FR2824114A1 - Spark plug for measuring the pressure in the combustion chamber of a combustion engine is designed to ensure that combustion gas does not enter the pressure sensor housing - Google Patents

Abstract

Spark plug (100) comprises a sensor (300) for measuring the combustion pressure with a housing (200) in which a tubular element (202) is inserted, the sensor being placed in a receptacle (201e) at the end of the housing (201), of which the interior surface is fixed to the exterior surface of the tubular element adjoining the extremity of the housing exposed to combustion gas. The spark plug maintains the housing sealed against air ingress and thus also prevents combustion gas entering the housing.

Description

for the motorization of a tool.

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  SPARK PLUG CONTAINING A PRESSURE SENSOR

COMBUSTION

  The present invention relates to spark plugs containing a combustion pressure sensor and which are used as assisting devices facilitating the starting of combustion engines.

  internal, such as diesel engines.

  In general, an example of this type of spark plug having a combustion pressure sensor is a spark plug equipped with an ignition detector, of the type described in the application for a utility model. Japanese publishes under N Hei 4-57056. The spark plug includes a cylindrical housing that allows the spark plug to be mounted in an internal combustion engine, a heating element that produces heat when an electric current is applied, a sheath (or a tube-shaped element) which houses the heating element and a central rod-shaped electrode for applying current to the heating element. The sheath and the central electrode are retained in the housing. Likewise, a piezoelectric element (i.e. a combustion pressure sensor) is retained in the housing for

  produce electrical signals when a charge (pres-

  sion) is applied to the sheath along the axis of the bou-

  ogy. This spark plug also includes an O-ring arranged between the sheath and the housing. When pressure builds up in the combustion chamber and an axial load is applied to the sheath, the O-ring allows the sheath to slide relative to the housing. This displacement of the sheath applies a charge to the piezoelectric element, which in turn produces electrical signals. This arrangement makes it possible to detect

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  the instant of ignition of the internal combustion engine.

  However in such a spark plug there is the risk that the combustion gases penetrate into the housing from the combustion chamber, since the maintenance of the airtight housing is obtained

  only by means of the O-ring, which is used to

  put the displacement of the sheath relative to the housing.

  If the flow of combustion gases entered the housing, there would be many durability problems.

  ity. This problem includes damage to the piezoelectric element.

  zoelectric, caused by the temperature in the combustion chamber, a rupture of the resulting heating element

  oxidation of the element and leakage of an electric charge

  stick delivered by the piezoelectric element, caused

by humidity.

  In addition the spark plug in such an agency-

  ment, in which the piezoelectric element, a main component of the combustion pressure sensor, is pushed against the rear end of the sheath and therefore is located relatively deep inside the housing, in a position away from its end surface, requires two elements. The first is a hole, through which an output line for transmitting signals from the piezoelectric element can be removed from the interior of the housing and the second is formed of associated sealing elements so as to close the hole tightly. This requirement to bring out the output line of the pressure sensor

  combustion increases the complexity of the structure.

  Given the problems mentioned previously, an object of the present invention is to guarantee the airtightness of the housing in spark plugs fitted with a pressure sensor, while seeking a simple construction to bring out the output line

  of the combustion pressure sensor.

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  This is why, in accordance with one aspect of the present invention, there is provided a spark plug pos sedating a combustion pressure sensor, characterized in that it comprises: a cylindrical housing having a first end and a second end, the housing being mounted in an internal combustion engine with its first end positioned in an engine combustion chamber, a tube-shaped element having first and second ends, the tube-shaped element being retained inside the case by its first

  end which projects from the first end

  mite from the housing and entering the combustion chamber, a heating element serving to produce heat during the application of the current, the heating element being disposed inside the tube-shaped element, a core metal retained inside the housing by a part which projects from the second end of the housing, the core communicating electrically with the heating element, and a combustion pressure sensor serving to

  detect the combustion pressure, the pressure sensor

  combustion pressure detecting combustion pressure by detecting a force acting on the tube-shaped element

  and transmitted through the nucleus when the pres-

  Combustion is established in the engine, and an interior surface of the housing is attached to an exterior surface of the tube-shaped member at the

  in the vicinity of the first end of the housing, leaving no

  sant subsist es substantially no gap between the housing and the tube-shaped element, and that a receptacle is defined between a portion of the interior surface of the housing near its second end, and an outer surface of the core, and that

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  minus part of the combustion pressure sensor

is housed in the receptacle.

  This arrangement guarantees the airtightness of the housing with respect to the combustion gases, since the internal surface of the housing is fixed to the external surface of the tube-shaped element in the vicinity of the first end of the housing, which is exposed to combustion gases. This essentially leaves no gap between the two components. In addition,

  the elasticity of the housing allows the element to be slightly offset

  tube-shaped even if the housing and the tube-shaped element are fixed together. This is why, when the combustion pressure is applied, the variation of the force acting on the tube-shaped element is transmitted to the combustion pressure sensor, which allows the detection of the combustion pressure. of the same

  way than in classic candles.

  This construction also makes it possible to make

  pull the outlet line of the combustion pressure sensor directly out of the opening of the second

  end of the housing. This is why the pressure sensor

  combustion sion is housed in the receptacle defined between the interior surface of the housing, adjacent to the second

  end of the housing and the outer surface of the core.

  This makes it possible to position the combustion pressure sensor in the vicinity of the end surface of the box on the second end of the latter. Therefore it is not necessary to provide an elaborate structure

  to bring the structure out of the housing.

  Therefore, not only does the spark plug according to the present invention having a combustion pressure sensor ensure the airtightness of the housing, but also it provides a simple construction with an easy removal path for the sensor

of the combustion pressure.

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  In the spark plug, at least part of the combustion pressure sensor is received in the receptacle defined between the interior surface of the housing adjacent to the second end of the housing and the exterior surface of the core. As a result, the length of the spark plug considered along the axis of the spark plug is reduced by an amount corresponding to the height of the pressure sensor relative to the spark plug without the receptacle for receiving the pressure sensor (i.e. the spark plug with the pressure sensor located outside the housing). The spark plug

  of reduced length is advantageous in that the length

  The path length, over which the combustion pressure must be transmitted, is also reduced, so that the efficiency of the combustion pressure transmission is

  as well as the sensitivity of the pressure sensor.

  Preferably, the housing has a hexagonal portion formed on the outer surface of the housing, near the second end of the housing, and the receptacle

  tackle is formed inside the hexagonal part.

  The hexagonal part is used when the

  the ignition is fixed, for example by screwing to the internal combustion engine. The arrangement indicated above allows the efficient use of the space occupied by the hexagonal part by forming a receptacle for

  inside the hexagonal part.

  Preferably, the spark plug having a combustion pressure sensor further comprises: a nut fixed to the core, and an insulating sleeve disposed between the nut and the combustion pressure sensor, and the combustion pressure sensor combustion is retained in position by the insulating sleeve between the housing

and the nut.

  The spark plug described in the publication

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  previously mentioned uses a spring to support the combustion pressure sensor and therefore is likely to be the seat of vibration since the combustion pressure sensor can be easily moved along the axis of the spark plug . The result

  that electrical signals due to vibrations are added

  tees at the output signals as noise, which reduces the detection accuracy of the combustion pressure

(low signal / noise ratio).

  In contrast in the spark plug according to the present invention, the combustion pressure sensor is fixed without the use of a spring and therefore the combustion pressure sensor is less sensitive to vibrations along the 'axis of the candle, the electrical signals resulting from vibration or parasitic signals are reduced. This allows precise detection of the combustion pressure (a high signal-to-noise ratio is obtained). This arrangement also facilitates repairs

pressure sensor.

  To fix the interior surface of the housing to the exterior surface of the housing vis-à-vis the exterior surface of the tube member in the vicinity of the first end of the housing so that essentially no gaps are formed between these two components, the tube-shaped element can be force-fitted into the housing, or a part of the internal surface of the housing can be welded to the external surface of the tube-shaped element in the vicinity of the first end

of the housing.

  According to another characteristic of the invention, the interior surface of the housing is welded to the exterior surface of the tube-shaped element, leaving essentially no gaps between the housing.

and the tube-shaped member.

  According to another characteristic of the invention,

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  the combustion pressure sensor includes an element

  which is housed in the receptacle.

  According to another characteristic of the invention, the combustion pressure sensor further comprises a housing which retains the detection element, and at least

  part of the housing is housed in the receptacle.

According to another characteristic of

  the invention, the entire housing is housed in the receiver

  tackle. According to another characteristic of the invention, the housing is completely housed entirely in the receptacle

tackle in an axial direction.

  According to another characteristic of the invention, the housing is fixed to the interior surface of the receptacle

tackle.

  Other features and benefits of the pre

  invention will emerge from the description given below

  after reference to the accompanying drawings, in which: - Figure 1 is a cross-sectional view showing the overall arrangement of a spark plug comprising a pressure sensor according to an embodiment of the present invention; - Figure 2 is a cross-sectional view on a larger scale of the pressure sensor shown in Figure 1; - Figure 3 is a partial cross-sectional view schematically showing a path along which the combustion pressure is transmitted; FIG. 4A is a diagram showing an example of a waveform of the combustion pressure detected in accordance with the present invention; FIG. 4B is a diagram illustrating an example of a waveform of a combustion pressure detected in accordance with the present invention;

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  - Figure 5 is a cross-sectional view of a spark plug, which is a variant of an embodiment of the present invention; - Figure 6 is a cross-sectional view showing a variant of an arrangement of the sensor

  pressure of an embodiment of the present invention

  tion; - Figure 7 is a cross-sectional view of a first variant of how the pressure ion sensor is fixed in accordance with an embodiment of the present invention; - Figure 8 is a cross-sectional view of a second variant of the manner in which the pressure sensor is fixed according to an embodiment of the present invention; - Figure 9 is a cross-sectional view of a third variant of the manner in which the pressure sensor is fixed in accordance with an embodiment of the present invention; - Figure 10 is a cross-sectional view of a fourth variant of the manner in which the pressure sensor is fixed in accordance with an embodiment of the present invention; - Figure 11 is a cross-sectional view of a fifth variant of how the pressure sensor is fixed in accordance with an embodiment of the present invention; - Figure 12 is a cross-sectional view of a fourth variant of an arrangement of the pressure sensor according to an embodiment of the present invention; - Figure 13 is a cross-sectional view

  of a second variant of an arrangement of the pressure sensor

  sion according to an embodiment of the present invention; and

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  - Figure 14 is a cross-sectional view of a sixth variant of the way in which the pressure sensor is fixed in accordance with an embodiment

of the present invention.

  Some embodiments of the present invention will be described with reference to the accompanying drawings. In Figure 1, there is shown, in the form of a longitudinal transverse section, a spark plug 100 having a combustion pressure sensor according to an embodiment of the present invention. The spark plug 100 is shown as being mounted on a cylinder head 1 t (i.e. a support) of a diesel engine

  (i.e. an internal combustion engine).

  In summary, the spark plug 100 is made up of

  killed by a spark plug body 200, which includes a heating element and serves as a support for conveying the combustion pressure, and a pressure sensor 300 (also designated as a combustion pressure sensor in this application), which serves as means for detecting the combustion pressure of the engine by converting the intensity of the force acting on the spark plug body 200 when the combustion pressure increases, into electrical signals based on the piezoelectric characteristics

  triques of a piezoelectric element.

  The spark plug body 200 includes: a metallic cylindrical housing 201, which is mounted on the cylinder head 1 of the engine so that one end of this housing (lower end in FIG. 1) is positioned in a combustion chamber 1a and the other end of the box (upper end in FIG. 1) is positioned outside the cylinder head 1 of the engine; a cylindrical sheath tube 202 (also referred to as a tube-shaped member in this application), one end of which extends outside the corresponding end of the housing 200 and the other end of which is retained at

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  the interior of the housing 201; an ignition coil 203 (also referred to as a heating element in this application), which is retained within the sheath tube 202 in the vicinity of one end of the sheath tube 202 and is used to produce heat when an electric current is applied to a metal rod-like core 204 (electrode element or electrode in

  rod shape), one end of which communicates electrical-

  ment with the heating coil 203 and the other end of which is held in place, in the housing 201 so

  that it extends out of the corresponding end of the box

tier 201.

  The cylinder head 1 of the engine has a tapped hole (that is to say a spark plug hole) which extends from the outer face of the cylinder head 1 of the engine through the combustion chamber 1a, inside the cylinder head 1 of the engine. The candle body 200 is inserted into the hole

  tapped along the longitudinal axis of the spark plug.

  The box 201 has a stepped profile, one of its ends located on the side of the combustion chamber 1a has a relatively small diameter, while its

  the other end has a relatively large diameter.

  The housing 201 has a threaded part 201b formed on its outer surface, essentially in the middle of the part of small diameter as can be seen along the axis of the spark plug. The housing 201 also has a hexagonal part 201a formed on the outer surface of the large-diameter part so as to retain the spark plug 100 screwed in the cylinder head 1 of the engine. The spark plug body 200 is screwed into the cylinder head 1 of the engine by means of the engagement of the threaded part 201b with the

threaded hole.

  On one end of the housing 201 is formed a seat surface of narrowed shape 201c which comes into intimate contact with a corresponding seat surface of the

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  tapped hole formed in the cylinder head 1 of the engine to prevent

  expensive gas leak from the combustion chamber there. The hexagonal part 201a of the housing 201 can be partially chamfered so as to form a united circumferential surface around the housing 201 and consequently reduce the diameter of the housing 201 so that the

  housing 201 can better adapt to a space for mounting

engine level (not shown).

  The sheath tube 202 can be formed from materials such as heat-resistant and corrosion-resistant alloys (for example, SUS-310 stainless steel). The lower end, as seen in FIG. 1, of the sheath tube 202 which projects from the corresponding end of the housing 201, is arranged in the form of a blind end, while

  the other end of the sheath tube 202, which is provided

  placed in the housing 201, is arranged in the form of an open end. The heating coil 203 is a resistive wire formed from materials such as Ni-Cr and Co-Fe and is

  disposed inside the sheath tube 202 adjacent to

  swims from the blind end of the sheath tube 202.

  The upper end (when looking at FIG. 2) of the sheath tube 202 houses the lower end of the core 204. The lower end (seen in FIG. 2) of the heating coil 203 is connected to the end lower of the tube forming the lower sheath 202, while the upper end of the heating coil 203 is connected to the lower end of the core 204 inserted in

the tube forming the sheath 202.

  A space is defined between the sheath tube 202 and the heating coil 203 and between the sheath tube 202 and the core 204 and is filled with an insulating powder 205 resistant to heat, such as for example magnesium oxide . The sheath forming 202 is embossed so that its diameter is reduced so that the powder

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  insulation 205 filling the space is compacted (the den-

  increased insulation powder 205 improves the heat conduction efficiency) and the core 204 and the heating coil 203 are therefore held firmly in position in the sheath tube 202 by the iso-

compacted roller 205.

  The part of the tube forming the sheath 202, which houses the changing coil 203, forms, con] ointment with the heating coil 203 and the insulating powder 205, a heating element 206. The heating element 206 is held in position at l inside the lower end (seen in FIG. 1) of the housing 201 so that the lower end of the changeable element 206 enters the

combustion chamber.

  The heating element (or the external surface of the tube forming the sheath 202) is joined to the internal surface of the housing 201 by force fitting or hard brazing such as for example silver brazing. As a result, the region K1 is formed in the vicinity of the lower end (as seen in FIG. 3) of the housing 201, in which the interior surface of the housing 201 is fixed to the exterior surface of the sheath tube 202. This does not

  essentially leaves no gaps between the two

  posants, on the whole of the conference of the tube forming

  sheath 202. The region K1 is used to prevent the com

  bustion does not enter the housing 201 from the

combustion chamber.

  The region K1 can be part of the entire interface, in which the interior surface of the housing 201 is kept in contact with the exterior surface of the sheath tube 202 as long as it extends over the entire circumference. candle. A sealing element 205a

  is arranged between the part of the tube forming the sheath 202 see

  sine from its open end and the core 204 so as to prevent the insulating powder 205 from coming out during the

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matting process.

  A cylindrical ring 207 made of silicone rubber, creep rubber, EPDM, NBR, H-NBR or the like, is inserted from the upper end (when looking at Figure 1) of the core 204 and is disposed around the core 204 inside the upper part (as it can be seen in FIG. 1) of the housing 201. The cylindrical ring 207 is provided for centering the ncyau 204, which reduces the vibration of the core

  204 and keeps the housing 201 waterproof and airtight.

  Preferably, the part of the housing 201 which comes into contact with the cylindrical ring 207 and has a narrowed shape so as to establish intimate contact with the cylindrical ring 207 and thereby improve the reduction of vibrations, the sealing against and

air tightness.

  An annular insulating sleeve 210, which is formed of an insulating material consisting of a resin (for example a phenolic resin and PPS) or an insulating ceramic material (for example of alumina) is arranged around the upper part (view in FIG. 1) of the core 204. Inside the hexagonal part 201a of the housing 201 is disposed a stepped recess 201d which has a relatively large diameter. A receptacle 201e is defined by the large stepped recess 201d and the outer surface

ncyau 204.

  With an annular pressure sensor 300 (described later in detail) housed in the receptacle 201e and the insulating sleeve 210 disposed around the core 204, a nut 11 is applied in leaktight manner to a ter minal thread 204a formed on the end upper (view in FIG. 1) of the neyau 204 so as to thus retain the pressure sensor 300 in position between the insulating sleeve

210 and the housing 201.

  An O-ring 208 is disposed between the on

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  inner face of the large recess 201d of the housing 201 and the outer surface of the pressure sensor 300, and a cylindrical ring 209 is disposed between the inner surface of the pressure sensor 300 and the outer surface of the channel 204. The O-ring 208 and the cylindrical ring 209 are made of materials such as sili rubber

  cone, fluorinated rubber, EPDM, NBR and H-NBR.

  The role of the O-ring 208 is to keep the housing 201 airtight and airtight, while the cylindrical beque 209 is intended to reduce the vibration of the channel 204 and to keep the airtight housing and water. Preferably, the part of the sensor 300 which comes into contact with the cylindrical ring 209 is narrowed so as to establish intimate contact with the cylindrical ring 209, and furthermore thus improves the property of reduction of vibrations, the tightness to the water and

air tightness.

  The pressure sensor 300 is electrically isolated from the nut 211 by the insulating sleeve 210 and

  vis-à-vis the ncyau 204 by the cylindrical ring 209.

  A connecting bar 2 is fixed to the final thread 204a formed on the upper end (seen in FIG. 1) of the core 204 by means of a terminal nut 212. The connecting bar 2 electrically connects the spark plug 100 spark plugs placed in other cylinders. The connecting bar 2 is connected to a power source (not shown) and is connected to earth at the cylinder head 1 of the engine by means of the core 204, the heating coil 203, the sheath tube 202 and the housing 201 In this way, the heating element 206 of the spark plug 100 can generate heat to facilitate the ignition of the fuel and therefore

start the diesel engine.

  The connection bar 2 can be a flexible conducting wire (wiring intended to be used in automobiles

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  biles) to allow small displacements of the tube

forming sheath 202.

  As previously described, in conventional spark plugs (such as those described in the Japanese utility model released for public inspection, Publication No. Hei 4-57056), the pressure sensor is pushed against the the rear end of the sheath and therefore is placed relatively deep inside the housing, in a position remote from the end surface of the housing. However, in this

  embodiment, the pressure sensor 300 is provided

  placed in the receptacle 201e formed in the upper end (seen in FIG. 1) of the housing 201, and the insulating sleeve 210 is

  interposed between the housing 201 and the nut 211 so as to hold the pressure sensor 300 in position. Hereinafter, the pressure sensor 300 will be described in detail with reference to FIG. 2, which represents a cross section on a larger scale from

  pressure sensor 100 shown in FIG. 1.

  In the pressure sensor 300, an annular polar piezoelectric ceramic body 302, formed of lead titanate or lead titanatezirconate, is placed on each side of an annular electrode 301. The two ceramic bodies 302 are electrically connected at parallel between them. The electrode 301 and the piezoelectric ceramic bodies 302 are housed and protected in a space defined by a metal housing 303 and a base 304, each of which has an essentially annular shape. The metal box 303 has a through hole which passes through a flanged part 303a of the metal box 303, along the axis of the spark plug. One end of a protective tube 303b is inserted into the protective tube 303b and joined there by welding, brazing or the like. The other end of the protective tube 303b is

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  placed in a similar through hole 210a, which extends through the insulating sleeve 210 along the axis of the spark plug. Shielded wire 305 for use as an output line to carry signals from the pressure sensor 300 is inserted into and is supported by the tube 303b. A wire channel 305a of armored wire 305, which

  enters the metal housing 303, is welded to the electro

  trode 301. A shield 305b for the wire, which is isolated from the ncyau 305a of the wire, is connected to the protective tube 303b by matting and therefore is electrically connected to the metal housing 303, which also serves as a ground wire.

for the candle body.

  The two parallel piezoelectric ceramic bodies 302 are connected in parallel so as to increase

  sensitivity to the output signal (doubling) and improvement

  r the signal-to-noise ratio of the output signal, although only a piezoelectric ceramic body can be used to detect the signal. In the latter case, an insulating element (for example a material formed of a resin - such

  than a polyimide yarn and phenol, or a ceramic material

  mica such as mica and integrated alumina) can be

  placed on one of the two sides of the electrode 301. The box

  metallic tier 303 is formed of a metallic foil which has a thickness of 0.5 µm or less, so that it has reduced rigidity, especially on its part

  ciraonférentielle. In this way, small displacements-

  elements of piezoelectric ceramic bodies 302, which occur when the combustion pressure is established,

  can be transmitted reliably.

  The pressure sensor 300 is assembled as follows. First of all, a large cylindrical part 303c and a small cylindrical part 303d are formed concentrically at the bottom (when looking at FIG. 2). Then we heat an insulating tube by

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  heat-shrinkable silicone 306 and it is adjusted tightly around the small cylindrical part 303d. Then we

  sequentially mounts one of the piezoelectric ceramic bodies

  triques 302, the electrode 301, then the other of the piezoelectric ceramic bodies 302 is sequentially mounted,

  around the small cylindrical part 303d. The iso- tube

  lant 306 is used to prevent a short circuit between the piezoelectric ceramic bodies 302 or an electrode 301 and the metal case 303. When the assembly is completed, connect the channel 305a of the shielded wire 305 to the electrode 301 placce in metal housing 303 by means of resistance welding, laser welding

or the like.

  Then we mount the base 304 in the metal metal case 303. Then, pushing the metal case 303 and the base 304 towards each other, we weld the outer circular surface of the base 304 to the large cylindrical part 303c of the metal housing 303 by means of YAG laser welding (yttrium and aluminum garnet) (the welds are indicated by Y1 in FIG. 2). In this way, the pressure sensor is assembled with all of its components in intimate contact with each other.

with the others.

  By matting the junction of the shielded wire 305 and the protective tube 303b including the shield 305b of the wire, an electrical connection is established between the shield 305b of the wire and the metal case 303, as is the fixing of the shielded wire 305 and a contact. intimate between the shielded wire 305 and the protective tube 303b. It follows that the metal housing 303, the base 304 and the shield 305b of the wire have the same electrical potential. The integration of the pressure sensor 300 in the spark plug body 200 allows connection of these components to the mass formed by the cylinder head 1 of the engine. As a result, a pressure sensor is obtained, which is perfectly hermetic and is

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  perfectly electrically protected.

  Below we will give the description of a process

  sus of assembly of the spark plug 100 comprising a combustion pressure sensor in accordance with the present invention, with reference to FIGS. 1 and 2. Firstly, the heating element 206 is prepared with the core integrated 204 and the plated case 201 is prepared. The sheath tube 202 of the heating element 206 has an outside diameter slightly greater than the inside diameter of the case 201. The difference between the diameters is

  for example between 60 and 140 µm.

  The sheath tube 202 of the heating element 206 is force-fitted into the housing 201. The resilience of the housing 201 and of the sheath tube 202 serves to hermetically fix these elements to one another. In this way the housing 201, the core 204 and the changing element 206 are integrated between them. Otherwise, we can integrate the

  housing 201 to the heating element 206 by welding them together

  completely between them, using for example silver welding. This guarantees the airtightness of the housing 201. Next, the cylindrical cap 207 is mounted around the ncyau 204 from the end of the ncyau 204 which poses the end thread 204a. Then the pressure sensor 300 is inserted into the receptacle 201e by plating the O-ring 208 around the large cylindrical part 303c. The cylindrical rod 209 is mounted around the core 204 from the upper end of the latter, as can be seen in FIG. 1, and it is held in place. In addition, an O-ring 309 is mounted around the shielded wire 305 connected to the pressure sensor 300 from the upper end (as can be seen in Figure 1) of the shielded wire 305 and held in place. At this stage, the insulating sleeve 210 is mounted around the core 204 from the upper end of the latter.

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  deny (as can be seen in Figure 1) and the shielded wire 305 is pulled out through the through hole 210a of the insulating sleeve 210. The O-ring 309 is made of materials such as silica cone rubber, rubber fluorinated, EPDM, NBR and H-NBR and the like and is compressed and inserted into the through hole 210a so that it is held resiliently in contact with the outer surface of the shielded wire 305, and the end surface of the tube protection 320b and the lower part of the through hole 210a. In this way the O-ring 309 can be used to guarantee the tightness as well

  to water than air tightness.

  Then the nut 211 is fixed to the terminal thread 204a so as to retain the pressure sensor 300 in position in the receptacle 201e. To prevent the nut from loosening under the effect of vibrations, a part of the hexagonal surface of the nut 211 which can be deformed by matting following the fixing of the nut 211, or else a screw locking agent on

  meshing faces (threads) before fixing nut 211.

  Finally, the housing 201 is mounted on the cylinder head 1 of the engine, with the connecting bar 2 fixed on the terminal thread 204a to the upper part of the nut 211 using the terminal nut 212. This completes the construction. illustrated

in figure 1.

  We will now describe in reference to Figures 1 to 3 the mechanism by which the spark plug 100 of an embodiment of the present invention detects the combustion pressure. Figure 3 is an explanatory view (partial cross section) which includes a model

  simplified to illustrate the journeys along the

  which the present combustion is transmitted. As shown in FIG. 1, the pressure sensor 300 is fixed to the spark plug body 200 by means of the nut 211. The incandescent spark plug 100 is mounted on the head 1 of the

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  motor with a preload of between 50 and 100 kg applied to piezoelectric ceramic bodies 302 in the

pressure sensor 300.

  When the engine starts, a voltage is applied by means of the connection bar 2, and an electric current flows in the core 204, the heating coil 203, the sheath tube 202, the housing 201 and the threaded part 201b , and is earthed at the cylinder head 1 of the engine. As a result, the heating element 206 of the spark plug 100 produces heat which therefore

  does facilitate fuel ignition to start

  rer. Once the engine has started, the pressure

  bustion, which is established in the engine, is transmitted along the two different paths R1 and R2 indicated by lines in bold lines in Figure 3 and acts on the heading

pressure sensor 300.

  Part of the combustion pressure applied to the changing element 206 is transmitted along the first path R1, passes through the housing 201 joined to the heating element fant 206 to the pressure sensor 300. The housing 201 located in the path R1 is strictly confined by the cylinder head 1 of the engine in the threaded part 201b so that the transmitted force is greatly reduced above the threaded part 201b. As a result, the region around the receptacle 201b of the housing 201, which surrounds the pressure sensor 300, is subjected to a very small displacement. The rest of the combustion pressure applied to the heating element 206 is transmitted along the second path R2 via four components, namely the insulating powder 205 which fills the heating element 206, the core 204, l nut 211 and the insulating sleeve 210, before acting on the pressure sensor 300. No disturbing factor of displacement of the four components is present along

of path R2.

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  Despite the presence of the region K1, in which the housing 201 is fixed to the sheath tube 202,

  the elasticity of the housing 201 makes it possible to move the formed tube

  mant sheath 202 along the axis of the spindle (ie S the vertical direction in Figure 3). This is why, when the combustion pressure is applied to the changing element R2 along the second path R2, the sheath tube 202 and the channel 204 are moved in one piece with the

  along the axis of the spark plug.

  Consequently, an important difference is obtained between the displacement of the region in the vicinity of the receptacle 201e of the housing 201, which occurs along the path R1, and the displacement of the channel 204 which occurs along the path R2 (this is that is to say that the displacement along the path R2 is significantly longer than along the route

  R1). This difference in displacement is used to reduce the pre-

  stress applied to the pressure sensor 300 by

through nut 211.

  This is why the load applied to the piezoelectric ceramic bodies 302 in the pressure sensor 300 varies, which in turn leads to a variation in the

  amount of electrical charge that ceramic bodies trap

  zoelectrics produce as an electrical signal, based on their piezoelectric characteristics. The resulting signals are delivered when the core 305a and the shield 305b of the shielded wire 305 via the electrode 300 shown in FIG. 2 through the housing 201 used as ground wire, the threaded part 201b, metal housing 393, protective tube

* tion 303b and base 304.

  By sending electrical signals both to a charge amplifier (not shown), which converts the charge output produced into a voltage, and to an electrical control unit (ECU unit, not shown) mounted in the vehicle, the combustion pressure may

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  be used to deliver electrical signals for the

  combustion of the engine. So far, the mechanics have been described

  nism by means of which the spark plug 100 of the pre-

  This invention detects the combustion pressure. An example of the combustion pressure waveform

  detected in accordance with the present invention is shown

felt in figure 4.

  FIGS. 4A and 4B each represent the results of a pressure detection carried out using the spark plug 100 as shown in FIG. 1, the engine operating at a speed of 1200 rpm under a load of 40 N. Figure 4A shows

  a comparison between the output waveform of an indi-

  pressure generator and that of the pressure sensor 300,

  while Figure 4B is a curve showing the cor-

  relationship between the output signal from the pressure sensor 300 of the spark plug 100 and that of the pressure indicator. In the graph represented in FIG. 4B, the horizontal axis represents the output signal from the pressure sensor 300 and the vertical axis represents the signal from

pressure indicator output.

  As can be seen in Figures 4A and 4B,

  the output signal from the pressure sensor 300 of the pre-

  The spark plug 100 has essentially the same waveform as the pressure indicator output signal. Correspondingly, the correlation curve is essentially linear over a wide range of pressures including the minimum combustion pressure and the maximum combustion pressure. This implies that the pre

  the spark plug 100 can detect pre-

  cise the variation of the load applied to the pressure sensor 300, which occurs in response to the variation of

pressure in the engine.

  In the present embodiment, the inner surface of the housing 201 is fixed to the outer surface

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  sheath tube 202 (i.e., the shaped member

  tube) near one end of the housing 201 expo-

  combustion gases, by means of pressure fitting or welding, so that essentially no gaps are formed between the two components. This arrangement guarantees the airtightness of the housing 201 and prevents the combustion gases from entering the housing 201. Consequently, the present embodiment not only eliminates the risk that the combustion gases enter the housing 201 from the combustion chamber la, but also prevents damage to the pressure sensor 300 caused by exposure to gases

  combustion and ruptured heating coil 203.

  As a result, a spark plug can be obtained

  equipped with a pressure sensor, of great durability.

  In the present embodiment, the pressure sensor 300 is provided in the receptacle 201e formed on one end of the housing 201 so that the pressure sensor 300 is positioned close to the end of the

  box 201. Unlike spark plugs -class-

  siques, this arrangement allows to bring out the shielded wire 305 directly out of the opening of the housing 201 on this end of the housing 201, which eliminates the process of forming an elaborate structure for pulling the wire out of the housing 201. C This is why, not only does the present embodiment make it possible to obtain an airtightness of the housing, but it also provides a simple configuration for bringing out the wiring of the

  combustion pressure sensor.

  In the present embodiment, the pressure sensor 300 is positioned in the receptacle 201e. As a result, the length of the spark plug 100 along its axis is reduced by a value corresponding to the height of the pressure sensor 300, relative to the spark plug having no receptacle 201e for receiving

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  see pressure sensor 300 (i.e. spark plug

  ignition, in which the pressure sensor is

  placed outside the housing 201).

  The shorter spark plug 100 is advantageous since the length of the path and along which the combustion pressure must be transmitted is reduced and therefore the efficiency of the transmission of the

  combustion pressure is increased, as is the sensitivity

  pressure sensor 300. One more spark plug

  short is also advantageous since it pos-

  sedes a shorter core 204, which is less sensitive to vibrations. Consequently, the electrical parasitic noise signal resulting from the vibration is reduced (we obtain

a high signal-to-noise ratio).

  In addition, the O-ring 208 serves to prevent radial movement of the pressure sensor 300 in accordance with the present embodiment. This arrangement reduces vibrations of the pressure sensor 300 in the radial direction. As a result, the noise signal or electrical noise caused by vibrations is reduced

  (a high signal-to-noise ratio is obtained).

  In the present embodiment, the pres-

  The combustion ion transmitted along the second path R2 is transmitted to the pressure sensor 300 via the core 204, which is massive and has a high rigidity. This arrangement allows precise detection of the combustion pressure. In addition, the arrangement, in which the pressure sensor 300 is supported without the use of a spring, is advantageous since the pressure sensor 300 is less sensitive to vibrations along its axis and therefore the noise produced by vibrations is reduced. This allows precise detection of the combustion pressure (a high signal-to-noise ratio is obtained). This arrangement also facilitates fixing

pressure sensor 300.

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  In the present embodiment, instead

  of the metallic heating element using the resistance wire

  metal tance (i.e. the heating coil 203) as shown in figure 1, one can use the element shown in figure 5 to serve as element

  heater 206. Figure S is a longitudinal sectional view

  nale representing a 110 spark plug as

  variant of this embodiment. For the most part

  tiel, the heating element 400 shown in FIG. 5 is arranged in the form of a ceramic changing element and comprises: a heating element 401, which consists mainly of silicon nitride and molybJene silicide or tungsten carbide, a pair of tungetene conducting wires 402, an insulator 403, which is formed from an insulating ceramic material mainly consisting of silicon nitride and is sintered with the heating element 401, while enclosing in it the heating element 401 and

  the pair of tungsten conducting wires 402.

  The heating element 400 is inserted into a protective tube 404 (designated as a tube-forming element in the present invention) formed of a heat and corrosion resistant alloy (for example SUS430), and is retains in the protective cloth 404 so that part of the heating element 400 projects from the lower end (as can be seen in FIG. 5) of the protective tube 404. The upper end (view in FIG. 5) of the protective tube 404 is inserted into the lower end of the housing 201. As in the case of the sheath tube described above, the outer surface of the protective tube 404 is fixed to the surface

  inside of the housing 201 by means of mounting under pressure

  welding or welding, which does not leave essential-

  There is absolutely no gap between the two components.

  A wire from the pair of conductive wires 402 is connected to the channel 204 via a conductor

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  cap-shaped 405, which is attached to the lower end

  lower (when looking at Figure 5) of the ncyau 204, while the other wire of the pair of conductive wires 402 is

  connected to the ground formed by the housing 201 by the inter-

  protection tube 404. In this way, the

  core 204 communicates electrically with the heating element

  fant 401 so that upon application of the current to the heating element 401, the heating element 400 produces heat. An insulator 407 and a welded glass body 406 serving to fix and center the ncyau 204 are arranged between the core 204 and the housing 201. The spark plug 110 has the same functionality as the spark plug 100

  shown in Figure 1 above except that it pos-

  reduced output sensitivity. The ceramic 400 heating element has a significantly extended useful life and is therefore essentially

maintenance free.

  The arrangement of the pressure sensor 300 can be that shown in FIG. 6, which is a variant of the present invention. The pressure sensor 300 as shown in FIG. 6 has essentially the same arrangement as the pressure sensor shown in FIG. 2 except that the large cylindrical cylindrical part 303c of the metal housing 303 has been eliminated, as well as the weld formed. by laser between the cylindrical part of

large size 303c and base 304.

  In the pressure sensor 300 as shown in FIG. 6, all of the load applied by the receptacle 201e and the nut 211 is required as preload. As a result, the sensitivity of the sensor increases

  and that the response to the combustion pressure trans-

  bet is improved. In this arrangement, the O-ring

  208 and the cylindrical ring 209 also serve to guarantee

  draw sufficient water and air tightness. Again

  calf, in the pressure sensor 300 shown in the

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  Figure 6, a single piezoelectric ceramic body 302 can

  be used for detection, in which case an iso-

  The lant (for example a material formed of resin such as a wire of polyimide or phenol, or a ceramic material such as mica and alumina incorporated) must be placed on

  one of the two sides of the electrode 301.

  The fixing and the support of the pressure sensor 300 can be obtained by means of structures as shown in FIGS. 7 to 11, each of which is a variant of the present invention. In each of these variants, the pressure sensor 300 is firstly fixed

  to the housing 201 in a manner which will be described below.

  Then install the cylindrical ring 209, the O-ring 309 and the insulating sleeve 210, and fix the nut

211 to terminal thread 204a.

  In the example shown in Figure 7 and in

  the following description, the pressure sensor 300

  is fixed to the housing 201. First of all, the difference between the outside diameter of the flanged portion 303a of the metal housing 303 and the inside diameter of the large recess 201d of the housing 201 is adjusted to 50 μm or less. then place the pressure sensor 300 in the receptacle 201e, and while the pressure sensor is pressed, the overhanging part is welded between the pressure sensor 300 and the housing 201, from the outside of the large recess size 201d of the housing 201, by laser welding, plasma welding or the like, over part or all of the circumference of the housing 201 (the welds are indicated by Y2 in FIG. 7). In the case of partial welding, the O-ring 208 is provided so as to guarantee water and air tightness. A portion of the outer periphery of the hexagonal portion, which is subjected to welding, is chamfered so as to form a cylindrical contour in order to obtain essentially a

282411 4

  uniform wall thickness to facilitate welding.

  In the example shown in FIG. 8, the internal diameter of the large recess 201d is adjusted so as to be less than the external diameter of the flanged part 303a, for example at a value between approximately 60 μm and 140 μm, so the sensor

  pressure 300 is fixed to the housing 201 by means of an adjuster

  tight (the tight adjustment zone is indicated by Y3 in figure 8). In the example shown in FIG. 9, the pressure sensor 300 is first placed in the receptacle 201e, and while the pressure sensor 300 is depressed, a part or all of the matting is carried out from the outside. of the conference of the large recess from the outside of the large recess 201d in the direction of the center of the large recess 201d, which fixes the pressure sensor 300 to the box

tier 201.

  In the example shown in FIG. 10, a stepped part 303e is formed on the end surface of the metal housing 303 opposite the insulating sleeve 210,

  on the whole of the conference of the insulating sleeve 210.

  The pressure sensor 300 is placed in the receptacle 201e, and a part or all of the circumference of the open end of the large recess 201d is mated and it is bent to cover the stepped part 303e (a bent part is indicated by Y5 in the figure). In this way, the pressure sensor 300 is fixed to the housing 201 when it is pushed in. A portion of the hexagonal part 201a used to form the elbow Y5 is chamfered so as to form a cylindrical part of

  so that a force is applied in a uni-

  form. In the example shown in Figure 11, a file-

  external stage 303f is formed on the external periphery of the flanged part 303a, and a thread 303g for the engagement of the external thread 303f on the bri part

282411 4

  dée 303a is formed in the inner periphery of the large reinforcement 201d. We fix the pressure sensor

  sion 300 to housing 201 using threads 303f and 303g (the threaded area is indicated by Y6 in Figure 11).

  As indicated, in each of the examples shown

  ted in Figures 7 to 11, the pressure sensor 300 is fixed in the receptacle 201e while being pushed back with a force of 50 kg between 50 kg and 150 kg before

  the nut 211 is fixed to the pressure sensor 300.

  In each of the examples shown in FIGS. 1, 2, 5 and 6, in which the pressure sensor 300 is not fixed before the fixing of the nut 211, a torque acts on the pressure sensor 300 during the fixing of the nut 211. On the contrary, no torque is applied to the pressure sensor 300 when the nut 211 is rotated to fix it, in the examples shown in FIGS. 7 to 10, and it follows that some quality problems can be avoided, including deformation or rupturing of the large cylindrical part 303c, which is the thinnest part of the metal housing 303, as well as rupturing of the wire core 305a shielded wire 305. This is for

  what, the reliability of the products is improved.

  In addition, in the examples shown in FIGS. 7 to 11, the pressure sensor 300 is supported over its entire circumference by the large recess 201d of the housing 201. This is advantageous given that, unlike a fixing provided only at the nut 211 (which is effective in reducing axial or vertical vibration), radial or lateral vibration

  pressure sensor 300 are greatly reduced.

  As a result, the electrical noise signal caused

by vibration is reduced.

  Regarding the examples shown on

282411 4

  Figure 1 and Figure 2 and in Figures 5 to 11, the pressure sensor 300 may be arranged as illustrated in Figures 12 and 13 as variants of the present invention. In each of the examples shown in FIGS. 12 and 13, the pressure sensor 300 is arranged so that it extends outside of the receptacle 201e (that is to say that the part of the pressure sensor 300 is arranged in the receptacle 201e). As shown, the shielded wire 305 is drawn along the axis of the spark plug in Figure 12, while it is pulled along the radius of the spark plug in Figure 13. The arrangements shown in the figures 12 and 13 also present the

  same advantages as those described above.

  The arrangement shown in Figure 13 is par-

  particularly effective when the space for mounting the

  engine is sufficient in the vicinity of the spark plug.

  This arrangement, in which the shielded wire 301 which is pulled radially (along the direction perpendicular to the core 204), is advantageous in that less care has to be taken with regard to electrical interference (short circuit) between the nut 211 and the protective tube 303b which protrudes from the end surface of the

  pressure sensor 300. This is why the thickness of the man-

  insulation 310b can be minimized (it must

  have a certain minimum dimension along the surface

  face to provide insulation. With this arrangement, the insulating sleeve 210b does not require the use of the

  O-ring 309 or the arrangement of the through hole 210a.

  As a result, the length of the core 204 and therefore the length of the spark plug 100 can be reduced so that the vibration noise produced by the spark plug can be further reduced. Therefore, the noise of the electrical signal results

so much of the vibration is reduced.

  Regarding the examples shown on

282411 4

  FIG. 1, FIG. 2 and FIGS. 5 to 13, the pressure sensor 300 can be fixed in the manner illustrated on

  Figure 14 as a variant of the present invention.

  In the example shown in FIG. 14, once the pressure sensor 300, the cylindrical ring 209, the O-ring 208 and the insulating sleeve 210 have been placed in their respective positions, a stop ring is force fitted annular 213 (having a thickness of for example 4 mm), formed of a metallic material, around the core 204 on a part of the intermediate diameter 204b of the channel 204, so that the pressure sensor 300 and the insulating sleeve 210 are supported between the stop ring 213 and the

housing 201.

  The inside diameter of the stop beque 213 is adjusted so as to be less than the outside diameter of the intermediate part 204b of the ncyau 204, for example by a value of between approximately 60 mm and mm, so as to provide a interference for tight grip. On the other hand, the inside diameter of the stop ring 213 is dimensioned so that the stop ring 213 can be arranged around the core 204 without interfering with the outside diameter of the end thread 204a of the core 204. From this In this way, the stop ring 213 can be force fitted around the core 204. As a result, not only can a desired prestressing be applied to the pressure sensor 300, but it is also possible to fix the pressure sensor 300 without that an undesirable torque does not act on the pressure sensor 300. Unlike the examples shown in FIGS. 7 to 11, this can be obtained without having to fix the pressure sensor 300 to the housing 201 by welding, matting or similar. Therefore, some of the quality issues can be eliminated, including distortion or breakage of the cylin

282411 4

  large dric 303c, which is the thinnest part of the metal casing 303, as well as the breakage of the channel 305a of the armored wire 305. This improves in a great way

  the reliability of the devices.

  This construction, in which the pressure sensor 300 is not fixed to the housing 201, has an additional advantage that all of the load applied by the annular stop ring 213 acts

  as preload on piezoelectric distance 302.

  This prevents a reduction in sensitivity. It is also envisaged to replace the nut 211 with the annular stop ring 213 to fix the pressure sensor 300,

  in the examples shown in Figures 7 to 11.

  While in Figure 1, Figure 2 and Figures 5 to 14, the pressure sensor 300 is maintained in direct contact with the receptacle 201c of the housing 201 to be connected to ground, a rigid spacer (for example formoe d ' metal) can be interposed between the pressure sensor 300 and the receptacle 201e of the housing 201, provided that the pressure sensor 300 is connected to

  the mass formed by the housing 201.

  While in Figure 1, Figure 2, Figure, Figure 6 and Figures 12 to 14 the pressure sensor 300 is maintained in direct contact with the receptacle 201e of the housing 201, an insulator (for example a formed material a resin such as for example a polyimide film and phenol or a ceramic material such as integrated mica and alumina) can be optionally interposed between the pressure sensor 300 and the receptacle 201e of the housing 201 (specifically between the base 304 and the receptacle 201e. Such an insulator is used, together with the O-ring 208 (insulating rubber) and the cylindrical ring 209 (insulating rubber), to isolate the ground line of the pressure sensor 300 from the rest of the spark plug. Therefore a common mass with

282411 4

  the ECU control unit mounted on the vehicle (engine control unit, not shown) can be used (or can be grounded to the same electrical potential) and therefore output signals are stabilized. But in general an engine body, a supply battery and an ECU unit mounted on the vehicle are each grounded, and a potential difference may appear between different points on an engine body since a body of motor uses different conductive joints

or non-conductive.

  When installing the spark plug 100 in an engine, it is desirable to choose an optimal construction from that described with reference to Figure 1, Figure 2 and Figures 5 to 14 taking into account parameters such as the space available for mounting the motor, the amplitude of the motor vibrations, the duration

  necessary to mount the spark plug and the sensitivity

required.

  It is also possible to use any combustion sensor which does not use any piezoelectric ceramic body, provided that it is able to detect the combustion pressure in an internal combustion engine on the basis of the applied load. For example, we can use

  serve as a pressure sensor based on a semiconductor.

  The description of the invention has been given sim

  plement by way of example and without limitation.

282411 4

Claims (10)

  1. Spark plug (100) having a combustion pressure sensor (300), characterized in that it comprises: a cylindrical housing (201) having a first end and a second end, the housing (201) being mounted in an internal combustion engine with its first end positioned in a combustion chamber (la) of the engine, a tobe-shaped element (202) having first and second ends, the tube-shaped element (202 ) being retained inside the housing (201) by its first end which projects from the first end of the housing and penetrating into the combustion chamber (la), a heating element (203) serving to produce heat during the application of the current, the changeable element (203) being arranged inside the tube-shaped element (202), a metal core (204) retained inside the housing (201) by a party that protrudes from r of the second end of the housing (201), the core (204) electrically communicating with the heating element (203), and a combustion pressure sensor (300) used to detect the combustion pressure, the sensor ( 300) of the combustion pressure detecting a combustion pressure by detecting a force acting on the tube-shaped element (202) and transmitted via the core (204) when the combustion pressure builds up in the engine , and that an inner surface of the housing (201) is fixed to an outer surface of the tube-shaped element (202) in the vicinity of the first end of the housing (201) leaving essentially no inter stice between the housing (201) and the tube-shaped element 282411 4   (202), and that a receptacle (201e) is defined between a part of the interior surface of the housing (201) near its second end, and an exterior surface of the core (204), and that at least one part of the sensor (300) of the   combustion pressure is housed in the receptacle (201e).   2. Spark plug (100) having an internal combustion sensor (300) according to claim 1, characterized in that the housing (201) includes a hexagonal part (201a) formed on the exterior surface of the housing, in the vicinity of the second end of the housing (201), and the receptacle is formed inside the hexagonal tie (201a).   3. Spark plug (100) having a combustion pressure sensor (300) according to claim 1, characterized in that it further comprises: a nut (200) fixed to the core (204), and a sleeve insulator (210) disposed between the nut (211) and the combustion pressure sensor (300), and that the combustion pressure sensor (300) is retained in position by the insulating sleeve (210) between   the housing (201) and the nut (211).   4. Spark plug (100) comprising a combustion pressure sensor (300) according to any one   claims 1 to 3, characterized in that the element   tube-shaped (202) is force-fitted into the housing (200) so that the interior surface of the housing (201) is attached to the exterior surface of the tube-shaped member (201) substantially free of play between the housing (201)   and the tobe-shaped element (202).   5. Spark plug (100) comprising a sensor (300) of the combustion pressure according to any one   claims 1 to 3, characterized in that the surface   interior of the housing (200) is welded to the exterior surface of the tube-like member (202) leaving no 282411 4   essentially no gaps between the housing   (201) and the tube-shaped element (202).   6. Spark plug (100) comprising a combustion pressure sensor (300) according to claim 1, characterized in that the combustion pressure sensor (300) comprises a detection element (302) which   is housed in the receptacle (201e).   7. Spark plug (100) comprising a combustion pressure sensor (300) according to claim 6, characterized in that the combustion pressure sensor (300) further comprises a housing (303) which   retains the detection element (302), and at least one part   tie of the housing (303) is housed in the receptacle (201e).   8. Spark plug (100) comprising a sensor (300) of the combustion pressure according to claim 7, characterized in that the entire housing (303) is housed in the receptacle (201e).   9. Spark plug (100) comprising a combustion pressure sensor (300) according to claim 8, characterized in that the housing (300) is completely   fully housed in the receptacle (201e) in a direction axial tion.   10. Spark plug (100) comprising a sensor (300) of the combustion pressure according to claim 9, characterized in that the housing (303) is fixed on the