EP3237861A1

EP3237861A1 - Temperature sensor

Info

Publication number: EP3237861A1
Application number: EP15823652.1A
Authority: EP
Inventors: Piotr ZAKRZEWSKI; Nicolas Gelez; Pascal Castro; Mahmoud Sfaxi
Original assignee: Valeo Systemes de Controle Moteur SAS
Current assignee: Valeo Systemes de Controle Moteur SAS
Priority date: 2014-12-22
Filing date: 2015-12-14
Publication date: 2017-11-01
Also published as: WO2016102809A1; FR3030733B1; FR3030733A1

Abstract

The invention relates to a temperature sensor with a thermocouple, comprising: a mineral insulated cable comprising a protective sheath (5) having an outer diameter of less than 4 mm and encapsulating a hot point (13) of a thermocouple, and a closed reinforcing tube (20) preferably fastened, in a tight manner, to the protective sheath, and defining a chamber (64) containing the part of the protective sheath that encapsulates said hot point.

Description

Temperature sensor

Technical area

The invention relates to a temperature sensor comprising a thermocouple for measuring temperatures which can vary between -40 ° C and + 1200 ^, in particular in a thermal engine group of a motor vehicle.

Prior art

As shown in FIG. 1, a temperature measuring device conventionally comprises a temperature sensor 2 extended by an extension cable 3 making it possible to connect the temperature sensor to a measuring device 4. The temperature sensor 2 conventionally comprises a metal protective sheath and a stop 6, mounted on the protective sheath 5 and adapted according to the intended application.

The measuring apparatus 4 is intended to interpret the electrical signal supplied by the temperature sensor 2 and transmitted via the extension cable 3. This interpretation allows an evaluation of the temperature at which the end of the temperature sensor is subject.

Inside the protective sheath 5, the temperature sensor 2 conventionally comprises a thermocouple 7 and an inorganic insulator 8, conventionally made of alumina or magnesia, which enables the thermocouple to withstand the environmental stresses, and especially the temperatures high.

As illustrated in FIG. 2, the thermocouple 7 is an assembly of first and second conductive wires, 10 and 12, respectively, connected to each other and end-to-end at a hot spot 13. The potential difference AU at the terminals of the first and second conductive son depends on the difference between the hot spot temperature ΤΊ and the temperature T _{0 at} said terminals, according to the Seebeck effect, well known.

To manufacture a temperature sensor for applications in which the temperature can vary between -40 ^ and + 1200 ^, one proceeds conventionally according to the following steps:

Firstly, a mineral insulated cable 14 or MIC ("ore insulated cable") cable is manufactured. A mineral insulated cable has a metal protective sheath and, inside the protective sheath 5, two thermocouple wires 10 and 12 made of materials adapted to form a thermocouple, the two thermocouple wires being insulated. one of the other and the protective sheath 5 by means of the mineral insulation 8 (fig.3a).

To form the junction between the two thermocouple wires, or "hot spot" 13, a little mineral insulation is extracted from one end of the cable, for example by sandblasting or scraping, typically to a depth between 2 and 10 mm. At this so-called "distal" end, the two thermocouple wires thus emerge from the insulator, while being encircled by the protective sheath 5 (FIG 3b).

The two ends of the thermocouple wires thus released are mechanically brought together until they are brought into contact with each other and then connected, for example by electric welding (FIG. 3c).

The recessed end of the protective sheath can then be optionally filled with insulating material, which is identical to or different from the mineral insulator of the mineral insulated cable, and then closed so as to protect the thermocouple, for example by electric welding (FIG. 3d).

Moreover, after closure of the protective sheath 5 or before the cutting of the mineral insulated cable, a shrinkage 15 is conventionally made at the distal end of the protective sheath 5, typically by drawing or hammering. The shrinkage conventionally makes it possible to improve the response time of the temperature sensor.

Such a manufacturing method is however difficult to automate and currently involves delicate manual operations.

There is therefore a need for a solution to facilitate the automation of the manufacture of a thermocouple temperature sensor.

An object of the invention is to meet this need. Summary of the invention

The invention proposes a method for manufacturing a thermocouple temperature sensor comprising the following successive steps:

i) closing a protective sheath of a mineral insulated cable having a thermocouple so as to encapsulate a hot spot of said thermocouple, the protective sheath having an outer diameter of less than 4 mm; ii) introducing, in a reinforcing tube, the portion of the protective sheath encapsulating said hot spot, and fixing said reinforcing tube on said protective sheath;

iii) independently of the preceding steps, closing the reinforcing tube so as to define a chamber housing the portion of the protective sheath encapsulating said hot spot.

As will be seen in more detail in the following description, the use of a small diameter mineral insulated cable and a closed reinforcement tube avoid having to deform the protective sheath on itself to to create a shrink, which greatly facilitates the automation of the manufacturing process, limits the mechanical degradation of the temperature sensor, and ultimately increases its life.

The invention also proposes a thermocouple temperature sensor comprising

a mineral insulated cable comprising a protective sheath having an outside diameter of less than 4 mm and encapsulating a hot spot of a thermocouple, and

- A closed reinforcement tube fixed, preferably sealingly, on the protective sheath, and defining a chamber in which is housed the portion of the protective sheath encapsulating said hot spot.

A temperature sensor according to the invention may also include one or more of the following optional features:

the outside diameter of the protective sheath is preferably less than 3.5 mm, preferably less than 3 mm, preferably less than 2.5 mm, preferably less than 2 mm, and preferably less than 1.5 mm; preferably less than 1.2 mm;

- Preferably, the outer diameter of the closed reinforcing tube is greater than 4 mm, preferably greater than or equal to 4.5 mm and / or less than 7 mm, preferably less than 6 mm;

- Preferably, the protective sheath is devoid of necking, at least near said chamber;

preferably, the closed reinforcing tube has a necking, the outside diameter of which at the hot point is preferably less than 3.5 mm, or even less than 3 mm, or even less than 2 mm, or even less than 1, 5 mm;

the closed reinforcement tube is fixed, preferably by welding, to the protective sheath, the closed reinforcing tube is hermetically fixed on the protective sheath, preferably by laser welding;

the closed reinforcing tube covers and, preferably, is in contact with more than 10%, more than 30%, more than 60%, more than 90%, preferably substantially 100% of the outer lateral surface of the protective sheath mineral insulated cable;

the closed reinforcement tube is monobloc or results from the assembly of several parts, in particular into two parts;

the closed reinforcement tube is a blind tube or a tube on which a cap has been fixed;

the temperature sensor comprises a fixed mechanical abutment, preferably welded, on the closed reinforcing tube.

A method according to the invention is preferably adapted for the manufactured temperature sensor to have one or more of the above optional features.

The invention also relates to the use of a temperature sensor according to the invention in an environment at a temperature greater than 800 ° C, at ΘΟΟ'Ό, at Ι ΟΟΟ 'Ό, at 1100 ° C and / or lower at -10 ^<€ at -20 ^"C to ^-30" C, preferably ranging between -40 ° C and 1200 ° C, in particular in an engine of a motor vehicle.

Finally, the invention relates to a thermal engine group of a motor vehicle comprising a temperature sensor according to the invention, and a motor vehicle comprising a heat engine unit according to the invention. The temperature sensor may in particular be disposed in the exhaust manifold upstream of a turbine of a turbocharger or in a fuel or oxidizer intake manifold or in an exhaust manifold.

Brief description of the figures

Other characteristics and advantages of the invention will become apparent on reading the following detailed description and on examining the appended drawing in which;

- Figure 1 shows schematically a temperature sensor connected to a measuring apparatus;

- Figure 2 schematically illustrates the operating principle of a thermocouple; Fig. 3 (Fig. 3a-3d) illustrates the method of manufacturing a temperature sensor according to the prior art;

FIG. 4 represents a temperature sensor according to the invention.

Definitions

- By "proximal" and "distal", there are two sides of a temperature sensor according to the invention. The "distal" side is that of the hot spot.

"Hot spot" conventionally refers to the junction between the two thermocouple wires, regardless of its temperature.

- "comprising a", "presenting a" or "including a" means "having at least one", unless otherwise indicated.

- Identical references are used to designate similar organs in the different figures.

detailed description

FIGS. 1 to 3 having been described in the preamble, reference is now made to FIG. 4. A thermocouple sensor according to the invention is manufactured from a mineral insulated cable 14 of small diameter. The mineral insulated cable has by definition a protective sheath.

The protective sheath 5 may be of any electrically conductive material, and for example of a metallic material.

The thermocouple wires 10 and 12 may be flexible or rigid. Preferably, they have a substantially circular cross section. Preferably, the material pair of the first and second thermocouple wires 10 and 12 is of the N or K type, preferably of the N type.

The projecting portions 50 and 52 of the thermocouple wires 10 and 12 which extend possibly beyond the proximal end 44 of the cable 14 may 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, to electrically connect the temperature sensor 2 of the measuring device 4. Of course, if the thermocouple wires are used as an extension cable, their projecting parts 50 and 52 must be electrically isolated. At their proximal end, the thermocouple wires 10 and 12 comprise electrical connection means, for example connection terminals allowing their connection to the measuring device 4 and / or to an extension cable 3.

As shown in FIG. 4, the protective sheath 5 of the mineral insulated cable is protected by a closed reinforcement tube 20.

Preferably, the closed reinforcing tube is made of a ceramic material, preferably selected from the group consisting of magnesia, aluminum nitride, boron nitride, aluminum nitride and mixtures thereof.

According to one embodiment of the invention the reinforcing tube is formed by an outer tube and a cap which encapsulate it. The cap and the outer tube can form a single piece or can be attached a posteriori. The encapsulation tube can also be filled with a mineral insulator.

Preferably, the closed reinforcement tube has a necking 56. The use of a blind reinforcement tube or an attached cap advantageously facilitates the obtaining of complex shapes for necking. In addition, the risk of damage to the thermocouple leads is reduced.

More preferably, the necking 56 extends to the distal end of the closed reinforcing tube 20 as shown. Advantageously, a necking 56 improves the response time of the temperature sensor.

To have a suitable response time, the outer diameter of the shrinkage at the hot spot is preferably less than 3.5 mm, or even less than 3 mm, or even less than 2 mm, or even less than 1, 5 mm.

The length of the necking 56 is preferably greater than 5 mm and / or less than 15 mm.

More preferably, the closed reinforcing tube 20 comprises a longitudinal lumen of shape substantially complementary to the outer lateral surface of the protective sheath 5 of the mineral insulated cable. The mineral insulated cable can thus guide the closed reinforcing tube 20 during its assembly.

Preferably, the closed reinforcing tube is filled with an insulating material, preferably of mineral nature, which may be identical to or different from that contained in the protective sheath of the mineral insulated cable. Preferably, the insulating material is of a material selected from the group consisting of alumina and / or magnesia; In one embodiment, the closed reinforcing tube 20 is fixed on the protective sheath, preferably by welding. Preferably, the minimum distance d between the hot spot 13 and any weld point 54 of the reinforcement tube closed on the protective sheath is greater than 30 mm. Preferably, the closed reinforcing tube 20 is fixed on the protective sheath 5 at the proximal end of said protective sheath.

According to the invention, the closed reinforcing tube defines a chamber 64 around the distal end of the mineral insulated cable. Preferably, this chamber is sealed at least in the portion of the temperature sensor which extends from the mechanical stop 6 to the distal end 62 of the temperature sensor, preferably in the portion of the temperature sensor which extends from the proximal end of the mineral insulated cable to the distal end 62 of the temperature sensor.

More preferably, a mechanical stopper 6 is fixed, preferably welded, on the closed reinforcement tube. The mechanical stop 6 advantageously allows a precise local adaptation of the diameter of the temperature sensor, and therefore a good match to the intended application.

Preferably, the greatest transverse dimension of the mechanical abutment (that is to say 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. .

According to the invention, the temperature sensor is manufactured according to steps i) and ii) above.

Step i) may in particular comprise, as in the prior art described in the preamble, the following steps:

a) manufacture of a mineral insulated cable having a protective sheath and two thermocouple wires extending the entire length of the cable and embedded in a mineral insulator, the outer diameter of the mineral insulated cable being less than 4 mm, preferably less than 3.5 mm, preferably less than 3 mm, preferably less than 2.5 mm, preferably less than 2 mm, preferably less than 1.5 mm, preferably less than 1.2 mm;

b) extracting mineral insulation from one end of the mineral insulated cable to a depth of between 2 and 7 mm so as to disengage ends of the thermocouple wires; c) connecting the ends of the thermocouple son thus released, so as to constitute a thermocouple hot spot;

d) closing said end of the mineral insulated cable by means of the protective sheath, so as to protect the thermocouple, for example by electric welding.

In step a), a mineral insulated cable or a section of insulated mineral cable is prepared.

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

In step c), as shown in FIG. 4, the distal ends 40 and 42 of the thermocouple wires 10 and 12 are connected to each other, that is to say placed in physical and electrical contact. , definitively, so as to form a hot spot 13. The connection is preferably made by hot welding.

In step d), the hot spot 13 is then encapsulated by deformation of the protective sheath and welding, as in the prior art illustrated by the arrows of Figure 3c. Preferably, however, no shrinkage is provided near the hot spot.

Before closing, the reinforcing tube is preferably partially filled with an insulating material, preferably in the form of a powder, which is identical to or different from the inorganic insulator of the mineral insulated cable, preferably made of a material chosen from alumina. and / or magnesia, so that after assembly, the distal portion of the mineral insulated cable in which are housed the ends of the thermocouple son is isolated from the outside by said insulating material.

In step ii), the distal end of the thermocouple is introduced into a reinforcing tube 20 comprising, preferably consisting of Inconel®, or a 31 OS, to another stainless steel according to the chosen application constraints.

Preferably, at the end of step ii), the distal end of the thermocouple is disposed near the distal end of the reinforcing tube, as shown in FIG. 4.

In step iii), the distal end of the reinforcing tube is sealed, or "closed" so as to define the chamber 64. This closure may in particular result from an addition of material, for example by welding, deformation or attachment of a cap. Preferably, before closing the protection tube, the chamber 64 is partially filled with an insulating material, which is identical to or different from the inorganic insulation of the mineral insulated cable, preferably in powder form. The powder of insulating material may in particular be an alumina powder or a magnesia powder.

Step iii) is independent of the other steps. It can in particular be carried out before or after step ii). Preferably, it is carried out before step ii).

Whatever the time at which step iii) is performed, the reinforcing tube 20 is fixed on the outer lateral surface 22 of the protective sheath. The closed reinforcing tube 20 may be fixed rigidly by any means, for example by means of a suitable glue, preferably welded.

In one embodiment, the closed end of the reinforcing tube has a necking. Closure by means of a hood with a necking further facilitates the manufacture of the temperature sensor.

The use of a small diameter mineral insulated cable, however, limits or even eliminates the shrinkage of the reinforcing tube.

As is clear now, the steps of a manufacturing method according to the invention are simple and can be automated. This results in a significant reduction in the manufacturing cost.

The invention also makes it possible to obtain complex shapes for shrinking. Finally, it leads to a very significant reduction in the risk of damaging the thermocouple wires.

Of course, the invention is not limited to the embodiment described and shown, provided for illustrative purposes only.

Claims

Thermocouple temperature sensor comprising

a mineral insulated cable comprising a protective sheath (5) having an outside diameter of less than 4 mm and encapsulating a hot spot (13) of a thermocouple, and

- A closed reinforcement tube (20) fixed, preferably in a sealed manner, on the protective sheath, and defining a chamber (64) in which is housed the portion of the protective sheath encapsulating said hot spot. Temperature sensor according to the preceding claim, wherein the outer diameter of the protective sheath is less than 2 mm. A temperature sensor as claimed in any one of the preceding claims, wherein the protective sheath is devoid of necking. A temperature sensor as claimed in any one of the preceding claims, wherein the closed reinforcing tube (20) has a necking (56). The temperature sensor of the immediately preceding claim, wherein the outer diameter of the necking at the hot spot is less than 2 mm. A temperature sensor as claimed in any one of the preceding claims, wherein the closed reinforcing tube is welded. A temperature sensor according to any one of the preceding claims, wherein the closed reinforcing tube (20) covers more than 90% of the outer side surface (22) of the protective sheath (5). A temperature sensor as claimed in any one of the preceding claims, wherein the closed reinforcing tube is a blind tube or a tube to which a cap has been attached. A method of manufacturing a thermocouple temperature sensor comprising the following steps: - Closing a protective sheath of a mineral insulated cable having a thermocouple so as to encapsulate a hot spot of said thermocouple, the protective sheath having an outer diameter of less than 4 mm;

- Introducing, in a reinforcing tube, the portion of the protective sheath encapsulating said hot spot, and fixing said reinforcing tube on said protective sheath;

- Independently of the preceding steps, closing the reinforcing tube so as to define a chamber housing the portion of the protective sheath encapsulating said hot spot. Use of a temperature sensor according to any one of the preceding claims in an environment at a temperature above 1100 ° C.

1 1 heat engine unit of a motor vehicle comprising a temperature sensor according to any one of claims 1 to 8.