GB2130733A

GB2130733A - Indicating electrically the level of a dielectric fluid

Info

Publication number: GB2130733A
Application number: GB08328513A
Authority: GB
Inventors: Constantino Broetto
Original assignee: Borletti SpA
Current assignee: Borletti SpA
Priority date: 1982-10-28
Filing date: 1983-10-25
Publication date: 1984-06-06
Also published as: ES275349U; FR2535454A1; SE8305770L; FR2535454B1; GB8328513D0; GB2130733B; IT8253867V0; ES275349Y; SE8305770D0

Abstract

A device (1) for indicating the level of a dielectric fluid in a tank consists of a float (14) with an electric contact (15, 16) which moves along a tubular slide (11) wound round with a resistive wire (13), the slide consisting of a metal tube (11) coated with a layer of polyamide material with a high molecular weight, the thickness of the said layer being much the same as or rather greater than the diameter of the said resistive wire (13). The ends of wire (13) can be secured by embedding them in the polyamide. The tube (11) can be coated with epoxy resin paint under the layer of polyamide. The position of the turns of wire (13) relative to tube (11) is said to be more stable, e.g. with temperature variations, than with prior devices. <IMAGE>

Description

SPECIFICATION Device for indicating the level of a dielectric fluid in a tank The present invention relates to a device for indicating the level of a dielectric fluid in a tank, in particular, the fuel level in a vehicle tank, the said device consisting of a float with a sliding contact which operates in conjunction with a resistive wire wound in the form of a solenoid round the float slide itself, the latter usually consisting of a tube through which the fuel is sucked up from the said tank.

On known indicators to which the present invention refers, the tube the resistive wire is wound round is made of either plastic or plasticcoated metal. This type of device poses a serious defect when subjected to very low operating temperatures, e.g. below -1 00C, in that, under such conditions, contraction on the plastic material is not compensated for by the same amount of contraction on the resistive wire.

Consequently, the turns on the wire are free to slide along the supporting element, with the result that accurate operation of the sliding contact on the float is totally impaired. Furthermore, when temperature is restored so as to secure the resistive wire back on to its supporting element, no guarantee exists that the position of the sliding contact on the resistive wire corresponds accurately with the fluid level in the tank, in that the mutual arrangement of the turns on the wire may no longer correspond with the original setting.

The aim of the present invention is to provide a device for indicating the level of a dielectric fluid in a tank of the type already described but which overcomes the aforementioned defect.

With this aim in view, the present invention relates to a device for indicating the level of a dielectric fluid in a tank, the said device consisting of a float with an electric contact, the said float being displaced by the thrust exerted by the said fluid, and a slide for the said float, the said slide having a resistive wire wound in the form of a solenoid round its outer surface along which the said electric contact slides during operation; characterised by the fact that the said slide consists of a metal tube coated with at least one layer of polyamide thermoplastic material with a heavy molecular wight the thickness of which is much the same as the diameter of the said resistive wire.A preferred arrangement of the present invention will now be described, by way of a non-limiting example, with reference to the attached drawings in which: Fig. 1 shows an elevated cross section of a level indicator according to the present invention; Fig. 2 shows a larger scale section along line Il-lI in Fig. 1.

Number 1 in Fig. 1 indicates a device for indicating the level of a dielectric fluid, in particular, fuel, in a tank (not shown), in particular, a vehicle tank. Of the said tank, the diagram actually shows part of a top panel (2) with a through hole (3) through which device 1 is inserted inside the said tank. The general features of device 1 are essentially known and consist of a flanged cover (4) resting on panel 2 of the said tank with seal 5 inbetween. Cover 4 is fitted with laminar electric terminals (6, 7, 8) and two ducts (9, 10), the first of which (9) acts as an intake duct for sucking up fuel from the tank, while the second (10) acts as a recirculating duct.Duct 9 is connected axially to tube 11 which, besides sucking up fluid from the tank, also acts as a support for resistive wire -13 wound in the form of a solenoid round practically the whole length of tube 11. The latter also acts as a slide for tubular float 14 which is fitted inside with a pair of diametrically opposed sliders (15, 16) end connected to annular component 17 which, via conducting wire 1 8 wound in the form of a cylindrical spring round tube 11, is connected to conducting laminar 7 on cover 4. The bottom end of tube 11 is fitted with an annular cap (20) with a through hole (21) and circular filter (22).

Between cap 20 and float 14, tube 11 is wound round with a spring (12) for balancing the weight of float 14 when it rests on cover 20. Finally, device 1 consists of a cylindrical tube (19), preferably made of metal sheet, which is forced into cover 4 for closing tube 11 inside with float 14.

According to the present invention, tube 11 is made of metal coated with two layers of insulating material (23, 24).

Layer 23 is about a few thousandths of a millimetre thick and is the one coming into direct contact with the outer surface of tube 11. The coating material requires a number of essential properties, i.e. it must provide for electric insulation, good high-temperature mechanical resistance and a good supporting base for layer 24. All these properties have been found to exist in epoxy resin paint.

Top layer 24, on the other hand, consists of a coat of polyamide with a heavy molecular weight, such as "RILSAN" (Registered Trade Mark of "polyamide 11"). The thickness of layer 24 is slightly greater than the diameter of resistive wire 13; e.g. if the diameter of the said wire is 0.2 mm, the thickness of layer 24 may, for example, be 0.3 mm. As the material used for layer 24 is thermoplastic with a high degree of elasticity, when being wound, resistive wire 13 is subjected to a preset amount of pull so as to form a furrow, indicated by 25 in Fig. 2, in coating 24 and so prevent any longitudinal displacement of the turns on wire 13. Furthermore, the thermoplastic properties of polyamide layer 24 can also be exploited for securing each end (26) of wire 13 to layer 24.In our case, the end of resistive wire 1 3 is secured by supplying the wire electrically so as to heat the end sufficiently to melt the corresponding area of polyamide and so fuse the said end 26 with layer 24.

Numerous tests have shown that device 1 is no longer affected by sharp changes in temperature.

Layer 24, in fact, is thin enough to adjust to any expansion on metal tube 11, caused by temperature change, which is essentialiy the same as expansion on resistive wire 1 3.

Consequently, the turns on resistive wire 13 are prevented from sliding longitudinally, thus providing for greater reliability of device 1.

The credit for this, however, also lies in the special material used for layer 24, i.e. polyamide 11, and its elastic properties (flexibility) and chemical characteristics (resistance to a wide range of acids and alkalis and all types of hydrocarbons). Finally, the thermoplastic properties of the said "polyamide 11' also provide for securing the opposite ends (26) of resistive wire 13 easily and quickly on to layer 24.

To those skilled in the art it will be clear that changes can be made to the device described by way of a non-limiting example without, however, departing from the scope of the present invention.

For example, layer 23 may be dispensed with, in that its main function is to prevent electric contact between the ends (26) of resistive wire 13 and metal tube 11. By way of an alterantive to layer 23, layer 24 could be made slightly thicker or a different system used for securing ends 26 on resistive wire 13.

Claims

1. Device for indicating the level of a dielectric fluid in a tank, the said device consisting of a float with an electric contact, the said float being displaced by the thrust exerted by the said fluid, and a slide for the said float, the said slide having a resistive wire wound in the form of a solenoid round its outer surface along which the said electric contact slides during operation; characterised by the fact that the said slide consists of a metal tube coated with at least one layer of polyamide thermoplastic material with a heavy molecular weight, the thickness of which is much the same as the diameter of the said resistive wire.

2. Device according to Claim 1, characterised by the fact that the said resistive wire is wound tightly round the surface of the said slide so as to produce a furrow on the surface of the said layer of polyamide material on account of the flexibility of the said layer.

3. Device according to Claim 1 or 2, characterised by the fact that the said layer of polyamide material is roughly a few tenths of a millimetre thick.

4. Device according to Claim 3, characterised by the fact that the diameter of the said resistive wire ranges from 0.1 to 0.3 mm.

5. Device according to any one of the previous Claims, characterised by the fact that the said polyamide material is resistant to hydrocarbons.

6. Device according to any one of the previous Claims, characterised by the fact that the said polyamide material is "polyamide 11" (Registered RILSAN Trade Mark).

7. Device according to any of the previous Claims, characterised by the fact that the opposite ends of resistive wire 1 3 are sunk into the said layer of thermoplastic material at opposite ends of the said metal tube (11).

8. Device according to any one of the previous Claims, characterised by the fact that a thin layer of grip material is coated between the said metal tube and the said layer of polyamide material.

9. device according to Claim 2, characterised by the fact that the said grip material is epoxy resin.

10. Device according to Claim 8 or 9, characterised by the fact that the said layer of grip material is roughly a few thousandths of a millimetre thick.

11. Device for indicating the level of a dielectric fluid in a tank, essentially as described and shown on the attached drawings.