GB1559659A

GB1559659A - Thermocoupe probe

Info

Publication number: GB1559659A
Application number: GB5089877A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1976-12-07
Filing date: 1977-12-07
Publication date: 1980-01-23
Also published as: JPS5370888A; DE2754271A1; CA1085967A

Description

(54) THERMOCOUPLE PROBE (71) We, NISSAN MOTOR COM PANY LIMITED, a corporation organized under the laws of Japan, of No. 2, Takaramachi, Kanagawa-ku, Yokohama City, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates in general to a temperature sensing device and more particularly to a thermocouple probe which is suitable for measuring the temperature of the exhaust gases issuing from an automotive internal combustion engine.

Modern automotive internal combustion engines are equipped at their exhaust systems with exhaust gas purifying devices, such as a catalytic converter and a thermal reactor, for converting the harmful compounds such as HC, CO and NOx in the exhaust gases into harmless compounds such as H2O, CO and N2. In order to operate these gas purifying devices at their optimum efficiency, it is necessary to check or monitor the temperatures of the exhaust gases passing through these devices by placing temperature sensors in the devices In most cases, however, such temperature sensors are located in positions where high temperature, severe vibration, exposure te water splashes and stone impingement very often occur.Thus, in practical use, not only the positioning of these temperature sensors in the purifying devices but also the assemblage of the same must be carefully done by taking the above-mentioned facts into consideration.

Hitherto, two types of temperature sensors have been widely used in the above-mentioned field, one of which is a thermistor type sensor comprising a semi-conductor in ceramic form, and the other of which is a thermocouple type sensor comprising two dissimilar metal wire connected or welded at their one ends tu form a so-called hot or measuring junction, a protective metal tube enclosing the two metal wires, insulating material packed in the tube for insulation between the wires and the tube.

In the thermistor type sensor, however, the temperature sensing section thereof is relatively large, and thus has a large thermal capacity, thus its responsiveness is relatively poor. Furthermore, because of the relatively early aging of the contacting section of the thermistor proper with electrodes, the life time of this type of sensor is relatively short.

In the thermocouple type sensor, the above mentioned troubles encountered in the thermistor type sensor are solved to some extent. However, its responsiveness has not satisfied the request in sensing the temperature sufficiently.

Therefore, it is an object of the present invention to provide an improved thermocouple temperature sensor which has improved responsiveness and high durability in practical use.

It is another object of the present invention to provide a thermocouple probe which can be used to measure the temperature of the exhaust gases issued from the internal combustion engine.

It is a further object of the present invention to provide a thermocouple probe, the measuring junction of which can be arranged to directly contact the medium, the temperature of which is to be measured; the thermocouple probe is thus extremely responsive.

It is a still further object of the present invention to provide a thermocouple probe in which one of the dissimilar thermoelectric metals which form the measuring junction acts as a so-called protective tube, so that the probe is simple in construction and easily assembled, and accordingly economical.

It is a still further object of the present invention to provide a thermocouple probe in which one of the dissimilar thermoelectric metals, exhibiting higher corrosion resistance than the other, is formed into a tube directly exposed to the measured medium.

Thus, the present invention consists in a thermocouple probe comprising: a tube member having a closed end and an open end and made of a nickel-based alloy containing from 5 to 25% by weight chromium and one or more of: (a) rare earth element(s) in an amount not exceeding 1% by weight; (b) aluminium in an amount not exceeding 5% by weight; and (c) one or more of the elements silicon, zirconium, titanium and niobium pro vided that each element does not ex ceed 1% by weight; the balance being nickel; a wire member disposed in and axially extending through said tube member and having one end welded to an inner wall of said closed end of said tube member, said wire member being made of a nickel-based alloy containing one or more of: (d) aluminium in an amount not exceeding 7% by weight; (e) silicon in an amount not exceeding 7% by weight, provided that the sum of aluminium and silicon does not exceed 10% by weight; (f) rare earth element(s) in an amount not exceeding 1% by weight; and (g) one or more of the elements carbon, cobalt, manganese and iron, provided that the sum of these elements does not exceed 1% by weight; the balance being nickel; and an electrically insulating material filling said tube member so as to support said wire member substantially immovably in said tube member.

The invention is further illustrated by the accompanying drawings, in which: Fig. 1 is a schematic sectional view of an exemplary prior art temperatture sensing theremocouple probe; Fig. 2 is a schematic sectional view of a first preferred embodiment of a thermocouple probe according to the present invention; Fig. 3 is a schematic sectional view of a second preferred embodiment of a thermocouple probe according to the present invention; Fig. 4 is a schematic sectional view of apparatus incorporating the thermocouple probe shown in Fig. 2; and Fig. 5 is a sectional view taken along the line V-V of Fig. 4.

Prior to describing the thermocouple probe according to the present invention, description of the prior art thermocouple probe will be given with the aid of Fig. 1 in order to clarify the inventive features of the subject invention.

In Fig. 1, a conventional thermocouple probe is illustrated, comprising: a protective metal tube 10 having a closed end 12 and an open end 14; a pair of dissimilar metal wires 16 and 18 spacedly disposed in the protective tube 10 and forming a hot or measuring junction 20 at one end thereof near the closed end of the protective tube; and an electrically insulating material 22, for example, magnesium oxide (MgO) filling the cavity of the protective tube 10 in order to electrically insulate the metal wires 16 and 18 from the protective tube. However, in such a conventional sensing element, there arises the problem that the measuring junction 20 fails to reach a suitable temperature rapidly due to heat absorption by the protective tube 2 and the filling insulating material 22, and therefore the responsiveness of the thermocouple probe is low.Of course, its responsiveness may be fairly improved by thinning the protective tube 10 as well as the metal wires 16. However, this procedure will lower the mechanical strength of the thermocouple probe.

Thus, as has been described, the present invention contemplates to eliminate the drawbacks encountered in the above-mentioned conventional thermocouple probe.

Referring now to Fig. 2, there is shown a thermocouple probe according to the present invention, which element comprises a metal tube 24 constructed of a thin thermoelectric metal and having a closed end 26 and an open end 28. Concentrically disposed in the tube 24 is a metal wire 30 made of another thermoelectric metal which has one end welded or brazed to an inner surface of the closed end 26 at a point 32 to form the measuring junction. The cavity of the tube 24 is packed or filled with an electrically insulating material 34 such as magnesium oxide (MgO) for reliable insulation between the wire 30 and the tube 24.For security against breakage during assembly - and durability in use of the thermocouple probe, the thickness of the tube 24, indicated by a letter T1 in Fig. 2, and the thickness T2 of the insulating material 34 should each be at least 10% of the outer diameter of the tube. Furthermore, the diameter T3 of the wire should be at least 20% of the outer diameter of the tube 24.

Preferably, the section substantially constituting the measuring junction 32 is formed compact or small in size for allowing the junction 32 to have a high sensitivity to temperature to be measured. An example for accomplishing this will be described herein next.

In Fig. 3, a second preferred embodiment of the thermocouple probe having more improved characteristics in responsiveness is illustrated, as comprising a metal tube 24' having a large diameter portion 24'a (for example 3.2mum+) and a small diameter portion 24'b (for example 1.6mum+) which are integrally connected via a conical portion 24'c.

The metal tube 24' has at the small diameter portion 24'b a closed end 26' and at the large diameter portion 24'a an open end 28'. Concentrically disposed in the tube 24' is a metal wire 30' which has a small diameter portion 3G'b welded or brazed to the closed end 26' of the tube 24' forming a measuring junction 32' and a large diameter portion 30'a concentrically located in the large diameter portion 24'a of the metal tube 24', as shown.

The metal tube 24' and the metal wire 30', similar to the case of the first embodiment, are constructed of dissimilar thermoelectric metals, respectively. The cavity of the tube 24' is also filled with an electrically insulating material 34'. Preferably, the axial length L of the small diameter portion 24'b is made at least ten times as long as the outer diameter D of the same.

Now, it should be noted that corrosion resistance of the tube 24 or 24' is synergetically increased by the deposition of at least one heat insulating compound such as Awl203, Cr2O3, SiO2, TiO2, BeO, MgO and ZrO2 on the outer surface of the tube.

According to the present invention, consideration on the materials for the tube 24 or 24' and the wire 30 or 30' is further required.

Several experiments conducted by the inventors have revealed that the following alloys are very suitable for the construction of the tube and the wire: Alloy for the tube 24 or 24'-A nickelbase alloy consisting of 5 to 25% Cr, up to 1% rare earth element(s), up to 5% Al, one or more of the elements Si, Zr, Ti and Nb (provided each does not exceed 1%), and the balance Ni; Alloy for the wire 30 or 30'-A nickelbase alloy consisting of one or more of up to 7% Al, up to 7% Si (provided the sum of Al and Si does not exceed 10%), up to 1% rare earth element(s), up to 1% sum of one or more of C, Co. Mn and Fe, and the balance Ni.

Tables 1 and 2 show nickel-base alloys (C) to (K) and (0) to (R) which can be respectively used for the construction of the tube 24 or 24' and the wire 30 or 30'. For the comparison, conventional alloys (A), (B) and (L) to (N) are also shown in these Tables.

In Tables 3 and 4, there are respectively shown the characteristics of the alloys (A) to (R), in which (1) indicates weight increase by oxidation, (2) thermo-electromotive force and (3) change in thermo-electromotive force by aging. These data were obtained under the following test conditions, in which: (1) weight increase by oxidation Supplied gas: the atmosphere Temperature: 11000 C Operation hours: 50 hr.

(2) thermo-electromotive force before aging test Temperature: 11000C in the case of (A) to (K) 1000"C in the case of (L) to (R) (3) change in thermo-electromotive force by aging Supplied gas: the atmosphere Temperature: 1 1000C Operation hours: 100 hr in the cases of (A) to (K) TABLE 1 NICKEL-BASE ALLOYS FOR THE TUBES (24 or 24')

Composition (%) Type Cr Al Si Zr Nb Ti R.E.* Note (A) 10 - - - - - - Conventional alloy (B) 10 - - - - - - " (C) 20 3 - - - - 0.5 According to the invention (D) 10 - 0.5 - - - 0.5 " (E) 15 - - 0.2 - - 0.5 " (F) 20 - - - 0.5 - 0.5 " (G) 15 - - - - 0.3 0.5 " (H) 10 1.0 0.3 - - - 0.5 " (I) 10 - 0.5 0.2 - - 0.5 " (J) 20 3 - 0.1 1.0 - 0.3 " (K) 20 20 - 1.0 - 1.0 - 0.2 *R.E:: Mischmetal (Ce50% + La50%) TABLE 2 NICKEL-BASE ALLOYS FOR THE WIRES (30 or 30')

Composition (c) Type Al Si Mn R.E.* Note (L) 1.0 1.0 1.0 - Conventional alloy (M) - - - - " (N) 1.5 - - (0) 5.0 - - 0.5 According to the invention (P) - 2.0 - 0.5 (Q) - 5.0 - 0.5 (R) 2.0 2.0 ~ 0.5 *R.E.:Mischmetal (Ce50% + La50%) TABLE 3 EXPERIMENTAL DATA ON THE NICKEL-BASE ALLOYS FOR THE TUBE (24 or 24')

Data (1) (2) (3) Thermo electromotive Change in Thermo Wt. increase by force before electromotive oxidation aging test force by aging (g/mm ) (mV) (mV) 11000C 11000C 50 hr 11000C 100 hr Atmosphere Atmosphere (A) 30 36 +0.1 (B) 20 23 +0.05 (C) 6 21 +0.01 (D) 15 35 +0.03 (E) 10 25 +0.02 (F) 8 23 +0 .02 (G) 10 25 +0.03 (H) 13 35 +0.03 (l) 15 36 +0.03 (J) 7 20 +0.01 (K) 10 20 +0.01 TABLE 4 EXPERIMENTAL DATA ON THE NICKEL-BASE ALLOYS FOR THE WIRES (30 or 30')

Data (1) (2) (3) Themo electromotive Change in Thermo Wt. increase by force before electromotive oxidation aging test force by aging ( g/mm2) (mV) (mV) 1100 C 1100 C 50 hr 1000 C 50 hr Atmosphere Atmosphere (L) 200 -88 -0.05 (M) 190 -10.1 (N) 200 -15.9 -0.05 (O) 140 -16.5 -0.01 (P) 120 -9.8 -0.01 (Q) 90 -10.5 -0.00 (R) 50 -12.8 -0.01 As is well understood from these Tables 1 to 4, the alloys (C) to (K) for the construction of the tube 24 or 24' and the alloys (o) to (R) for the wire 30 or 30! respectively have improved characteristics with respect to corrosion resistance, thermal electromotive-force and durability in high temperature compared with the respective conventional alloys (A), (B) and (L) to (N).

According to the several experiments regarding the nickel-base alloys of various compositions, the following results were further obtained: In the case of alloys for the tube (24 or 24').

(a) The addition of more than 1% of rare-earth elements such as lanthanum (La), cerium (Ce), samarium (Sm) and praeseodymium (Pr) into each of the nickel-base alloys causes a remarkable decrease in hot working characteristic of the tube.

(b) If chromium (Cr) is decreased below 5%, the corrosion resistance of the alloy goes down sharply, more than 25% of chromium (Cr) content causes not only a remarkable drop in hot working characteristics of the alloy, but also a drop in the thermo-electromotivc force of the alloy.

(c) The addition of more than 5% of aluminum (Al) into the alloy lowers the cold working characteristic of the alloy.

(d) The addition of more than 1% of silicon (Si), zirconium (Zr), titanium (Ti) and/or niobium (Nb) to the alloy does slightly enhance the corrosion resistance of the alloy, but lowers the thermo-electromotive force of the alloy.

In the case of alloys for the wire (30 or 30') (e) The addition of more than 7% of aluminium (Al) and/or silicon (Si) to each of the nickel-base alloys causes the cold working characteristic of the alloy to decrease.

Furthermore, if aluminium (Al) is decreased below 2% and silicon (Si) is zero, the corroslon resistance characteristic of the alloy is hardly improved.

(f) The corrosion resistance of the alloy is increased by addition of a trace of a rareearth element or elements. However, the addi tion of more than 1% lowers the hot working characteristic and the corrosion resistance of the alloy.

Referring to Figs. 4 and 5, particularly to Fig. 4, there is shown an entire apparatus employing therein the thermocouple probe of Fig. 2. The apparatus comprises the thermo couple probe, a portion of an extension or compensation wire 36 and a transition fitting 38 therebetween.

Since the construction of the probe of Fig.

2 has been explained in detail hereinbefore, description about it will be omitted here. A cross sectional view of the probe is shown in Fig. 5.

The portion of the extension wire 36 com prises two electrically conductive wires 40 which transmit current developed at the measuring junction 32 to a remote utilization device (not shown) for any intended purpose.

Preferably, the wires 40 are constructed of materials having substantially the same thermo-electrical characteristics as those of the tube 24 and the wire 30 respectively.

Each wire 40 is encased in insulation (such as polyethylene insulation), the two wires 40 being further supported and insulated with a woven glass fiber jacket 42 and a silicon rubber tube 44. The jacket 42 and insulation are stripped away to provide free lengths of the conductive wires 40 which are respectively welded to the tube 24 and the wire 30 of the thermocouple probe and typically brazed to produce permanent electrical junctions 46.

In order to protect the electrical junctions 46 and provide a relatively rigid coupling between the thermocouple probe and the ex tension wire 36, the transition fitting 38 is employed for joining the two elements. In this embodiment, the transition fitting 38 com prises an outer cylindrical casing 48 made of a heat resisting metal such as stainless steel, having at its one end a small diameter ex ternally threaded portion 50 terminating in a radial shoulder portion 52. The casing 48 is - formed at its other end with a thin cylindrical portion 54 terminating in the radial shoulder portion 52. The shoulder portion 52 is used for facilitating acceptance and seating of the thermocouple probe in a threaded bore formed in a suitable support member (not shown) such as an exhaust tube of an internal com bustion engine.As shown, the cylindrical casing 48 is arranged to hold therein gener ally half a section of the above-mentioned thermocouple probe, that is the section containing the open end 28 of the tube 24. Within the outer cylindrical casing 48 is tightly disposed an inner cylindrical holder - 56 which has a small diameter section 56a positioned in the externally threaded portion 50 of the casing 48 and a large diameter section 56b positioned in the shoulder and the thin cylin drical portions 52 and 54, respectively, of the casing 48. The small diameter section 56a protrudes outwardly from the casing 48 and the large diameter section 56b also protrudes from the casing 48, as shown.The cylindrical holder 56 is made of a chemically stable insulating solid material such as alumina ceramic and is formed with a longitudinally extending through bore consisting of a small diameter bore section 58a and a large diameter bore section 58b, the small diameter bore section 58a receiving therein the tube 24 of the probe.

For tight setting of the tube 24 in the bore section 58a, alumina cement is filled in a clearance defined between the outer cylindrical surface of the tube 24 and the inner cylindrical surface of the bore section 58a. Designated by numeral 60 is a metal gasket which is tightly disposed between the inner surface of the casing 48 and the outer surface of the holder 56.In order to tightly fix the end portions of the extension wires 40 to the transition fitting 38, a generally conical supporter 62 made of an insulating material such as fluorinecontaining plastics (Teflon-registered Trade Mark) is used, which has two parallel through bores (no numerals) for respectively receiving therein the end portions of the wires 40 and is attached to the large diameter section 56h of the cylindrical holder 56 at a large diameter portion thereof by the aid of a metal cylinder 64.As shown, the metal cylinder 64 has at its one end a flange 64a engaged via a metal ring 66 with an inwardly bent portion 54a of the thin cylindrical portion 54 of casing 48, and at its other end a flange 64b engaged via a plastic ring 68 (such as a Teflon ring) with a shoulder formed at the large diameter portion of the supporter 62. The conical surface of the supporter 62 is covered with an enlarged extension section of the aforementioned silicon rubber tube 44. The bore 58b thus enclosed receives therein the beforementioned permanent electrical junctions 46 and is packed with an alumina cement 70 for tightly holding the junctions 46. Numeral 72 is a wire for supporting the wires 40 projected into the bore 58b.

WHAT WE CLAIM IS:- 1. A thermocouple probe comprising: a tube member having a closed end and an open end and made of a nickel-based alloy containing from 5 to 25% by weight chromium and one or more of: (a) rare earth element(s) in an amount not exceeding 1% by weight; (b) aluminium in an amount not exceeding 5% by weight; and (c) one or more of the elements silicon, zirconium, titanium and niobium, pro vided that each element does not ex ceed 1% by weight; the balance being nickel; a wire member disposed in and axially ex

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

tion of more than 1% lowers the hot working characteristic and the corrosion resistance of the alloy.

Referring to Figs. 4 and 5, particularly to Fig. 4, there is shown an entire apparatus employing therein the thermocouple probe of Fig. 2. The apparatus comprises the thermo couple probe, a portion of an extension or compensation wire 36 and a transition fitting

38 therebetween.

Since the construction of the probe of Fig.

2 has been explained in detail hereinbefore, description about it will be omitted here. A cross sectional view of the probe is shown in Fig. 5.

The portion of the extension wire 36 com prises two electrically conductive wires 40 which transmit current developed at the measuring junction 32 to a remote utilization device (not shown) for any intended purpose.

Preferably, the wires 40 are constructed of materials having substantially the same thermo-electrical characteristics as those of the tube 24 and the wire 30 respectively.

Each wire 40 is encased in insulation (such as polyethylene insulation), the two wires 40 being further supported and insulated with a woven glass fiber jacket 42 and a silicon rubber tube 44. The jacket 42 and insulation are stripped away to provide free lengths of the conductive wires 40 which are respectively welded to the tube 24 and the wire 30 of the thermocouple probe and typically brazed to produce permanent electrical junctions 46.

In order to protect the electrical junctions

46 and provide a relatively rigid coupling between the thermocouple probe and the ex tension wire 36, the transition fitting 38 is employed for joining the two elements. In this embodiment, the transition fitting 38 com prises an outer cylindrical casing 48 made of a heat resisting metal such as stainless steel, having at its one end a small diameter ex ternally threaded portion 50 terminating in a radial shoulder portion 52. The casing 48 is - formed at its other end with a thin cylindrical portion 54 terminating in the radial shoulder portion 52. The shoulder portion 52 is used for facilitating acceptance and seating of the thermocouple probe in a threaded bore formed in a suitable support member (not shown) such as an exhaust tube of an internal com bustion engine.As shown, the cylindrical casing 48 is arranged to hold therein gener ally half a section of the above-mentioned thermocouple probe, that is the section containing the open end 28 of the tube 24. Within the outer cylindrical casing 48 is tightly disposed an inner cylindrical holder - 56 which has a small diameter section 56a positioned in the externally threaded portion 50 of the casing 48 and a large diameter section 56b positioned in the shoulder and the thin cylin drical portions 52 and 54, respectively, of the casing 48. The small diameter section 56a protrudes outwardly from the casing 48 and the large diameter section 56b also protrudes from the casing 48, as shown.The cylindrical holder 56 is made of a chemically stable insulating solid material such as alumina ceramic and is formed with a longitudinally extending through bore consisting of a small diameter bore section 58a and a large diameter bore section 58b, the small diameter bore section 58a receiving therein the tube 24 of the probe.

For tight setting of the tube 24 in the bore section 58a, alumina cement is filled in a clearance defined between the outer cylindrical surface of the tube 24 and the inner cylindrical surface of the bore section 58a. Designated by numeral 60 is a metal gasket which is tightly disposed between the inner surface of the casing 48 and the outer surface of the holder 56.In order to tightly fix the end portions of the extension wires 40 to the transition fitting 38, a generally conical supporter 62 made of an insulating material such as fluorinecontaining plastics (Teflon-registered Trade Mark) is used, which has two parallel through bores (no numerals) for respectively receiving therein the end portions of the wires 40 and is attached to the large diameter section 56h of the cylindrical holder 56 at a large diameter portion thereof by the aid of a metal cylinder 64.As shown, the metal cylinder 64 has at its one end a flange 64a engaged via a metal ring 66 with an inwardly bent portion 54a of the thin cylindrical portion 54 of casing 48, and at its other end a flange 64b engaged via a plastic ring 68 (such as a Teflon ring) with a shoulder formed at the large diameter portion of the supporter 62. The conical surface of the supporter 62 is covered with an enlarged extension section of the aforementioned silicon rubber tube 44. The bore 58b thus enclosed receives therein the beforementioned permanent electrical junctions 46 and is packed with an alumina cement 70 for tightly holding the junctions 46. Numeral 72 is a wire for supporting the wires 40 projected into the bore 58b.

WHAT WE CLAIM IS:- 1. A thermocouple probe comprising: a tube member having a closed end and an open end and made of a nickel-based alloy containing from 5 to 25% by weight chromium and one or more of: (a) rare earth element(s) in an amount not exceeding 1% by weight; (b) aluminium in an amount not exceeding 5% by weight; and (c) one or more of the elements silicon, zirconium, titanium and niobium, pro vided that each element does not ex ceed 1% by weight; the balance being nickel; a wire member disposed in and axially ex

tending through said tube member and having one end welded to an inner wall of said closed end of said tube member, said wire member being made of a nickel-based alloy containing one or more of: (d) aluminium in an amount not exceeding 7% bv weight; (e) silicon in an amount not exceeding 7% by weight, provided that the sum of aluminium and silicon does not exceed 10% by weight; (f) rare earth element(s) in an amount not exceeding 1% by weight; and (g) one or more of the elements carbon, cobalt, manganese and iron, provided that the sum of these elements does not exceed 1% by weight; the balance being nickel; and an electrically insulating material filling said tube member so as to support said wire member substantially immovably in said tube member.
2. A thermocouple probe according to Claim 1, in which the outer surface of said tube member has a coating comprising one or more of Al2O , Cur203, SiO2, TiO2, BeO and Zero2.
3. A thermocouple probe according to Claim 1 or Claim 2, in which said tube member is formed at its closed end with a portion of reduced diameter and said wire member is formed at said one end with a portion of reduced diameter.
4. A thermocouple probe according to Claim 1, substantially as hereinbefore described with reference to, and as shown in, Figures 2, 4 and 5 of the accompanying drawings.
5. A thermocouple probe according to Claim 1, substantially as hereinbefore described with reference to, and as shown in, Figure 3 of the accompanying drawings.