EP3247942B1

EP3247942B1 - Glow plug including a load sensor and a welded flexible distal membrane having a transversal flexible collar

Info

Publication number: EP3247942B1
Application number: EP16707746.0A
Authority: EP
Inventors: Alain Ramond; Gverino Ratosa
Original assignee: SIEVA d o o PE SPODNJA IDRIJA; Sieva doo PE Spodnja Idrija
Current assignee: SIEVA d o o PE SPODNJA IDRIJA; Sieva doo PE Spodnja Idrija
Priority date: 2015-03-04
Filing date: 2016-03-02
Publication date: 2018-12-12
Anticipated expiration: 2036-03-02
Also published as: EP3064835B1; EP3247942A1; WO2016139251A1; EP3064835A1

Description

The invention relates to a glow plug, especially for a diesel engine, comprising a heating rod and an integrated load sensor allowing cylinder pressure measurements to be carried out, in particular for real time control of the engine.
A heating rod of a glow plug is in the form of a rigid rod or bar which extends axially from the body of the plug into the combustion chamber. Throughout the text, the term "distal" and its derivatives denote directions, elements or parts that are situated axially on the side of the free extremity of the heating rod which is to extend into the combustion chamber, and the term "proximal" and its derivatives denote directions, elements or parts that are situated axially on the opposite side, that is to say towards the connection to the outside of the cylinder head of the engine on which the glow plug is to be mounted.
A heating rod extends towards the proximal side into the plug body and has a proximal extremity provided with an electrical connection forming a first electrical power supply terminal of the heating rod, generally with an electrode which extends axially beyond the proximal extremity of the heating rod. Throughout the text, a power supply electrode of a heating rod, where provided, is not considered to form an integral part of the heating rod itself.
The plug includes a cylindrical plug body having a threaded external portion for fitting on a cylinder head, and forming a cylindrical internal housing for receiving the proximal portion of the heating rod extending towards said proximal extremity, said housing having an opening for the passage of the heating rod such that the latter extends axially, projecting (on the distal side) beyond said proximal portion and the opening, and having a heating distal portion as far as the distal extremity of the heating rod.
The heating rod is either in the form of a ceramic bar which has been machined to shape and set (fixed by brazing or inserted by force (bracing)) into an external metal tube for mounting in the plug body; or in the form of a metal tube which is closed at its distal extremity and is of invariable standardized dimensions (this metal tube receiving an electrical power supply electrode). Whatever the form, the heating rod therefore always comprises an external metal tube. The outer diameter of this external metal tube is, in the proximal portion of the heating rod extending into the plug body, at least substantially constant, and according to the standards must be equal to 4 mm.
WO 2014/122958 discloses a glow plug, comprising:

a heating rod which has a proximal portion with a proximal extremity, provided with an electrical power supply connection,
a plug body having a receiving housing for the proximal portion of the heating rod,
a mounting bush for mounting the proximal portion of the heating rod in said receiving housing, the mounting bush comprising:
- -- a receiving sleeve for the heating rod, the receiving sleeve comprising a cylindrical body which is fixed rigidly and impermeably around said proximal portion of the heating rod,
- -- a fixing ring which is welded to an internal face of the receiving housing and extends around said proximal portion of the heating rod,
- -- a distal flexible membrane:
  - --- extending axially and then radially towards the exterior from an axial extremity in the distal direction, called the distal extremity, of the body of the receiving sleeve, the body of the receiving sleeve extending axially in the proximal direction around the heating rod starting from that distal extremity of the body of the receiving sleeve,
  - --- being connected rigidly to the plug body by a gas-impermeable connection comprising at least one weld of the flexible membrane to the fixing ring,
  - --- being impermeable to gases and delimiting a proximal zone of the receiving housing which is not exposed to the atmosphere of a combustion chamber of an engine which receives the glow plug,
  - --- being elastically deformable in flexion and having suitable elasticity in flexion to make axial translation movements of the heating rod relative to the plug body possible,
  - --- comprising a flexible collar which extends radially orthogonally relative to the body of the receiving sleeve,
  - --- being connected to said fixing ring at least by a radial extremity portion of said flexible membrane,
a load sensor extending entirely within said proximal zone of the receiving housing.

EP2469169 and EP2472181 describe a glow plug having a load sensing sleeve surrounding the heating rod in the receiving housing of the plug body, and a mounting bush for mounting the proximal portion of the heating rod in the receiving housing, the mounting bush comprising:

a receiving sleeve for the heating rod, this receiving sleeve comprising a cylindrical body which is fixed rigidly and impermeably around said proximal portion of the heating rod,
a fixing ring which is welded to a cylindrical internal face of the receiving housing and extends around said proximal portion of the heating rod,
a distal flexible membrane turned up in a U-shape or a J-shape:
- ▪ extending radially towards the exterior from a distal extremity of the body of the receiving sleeve, the body of the receiving sleeve extending axially in the proximal direction around the heating rod starting from that distal extremity,
- ▪ being connected rigidly to the plug body by a gas-impermeable connection comprising welding the flexible membrane to the fixing ring,
- ▪ being impermeable to gases and delimiting a proximal zone of the receiving housing which is not exposed to the atmosphere of a combustion chamber of an engine which receives the glow plug,
- ▪ being elastically deformable in flexion and having suitable elasticity in flexion to make axial translation movements of the heating rod relative to the plug body possible.

Such a glow plug comprising a mounting bush with a flexible membrane turned up in a U- or J-shape is satisfactory, especially with regard to the previous solutions mentioned in EP2469169 . It makes it possible in particular to obtain cylinder pressure measurements which are as good as those of dedicated laboratory sensors which are controlled in terms of temperature and can be mounted in place of a plug on an engine being tested in a laboratory. Nevertheless, the inventors have found, surprisingly, that it is in fact possible to improve the mounting still further. The signal supplied by the load sensing sleeve exhibits a slight lack of linearity in the form of a depression (called "undershoot") following each pressure pulse. Although this systematic and repetitive defect can easily be compensated by electronic processing of the signal, it is desirable to eliminate it without, however, damaging the advantages resulting from the mounting device set out in EP2469169 and EP2472181 .
The invention therefore aims to overcome those disadvantages by proposing a glow plug with which the depression defect ("undershoot") after a pressure pulse in the signals supplied by the load sensing sleeve is reduced and substantially eliminated, and which additionally have the advantages of the plugs according to EP2469169 and EP2472181 , especially with regard to the mechanical and thermal characteristics of the mounting -especially of the flexible membrane-, the possibility of mounting by inserting the heating rod by its proximal extremity into the mounting bush, the sensitivity of the sensor and its robustness towards thermal phenomena, the reliability and lifetime of the plug, and the possibilities of certification.
To that end, the invention relates to a glow plug according to claim 1.
After a lengthy and fruitless test campaign during which variations of different dimensional and material parameters of the mounting of EP2469169 were tested in order to explain and/or eliminate the phenomenon of a depression after a pressure pulse ("undershoot"), it was found, surprisingly, and without its being possible to give any clear explanation for this result, that simply modifying the flexible membrane according to the invention makes it possible on the one hand to preserve all the properties and all the advantages of a glow plug according to EP2469169 -especially in terms of sensitivity-, and on the other hand to greatly reduce, and substantially eliminate the depression defect after a pulse ("undershoot") in the signal supplied by the load sensing sleeve.

a receiving sleeve for the heating rod, the receiving sleeve comprising a cylindrical body which is fixed rigidly and impermeably around said proximal portion of the heating rod,
a fixing ring which is welded to an internal face of the receiving housing and extends around said proximal portion of the heating rod,
a distal flexible membrane:
- ▪ extending radially towards the exterior from an axial extremity in the distal direction, called the distal extremity, of the body of the receiving sleeve, the body of the receiving sleeve extending axially in the proximal direction around the heating rod starting from that distal extremity of the body of the receiving sleeve,
- ▪ being connected rigidly to the plug body by a gas-impermeable connection comprising at least one weld of the flexible membrane to the fixing ring,
- ▪ being impermeable to gases and delimiting a proximal zone of the receiving housing which is not exposed to the atmosphere of a combustion chamber of an engine which receives the glow plug,
- ▪ being elastically deformable in flexion and having suitable elasticity in flexion to make axial translation movements of the heating rod relative to the plug body possible,
- ▪ comprising a flexible collar which extends radially orthogonally relative to the body of the receiving sleeve,
- ▪ being connected to said fixing ring at least by a radial extremity portion of said flexible membrane,
a load sensor extending entirely within said proximal zone of the receiving housing,

extends radially towards the exterior in prolongation of said flexible collar,
is welded to the fixing ring to form said radial extremity portion,
extends axially starting from and beyond said flexible collar in the distal direction.

After a lengthy and fruitless test campaign during which variations of different dimensional and material parameters of the mounting of EP2469169 were tested in order to explain and/or eliminate the phenomenon of a depression after a pressure pulse ("undershoot"), it was found, surprisingly, and without its being possible to give any clear explanation for this result, that simply modifying the flexible membrane according to the invention makes it possible on the one hand to preserve all the properties and all the advantages of a glow plug according to EP2469169 -especially in terms of sensitivity-, and on the other hand to greatly reduce, and substantially eliminate the depression defect after a pulse ("undershoot") in the signal supplied by the load sensing sleeve.
In some particularly advantageous embodiments, in a glow plug according to the invention, said flexible collar is of constant axial thickness (that is to say which is the same throughout its extension in the radial direction, the collar having the general shape of a flat washer).
Furthermore, advantageously and according to the invention, the flexible membrane is welded to a distal extremity of the fixing ring, and an axial space is formed between the flexible collar and the distal portion of the fixing ring, for example by an internal bevel of that distal portion of the fixing ring, so as to allow the collar to deform in flexion in the proximal direction.
Advantageously and according to the invention, the flexible membrane also comprises an annular linking reinforcement which extends radially towards the exterior in a prolongation of the collar and is welded to said fixing ring to form said radial extremity portion. In some embodiments, advantageously and according to the invention, the annular linking reinforcement extends axially in the distal direction starting from and beyond the collar in the distal direction, that is to say the annular linking reinforcement has an axial thickness which is greater than the axial thickness of said collar. In those embodiments, the annular linking reinforcement extends in the distal direction beyond said collar.
In some possible embodiments, which can be combined with the preceding ones, the annular linking reinforcement may extend axially in the proximal direction starting from the periphery of the collar towards said fixing ring, forming a turned-up portion of the membrane. Thus, there again, the annular linking reinforcement has an axial thickness which is greater than the axial thickness of said flexible collar.
The flexible collar formed by the flexible membrane is, however, orthogonal to the receiving sleeve, and therefore also to the heating rod and to its principal axis. It therefore constitutes a portion which is transversal, flat and in particular without curvature except for the flared portion described herein below for connection to the body of the receiving sleeve, and the annular linking reinforcement for connection to the fixing ring.
In some embodiments, advantageously and according to the invention, the annular linking reinforcement has a proximal radial face welded to a distal extremity of said fixing ring -especially to a distal radial face of said fixing ring-. This method of fixing is particularly simple and effective. However, there is nothing to prevent the annular linking reinforcement, in a variant, from being welded in a recess formed at the external periphery of the distal extremity of said fixing ring.
In some embodiments, advantageously and according to the invention, the annular linking reinforcement has a radial thickness greater than the axial thickness of said collar. The annular linking reinforcement forms a distal peripheral portion of the membrane, ensuring optimum assembly of the membrane to said fixing ring, especially in the embodiments where the annular linking reinforcement has a proximal radial face welded to the distal extremity of the fixing ring.
Furthermore, in some preferable embodiments, advantageously and according to the invention, the proximal radial face of the annular linking reinforcement and the distal extremity of said fixing ring being in contact to each other according to a facing radial thickness, the proximal radial face of the annular linking reinforcement is welded to the distal extremity of said fixing ring over the whole of their facing radial thickness. Accordingly, the junction of the proximal radial face of the annular linking reinforcement and the distal extremity of said fixing ring does not have any non-welded contact surface between those two elements, which could be liable to cause disturbances (linearity defects) in the signals supplied by the load sensing sleeve. In addition, advantageously and according to the invention, the annular linking reinforcement preferably has a radial thickness which is greater than or equal to the radial thickness of said distal extremity face of said fixing ring to which it is welded.
In addition, in some embodiments, advantageously and according to the invention, the annular linking reinforcement extends radially so as to have a peripheral contact face in contact with an internal face of the receiving housing. It is to be noted that this close contact without radial gap avoids the insertion of calamine between the annular linking reinforcement and this internal face. A large radial thickness of the annular linking reinforcement allows its deformations to be minimized, and contact with the internal face of the receiving housing to be maintained. Said peripheral contact face of the annular linking reinforcement has shapes and dimensions which are conjugate with those of said internal face of the receiving housing, in particular and preferably cylindrical in revolution. Said peripheral contact face of the annular linking reinforcement constitutes a portion of the annular linking reinforcement and of the flexible membrane which, in the receiving housing, is situated furthest towards the exterior radially.
Furthermore, in some embodiments, advantageously and according to the invention, the annular linking reinforcement has a distal extremity face which has a junction with said peripheral contact face, said distal extremity face extending, at that junction, radially orthogonally to said peripheral contact face. Furthermore, at that junction, said distal extremity face also extends radially orthogonal to said internal face of the receiving housing. Other embodiments are possible, for example with said distal extremity face extending radially in a non-orthogonal direction and/or at least partially curved.
In some embodiments, advantageously and according to the invention, said peripheral contact face of the annular linking reinforcement is welded to said internal face of the receiving housing by at least one peripheral weld -especially at said junction-. Such a weld, in addition to the weld of the radial extremity portion of the collar to said fixing ring (which is itself welded to the internal face of the receiving housing), avoids separation of said peripheral contact face of the annular linking reinforcement relative to said internal face of the receiving housing.
In addition, in some embodiments, advantageously and according to the invention, said collar is connected to the distal extremity of the body of the receiving sleeve by a curved flared portion with continuous curvature having a concavity oriented towards the proximal extremity of the heating rod. Preferably, the curvature of this flared portion remains in the same direction with the concavity oriented in the proximal direction along the flared portion. Furthermore, this curvature is preferably constant (as an arc of a circle), but any other form is possible.
Furthermore, advantageously and according to the invention, said curved flared portion is welded to the heating rod at a junction zone of said curved flared portion with the heating rod. Undesired separation of the distal extremity of the receiving sleeve relative to the heating rod during deformation of the flexible membrane is thus avoided. The deformations of the flexible membrane are thus only flexion deformations of the flared portion and/or of the collar.
In some embodiments, advantageously and according to the invention, said curved flared portion has an external radius of curvature of less than 0.5 mm -in particular between 0.1 mm and 0.3 mm-. Other values are possible.
Furthermore, the radial thickness of the receiving sleeve is determined according to criteria which are different than the ones used for determining for the thickness of the flexible membrane. Thus, in some embodiments, advantageously and according to the invention, the body of the receiving sleeve is formed of a cylindrical wall having a smaller radial thickness in a distal portion of this cylindrical wall, said distal portion extending at the distal extremity of the body of the receiving sleeve.
Furthermore, advantageously and according to the invention, said collar has an axial thickness of the same order as the radial thickness of said distal portion - in particular identical to that radial thickness-. The same is true of the flared portion.
For example, the distal portion and the collar have a radial thickness of less than 0.5 mm - in particular between 0.2 mm and 0.5 mm-, for example of the order of 0.4 mm. Other values are possible. Preferably, in some embodiments according to the invention, the receiving sleeve has a constant thickness from its proximal extremity to the distal portion.
Furthermore, the distal portion extends over an axial length which is, for example, between 0.5 mm and 5 mm, in particular of the order of 1 mm. Other values are possible.
The invention is, moreover, as compatible with a heating rod in the form of a ceramic bar as with a heating rod in the form of a metal tube. In any case, in some embodiments, advantageously and according to the invention, the receiving sleeve is placed around a peripheral metal tube of said proximal portion of the heating rod, the peripheral metal tube extending axially also into said proximal zone of the receiving housing. In a first variant embodiment, the heating rod is formed substantially of a metal tube, and said receiving sleeve extends around the proximal portion of the metal tube. In another variant embodiment, the heating rod is formed of a ceramic bar set in at least one external metal tube, said receiving sleeve extends around a proximal portion of such an external metal tube of the heating rod. Other variants are possible, for example a heating rod whose external surface inserted in the receiving sleeve is not metal but formed of ceramic material.
In addition, a plug according to the invention is advantageously further characterized in combination by all or some of the characteristics described by EP2469169 and/or EP2472181 .
In particular, in some embodiments, advantageously and according to the invention, the tubular load sensor immediately axially adjoins a proximal axial extremity of the receiving sleeve opposite said distal extremity of the receiving sleeve.
Furthermore, advantageously and according to the invention:

said mounting bush has a face, called the first fixing face, of the fixing ring which is fixed rigidly and impermeably by at least one peripheral weld to an internal wall facing the receiving housing,
said mounting bush has a face, called the second fixing face, of said receiving sleeve which is fixed rigidly and impermeably around said proximal portion of the heating rod,
said receiving sleeve is guided in axial translation in the fixing ring,
said mounting bush formed of said receiving sleeve, said distal flexible membrane and said fixing ring, is adapted to ensure impermeability between the heating rod and the plug body at the distal extremity thereof.

In a plug according to the invention, the fixing ring simultaneously permits good guiding of the receiving sleeve, good fixing of the flexible membrane and of the whole inside the receiving housing of the plug body, perfect impermeability with respect to the corrosive atmosphere of the combustion chamber, and optimization of the heat transfers between the heating rod and the plug body on the one hand via the flexible membrane and on the other hand by radial thermal conduction between the two fixing faces, which preferably face one another radially.
It further allows an easy mounting of the load sensor, which can advantageously be in the form of a tubular sleeve provided with sensitive piezoelectric elements. This load sensing sleeve can be mounted with a distal extremity fixed to a proximal extremity of the receiving sleeve, and with a proximal extremity fixed to a proximal extremity of the fixing ring, especially via an external linking tube.
Mounting of a plug according to the invention can be carried out by axial insertion in the proximal direction of the proximal extremity of the heating rod into the receiving sleeve of the mounting bush, and then, after execution of each weld of the receiving sleeve to the heating rod, by axial insertion in the distal direction of the fixing ring around the receiving sleeve, and then, after execution of the weld between the fixing ring and the flexible membrane, by axial insertion in the distal direction of the load sensing sleeve around the proximal extremity of the heating rod against the mounting bush.
Accordingly, in some embodiments, advantageously a plug according to the invention is characterized by at least one of the following features:

the load sensor is a tubular load sensing sleeve which extends entirely within said proximal zone of the receiving housing, around said proximal portion of the heating rod,
the tubular load sensing sleeve has:
- ▪ a first axial extremity which is connected to the heating rod in such a manner that it is driven in axial translation by the movements of the heating rod at least in the proximal direction towards said proximal extremity of the heating rod, and in which the heating rod tends to return to the interior of the plug body, and
- ▪ a second axial extremity opposite said first axial extremity, the second axial extremity being connected to the plug body in such a manner that the axial translation movements of the heating rod relative to the plug body generate axial compression and/or traction stresses in said load sensing sleeve,
said first axial extremity is a distal axial extremity of the tubular load sensing sleeve axially opposite said proximal extremity of the heating rod, and wherein said second axial extremity is a proximal axial extremity of the tubular load sensing sleeve oriented axially towards said proximal extremity of the heating rod,
said first axial extremity is connected to the peripheral metal tube of said proximal portion of the heating rod,
said second axial extremity is connected to said fixing ring.

The invention also concerns a glow plug, which is characterized in combination by all or some of the characteristics mentioned above or below.
Other objects, characteristics and advantages of the invention will appear on reading the following description, which refers to the attached figures, which represent embodiments of the invention as non-limiting examples, and in which:

Fig. 1 is a schematic view in elevation of a glow plug according to an embodiment of the invention,
Figs. 2 is a schematic view in axial cross-section of the distal part of a glow plug according to an embodiment of the invention,
Fig. 3 is a schematic view in axial cross-section of the distal part of a glow plug according to an embodiment of the invention,
Fig. 4 to 6 are schematic views in axial cross-section of the distal part of a plug body according to three different embodiments of the invention,
Fig. 7 is a diagram illustrating curves of variation over time of the pressure in a diesel engine in particular as measured by a glow plug according to the invention.

A glow plug according to the invention includes a heating rod 11 which, in the example of Fig. 1, is of the so-called all-metal type, consisting essentially of a metal tube 59. This metal tube 59 is thus a metal tube which can be called peripheral, and receives an electrical power supply electrode 12 (which is not considered to form an integral part of the heating rod itself), so that power can be supplied to it by a current which is capable of heating at least one electrical resistance 69 which is connected to the distal extremity of the electrode 12 within the metal tube 59, and capable of generating (by Joule effect) heating of the distal extremity of the heating rod 11. The electrode 12 extends into the metal tube 59, on a certain length of the latter, and is insulated from it by an inserted insulating material 64. The electrode 12 extends axially in a projection beyond the proximal extremity 38 of the heating rod 11. The electrode 12 has a proximal extremity which is connected to an electrical power supply connector 98. This heating rod 11 is received in a plug body 13, which for this purpose forms a receiving housing 14.
The heating rod 11 extends longitudinally according to a principal axis 41, which is also an axis of the plug body 13, of the receiving housing 14, and of a threaded portion 43 of the external wall 42 of the plug body 13, said threaded portion being configured and intended to make it possible to fix the glow plug in an internally threaded hole which passes through the cylinder head of an engine. Throughout the text, the terms "axial" and "radial" and their derivatives refer to the principal axis 41, "axial" meaning parallel to said axis 41, "radial" meaning orthogonal to said axis 41.
The plug body 13, its external wall 42, the receiving housing 14 and the internal wall 44 of the plug body 13, which delimits the receiving housing 14, is preferably rotationally symmetrical around the principal axis 41, but any other form which does not conform to such a symmetry of revolution is equally conceivable. That being so, the plug body 13, in its distal portion forming the receiving housing 14, is in the form of a tube 45, the internal wall 44 of which is cylindrical (rotationally symmetrical or not, i.e. its base is not necessarily circular) relative to the principal axis 41. This tube 45 has a distal extremity 46, which is closed by a truncated washer 47, which forms the distal extremity of the plug body 13. The receiving housing 14 thus extends from the truncated washer 47 axially in the proximal direction.
The heating rod 11 extends axially in the distal direction beyond the plug body 13 and the washer 47, through the central opening of the latter, and has a distal portion 49 which is designed to extend into the atmosphere of the combustion chamber of an engine. The heating rod 11 also has a proximal portion 50, which extends into the receiving housing 14.
The receiving housing 14 contains a mounting bush 48 of the heating rod 11. The function of this mounting bush 48 is to fix the heating rod 11 solidly relative to the plug body 13, while making slight axial translation movements of the heating rod 11 relative to the plug body 13 possible, under the effect of variations of the pressure of the atmosphere of the combustion chamber. The mounting bush 48 also includes sealing means 15, 16, ensuring impermeability between the heating rod 11 and the plug body 13, in such a way as to delimit a proximal zone 51, which is not exposed to the atmosphere of the combustion chamber, of the receiving housing 14.
The mounting bush 48 includes a fixing ring 15, which is cylindrical overall and has an external cylindrical wall 19, which faces radially towards the exterior and is fixed rigidly and impermeably to the internal wall 44 (which faces radially towards the interior) of the tube 45 delimiting the receiving housing 14, in particular by at least one peripheral weld 21, which can be implemented by laser through the thickness of the tube 45. The external wall 19 of the fixing ring 15 thus forms a first fixing face of the mounting bush 48, to the facing internal wall 44 of the tube 45. Preferably, the fixing ring 15 is fixed to the internal wall 44 of the tube 45 (plug body 13) by only one peripheral weld 21, so that any deformation of the plug body 13 (due to thermal and/or pressure variations) does not produce stresses or deformations in said fixing ring.
The fixing ring 15 has an internal cylindrical wall 20, which forms a hole which axially extends through the fixing ring 15. The internal diameter of this internal wall 20 of the fixing ring 15 is greater than the peripheral outer diameter of the proximal portion 50 of the heating rod 11 facing it, so as to provide for a radial space allowing the insertion of a receiving sleeve 16 between the fixing ring 15 and the proximal portion 50 of the heating rod 11.
The receiving sleeve 16 has a tubular principal body 60 in the form of a fine metal tube. This fine metal tube is preferably of stainless steel with high characteristics, in particular having a Young's modulus greater than 150 GPa, in particular of the order of 200 GPa, an elastic limit greater than 600 MPa, e.g. of the order of 800 MPa, and a fatigue strength (maximum stress for which the number of cycles is infinite) of at least 300 MPa, e.g. of the order of 400 MPa. For example, it is of 17-4PH steel or inconel steel.
The tubular body 60 of the receiving sleeve 16 has an internal cylindrical wall 22 (facing radially towards the interior), the internal diameter of which corresponds to that of the proximal portion 50 of the heating rod 11 (in particular typically of 4 mm according to the standards in force), so as to be in contact with this proximal portion 50 and fixed rigidly and impermeably to the latter by at least one peripheral weld 23 (in particular two peripheral welds 23a, 23b in the example shown in Fig. 1). The internal wall 22 of the receiving sleeve 16, which is fixed rigidly and impermeably around the proximal portion 50 of the heating rod 11, thus forms a second face 22 for fixing the mounting bush 48 on the heating rod 11.
The tubular body 60 of the receiving sleeve 16 has a peripheral cylindrical wall 52 which faces radially towards the exterior, i.e. facing the internal wall 20 of the fixing ring 15. A very small gap - in particular of the order of 0.2 mm - is created radially between these cylindrical facing walls 52, 20, so as to make axial translation movements of the receiving sleeve 16 relative to the fixing ring 15 possible. The receiving sleeve 16 has a flexible distal membrane which is fixed rigidly and impermeably at least to the distal extremity 25 of the receiving ring 15.
The flexible distal membrane is an extension of the tubular body 60 of the receiving sleeve 16, at a distal extremity 24 thereof.
Said flexible membrane comprises a flexible collar 26 which extends radially orthogonally relative to the body 60 of the receiving sleeve. Said collar 26 is flat (in the form of a flat washer), with a constant axial thickness over the whole of its radial extent. It is prolonged radially by an annular linking reinforcement 58 which:

extends radially outside the collar 26,
forms a radial extremity portion of said flexible membrane,
is welded to the fixing ring 15,
extends axially in the distal direction starting from and beyond the collar 26 in the distal direction.

The flexible membrane is thus welded to said fixing ring 15 at least by the annular reinforcement 58, which constitutes a radial extremity portion of the flexible membrane welded to the fixing ring 15. In this way, any deformation of the plug body 13 (due to thermal and/or pressure variations) does not produce stresses or deformations in the flexible membrane. The flexible membrane is thus isolated from such deformations of the plug body 13 by the fixing ring 15, which has a greater inertia and is preferably fixed to the plug body 13 by only one welding line, as above mentioned.
The annular reinforcement 58 is welded to the distal extremity 25 of the fixing ring 15 by a weld 39 between a proximal (that is to say oriented in the proximal direction) radial face 61 of the annular reinforcement 58 and a distal (that is to say oriented in the distal direction) radial face 62 of the distal extremity 25 of the fixing ring 15. The weld 39 extends radially over the whole of the contact surface between the facing radial faces 61, 62, so that there is no contact or gap without welding between those facing radial faces 61, 62 welded to one another over the whole of their common surface. This has the result in particular that the signal is not disturbed by the variation of a gap between those pieces under pressure variations, and remains representative of the pressure values.
Preferably, the annular reinforcement 58 has a radial thickness which is slightly greater than the radial thickness of the distal radial face 62 of the extremity 25 of the fixing ring 15, that is to say which extends radially towards the interior slightly beyond that distal radial face 62.
The proximal radial face 61 of the annular reinforcement 58 extends radially in a prolongation of the proximal radial face of the flexible collar 26, that is to say it constitutes a radial extension thereof. The flexible collar 26 is connected to the distal extremity 24 of the body 60 of the receiving sleeve 16 by a curved flared portion 40 with continuous curvature and whose concavity is oriented towards the proximal extremity 38 of the heating rod 11. In the embodiment shown, and preferably, this continuous curvature is an arc of a circle, but there is nothing to prevent other forms from being provided. This curved flared portion 40 has an external radius of curvature (concavity side) of preferably less than 0.5 mm -especially between 0.1 mm and 0.3 mm-. It thus forms a linking fillet between the proximal radial face of the flexible collar 26 and the peripheral cylindrical face of the body 60 of the receiving sleeve 16.
The distal extremity 25 of the fixing ring 15 additionally has an internal bevel 63 which extends radially towards the interior and in the proximal direction starting from the distal radial face 62 so as to form an axial space 65 between the flexible collar 26 and the distal portion of the fixing ring 15, which axial space 65 allows the collar 26 to deform in flexion in the proximal direction as required.
The flared portion 40, the collar 26 and the annular reinforcement 58 are formed by an extension of the body 60 of the receiving sleeve 16. The flared portion 40, the collar 26, the annular reinforcement the body 60 are thus formed in one piece, which can be obtained by stamping and machining a metal tube.
The tubular body 60 of the receiving sleeve 16 is formed of a cylindrical wall having a constant radial thickness over the whole of its length, apart from a distal portion 66 having a smaller thickness at the distal extremity of the body 60 of the receiving sleeve 16. To that end, a peripheral recess 71 is formed radially towards the interior starting from the external cylindrical peripheral face of the cylindrical wall forming the body 60. The flexible collar 26 and the flared portion 40 advantageously have an axial thickness of the same order as the radial thickness of that distal portion 66. In fact, the collar 26 and the flared portion 40 are advantageously formed by stamping the tube constituting the tubular body 60 after machining thereof to form said recess 71. This smaller thickness allows the flexibility of the flexible collar 26 and of the flared portion 40, and therefore that of the flexible membrane, to be adjusted.
The annular reinforcement 58 has a radial thickness which is greater than the axial thickness of the flexible collar 26. It is in the general form of a cylindrical ring which extends beyond the axial thickness of the collar 26 in the distal direction and has an external cylindrical face 67, an internal cylindrical face 68 and radial distal extremity face 70. The external cylindrical face 67 of the annular reinforcement 58 constitutes a peripheral face which comes into contact with the internal face 44 of the receiving housing 14. Because the distal extremity face 70 of the annular reinforcement 58 is radial, it is orthogonal to the external cylindrical face 67 at their junction (formed by a circular edge).
For example, the internal diameter of the receiving sleeve 16 being of the order of 4 mm, the thickness of the distal portion 66, of the flared portion 40 and of the flexible collar 26 is between 0.1 and 0.3 mm, in particular of the order of 0.2 mm; the thickness of the cylindrical wall forming the body 60 of the receiving sleeve 16 is between 0.2 mm and 0.5 mm, in particular of the order of 0.35 mm. The flexible collar 26 extends radially over a distance of between 0.5 mm and 2 mm, in particular of the order of 1 mm (distance considered between the internal cylindrical face of the body 60 of the receiving sleeve 16 and the internal cylindrical face of the annular reinforcement 58). The annular reinforcement 58 has a radial thickness and an axial thickness of between 0.4 mm and 1 mm, in particular of the order of 0.6 mm. Other values are possible.
As is shown in Figures 4 to 6, different variants are possible for executing the welds between the tube 45 forming the plug body 13, the fixing ring 15, the flexible membrane, the receiving sleeve 16 and the heating rod 11. All these welds are peripheral welds which can be implemented by means of a laser.
In the first variant of Figure 4, the fixing ring 15 is welded to the tube 45 forming the plug body 13 by a weld 21 which passes through the thickness of the tube 45. The receiving sleeve 16 is welded to the heating rod 11 by a weld 23 which passes through the thickness of the body 60 of the receiving sleeve 16, offset slightly towards it proximal extremity 27. The flexible membrane is welded to the fixing ring 15 by a weld 39 between the annular reinforcement 58 and the distal extremity of the fixing ring 15. This weld 39 radially extends over the whole of the axially facing surfaces of the annular reinforcement 58 and of the distal extremity of the fixing ring 15.
The variant of Figure 5 differs from the preceding variant in that the receiving sleeve 16 is welded to the heating rod 11 by a first weld 23a, which is similar to the weld 23 of the variant of Figure 4, and by a second weld 23b, which is located at the junction of the flared portion 40 with the heating rod 11, that is to say at the distal extremity of the tubular body 60, the second weld 23b passing through the thickness of the distal portion 66 of the tubular body 60. In this manner, undesired separation of the distal portion 66 relative to the heating rod 11 is avoided when the flared portion 40 and/or the collar 26 of the flexible membrane is(are) deformed.
The variant of Figure 6 differs from the preceding variant in that said peripheral contact face 67 of the annular linking reinforcement 58 is welded to said internal face 44 of the receiving housing 14 by a peripheral weld 57 which, in the example shown, is situated at the junction of the peripheral contact face 67 of the annular reinforcement 58 with its distal extremity face 70. This weld 57 especially avoids undesired separation of the peripheral face 67 of the annular reinforcement 58 relative to the internal face 44 of the plug body 13.
The flexible collar 26 forms an extremity portion of the receiving sleeve 16 having elasticity in flexion, and thus allowing axial translation movements of the heating rod 11 relative to the fixing ring 15 (and thus relative to the plug body 13) in a sufficiently large amplitude range, and with elastic retraction of the heating rod in axial translation according to a predetermined stiffness coefficient K1, which can be adjusted to a relatively low value by an appropriate choice of the material forming the receiving sleeve 16 and its thickness. Preferably, the receiving sleeve 16, including the flexible collar 26, has approximately constant thickness.
It should be noted that the flexible collar 26 of the distal extremity of the receiving sleeve 16 has numerous advantages. In particular, such a flexible collar 26 can be manufactured simply by pressing. It makes it possible to insert the receiving sleeve via the proximal extremity of the heating rod 11, with no risk of damaging the latter. When deformation occurs, the stresses within the flexible collar 26 are at their maximum value on the proximal side, which is not exposed to the corrosive atmosphere of the combustion chamber. Despite relatively large thickness, in particular of the order of 0.2 mm, a relatively low coefficient of elasticity is obtained, making relatively large movements of the heating rod 11 possible. It also makes it possible to implement a thermally conductive element of small dimensions, and thus of low thermal resistance, between the heating rod 11 and the plug body 13, at the distal extremity of the latter.
The tubular body 60 of the receiving sleeve 16 passes axially throughout the length of the fixing ring 15, and extends slightly beyond the proximal extremity 28 of the latter. The cylindrical walls 52, 20 facing each other, and the small gap (typically of the order of 0.2 mm) which separates them, as well as the materials forming the receiving sleeve 16 and the fixing ring 15, which are metallic and thermally conductive, facilitate thermal exchanges between the proximal portion 50 of the heating rod 11 and the plug body 13 radially, at the level of the receiving sleeve 16 and the fixing ring 15. In other words, a radial thermal bridge is thus implemented by the receiving sleeve 16 and the fixing ring 15. The result, in particular, is that the elements in the receiving housing 14, beyond the receiving sleeve 16 and the fixing ring 15 of the proximal side, including the load sensing sleeve 17 described below, are less exposed to the high temperatures of the heating rod 11 and the combustion chamber.
The proximal extremity 27 of the receiving sleeve 16 comes into contact with a distal extremity 32 of a load sensing sleeve 17, which is tubular overall, and extends axially, in prolongation of the receiving sleeve 16, entirely around the proximal portion 50 (of greater diameter, equal to 4 mm) of the metal tube 59 of the heating rod 11. The load sensing sleeve 17 has symmetry of revolution around the axis 41, and is coaxial to the heating rod 11 and the receiving housing 14. The load sensing sleeve 17 adjoins, axially and directly, the mounting bush 48 on the proximal side thereof.
The load sensing sleeve 17 can be made as described in EP2472181 . In particular, the load sensing sleeve 17:

is above the fixing ring 15 on the proximal side,
immediately axially adjoins the proximal axial extremity of the receiving sleeve 16 opposite to said distal extremity 24 of the receiving sleeve 16,
entirely extends in said proximal zone of the receiving housing, around said proximal portion of the heating rod,
is made of stacked washers comprising at least one washer of piezoelectric material and at least one washer of electrically conductive material.

Furthermore, the load sensing sleeve 17 comprises a first axial extremity, which is connected rigidly to the heating rod 11 -more precisely to the metal tube 59 of the heating rod 11- via the receiving sleeve 16. In the embodiments of the drawings, this first axial extremity is the distal extremity 32 of the load sensing sleeve 17, axially opposite said proximal extremity 38 of the heating rod 11 This first axial extremity 32 is fixed to said peripheral metal tube 59 of the proximal portion of the heating rod. This first axial extremity 32 is thus driven in axial translation by the movements of the heating rod 11 according to the axis 41, at least in the proximal direction, and, in the shown embodiments, in both directions.
The load sensing sleeve 17 also comprises a second axial extremity, opposite the first axial extremity, this second axial extremity being connected to the plug body in such a way that axial translation movements of the heating rod 11 relative to the plug body generate axial compression and/or traction stresses in said load sensing sleeve17. In the embodiments of the drawings, this second axial extremity is a proximal extremity 37 of the load sensing sleeve 17, and is linked to said fixing ring 15.
A fine metal linking tube 18 extends around the load sensing sleeve 17 from a proximal ring 36 thereof, and on the distal side as far as the fixing ring 15. The proximal ring 36 has a proximal extremity which is the proximal extremity 37 of the load sensing sleeve 17. This linking tube 18 is thus interposed between the load sensing sleeve 17 and the internal wall 44 of the receiving housing 14. The linking tube 18 has a proximal extremity 30 which is fixed rigidly to the proximal ring 36 of the load sensing sleeve 17 by at least one peripheral weld 54, and a distal extremity 29 which is fixed rigidly by at least one peripheral weld 55 to the proximal extremity 28 of the fixing ring 15, preferably in a recess which is made in the wall of the latter and faces radially towards the exterior to avoid any excess thickness.
A radial gap is made between the washers of the load sensing sleeve 17 and the linking tube 18. Similarly, the linking tube 18 is sufficiently fine for a radial gap to be made throughout its axial length, between its cylindrical wall facing the exterior radially and the internal wall 44 of the receiving housing 14 of the plug body 13 facing it. In this way, the linking tube 18 does not come into contact with the plug body 13.
The linking tube 18 thus connects the proximal extremity 37 of the load sensing sleeve 17 to the fixing ring 15, and thus to the plug body 13. But since this link transfers the point of support of the proximal extremity 37 of the load sensing sleeve 17 to the fixing ring 15, the compression stresses which are generated in the load sensing sleeve 17 are in fact representative of the shear loads, which are generated by the axial movements of the heating rod 11, between the proximal portion 50 of the heating rod 11 in contact with the receiving sleeve 16 and the fixing ring 15. Also, since the two axial extremities of the load sensing sleeve 17 rest respectively on the heating rod 11 (more precisely on the metal tube 59 of the heating rod 11) and on the plug body 13, in zones which at least approximately face each other radially, the signals which the load sensing sleeve 17 supplies are not perturbed by deformation of the cylinder head, the plug body 13 or other intermediate elements, except the linking tube.
The linking tube 18, which is very fine, has some elasticity in axial traction, retracting the proximal extremity 37 of the load sensing sleeve 17 in the distal direction, with a predetermined stiffness coefficient K2, the value of which can be adjusted by an appropriate choice of material forming the linking tube 18 and its dimensions. For example, the linking tube 18 is formed of a material chosen from stainless steels with high characteristics, and its thickness (difference between the radius of its external wall and that of its internal wall) is of the order of 0.2 mm. The linking tube 18 is preferably of stainless steel with high characteristics, having a Young's modulus greater than 150 GPa, in particular of the order of 200 GPa, an elastic limit greater than 600 MPa, e.g. of the order of 800 MPa, and a fatigue strength (maximum stress for which the number of cycles without breakage is infinite) of at least 300 MPa, e.g. of the order of 400 MPa. For example, it is of 17-4PH steel or inconel steel.
The electrical connection of electrode 12 can be made as described in EP2472181 .
Preferably, at least in the embodiments where the load sensing sleeve 17 includes at least one piezoelectric washer, the latter is assembled with a preload in axial compression, e.g. of the order of 100 N, to ensure that each piezoelectric washer is always compressed (by the elastic retractions K1 of the flexible collar 26 and K2 of the linking tube 18, which are prestressed), whatever the axial position of the heating rod 11, including in the case of low pressure in the combustion chamber. Consequently, the load sensing sleeve 17 supplies signals representing the variation of the axial compression stress to which it is subjected in the course of the axial movements of the heating rod 11 relative to the plug body 13. This axial compression preload can be obtained by exerting an axial compression load between the fixing ring 15 (which has a shoulder extending radially towards the exterior and facing towards the distal side) and the proximal extremity 30 of the linking tube 18, at the instant of executing the peripheral weld 55 of the distal extremity 29 of the linking tube 18 onto the proximal extremity 28 of the fixing ring 15.
A process for manufacturing a glow plug according to the invention can be as follows.
First the receiving sleeve 16 is fixed around the heating rod 11 by peripheral welding, then the fixing ring 15 is inserted and fixed around the receiving sleeve 16, in the flexible collar 26, by peripheral welding. Then the load sensing sleeve 17 is introduced via the proximal extremity 38 of the heating rod 11, until it comes against the proximal extremity of the receiving sleeve 16. A peripheral weld 53 of a distal ring 31 of the load sensing sleeve 17 onto the receiving sleeve 16 is executed. Then the linking tube 18 is introduced, via the proximal extremity 38 of the heating rod 11, around the load sensing sleeve 17. Then the peripheral weld of the proximal extremity 30 of the linking tube 18 onto the proximal extremity 37 of the load sensing sleeve 17 is executed. Then, by axial compression (of the order of 100 N), the peripheral weld of the distal extremity 29 of the linking tube 18 onto the proximal extremity 28 of the fixing ring 15 is executed. Then the electrical connections of the heating rod 11 (via the electrode 12) and load sensing sleeve 17 are executed, and the various elements in the proximal portion of the glow plug are assembled. Then, via the distal extremity of the heating rod 11, the tube 45 of the plug body 13, which forms the receiving housing 14, is inserted, then the truncated distal extremity washer 47, and the whole is fixed by peripheral welding.
When the cylinder pressure increases, the heating rod 11 moves slightly axially in translation in the proximal direction, which compresses the load sensing sleeve 17, the piezoelectric washer(s) of which supply the electrical charges representing this compression.
The flexible collar 26 of the flexible membrane retracts the heating rod 11 of the distal side against the cylinder pressure, according to the stiffness coefficient K1. This retraction makes it possible to reduce, for the same value of pressure increase, the compression stresses to which the load sensing sleeve 17 is subjected, which increases its working range. It also makes it possible to limit the stresses to which the linking tube 18 is subjected.
The elasticity of the linking tube 18, according to the stiffness coefficient K2, makes it possible to reduce, on the one hand, the load to which the load sensing sleeve 17 is subjected for the same cylinder pressure, and on the other hand the compression stresses to which the flexible collar 26 is subjected. The greater the value of the stiffness coefficient K2, the greater is the stress to which the load sensing sleeve 17 is subjected (for the same cylinder pressure). Also, the elasticity of the linking tube 18 according to the stiffness K2 makes it possible to retain an impermeability membrane (formed by the flexible collar 26) of sufficient thickness (in particular of the order of 0.2 mm), to the advantage of good disposal of calories by thermal conduction via this impermeability membrane, while avoiding this impermeability membrane being subjected to excessive stresses (at the risk of causing deformations in plasticity or deterioration of the membrane) under the effect of differential thermal expansion.
The choice of the two stiffness coefficients K1 and K2 makes it possible to adjust the pass band of the thus formed mechanical system, e.g. so that it has a first normal mode (fundamental or natural frequency) with axial oscillations greater than 10 kHz. For example, it has been possible to obtain good results with K1 = K2 ≈ 40 N/µm.
As is seen, a glow plug of standard dimensions is obtained, incorporating a load sensor which supplies signals representing the cylinder pressure in a perfectly reliable and precise manner, not perturbed by the normal modes of deformation of the heating rod 11 or of the electrical power supply electrode 12, or by deformation of the plug body 13 or cylinder head. In practice, it is noticed that the load sensing sleeve 17 is not subjected to temperatures greater than 170 °C.
The invention is as compatible with a heating rod 11 in the form of a metal tube 59, as with a heating rod in the form of a ceramic bar set in a peripheral metal tube.
The invention provides with a glow plug with which the "undershoot" (i.e. improper depression of the signal after a pressure pulse) are substantially deleted, and no longer detectable.

EXAMPLE:

A series of test were conducted with glow plugs according to the invention and with glow plugs according to the prior art ( EP2469169 ).
A hundred of glow plugs according to the invention (variant of figure 5) were manufactured, the half of which with metallic heating rod, the other half with a ceramic rod. A hundred of glow plugs according to EP2469169 were manufactured, the half of which with metallic heating rod, the other half with a ceramic rod.
Those glow plugs were tested on three different standard car diesel engines of following maximum power and maximum cylinder pressure: 200 HP (147.2 kW), 11 MPa; 200 HP (147.2 kW), 21 MPa; 160 HP (117.16 kW), 16 MPa.
The pressure signals were obtained with various engine speeds from idle to maximum engine speed.
As shown on figure 7, the glow plugs according to EP2469169 (curve C1) produced an undershoot with a mean value of about 1% of the maximum value of the pressure Pmax of each pressure pulse, whereas the glow plugs according to invention (curve C2) produced an undershoot with a mean value of about 0.1% of the maximum value of the pressure Pmax of each pressure pulse, which is substantially insignificant when compared to the theoretical curve C0, and does not have to be electronically compensated.
The invention can be the subject of numerous variants in relation to the embodiments described above and shown in the figures. In particular, the load sensing sleeve 17 can include a single piezoelectric washer or more than two piezoelectric washers, the proximal extremity of the load sensing sleeve 17 can be welded directly onto the heating rod, etc. Also, it is possible to provide that the axial extremity of the load sensing sleeve connected to the heating rod is its proximal extremity (and not its distal extremity), the distal extremity of the load sensing sleeve being connected to the plug body. The welds can be implemented by laser welding or otherwise.

Claims

A glow plug, comprising:
- a heating rod (11) which has a portion, called the proximal portion (50), having an axial extremity, called the proximal extremity (38), provided with an electrical power supply connection for the heating rod, an axial direction of the heating rod (11) oriented towards that proximal extremity (38) being called the proximal direction, an axial direction of the heating rod (11) opposite the proximal direction being called the distal direction,

- a plug body (13) having a receiving housing (14) for the proximal portion of the heating rod, the heating rod having a distal portion which extends axially in the distal direction projecting beyond a distal axial extremity of the plug body opposite said proximal extremity of the heating rod,

- a mounting bush (48) for mounting the proximal portion of the heating rod in said receiving housing (14), the mounting bush comprising:
-- a receiving sleeve (16) for the heating rod, the receiving sleeve comprising a cylindrical body which is fixed rigidly and impermeably around said proximal portion of the heating rod,

-- a fixing ring (15) which is welded to an internal face of the receiving housing (14) and extends around said proximal portion of the heating rod,

-- a distal flexible membrane:
▪ extending radially towards the exterior from an axial extremity in the distal direction, called the distal extremity, of the body of the receiving sleeve, the body of the receiving sleeve extending axially in the proximal direction around the heating rod starting from that distal extremity of the body of the receiving sleeve,

▪ being connected rigidly to the plug body by a gas-impermeable connection comprising at least one weld of the flexible membrane to the fixing ring,

▪ being impermeable to gases and delimiting a proximal zone of the receiving housing which is not exposed to the atmosphere of a combustion chamber of an engine which receives the glow plug,

▪ being elastically deformable in flexion and having suitable elasticity in flexion to make axial translation movements of the heating rod relative to the plug body possible,

▪ comprising a flexible collar which extends radially orthogonally relative to the body of the receiving sleeve,

▪ being connected to said fixing ring (15) at least by a radial extremity portion of said flexible membrane,

- a load sensor extending entirely within said proximal zone of the receiving housing,
wherein said flexible membrane is welded to said fixing ring (15) at least by a radial extremity portion of said flexible membrane welded to said fixing ring (15), and wherein said flexible membrane also comprises an annular linking reinforcement (58) which:
- extends radially towards the exterior in prolongation of said flexible collar,

- is welded to the fixing ring (15) to form said radial extremity portion,

- extends axially starting from and beyond said flexible collar in the distal direction.
A glow plug as claimed in claim 1, wherein said annular linking reinforcement (58) has a proximal radial face welded to a distal extremity of said fixing ring (15).
A glow plug as claimed in either claim 1 or claim 2, wherein said flexible collar is of constant axial thickness and said annular linking reinforcement (58) has a radial thickness greater than the axial thickness of said collar.
A glow plug as claimed in any one of claims 1 to 3, wherein said flexible collar is of constant axial thickness and said annular linking reinforcement (58) has an axial thickness greater than the axial thickness of said collar.
A glow plug as claimed in any one of claims 2 to 4, wherein the proximal radial face of the annular linking reinforcement (58) and the distal extremity of said fixing ring (15) being in contact to each other according to a facing radial thickness, the proximal radial face of the annular linking reinforcement is welded to the distal extremity of said fixing ring over the whole of their facing radial thickness.
A glow plug as claimed in any one of claims 1 to 5, wherein the annular linking reinforcement (58) extends radially so as to have a peripheral contact face in contact with an internal face of the receiving housing.
A glow plug as claimed in claim 6, wherein the annular linking reinforcement (58) has a distal extremity face which has a junction with said peripheral contact face, said distal extremity face extending, at that junction, radially orthogonally to said peripheral contact face.
A glow plug as claimed in either claim 6 or claim 7, wherein said peripheral contact face of the annular linking reinforcement (58) is welded to said internal face of the receiving housing by at least one peripheral weld.
A glow plug as claimed in any one of claims 1 to 8, wherein said collar is connected to the distal extremity of the body of the receiving sleeve (16) by a curved flared portion (40) with continuous curvature having a concavity oriented towards the proximal extremity of the heating rod.
A glow plug as claimed in claim 9, wherein said curved flared portion (40) is welded to the heating rod at a junction zone of said curved flared portion (40) with the heating rod.
A glow plug as claimed in either claim 9 or claim 10, wherein said curved flared portion (40) has an external radius of curvature of less than 0.5 mm.
A glow plug as claimed in any one of claims 1 to 11, wherein the body of the receiving sleeve (16) is formed of a cylindrical wall having a smaller radial thickness in a distal portion (66) of this cylindrical wall, said distal portion extending at the distal extremity of the body of the receiving sleeve.
A glow plug as claimed in claims 2 and 12, wherein said collar has an axial thickness of the same order as the radial thickness of said distal portion (66).
A glow plug as claimed in any one of claims 1 to 13, wherein the receiving sleeve (16) is placed around a peripheral metal tube of said proximal portion of the heating rod, the peripheral metal tube extending axially also into said proximal zone of the receiving housing (14).
A glow plug as claimed in any one of claims 1 to 14, wherein the tubular load sensor immediately axially adjoins a proximal axial extremity of the receiving sleeve (16) opposite said distal extremity of the receiving sleeve.
A glow plug as claimed in any one of claims 1 to 15, wherein the load sensor is a tubular load sensing sleeve (17) which extends entirely within said proximal zone of the receiving housing (14), around said proximal portion (50) of the heating rod (11).
A glow plug as claimed in claim 16, wherein the tubular load sensing sleeve (17) has:
- a first axial extremity (32) which is connected to the heating rod in such a manner that it is driven in axial translation by movements of the heating rod at least in the proximal direction towards said proximal extremity of the heating rod, and in which the heating rod tends to return to the interior of the plug body, and

- a second axial extremity (37) opposite said first axial extremity, the second axial extremity being connected to the plug body in such a manner that axial translation movements of the heating rod relative to the plug body generate axial compression and/or traction stresses in said load sensing sleeve.
A glow plug as claimed in claim 17, wherein said first axial extremity (32) is a distal axial extremity of the tubular load sensing sleeve (17) axially opposite said proximal extremity of the heating rod, and wherein said second axial extremity (37) is a proximal axial extremity of the tubular load sensing sleeve (17) oriented axially towards said proximal extremity of the heating rod.
A glow plug as claimed in either claim
17 or claim 18, wherein said first axial extremity (32) is connected to the peripheral metal tube of said proximal portion (50) of the heating rod (11).
A glow plug as claimed in any one of
claims 17 to 19, wherein said second axial extremity (32) is connected to said fixing ring.