JP2009186209A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce deformation of a diaphragm due to reception of heat. <P>SOLUTION: An in-cylinder pressure sensor includes a housing, a metal stem 13 and a diaphragm 14. The housing, metal stem and diaphragm are integrated through welding. The diaphragm 14 includes an inner layer 14i and an outer layer 14o. The inner layer 14i and the outer layer 14o are formed from precipitation-hardened stainless steel. The linear expansion coefficient of the inner layer 14i is made larger than the linear expansion coefficient of the outer layer 14o by applying different precipitation hardening heat treatments. The inner layer 14i and the outer layer 14o are jointed by cold rolling welding method or by electron beam welding method. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pressure sensor that detects pressure in a situation where a large temperature difference occurs between the inside and outside of the sensor.

  In order to monitor the combustion state in the combustion chamber of an engine, it is known to detect the pressure in the combustion chamber. In order to detect the pressure in the combustion chamber, an in-cylinder pressure sensor is attached to the engine body.

  A diaphragm that deforms according to the pressure in the combustion chamber is provided at the tip of the in-cylinder pressure sensor on the combustion chamber side. Along with the deformation of the diaphragm, the pressure in the combustion chamber is transmitted to a pressure detection unit such as a piezoelectric element. The pressure transmitted by the pressure detector is detected. Therefore, when the diaphragm is deformed due to a factor other than the pressure in the combustion chamber, the pressure detection accuracy decreases.

  For example, when the cylinder pressure sensor is attached to the engine body, the diaphragm may be damaged. For such a problem, it has been proposed to cover the diaphragm with a combustible buffer member (see Patent Document 1). The buffer member prevents the diaphragm from being deformed. Further, since the buffer member is burned out by combustion of the engine, the buffer member does not affect the detection of pressure.

In addition, the diaphragm may be deformed by heat. Since the diaphragm receives a large pressure, the diaphragm needs to be formed to have a thickness having durability against the pressure. Such a thickness may cause a large temperature difference between the outside and the inside of the diaphragm, and the diaphragm may be deformed.
JP-A-5-180060

  Therefore, an object of the present invention is to provide a pressure sensor that can accurately detect pressure under a situation where a large temperature difference occurs between the inside and the outside of the sensor.

  The pressure sensor according to the first invention includes a diaphragm and a pressure detector. The diaphragm has a different coefficient of thermal expansion between the outer surface side in contact with the detection target and the inner surface side opposite to the outer surface. The diaphragm deforms according to the pressure applied to the outer surface side. The pressure detector generates an electrical signal corresponding to the deformation of the diaphragm.

  According to the first invention, since the thermal expansion coefficient of the diaphragm is different between the outer surface side and the inner surface side, even if a temperature difference occurs between the outer surface side and the inner surface side of the diaphragm, deformation due to heat reception of the diaphragm is prevented. . Therefore, the detection accuracy of the pressure detected by the pressure detection unit is improved.

  In the pressure sensor according to the second invention, in addition to the configuration of the first invention, the thermal expansion coefficient on the inner surface side is larger than the thermal expansion coefficient on the outer surface side in the diaphragm.

  According to the second invention, when the pressure sensor is used in a high temperature atmosphere, the difference between the expansion amount on the outer surface side of the diaphragm that becomes high temperature and the expansion amount on the inner surface side that becomes lower than the outer surface side is small, and the diaphragm due to heat reception This makes it possible to reduce the deformation.

  In the pressure sensor according to the third aspect of the invention, in addition to the configuration of the second aspect of the invention, the outer surface side is disposed so as to face the combustion chamber of the internal combustion engine. The pressure sensor is a combustion pressure sensor for detecting the pressure in the combustion chamber.

  According to the third invention, when the combustion pressure is detected in the combustion chamber of the internal combustion engine as a use condition under a high temperature atmosphere, the pressure can be accurately detected by exposing the outer surface to the combustion chamber. is there.

  In the pressure sensor according to the fourth invention, in addition to the configuration of the first invention, the diaphragm has a multilayer structure in which the first and second layers having different thermal expansion coefficients are arranged on the outer surface side and the inner surface side, respectively. Have.

  According to the fourth invention, by laminating layers having different thermal expansion coefficients, it is possible to change the thermal expansion coefficient between the outer surface side and the inner surface side of the diaphragm.

  In the pressure sensor according to the fifth invention, in addition to the configuration of the third invention, a multilayer structure is formed by welding metals having different coefficients of thermal expansion.

  According to 5th invention, it becomes possible to make a diaphragm have high durability by forming a diaphragm by metal welding.

  In the pressure sensor according to the sixth aspect of the invention, in addition to the configuration of the fourth aspect of the invention, the metal welding is cold rolling pressure welding or electron beam welding.

  According to the sixth aspect of the invention, the metal is integrated extremely firmly by cold rolling pressure welding or electron beam welding, so that it is possible to make the diaphragm more durable.

  In the pressure sensor according to the seventh invention, in addition to the configuration of the third invention, a multilayer structure is formed by coating the metal member with a ceramic member having a coefficient of thermal expansion different from that of the metal member.

  According to the seventh invention, the ceramic coating makes it possible to make the diaphragm highly durable.

  According to the present invention, it is possible to prevent deformation of the diaphragm due to heat reception. Therefore, it is possible to improve the detection accuracy of the detected pressure.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing an in-cylinder pressure sensor (pressure sensor) to which an embodiment of the present invention is applied attached to an engine head of an engine body.

  The engine head 1 is formed with a mounting hole 2 penetrating from the outer surface to the combustion chamber. The in-cylinder pressure sensor 10 is formed in a rod shape. The in-cylinder pressure sensor 10 is inserted into the mounting hole 2 along the longitudinal direction.

  The in-cylinder pressure sensor 10 includes a connector portion 11, a housing 12, a metal stem 13, and a diaphragm 14. The housing 12 and the metal stem 13 are integrated by welding the metal stem 13 and the diaphragm 14. The connector part 11 is attached to the housing 12.

  The housing 12 is formed of a metal such as stainless steel and has a main body portion 12b and a storage portion 12s. The main body 12b has a two-stage hollow cylindrical shape with both ends open. The storage portion 12s has a stepped hole portion 12h formed therein, and the stepped hole portion 12h is connected to the hollow inside of the main body portion 12b on the large diameter cylinder side.

  A male screw portion 12sc is formed on the outer peripheral surface of the main body portion 12b. A female screw portion 2 s is formed on a part of the mounting hole 2 on the outer surface side. The in-cylinder pressure sensor 10 is attached to the engine head 1 by screwing the male screw portion 12sc of the main body portion 12b with the female screw portion 2s of the attachment hole 2.

  The step between the large diameter cylinder and the small diameter cylinder of the main body 12b is formed in a taper shape. The mounting hole 2 is formed in a stepped shape having a large diameter on the outer surface side and a small diameter on the combustion chamber side. When the male screw portion 12sc is screwed into the female screw portion 2s, the step of the mounting hole 2 and the tapered surface of the main body portion 12b are brought into close contact with each other, and the combustion chamber is sealed.

  The metal stem 13 is formed in a cylindrical shape with both ends open by a metal such as stainless steel. The housing 12 and the metal stem 13 are welded in a state where the metal stem 13 is inserted into the end of the main body 12b on the small diameter cylinder side.

  A diaphragm 14 is welded to the end of the metal stem 13 on the combustion chamber side. The diaphragm 14 is formed in a shape having a bottom portion of a thin circular plate and a cylindrical side portion. The side has the same outer diameter as the metal stem 13 and the bottom is perpendicular to the axis of the metal stem 13. The outer periphery of the tip end of the metal stem 13 has a reduced diameter, and is welded while being inserted inside the side portion of the diaphragm 14.

  The diaphragm 14 is a bimetallic diaphragm, and includes an inner layer 14i and an outer layer 14o as shown in FIG. The inner layer 14i and the outer layer 14o are formed of members having a lower linear expansion coefficient of the outer layer 14o than the inner layer 14i. Further, since the inner layer 14i and the outer layer 14o are required to be durable against deformation, they are preferably formed integrally, and further, durability against high pressure is also required.

  As a member that satisfies such conditions, for example, it is conceivable to use precipitation hardening stainless steel. Precipitation hardening type stainless steel can change a linear expansion coefficient by the precipitation hardening heat processing to perform. Stainless steel SUS630 subjected to heat treatment defined by JIS H900 and H1150 is used for the outer layer 14o and the inner layer 14i, respectively.

  The inner layer 14i and the outer layer 14o are joined and integrated by welding. As described above, since the inner layer 14i and the outer layer 14o need to be firmly integrated, an electron beam is used for bonding by a cold rolling pressure welding method in order to bring them into close contact at the atomic level, or for deep penetration. It is conceivable to join them by welding.

  A strain plate 15 is welded to the end of the metal stem 13 on the housing 12 side (see FIG. 1). The strain plate 15 is formed of a metal such as stainless steel into a shape having a bottom portion of a thin circular plate and a cylindrical side portion. The side has the same outer diameter as the metal stem 13 and the bottom is parallel to the bottom of the diaphragm 14. The outer periphery of the tip end of the metal stem 13 is reduced in diameter, and is inserted into the strain plate 15 and welded.

  A pressure transmission rod 16 is disposed inside the metal stem 13. The pressure transmission rod 16 is formed in a rod shape from a metal such as stainless steel or ceramic. The pressure transmission rod 16 is sandwiched between the diaphragm 14 and the strain plate 15, whereby a preload is applied to the diaphragm 14 and the strain plate 15 in the axial direction.

  As described above, the bottom of the diaphragm 14 has a thin wall shape, and is deformed in a direction perpendicular to the bottom (see P in FIG. 3) due to the pressure in the combustion chamber. The pressure transmission rod 16 is displaced toward the strain plate 15 while the bottom of the diaphragm 14 is deformed.

  The force acting on the bottom due to the displacement of the pressure transmission rod 16 is transmitted to the strain plate 15 side via the pressure transmission rod 16. The strain plate 15 is pressed by the transmitted force, and is deformed in a direction perpendicular to the plate surface in the same manner as the diaphragm 14. A detection element 17 is provided on the strain plate 15. The detection element 17 outputs an electrical signal corresponding to the deformation of the strain plate 15 as a distortion signal (first signal).

  The detection element 17 is connected to the IC chip 19 via the signal line 18, and the distortion signal is transmitted to the IC chip 19. The IC chip 19 performs signal processing such as gain control on the distortion signal.

  The IC chip 19 is mounted on the printed board 20. The printed circuit board 20 is disposed in the stepped hole portion 12h in the storage portion 12s. Further, the connector portion 11 is inserted into the stepped hole portion 12h of the storage portion 12s, and the printed circuit board 20 is sandwiched between the stepped hole portion 12h and the connector portion 11.

  The connector portion 11 is made of a resin such as PPS (polyphenylene sulfide). On the side surface of the connector portion 11, a flange portion 11b having an outer diameter substantially equal to the inner diameter of the stepped hole portion 12h is formed. By inserting the connector portion 11 into the stepped hole portion 12h with the O-ring 21 fitted between the flange portion 11b and the flange portion 11b, the hollow in the main body portion 12b is sealed. The edge of the opening of the storage part 12s is caulked to the connector part 11, whereby the connector part 11 is fixed to the storage part 12s.

  A metal terminal 22 is formed on the connector portion 11 by a molding method such as insert molding. The terminal 22 is connected to the printed circuit board 20 in the connector portion 11. By connecting the connector portion 11 to an ECU (not shown) via a connection cable (not shown), a pressure signal subjected to signal processing can be transmitted to the ECU.

  According to the in-cylinder pressure sensor of the present embodiment configured as described above, it is possible to suppress deformation due to heat reception of the diaphragm exposed to the combustion chamber, as will be described below.

  In a conventional in-cylinder pressure sensor, a diaphragm formed of a single member having a uniform thermal expansion coefficient has been used. As described above, there is a large temperature difference between the outside and the inside of the diaphragm that receives heat during combustion of the engine. As shown in FIG. 4, when a temperature difference occurs, the expansion amount on the outer side becomes larger than the expansion amount on the inner side of the diaphragm 140, so that the diaphragm 140 is deformed so as to expand outward. Since the pressure transmission rod 16 is displaced downward due to the deformation of the diaphragm 140, an output error corresponding to the displacement is generated.

  On the other hand, in the in-cylinder pressure sensor according to this embodiment, the linear expansion coefficient of the inner layer 14i is larger than the linear expansion coefficient of the outer layer 14o. It is possible to reduce more than this diaphragm. Therefore, since the amount of deformation due to heat is reduced, the output error is reduced and the pressure detection accuracy is improved.

  In the present embodiment, the inner layer 14i is formed using a member having a linear expansion coefficient larger than that of the member forming the outer layer 14o. However, depending on the environment to which the in-cylinder pressure sensor is exposed, the wire of any layer is used. What is necessary is just to enlarge an expansion coefficient. For example, when the in-cylinder pressure sensor is used in a low temperature atmosphere, if the inner layer 14i is formed using a member having a smaller linear expansion coefficient than the member forming the outer layer 14o, the diaphragm is prevented from being deformed inward due to low temperature. It is possible.

  In this way, in a situation where a large temperature difference occurs between the outside and the inside, it is possible to improve the pressure detection accuracy by the pressure sensor by changing the linear expansion coefficient between the outer surface side and the inner surface side of the diaphragm. is there.

  In the present embodiment, the diaphragm 14 has a two-layer structure formed by the inner layer 14i and the outer layer 14o, but may have a multilayer structure in which another layer such as an adhesive layer is interposed. Alternatively, if the inner and outer linear expansion coefficients can be changed, the diaphragm may be formed by a single member without forming a multilayer structure.

  In the present embodiment, the diaphragm 14 is formed by precipitation hardening stainless steel, but may be formed by other metals. Alternatively, other members may be used as long as they can be deformed according to pressure. For example, the outer layer 14o may be formed by coating the inner layer 14i formed of precipitation hardening stainless steel with a ceramic such as silicon nitride or silicon carbide.

  In addition, when forming the diaphragm 14 by another member, it is preferable that it is a member provided with durability with respect to the use environment to which a diaphragm is exposed. For example, when detecting the pressure in the combustion chamber as in this embodiment, it is preferable to have heat resistance against the combustion temperature. Further, when the pressure sensor is used in a low temperature atmosphere, it is preferable to have cold resistance.

  In the present embodiment, the inner layer 14i and the outer layer 14o are joined by cold rolling pressure welding or electron beam welding, but may be joined by any other method. However, as described above, since the diaphragm is required to have durability against deformation, it is preferable to apply a bonding method in which the inner layer and the outer layer are firmly bonded.

It is a longitudinal cross-sectional view shown in the state which attached the in-cylinder pressure sensor to which one Embodiment of this invention was applied to the engine head of the engine main body. It is an enlarged view of a diaphragm. It is an enlarged view of the diaphragm side front end for demonstrating the mechanism which detects a pressure. It is an enlarged view of the conventional diaphragm for showing the deformation | transformation state by heat receiving.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine head 10 In-cylinder pressure sensor 14, 140 Diaphragm 14i, 14o Inner layer, outer layer 16 Pressure transmission rod 17 Detection element

Claims (7)

A diaphragm that deforms in accordance with a pressure applied from the detection target to the outer surface side, and having a different coefficient of thermal expansion on the outer surface side that is in contact with the detection target and the inner surface side that is opposite to the outer surface side;
A pressure sensor comprising: a pressure detection unit that generates an electrical signal corresponding to the deformation of the diaphragm.   2. The pressure sensor according to claim 1, wherein the diaphragm has a larger coefficient of thermal expansion on the inner surface side than a coefficient of thermal expansion on the outer surface side.   The pressure sensor according to claim 2, wherein the pressure sensor is a combustion pressure sensor that is arranged so that the outer surface side faces a combustion chamber of an internal combustion engine, and detects a pressure in the combustion chamber.   4. The diaphragm according to claim 1, wherein the diaphragm has a multilayer structure in which first and second layers having different coefficients of thermal expansion are arranged on the outer surface side and the inner surface side, respectively. The pressure sensor according to claim 1.   The pressure sensor according to claim 4, wherein the multilayer structure is formed by welding metals having different coefficients of thermal expansion.   The pressure sensor according to claim 5, wherein the metal welding is cold rolling pressure welding or electron beam welding.   The pressure sensor according to claim 4, wherein the multilayer structure is formed by coating a metal member with a ceramic member having a coefficient of thermal expansion different from that of the metal member.

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