Abstract:
The invention relates to a device for measuring at least the pressure of a fluid present in a chamber ( 16 ), comprising a sensitive element ( 36 ) arranged in a housing ( 38 ), supported by a joint ( 10 ) inserted between two elements ( 12, 14 ) which form said chamber. According to the invention, the housing ( 38 ) is open in the direction of the chamber ( 16 ) and the sensitive element ( 36 ) is enclosed in a material ( 67 ) filling said housing.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a device for measuring at least the pressure of a fluid present in a chamber. 
   It more particularly relates to a device for measuring the pressure in a combustion chamber of an internal-combustion engine. 
   More specifically, it is aimed at a device allowing to control the combustion and more particularly the engine knock that occurs in this combustion chamber of the engine. 
   BACKGROUND OF THE INVENTION 
   Document EP -0,472,219 describes a device for measuring the pressure that prevails in a combustion chamber of an internal-combustion chamber. 
   This device comprises a seal interposed between the cylinder head of this engine and the engine block, and it is in tight contact with the respective faces of this cylinder head and of this engine block. The seal, of multisheet type, comprises an upper metal sheet and a lower metal sheet between which an intermediate sheet bearing a housing that receives a pressure-sensitive element is arranged. 
   A pressure inlet bringing the pressure to a measuring surface arranged parallel to the face of the cylinder head or to the face of the engine block is provided to measure the pressure prevailing in the combustion chamber. 
   This measuring device however has significant drawbacks. 
   In fact, the pressure inlet can be clogged, or its section at least reduced, by a coke deposit usually generated by combustion. Transfer of the fluid under pressure from the combustion chamber to the measuring surface may therefore be non-existent or greatly disturbed. 
   Furthermore, it is necessary to either use a seal of great thickness to make the housing intended to receive the sensitive element and the measuring inlet, which requires adjustment of the assembly made up of the cylinder head, the engine block and the piston, or to provide machining work at the level of the cylinder head, thus embrittling it, which may even lead to sealing losses at these machined points or require additional sealing at this level. 
   Finally, the presence of such a pressure inlet changes the level, the shape, the frequency and the phase of the pressure wave coming from the combustion chamber. 
   The present invention aims to overcome the aforementioned drawbacks by means of a measuring device of simple design, of relatively low cost and quasi-reliable as regards measurement. 
   SUMMARY OF THE INVENTION 
   The present invention thus proposes a device for measuring at least the pressure of a fluid present in a chamber, said device comprising a sensitive element placed in a housing borne by a seal interposed between two elements forming said chamber, characterized in that the housing is open in the direction of the chamber and the sensitive element is coated with a material filling said housing. 
   The seal can comprise a pile of two extreme sheets between which a multiplicity of intermediate sheets is arranged and the housing can be delimited by said extreme sheets and at least one intermediate sheet. 
   At least one intermediate sheet can comprise a cut open in the direction of the chamber. 
   At least one intermediate sheet can comprise electric connection means between the sensitive element and a measuring means. 
   The electric connection means can be borne by an intermediate sheet in form of a film on which a printed circuit comprising at least one electric conductor between the sensitive element and the measuring means can be formed. 
   The sheets can be electrically insulated in relation to one another by at least one sheet in form of a plate, a layer or an insulating deposit. 
   Two of the opposite vertical faces of the sensitive element can be connected to the electric connection means. 
   Two of the opposite horizontal faces of the sensitive element can be connected to the electric connection means. 
   The sensitive element can be connected to the electric connection means by a conducting glue. 
   The sensitive element can be connected to the electric connection means by at least one conducting element. 
   The sheets can be joined together by glueing and this glueing operation can be carried out by interposing a glue layer. 
   At least the extreme sheets can be made of metal and at least the central sheet of the intermediate sheets can also be made of metal. 
   The material filling the housing can be a resin withstanding high temperatures. 
   The face of the housing in the direction of the chamber can be covered by a protective element. 
   The protective element can comprise a wall covering said face and the ends of said wall can be folded back over the extreme sheets of the seal. 
   The sensitive element can be of piezoelectric or piezoresistive type. 
   The seal can be a cylinder head gasket arranged between the cylinder head and the engine block of an internal-combustion engine. 
   The seal can comprise a temperature-sensitive element. 
   The present invention can be applied to the measurement, detection or analysis of engine knock in the combustion chamber of an internal-combustion chamber. 
   The invention can also be applied to characterization of the combustion in at least one combustion chamber of an internal-combustion engine. 
   This invention can also be applied to engine knock location in the combustion chamber of an internal-combustion engine. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     Other features and advantages of the invention will be clear from reading the description hereafter, given by way of non-limitative example, with reference to the accompanying figures wherein: 
       FIG. 1  is a large-scale diagrammatic view, in partial section, of a measuring device according to the invention, 
       FIG. 2  is a diagrammatic view in partial section along line  2 - 2  of  FIG. 1  with a local section along line  2   a - 2   a  of the same figure, 
       FIG. 3  is a variant of  FIG. 1 , 
       FIG. 4  is another embodiment variant of  FIG. 1 , 
       FIG. 5  is another variant of the invention, and 
       FIG. 6  yet another variant of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a device for measuring the pressure of a fluid present in a chamber. 
   More precisely, in connection with the description hereafter, which is only given by way of example, the measured pressure is the pressure resulting from the combustion of a fuel mixture in a combustion chamber of an internal-combustion engine. 
   Of course, any other parameter of the fluid, such as its temperature, can be measured by the device according to the invention. 
   With reference to  FIG. 1 , the measuring device comprises a seal  10  interposed between a first element such as a cylinder head  12  and a second element such as an engine block  14  of an internal-combustion engine whose combustion chamber  16  is delimited by the upper face  18  of a piston  20 , the circular wall  22  of a cylinder  24  arranged in engine block  14  and the cavity  26  of cylinder head  12  opposite piston  20 . 
   This seal, commonly referred to as cylinder head gasket, is generally used mainly to prevent leakage between the opposite faces  28 ,  30  of cylinder head  12  and engine block  14  respectively, and it mainly comprises circular openings  31  having the same diametral dimension as combustion chambers  16  and corresponding therewith. 
   Seal  10  is a seal in form of a pile of sheets, layers, plates, strips or films on top of each other comprising each at least one circular opening forming opening  31  of the seal. It comprises an upper extreme sheet  32  and a lower extreme sheet  34  arranged at a distance from the upper sheet, these sheets being preferably rigid and made of metal, advantageously steel, and extending over the surface of face  28  of cylinder head  12  and of face  30  of engine block  14 . 
   At least one sensitive element  36 , preferably a pressure-sensitive element, advantageously at least four, whose purpose is to measure the pressure prevailing in combustion chamber  16 , is housed between these two sheets. 
   A housing  38  intended to receive each sensitive element is therefore provided between the extreme sheets. This housing consists of a cut  40  with an open face, for example a lying U-shaped cut, provided in a multiplicity of intermediate sheets. This housing is so arranged that its open face opens onto combustion chamber  16  (see  FIG. 2 ). 
   The intermediate sheets include a central intermediate sheet  42 , preferably rigid and made of metal, advantageously steel, having the same extension as said extreme sheets and comprising a lying U-shaped cut  40  and additional intermediate sheets, plates or layers arranged between extreme sheets  32  and  34  and central sheet  42 . Part of these additional sheets also comprises a U-shaped cut so as to provide housing  38  when piling up this part of additional sheets and the central sheet. 
   Two of these additional intermediate sheets consist of films  48 ,  54  bearing electric circuits  44  and  46 , preferably opposite sensitive element  36 , allowing to connect this sensitive element to an external measuring means comprising a supply or polarization or amplification or conditioning circuit (not shown) for the sensitive element. One  48  of these films is positioned between upper sheet  32  and central sheet  42 , and the other  54  is positioned between this central sheet  42  and lower sheet  34 . 
   Advantageously, these circuits are electrically insulated from sheets  32 ,  34  and  42  by other additional intermediate sheets in form of insulating plates arranged on either side of these electric circuits. 
   Electric insulations can also be obtained by depositing an insulant on the electric circuits, such as a varnish or paint layer deposit on the circuits. This insulation can also be obtained by means of an insulating surface treatment such as an anodizing, which creates an insulating surface layer on the electric circuits. 
   As can be seen in  FIG. 1 , an insulating plate  50  is arranged between circuit  44  borne by film  48  and central sheet  42 , with the same extension as central sheet  42  and the same cut as this central sheet. Similarly, an insulating plate  52  identical to plate  50  is arranged between central sheet  42  and electric circuit  46  borne by film  54 . The sheets, plates and films are joined together fixedly, preferably by means of glue layers  56 , advantageously insulating glue layers. 
   Housing  38  thus results from piling the sheets and plates, it consists of the U-shaped cuts  40  provided in central sheet  42  and plates  50  and  52 , and it comprises a vertical face  57  open onto the combustion chamber. This housing thus comprises two horizontal walls made up of extreme sheets  32 ,  34  and intermediate sheets  48 ,  54 , and three vertical walls provided by the U-shaped cuts in central sheet  42  and insulating plates  50 ,  52 . 
   The electric circuits are provided in form of printed circuits and can be produced by means of the serigraphic film connection technology as shown in  FIG. 2 . 
   With reference to this figure, each circuit  46  provided on film  54  comprises a connection pin  58  arranged in housing  38  in line with sensitive element  36  and opposite the latter, a connection plug  59  arranged on the edge of the cylinder head and to which the external measuring means is connected, and a conductor  60  connecting the pin to the plug. 
   Of course, each circuit  44  provided on film  48  is equally designed and made by means of the same technology as the circuits of film  54 , and it therefore comprises a pin  62 , a connection plug and a conductor  63 . 
   Sensitive element  36 , which is a thin sensitive element, has a sensitivity of some tenths of a bar, it withstands the maximum pressures and temperatures that prevail in the combustion chambers of engines and withstands chemical attacks such as those of gases generated by the combustion. 
   Advantageously, this sensitive element is a piezoelectric or piezoresistive type sensitive element. 
   With reference to  FIG. 1 , sensitive element  36  is placed in housing  38  in such a way that, on the one hand, it is slightly set back in relation to the surface of cylinder  24  and that, on the other hand, none of its vertical faces, in relation to the plane of the extreme sheets, rests against any vertical face of housing  38 . 
   Preferably, this sensitive element is electrically connected by any means to pins  58 ,  62  by two of its opposite horizontal faces. 
   This electric connection can be obtained by glueing, for example with a conducting glue  64  as shown in  FIG. 1 , or by interposing between the face(s) of the sensitive element and the pin(s) at least one conducting cylindrical element  66  as illustrated in  FIG. 3 . 
   Once the sensitive element set and the connections achieved, the sensitive element is coated with a material  67  so as to fill in all of housing  38 . This embodiment allows to seal the sensitive element in relation to the combustion chamber, to protect this sensitive element against the chemical and thermal attacks due to combustion and to provide good transmission of the pressure waves, notably at high frequencies. This material is flush with the surface of cylinder  24  on open face  57  of this housing. 
   The coating material used is preferably a resin withstanding high temperatures. 
   Thus, the pressure prevailing in the combustion chamber is retransmitted to the faces of the sensitive element which deforms by generating a voltage or a voltage fluctuation transmitted to the external measuring means by electric circuits  44  and  46 , via the horizontal faces of this sensitive element, the conducting glue and/or the conducting cylindrical element. 
   The sensitive element thus provides real-time measurement of the pressure or the pressure range prevailing in the combustion chamber in the vicinity of the sensitive element. 
   The seal  10  can also include a temperature-sensitive element  37  as shown in  FIG. 2 . 
   Furthermore, the seal obtained affords the advantage of being a very thin seal of thickness ranging between 0.5 and 1.5 mm, advantageously between 0.8 and 1 mm, preferably 1 mm. 
   Advantageously, with reference to  FIG. 4 , the peripheral edge of opening  31  and consequently the open face  57  of housing  38  can be covered by a protective element  68  that protects sensitive element  36  and the electric connections against the high temperatures prevailing in the combustion chamber and also provides sealing of the sheet piles as regards the combustion gases. 
   This protective element, referred to as fire break, is a ring having a U-shaped section where the base of the U rests on the whole of the peripheral edge of opening  31  while covering the open face  57  of each housing and where the stems of the U respectively rest against upper sheet  32  and lower sheet  34 . 
   This fire break is advantageously made of coppery metal or of any other metal allowing easy forming and having a low rigidity so as not to hinder transmission of the pressure wave to the sensitive element. 
   With reference to  FIG. 5 , which shows a variant of the invention and therefore comprises the same reference numbers as  FIG. 1 , sensitive element  36  is arranged in housing  38  in such a way that the rear vertical face of this element rests by means of an insulating plate  70  against the edge of central sheet  42 . The rear face is understood to be the face of the sensitive element opposite that facing the combustion chamber. 
   In this case, the electric connections between the horizontal faces of sensitive element  36  and pins  58 ,  62  are provided, as previously described in connection with  FIG. 1 , by a conducting glue  64  or by at least one conducting cylindrical element, as shown in  FIG. 3 . 
     FIG. 6  shows another variant for mounting sensitive element  36  in housing  38 . 
   In this variant, the faces of sensitive element  36  connected to pins  58  and  62  are two opposite vertical faces forming the continuation of the open face  57  of housing  38 . 
   In order to provide the electric connections, always opposite one another, pins  58  and  62  are orthogonal in relation to conductors  60 ,  63  and they are connected to the vertical faces of the sensitive element by a conducting glue  64 . 
   In the example of this figure, the intermediate sheet in form of film  48  bearing electric circuit  44  is located at the same point as that described in connection with  FIG. 1  and comprises an orthogonal part, in the vicinity of open face  57 , while facing sensitive element  36 , and bearing connection pin  62 . In this case, an insulating plate  50  is arranged between circuit  44  borne by intermediate sheet  48  and central sheet  42 , with the same extension as central sheet  42 , and it is provided with a cut identical to that of this central sheet. 
   Intermediate sheet  54  bearing electric circuits  46  is also arranged between central intermediate sheet  42  and the lower extreme sheet, and it comprises an orthogonal part, located at a distance from the orthogonal part of film  48  and in the vicinity of the edge of intermediate sheet  42 , while facing sensitive element  36  and bearing connection pin  58 . Insulating plate  52  is positioned, in this seal configuration, between circuit  46  borne by intermediate sheet  54  and lower extreme sheet  34 . 
   Of course, as described above, the sheets, the plates and the films are joined together fixedly, preferably by means of glue layers  56 . 
   The present invention finds its application in many fields such as measurement of the temperature of a fluid in gaseous or liquid form present in a chamber. 
   In case of pressure measurement, its application can be mainly directed towards characterization and control of normal combustion, such as evaluation of the indicated mean effective pressure (IMEP) or of the maximum cylinder pressure, or characterization and control of abnormal combustion. 
   A particular application lies in the detection and analysis of engine knock, or its location as described in French patent application No. 00/14,085, filed Oct. 31, 2000, corresponding to U.S. patent application Ser. No. 09/984,832, filed Oct. 31, 2001, published as US 2002/0050162 A1. 
   The present invention is not limited to the examples described above and it includes all equivalent variants. 
   Notably, the sensitive element can be of another type, such as a sensitive element with a semiconductor element.