Patent Publication Number: US-2019195716-A1

Title: Pressure sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Japan patent application serial no. 2017-246118, filed on Dec. 22, 2017. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to a pressure sensor configured to detect a pressure of a pressure medium, and more particularly, to a pressure sensor configured to detect a pressure of a high temperature pressure medium such as a combustion gas or the like in a combustion chamber of an engine. 
     Description of Related Art 
     As a pressure sensor in the related art, a pressure sensor including a tubular housing, a diaphragm bonded to a tip side of the housing and bent according to the received pressure, a sensor part disposed in the housing, a connecting part configured to connect the diaphragm to the sensor part, and a heat receiving part serving as a heat shield plate connected to a substantially central section of an outer surface of the diaphragm through welding is known (for example, Patent Document 1). 
     In this pressure sensor, when the diaphragm is deformed in an outward convex shape due to a preload upon assembly, a gap is generated between the diaphragm and the heat shield plate in an outer circumferential region of the diaphragm. The diaphragm is directly exposed to a high temperature pressure medium through the gap, and thus, the diaphragm cannot minimize or prevent an influence of heat. 
     In addition, since the heat shield plate is fixed to the diaphragm through welding, X-ray radiography, a destruction test, or the like, is needed to guarantee a welding strength, an increase in management man-hours and management costs occurs, and the heat shield plate is limited to a metal material. 
     PATENT DOCUMENTS 
     [Patent Document 1] Japanese Laid-open No. 2017-40516 
     SUMMARY 
     A pressure sensor of an embodiment of the disclosure includes a housing including a tubular tip portion; a pressure measuring part including a piezoelectric substance while being accommodated in the housing; a diaphragm including a flexible plate-shaped section fixed to an inner side of the tubular tip portion and a rod section interposed between the flexible plate-shaped section and the pressure measuring part; and a heat shield plate held on an inner side of the tubular tip portion to shield the diaphragm from a pressure medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing an embodiment of a pressure sensor according to the disclosure. 
         FIG. 2  is a partially enlarged cross-sectional view showing a housing including a tubular tip portion, a diaphragm, a heat shield plate, a pressure measuring part, and so on, in the pressure sensor shown in  FIG. 1 . 
         FIG. 3  is a partially enlarged cross-sectional view showing a mutual relationship between the tubular tip portion, the diaphragm and the heat shield plate in the pressure sensor shown in  FIG. 1 . 
         FIG. 4  is a partially enlarged cross-sectional view showing the tubular tip portion, the diaphragm and the heat shield plate in states before and after folding processing is performed on an opening edge region of the tubular tip portion in the pressure sensor shown in  FIG. 1 . 
         FIG. 5  is a cross-sectional view showing another embodiment of the pressure sensor according to the disclosure. 
         FIG. 6  is a partially enlarged cross-sectional view showing the housing including the tubular tip portion, the diaphragm, the heat shield plate, the pressure measuring part, and so on, in the pressure sensor shown in  FIG. 5 . 
         FIG. 7  is a partially enlarged cross-sectional view showing a mutual relationship between the tubular tip portion, the coupling member, the diaphragm, and the heat shield plate in the pressure sensor shown in  FIG. 5 . 
         FIG. 8  is a partially enlarged cross-sectional view showing the tubular tip portion, the diaphragm, the coupling member, and the heat shield plate in states before and after a coupling member that defines a part of the tubular tip portion is coupled to the housing in the pressure sensor shown in  FIG. 5 . 
         FIG. 9  is a graph in which sensor outputs are compared with the pressure sensor according to the embodiment of the disclosure and the pressure sensor in the related art. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The embodiments of the disclosure are directed to providing a pressure sensor capable of securely shielding a diaphragm from a high temperature pressure medium, minimizing an influence of heat and accurately detecting a pressure of the high temperature pressure medium. 
     A pressure sensor of an embodiment of the disclosure includes a housing including a tubular tip portion; a pressure measuring part including a piezoelectric substance while being accommodated in the housing; a diaphragm including a flexible plate-shaped section fixed to an inner side of the tubular tip portion and a rod section interposed between the flexible plate-shaped section and the pressure measuring part; and a heat shield plate held on an inner side of the tubular tip portion to shield the diaphragm from a pressure medium. 
     In the pressure sensor having this configuration, the tubular tip portion may include an annular tip portion that defines an opening having a reduced diameter at a tip thereof, and the heat shield plate may be held by the annular tip portion. 
     In the pressure sensor having this configuration, the annular tip portion may be formed by folding an opening edge region of the tubular tip portion inward. 
     In the pressure sensor having this configuration, the heat shield plate may be held to come in contact with the flexible plate-shaped section with no load or faces the flexible plate-shaped section with a predetermined play gap therebetween in a state in which a pressure of a pressure medium is not received. 
     In the pressure sensor having this configuration, the play gap may be set be in a range of a plate thickness or less of the heat shield plate. 
     In the pressure sensor having this configuration, the tubular tip portion may be formed in a cylindrical shape, the flexible plate-shaped section may be formed in a disk shape disposed on an inner side of the tubular tip portion, and the heat shield plate may be formed in a disk shape having an outer diameter smaller than an inner diameter of the tubular tip portion. 
     In the pressure sensor having this configuration, the tubular tip portion may include a first tubular section, a second tubular section disposed on a tip side of the first tubular section and having a wall thickness smaller than that of the first tubular section, and a stepping surface formed on a boundary between the first tubular section and the second tubular section, the flexible plate-shaped section may be fixed to the stepping surface, the second tubular section may include an annular tip portion that defines an opening having a reduced diameter at a tip thereof, and the heat shield plate may be held by the annular tip portion. 
     In the pressure sensor having this configuration, the annular tip portion may be constituted by a coupling member coupled to the housing to define the second tubular section. 
     In the pressure sensor having this configuration, the pressure measuring part may include a first electrode, a piezoelectric substance and a second electrode, which are sequentially laminated from a tip side of the tubular tip portion, and the diaphragm may function as the first electrode. 
     According to the pressure sensor having this configuration, it is possible to provide a pressure sensor capable of minimizing an influence of heat and accurately detecting a pressure of a high temperature pressure medium. 
     Hereinafter, embodiments of the disclosure will be described with reference to the accompanying drawings. 
     A pressure sensor according to the first embodiment is attached to a cylinder head H of an engine, and detects a pressure of a combustion gas in a combustion chamber as a pressure medium. 
     As shown in  FIG. 1  and  FIG. 2 , the pressure sensor includes a housing  10 , a diaphragm  20 , a pressure measuring part  30 , a pressing member  40 , a lead wire  50 , a connector  60 , and a heat shield plate  70 . 
     The housing  10  is formed in a multi-stage cylindrical shape that defines an internal space A extending in an axis S direction using a metal material such as a precipitation hardening-based or ferrite-based stainless steel, or the like. 
     Further, the housing  10  includes a tubular tip portion  11 , a seal section  12 , a male screw section  13 , an opening end portion  14 , inner wall surfaces  15  and  16 , and a female screw section  17 . 
     The tubular tip portion  11  is formed in a cylindrical shape having a two-stage wall thickness in a region disposed on a tip side in the axis S direction of the seal section  12 , and includes a first tubular section  11   a , a second tubular section  11   b , a stepping surface  11   c , an annular tip portion  11   d , and an opening  11   e  defined by the annular tip portion  11   d.    
     The first tubular section  11   a  defines an inner wall surface  11   a   1  having a cylindrical shape, and an outer wall surface thereof is disposed to close to or be in close contact with an inner circumferential surface H 1  of an attachment hole of the cylinder head H such that the outer wall surface cannot be easily exposed to a combustion gas. 
     The second tubular section  11   b  defines a cylindrical inner wall surface  11   b   1  having a thickness smaller than that of the first tubular section  11   a  in a state before folding processing. The stepping surface  11   c  is formed as an annular plane perpendicular to an axis S in a boundary between the first tubular section  11   a  and the second tubular section  11   b.    
     Then, the stepping surface  11   c  functions as a fixing surface that fixes a flexible plate-shaped section  21  of the diaphragm  20  through welding or the like. 
     The annular tip portion  11   d  is folded by folding an opening edge region of the second tubular section  11   b  inward, and defines the circular opening  11   e  in a central region thereof. 
     The opening  11   e  has a diameter smaller than an outer diameter D of the heat shield plate  70 , i.e., is formed to have a small inner diameter. 
     That is, the annular tip portion  11   d  plays a role of holding the heat shield plate  70  accommodated inside the second tubular section  11   b  such that the heat shield plate  70  does not fall. 
     The seal section  12  is formed in a conical surface shape at a predetermined position retracted from a tip of the tubular tip portion  11  in the axis S direction, and abuts a seal surface H 2  of the cylinder head H to play a role of preventing leakage of a combustion gas in a combustion chamber CH. 
     The male screw section  13  is threadedly engaged with a female screw section H 3  of an attachment hole formed in the cylinder head H to fix the housing  10 , and formed in a diameter-enlarged region retracted from the seal section  12  in the axis S direction. 
     The opening end portion  14  functions as an insertion port when the pressing member  40  or the like is attached therethrough, and is formed such that the connector  60  is fixed thereto via a spacer  61 . 
     The inner wall surface  15  is formed as a cylindrical inner circumferential surface that forms an inner diameter dimension such that the pressing member  40  can be inserted therethrough. 
     The inner wall surface  16  is formed as a cylindrical inner circumferential surface that forms an inner diameter dimension having a diameter smaller than that of the inner wall surface  15 , and the pressure measuring part  30  is accommodated in this region. 
     The female screw section  17  is formed in a region between the inner wall surface  15  and the inner wall surface  16  such that the pressing member  40  can be fixed by being screwed with the female screw section  17 . 
     The diaphragm  20  is formed using a metal material such as stainless steel or the like having a precipitation hardening property. 
     Then, the diaphragm  20  includes the flexible plate-shaped section  21 , and a rod section  22  formed to be continuous with the flexible plate-shaped section  21 . 
     The flexible plate-shaped section  21  is formed in a disk shape having a plate thickness t 1 , and an outer edge region thereof is fixed to the stepping surface  11   c  of the tubular tip portion  11  through welding or the like. 
     The flexible plate-shaped section  21  is a region to which a load according to a pressure of a combustion gas is transmitted via the heat shield plate  70  and is elastically deformed in the axis S direction according to the load. 
     Here, the plate thickness t 1  of the flexible plate-shaped section  21  is about 0.2 mm to 0.6 mm. 
     The rod section  22  is formed in a columnar shape extending from a substantially central region of the flexible plate-shaped section  21  in the axis S direction. 
     Then, an outer circumferential surface of the rod section  22  is disposed such that a gap between it and the inner wall surfaces  11   a   1  and  16  of the housing  10  is provided, and an end surface of the rod section  22  is disposed to abut a piezoelectric substance  32  of the pressure measuring part  30 . 
     That is, the rod section  22  is interposed between the flexible plate-shaped section  21  and the piezoelectric substance  32  of the pressure measuring part  30  and has a function of transmitting a force received by the flexible plate-shaped section  21  to the piezoelectric substance  32 . 
     The pressure measuring part  30  functions as a piezoelectric element, and as shown in  FIG. 2 , includes a first electrode  31 , the piezoelectric substance  32  and a second electrode  33 , which are sequentially stacked from a tip side of the tubular tip portion  11  in the axis S direction. 
     The first electrode  31  is formed of a conductive metal material, and in the embodiment, the diaphragm  20  functions as the first electrode  31 . 
     Then, the first electrode  31 , i.e., the diaphragm  20  is disposed such that the rod section  22  is in close contact with the piezoelectric substance  32 , and electrically connected to a ground (a negative side) via the housing  10  and the cylinder head H. 
     The piezoelectric substance  32  is formed in a rectangular columnar shape, sandwiched between the rod section  22  of the first electrode  31 , i.e., the diaphragm  20  and the second electrode  33 , and outputs an electrical signal on the basis of distortion due to a load received in the axis S direction, and a piezoelectric element, zinc oxide, a crystal, or the like, is applied thereas. 
     The second electrode  33  is formed of a conductive metal material in a columnar or disk shape, disposed to be in close contact with the piezoelectric substance  32 , and electrically connected to a positive side via the lead wire  50 . 
     In the pressure measuring part  30 , since the diaphragm  20  functions as the first electrode  31 , in comparison with the case in which a dedicated electrode is provided, the number of parts can be reduced, and a structure can be simplified. 
     Further, the disclosure is not limited to this configuration, and a separate electrode from the diaphragm  20  may be included as the first electrode  31 . 
     As shown in  FIG. 2 , the pressing member  40  is constituted by a screw member  41  and an insulating member  42 . 
     The screw member  41  is formed of a metal material such as a precipitation hardening-based or ferrite-based stainless steel or the like in a substantially columnar shape, and includes a male screw section  41   a  threadedly engaged with the female screw section  17  of the housing  10 , a through-hole  41   b  through which the lead wire  50  passes, and an abutting surface  41   c  that abuts the insulating member  42 . 
     The insulating member  42  is formed of an insulating material having highly electrically insulating properties, for example, alumina or the like, in a substantially circumferential shape and includes an end surface  42   a  that abuts the abutting surface  41   c  of the screw member  41 , an end surface  42   b  that abuts the second electrode  33 , and a through-hole  42   c  through which the lead wire  50  passes. 
     Then, as shown in  FIG. 1  and  FIG. 2 , as the insulating member  42  is inserted in a state in which the pressure measuring part  30  is disposed at a predetermined position and the screw member  41  is screwed from above the insulating member  42 , a preload being applied to the pressure measuring part  30  in the axis S direction or the pressure measuring part  30  being positioned and held at a predetermined position in the housing  10 . 
     As shown in  FIG. 1 , the lead wire  50  is electrically connected to the second electrode  33  of the pressure measuring part  30 , passes through the through-hole  42   c  of the insulating member  42 , the through-hole  41   b  of the screw member  41  and the internal space A of the housing  10 , and is guided to the connector  60 . 
     The connector  60  is formed as a receptacle, coupled to the opening end portion  14  of the housing  10  via the spacer  61 , and detachably connected to an external connector (plug). 
     The heat shield plate  70  is disposed inside the tubular tip portion  11  such that the diaphragm  20  is shielded from a combustion gas that is a pressure medium, and formed of a material having a heat resistance and a low thermal conductivity, for example, a stainless steel plate in a disk shape. 
     Here, a plate thickness t 2  of the heat shield plate  70  is, for example, about 0.2 mm to 0.5 mm. 
     As a material of the heat shield plate  70 , a material having a low thermal conductivity, good durability and high rigidity is adopted, for example, and in addition to stainless steel, carbon steel on which nickel plating has been performed, a nickel alloy, an iron-based alloy, a titanium alloy, or the like, may be used. 
     Then, as shown in  FIG. 4 , the heat shield plate  70  is inserted inside the second tubular section  11   b  of the tubular tip portion  11 , and then, held on an inner side of the second tubular section  11   b  such that the heat shield plate  70  does not fall outward by the annular tip portion  11   d  formed by bending an opening edge region of the second tubular section  11   b  inward using a folding machine M. 
     Here, the heat shield plate  70  is held in contact with the flexible plate-shaped section  21  with no load in a state in which a pressure of a combustion gas is not being received. 
     In addition, the outer diameter D of the heat shield plate  70  is larger than an effective diameter of the flexible plate-shaped section  21  that functions as a diaphragm and smaller than an inner diameter of the second tubular section  11   b  such that the heat shield plate  70  does not become immovable inside the second tubular section  11   b  due to scuffing, sticking, or the like. 
     Further, while the heat shield plate  70  is held to be in contact with the flexible plate-shaped section  21  with no load, the heat shield plate  70  may be disposed to face the flexible plate-shaped section  21  with a predetermined play gap therebetween in the axis S direction. 
     In this case, the play gap is set to be in a range of the plate thickness t 2  or less of the heat shield plate  70 , specifically, about 0.1 to 0.2 mm. 
     In this way, since the play gap is provided, there is no need to accurately manage the folding processing such that the heat shield plate  70  is pressed against the flexible plate-shaped section  21  and does not exert a load. 
     Next, assembly of a pressure sensor that constitutes the configuration will be described. 
     First, the housing  10 , the diaphragm  20 , the piezoelectric substance  32 , the second electrode  33  to which the lead wire  50  is connected, the screw member  41 , the insulating member  42 , the connector  60 , the spacer  61 , and the heat shield plate  70  are prepared. 
     Next, the diaphragm  20  is assembled on the housing  10 . 
     That is, the flexible plate-shaped section  21  is joined to the stepping surface  11   c  of the tubular tip portion  11  and fixed thereto through welding or the like. 
     Next, the piezoelectric substance  32 , the second electrode  33 , the insulating member  42  and the screw member  41  are inserted into the housing  10  from the opening end portion  14  to overlap each other in sequence. 
     Further, the piezoelectric substance  32 , the second electrode  33  and the insulating member  42  may be previously stacked and temporarily assembled. 
     Then, the screw member  41  is appropriately screwed, and a predetermined preload is applied to provide linear characteristics to the pressure measuring part  30  as a sensor. 
     Next, the spacer  61  is fixed to the opening end portion  14  of the housing  10 , an extracted lead wire  50  is connected to the connector  60 , and the connector  60  is connected to the spacer  61 . 
     Next, the heat shield plate  70  is attached to be held inside the tubular tip portion  11  of the housing  10 . Here, “holding” means that a member is supported such that it does not fall without being immovably fixed to the tubular tip portion  11 . 
     That is, the heat shield plate  70  is disposed on an inner side of the second tubular section  11   b  of the tubular tip portion  11 . 
     Next, as shown in  FIG. 4 , an opening edge region of the second tubular section  11   b  is folded inward using the predetermined folding machine M, and the annular tip portion  11   d  is formed. Here, the opening  11   e  having a diameter smaller than the outer diameter D of the heat shield plate  70  is defined by the annular tip portion  11   d.    
     As described above, assembly of the pressure sensor is terminated. 
     Further, this assembly sequence is merely an example and is not limited thereto, and another assembly sequence may be employed. 
     In the pressure sensor that constitutes this configuration, the tubular tip portion  11 , the diaphragm  20  and the heat shield plate  70  have a disposition relationship shown in  FIG. 3 . 
     That is, the heat shield plate  70  is held inside the tubular tip portion  11  and disposed on an outer side of the diaphragm  20  such that the heat shield plate  70  is in contact with the flexible plate-shaped section  21  with no load in a state in which a pressure of a combustion gas is not being received. 
     Accordingly, when the heat shield plate  70  receives a pressure of a combustion gas through the opening  11   e , the load according to the pressure is immediately applied to the flexible plate-shaped section  21  via the heat shield plate  70 . Then, the diaphragm  20  deforms according to the received load while being shielded from the combustion gas by the heat shield plate  70 . 
     Accordingly, heat of the combustion gas is substantially shielded by the heat shield plate  70 , and heat transfer toward the diaphragm  20  is minimized or prevented. Accordingly, in the flexible plate-shaped section  21  of the diaphragm  20 , an influence of heat due to a combustion gas is minimized or prevented, and only a pressure of a combustion gas is substantially received. 
     In addition, since the heat shield plate  70  is disposed to come in contact with the flexible plate-shaped section  21 , no impact force or impact sound according to the movement occurs, and there is no influence on characteristics of the diaphragm  20 . 
     In addition, the heat shield plate  70  is held on an inner side of the tubular tip portion  11  and not fixed through welding or the like. Accordingly, as a material of the heat shield plate  70 , materials other than a metal material may be used as long as a heat shielding action is obtained by the material. 
     As described above, even in a measurement environment exposed to a high temperature pressure medium, deformation of the diaphragm  20  due to heat can be minimized, and a contact position between the rod section  22  of the diaphragm  20  and the piezoelectric substance  32  of the pressure measuring part  30  can be maintained in an expected setting state. 
     Accordingly, fluctuation of a preload applied to the pressure measuring part  30  can be prevented, and output noise from the piezoelectric substance  32  due to fluctuation of a preload can be prevented. 
     For this reason, measurement error due to thermal deformation or the like can be minimized, and a pressure of a combustion gas in the combustion chamber CH of the engine can be accurately detected. 
     That is, when the diaphragm  20  is temporarily deformed by heat as a mechanism, while a preload applied to the pressure measuring part  30  varies and the accuracy of the detected pressure is decreased, in the embodiment of the disclosure, since deformation of the diaphragm  20  due to heat is minimized by the heat shield plate  70 , the pressure can be accurately detected by heat shielding→minimization of thermal deformation of the diaphragm  20 →prevention of fluctuation of a preload. 
       FIG. 5  to  FIG. 8  show another embodiment of the pressure sensor according to the disclosure, constituting the same configuration as the above-mentioned embodiment except that the second tubular section  11   b  holding the above-mentioned heat shield plate  70  is changed. Accordingly, components which are the same are designated by the same reference numerals and description thereof will be omitted. 
     The pressure sensor according to the embodiment includes a housing  100 , the diaphragm  20 , the pressure measuring part  30 , the pressing member  40 , the lead wire  50 , the connector  60  and the heat shield plate  70 . 
     The housing  100  is formed in a multi-stage cylindrical shape that defines the internal space A extending in the axis S direction using a metal material such as a precipitation hardening-based or ferrite-based stainless steel or the like. 
     Then, the housing  100  includes a tubular tip portion  110 , the seal section  12 , the male screw section  13 , the opening end portion  14 , the inner wall surfaces  15  and  16 , the female screw section  17 , and a coupling member  120  coupled to the tubular tip portion  110 . 
     The tubular tip portion  110  is formed in a cylindrical shape having a two-stage thickness in a region disposed from the seal section  12  toward a tip side in the axis S direction, and includes a first tubular section  111 , an end surface  112 , and the coupling member  120  coupled to the end surface  112 . 
     Then, the coupling member  120  includes a second tubular section  121  coupled to the first tubular section  111  such that an outer circumferential wall is continuous, an annular tip portion  122  formed on a tip side of the second tubular section  121 , an end surface  123  formed on a rear end side of the second tubular section  121 , and an opening  124  defined by the annular tip portion  122 . 
     The first tubular section  111  defines an inner wall surface  111   a  having a cylindrical shape, and an outer wall surface thereof is disposed to close to or be in close contact with the inner circumferential surface H 1  of the attachment hole of the cylinder head H such that the outer wall surface cannot be easily exposed to a combustion gas. 
     The end surface  112  defines a stepping surface that forms an annular plane perpendicular to the axis S at a boundary between the first tubular section  111  and the second tubular section  121  in a state in which the first tubular section  111  and the second tubular section  121  are coupled to each other. 
     Then, the stepping surface disposed in an inner edge region of the end surface  112  functions as a fixing surface to which the flexible plate-shaped section  21  of the diaphragm  20  is fixed through welding or the like. 
     The second tubular section  121  defines an inner wall surface  121   a  having a cylindrical shape with a wall thickness smaller than that of the first tubular section  111 . An inner diameter of the inner wall surface  121   a  is slightly larger than the outer diameter D of the heat shield plate  70 . 
     The annular tip portion  122  is formed in an annular disk shape on a tip side of the second tubular section  121 , and defines the circular opening  124  in a central region thereof. 
     The end surface  123  is formed in an annular planar shape and coupled to an outer circumferential edge region of the end surface  112 . 
     The opening  124  is formed to have a diameter smaller than the inner diameter of the second tubular section  121  as the tubular tip portion such that the inner diameter of the opening  124  is smaller than the outer diameter D of the heat shield plate  70 . 
     That is, the annular tip portion  122  plays a role of holding the heat shield plate  70  accommodated on an inner side of the second tubular section  121  such that the heat shield plate  70  is movable in the axis S direction and does not fall. 
     Here, the heat shield plate  70  is held to face the flexible plate-shaped section  21  with a predetermined play gap C therebetween in a state in which a pressure of a combustion gas is not received. 
     Here, the play gap C is set to be in a range of the plate thickness t 2  or less of the heat shield plate  70 , specifically, about 0.1 to 0.2 mm. 
     In addition, the outer diameter D of the heat shield plate  70  is larger than an effective diameter of the flexible plate-shaped section  21  that functions as a diaphragm and smaller than the inner diameter of the second tubular section  121  such that the heat shield plate  70  is not immovable due to scuffing, sticking, or the like or does not cause an increase in resistance due to sliding on an inner side of the second tubular section  121 . 
     Further, the heat shield plate  70  may be held to come in contact with the flexible plate-shaped section  21  with no load in a state in which a load is not being applied. 
     Next, assembly of the pressure sensor that constitutes the configuration will be described. 
     First, the housing  100 , the coupling member  120 , the diaphragm  20 , the piezoelectric substance  32 , the second electrode  33  to which the lead wire  50  is connected, the screw member  41 , the insulating member  42 , the connector  60 , the spacer  61  and the heat shield plate  70  are prepared. 
     Next, the diaphragm  20  is assembled on the housing  100 . That is, the flexible plate-shaped section  21  is coupled and fixed to the end surface  112  of the tubular tip portion  110  through welding or the like. 
     Next, the piezoelectric substance  32 , the second electrode  33 , the insulating member  42  and the screw member  41  are inserted into the housing  100  from the opening end portion  14  to sequentially overlap each other. 
     Further, the piezoelectric substance  32 , the second electrode  33  and the insulating member  42  may be previously laminated and temporarily assembled together. 
     Then, the screw member  41  is appropriately screwed and a predetermined preload is applied to provide linear characteristics to the pressure measuring part  30  as a sensor. 
     Next, the spacer  61  is fixed to the opening end portion  14  of the housing  100 , the extracted lead wire  50  is connected to the connector  60 , and the connector  60  is connected to the spacer  61 . 
     Next, as shown in  FIG. 8 , in a state in which the heat shield plate  70  is accommodated inside the coupling member  120 , the end surface  123  of the coupling member  120  is coupled and fixed to the end surface  112  of the tubular tip portion  110  through welding or the like. 
     Accordingly, the heat shield plate  70  is assembled to be held on an inner side of the tubular tip portion  110  of the housing  100 . 
     Here, “holding” means that a member is supported such that it does not fall without being immovably fixed to the tubular tip portion  110  and movable in the axis S direction. 
     As described above, assembly of the pressure sensor is terminated. 
     Further, the assembly sequence is an example and not limited thereto, and another assembly sequence may be employed. 
     In the pressure sensor that constitutes the configuration, the tubular tip portion  110 , the diaphragm  20 , and the heat shield plate  70  have a disposition relation shown in  FIG. 7 . 
     That is, the heat shield plate  70  is held on an inner side of the tubular tip portion  110  and disposed on an outer side of the diaphragm  20  to face the flexible plate-shaped section  21  with a predetermined play gap C therebetween in a state in which a pressure of a combustion gas is not received. 
     Accordingly, when the heat shield plate  70  receives a pressure of a combustion gas through the opening  124 , the heat shield plate  70  immediately comes into contact with the flexible plate-shaped section  21 . 
     Then, the diaphragm  20  deforms according to the received pressure while being shielded from the combustion gas by the heat shield plate  70 . 
     Accordingly, heat of the combustion gas is substantially shielded by the heat shield plate  70  and heat transfer to the diaphragm  20  is minimized or prevented. 
     Accordingly, the flexible plate-shaped section  21  of the diaphragm  20  substantially receives only a pressure of a combustion gas by minimizing or preventing an influence of heat due to the combustion gas. 
     In addition, since the play gap C of the heat shield plate  70  is set to be in a range of the plate thickness t 2  or less of the heat shield plate  70 , an impact force according to the movement is reduced, and thus, an impact sound or the like does not occur and also there is no influence on the characteristics of the diaphragm  20 . 
     In this way, since the play gap C is provided, management of a dimension of the second tubular section  121  in the axis S direction is facilitated, and management costs or the like can be reduced. 
     In addition, the heat shield plate  70  is held on an inner side of the tubular tip portion  110 , and is not fixed through welding or the like. Accordingly, as the material of the heat shield plate  70 , according to a material in which a heat shield action is obtained, a material other than a metal material can be used. 
     As described above, even under a measurement environment exposed to a high temperature pressure medium, deformation of the diaphragm  20  due to heat can be minimized, and a contact position between the rod section  22  of the diaphragm  20  and the piezoelectric substance  32  of the pressure measuring part  30  can be maintained in an expected set state. Accordingly, fluctuation of a preload applied to the pressure measuring part  30  can be prevented, and output noise from the piezoelectric substance  32  due to fluctuation of the preload can be prevented. 
     For this reason, measurement error due to thermal deformation or the like can be minimized, and a pressure of a combustion gas in the combustion chamber CH of the engine can be detected accurately. 
       FIG. 9  is a graph showing comparison test data obtained by measuring a pressure of a combustion gas in a combustion chamber of an engine using the pressure sensor according to the embodiment of the disclosure and a pressure sensor in the related art.
         Engine used: two-cylinder gasoline engine, exhaust volume 1000 cc   Operation conditions: engine rotation speed 5000 rpm, full throttle   Reference sensor: sensor for precision analysis (manufactured by AVL Co., Ltd.)   Results data: dotted line→sensor for precision analysis (actual combustion pressure), solid line→pressure sensor of the embodiment of the disclosure, dotted-dashed line→pressure sensor in the related art       

     As is apparent from the results shown in  FIG. 9 , in the pressure sensor of the embodiment of the disclosure including the heat shield plate  70 , in comparison with the pressure sensor in the related art, a deviation amount from the actual combustion pressure, i.e., a measurement error is reduced. 
     In this way, according to the pressure sensor of the embodiment of the disclosure, sensor accuracy can be improved, and a pressure of a pressure medium such as a combustion gas or the like in the combustion chamber of the engine can be accurately detected. 
     In the embodiment, while the diaphragm  20  in which the flexible plate-shaped section  21  and the rod section  22  are integrally provided is shown as a diaphragm, the embodiment is not limited thereto, and a configuration in which the flexible plate-shaped section  21  and the rod section  22  are separately formed, the flexible plate-shaped section  21  functions as a diaphragm and the rod section  22  functions as a power transmission member may be employed. 
     In the embodiment, while a configuration in which the diaphragm  20  functions as the first electrode  31  of the pressure measuring part  30  is shown, there is no limitation thereto, and a configuration in which a dedicated electrode is provided as the first electrode  31  may be employed. 
     As described above, since the pressure sensor of the embodiment of the disclosure can minimize an influence of heat and accurately detect a pressure of a high temperature pressure medium, in particular the pressure sensor of the embodiment of the disclosure can be applied as a pressure sensor configured to detect a pressure of a high temperature pressure medium such as a combustion gas or the like in the combustion chamber of an engine, and is useful as a pressure sensor configured to detect a pressure of a high temperature pressure medium other than a combustion gas, or a pressure of another pressure medium.