    are similar to  FIG. 2 a    and show the pressurization device in two different opening states, depending on the pressure level present in the tank; 
           [0012]      FIGS. 3 a , 3 b  and 3 c    are similar to  FIGS. 2 a , 2 b  and 2 c    respectively and show a first variant of the device of  FIG. 1 ; and 
           [0013]      FIGS. 4 a , 4 b  and 4 c    are similar to  FIGS. 2 a , 2 b  and 2 c    respectively and show a second variant of the device of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In  FIG. 1 , the reference number  1  indicates, in its entirety, a vehicle fuel tank (partially illustrated). The tank  1  comprises a shell  3  defining an inner chamber  4  consisting of a lower region  5  occupied by fuel and by an upper region  6  occupied by air and/or fuel vapours. 
         [0015]    The shell  3  comprises a wall  7 , which defines the top of region  6  and supports a pressurization device  8  comprising a unidirectional valve, which is normally closed and configured so as to open when the pressure in region  6  exceeds a predetermined threshold value. 
         [0016]    This unidirectional valve comprises a valve seat  10  defining a passage or opening  11  that has a vertical axis  12  and communicates directly and permanently with region  6 . With reference to  FIG. 2 a   , the device  8  comprises a chamber  13  formed above the valve seat  10  and communicating directly or indirectly with the atmosphere; and a shutter  14  which is positioned in chamber  13 , coaxially with the chamber  13  itself along a vertical axis  15 . 
         [0017]    Shutter  14  is defined, in the specific example shown, by a plate of substantially cylindrical shape, but other shapes and geometries may be provided as appropriate. 
         [0018]    Shutter  14  moves within chamber  13  towards and away from valve seat  10  to open/close opening  11  in response to the pressure present in region  6 . Shutter  14  has a lower surface  16  facing valve seat  10  and comprising a middle area  17  which blocks opening  11  when the shutter  14  is completely lowered against the valve seat  10 . At the same time, the pressure in region  6  acts on area  17  and tends to raise shutter  14  to open opening  11 , thus putting the inside of the tank in communication with the outside atmosphere: as can be seen in  FIG. 2 b   , axis  12  determines the direction along which the pressure applies its own opening force (Fa) upwards on area  17 . On the other hand, the weight of shutter  14  determines the downwards closing force (Fc) to balance this opening force and tends to keep opening  11  closed. The weight of shutter  14  is set by design in a relatively precise manner so as to define the abovementioned threshold value, beyond which shutter  14  is lifted by the pressure acting on area  17 , in such a way as to discharge air and/or fuel vapours through opening  11  and so to restore the pressure in tank  1  below the abovementioned threshold value. 
         [0019]    In the case shown, there is no coupling system or any constraint that limits or imposes a given movement to shutter  14 . Alternatively, the only constraint is given by a set point spring not shown that exerts a relatively small additional closing force in accordance with the weight of shutter  14 , to prevent shutter  14  from lifting in an undesirable manner due to vibrations or jolting during normal operation of the vehicle. In this case, the threshold value to produce venting through opening  11  is determined on the basis of the combination of the weight of shutter  14  and the thrust of the set point spring. 
         [0020]    Under the present invention, the center of gravity of shutter  14  is offset or eccentric with respect to axis  12 . In this way, shutter  14  may be more easily moved by the pressure present in region  6  and, furthermore, a greater fluid flow vented through opening  11  is produced, at an equal pressure to that inside tank  1 , especially when such pressure is only slightly greater than the predetermined set threshold value. 
         [0021]    In the embodiment of  FIGS. 2 a , 2 b  and 2 c   , the center of gravity of shutter  14  lies on axis  15 , while the latter is offset from axis  12 . In other words, axis  12  is offset laterally with respect to the center of chamber  13  and shutter  14 . 
         [0022]      FIG. 2 b    shows the behaviour of shutter  14  when the pressure in region  6  slightly exceeds the threshold value. It can be seen that the offset of the center of gravity of shutter  14  from axis  12  leads to a couple or tilting moment on shutter  14  and then to a tilting of shutter  14  itself into chamber  13 . 
         [0023]    This tilting, in turn, leads to a larger space or section area for the outflow of air and/or of fuel vapours from opening  11  to chamber  13 , on one side of valve seat  10 , with respect to the operating conditions of the prior art where the center of gravity of shutter  14  lies on axis  12  which therefore travels parallel to itself along axis  12  during the opening. In the opening operating condition under the present invention, the venting starts more readily and is completed more quickly than in the operating condition of the prior art, described above. 
         [0024]      FIG. 2 c    shows the behaviour of shutter  14  when the pressure in region  6  of tank  1  exceeds the threshold value to a large extent: in this case, the discharge conditions are similar to those that occur in the operating conditions of the prior art. 
         [0025]      FIGS. 3 a , 3 b  and 3 c    and  FIGS. 4 a , 4 b  and 4 c    show two variants, in which the same reference numbers as in  FIGS. 2 a , 2 b  and 2 c    have, where possible, been used. In these variants, shutter  14  is replaced, respectively, by shutter  14   a  and by shutter  14   b,  which have shapes that are asymmetrical with respect to axis  15 , so as to have the center of gravity displaced horizontally at one side with respect to axes  15  and  12 , while preferably being made from materials having homogeneous density. In other words, each of the shutters  14   a  and  14   b  consists of two portions, which are diametrically opposite and have different shapes. 
         [0026]    In particular, shutter  14   a  consists of two portions  19  and  20 , of which one has an average axial height smaller than the other. In the case of shutter  14   b,  the latter has, instead, a cavity  21  set at an eccentric position with respect to axis  15 , so as to displace the center of gravity on the diametrically opposite side. 
         [0027]      FIGS. 3 b  and 4 b    are similar to  FIG. 2 b    and show the effectiveness of the behaviour of shutters  14   b  and  14   c  respectively, when the pressure in region  6  slightly exceeds the threshold value. 
         [0028]    Under a variation not shown, a shutter is provided that has a symmetrical shape with respect to axis  15 , as in the case of  FIG. 2 a   , but consisting of one or more materials in such a way as to have non-homogeneous density in order to make its center of gravity eccentric. 
         [0029]    From the above description it is evident how, with a center of gravity which is eccentric with respect to axis  12 , the opening force exerted by the pressure causes the shutter not only to translate axially but also to rotate, whereby a readier opening and a greater outflow of air and/or fuel vapours is achieved. 
         [0030]    The method by which to obtain the eccentricity of the center of gravity may be different, as apparent from the abovementioned examples, and can be chosen on the basis of needs and benefits (dimensions, production techniques, etc.) depending on the specific practical case. 
         [0031]    Finally, it is clear that the device  8  described and illustrated herein with reference to the appended schematic figures can be subject to modifications and variations without thereby departing from the protective scope of the present invention as defined in the appended claims. 
         [0032]    In particular, the shapes of the various components may be different and/or be defined by a combination of examples that have been indicated above by way of example. 
         [0033]    Furthermore, tank  1  could be provided on the vehicle to contain chemical reducing agents needed for operating devices for selective catalytic reduction in Diesel cycle engines.