FR2838804A1 - METHOD AND DEVICE FOR PRODUCING A PRESSURE SENSOR INTEGRATED IN A TANK - Google Patents

Abstract

Method for forming a piezoelectric pressure sensor integral with the internal aluminum wall (12) of a liquefied gas tank (10). Accordingly the superficial surface of the inner wall of the container is converted into corundum, by oxidation and then crystallization, and then an electrical connection is made to the corundum so that it forms one terminal of a voltmeter. The invention also relates to a corresponding device for method implementation with an electrode (42) and a current generator. The electrode rotates with respect to the tank around its axis (A). The gas tank is placed in a water trough (22) with a temperature regulator (36).

Description

"Method and device for producing a pressure sensor

  The invention relates to a method for producing a pressure sensor integrated in the wall of a tank for measuring the pressure of a fluid compressed in said tank which comprises at least one supply inlet and of which the inner wall is made of aluminum. Wile also concerns a

  device for implementing such a process.

  The invention relates more particularly to the integration, in the wall of a tank, of a pressure sensor of the piezoelectric type and more particularly piezo-ceramic which comprises a membrane of piezoelectric material, the one of the faces is exposed to the pressure to be measured and of which at least

  one face is connected to one of the terminals of a voltmeter.

  s This type of pressurized gas storage tank is used in particular in motor vehicles powered by: - an internal combustion engine powered by gas, natural or otherwise; - a fuel cell powered by hydrogen o stored in compressed form or manufactured in a reformer

  shipped, from natural gas stored in compressed form.

  These tanks, cylindrical in shape, may in particular comprise a metallic aluminum envelope and a reinforcement

  in composite material coil around the envelope.

  s The amount of fuel in the tank is generally estimated from a measurement of the gas pressure

in the tank.

  It is known, to measure the pressure of a compressed gas in a reservoir, to use sensors of the tube or manometric type, called the Bourdon tube. 11 is an oval cross-section hanger tube, a fixed end of which is subjected to

  gas pressure and the other free end of which is closed.

  As the pressure in the tube increases, the cross section is rounded and the tube straightens in proportion to the increase in pressure. The displacement of the free end of the tube thus makes it possible to measure the pressure in the reservoir. The risk of pressure surges, for example when filling the tank, requires the presence of a brake screw in

  stainless steel on the pressure gauge to filter the pressure pulsations.

  This piece represents an additional cost in the cost price of the pressure gauge. It is also known to measure the pressure of a gas o contained in a reservoir using a piezo resistive type sensor which includes a potentiometer whose resistance varies in proportion to the pressure applied to the piezo resistive sensor. The sensors of the two types described above are connected to gas pipes connected to the reservoir, in particular at the level of the supply neck, between the neck and a regulator, for example. Screw or welded type connections on the gas pipes can cause gas leaks if they are not made rigorously. This connection operation must be carried out by qualified operators, this

  which causes an additional cost in the price of the sensor.

  The sensors connected to the vehicle's gas pipes and in particular the wind-sensitive sensors sensitive to

  vibrations created when using the vehicle.

  In addition, the sensors of the types described above measure the pressure of the gas outside the tank, and in particular at the supply inlet. The measurement outside the tank has the disadvantage of not taking into account the pressure drops between the measurement point o and the inside of the tank. Fuel quantity estimation

in the reservoir is therefore false.

  In order to provide a solution to the problems described above, the invention provides a method for integrating into the

  internal wall of the tank a piezo type pressure sensor

  electric characterized in that it comprises: - a) a first stage of surface oxidation of a portion of the internal wall of aluminum into a layer of alumina by means of an oxidizing agent; and - b) a second stage of crystallization by fusion and cooling of the layer of alumina which is transformed into a layer of corundum which constitutes a membrane of piezoelectric material; and o - c) a third step of electrical connection of the internal face of the corundum layer, by a conducting element, to a terminal of a voltmeter, the second terminal of the

  voltmeter being electrically connected to ground (M).

  According to other characteristics: - the oxidizing agent used during the first oxidation step is an aqueous electrolytic liquid; - The second crystallization step includes a phase of melting the alumina layer which is brought to high temperature by heating means which produce arcs or electrics on the surface of the internal wall of the tank; and a solidification phase in which the molten alumina layer is cooled by contact with the aqueous electrolytic liquid; the temperature of the electrolytic aqueous liquid is regulated by means of regulating the temperature in such a way that it remains constant; - the process is applied substantially to the whole of the

inner wall of the tank.

  The invention also provides a device for implementing the method according to the invention which comprises: o Heating means which comprise an electrode of shape complementary to an axial half-profile of the internal wall of the reservoir, and a current generator thanks to which there is applied, between the electrode and the internal wall, a potential difference sufficient to create an electric arc which gives off the heat necessary for the melting of the alumina; means for rotating the electrode relative to the reservoir about its axis; and to a tank which contains an electrolytic type liquid and

  with sufficient wind dimensions to immerse the tank.

  According to other characteristics of the device: - the device comprises means for regulating the temperature of the liquid; o - the means for rotating the electrode relative to the wind reservoir, in particular consisting of a system of at least two rollers of axes parallel to the axis of the reservoir and on

which rests the tank.

  Other features and advantages of the invention

  will appear on reading the detailed description which follows, for

  the understanding of which reference will be made to the appended figures in which: FIG. 1 is a view in axial section of a reservoir illustrated in a production device during a first phase of the process according to the invention; - Figure 2 is a view similar to that of Figure 1, which shows the reservoir during a second step of the method according to ['invention; - Figure 3 is a cross-sectional view of the reservoir and the device shown in Figure 1; - Figure 4 is an axial section view showing the reservoir filled with pressurized gas and equipped with a sensor

  pressure according to the teachings of the invention.

  FIG. 1 shows a reservoir 10 which here has the form of a cylinder with a cross section of a horizontal axis. It is for example a tank intended to be loaded on board a motor vehicle. The interior volume of the reservoir 10 is delimited by an internal wall 12 made of aluminum. The reservoir 10 comprises a barrel 13 delimited by a front end 14 which comprises a feed neck 16, and by a closed rear end 18 which here constitutes the bottom of the

tank 10.

  The invention proposes a method for transforming the aluminum which constitutes the internal wall 12 of the reservoir 10 into corundum, then exploiting the piezoelectric properties in order to

  to indirectly measure the pressure inside the reservoir 10.

  Wile also offers a device 20 for the implementation

of such a process.

  o The device 20 comprises in particular a tank 22 filled with a bath 24 which is an aqueous liquid of the electrolyte type. The tank 22 is here a rectangular parallelepiped whose wind dimensions are sufficient to completely immerse the tank 10, as

  shown in Figure 1. The tray has a bottom 26.

  The surface of the liquid 24 contained in the tank 22, as shown in FIGS. 1 and 2, defines a horizontal plane H. The tank 22 comprises, in this embodiment, a motorized system of rollers 28, 30, 32 and 34 mounted at rotation relative to the bottom 26 of the tank 22. This system is intended to keep the axis A of the tank 10 horizontal and stationary relative to the tank 22, while allowing the tank to rotate around its axis A. The system comprises here four rollers 28, 30, 32 and 34 which wind arranged by padre according to two axial alignments B and C. The two alignments B. C wind parallel to the horizontal axis A of the reservoir 10 and wind arranged in a symmetrical direction from side and on the other said axis A. The two alignments B and C wind apart transversely so that the rollers 28, 30, 32, 34 constitute a cradle on which the barrel 13 of the reservoir 10 rests by gravity. At least one of the rollers 28, 30, 32, 34 has

  rotary drive means (not shown).

  The tank 22 also includes a system 36 for regulating the temperature of the bath 24 visible in FIG. 1, which here comprises a heating resistor 38 connected to a thermostat 40. As illustrated in FIG. 2, the device comprises an electrode 42 intended for be introduced into the reservoir 10 through the neck 16. The electrode 42 extends here in an axial plane of the reservoir 10 and has a homothetic shape of a half-profile

longitudinal axial of the reservoir 10.

  The device 20 includes a current generator 44

  to which wind connects the electrode 42 and the reservoir 10.

  o According to a variant of the invention, not shown, the current generator 44 includes a transformer connected to the sector as well as an energy regulation device.

electric.

  The method according to the teaching of the invention comprises three stages: a) a first stage of surface oxidation of the internal wall 12 of aluminum into a layer of alumina 46 by means of an oxidizing agent 24; and - b) a second stage of crystallization by fusion of o alumina constitute the layer of alumina 46 which is transformed into a layer of corundum 48 which constitutes the membrane of piezoelectric material; and c) a third step of connection of the internal wall 12 of the corundum layer 48, by a conducting wire 50, to a terminal of a voltmeter 42, a second terminal of the voltmeter 52 being electrically connected to the ground M. La first step according to the invention consists in oxidizing the internal wall 12 of the tank 10. In this embodiment, the tank 10 is immersed in the tank 22, as illustrated in FIG. o 1. The tank 10 is positioned on the rollers 28,, 32, 34. The aqueous liquid 24 penetrates inside the reservoir

through the supply neck 16.

  The aqueous liquid 24 thus oxidizes the aluminum constituting the internal wall 12. The result of this operation is the formation

  an alumina surface layer 46 forming an internal wall 12.

  FIG. 2 shows the reservoir 10 and the device 20 during the second step. The reservoir 10 is here immersed in the same tank 22 which contains the same bath 24 as during the

first stage.

  Before the start of the second stage, the electrode 42 is introduced into the interior of the reservoir 10 by the neck 16. The electrode o 42 is here immobilized relative to the tank 22 by means

  fixing (not shown). This operation is advantageous-

  sement performed before the first step of the process, that is to say before ['immersion of the reservoir 10 in the tank 22. It is thus possible to successively carry out the first two steps of the

  process, without intermediate manipulation of the reservoir 10.

  The electrode 42 and the internal wall 12 of the reservoir 10 are each connected to a terminal of the current generator 44. A potential difference is then applied by the current generator 44 between the electrode 42 and the internal wall 12 of the reservoir 10 This operation triggers the formation of electrical arcs 54 between the electrode 42 and a heating zone 56 of the wall.

  internal 12 which is located opposite the electrode 42, at this time.

  This phenomenon is advantageously facilitated by the character

electrolytic bath 24.

  The heat given off by the electric arcs 54 in contact with the internal wall 12 causes an increase in the temperature in the heating zone 56. The temperature in the heating zone 56 must be at least equal to the temperature or melting point of the alumina which is around 2050 C under normal atmospheric pressure. The alumina layer 46 located in the

  heating zone 56 is thus locally melted.

  During this operation, the rotary drive means confer on the reservoir 10 a rotational movement senestrorsum about its axis A by means of the system of rollers 28, 32 and 30, 34 which for this purpose are driven by a movement of dextrorsum rotation respectively around

axes B and C, according to Figure 3.

  s With the electrode 42 fixed, the internal wall 12 of the reservoir is progressively completely swept away by the heating zone 56. The speed of rotation of the reservoir 10 is sufficiently slow to allow the layer to merge

  alumina 46 during its passage through the heating zone 56.

  o The layer of molten alumina 46 is entrained outside the range of the heating zone 56 due to the rotation of the reservoir 10 around the axis A. Wile then solidifies in

  cooling in contact with liquid 24.

  The temperature of the liquid 24 is kept constant by the regulating means 36 so that the molten alumina solidifies so that it is homogeneous over the entire internal wall 12 under

form of corundum.

  When the reservoir 10 has generally carried out a complete revolution around the axis A, the internal wall 12 is entirely made up of a layer of corundum 48. Thanks to this process, the layer of corundum 48 is very adherent because it is formed from aluminum originally constitute the internal wall 12. In a variant not shown of this process, the reservoir 10 is kept stationary in the tank 22 and the electrode 42 comprises means for driving in rotation around

  the axis A of the reservoir fa, con a to sweep the internal wall 12 thereof.

  In a behind step, a wire 50 is put in place to connect the internal wall 12 of the corundum layer 48 o (advantageously to the neck 16 of the reservoir 10) to a terminal of the

voltmeter 52.

  The second terminal of the voltmeter 52 is connected to the ground M. The voltmeter 52 thus makes it possible to collect the pressure measurements inside the tank 10. The corundum layer 48, the wire 50 and the voltmeter 52 thus form a sensor of pressure 60. We now describe the operation of the pressure sensor 60 obtained by the method according to the teachings of the invention. FIG. 4 shows the reservoir 10 filled with compressed gas 58. The reservoir 10 is here fitted with the

pressure 60.

  The compressed gas 58 exerts a pressure on the internal wall 12 consisting of corundum. The corundum layer 48 is thus deformed in proportion to the pressure of the gas 58. The corundum having piezoelectric properties, the surface of the internal wall 12 is polarized, in particular at the point of contact between the wire 50 and the internal wall 12, in proportion to the

  deformation of the corundum layer 48.

  The voltmeter 52 measures the potential difference between the internal wall 12 and the mass M. The tension thus measured is proportional to the pressure exerted on the internal wall 12 of the

tank 10.

  o In another variant, not shown, it is advantageous, to avoid current leaks, to insert an amplifier with high input impedance near the point of

  contact between the wire 50 and the internal wall 12.

Claims (9)

  1. Method for producing a piezoelectric pressure sensor (60) integrated into the internal wall (12) of aluminum of a reservoir (10) capable of containing a compressed fluid (58) and comprising at least one inlet d 'feed (16), characterized in that it comprises: - a) a first step surface oxidation of a portion of the internal wall (12) of aluminum into an alumina layer (46) by means of a oxidizing agent (24); and o - b) a second stage of crystallization by fusion and cooling of the alumina layer (46) which transforms into a layer of corundum (48) which constitutes a membrane of piezoelectric material (48); and - c) a third step of electrical connection of the internal face (12) of the corundum layer (48), by a conductive element (50), to a terminal of a voltmeter (52), the second terminal of the voltmeter (52) being electrically connected to ground (M) 2. Method for producing a pressure sensor (60) according to the preceding claim, characterized in that the oxidizing agent (24) used during the first oxidation step is a electrolytic aqueous liquid (24).   3. Method for producing a pressure sensor (60)   according to one of claims 1 or 2, characterized in that the   second crystallization step comprises: - a phase of melting the alumina layer (46) which is brought to high temperature by heating means (20) which produce electric arcs (54) on the surface (56) of the inner wall (12) of the reservoir (10); and - a solidification phase in which the molten alumina layer (46) is cooled by contact with the liquid aqueous electrolytic (24).   4. Method for producing a pressure sensor (60) according to the preceding claim, characterized in that g) : 2838804   temperature of the electrolytic aqueous liquid (24) is regulated by means of temperature regulation (36) in such a way that that it remains constant.   5. Method for producing a pressure sensor (60)   according to any one of the preceding claims,   characterized in that it is applied substantially to the whole of the   internal wall (12) of the reservoir (10).   6. Device for covering the process according to the   Claims 1 to 5, characterized in that it comprises:   o - heating means which comprise an electrode (42) of shape complementary to an axial half-profile of the internal wall (12) of the reservoir (10), and a current generator (44) by which is applied, between the electrode (42) and the internal wall (12), a difference in potential sufficient to create an electric arc (54) which gives off the heat necessary for the melting of the alumina; - means for rotating (28, 30, 32, 34) the elec trode (42) relative to the reservoir (10) about its axis (A); and - a tank (22) which contains a liquid (24) of the electrolytic type and whose dimensions are sufficient for immerse the tank (10).   7. Device according to the preceding claim, characterized in that it comprises means for regulating the temperature (36) liquid (24).   8. Device according to claim 6, characterized in that the means for rotating (28, 30, 32, 34) of ['electrode (42) relative to the reservoir (10) wind including a system of at least two axis rollers (B. C) parallel to the axis   (A) of the reservoir (10) and on which the reservoir (10) rests.   n 9. Cylinder (10) of pressurized gas storage bottle (58) which is carried on board a vehicle, characterized in that it comprises a pressure sensor