FR2868360A1 - CANISTER FOR FUEL TANK - Google Patents

Abstract

Canister for a fuel tank comprising a casing (2) and a monolithic cellular structure (1) based on activated carbon, the monolithic structure (1) being fixed in the casing (2) using a fixing system comprising at least one foam (4, 5).

Description

2868360 1

  The present invention relates to a canister for fuel tank and a method for the manufacture of such a canister.

  Current liquid or gaseous fuel tanks must meet a set of standards because of the highly flammable and often toxic nature of the fuel they contain. Fuel leaks due to lack of leakage as well as evaporation losses have been the subject of increasingly stringent regulations, particularly for applications in motor vehicles.

  However, the fuel tanks, in particular for motor vehicles, most often comprise an air vent for balancing the internal pressure and the atmospheric pressure, for example during changes in the resulting fuel level. filling the tank or fuel consumption by the engine, or during temperature changes. Thus, to meet the above-mentioned standards, this venting orifice is conventionally connected to the atmosphere via a conduit and a chamber, commonly known as a canister, containing a substance that adsorbs fuel vapors. usually activated carbon. The role of the canister is to avoid the release of fuel vapors into the atmosphere. Regularly, the canister is purged i.e. that the vapors are desorbed generally by means of a stream of air and sent into the engine air intake system for burning.

  The active carbon usually used as an adsorbent may be in the form of a bed of particles, a coating on a support or an alveolar monolith whose shape and porosity are controlled to obtain good adsorption while limiting the pressure losses. . Such a monolith is generally manufactured by shaping (extruding) and pyrolyzing a binder mixture (for example ceramic) / carbon black, as described in US Pat. No. 5,914,294.

  It is also known to use a combination of a bed of particles and a monolith as described in US Pat. No. 6,540,815. Such mixed canisters are actually available on the market. They generally include the reservoir side, a main canister comprising a bed of particles held by a perforated grid, and the atmosphere side, an auxiliary canister comprising a cellular monolith. The latter is usually fixed in a housing using gasket (s). This method of attachment has a major disadvantage: it does not make it possible to effectively use the entire volume of activated carbon honeycomb seen the partial closure of some of these channels and the improper exploitation of the outer surface thereof this. In addition, by its nature (generally solid elastomeric material), the seal does not participate in the adsorption function of the canister.

  The present invention therefore aims to provide an improved method of attachment for monolithic canister, which overcomes the aforementioned drawbacks in a simple manner.

  For this purpose, the present invention relates to a fuel tank canister comprising a housing and a monolithic honeycomb structure based on activated carbon, the monolithic structure being fixed in the housing by means of a fastening system comprising at least one foam. The use of a foam makes it possible to make maximum use of the surface and the pores of the honeycomb structure in contact therewith and, in so doing, not to disturb the adsorption of the vapors by the monolithic structure.

  The canister according to the invention is particularly intended for thermal engines powered with volatile liquid fuels and in particular, engines for motor vehicles (cars, trucks, motorcycles ...).

  The term "fuel" is intended to mean a liquid or gaseous volatile hydrocarbon suitable for supplying internal combustion engines. The canister according to the invention is particularly suitable for volatile liquid hydrocarbons. The expression "volatile liquid hydrocarbon" means a liquid hydrocarbon (which, under normal engine operating conditions, is in the liquid state in the fuel tank of the fuel system) which has a saturated vapor pressure greater than 1 bar at 293 K (20 C). Volatile liquid hydrocarbons commonly used for the supply of thermal engines of motor vehicles are those sold commercially under the name of gasoline and intended for thermal engines with instigated ignition, known as explosion.

  The canister according to the invention comprises at least one housing in which is fixed at least one monolithic alveolar structure, which constitutes the active element (adsorbent) of the canister. It is understood that the canister according to the invention may comprise several housings and that each of them may comprise several monolithic structures and / or a combination of monolithic (s) alveolar structure (s) (i.e. one-piece porous structures) and particle (s) (ie, particle beds). Note also that the housing of the canister according to the invention can be molded in one piece with the tank for which it is intended and / or with its filler neck. It can also integrate some of its accessories such as a liquid / vapor separator for example.

  According to a preferred variant of the present invention, the canister according to the invention is in fact an auxiliary canister, attached to a main canister comprising a bed of activated carbon particles. By main and auxiliary canisters are meant respectively a canister with a high adsorption capacity and a canister with a lower adsorption capacity. As described in the aforementioned US Pat. No. 6,540,815, the main canister is preferably located on the reservoir side (i.e. is near and in direct communication with it) and particularly preferably also in contact with the system. engine air intake (to allow the purge of the canister), while the auxiliary canister is located on the side of the venting (ventilation). For this purpose, monolithic structure and particulate bed (which constitute the active elements of the canisters) can be fixed in separate housings. Advantageously, they are fixed in one and the same housing. This may have been manufactured in one piece, or consist of several pieces manufactured separately and assembled.

  In the mixed canister according to this variant of the invention, the bed of particles can be fixed in its housing in any known manner; it can for example be based on a perforated grid (it being understood that the size of the perforations must be sufficient to let the evaporations to adsorb without too much loss of charge, but not too important not to let the particles pass), to be contained in a bag (bag) of permeability given ... A perforated plate placed on springs gives good results.

  The monolithic structure of the canister according to the invention is a honeycomb structure (porous) based on activated carbon which may be a foam or a honeycomb. By foam is meant an expanded structure with open or closed cells of substantially spherical shape. This foam may consist of a polymer loaded with carbon black and expanded. By honeycomb is meant a structure comprising open or closed cells having any cross section, generally circular or hexagonal, with substantially parallel walls from one cell to another.

  Honeycomb structures are particularly suitable in the context of the present invention and in particular those described in the aforementioned US patents.

  The monolithic structure can have any shape. Preferably, it is substantially cylindrical (ie of elongated shape with a substantially circular section) or parallelepipedic (idem, but with a square section). In the case of a honeycomb, the cells of the latter are generally placed with their walls parallel to the flow direction of the gases to be adsorbed. These cells can have any section (circular, square, triangular ...). Honeycombs with square or triangular cells are commercially available and give good results.

  The housing of the canister according to the invention can be made in one piece or in several assembled parts. It is preferably a material compatible with hydrocarbons that the canister is likely to treat. This material may be a plastic material or a metal. Thermoplastics give good results in the context of the invention, in particular because of the advantages of weight, mechanical and chemical resistance and easier implementation. Thermoplastic means any thermoplastic polymer, including thermoplastic elastomers, and mixtures thereof. The term "polymer" denotes both homopolymers and copolymers (especially binary or ternary). Examples of such copolymers are, but are not limited to: random copolymers, block copolymers, block copolymers and graft copolymers.

  Any type of thermoplastic polymer or copolymer whose melting point is below the decomposition temperature is suitable. Synthetic thermoplastics having a melting range spread over at least 10 degrees Celsius are particularly suitable. Examples of such materials are those having a polydispersion of their molecular weight.

  In particular, it is possible to use polyolefins, polyvinyl halides, thermoplastic polyesters, polyketones, polyamides and their copolymers. A mixture of polymers or copolymers may also be used, as well as a mixture of polymeric materials with inorganic, organic and / or natural fillers such as, for example, but not limited to: carbon, salts and other inorganic derivatives, natural fibers, glass fibers and polymeric fibers. It is also possible to use multilayer structures consisting of stacked and solid layers comprising at least one of the polymers or copolymers described above.

  Polyvinyl halides and polyolefins are generally preferred. A polymer often used is polyethylene. Excellent results have been obtained with high density polyethylene (HDPE or High Density Poly-Ethylene). In known manner, the impermeability of this plastic material to volatile hydrocarbons can be improved by surface treatment (fluorination, sulfonation, etc.) and / or by the use of a barrier layer (for example based on polyamide (PA) or of a vinyl alcohol polymer [homopolymer (PVOH) or ethylene-vinyl alcohol copolymer (EVOH)].

  According to the invention, the monolithic structure (active element of the canister) is fixed in its housing by means of a fastening system comprising at least one foam (as defined above). Preferably, it is predominantly even consisting essentially of one or more foams.

  By this is meant that it consists of more than 50% (by volume) and preferably at least 90% or 100% foam (s) to not close the cells of the monolith.

  This foam is advantageously charged with activated carbon so as to participate in the adsorption function of the canister. Such filled foams are commercially available and well known to those skilled in the art. The choice of the foam will be made according to its adsorption properties, the pressure losses that it generates and its mechanical properties. Preferably, it is a flexible, compressible foam. Similarly, the shape of the foam will be adapted to the attachment mode chosen, to prevent movement of the monolith in its housing.

  Preferably, the fastening system comprises at least two foams each located at one end of the monolithic structure, and of suitable shape to marry said ends. In particular when it is a cylindrical or parallelepiped canister, one can use 2 circular or square foams to wedge the ends of the monolith and block the axial movements. One can also alternatively use a foam located at least partly on the lateral surface of the monolithic structure, to block the radial movements. According to one variant, the foam on the lateral surface has the shape of a hollow cylinder in which the monolith is slid down. According to another variant, the foam on the lateral surface is in the form of a band wound around the monolith.

  The present invention also relates to a method for manufacturing a canister as described above. This method consists in fixing a monolithic structure based on active charcoal inside a housing using a fixing system comprising at least one foam loaded with activated charcoal. The foam and the monolithic structure can be secured before insertion into the casing (preferred solution for foams on the lateral surface (so-called lateral surfaces) for example), or first introduce the structure into the casing and come to wedge it with the foam (preferred solution for end foams (say end) for example).

  Preferably, the monolith is first secured with a side foam, the assembly is inserted into at least a portion of the housing and is wedged with at least one end foam.

  The present invention is illustrated in a nonlimiting manner in FIGS. 1 to 5. FIG. 1 illustrates a canister according to the prior art, while FIGS. 2 to 5 show some preferred variants of the canister according to the present invention. In these figures, identical numbers designate identical elements.

  FIG. 1 represents a canister according to the prior art, of substantially cylindrical shape, in which a honeycomb monolith based on activated carbon (1) is fixed in a housing (2) by means of a simple joint circular sealing (3). This method of attachment does not make optimal use of the entire volume of the honeycomb. Indeed, not only the hatched area but also the entire outer surface of the honeycomb are not directly accessible for the hydrocarbon vapors because the entrances of the channels are blocked by the seal. These areas are reached only by diffusion through the porosity of the coal, which implies a very poor hydrocarbon charge and a very poor purge.

  In the canister according to the invention shown in FIG. 2, the monolith fixing system comprises a first pair of activated carbon foams (4) to prevent radial movements and a pair of foams with low pressure drop (5). ) to prevent longitudinal movements and ensure a good flow distribution over the entire section of the housing (2). It consists of two separate pieces of plastic assembled by a sealing device (2 '). The zone (6) between the two first zones of activated carbon laden foam (4) is filled with air.

  The use of foams (4) (5) as a permeable fastening system allows the vapors to be in contact with the outer surface of the monolith. Moreover, this foam is loaded with active carbon and also contributes to the adsorption of hydrocarbon vapors. The use of foam with low pressure drop to prevent axial movements contributes to the homogenization of the flow distribution over the entire section and eliminates the less accessible area of the honeycomb.

  In the variant of FIG. 2, the foams (5) are in the form of disks whereas the foams (4) can be in several different forms, of which two preferred variants are illustrated in FIGS. 3 and 4.

  In these Figures 3 and 4, there are two sections (one in a plane passing through the axis of the canister and one in a plane perpendicular to this axis) in a canister according to each of these variants. In the variant of Figure 3, the foam loaded with active carbon (4) has the shape of a hollow cylinder in which is slid the monolith (1). In the variant of Figure 4, the foam (4) is in the form of a winding of a band around the monolith (1).

  Finally, the canister of Figure 2 is shown in Figure 5 as an auxiliary canister (7) fixed in the same housing (2) as a main canister (8) containing activated carbon particles. According to this variant, the auxiliary canister (7) is connected to the atmosphere (9), while the main canister (8) is connected to the tank (10) and to the air intake system ( to be able to purge) on the other hand (11). The housing (2) comprises an outer enclosure and an inner wall (2 ') delimiting with the outer wall, a housing for the monolithic structure of the auxiliary canister (7) .Celle latter is fixed in said housing according to the variant shown in Figure 2.

Claims (9)

  1 - Canister for a fuel tank comprising a housing (2) and a monolithic honeycomb structure (1) based on activated carbon, the monolithic structure (1) being fixed in the housing (2) using a system of fastener comprising at least one foam (4, 5).   2 - Canister according to the preceding claim, characterized in that it constitutes an auxiliary canister (7), attached to a main canister (8) comprising a bed of activated carbon particles.   3 - Canister according to the preceding claim, characterized in that the main canister (8) is located on the side of the tank, while the auxiliary canister (7) is located on the side of the venting.   4 - Canister according to claim 2 or 3, characterized in that the monolithic structure (1) and the bed of particles are fixed in one and the same housing which is common to them.   5 - Canister according to any one of the preceding claims, characterized in that the monolithic structure (1) is a honeycomb structure.   6 - Canister according to any one of the preceding claims, characterized in that the housing (2) is based on high density polyethylene (HDPE or High Density Poly-Ethylene).   7 - Canister according to any one of the preceding claims, characterized in that the foam (4, 5) is charged with active charcoal.   8 - Canister according to any one of the preceding claims, characterized in that the fixing system comprises at least two foams (5) each located at one end of the monolithic structure (1).   9 - Canister according to any one of the preceding claims, characterized in that the fixing system comprises at least one foam (4) located at least partly on the lateral surface of the monolithic structure (1).   A method for manufacturing a canister according to any one of the preceding claims, wherein an activated charcoal-based monolithic honeycomb structure (1) is fixed in a housing (2) by means of a system. fixing device comprising at least one foam (4, 5).