FR2707004A1 - Device for measuring the level of a liquid, in particlar oil, with a resistive probe - Google Patents

Abstract

The present invention relates to a method of manufacture of a device for measuring the level of a liquid, which comprises the steps consisting in placing two elongate supports (200) made of an electrically conductive material in a generally coplanar and aligned arrangement, welding the ends (302, 304) of a resistive metallic element (300) onto the supports (200), pivoting the supports (200) on an articulation part (250) made of an electrically insulating material, in order to bring the supports into a parallel arrangement, the articulation part (250) being used to tension a loop (314) formed on the metallic element (300), and arranging the assembly (200, 300) thus formed in a casing (100). The invention also relates to the devices thus obtained.

Description

 The present invention relates to the field of controlling the level of liquid contained in a reservoir.

 It applies in particular, but not exclusively, to the control of the oil level in the engine, on board vehicles fitted with an internal combustion engine.

 Even more precisely, the present invention relates to improvements to the device described in document FR-A-2367276 in the name of the Applicant.

 There has been described in this document FR-A-2367276, a measuring device comprising a probe formed by a resistive metallic element with a high temperature coefficient, intended to be immersed in the liquid of a reservoir, a current supply element. of the probe, and means making it possible to compare the initial voltage Uo at the terminals of the probe, with the voltage Ut present at the terminals thereof after a time t, for which the probe has practically reached its state of stability thermal. By initial voltage Uo is meant the voltage present at the terminals of the probe at the instant to put the supply device into operation. It is known in fact that a resistive metallic element having a positive temperature coefficient sees its own resistance increase as a function of its temperature, the latter depending on the thermal mass of the wire, the energy supplied and the heat exchanges. Thus when such a resistive element is immersed in a liquid, the variation of its resistance between instants to and t depends on the level of liquid in which it is immersed since the part of the resistive element located above the liquid and therefore exposed to air, is much less cooled than the submerged part.

 When the liquid level in which the resistive element is immersed increases, the heating of said element decreases, the same is true of its resistance.

 Of course the opposite phenomenon occurs for a decrease in the level of liquid in which the resistive element is immersed.

 Therefore, the difference between the initial voltage Uo at the terminals of the probe and the voltage Ut at the terminals of the latter at time t, is directly representative of the level of liquid in which the probe is immersed.

Improvements to the measurement device of document FR-A-2367276 have been described in the documents
FR-A-2573866, FR-A-2485726 and FR-A-2674953.

The Applicant has marketed numerous measurement devices of the type described in the document FR
A-2367276.

 The devices thus marketed include a probe formed by an elongated support which carries the resistive metallic element with a high temperature coefficient and two connection pieces connected to the ends of the metallic element. These devices further comprise a connector cap, connected to the support, and on which is fixed a ring provided with a thread to allow the probe to be fixed on the casing of the tank to be checked, for example on the casing of a motor to internal combustion.

 The present invention now aims to improve the known liquid level measuring devices with resistive probe.

 In particular, the present invention aims to facilitate the installation of the resistive element on the probe.

 In the context of the present invention, this object is achieved by a method of manufacturing a device for measuring the level of liquid, in particular oil, with a resistive probe, comprising the steps which consist in - placing in a relative arrangement controlled, generally coplanar and aligned, two elongated supports made of electrically conductive material, - weld the respective ends of a resistive metal element with a high temperature coefficient, on the supports, - rotate the two supports on an articulation piece of material electrically insulating, placed between the adjacent ends of the supports, to bring them in a generally parallel arrangement, the articulation piece then serving as a tensioner to a loop formed on the metal element during the pivoting of the supports, and - arrange the assembly thus formed in a housing.

 The present invention also relates to the measurement devices thus obtained comprising two elongated supports made of electrically conductive material on which are welded the respective ends of a resistive metallic element, the supports being articulated on a hinge piece of electrically insulating material placed between first ends of the supports, which articulation piece serves as a tensioner for a loop formed on the metal element.

 Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the appended drawings given by way of nonlimiting example and in which - FIG. 1 represents a sectional view axial longitudinal view of a device according to the present invention, according to the sectional plane referenced II in FIG. 2, - FIG. 2 represents a second view in longitudinal axial section of the same device according to a sectional plane orthogonal to that of FIG. 1 and referenced II-II in this FIG. 1, - FIG. 3 represents an end view of the same device, - FIGS. 4 and 5 represent two cross-sectional views of the same device according to the cutting planes referenced IV-IV and VV in FIG. 2, FIG. 6 represents a view in general coplanar and aligned position of two elongated supports equipped with a resistive metallic element with temperature coefficient high erection and mounted on an intermediate articulation piece, before pivoting of the supports for engagement in a housing, - Figure 7 shows a schematic side view of the same supports and illustrates more precisely the step of pivoting of these supports on the hinge part, - Figure 8 shows a first front view of a support according to the present invention, - Figure 9 shows another view of the same support according to the invention in a view orthogonal to that of Figure 8, - Figures 10, 11 and 12 show three cross-sectional views of the same support according to the sectional planes referenced XX, XI-XI and XII-XII in Figure 9, - Figure 13 shows a top view of a hinge part according to the present invention and - Figures 14 and 15 show two orthogonal sectional views between them of the same hinge part, according to the sectional planes referenced XIV-XIV and XV- XV in Figure 13.

 The probe according to the present invention shown in the appended figures essentially comprises a housing 100, two supports 200 and a resistive metal element with a high temperature coefficient 300.

 The housing 100 can be the subject of numerous variant embodiments.

 Preferably, the housing 100 comprises a cap 110 mounted on an elongated cylindrical barrel 150.

 The barrel 150 is adapted to accommodate the two supports 200 and the metal element 300. If necessary, the barrel 150 can be formed of a complete cylinder, for example a molded plastic cylinder.

 Preferably, however, as shown in the appended figures, the elongated cylindrical barrel 150 is formed by two complementary semi-cylindrical shells 152, 154, defining in combination an internal chamber 156 capable of receiving and immobilizing the two supports 200 equipped with the metallic element. 300.

 The two shells 152, 154 can be assembled by any suitable known means, such as for example gluing, ultrasonic welding or the like.

However, preferably, as can be seen in particular in FIG. 5 as well as on the right of FIGS. 1 and 2, the two shells 152, 154 are adapted to be fixed to one another by snap-fastening.

 In a manner known per se, the barrel 150, and therefore the two shells 152, 154 are provided with through passages 151. These passages 151 are provided to allow the liquid whose level must be controlled to enter the chamber 156 and thus bathe the resistive metal element 300.

 The cap 110 is formed, according to the preferred embodiment shown in the appended figures, of the assembly of a connector 120 and a fixing ring 130.

 The connector 120 is formed of a body, generally of revolution around the axis 102 of the device. The connector 120 is advantageously formed on the basis of plastic and molded onto two connection blades 122, 124. The connection blades 122, 124 emerge on either side of the connector 120, that is to say, d on the one hand in a connector chamber 126 which opens axially on the end of the connector 120, on the other hand on the end of this connector 120 placed opposite the internal chamber 156 of the barrel 150.

 The ring 130 is preferably formed of a metal ring crimped on the one hand at four points referenced 132 on the barrel 150, and crimped on the other hand on a rib 128 of the connector 120 at a flange referenced 134, with interposition of an O-ring seal 133.

 The ring 130 preferably comprises a threaded part 135 and a part 136 of straight section not of revolution, typically hexagonal, making it possible to fix the measurement probe in a tapped bore of the tank casing to be checked, typically the casing of a motor of internal combustion.

 Preferably, in the context of the invention, the two supports 200 are identical. They are formed by simple machining operations of the cutting, stamping and folding type, in a metal strip, for example a brass strip or any equivalent electrically conductive material.

 To make the description easier, the device will be called the "proximal end" of the device, the end of the probe placed towards the top of the tank casing to be checked, corresponding to the cap 110, and the "distal end" of the probe will be called end of the latter most internal to the tank to be checked, after installation.

 As can be seen in the appended figures, in particular Figures 6 to 12, according to the invention the supports 200 are each formed by an elongated blade which is generally flat and straight. Each blade 200 comprises over its length a tab 210, cut in its width then folded substantially to 900.

 The tabs 210 formed respectively on each of the supports 200 serve as supports at the ends of the resistive element 300. As can be seen in particular in FIG. 11, preferably the tab 210 is provided with two notches 211, 212, respectively in its edges perpendicular to its connection zone 213 with the blade 200. These notches 211, 212 are intended to improve the retention of the metal element 300 on said tabs 210 by winding. More specifically, as seen in particular in Figure 6 and as will be explained in more detail later, after winding on the legs 210 the ends of the metal element 300 are advantageously welded to these legs.

 Each blade 200 is further provided, at its proximal end 202 with curvature 220. These curvatures 220 are intended to ensure direct electrical contact between the supports 200 and the connection blades 122, 124 integrated into the cap 110, when this is crimped onto the barrel 150. According to the particular and nonlimiting embodiment shown in the appended figures, the bends 220 have the general shape of a Z.

 More precisely still, according to the preferred embodiment shown in the appended figures, there is provided at the proximal end 202 of each support 200, a pair of such bends 220 in Z.

 Finally, at its distal end 204, each blade is provided, at each of its longitudinal edges with two tabs 230, folded substantially at 900 and thus forming a joint yoke in pairs. These articulation yokes formed by the tongues 230 are adapted to ensure the pivoting of the supports 200 on a hinge part 250, the structure of which will be described later.

 Preferably, said tabs 230 protrude from the support 200, on the same main face 205 thereof as the tab 210 above.

 Furthermore, to guarantee self-maintenance of the supports 200 on the articulation piece 250, preferably the tongues 230 define housing for receiving pins 256 formed on the piece 250, with slightly convergent edges. Those skilled in the art will readily understand that the convergence of the edges of these housings makes it possible to trap the pins 256 once they have been introduced between the pairs of tongues 230, by elastic deformation of material.

 As can be seen in the appended figures, and in particular in FIG. 10, according to the invention the supports 200 are also preferably provided, at their distal end 204, with a longitudinal rectilinear stamp 240 centered on the width of the supports 200.

These stamps 240 are formed projecting from the main face 206 of the supports 200 opposite the tab 210 and the tongues 230.

 As can be seen in particular in FIG. 4, the purpose of these stampings 240 is to avoid any contact between the resistive metallic element 300 during its circumvention of the articulation part 300 and the distal ends 204 of the supports 200.

 The articulation piece 250 is made of electrically insulating material in order to electrically isolate between them the distal ends 204 of the supports 200.

 The articulation piece 250 is thus preferably produced by molding plastic material.

 Essentially, this articulation piece 250 is formed of a parallelepipedic body 252 with flat main faces, having two grooves 254 and provided with four pins 256. The grooves 254 have a cross section in V and are supported on a circular convex bottom. They extend on two opposite sides of the body 252, as seen in particular in FIG. 13.

These grooves 254 are intended to receive the metallic element 300.

 In use, these grooves 254 are centered on a diametrical plane of symmetry of the device passing through the axis 102 and which coincides with the cutting plane XIV-XIV.

The four pins 256 are intended to be engaged in the yokes formed by the tongues 230 provided on the distal ends 204 of the supports 200 as indicated above. The four journals 256 are coaxial two by two and disposed respectively on either side of the grooves 254. They have their axes perpendicular to the plane of symmetry XIV-XIV of the grooves 254. In use, the journals 256 have a double symmetry : with respect to two orthogonal diametrical planes between them passing through the longitudinal axis 102 of the device and which coincide respectively with the cutting planes XIV-XIV and XV-XV.

Furthermore preferably the part 250 is crossed by a central passage 258 centered on an axis formed by the intersection of the cutting planes XIV-XIV and XV
XV.

 The resistive metal element 300 can be formed from any conventional structure known to those skilled in the art.

It is preferably a wire, advantageously cylindrical, made of nickel-chromium.

 To assemble the measuring device according to the present invention composed of the parts described above, the procedure is essentially as follows a) - as shown in FIG. 6, the two elongated supports 200 made of electrically conductive material are placed in a relative controlled arrangement, generally coplanar and aligned; b) - the ends 302, 304 of the metal wire 300 are then wound and welded respectively on the tabs 210 formed on the supports 200. Preferably the wire 300 is wound by 1.5 turns on each tab 210. During this operation , care is taken to make an adjustment to the appropriate length of the measuring wire 300. Furthermore, as shown in FIG. 6, care is preferably taken to ensure winding of the ends 302, 304 of the wire 300 in the same direction on both legs 210 so that the outlets of these ends 302, 304 are reversed up / down on the supports 200. Thanks to this arrangement, the midpoint of the wire 300 placed in the groove 254 of the articulation piece 200 is located in a diametral plane of the measuring device and not point offset by a relation to such a plane. In addition, as can be seen in FIG. 6, care is preferably taken to make the welds 303, 305 of the wire 300 on the legs 210 in opposition to the outlets of the wire on the legs 210.

 The articulation piece 250 can be placed between the distal ends 204 of the supports 200 before fixing the measuring wire 300 to the supports 200, or only after this fixing.

 Preferably, the part 250 is not mounted on the supports 200, until after the wire 300 has been fixed on them.

Thus the wire 300 being placed on the inside of the supports 200, it is located on the outside of the part 250. Of course, during the fixing of the wire 300 on the supports 200 these must be immobilized in a position relative known with precision, to allow the wire 300 to be calibrated. Very advantageously during the fixing of the wire 300, the two supports 200 are supported by their distal ends 204.

c) - as shown diagrammatically in FIG. 7, the two supports 200 are then pivoted on the articulation piece 250, around the axes of the journals 256 to bring these supports 200 into a generally parallel arrangement, as shown in FIG. 2 It will be understood on examining the appended figures that in this arrangement the measuring wire 300 is in the form of two parallel rectilinear strands 310, 312 and a bypass segment 314. The two rectilinear strands 310, 312 extend between the articulation piece 250 and the fixing lugs 210. They are placed on the inside of the supports 200. The bypass segment 314 is placed on the outside of the articulation piece 250. It comprises a rectilinear central element 3140 resting against the outer planar main face 251 of the part 250 and two lateral elements 3141 and 3142 in the form of a quarter of a circle which rest against the bottom of the grooves 254 respectively.

 Thanks to the stampings 240, any risk of contact between the metallic element 300 and the supports 200 is avoided.

 Preferably the position of the yokes formed by the tongues 230 on the supports 200 on the one hand, and the position of the pins 256 formed on the articulation piece 250 on the other hand, are adapted so that the distance separating the points of fixing the ends 302, 304 of the resistive element 300 on the legs 210 is not modified during the pivoting of the supports 200 on the articulation piece 250. Thanks to this arrangement, the measuring wire 300 retains the same tension as that established during calibration when these ends 302, 304 are fixed to the tabs 210.

 To meet this condition, for example, according to a particular embodiment given by way of nonlimiting example, provide a center distance L3 (see FIG. 13) between the pins 256 equal to the length L1 (see FIGS. 13 and 14) of the main planar surface 251 separating the bottoms of the grooves 254, increased by sR, by calling R the radius of the bottom of the grooves 254; Furthermore, in the context of this embodiment, the axes 257 of the pins 256 are placed in a plane 259 of median symmetry of the articulation piece 250 perpendicular to the section planes XIV-XIV and XV-XV and passing through the axes of the bottoms of the grooves 254. The length L2 (see FIG. 7) of the two supports 200 projecting beyond the axes of the yokes 230 is equal to (L1 + sR) / 2, to allow the distal ends 204 of the supports 200 to be placed support when fixing the wire 300. Finally, the height of the legs 210, as well as the radius R are advantageously small compared to the length of the wire 300.

d) - the assembly thus obtained can then be engaged in chamber 156 of the barrel 150. Then the cap 110 is crimped at 132 on this barrel 150.

 Preferably, as can be seen in FIG. 2, a correction resistor 123 is welded between the connection blades 122, 124. This arrangement is known in itself and exploited on the probes marketed to date by the Applicant. This correction resistance 123 is chosen to correct the non-negligible and unavoidable dispersions observed on the resistive metallic elements based on nickel-chromium.

 According to the particular embodiment shown in the appended figures, the correction resistor 123 is thus fixed by welding inside the ring 130 on the connection blades 122, 124.

 The main advantage of the structure according to the present invention over known systems is to facilitate the installation and calibration of the metal element 300.

 It should also be noted that the present invention allows, by simple adaptation of the length of the barrel 150, and of the different sections making up the supports 200, to adapt the length of the probe, on the one hand to the required gauging height, d on the other hand at the height of the tank. With regard to the supports 200, the adjustable height is obtained by adapting the length of the section separating the distal end 204 and the fixing tab 210. The height of the reservoir is itself adjusted by adapting the length of the section separating the fixing tab 210 and the proximal end 202.

 Of course the present invention is not limited to the particular embodiment which has just been described but extends to any variant in accordance with its spirit.

Claims (17)

 1. A method of manufacturing a device for measuring the level of liquid in a tank, using a resistive metal element with a high temperature coefficient, characterized in that it comprises the steps consisting in - placing in a relative and controlled arrangement, generally coplanar and aligned, two elongated supports (200) made of electrically conductive material, - welding the respective ends (302, 304) of a resistive metallic element (300) with a high temperature coefficient on the supports ( 200), - rotate the two supports (200) on a hinge piece (250) of electrically insulating material, placed between the adjacent ends (204) of the supports (200), to bring the latter into a generally parallel arrangement , the articulation piece (250) then serving as a tensioner to a loop (314) formed on the metal element (300) during the pivoting of the supports (200), and - placing the assembly (20 0, 300) thus formed in a housing (100).  2. Method according to claim 1 characterized in that the two supports (200) are placed in abutment by their ends (204) during the welding of the metal element (300).  3. Device for measuring the level of a liquid contained in a reservoir, comprising a resistive metal element (300) with a high temperature coefficient, characterized in that it comprises two elongated supports (200) made of electrically conductive material, on which are welded the respective ends (302, 304) of the metal element (300), the supports (200) being articulated on a articulation piece (250) of electrically insulating material placed between respective ends (204) of the support (200), which articulation piece (250) serves as a tensioner for a loop (314) formed on the metallic element (300).  4. Device according to claim 3, characterized in that the supports (200) are produced by cutting, stamping and folding of a metal strip.  5. Device according to one of claims 3 or 4, characterized in that the two supports (200) are of identical structure.  6. Device according to one of claims 3 to 5, characterized in that each support (200) comprises a fixing lug (210) cut along its length and folded substantially to 900.  7. Device according to claim 6, characterized in that each fixing lug (210) is provided with two notches (211, 212), respectively on these edges orthogonal to its connection zone (213) on the supports (200) .  8. Device according to one of claims 6 or 7, characterized in that the ends (302, 304) of the resistive metal element (300) are fixed by winding and welding on the fixing lugs (210).  9. Device according to one of claims 3 to 8, characterized in that each support (200) is provided with a double yoke (230) on its distal end, for articulation on the articulation piece (250 ).  10. Device according to one of claims 3 to 9, characterized in that each support (200) is provided with a central rectilinear stamp (240) to avoid contact at this level with the resistive metal element (300) .  11. Device according to one of claims 3 to 10, characterized in that each support (200) is provided with elastic curvatures (220) at its proximal end, for establishing direct electrical contact with connection blades (122, 124) integrated in a cap (110).  12. Device according to one of claims 3 to 11, characterized in that the articulation part (250) is produced by plastic molding.  13. Device according to one of claims 3 to 12, characterized in that the articulation part (250) comprises at least one V-shaped groove (254).  14. Device according to one of claims 3 to 13, characterized in that the articulation piece (250) is provided with four pins (256) coaxial two by two serving to articulate the support (200).  15. Device according to claim 14, characterized in that the articulation piece (250) comprises on its flanks two V-shaped grooves (254) with circular convex bottom separated by a main surface (251) planar, the center distance between the pins (256) is equal to the length (it) of said main surface (251) separating the bottom of the grooves (254) increased by z times the radius (R) of the bottom of the grooves (254) and the axes of the pins ( 256) are placed in a plane passing through the axes of the bottoms of grooves (254).  16. Device according to Claim 15, characterized in that the length (L2) of the two supports (200) projecting beyond the axes of the yokes (230) provided thereon is equal to (L1 + aR) / 2, to allow the distal ends (204) of the supports (200) to be placed in support when the metal element (300) is fixed.  17. Device according to one of claims 3 to 16, characterized in that the housing (100) is formed by the assembly of a cap (110) on a cylindrical barrel (150) defining an internal chamber (156) able to accommodate the two supports (200) and the resistive metallic element (300).