EP3559422B1 - Pressure compensator in a bubble of liquid encased in ice - Google Patents

Description

The invention relates to the field of motor vehicles, and more specifically to reservoirs intended to contain a liquid liable to freeze under normal conditions of use of the vehicle. These elaborate tanks generally include a technical module, partly submerged, in which the pumping means are installed as well as the level or temperature measuring devices making it possible to manage the distribution of the liquid contained in the tank.

This is the case in particular with tanks containing urea, and which are the subject of current use for supplying the vehicle's exhaust gas pollution control system. This liquid begins to freeze when the temperature drops below -11 ° C.

For this purpose, heating means are provided in the reservoir to prevent urea freezing.

However, these means are deactivated when the vehicle is stopped after a period of driving and, when the vehicle is parked outside in severe external winter conditions, which may for example reach temperatures of the order of - 40 ° C, the transformation into ice of the urea contained in the tank begins and can lead to the freezing of all the urea in a few tens of minutes.

Under these rapid freezing conditions, degradation of the technical module was observed, which had remained unexplained for a long time, and which could lead to the total destruction of the technical module or the organs it contains.

Laboratory analyzes made it possible to highlight the physical phenomena occurring during this period.

A closed tank equipped with a technical module and containing a certain volume of urea was placed in a cold chamber maintained at a temperature of the order of -40 ° C. The technical module is completely immersed in the volume of liquid. This volume of liquid is surmounted by a gaseous portion remaining throughout the experiment at atmospheric pressure. Likewise, certain components of the technical module such as the pump or the level floats are also at atmospheric pressure.

It is observed that the ice begins to form near the walls of the reservoir through which the heat exchanges take place. The growth of the volume of ice then takes place by progressing towards the central region of the reservoir occupied by the technical module. After a given time, the surface of the liquid in turn freezes.

We then observe the creation of a liquid bubble trapped on all sides by frozen material and in which the upper part of the technical module is immersed.

Further observation makes it possible to demonstrate that the pressure prevailing inside this liquid bubble entirely surrounded by ice can then reach very high values, of the order of several tens of bars.

This phenomenon is linked to the fact that the compressibility of the liquid forming the bubble is low and that, the formation of ice continuing, the increase in volume linked to this transition subjects the liquid bubble to rapidly progressing pressures.

The result is that the members of the technical module remaining at atmospheric pressure undergo mechanical stresses much greater than the resistance of the materials which constitute them, which deform until they break.

By continuing the experiment, the liquid bubble is gradually reabsorbed until all of the liquid previously contained in the tank is transformed into ice.

To resolve this known issue, the publication EP2829699 provides for a deformable cavity under the exertion of pressure, connected to an exhaust in communication with the outside atmosphere. The volume expansion linked to the formation of ice is then compensated by the reduction in the volume of the deformable cavity. Similar embodiments are also described in the publications. DE102009029375 , DE102006050808 , or DE102015204621 also provide deformable elements to absorb the variation in the volume of ice. These devices require suitable means to maintain the compressible bubble in the submerged volume. In addition, these flexible membranes operating at low temperature have reduced mechanical characteristics and reduced lifetimes.

The publication DE102008054629 provides for a fixed conduit penetrating into the liquid bubble and through which the pressurized liquid can rise to the surface. To prevent the liquid from freezing inside the conduit, it is then necessary to provide special insulation or heating means.

The object of the reservoir comprising a pressure compensation device according to the invention is to provide an original solution making it possible to overcome the problems mentioned above and to control this phenomenon of overpressure in the liquid bubble completely enclosed in a volume of ice. in formation surmounted by a volume of gas and contained in a tank closed by walls, in order to avoid degradation of the components of the technical module immersed in the liquid contained in the tank.

This reservoir, closed by walls, therefore comprises a pressure compensator for regulating the pressure in a liquid bubble entirely trapped in a volume of ice being formed topped by a volume of gas.

The pressure compensator comprises a plunger, movable along a vertical axis, formed of a head surmounting a body, and the faces of the plunger's body have a positive or zero clearance in a vertical direction and oriented from top to bottom, a height body of the diver being adjusted so that a lower part of the body remains submerged in the bubble of liquid, and so that an upper part of the body passes through the upper layer of ice and remains in the volume of gas so that when the The diver rises under the action of the pressure prevailing in the liquid bubble and acting on the part of the diver's body remaining immersed in the liquid, an additional volume is created within the space occupied by the liquid bubble and helps to reduce the pressure in this space.

When the compensator is placed in the tank so that the body of the diver is disposed substantially above the technical module and plunges into the liquid bubble surrounding said module, the rise of the diver under the effect of the pressure prevailing in the bubble of liquid, will make it possible to release an additional volume within the space occupied by the bubble and help reduce the pressure in this space.

In addition, by carefully choosing the draft angle, a space is created during the ascent of the diver between the diver and the ice which trapped the latter, allowing the liquid contained in the bubble to escape towards the frozen surface. forming the interface between the block of ice and the volume of gas generally placed at atmospheric pressure. The pressure in the liquid bubble drops again and the diver's body drops back down to come into contact with the ice. These little reciprocating movements continue until the entire liquid bubble turns to ice.

The combination of the two mechanisms described above makes it possible to reduce the negative effects of overpressure on the components of the technical module and protects the latter from any deterioration liable to put these devices out of use.

The explanations serving as a support for the present description relate to a reservoir containing urea, but it goes without saying that the reservoir can contain any kind of liquid passing into solid phase under temperature conditions likely to be observed during use. current of said reservoir. A reservoir containing water, or water mixed with an alcohol such as a reservoir containing window cleaning fluid, may usefully include a pressure compensator as described above. to avoid degradation of the components contained in the technical module mounted in said tank.

• L'angle de dépouille du corps du plongeur est compris entre 2° et 15° de sorte que, lorsque le plongeur remonte, un espace entre la glace et la surface du corps du plongeur se forme et permet au liquide contenu dans la bulle de s'échapper.
• Le corps du plongeur a une forme sensiblement tronconique.
• Le corps du plongeur est substantiellement incompressible.
• Le corps du plongeur est en polyoxyméthylène.
• La tête du plongeur circule selon la direction verticale entre une limite haute et une limite basse, dans un cylindre creux fixé à une paroi supérieure du réservoir.
• Le cylindre creux comprend un évent.
• Un dispositif exerce sur la tête du plongeur une force constante prédéterminée dirigée du haut vers le bas.
• Le dispositif exerçant sur la tête du plongeur une force constante prédéterminée dirigée du haut vers le bas est formé par un ressort disposé dans le cylindre creux et interposé entre la tête du plongeur et la paroi supérieure du réservoir.
• La tête et le corps du plongeur forment un corps creux fermé en partie supérieure par une membrane hydrophobe.
• La tête et le corps du plongeur forment un corps creux rempli d'une mousse à cellules fermées.
• Un module technique immergé, installé verticalement au-dessous du compensateur de pression.

The tank equipped with a pressure compensator according to the invention can also comprise, separately or in combination, the following characteristics:

• The diver's body rake angle is between 2 ° and 15 ° so that as the diver ascends, a space between the ice and the surface of the diver's body is formed and allows the liquid in the bubble to s 'escape.
• The diver's body has a substantially frustoconical shape.
• The diver's body is substantially incompressible.
• The body of the diver is made of polyoxymethylene.
• The plunger's head circulates in the vertical direction between an upper limit and a lower limit, in a hollow cylinder fixed to an upper wall of the tank.
• The hollow cylinder includes a vent.
• A device exerts a predetermined constant force on the head of the diver directed from the top to the bottom.
• The device exerting a predetermined constant force on the head of the diver directed from the top to the bottom is formed by a spring arranged in the hollow cylinder and interposed between the head of the plunger and the upper wall of the reservoir.
• The diver's head and body form a hollow body closed at the top by a hydrophobic membrane.
• The diver's head and body form a hollow body filled with closed cell foam.
• A submerged technical module, installed vertically below the pressure compensator.

• La figure 1 représente une vue en coupe d'un réservoir dans lequel est implanté un compensateur de pression selon l'invention.
• La figure 2 est une vue de détail du compensateur de la figure 1.
• La figure 3 illustre la situation dans laquelle le compensateur se soulève et laisse échapper une partie du liquide contenu dans la bulle de liquide.
• La figure 4 illustre une forme alternative de réalisation du compensateur de pression.

The invention will be better understood on reading the appended figures, which are provided by way of examples and are in no way limiting, in which:

• The figure 1 shows a sectional view of a reservoir in which a pressure compensator according to the invention is installed.
• The figure 2 is a detail view of the compensator of the figure 1 .
• The figure 3 illustrates the situation in which the compensator lifts up and lets out part of the liquid contained in the liquid bubble.
• The figure 4 illustrates an alternative embodiment of the pressure.

The figure 1 schematically shows a reservoir 1, closed by an upper wall 10, a lower wall 11 and side walls 12. A filler pipe 13 makes it possible to fill the reservoir.

A technical module 2 is installed on the wall 11 forming the bottom of the tank 1. This technical module crosses the bottom of the tank to allow the components contained in the module to be connected to an electrical power source, to the control and command modules. or again to the liquid outlet ducts leading to the exhaust gas depollution system and placed at atmospheric pressure outside the tank. The other secondary components such as the vents and the heating means are not shown.

The reservoir contains a liquid in the process of freezing and comprising a volume in solid phase G and a volume still in liquid form L, and forming a liquid bubble, delimited by the dotted line, entirely trapped in the volume of ice G.

The level N symbolizes the line of separation between the upper part of the tank filled with gas V and the block of ice G. This level N substantially corresponds to the level of the liquid contained in the tank before the latter begins to freeze. The gaseous part V of the reservoir is at atmospheric pressure, and the gas contained in this part is formed from a mixture of liquid in vapor phase and air.

The pressure compensator 3 is arranged vertically above the technical module 2 so as to protect the latter from the harmful effects which a liquid bubble L forming in this zone could produce. It will be observed here that the liquid bubble L can extend into other areas of the reservoir in which the effects of the overpressure are of no consequence.

The pressure compensator comprises a plunger 30 formed of a head 300 surmounting a body 301. The body of the plunger, 301 visible in detail at figure 2 , has here the shape of a truncated cone of vertical axis.

This frustoconical shape is particularly well suited for the surface of the body 301 of the plunger 30 to have a positive relief with a vertical axis in a direction going from top to bottom. In other words, this means that the body 301 of the plunger 30 can be extracted upwards from the ice which surrounds it without being prevented by a particular relief forming an undercut. This requirement indicates that that no surface of the diver's body, or in other words no plane tangent to the surface of the diver's body, is strictly parallel or forms a negative angle with the vertical. Also the body of the diver can have shapes as varied as for example the shape of an inverted pyramid truncated at its top.

In the present case, the frustoconical shape makes a constant positive draft angle α with the vertical direction. This angle could be equal to zero but it will then be observed that the radial stresses exerted by the ice on the surface of the diver's body and the frictional forces exerted between the wall of the diver's body and the ice can prevent the diver from rising. . It is therefore preferable to choose a clearance angle at least equal to 2 °.

It will be noted here that the greater the relief angle, the more the space created between the ice and the body of the diver increases, and the more easily the liquid present in the bubble can escape. An angle between 2 ° and 15 ° seems to be able to satisfy all the conditions of use. Too great a clearance angle would have the effect of unnecessarily increasing the size of the compensator. And too small a draft angle does not allow a space to be released for the liquid to escape.

Obviously, so that the pressure force generated on the body 301 of the plunger causes said plunger to rise, arrangements are made so that the body 301 of the plunger is substantially incompressible. The term “substantially” is understood here to mean the fact that any variation in volume linked to the pressure exerted on the body of the diver is not such as to modify the resultant of the forces allowing the diver to ascend.

The body of the plunger may be formed of a metal suitable for being immersed in the solution contained in the reservoir.

However, to reduce the frictional forces between the ice and the plunger as well as the erosion of the surface of the plunger 30, the plunger 30 can advantageously be made from a material such as polyoxymethylene. Thanks to its structure and high crystallinity, this material offers very good physical characteristics: a low coefficient of friction and very good abrasion resistance, high tensile and impact resistance, very good resistance to chemical agents , excellent dimensional stability, good resistance to creep and finally a wide temperature range of use.

The figure 3 makes it possible to visualize the movement during which the plunger 30 ascends and clears a space between the ice G and the surface of the plunger, thus allowing the liquid contained in the bubble L to escape.

The height h of the body 301 of the plunger 30 is adapted so that, when the pocket L of liquid appears during the freezing process, the lower part 303 of the body 301 is immersed in the liquid, the intermediate part 303 of the body being trapped in the volume G of ice surmounting the liquid bubble and the upper part 302 of the body of the diver remaining in the aerial part V of the reservoir.

This adaptation can be done by calculation by applying the laws of thermodynamics and heat exchanges between the walls of the tank and the liquid, or more simply by an experimental observation of the evolution of the freezing of the liquid contained in the tank. In practice, this amounts to positioning the lower part of the plunger 30 as close as possible to the center of the liquid bubble, the location of which is made by an experimental process.

The body 301 of the plunger 30 is surmounted by a head 300.

This head 300 slides in a substantially vertical direction in a hollow cylinder 31, the upper part of which is made integral with the upper wall 10 of the reservoir 1. The term “substantially vertical” is understood here to mean a direction forming an angle of +/- 15 ° and preferably of +/- 10 ° with vertical direction.

Advantageously, the hollow cylinder is formed from a thermoplastic material compatible with the material forming the walls of the tank to which it is welded. In practice, this hollow cylinder can advantageously be made of high density polyethylene (HDPE).

A vent 310 is positioned in the upper part of the hollow cylinder 31.

The stroke of the head 300 of the plunger is blocked downward by a collar 311 interacting with a shoulder 305 disposed on the head of the plunger 30. Likewise, the stroke of the plunger is limited upwards by the wall 11 of the reservoir, or by a high mechanical stop similar to the lower stop described above, or by the contiguous turns of the spring.

A spring 32 is interposed between the top of the head 300 and the wall 11. This spring exerts a constant force directed from the top downwards on the head 300 of the plunger 30.

By judiciously adapting the calibration of the spring, it is thus possible to control the threshold of the pressure prevailing in the liquid bubble L from which the plunger 30 will rise. Above this threshold, the plunger 30 rises and releases the pressure in the liquid bubble L, below this threshold the plunger 30 comes back to bear on the shoulder 305 or, in the case where the space in which the liquid would come to freeze itself, on the ice itself.

It will be observed here that the spring can be replaced by any kind of equivalent means allowing the plunger to be raised or lowered in a controlled manner. By way of example, and although it has the drawback of increasing the on-board mass, a weighted diver could also be suitable.

The walls of the head 300 and of the body 301 of the plunger 30 define an internal volume in which care should be taken that the liquid contained in the reservoir does not penetrate. For this purpose, it is useful to cover the upper part of the diver's head with a hydrophobic membrane 306 which does not allow liquid to pass, or else to fill this volume with a closed-cell foam.

The figure 4 illustrates an alternative embodiment of the invention, in which the head 300 of the plunger 30 comprises a reduction 307 forming an inclined support on which the spring 32 comes to rest. This reduction makes it possible to facilitate the downward flow of the liquid in the unwanted case where the latter enters through the vent 310.

NOMENCLATURE

• 1 Tank.
• 10 Upper wall of the tank.
• 11 Bottom wall of the tank.
• 12 Side wall of the tank.
• 13 Filler neck.
• 2 Technical module.
• 3 Pressure compensator.
• 30 Diver.
• 300 Head of the diver.
• 301 Body of the diver.
• 302 Upper aerial part of the diver's body.
• 303 Intermediate part of the diver's body crossing the upper layer of ice.
• 304 Lower part of the diver's body immersed in the liquid bubble.
• 305 Shoulder.
• 306 Hydrophobic membrane.
• 307 Reduction
• 31 Hollow cylinder.
• 310 Event.
• 311 Collar.
• 32 Spring.
• a Clearance angle.
• h Height of the diver's body.
• G Liquid transformed into ice.
• L Liquid bubble trapped in ice.
• V Aerial part above the ice.
• N Level of the ice surface forming the interface between the volume of liquid in solid phase G and the aerial part N.

Claims (12)

1. A reservoir (1) closed by walls (10, 11, 12) comprising a pressure compensator (3) to regulate the pressure in a bubble of liquid (L) entirely trapped in a volume of ice (G) being formed, topped by a volume of gas (V); characterized in that the pressure compensator (3) comprises a plunger (30), which is mobile along a vertical axis, formed by a head (300) topping a body (301), and in that the faces of the body (301) of the plunger (30) have a taper (a) that is positive or zero, in a direction which is vertical and oriented from the top downwards, with a height (h) of the body (301) of the plunger (30) being adjusted such that a lower part (304) of the body (301) remains immersed in the bubble of liquid (L), and such that an upper part (302) of the body (301) passes through the upper layer of ice, and remains in the volume of gas (V), so that, when the plunger (30) rises under the action of the pressure, prevailing in the bubble of liquid (L) and exerting on the part of the body (301) of the plunger, remaining immersed in the liquid (L), an additional volume is created within the space occupied by the bubble of liquid (L), and contributes towards reducing the pressure in this space.
2. Reservoir (1) according to claim 1, wherein the taper angle (a) of the body (301) of the plunger (30) is between 2° and 15°, so that, when the plunger rises, a space is formed between the ice (G) and the surface of the body (301) of the plunger, and allows the liquid contained in the bubble L to escape.
3. Reservoir (1) according to any of the preceding claims, wherein the body (301) of the plunger (30) has a substantially frustoconical form.
4. Reservoir (1) according to any of the preceding claims, wherein the body (301) of the plunger (30) is substantially non-compressible.
5. Reservoir (1) according to any of the preceding claims, wherein the body (301) of the plunger (30) is made of polyoxymethylene.
6. Reservoir (1) according to any of the preceding claims, wherein the head (300) of the plunger (30) circulates in the vertical direction, between a high limit and a low limit, in a hollow cylinder (31), which is secured on an upper wall (10) of the reservoir (1).
7. Reservoir (1) according to claim 6, wherein the hollow cylinder (31) comprises a vent (310).
8. Reservoir (1) according to any of the preceding claims, wherein a device (32) exerts a predetermined constant force directed from the top downwards on the head (300) of the plunger.
9. Reservoir (1) according to claim 8 in combination with claim 6, wherein the device which exerts a predetermined constant force directed from the top downwards on the head of the plunger is formed by a spring (32) which is disposed in the hollow cylinder (31), and is interposed between the head (300) of the plunger and the upper wall (10) of the reservoir (1).
10. Reservoir (1) according to any of the preceding claims 1 to 9, wherein the head (300) and the body (301) of the plunger (30) form a hollow body which is closed in the upper part by a hydrophobic membrane (306).
11. Reservoir (1) according to any of the preceding claims 1 to 9, wherein the head (300) and the body (301) of the plunger (30) form a hollow body filled with a closed-cell foam.
12. Reservoir (1) according to any of the preceding claims, comprising an immersed technical module (2), installed vertically below the pressure compensator (3).

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