FR2628526A1 - Potentiometer and electrical contact liquid level indicator - has metal contact fingers with plastic coating which expands on immersion in liquid - Google Patents

Abstract

The level indicator consists of a resistance element (11) and a multiple contact blade (12). The resistance element may be a printed circuit and is arranged as a potentiometer with multiple tappings (22). The ends of the resistance are connected to an external supply and measurement unit (30) via terminals 24) and connectors (18). The multiple contact blade encloses the resistance element (11) on both sides with contact fingers (14a) (14b) and each finger has an external coating of a plastic which will expand when immersed in the liquid whose level is to be determined. This expansion cuses the associated contact finger to bend and its tip (15) to touch one o the resistance contacts (22). The liquid level can then be found from a resistance measurement. USE/ADVANTAGE - In vehicle there is no mechanical linkage to cause jamming and little wear in operation.

Description

 The invention relates to an electrical contact device sensitive to the presence of a liquid and a level gauge using such a device, in particular a fuel level gauge of a motor vehicle.

 In motor vehicles, a certain number of levels of liquids in tanks are continuously measured and in particular the level in the fuel tank. This level is then displayed on an analog or digital dial in the driving position of the vehicle. The level measurement also serves to cause the lighting of a warning light to attract the driver's attention when the fuel level is very low.

 Conventionally. such gauges include an electric resistance element immersed in the liquid over a height variable with the level, a float comprising an electric contact element and a circuit for measuring an electric current passing through at least part of the resistance as well as means for displaying the level measurement. An electric current is circulated in the resistor, between the contact of the float and one of the ends of this resistor. so that the current depends on the position of the float and therefore on the level of liquid in the tank.

 Such devices, which are extremely conventional, however have drawbacks due to the fact that the float can become jammed during its movements and. have a certain porosity after a certain operating time. The indication of the display device no longer corresponds to the level in the tank.

 In addition, the practically continuous movement of the float tends to wear down the contact parts of the resistor and of the float itself.

 We therefore proposed level gauges no longer having a movable part such as a float.

For example, capacitive gauges have been proposed based on the dielectric effect of the fuel whose level is measured. However, such gauges do not give a satisfactory result when the composition or the temperature of the fuel varies.

 More generally, it may be necessary to have electrical contacts whose tripping occurs when they pass from an emerged state to a submerged state to vice versa. Such contacts can be used for example to trigger an alarm or a backup action, in the event of a significant drop in level in a tank, for example following a leak.

 The object of the invention is therefore to propose an electrical contact device with a blade, sensitive to the presence of a liquid comprising at least one flexible blade capable of moving by bending between a position of contact with a conductive element and a position out contact, this device being reliable, not very sensitive to wear and tear for long-term use and simple construction.

 For this purpose, the flexible blade is produced in the form of a bimetallic strip comprising a metal blade on one face of which is fixed a layer of thermosetting plastic material capable of undergoing swelling by absorption of liquid.

 The invention also relates to a device for measuring the level of a liquid in a tank, in particular a fuel level gauge of a motor vehicle comprising an electric resistance element immersed in the liquid over a variable height with the level, an electrical contact device sensitive to the level of the liquid and a circuit for measuring an electric current in at least part of the electrical resistance and for displaying the level, this device being of a safe, not very sensitive operation to wear and a simple and inexpensive realization.

 For this purpose, the electrical contact device is constituted by an elongated metal body forming a plurality of flexible blades of transverse direction spaced along the length of the metal body and covered on one of their faces by a blade of thermosetting plastic and an element to electrical resistance of elongated shape which has a plurality of contact zones between which the element has a determined electrical resistance, the electrical contact device being arranged along the length of the element with electrical resistance so that each of its blades has vis-à-vis a contact zone, a conductive part capable of moving relative to the contact zone, between a contact position and a non-contact position.

In order to clearly understand the invention, we will now describe, with reference to the appended figures, several embodiments of an electrical contact device with a blade and a fuel level gauge, according to the invention ,
FIGS. 1A and 15 are sectional views of an electrical contact device with a blade according to the invention, in its non-liquid configuration and in its configuration in liquid immersion, respectively.

 Figure 2 is a perspective view with cutaway of a fuel level gauge of a motor vehicle according to the invention.

 Figure 3A is a sectional view along 3-3 of Figure 2, showing contact elements of the gauge shown in Figure 2 in their emerged and submerged position, according to a first embodiment.

 Figure 38 shows, in a sectional view along 3-3 of Figure 2, contact elements in their emerged configuration and in their submerged configuration, according to a second embodiment.

 FIG. 4 is a side view of an embodiment of the electric resistance element of the gauge shown in FIG. 2.

 FIGS. 1A and 18 show schematically an electrical contact device with a blade according to the invention. This device comprises a flexible and conductive strip 1 which is preferably constituted by a metal with high electrical conductivity such as copper. The metal strip 1 is embedded at one of its ends in a conductive part 2. The second end of the flexible strip is placed opposite a conductive element 3.

When brought into contact, as shown in FIG. 18, the electrical contact device according to the invention makes it possible to pass the current between the part 2 and the conductive element 3, by means of the conductive strip 1. The blade 1 is covered on part of its upper face by a blade 4 of thermosetting plastic material such as a polyester or polyepoxy resin. Other materials can be used such as thermoplastics (polyamides, polypropilene) depending on the liquid used (water, alcohol),
The plastic blade 4 is fixed to the metal blade 1 by gluing or by welding or can be constituted by a layer of plastic material deposited on the metal blade 1 by any process, The blades 1 and 4 superimposed and fixed on their whole contact surface constitute a bimetallic strip susceptible to bending deformation in the presence of liquid.

 The plastic blade 4 is susceptible to swelling by absorption of liquid, when it is immersed in a liquid such as a motor vehicle fuel.

 In the case where the bimetallic strip 1, 4 is immersed in a liquid such as an automobile fuel, it deforms by bending, to pass from the configuration shown in FIG. 1A to the configuration shown in FIG. 18, the metal blade 1 then undergoing no expansion.

 When the bimetallic strip is immersed, the metal blade 1 comes into contact with the conductive element 3, by bending, as shown in FIG. 18 and thus ensures the passage of current between the part 2 and the conductive element 3.

 When the bimetallic strip 1, 4 is again emerged, the blade 4 gradually regains its dimensions and its initial shape shown in FIG. 1A and the bimetallic strip returns to its upright position in which the conductive parts 2 and 3 are isolated from one of the other.

 A device as shown in FIGS. 1A and 1B can be used as a means of triggering an alarm or a backup action in the event that a liquid has to be kept in a reservoir at a certain level. The bimetallic strip 1, 4 can be placed at a level slightly lower than the reference level so as to ensure the closing of an electric circuit l'intermédiaire through the conductive elements 2 and 3. As soon as the level of the liquid drops in below the bimetallic strip, this resumes its straight shape and ensures the opening of the electrical circuit; the opening of the circuit can result in the triggering of an alarm such as the lighting of an indicator light.

 In Figure 2, there is shown a level gauge of a motor vehicle fuel tank generally designated by the reperde 6. This level gauge 6 uses a principle identical to that ensuring the operation of the electrical contact device shown in Figures 1A and 18.

 The gauge 6 comprises a tubular body 7 secured at its upper part to a head 8 which allows the gauge to be fixed on the fuel tank of a motor vehicle.

 The gauge 6 as a whole is produced in elongated form so as to occupy a substantial part of the height of the fuel tank, in the axial direction of the tubular body 7.

 Inside this tubular body 7, are mounted an electrical contact device 10 and an electric resistance element II, both of which are of elongated shape and arranged in the axial direction of the gauge.

 As can be seen in FIG. 2 and FIGS. 3A and 38, the electrical contact device 10 is constituted by a profiled element in the form of a jumper formed by a metal blade 12 folded along two edges 12a and 12b and having two faces 13a, 13b substantially parallel.

 Each of the faces 13a, 13b is cut to form successive blades 14 parallel to each other and spaced regularly along the length of the electrical contact device 10.

 Each of the blades 14 has an end portion 15 folded to form a rounded contact surface projecting towards the inside of the rider relative to the faces 13a and 13b and to the blades 14.

In the case of the embodiment shown in FIG. 3a, each of the blades 14 of the electrical contact device 10 is covered on its outer surface by a blade of thermosetting plastic 16 to form a bimetallic strip of the same type as the bimetallic strip shown on the Figures 1A and 16,
In FIG. 3A, the blade 14a corresponding to the face 13a of the contact device 10 has been shown in its configuration corresponding to the immersion of the part of the corresponding gauge. The plastic blade 16 undergoes swelling which causes a curvature of the blade 14 and bringing the end portion 15 into contact with the corresponding face of the electric resistance element 11. Conversely, the blade 14b corresponding to the face 13b of the contact device 10 has been represented in its configuration corresponding to the emerged state of the gauge. In this configuration, the plastic blade 16 is in an unexpanded state, the blade 14b which does not undergo bending is rectilinear and the end portion 15 of this blade is in an out of contact position relative to the element with electric resistance 11.

 In Figure 36, there is shown an alternative embodiment of the flexible blades 14'a and 14'b of the electrical contact device 10, plastic blades 1-6 'being coupled to the internal face of the metal blades 14'a and 14'b.

In the configuration of the flexible blade 14 ′ a corresponding to the emerged state of the device, the plastic blade 16 ′ does not undergo any swelling and the end 15 of the flexible metal blade 14 ′ a is in contact with the element of resistance there
On the contrary, in the configuration corresponding to the submerged state of the contact device, the plastic blade 16 has undergone swelling and causes the blade 14'b to bend, which moves its end contact part 15 'away from the resistance element there
As can be seen in FIG. 4, the element with electrical resistance 11 (or 11 ′) consists of a strip of insulating material on the faces of which an engraved electrical resistance 20 has been produced by screen printing. This resistance 20 is continuous but comprises successive sections 21 at the terminals of each of which are placed contact zones 22 produced by screen printing on the faces of the plate 11.

 As can be seen in FIG. 2, the electrical contact device 10 is fixed by rivets such as 19 on one of the lateral sides of the electric resistance element 11 which corresponds to the side closest to the contact zones 22 electrical resistance sections. The contact device 10 is fixed along the length of the electric resistance element 11, so that each of the blades 14 is disposed at a contact area 22, the end portion 15 of the corresponding blade 14 is located exactly opposite the contact zone 22.

 In the submerged state (in the case of the arrangement in FIG. 3A) or in the emerged state (in the case of FIG. 38), the end part 15 (or 15 ′) of the blades 14 comes into contact with the corresponding contact area 22.

The end points of the resistor 20 are connected by linear conductive traces 23 to connection zones 24 arranged at the upper end of the electric resistance element 11,
An additional contact area 25 is arranged below the lower section of the electrical resistance 20 and connected by a linear conductive trace 26 to a connection area 27 at the top of the electrical resistance element 11.

 At the level of the gauge head 8, a connector 17 comprising output terminals 18 is electrically connected to the connection zones 24 and 27 and to the electrical contact element 10. The output terminals 18 of the connector 17 of the gauge 6 are connected to the terminals of an electrical supply and measurement circuit represented schematically and designated by the reference 30.

 The circuit 30 makes it possible to supply the resistor 20 with direct current and to measure the current or the voltage between one of the end terminals of the resistor 20 and the electrical contactor 10.

 This current or voltage measurement between one of the end terminals of the resistor and the electrical contactor depends on the level of immersion of the gauge in the fuel. Indeed, in the case of the embodiment shown in FIG. 3A, the assembly of the blades 14 of the contact device 10 immersed in the fuel is in a position corresponding to that of the blade 14a, the end portion of which mite 15 came into contact with the corresponding contact area 22.

The submerged lower sections 21 of the resistor 20 are then short-circuited and the measurement current only flows in the sections 21 on the periorals emerged from the resistor 20. The intensity or the voltage of the current measured in the resistor are therefore representative the level of immersion of the gauge 6 and therefore the level of fuel in the tank of the motor vehicle,
In the case of the embodiment shown in FIG. 3a, the electrical resistance of the element 11 is minimal when the fuel tank is full and ma-ximal when the tank is empty. In addition, when the lower blade of the electrical contact device 10 has emerged and goes into a non-contact position relative to the alert contact zone 25, an alert indicator light lights up in the driver's position. vehicle.

 In the case of the embodiment shown in FIG. 38, the resistance inserted in the measurement circuit is maximum when the fuel tank is full and minimum when the fuel tank is empty, the ends of the blade assembly of the device 10 then being in contact with the corresponding zones 22.

 It therefore appears that the electrical contact devices according to the invention used for opening or closing an electrical alarm circuit or as elements of a level gauge of a liquid in a tank have a very safe operation which does not cause significant wear of the contact areas.

 In the case of a level gauge, in particular a fuel gauge in a motor vehicle tank, the use of floats liable to get caught or deteriorate is avoided.

The only moving parts of the device, namely the blades, experience displacements of very small amplitude, with a relatively low frequency.

 On the other hand, the gauge can have a very small footprint, its various elements can be easily miniaturized. In addition, the measurement is particularly stable, the gauge ensuring by its structure its own damping.

 The invention is not limited to the embodiments which have been described.

 This is how the electrical contact device can be produced not only by using a copper plate but also any other suitable element made of a conductive and perfectly elastic material.

 The structure of the supply and measurement circuit can be arbitrary and the level measurement displayed in any analog or digital form.

 The covering of the contact blades with thermosetting plastic can be carried out by any technique such as gluing, welding or hot or cold coating of a layer of material on the flexible metal blade.

 The element with electrical resistance can have any shape making it possible to produce contact zones between which the element of resistance allows the passage of current.

 In the case of a wafer where the resistance is produced by screen printing in an etched layer, the two faces of the wafer may be identical or, on the contrary, different.

 The gauge can be arranged substantially vertically in the container or in an inclined arrangement in order to get as close as possible to the line of least fluctuation during the level measurement. An inclined gauge also makes it possible to have an electrical resistance of greater length and therefore to obtain a more sensitive measurement.

 Although the invention applies preferentially to the measurement t for locating the level in the fuel tank of a motor vehicle, it can also be applied to other liquid level measurements or to triggering an alarm. me by presence or absence of liquid in a tank of any type.

Claims (8)

 1.- Electric blade contact device, sensitive to the presence of a liquid, comprising at least one flexible blade (1) capable of moving by bending between a position of contact with a conductive element (3) and a position out contact, ca characterized in that the flexible blade (1, 4) is produced in the form of a bimetallic strip comprising a metal blade (1) on one face of which is fixed a layer of thermosetting plastic material (4) capable of undergo swelling by absorption of liquid.  2.- Device. for measuring the level of a liquid in a tank, in particular a level gauge (6) for the fuel of a motor vehicle, comprising an electric resistance element (11) immersed in the liquid over a height variable with the level, a electric contact device (10) sensitive to the level of liquid and a circuit (30) for measuring an electric current in at least part of the resistance and for displaying the level, characterized in that the electric contact device (10) consists of an elongated metal body forming a plurality of flexible blades (14) of transverse direction, spaced along the length of the metal body and covered on one of their faces by a blade (16) of thermosetting plastic and that l the electric resistance element (11) of elongated shape has a plurality of contact zones (22) between which the element has a determined electric resistance, the electric contact device (10) being arranged along the length of the electric resistance element (11), so that each of its blades (14) has, opposite a contact zone (22) a conductive part (15) capable of being moving relative to the contact area (22) between a contact position and an off-contact position.  3.- Device according to claim 2, characterized by f, has that the element with electrical resistance (11) is produced in the form of a plate of insulating material on at least one of the faces of which is arranged an electrical resistance (20) occupying a substantial part of the length of the plate (11).  4.- Device according to claim 3, characterized in that the electrical resistance (20) is produced by screen printing on the insulating plate (11).  5.- Device according to any one of claims 3 and 4, characterized in that the dis-positive electrical contact (10) consists of a plate of conductive metal such as copper, folded in the form of a jumper for form two faces (13a, 13b) and cut to form successive flexible blades (14) on each of its faces, the device (10) being fixed along an edge of the plate (11) so that its faces 613a, 13b ) are located on either side of this plate, each of the blades (14) having an end portion (15) projecting inwardly relative to the corresponding face (13a, 13b).  6.- Device according to claim 5, characterized in that each of the blades (14) is covered, on its outer side, by the blade of thermosetting plastic (16).  7.- Device according to claim 5, characterized in that each of the blades (14'a, 14 'b) is covered on its inner side by the blade of thermosetting plastic (16').  8.- Fuel level gauge in the tank of a motor vehicle according to claim 2, characterized in that the electrical contact device (10) and the electrical resistance element (11) are arranged in an inclined manner by compared to the vertical.