Abstract:
Filter ( 28 ) for an aqueous solution, such as urea, of a diesel vehicle selective catalytic reduction system, comprising a housing provided with an inlet and with an outlet and, inside which, is arranged a filter element, and with a means of detecting variations in volume associated with the changes in phase of the aqueous solution, characterized in that the filter additionally is provided with signaling means ( 17 ) for signaling said changes in volume of the phase of the aqueous solution.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of aqueous-solution filters applied to selective catalytic reduction systems for internal combustion engines. 
       TECHNOLOGICAL BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to the filtration devices used in selective catalytic reduction (SCR) systems. An SCR system is a pollution-control system which reduces emissions of nitrogen oxides (NOx), making it possible to comply with the Euro 6 standard in NOx emission limits. Various SCR technologies have been developed, based on solutions of urea. Injecting urea into the exhaust allows reduction of nitrogen oxides NOx using catalysts in the presence of oxygen. The aqueous solution containing 32% urea is the eutectic aqueous solution and defines the standard reducing agent referred to as AUS32, AdBlue®, or DEF (Diesel Exhaust Fluid). However, this eutectic aqueous solution suffers from problems which increase the complexity of installing it, such as, amongst other things, its −11° C. freezing point, which means that solutions such as heating the aqueous liquid so that the SCR system remains functional have been researched. There is another aqueous solution made up of urea and ammonium formate the freezing point of which is at −30° C. Heating solutions have been proposed for solving the problem of a −11° C. freezing point, such as in-built heating elements (FR2916188). For its information, the control logic conventionally uses the temperature information to trigger the heating of the aqueous solution. In addition, because the solutions may contain impurities and the freezing point values may range from −11° C. to 0° C., the control logic has therefore to actuate the heating up to 0° C. in order to ensure the switch from the solid phase to the liquid phase. WO 2013/178352 discloses the use of a pressure sensor arranged in the filter and allowing indirect determination of variations in volume. 
         [0003]    We are going to set out the invention which proposes a device for triggering the system for heating the aqueous solution when the aqueous solution is in the solid phase. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention seeks notably to address the abovementioned problems by proposing a solution that detects the phase of the solution, whether it be solid or liquid, thus allowing the heating of the aqueous solution to be triggered. The aqueous solution may be a solution based on urea. The diesel vehicle selective catalytic reduction system comprises a housing provided with an inlet and with an outlet and, inside which, is arranged a filter element, and with a means of detecting variations in volume associated with the changes in phase of the aqueous solution, characterized in that the filter additionally is provided with signaling means for signaling said changes in volume of the phase of the aqueous solution. The signaling means may comprise a switch that switches upon changes in phase. In addition, the signaling means comprise a deformable membrane collaborating with the switch to signal a change in phase. Also, the membrane defines an expansion chamber for said variations in volume. The chamber may be filled with a gas or with a soft foam. The membrane may also be planar. 
         [0005]    The switch may also be situated in the expansion chamber. 
         [0006]    The switch may comprise at least one contact arranged on the membrane. 
         [0007]    The Reed-type switch may also be activated by a magnet, the switch or the magnet being arranged on the membrane. The filter additionally comprises a heating means built into the filter element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Further features, objects and advantages of the invention will become apparent from reading the detailed description which will follow, and from studying the attached drawings, given by way of nonlimiting example and in which: 
           [0009]      FIG. 1  is a view in section depicting the mechanical switch control system when the phase is liquid 
           [0010]      FIG. 2  is a view in section depicting the mechanical switch control system when the phase is solid 
           [0011]      FIG. 3  is a view in section depicting the switch control system with contacts built into the deformable element when the phase is liquid 
           [0012]      FIG. 4  is a view in section depicting the switch control system with contacts built into the deformable element when the phase is solid 
           [0013]      FIG. 5  is a view in section of the Reed switch control system when the phase is liquid 
           [0014]      FIG. 6  is a view in section of the Reed switch control system when the phase is solid 
           [0015]      FIG. 7  is a depiction of the pleated filter element. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    In the remainder of the description, elements that are identical or similar will be denoted by the same references. For the sake of clarity and conciseness of the description, a top to bottom orientation according to the direction of the figure will be used without implying any limitation as to the extent of the protection, notably with regard to the various ways in which a filter housing can be installed. Words such as “top, bottom, lower, upper, etc.” will be used without implying limitation. 
         [0017]    In a first embodiment ( FIG. 1 ,  FIG. 2 ), the invention describes a triggering means which has a mechanical type switch  16  control system triggering an electrical signal upon a change in phase of the aqueous solution. A system for triggering an electrical signal is situated inside an aqueous solution filter housing  10 . The housing  10  is made up of two filter half-housings  28 , which are produced by systems for injection-molding of plastics or by systems for the shaping of metal materials. The two parts correspond, one of them, to the bottom part  10 B of the housing and, the other, to the top part of the housing  10 A. The triggering system comprises a membrane  14  which is preferably situated in the bottom of the housing  10 B, below the filter layer  12 . The membrane  14  can deform when the aqueous solution passes from the liquid phase to the solid phase. Upon the change in phase, the volume of the aqueous solution increases and pushes against the membrane  14  situated beneath. The membrane  14  is fixed and held at its periphery by bonding, overmolding or by a clamping system which consists in closing the two half-housings onto the membrane  14  using various means of sealed assembly which are as follows in the case of plastics materials: hot-welding method, the three methods of vibration welding (ultrasound welding, vibration welding or even a combination of the two ultrasound and vibration methods). The membrane  14  comprises the first electrical contact  16 A of the mechanical switch control system bonded to the membrane  14  facing toward the bottom of the lower housing  10 B. The second electrical contact  16 B of the mechanical switch control system is mounted opposite and bonded into the bottom of the lower housing  10 B, and oriented toward the upper part of the housing  10 A. Upon the change in phase of the aqueous solution from the liquid phase to the solid phase, its volume increases and deforms the membrane  14  and this causes the two electrical contacts  16 A and  16 B of the signaling system  16  to touch (see R1) and results in the closing of the switch, which then triggers an electrical signal S 1  which will allow the system for heating the aqueous solution to be started. 
         [0018]    In a second embodiment ( FIG. 3 ,  FIG. 4 ), the invention describes a system for triggering an electrical signal upon a change in phase of the aqueous solution which has a system for controlling the switch  16  that is of the electrical contact on membrane type. The system for triggering an electrical signal is situated inside an aqueous solution filter housing  10 . The triggering system comprises a membrane  14  preferably situated in the bottom of the housing  10 B, underneath the filter layer  12 . The membrane  14  is made up of a closed envelope of round, spheroidal, rounded-corner rectangular or rugby-ball shape. The membrane  14  can be deformed upon the change in phase of the aqueous solution from the liquid phase to the solid phase and vice versa. The membrane  14  contains either a gas or a soft foam. Upon the change of the freezing of the liquid phase, its volume increases and pushes against the membrane  14  situated beneath. The membrane  14  comprises two electrical contacts, situated one facing the other, on each side of the membrane, the first contact at the top on the membrane and the second contact at the bottom on the membrane, which are either overmolded or bonded to the membrane  14 , inside the interior chamber (C). When the aqueous solution passes from the liquid phase to the solid phase, its volume increases and deforms the membrane  14  causing the two contacts of the switch  16  system to touch, thereby closing the switch which itself triggers an electrical signal S 1  so as to allow the aqueous solution heating system to be started. 
         [0019]    In a third embodiment ( FIG. 5 ,  FIG. 6 ), the invention describes a device for triggering an electrical signal upon a change in phase of the aqueous solution from the liquid phase to the solid phase and vice versa. This device has a switch  16  control system of the Reed contact type (magnetic switch placed in a protective bead of glass). The device for triggering an electrical signal is situated inside a housing  10  of the filter. The triggering device comprises a membrane  14  which is preferably situated in the bottom of the housing  10 B, beneath the filter layer  12 . The membrane  14  can be deformed when the aqueous solution passes from the liquid phase to the solid phase. The membrane  14  is made up of a closed envelope of round, spheroidal, rounded-corner rectangular or rugby-ball shape. The membrane  14  contains either a gas or a soft foam. Upon the change in phase, the volume of the aqueous solution increases and pushes against the membrane  14  situated beneath. The membrane  14  comprises a magnet and a Reed switch, situated one facing the other with respect to the center of the volume and which are either fixed by bonding or by some other system of attachment. Upon the passage of the aqueous solution to the solid phase, its volume increases and deforms the membrane  14  which moves the magnet  26  closer to the Reed switch  24 . As the magnet nears the Reed switch  24 , the Reed switch  24  closes and triggers an electrical signal Si to allow the aqueous solution heating system to be started. The switch logic may be reversed: the increase in volume of the solid phase may bring the magnet closer to the Reed switch which then opens; the heating controller, of the electronic circuit or electromechanical relay type, then supplies power for the heating. 
         [0020]    In accordance with  FIG. 7 , we have, for example, an aqueous solution filter element  8  provided with a heating means  12  for example incorporated into a filter layer  10 . 
         [0021]    In a first embodiment, a heating means  12  is completely incorporated into the filter layer  10 . The filter layer  10  is preferably made up of a cellulose-based medium with carbon fillers, carbon being a conductor of electricity. Alternatively, the carbon filler may be replaced by tracks printed in conductive ink or any other electrically conducting element. The electrical conduction property of the carbon fillers and of the tracks printed in conductive ink or any other electrically conducting element means that heat can be released through these elements through a Joule-heating effect. The filter layer may also be made up of a medium based on synthetic fabric. A heating means device is fully described in the application filed on this day under the title “Filtre à solution aqueuse avec moyen de chauffage [Aqueous solution filter with heating means]”.