JP2011163915A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensor capable of preventing thermal deformation of a diaphragm, and capable of also preventing pressure detection accuracy from being lowered by soot generated in a combustion chamber. <P>SOLUTION: The pressure sensor 10 is arranged at a position facing a combustion chamber of an internal combustion engine. The pressure sensor 10 includes: a housing 20; a diaphragm 30 which is fixed to the housing 20 and partitions the inside from the outside of the housing 20; a sensor part 50 whose output value changes in accordance with the deformation of the diaphragm 30; and a fire-resistant heat-insulating member 40 which foams on the outside surface of the diaphragm 30 and covers the whole of the outside surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pressure sensor that detects a pressure in a combustion chamber of an internal combustion engine.

  Patent Document 1 discloses a pressure sensor that detects the pressure of a combustion chamber of an internal combustion engine. The pressure sensor includes a substantially cylindrical housing, a diaphragm that is fixed to the housing, thereby partitioning the inside and outside of the housing, and an output value that is disposed on the inside of the housing and corresponds to deformation of the diaphragm. The sensor part which changes is provided. When the housing is fixed in the hole formed in the wall defining the combustion chamber, the diaphragm faces the combustion chamber. In this pressure sensor, the diaphragm is deformed as the pressure in the combustion chamber changes, and the output value of the sensor unit changes, so that the pressure in the combustion chamber can be detected.

In this type of pressure sensor, there is a possibility that the diaphragm is thermally deformed because the diaphragm is exposed to high-temperature heat in the combustion chamber. Therefore, both the pressure of the combustion chamber and the temperature of the combustion chamber may affect the output value from the sensor unit.
In the pressure sensor described in Patent Document 1, the diaphragm is covered with a highly thermally conductive member having good thermal conductivity. An opening is formed in the high thermal conductivity member, and the pressure in the combustion chamber is transmitted to the diaphragm through this opening. The high heat conductive member is disposed at a predetermined gap from the diaphragm, and the periphery of the heat conductive member is in contact with the inner periphery of the housing. Thereby, the high temperature heat in the combustion chamber is conducted to the housing through the high thermal conductivity member, and is radiated from the housing to the combustion chamber wall. Thus, in the pressure sensor of Patent Document 1, high-temperature heat in the combustion chamber is hardly transmitted to the diaphragm, and the diaphragm is difficult to be thermally deformed.

Japanese Patent Application Laid-Open No. 2004-286753

  In the pressure sensor described in Patent Document 1, an opening is formed in the high thermal conductivity member. Therefore, there is a possibility that a situation in which the pressure in the combustion chamber is not properly transmitted to the diaphragm due to clogging of the soot generated in the combustion chamber in this opening. In addition, there is a case where a flaw enters the gap between the high thermal conductivity member and the diaphragm through the opening, and the high thermal conductivity member and the diaphragm are fixed through the flaw. In such a case, the relationship between the pressure acting on the diaphragm and the amount of deformation of the diaphragm changes, which may reduce the pressure detection accuracy by the pressure sensor.

  The technology disclosed in the present specification has been made in view of such circumstances, and the purpose thereof is to suppress thermal deformation of the diaphragm and to reduce pressure detection accuracy due to soot generated in the combustion chamber. It is in providing the pressure sensor which can also suppress this.

  The pressure sensor disclosed in this specification is used by being disposed at a position facing the combustion chamber of the internal combustion engine. The pressure sensor includes a substantially cylindrical housing, a diaphragm fixed to the housing and defining an inner side and an outer side of the housing, and disposed inside the housing and according to deformation of the diaphragm. A sensor unit whose output value changes is provided.

  In one pressure sensor disclosed in the present specification, a heat insulating member that suppresses thermal deformation of the diaphragm is completed before being attached to the internal combustion engine. That is, the heat-resistant heat insulation member which foams on the outer surface of the diaphragm and covers the entire outer surface of the diaphragm is provided.

According to the above configuration, the diaphragm can be prevented from being exposed to the flame by the fireproof heat insulating member, so that the diaphragm can be prevented from being thermally deformed by the high-temperature heat in the combustion chamber.
The heat insulating member is foamed on the surface of the diaphragm and is in close contact with the diaphragm. Therefore, the heat insulating member and the diaphragm are integrally deformed according to the pressure in the combustion chamber. Thus, since the diaphragm is deformed according to the pressure in the combustion chamber, the sensor unit can output an output value reflecting the pressure in the combustion chamber.
The heat insulating member covers the entire outer surface of the diaphragm, and an opening such as a slit that exposes a part of the surface of the diaphragm to the combustion chamber is not formed. Therefore, the opening does not get clogged and the pressure detection accuracy is not lowered.

  In addition, another pressure sensor disclosed in the present specification is in a state of exhibiting a function by being attached to the internal combustion engine and operating the internal combustion engine. In this type of pressure sensor, a material that foams and changes into a refractory heat insulating member when exposed to the flame of the combustion chamber is applied to the entire outer surface of the diaphragm before being attached to the internal combustion engine.

  Applying a pressure sensor to the internal combustion engine to operate the internal combustion engine if the entire surface of the outer surface of the diaphragm is coated with a material that foams and becomes a refractory heat insulating member when exposed to the flame of the combustion chamber This exposes the material to the flame of the combustion chamber and completes a refractory insulation that foams over the outer surface of the diaphragm and covers the entire outer surface of the diaphragm. As a result, it is possible to suppress thermal deformation of the diaphragm, and it is also possible to suppress a decrease in pressure detection accuracy due to soot generated in the combustion chamber.

In addition, it is preferable that a metal guide extending from the periphery of the diaphragm toward the outside of the diaphragm is provided, and a space defined by the surface of the diaphragm and the inner surface of the guide is filled with a heat insulating member.
According to the said structure, while the heat insulation member is closely_contact | adhered to the surface of a diaphragm, the circumference | surroundings are supported by the metal guide. Therefore, it can suppress that a heat insulation member falls from the surface of a diaphragm.

  In addition, it is preferable that a portion that protrudes toward the center side of the diaphragm is formed in the guide when it is separated from the diaphragm. According to this structure, it can suppress reliably that a heat insulation member falls from the surface of a diaphragm.

Moreover, it is preferable that the guide is formed continuously over the entire circumference of the diaphragm.
According to this structure, it can suppress more reliably that a heat insulation member falls from the surface of a diaphragm.

The heat insulating ability of the heat insulating member is preferably such that the amount of heat transferred to the diaphragm is reduced to ½ or less as compared with the case where there is no heat insulating member. Moreover, it is preferable that the rigidity of a heat insulation member is below the rigidity of a diaphragm.
If the amount of heat transfer to the diaphragm is suppressed to ½ or less, the amount of thermal deformation of the diaphragm is significantly reduced. If the rigidity of the heat insulating member is equal to or lower than the rigidity of the diaphragm, the required detection sensitivity can be ensured without impairing the flexibility required of the diaphragm due to the presence of the heat insulating member.

FIG. 3 is a cross-sectional view illustrating a pressure sensor according to the first embodiment. FIG. 3 is a plan view showing a pressure sensor according to the first embodiment. Sectional drawing which shows the state which the diaphragm and heat insulation member of the pressure sensor of Example 1 deform | transformed. Sectional drawing which shows the manufacturing process of the pressure sensor of Example 1. FIG. Sectional drawing which shows the pressure sensor of Example 2. FIG. Sectional drawing which shows the pressure sensor of Example 3. FIG.

The features of the embodiments of the present invention will be described below.
(Feature 1) The pressure sensor is attached to the cylinder head by screwing a screw portion formed on the outer periphery of the housing with a screw hole formed in the wall of the combustion chamber.

A first embodiment in which a pressure sensor according to the technology disclosed in the present specification is embodied will be described with reference to FIGS.
FIG. 1 is a cross-sectional view of the pressure sensor 10 according to the first embodiment. The pressure sensor 10 is attached to the cylinder head so that a heat insulating member 40 formed at the tip thereof faces a combustion chamber of an internal combustion engine (not shown). As shown in FIG. 1, the pressure sensor 10 includes a housing 20, a diaphragm 30, a guide 35, a heat insulating member 40, and a sensor unit 50. In the pressure sensor 10, the diaphragm 30 is deformed in accordance with the pressure in the combustion chamber, and the sensor unit 50 detects the pressure in the combustion chamber by changing the output value in accordance with the deformation.

The housing 20 is formed in a substantially cylindrical shape and includes an outer housing 21 and an inner housing 22. A screw portion 25 is formed on the outer peripheral portion of the outer housing 21. The pressure sensor 10 is attached to the cylinder head by screwing the screw portion 25 into a screw hole formed in the cylinder head (not shown).
An inner housing 22 is fitted on the front end side of the outer housing 21. The outer peripheral surface of the inner housing 22 is welded to the inner peripheral surface on the front end side of the outer housing 21. A front end portion of the inner housing 22 serves as a diaphragm support portion 31.

  The diaphragm 30 is fixed by integrally connecting the peripheral edge portion to the diaphragm support portion 31 of the inner housing 22. In this way, the diaphragm 30 is formed integrally with the inner housing 22 and defines the inside and outside of the housing 20. The housings 21 and 22 and the diaphragm 30 are made of metal. Moreover, the film thickness of the diaphragm 30 is substantially uniform.

  The guide 35 is made of metal and is formed so as to extend from the diaphragm support portion 31 located at the peripheral edge of the diaphragm 30 to the outside (combustion chamber side) of the housing 20. FIG. 2 is a plan view of the pressure sensor 10. In FIG. 2, the housing 20 is omitted, and the broken line indicates the outline of the diaphragm 30. As shown in FIG. 2, the guide 35 is formed continuously over the entire circumference of the diaphragm 30. That is, the guide 35 is formed in a substantially cylindrical shape. As shown in FIG. 1, the guide 35 includes a base end portion 37 on the diaphragm 30 side and a tip end portion 38 on the side away from the diaphragm 30 with the central portion 36 as a boundary. The base end portion 37 has a substantially cylindrical shape and is welded to the surface of the diaphragm support portion 31. The tip portion 38 is formed in a substantially truncated cone shape, and protrudes toward the center side of the diaphragm 30 as it is separated from the diaphragm 30. As a result, the inner space surrounded by the guide 35 is smaller at the tip side than at the diaphragm 30 side.

  A space defined by the outer surface of the diaphragm 30 and the inner surface of the guide 35 is filled with a refractory heat insulating member 40 as shown in FIGS. The bottom surface of the heat insulating member 40 is in close contact with the surface of the diaphragm 30, and the side surface of the heat insulating member 40 is in close contact with the guide 35. The heat insulating member 40 is formed by foaming a material applied to the surface of the diaphragm 30. In addition, as a material of the heat insulation member 40, for example, Taikarit (registered trademark) manufactured by Nippon Paint Co., Ltd. can be used. Since the surface of the diaphragm 30 is covered with the heat insulating member 40, the diaphragm 30 can be prevented from being exposed to a flame. Moreover, since it can suppress that the high temperature heat of a combustion chamber is directly transmitted to the diaphragm 30, it can suppress that the diaphragm 30 is thermally deformed with the high temperature heat of a combustion chamber. As described above, the guide 35 is continuously formed over the entire circumference of the diaphragm 30, and the distal end portion 38 of the guide 35 protrudes toward the center side of the diaphragm 30. Therefore, it can suppress suitably that the heat insulation member 40 falls from the surface of the diaphragm 30. FIG.

  The heat insulating member 40 covers the entire surface of the diaphragm 30, and an opening such as a slit that exposes a part of the surface of the diaphragm 30 to the combustion chamber is not formed. Therefore, even if soot generated by the combustion of the internal combustion engine adheres to the heat insulating member 40, the diaphragm 30 is not fixed by the soot. Thereby, it can suppress that the detection accuracy of a pressure falls by the soot which generate | occur | produces in a combustion chamber. Further, the pressure sensor 10 is attached to the cylinder head by screwing a screw portion 25 formed on the outer peripheral portion of the housing 20 with a screw hole formed in the cylinder head. In the conventional pressure sensor, soot accumulates from the surface of the high thermal conductivity member to the wall of the combustion chamber, and the soot is clogged inside the opening of the high thermal conductivity member. There is a possibility of sticking to the head. Moreover, since the opening is formed in the high thermal conductivity member, the mechanical strength is lower than other components. Therefore, in the conventional pressure sensor, if the pressure sensor is rotated and removed, the high thermal conductivity member may be damaged. In such a case, it is difficult to re-mold the high thermal conductivity member in the pressure sensor, and thus it is difficult to reuse the pressure sensor. On the other hand, in the pressure sensor 10 of the present embodiment, since the heat insulating member 40 has a lower mechanical strength than other components, if soot accumulates around the heat insulating member 40, the pressure sensor 10 is removed. Although there is a possibility that the heat insulating member 40 may be damaged, other components are not damaged. Further, even if the heat insulating member 40 is damaged, the heat sensor 40 can be reshaped by foaming a fire-resistant material on the surface of the diaphragm 30, so that the pressure sensor 10 can be reused. .

The heat insulating member 40 has a heat insulating ability for suppressing high-temperature heat in the combustion chamber from being transmitted to the diaphragm 30, and even when the heat insulating member 40 is formed, the diaphragm 30 can be bent according to pressure. It is required to have rigidity. In addition, since the heat insulating member 40 is in close contact with the diaphragm 30, the diaphragm 30 and the heat insulating member 40 bend integrally according to pressure.
The heat insulating member 40 of the present embodiment has a heat insulating ability to reduce the amount of heat transferred to the diaphragm 30 due to combustion in the combustion chamber to ½ or less as compared with the case where the heat insulating member 40 is not provided. That is, if the heat quantity received by the diaphragm 30 from the high temperature gas in the combustion chamber when the heat insulation member 40 is not provided is Q, the heat quantity that the diaphragm 30 receives from the high temperature gas in the combustion chamber is 1 by providing the heat insulation member 40. / 2Q. Thus, since the heat transfer amount to the diaphragm is suppressed to ½ or less, the thermal deformation amount of the diaphragm 30 becomes ½ or less of the case without the heat insulating member 40, and the thermal deformation amount of the diaphragm 30 is significantly reduced. To do.

  Further, when the amount of deflection with respect to pressure is defined as rigidity, the rigidity of the heat insulating member 40 is equal to or less than the rigidity of the diaphragm 30. Here, when the pressure in the combustion chamber is the predetermined pressure P, the amount of deformation of the diaphragm when the heat insulating member is not formed is defined as an amount d. In this case, when the rigidity of the diaphragm 30 and the heat insulating member 40 is the same, in the diaphragm 30 in which the heat insulating member 40 is formed, the predetermined pressure P acts on the diaphragm 30 and the heat insulating member 40, respectively. Therefore, the amount of deflection of the diaphragm 30 with respect to the pressure is ½ that when there is no heat insulating member. In this embodiment, since the rigidity of the heat insulating member 40 is less than that of the diaphragm 30, the deformation amount according to the pressure of the diaphragm 30 is 1/2 or more of the deformation amount when the heat insulating member 40 is not formed. Can be secured. Therefore, the diaphragm 30 can be appropriately deformed according to the pressure in the combustion chamber. That is, the required detection sensitivity can be secured without impairing the flexibility required of the diaphragm 30 due to the presence of the heat insulating member 40.

The rigidity of the heat insulating member 40 is preferably less than or equal to ½ of the rigidity of the diaphragm 30. Thereby, the individual product difference of the deformation amount according to the pressure of the diaphragm 30 can be sufficiently suppressed.
That is, in the diaphragm in which the heat insulating member is not formed, when the square tolerance indicating the variation of the deformation amount according to the pressure of the diaphragm is “1”, when the rigidity of the diaphragm 30 and the heat insulating member 40 is the same, The square tolerance becomes approximately 1.4 of √ (1 ² +1 ² ), and the variation of the deformation amount according to the pressure of the diaphragm 30 increases by 40%. When the rigidity of the heat insulating member 40 is set to ½ or less of the rigidity of the diaphragm 30 as in the present embodiment, the square tolerance is √ (1 ² +0.5 ² ) or less, which is approximately 1.1 or less. . Therefore, although the variation in the deformation amount of the diaphragm 30 according to the pressure in the combustion chamber increases as compared with the case where the heat insulating member is not formed on the diaphragm, the increase amount of the variation can be suppressed to about 10%. In view of aging deterioration of the heat insulating member 40, the heat insulating member 40 preferably has a lower rigidity, and more preferably, the heat insulating member 40 has a rigidity set to 1/10 or less of the diaphragm rigidity.

  The sensor unit 50 is disposed inside the housing 20. The sensor unit 50 includes a force transmission rod 51, a stem 52, a sensor element 53, a terminal 60, a wire 63, and the like. The force transmission rod 51 has a substantially cylindrical shape, and the front end surface is attached to the rear end surface of the diaphragm 30. As shown in FIG. 3, when the diaphragm 30 and the heat insulating member 40 act on the pressure in the combustion chamber and the diaphragm 30 and the heat insulating member 40 are deformed, the force transmission rod 51 is displaced downward. Thereby, the force transmission rod 51 applies a force to the sensor element 53 shown in FIG. Further, the force transmission rod 51 is made of a heat insulating material.

  A metal stem 52 is fitted on the rear end side of the inner housing 22. The stem 52 is welded to the inner peripheral surface of the inner housing 22 on the rear end side of the inner housing 22 in a state where a preload forcing the front end surface of the force transmission rod 51 against the diaphragm 30 is applied. ing. The rear end surface of the sensor element 53 is bonded to the front end surface of the stem 52. Thereby, the sensor element 53 is positioned and fixed with respect to the stem 52. The front end of the sensor element 53 is in contact with the rear end surface of the force transmission rod 51.

  The sensor element 53 includes a force detection block 55 and force transmission blocks 56 and 58. The force detection block 55 has a substantially rectangular parallelepiped shape, and is mainly formed of a silicon substrate. A piezoresistive element is formed on the front end face of the force detection block 55 (not shown). When stress acts on the piezoresistive element, the electric resistance value changes due to the piezoresistive effect. The force detection block 55 is formed with a metal electrode group. The electrode group is connected to the piezoresistive element. Note that the sensor element 53 may be composed of a piezoelectric element or the like.

  The first force transmission block 58 has a rectangular parallelepiped shape and is made of glass. The rear end surface of the first force transmission block 58 is anodically bonded to the top surface of the protruding portion of the force detection block 55. The second force transmission block 56 is hemispherical and is made of a hard material such as a metal such as iron or a ceramic. The rear end surface of the second force transmission block 56 is bonded to the front end surface of the first force transmission block 58. Note that the second force transmission block 56 may also be formed of silicon, glass, or the like.

  A plurality of cylindrical through holes are formed in the stem 52 in the vertical direction of FIG. A metal elongated terminal 60 is fixed to the stem 52 via a sealing material 61 inserted into the through hole. Thereby, the internal space of the housing 20 is a sealed space. Thus, the stem 52, the terminal 60, and the sealing material 61 constitute a hermetic seal terminal. One end of the terminal 60 is connected to the electrode of the force detection block 55 of the sensor element 53 via a metal wire 63. The other end of the terminal 60 group is connected to a power source (current source or voltage source) and a measuring instrument (ammeter or voltmeter) through a circuit unit including an amplifier circuit and the like.

In the pressure sensor 10, when the pressure in the combustion chamber acts, the diaphragm 30 and the heat insulating member 40 bend and change from the state shown in FIG. 1 to the state shown in FIG. 3. As a result, when the force transmission rod 51 is displaced toward the sensor element 53 side, compressive stress acts on the piezoresistive element of the sensor element 53, so that the electric resistance value of the piezoresistive element changes. For example, when a constant current is passed from the current source to the piezoresistive element, an output voltage (output value) changed from the reference value appears between the electrodes in accordance with a change in the electrical resistance value of the piezoresistive element. By measuring this output voltage with a voltmeter, the amount of change in the electrical resistance value of the piezoresistive element, that is, the magnitude of the pressure applied to the diaphragm 24 can be detected.
In the present embodiment, the heat insulating member 40 is formed on the surface of the diaphragm 30, and the heat insulating member 40 has the above heat insulating ability and rigidity. Therefore, the thermal deformation of the diaphragm 30 can be appropriately suppressed, and the diaphragm 30 can be appropriately deformed according to the pressure of the combustion chamber without impairing the flexibility of the diaphragm 30. Therefore, the output voltage output by the sensor unit 53 appropriately reflects the pressure in the combustion chamber.

Next, the manufacturing method of the heat insulation member 40 is demonstrated with reference to FIG. As described above, the heat insulating member 40 is formed by foaming the material applied to the surface of the diaphragm 30.
First, as shown in FIG. 4A, in the state where the guide 35 is welded to the surface of the diaphragm support portion 31, the material of the heat insulating member 40 is applied to the entire outer surface of the diaphragm 30, and the thickness is 20 A coating film 41 of ˜100 μm is formed. As the material of the coating film 41, a material that foams and changes to a heat-resistant heat insulating member 40 when exposed to a flame is selected. Next, this coating film 41 is exposed to a flame. Thereby, as shown in FIG.4 (b), it foams until the coating film 41 becomes 10 to 100 times the thickness at the time of application | coating, and the fireproof heat insulation member 40 is completed. In the case of Taikalit (registered trademark) manufactured by Nippon Paint Co., Ltd., foaming starts when the surface reaches about 250 ° C. due to the flame. In the state shown in FIG. 4B, the central portion of the heat insulating member 40 swells due to the foaming and expansion of the coating film 41, and protrudes beyond the tip of the guide 35. At the position indicated by the broken line A in FIG. 4B, the heat insulating member 40 is cut and the thickness of the heat insulating member 40 is adjusted. In this embodiment, the tip of the heat insulating member 40 and the tip of the guide 35 are located on the same plane. The pressure sensor 10 is attached to the cylinder head with the heat insulating member 40 formed on the surface of the diaphragm 30.
(Modification of Example 1)

  In the first embodiment, the pressure sensor 10 is attached to the cylinder head while the heat insulating member 40 is formed on the surface of the diaphragm 30. However, as shown in FIG. 4A, the pressure sensor 10 may be attached to the cylinder head in a state where the coating film 41 is formed on the surface of the diaphragm 30. When the pressure sensor 10 is attached to the cylinder head in the state shown in FIG. 4A, the coating film 41 foams by being exposed to the flame generated by the combustion in the combustion chamber. As shown, the refractory heat insulating member 40 covering the entire outer surface of the diaphragm 30 is completed. In this case, as shown in FIG. 4B, the pressure sensor 10 is used in a state where the bulge of the surface of the heat insulating member 40 is not cut. Therefore, in this modification, the thickness of the heat insulating member 40 formed by the flame of the combustion chamber is adjusted by adjusting the thickness of the coating film 41 in advance.

In the case where the coating film 41 is exposed to a flame before the pressure sensor 10 is mounted as in the first embodiment, a countermeasure for suppressing the flame from reaching the housing 20 or the like and causing the sensor unit 53 to become a high temperature. It is necessary to apply. In this regard, in this modification, the coating film 41 is exposed to the flame in a state where the pressure sensor 10 is attached to the cylinder head, and the housing 20 is covered with the combustion chamber wall, so that it may be exposed to the flame. Absent. Therefore, it is not necessary to take measures to protect the housing 20 from the flame.
Other configurations and operational effects in the modification are the same as those in the first embodiment.

Next, a pressure sensor according to Example 2 will be described with reference to FIG.
As shown in FIG. 5, the pressure sensor 70 of the second embodiment is different from the pressure sensor 10 of the first embodiment in the structure of the guide 71. Other configurations are the same as those in the first embodiment.
In the pressure sensor 70 according to the second embodiment, the guide 71 extends from the entire surface of the diaphragm support portion 31 to the outside of the housing 20 and is continuously formed over the entire circumference of the diaphragm 30. The outer surface of the guide 71 extends vertically from the outer periphery of the diaphragm support portion 31. The inner surface of the guide 51 is inclined so as to protrude toward the center of the diaphragm 30 as the distance from the diaphragm 30 increases. Also in this embodiment, the heat insulating member 40 is filled in the space defined by the outer surface of the diaphragm 30 and the inner surface of the guide 71. The guide 71 having such a configuration can reliably prevent the heat insulating member 40 from falling off the surface of the diaphragm 30.
Also in the present embodiment, the thermal deformation of the diaphragm 30 can be suppressed by the heat insulating member 40. Moreover, it can suppress that the detection accuracy of the pressure by the pressure sensor 70 falls by the soot generated in a combustion chamber. Further, even if the heat insulating member 40 is damaged when the pressure sensor 70 is removed, the heat insulating member 40 can be remolded by foaming a refractory material on the surface of the diaphragm 30. Can be reused.

Next, a pressure sensor according to Example 3 will be described with reference to FIG.
As shown in FIG. 6, the pressure sensor 80 of the third embodiment is different from the pressure sensor 10 of the first and second embodiments in the structure of the guide 81. Other configurations are the same as those in the first embodiment.
In the pressure sensor 80 of the third embodiment, the guide 81 extends outward from the entire surface of the diaphragm support portion 31, and is formed continuously over the entire circumference of the diaphragm 30. The guide 81 includes a cylindrical portion 82 and a convex portion 83 that is formed on the distal end side of the cylindrical portion 82 and protrudes toward the inside of the cylindrical portion 82 (center side of the diaphragm 30). Also in this embodiment, the heat insulating member 40 is filled in the space defined by the outer surface of the diaphragm 30 and the inner surface of the guide 81. Such a guide 81 can reliably prevent the heat insulating member 40 from falling off the surface of the diaphragm 30.
Also in the present embodiment, the thermal deformation of the diaphragm 30 can be suppressed by the heat insulating member 40. Moreover, it can suppress that the detection accuracy of the pressure by the pressure sensor 80 falls by the soot generated in a combustion chamber. Further, even if the heat insulating member 40 is damaged when the pressure sensor 80 is removed, the heat insulating member 40 can be remolded by foaming a refractory material on the surface of the diaphragm 30. Can be reused.
(Other examples)

  In each of the above embodiments, the heat insulating member reduces the amount of heat transfer to the diaphragm to ½ or less, and has a rigidity equal to or less than the rigidity of the diaphragm. However, the heat insulating member does not have to satisfy these conditions. Even when these conditions are not satisfied, thermal deformation of the diaphragm can be suppressed by providing the heat insulating member on the surface of the diaphragm. Moreover, even if the rigidity of the heat insulating member is higher than the rigidity of the diaphragm, the diaphragm can be deformed according to the pressure as long as it has a certain degree of flexibility.

  In each of the above embodiments, the guide protrudes toward the center of the diaphragm when it is separated from the diaphragm. However, the guide need not have such a shape. Even in this case, since the heat insulating member can be supported by the guide from the periphery by forming the guide, it is possible to suppress the heat insulating member from dropping from the diaphragm. In each of the above embodiments, the guide is continuously formed over the entire circumference of the diaphragm. However, the guide may be formed on a part of the periphery of the diaphragm. In the case where a plurality of guides are provided on a part of the periphery of the diaphragm, the heat insulating member can be evenly supported from the periphery if the guides are provided at equal intervals on the periphery of the diaphragm. In each of the above embodiments, the height of the guide and the thickness of the heat insulating member are substantially the same. However, the height of the guide may be made lower than the thickness of the heat insulating member, and only the diaphragm side portion of the heat insulating member may be supported by the guide. Furthermore, the pressure sensor may be configured without a guide. Even in such a case, if the heat insulating member is in close contact with the diaphragm, the heat deformation of the diaphragm can be suppressed by the heat insulating member.

As mentioned above, although the specific example of the technique disclosed by this specification was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

10, 70, 80: Pressure sensor 20: Housing 21: Outer housing 22: Inner housing 24: Diaphragm 25: Screw part 30: Diaphragm 31: Diaphragm support parts 35, 71, 81: Guide 36: Central part 37: Base end part 38: tip 40: heat insulating member 41: coating film 50: sensor

Claims (6)

A pressure sensor disposed at a position facing a combustion chamber of an internal combustion engine,
A substantially cylindrical housing;
A diaphragm fixed to the housing and defining an inner side and an outer side of the housing;
A sensor unit that is disposed inside the housing and whose output value changes according to deformation of the diaphragm;
A pressure sensor comprising: a fire-resistant heat insulating member that foams on an outer surface of the diaphragm and covers the entire outer surface. A pressure sensor disposed at a position facing a combustion chamber of an internal combustion engine,
A substantially cylindrical housing;
A diaphragm fixed to the housing and defining an inner side and an outer side of the housing;
The sensor unit is disposed inside the housing and includes a sensor unit whose output value changes according to deformation of the diaphragm.
A pressure sensor, which is applied to the entire outer surface of the diaphragm, and is applied with a material that foams and changes into a refractory heat insulating member when exposed to a flame in a combustion chamber. A metal guide extending from the periphery of the diaphragm toward the outside of the diaphragm;
The pressure sensor according to claim 1 or 2, wherein the heat insulating member is filled in a space defined by an outer surface of the diaphragm and an inner surface of the guide.   The pressure sensor according to claim 3, wherein the guide includes a portion that protrudes toward a center side of the diaphragm when the guide is separated from the diaphragm.   The pressure sensor according to claim 3 or 4, wherein the guide is formed continuously over the entire circumference of the diaphragm.   The pressure sensor according to any one of claims 1 to 5, wherein the heat insulating member reduces a heat transfer amount to the diaphragm to ½ or less, and has a rigidity equal to or less than a rigidity of the diaphragm. .

Images