JP2005340069A - Spark plug with integrated sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug with an integrated sensor, of which, freedom of selecting a combustion state detection sensor is heightened, prevented from dielectric breakdown. <P>SOLUTION: The spark plug comprises a main metal fitting 12; an insulator 13 having an electrode insertion hole 13a penetrated from a top end face to a base end face and a sensor housing hole 13b housing a sensor 15, held by the main metal fitting 12; a central electrode 14 inserted into the electrode insertion hole 13a; a grounding electrode 20, of which, one end part is connected to the main metal fitting 12 and the other end part is facing the central electrode 14; and a sensor 15 inserted into the sensor housing hole 13b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sensor-integrated spark plug having a sensor for detecting a combustion state in a combustion chamber of an internal combustion engine in a spark plug of an internal combustion engine such as an automobile.

  In recent automobiles, the air-fuel ratio, ignition timing, and EGR (exhaust gas recirculation) amount of the internal combustion engine are measured by using a sensor (hereinafter referred to as “combustion state detection sensor”) that detects the combustion state in the combustion chamber of the internal combustion engine. Accordingly, attempts have been made to control the combustion of an internal combustion engine.

  An example of such a combustion state detection sensor is a pressure sensor that detects the pressure in the combustion chamber. And this pressure sensor is inserted in the sensor attachment hole formed in the cylinder head, and it installs so that the front-end | tip may be exposed to a combustion chamber. However, a lot of spark plugs and other structural parts of the internal combustion engine are arranged around the sensor mounting hole of the cylinder head, and the mounting space for the combustion state detection sensor is extremely limited.

Therefore, an integrated pressure sensor and spark plug has been proposed (for example, Patent Document 1 and Patent Document 2).
Japanese Utility Model Publication No. 62-126092 US Pat. No. 6,094,990

  The sensor-integrated spark plug described in Patent Document 1 described above is provided with a sensor mounting hole penetrating from the distal end side to the proximal end side of the metal shell, and the sensor is disposed in the through hole.

  However, in the structure described in Patent Document 1, since the metal shell is not sufficiently thick, only a sensor mounting hole having a very small diameter can be formed, and applicable combustion state detection sensors are limited.

  In the sensor-integrated spark plug described in Patent Document 2, a part of the insulator is provided with a through hole coaxially or parallel to the central axis, and the sensor is disposed in the through hole.

  However, in the structure described in Patent Document 2, a sufficient installation space for the center electrode cannot be secured, and the conductive wire of the center electrode is taken out from the side peripheral surface of the insulator, and the metal shell, the conductive wire, The distance is shortened. For this reason, insulation cannot be maintained when a high voltage is applied to the center electrode, and there is a possibility that dielectric breakdown may occur between the metal shell and the conductive wire.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a sensor-integrated spark plug that increases the degree of freedom in selecting a combustion state detection sensor and prevents dielectric breakdown.

  According to the first aspect of the present invention, an insulator having a metal shell, an electrode holding hole that is held by the metal shell and penetrates from the front end surface to the base end surface, and a sensor storage hole that stores the sensor, and the electrode holding hole are disposed. A sensor-integrated type comprising: a center electrode formed; a ground electrode having one end joined to the metal shell and the other end facing the center electrode; and a sensor disposed in the sensor housing hole. It is a spark plug.

  In this way, by disposing the center electrode in the electrode holding hole penetrating from the front end surface to the base end surface provided on the insulator, a sufficient insulation distance between the metal shell and the center electrode can be secured, thereby suppressing dielectric breakdown. it can. Further, by providing a sensor housing hole in the insulator and arranging the sensor, it is possible to form a sensor housing hole having a larger diameter compared to the configuration in which the sensor is arranged in the metal shell. Increased freedom of choice.

  The invention according to claim 2 is the sensor-integrated spark plug, wherein the sensor is a pressure sensor.

  Thus, by using the pressure sensor, the pressure in the combustion chamber of the internal combustion engine can be detected, and the combustion state can be confirmed.

  A third aspect of the present invention is the sensor-integrated spark plug, wherein the sensor is an optical pressure sensor.

  As described above, by using the optical pressure sensor, it is difficult to be affected by noise, and high-precision detection is possible.

  According to a fourth aspect of the present invention, there is provided the sensor-integrated spark plug, wherein the sensor housing hole is opened at a distal end surface of the insulator.

  Thus, since the sensor housing hole is configured to open to the tip surface of the insulator, the sensor can be disposed so as to be directly exposed to the combustion chamber, so that the combustion state in the combustion chamber can be detected more accurately. it can.

  A fifth aspect of the present invention is the sensor-integrated spark plug, wherein the sensor housing hole is a through-hole penetrating from the distal end surface to the proximal end surface of the insulator.

  Thus, by arranging the sensor in the through-hole penetrating from the distal end surface of the insulator to the proximal end surface, the signal cable extending from the sensor disposed on the distal end side of the insulator can be taken out from the proximal end side of the insulator. In addition, the structure of the sensor-integrated spark plug can be simplified.

  The invention according to claim 6 is the sensor-integrated spark plug, wherein the electrode holding hole and the sensor housing hole are arranged in parallel to each other.

  Thus, by arranging the electrode holding hole and the sensor housing hole in parallel with each other, the insulator can be easily formed.

  The invention of claim 7 is characterized in that it has a terminal electrically connected to the center electrode and a connector connected to the sensor, and includes a joint detachably disposed on the base end side of the insulator. This is a sensor integrated spark plug.

  As described above, the metal shell is attached to the internal combustion engine by including a joint electrically connected to the center electrode and a connector connected to the sensor and detachably disposed on the base end side of the insulator. After the attachment, the joint can be fitted and the sensor-integrated spark plug can be easily attached.

(First embodiment)
Hereinafter, the first embodiment shown in FIG. 1 will be described. FIG. 1 is a cross-sectional view showing the overall configuration of a sensor-integrated spark plug 1 according to a first embodiment of the present invention.

  The sensor-integrated spark plug is a spark plug in which a spark plug that performs spark discharge in a combustion chamber of an engine and a sensor attached to the spark plug are incorporated in the spark plug, and the structure will be described in detail below.

  In the present specification, the side where the ground electrode 20 is provided in the axial direction of the sensor-integrated spark plug 1 will be described as the “front end side” and the opposite side as the “base end side”.

  The sensor-integrated spark plug 1 includes a metal shell 12, an insulator 13 having a metal shell 12, an electrode holding hole 13 a that is held by the metal shell 12 and penetrates from the distal end surface to the base end surface, and a sensor housing hole 13 b that houses the sensor 15; Insulating the center electrode 14 disposed in the electrode holding hole 13a, the ground electrode 20 having one end joined to the metal shell 12 and the other end facing the center electrode 14, and the sensor 15 disposed in the sensor housing hole 13b. And a joint 16 that covers the base end of the insulator 13.

  The metal shell 12 has a cylindrical shape and includes an external thread 12b attached to the combustion chamber of the internal combustion engine on the outer diameter thereof.

An insulator 13 made of alumina ceramic (Al ₂ O ₃ ) or the like is held inside the metal shell 12. The insulator 13 is provided with an electrode holding hole 13a penetrating from the distal end surface to the proximal end surface at a position shifted from the center axis of the sensor-integrated spark plug 1. Further, a sensor accommodation hole 13b in which the sensor 15 is arranged is provided. The sensor housing hole 13b is cylindrical and penetrates from the distal end side 13c of the insulator 13 to the proximal end side 13d, and is provided at a position shifted from the center axis of the spark plug 1. The center electrode 14 is arranged in parallel with the electrode holding hole 13 a where one end is on the distal end surface 13 c of the insulator 13 and the other end is on the proximal end surface 13 d of the insulator 13. Further, the wall thickness is 1 mm or more between the electrode holding hole 13a and the sensor housing hole 13b. This is because when a sensor using a metal part is used for the sensor housing hole, if the thickness of the insulator cannot be secured, the insulator causes dielectric breakdown and a failure occurs in the plug function.

  Inside the electrode holding hole 13a, a center electrode 14 from the front end side, a resistor 42 formed by welding a resistive material having a conductive glass seal member 41 bonded to both ends, and a central shaft 43 are disposed. A proximal end portion of the middle shaft 43 is connected to the conductive wire 17 via a coil spring 44, and a voltage is supplied from the conductive wire 17 to the center electrode 14. The conductive wire 17 is covered with a high voltage cable 18 made of an insulating resin.

  The center electrode 14 is a cylindrical body whose inner material is made of copper and whose outer material is made of a Ni-based alloy. The center electrode 14 is provided so that its tip protrudes from the lower end of the insulator 3. A noble metal tip 14 b is provided on the flat surface 14 a at the tip of the center electrode 14.

  The middle shaft 43 and the center electrode 14 are heated and welded by the resistor 42 and the glass seal member 41 so as to be electrically connected.

  As shown in FIG. 2, the sensor 15 is an optical pressure sensor that measures pressure based on the intensity of light, and includes an optical fiber 51 that is an optical fiber part, a reflection filter 52 that is a sensor part, and a selective transmission filter 53. It comprises a diaphragm 54, a light emitter that emits light of three different wavelengths (not shown), and a photodetector. The optical fiber 51 is inserted through the inside of the sensor housing hole 13b from the base end side to the tip end side, and is joined to the insulator 13 via the optical fiber fixing member 56. The selective permeation filter 53 and the reflection filter 52 are joined to the opening on the distal end side of the optical fiber 51 in this order from the distal end side. There is a gap between the distal end surface of the sensor housing hole 13b of the insulator 13 and the distal end surface of the optical fiber 51 where the reflection filter is joined all around, and the distal end surface of the sensor housing hole 13b of the insulator 13 is The diaphragm 54 is joined all around the end face. By this diaphragm 54, airtightness between the combustion chamber and the second hole 13b is maintained. The proximal end portion of the optical fiber 51 is inserted through the joint 16 and is connected to a light emitter and a photodetector (not shown).

  In the optical fiber 51, the optical fiber bundle is insulated and held by a heat-resistant filler. This filler has heat resistance such as silicon-based or metal powder-containing ceramic.

  The reflective filter 52 and the selective transmission filter 53 have multiple layers of dielectric materials, such as titanium dioxide and silicon dioxide.

  The diaphragm 54 is a thin metal plate that is manufactured with high-precision wall thickness and flatness.

  The light emitter is a laser, preferably an LED.

  The joint 16 is made of resin or the like, is cylindrical, has a large diameter portion and a small diameter portion from the front end side, a through hole 16a through which a high voltage cable 18 for supplying power is inserted, and a signal cable 19 that transmits a sensor signal. Through hole 16b and a cylindrical hole 16c into which the base end of the insulator 13 is inserted. The through hole 16 a and the through hole 16 b are parallel to each other and are offset from the central axis of the joint 16.

  Next, the operation of the sensor-integrated spark plug 1 of the present invention will be described below. The sensor-integrated spark plug 1 is attached to a cylinder head of a well-known combustion engine. When a high voltage is applied to the center electrode, a spark discharge is generated between the center electrode and the ground electrode, thereby compressing the air-fuel mixture. Ignite and burn. Due to the pressure change in the combustion chamber due to this combustion, the diaphragm 54 is bent. Further, in order to measure this pressure change, the curved diaphragm 54 is irradiated with light having a wavelength λ 1 that is irradiated from the light emitter, passes through the optical fiber, and passes through the reflection filter 52 and the transmission filter 53. In addition, the light of wavelength λ1 is a wavelength region that transmits through the reflection filter 52 and the transmission filter 53. As shown in FIG. 3, the irradiated light is divided into light A that is reflected back into the optical fiber 51 or light B that is reflected outside the optical fiber 51 depending on the incident angle. The intensity of the light that returns after being reflected differs from the irradiated light. In addition, since the degree of curvature of the diaphragm 54 varies depending on the pressure change, the incident angle to the diaphragm 54 changes, and the intensity of the optical signal reflected back from the optical fiber 51 changes. The pressure value is measured by the amount of change in intensity.

  In addition, the light of wavelength λ1 is a wavelength region that transmits through the reflection filter 52 and the transmission filter 53.

  In addition, in order to correct the decrease in light intensity when passing through the optical fiber due to the output difference of the light source, fluctuation between optical fibers, bending, etc., the light of the wavelength λ2 for correction is irradiated. . The intensity of the light that is reflected and returned by the reflection filter 52 that is reflective to the light of wavelength λ2 is measured, and the amount of change from the intensity of the irradiated light is the light intensity when transmitted through the optical fiber. Decrease. This decrease is added to the light of wavelength λ1 for pressure measurement, and the pressure is calculated.

  Furthermore, temperature correction is performed in order to prevent deterioration in sensor accuracy due to temperature fluctuations. This is because the diaphragm 54 in contact with the combustion chamber is exposed to an extremely high temperature, so that the mechanical properties, mainly the Young's modulus, change, and as a result, deflection occurs due to the temperature. This deflection changes the intensity of the reflected light, reducing the accuracy of the resulting sensor. Therefore, in order to correct the influence of temperature, the light of wavelength λ3 is irradiated. This light is partially blocked by the selective transmission filter 53 and the other is transmitted. As the selective transmission filter 53, a filter having a different wavelength range depending on the temperature is used. Therefore, the temperature is detected by measuring the intensity of the light reflected and returned. The pressure output can be temperature compensated using a calculation algorithm derived from the basic relationship between diaphragm deflection, pressure, and temperature.

  With these corrections, the pressure value in the fuel chamber is detected and transmitted to feedback control.

  From the above, when an optical pressure sensor is used, it is less affected by noise, etc. compared to other sensors, and performs excellent control to accurately detect the pressure value in the combustion chamber. Can do. In addition, a sensor-integrated spark plug having excellent durability can be obtained by using a highly durable member as an optical fiber.

(Second Embodiment)
In the present embodiment, as shown in FIG. 4, the sensor joint 16 and the insulator 13, the coil spring 44 and the central shaft 43, and the optical fiber 51 and the joint 16 in the first embodiment are separated. Thereby, the joint 16 part is a detachable structure.

  Other structures are the same as those of the first embodiment.

  By making the joint 16 detachable, both the high-voltage cable 18 and the signal cable 19 are connected when the sensor-integrated spark plug 1 is attached to the cylinder head attachment hole of the combustion chamber by screw connection. Because it is very difficult. Therefore, after the joint 16 is removed and the sensor-integrated spark plug 1 that is not connected to the high voltage cable 18 is attached to the combustion chamber, the joint 16 that is connected to the high voltage cable 18 is attached. .

  Further, when the joint 16 can be attached and detached, as shown in FIG. 5 when the insulator 13 is viewed from the base end side, by providing the slit 21 on the base end side of the insulator 13, the mountability is higher. Become. This is because the insulator 13 has the first through hole and the second hole, so that the mounting position of the joint 16 is difficult to understand. Therefore, by providing the slit 21, the position where the joint 16 is mounted can be confirmed.

(Third embodiment)
In this embodiment, as shown in FIG. 6, instead of the sensor in the first embodiment, the piezoelectric sensor 120 is inserted into the sensor storage hole 13 b provided in the insulator 13, and the outer periphery of the insulator 13 is inserted. A ring-shaped ring terminal 114 is provided, and the ring terminal 114 and the cable 113 joined to the piezoelectric sensor 120 are joined via connectors 111 and 112. A ring-shaped ring terminal 115 is also provided on the inner diameter side of the joint 16, and the ring terminal 115 and the sensor signal lead wire 116 built in the joint 16 are joined.

  The piezoelectric sensor 120 includes two parts: a diaphragm 121 that receives and transmits combustion pressure, a rod 122, a hemispherical part 123, and a piezoelectric element 124 that converts pressure into voltage.

  Other structures are the same as those of the first embodiment.

  Due to the pressure fluctuation in the combustion chamber, the diaphragm 121 is curved as in the first embodiment. Due to this bending, force is applied to the rod 122 and the hemispherical portion 123. This force is transmitted to the piezoelectric element 124 to generate a voltage. This voltage is transmitted through the electric wire 125 joined to the piezoelectric element 124, and is transmitted to the ring terminal 114 via the connectors 111 and 112. The ring terminal 114 on the outer periphery of the insulator 13 and the ring terminal 115 on the inner diameter side of the joint 16 are brought into contact with each other, and a voltage is transmitted to a control device (not shown) from the sensor signal lead wire 116 joined to the ring terminal 115. . The pressure in the combustion chamber is detected by this voltage.

  In the present embodiment, only the center electrode may be connected to the joint 16 on the base end side of the insulator 13. As shown in FIG. 7, the base end side 43 a of the middle shaft 43 has a disk shape, has the same central axis as the base end surface of the insulator 13, and is joined to the base end surface of the insulator 13. Accordingly, when the joint 16 is mounted, the coil spring 44 and the central shaft 43a are in contact with each other without determining the mounting position in the circumferential direction, so that voltage can be supplied. Therefore, it is not necessary to determine the mounting position of the joint 16 in the circumferential direction, and the mountability is improved.

(Fourth embodiment)
In the present embodiment, as shown in FIG. 8, in the sensor-integrated spark plug 1 according to the first embodiment, the optical fiber 51 is inserted into the joint 16 through the optical fiber connector 131 at the base end portion of the insulator 13. The signal cable is connected to the light emitter and the photodetector.

  The optical fiber connector 131 is a component that detachably connects the optical fiber and the optical fiber connector 131. A plug containing a cylindrical zirconia ceramic called a ferrule into which the optical fiber is inserted, and the ferrule are aligned and do not bend. In order to connect them, it is composed of an adapter with a built-in component called a sleep with a position adjustment slit. By inserting the plug from both sides into the adapter, the ferrules built in the plug are positioned by the sleep, and the ferrules are connected to connect the optical fibers.

  Other structures are the same as those of the first embodiment.

  Since the optical fiber 51 can be separated at the base end portion of the insulator 13 by the optical fiber connector 131, the joint 16 and the insulator 13 can be further easily separated. In addition, when mounting in the combustion chamber, the trouble of inserting the optical fiber 51 into the joint 16 can be saved, and the mountability is improved.

(Fifth embodiment)
In this embodiment, as shown in FIG. 9, the joint 16 and the insulator 13 are integrated, and as shown in FIG. 10, the outer diameter of the joint 16 is larger than the diameter of the inscribed circle of the engaging portion 12 a of the metal shell 12. small.

  Other structures are the same as those of the first embodiment.

  When the spark plug is mounted on a vehicle, the spark plug is attached to the spark plug mounting position of the combustion chamber by screwing. At this time, the spark plug is inserted into the tool for attachment. If the outer diameter of the joint 16 is larger than the diameter of the inscribed circle of the engaging portion 12a of the metal shell 12, the sensor-integrated spark plug is inserted into the tool. 1 will not enter, making installation difficult. Therefore, the outer diameter of the joint 16 is made smaller than the diameter of the inscribed circle of the engaging portion 12a of the metal shell 12, so that it can be inserted into the tool.

(Other embodiments)
In addition to the optical fiber sensor, a combustion light sensor, a piezoelectric sensor, or a semiconductor sensor can be used as the sensor.

  The combustion light sensor uses a method of capturing the brightness and darkness of the combustion light in the combustion chamber and converting it into an electrical signal. This combustion light sensor is excellent in measurement accuracy and durability like the optical fiber sensor.

  The piezoelectric sensor uses a piezoelectric element, and can detect a pressure change in the combustion chamber by measuring a voltage generated by pressure applied to the piezoelectric element.

  A semiconductor sensor uses the piezoresistance effect of a semiconductor whose electrical conductivity changes due to stress as a detection principle, detects an output as a change in electrical resistance, and obtains a pressure change.

Sectional drawing of the sensor integrated spark plug in 1st Embodiment. Sectional drawing of the optical fiber sensor in 1st Embodiment. Operation | movement explanatory drawing of the optical fiber sensor in 1st Embodiment. Sectional drawing of the sensor integrated spark plug in 2nd Embodiment. Sectional drawing of the radial direction of a joint in 2nd Embodiment. Sectional drawing of the sensor integrated spark plug in 2nd Embodiment. The figure seen from the insulator base end side in 2nd Embodiment. Sectional drawing of the sensor integrated spark plug in 3rd Embodiment. Sectional drawing of the sensor integrated spark plug in 4th Embodiment. The figure seen from the base end side of the sensor integrated spark plug in 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sensor-integrated spark plug 12 ... Main metal fitting 13 ... Insulator 13a ... Electrode holding hole 13b ... Sensor accommodation hole 14 ... Center electrode 15 ... Sensor 16 ... Joint 51 ... Optical fiber 52 ... Reflection filter 53 ... Selective transmission filter 54 ... Diaphragm

Claims (7)

An insulator having a metal shell, an electrode holding hole that is held by the metal shell and penetrates from the front end surface to the base end surface, and a sensor housing hole that houses the sensor; a center electrode disposed in the electrode holding hole; and one end A sensor-integrated spark plug, comprising: a ground electrode having a portion joined to the metal shell and the other end facing the center electrode; and a sensor disposed in the sensor housing hole. The sensor-integrated spark plug according to claim 1, wherein the sensor is a pressure sensor. 3. The sensor-integrated spark plug according to claim 2, wherein the sensor is an optical pressure sensor. The sensor-integrated spark plug according to any one of claims 1 to 3, wherein the sensor housing hole is opened at a distal end surface of the insulator. 5. The sensor-integrated spark plug according to claim 1, wherein the sensor housing hole is a through-hole penetrating from a distal end surface of the insulator to a proximal end surface. 6. The sensor-integrated spark plug according to claim 1, wherein the electrode holding hole and the sensor housing hole are arranged in parallel to each other. In Claims 1-6, it has a terminal connected with the central electrode, and a connector connected to the sensor, and provided with a joint detachably arranged on the base end side of the insulator. Sensor integrated spark plug.