TEMPERATURE SENSOR

Abstract

The invention relates to a temperature sensor comprising a thermocouple (7) defining a hot point (13), said temperature sensor comprising a mineral insulated cable (14) with an outer diameter greater than 2 mm and less than 5 mm and a reinforcement tube (60) from which projects the mineral insulated cable at the hot point end, so as to form a swaging.

Claims

1. A temperature sensor comprising: a thermocouple defining a hot point; a mineral insulated cable with an outer diameter greater than 2 mm and less than 5 mm; and a reinforcement tube from which projects the mineral insulated cable at the hot point end, so as to form a swaging.

2. The temperature sensor according to claim 1, wherein the outer diameter of the mineral insulated cable is less than 3.5 mm.

3. The temperature sensor according to claim 1, wherein the reinforcement tube covers more than 90% of the outer lateral surface of the protective sleeve of the mineral insulated cable.

4. The temperature sensor according to claim 1, wherein the reinforcement tube comprises a lateral wall with a thickness greater than or equal to 0.3 mm.

5. The temperature sensor according to claim 1, wherein the length of the part of the mineral insulated cable that projects beyond the reinforcement tube, at the hot point end, is greater that 5 mm.

6. The temperature sensor according to claim 1, wherein the protective sleeve has no swaging or comprises a swaging with an outer diameter greater than the inner diameter of the protective sleeve beyond the region of said swaging.

7. The temperature sensor according to claim 1, comprising a mechanical stop fixed on the reinforcement tube.

8. A method for the manufacture of a temperature sensor with a thermocouple according to claim 1, said method comprising the following, executed successively: manufacturing a mineral insulated cable comprising two thermocouple wires extending along the entire length of the cable and embedded in a mineral insulation, the mineral insulation being encircled by a protective sleeve, the outer diameter of the mineral insulated cable being less than 4 mm; extracting mineral insulation from one of the ends of the mineral insulated cable to a depth of between 2 and 7 mm so as to release the terminal parts of the thermocouple wires; connecting the terminal parts of the thermocouple wires thus released, to form a thermocouple hot point; protecting said hot point by encapsulation by the protective sleeve; and independently of the preceding steps, and after protecting the hot point by encapsulation, after protecting of the protective sleeve by a reinforcement tube, the reinforcement tube allowing said protective sleeve to pass beyond said protection sleeve at said hot point end.

9. The temperature sensor according to claim 1, wherein the sensor is use in an environment at a temperature of above 100° C.

10. A heat engine of a motor vehicle comprising a temperature sensor according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0041] Further features and advantages of the invention will emerge from the following detailed description and an examination of the accompanying drawings, in which:

[0042] FIG. 1 is a schematic representation of a temperature sensor connected to a measuring device;

[0043] FIG. 2 is a schematic illustration of the principle of operation of a thermocouple;

[0044] FIG. 3 (FIGS. 3a to 3d) shows the method of manufacture of a temperature sensor according to the prior art; and

[0045] FIG. 4 is a longitudinal section of a temperature sensor according to the invention.

DEFINITIONS

[0046] “Proximal” and “distal” distinguish the two ends of a temperature sensor according to the invention. The “distal” end is that of the hot point.

[0047] “Hot point” conventionally describes the connection between the two thermocouple wires, regardless of its temperature.

[0048] The mineral insulated cable has a smaller outer diameter than that of the reinforcement tube. This is why the part of the mineral insulated cable that extends beyond the reinforcement tube, at the hot point end, is called a “swaging”.

[0049] An “insulating material” or “mineral insulation” means, unless stated otherwise, any material having an electrical resistance greater than 10 MV/m and resistivity at room temperature greater than 1 GΩm, typically made of ceramic materials;

[0050] “Comprising a”, “having a” or “including a”, means “comprising at least one”, unless stated otherwise.

[0051] Identical reference numerals are used to identify the same parts in the different Figures.

DETAILED DESCRIPTION

[0052] As FIGS. 1 to 3 have been described in the preamble, reference will now be made to FIG. 4.

[0053] A thermocouple sensor according to the invention is manufactured from a small-diameter mineral insulated cable 14.

[0054] The protective sleeve 5 can be made of any electrically conductive material, preferably of a material chosen from stainless steels, preferably of the Inconel family with a wall typically of a thickness of around 10% of the outer diameter of the mineral insulated cable, preferably of a thickness exceeding 10% in order to promote mechanical strength. The thermocouple wires 10 and 12 can be flexible or rigid. Preferably, they have a substantially circular cross section.

[0055] Preferably the pair of materials of the first and second thermocouple wires 10 and 12 is NiSil/NiCroSil.

[0056] The projecting distal terminal parts 40 and 42 of the thermocouple wires 10 and 12 that extend beyond the mineral insulation 8 conventionally connect together at the hot point 13. They are housed in a chamber 43 resulting from encapsulation, preferably filled with an insulating material, preferably of a mineral nature, that can be identical or different to that contained in the protective sleeve of the mineral insulated cable. Preferably, the insulating material is a material chosen from the group formed by aluminum and/or magnesium.

[0057] The projecting proximal terminal parts 50 and 52 of the thermocouple wires 10 and 12 that may extend beyond the proximal end 44 of the mineral insulated cable 14 can have a length greater than 5 cm, greater than 10 cm, greater than 20 cm, greater than 50 cm. Advantageously, these wires can thus serve as an extension cable 3 so as to electrically connect the temperature sensor 2 to the measuring device 4. Clearly, if the thermocouple wires are used as an extension cable, their projecting proximal end parts 50 and 52 must be electrically insulated.

[0058] At their proximal end, the thermocouple wires 10 and 12 comprise electrical connection means, for example connection terminals enabling their connection to the measuring device 4 and/or to an extension cable 3.

[0059] In an embodiment shown in FIG. 4, the protective sleeve 5 of the mineral insulated cable has no swaging. Its diameter is substantially constant from its proximal end 44 to its distal end 62. As a variation, the protective sleeve 5 of the mineral insulated cable has a reduced swaging, preferably a swaging with an outer diameter greater than the inner diameter of the protective sleeve 5 beyond the region of said swaging.

[0060] The temperature sensor comprises a reinforcement tube 60, preferably made of Inconel, partially covering the protective sleeve.

[0061] In an embodiment, the reinforcement tube 60 is fixed to the protective sleeve preferably by welding.

[0062] Preferably, the outer diameter of the reinforcement tube 60 is less than 7 mm, than 6 mm, than 5 mm, than 4 mm, than 3 mm.

[0063] The inner lateral surface of the reinforcement tube, which delimits the bore of the reinforcement tube, rests on the outer lateral surface 22 of the protective sleeve 5. Preferably, the bore of the reinforcement tube is of a shape that is substantially complementary to the outer lateral surface 22 of the protective sleeve 5, which allows close contact between the inner lateral surface of the reinforcement tube and the outer lateral surface 22 of the protective sleeve 5. Preferably, the reinforcement tube extends to the proximal end 44 of the protective sleeve. However, the reinforcement tube does not extend to the distal end 62 of the protective sleeve. Preferably, the reinforcement tube comprises a tapered distal terminal part so that its outer diameter gradually joins the outer diameter of the protective sleeve.

[0064] More preferably, a mechanical stop 6 is fixed, preferably welded, to the reinforcement tube 60. The mechanical stop 6 advantageously enables a precise local adaptation of the diameter of the temperature sensor, and thus good compatibility with the application envisaged. Preferably, the largest transverse dimension of the mechanical stop (i.e. in a plane perpendicular to the longitudinal direction corresponding to the length of the mineral insulated cable) is greater than 8 mm and/or less than 25 mm.

[0065] Travelling along the temperature sensor from the mechanical stop 6, or even from the proximal end 44 (passing over the mechanical stop 6), up to the distal end 62, the outer lateral surface of the temperature sensor thus comprises a cylindrical portion 64 the outer diameter of which is defined by the reinforcement tube 60, an intermediate portion 66, corresponding to the tapered distal terminal part of the reinforcement tube, and a swaging 56. Advantageously, the swaging 56 improves the response time of the temperature sensor. In order to have a sufficient response time, the outer diameter of the swaging at the hot point is preferably less than 3.5 mm, or less than 3 mm, or less than 2 mm, or less than 1.5 mm.

[0066] The length of the swaging 56 is preferably greater than 5 mm and/or less than 15 mm.

[0067] A temperature sensor according to the invention can be manufactured by following the above steps a) to e).

[0068] Steps a) to c) can correspond to the steps conventionally implemented according to the prior art, as described in the preamble.

[0069] At step a), a mineral insulated cable or section of mineral insulated cable is prepared.

[0070] At step b), the mineral insulation material can be extracted from one of the ends of the mineral insulated cable, as in the prior art, preferably to a depth of between 2 and 7 mm, so as to release the distal end parts of the thermocouple wires.

[0071] At step c), as shown in FIG. 4, the distal terminal parts 40 and 42 of the thermocouple wires 10 and 12 are connected to each other, i.e. placed in physical contact and electrically connected, in a final manner, so as to form a hot point 13. The connection is preferably achieved by hot welding.

[0072] At step d), the thermocouple resulting from the connection of the two thermocouple wires is encapsulated so as to be protected from the environment.

[0073] In a preferred embodiment, the hot point 13 is encapsulated by deformation of the protective sleeve, then by welding, as according to the prior art illustrated by the arrows in FIG. 3c.

[0074] Preferably, the encapsulation in the protective sleeve is performed without forming a swaging from said protective sleeve. The outer diameter of the mineral insulated cable is therefore substantially constant up to its distal end 62.

[0075] Preferably, the chamber 43 resulting from the encapsulation is filled with an insulating material, identical or different to the mineral insulation of the mineral insulated cable, preferably of powder. The insulation material powder can, in particular, be aluminum powder or magnesium powder.

[0076] At step e), the mineral insulated cable is introduced, preferably by force, into the longitudinal bore of the reinforcement tube to a position in which its distal terminal part extends beyond the distal end of the reinforcement tube. This distal terminal part thus defines the swaging 56.

[0077] Preferably, the reinforcement tube is fixed, preferably welded to the protective sleeve 5.

[0078] As is now clear, the steps of a manufacturing method according to the invention, and particularly obtaining a swaging, are simple and can be automated. This results in a significant reduction in manufacturing costs. Obviously, the invention is not limited to the embodiment described and represented, provided for illustration purposes only.