JP4530418B2 - Spark plug with combustion pressure detection function - Google Patents

Description

  The present invention relates to a spark plug with a combustion pressure detecting function in which an annular pressure sensor for measuring a combustion pressure of an internal combustion engine is fastened together with a gasket by a spark plug.

A spark plug with a combustion pressure detecting function in which a spark pressure detecting function is added to a spark plug as an ignition device for an internal combustion engine such as an engine includes a pressure detecting device (pressure sensor) including a piezoelectric element described in Patent Document 1, for example. Spark plugs have been proposed.
This pressure detection device is inserted so as to come into contact with the seat surface of the flange formed on the rear end side of the male thread of the metal shell of the spark plug, and is attached to the internal combustion engine (cylinder head) together with the spark plug. In order to prevent gas leakage during the operation of the internal combustion engine, an annular flat gasket made of copper or an alloy mainly composed of these is disposed between the seat surface of the metal shell and the pressure detection device. A preload is applied to the piezoelectric element in the pressure detection device by a tightening torque for attaching the spark plug (see Patent Document 2).

This pressure detection device operates as follows. When the mixed gas of fuel and air explodes in the combustion chamber of the internal combustion engine, the internal pressure in the combustion chamber increases. Then, the spark plug attached to the cylinder head is slightly displaced in the axial direction. The preload applied to the piezoelectric element is changed by the displacement, and the electric charge generated with the change in the load is taken out as a sensor output.
Japanese Utility Model Publication No. 61-57830 Japanese Patent Laid-Open No. 2002-24369

  In the above-mentioned Patent Document 1, in order to solve the problem that a predetermined output cannot be obtained with the conventional iron S-shaped and U-shaped gaskets, and that the output greatly fluctuates with respect to the tightening torque. The use of an annular flat gasket made of material is disclosed. Further, although Patent Document 2 suggests using a copper alloy gasket, it does not mention characteristics required for the gasket and means for satisfying the characteristics.

  By the way, in recent years, there is a tendency that the combustion pressure increases with the realization of high output of the engine, and there is a background that highly accurate sensor output is required for engine control by the combustion pressure. There is a possibility that the sealing performance, the loosening resistance performance, and the like as expected with a gasket made of the above-described conventional material for such an engine may not be obtained. If the gasket is loosened or an airtight leak occurs, the displacement of the spark plug caused by the combustion pressure becomes small. Therefore, the sensor output becomes small, and the accurate combustion pressure and combustion state cannot be detected. Not only that, but an airtight leak for the engine also leads to deterioration in output and fuel consumption.

  Therefore, when the present inventors conducted extensive research, the characteristics required of the gasket in order to obtain the above performance are that the spring constant is large, the true contact area is large, the gasket displacement is small, and the stress relaxation characteristics. It was found that it is important to have excellent resistance (small stress relaxation rate).

  The present invention has been made in view of the above, and provides a spark plug with a combustion pressure detection function including a gasket that has a small loss of sensor output, good airtightness, and can suppress loosening. Objective.

The solution is
A spark plug having a metal shell provided with a flange portion projecting in a direction perpendicular to the axial line on the rear end side of the male screw, performing a spark discharge at the front end side in the axial direction;
An annular flat gasket disposed on the distal end side of the flange,
An annular pressure sensor comprising a pressure sensitive element;
A spark plug with a combustion pressure detection function, comprising:
The gasket comprises 0.80 to 1.20 mass% Ni, 0.50 to 1.10 mass% Sn, 0.03 to 0.07 mass% P, 97.63 to 98.67 mass%. It consists of a copper-based alloy as Cu,
When the Young's modulus of the gasket is E (kN / mm2),
100 ≦ E ≦ 170
Is to satisfy.

When the Young's modulus of the material constituting the gasket is 100 kN / mm ² or more, the gasket is not easily elastically deformed and can maintain a mechanically rigid state. On the other hand, if it is less than 100 kN / mm ² , the combustion pressure that propagates through the spark plug is absorbed by the gasket, and the change of the combustion pressure cannot be propagated linearly to the pressure sensor. Therefore, the sensor output is small (loss is large), and the S / N ratio (signal-noise ratio) is deteriorated. On the other hand, those having a Young's modulus exceeding 170 are hard and difficult to be elastically deformed when the spark plug is tightened, so that the airtightness cannot be maintained and the combustion gas leaks. Then, when the spark plug is displaced in the axial direction by the combustion pressure, a minute gap is formed between the seat surface of the metal shell and the gasket, and combustion gas leaks from the gap, so that a normal sensor output is obtained. It will not be possible.

  In general, the Young's modulus of the material and the spring constant are in a proportional relationship. When the gasket is elastically deformed (deformation amount x) by the force F (hereinafter also referred to as axial force) due to tightening of the spark plug or combustion pressure, the relational expression deforms the spring having the spring constant k by the deformation amount x. It can be considered in the same way as the force required for (see Equation 1). If the axial force applied to the gasket is constant, the deformation amount x decreases as the spring constant k increases. If the deformation amount x is small, the gasket is less likely to be deformed when the combustion pressure is transmitted to the pressure sensor, and the S / N ratio is improved. On the other hand, if the spring constant k is too large, the amount of deformation x itself will be small, but the gasket will not be able to maintain sufficient airtightness in the combustion chamber, causing combustion gas leakage, and the combustion pressure will not be sufficiently transmitted to the pressure sensor. It will end up.

(Equation 1)
F = kx

The 0.2% proof stress of the gasket is preferably 250 N / mm ² or less. The role of the gasket in the spark plug with the combustion pressure detection function is to provide the effect (sealability) of suppressing the leakage of combustion gas, which is the original function of the gasket, in addition to reliably transmitting the combustion pressure to the pressure sensor. desired. Regarding the leakage of the combustion gas, the true contact area shown in the equation 2 of the gasket is required. The true contact area is represented by a value obtained by dividing the pressure applied to the surface (upper and lower surfaces of the gasket when the axial direction of the spark plug is the vertical direction) by 0.2% proof stress. If this true contact area is large, that is, if the 0.2% proof stress is 250 N / mm ² or less, it is possible to obtain good sealing properties that reduce the amount of combustion gas leakage. On the other hand, if the 0.2% proof stress is less than 10, it is soft and has good sealing properties, but the output is distorted and a sufficient output as a pressure sensor cannot be obtained. When the 0.2% proof stress exceeds 250 N / mm ² , the pressure applied to the surface, that is, the tightening torque of the spark plug to the engine in order to increase the real contact area, is a value defined for each spark plug (for example, The nominal diameter of the tool engaging portion of the metal shell must be over 27.5 N · m for M14 and about 17.5 N · m for M12), and the spark plug may be destroyed. .

(Equation 2)
Real contact area = (pressure applied to the surface / 0.2% proof stress of the surface)

  The gasket preferably has a surface roughness Ry of 3.2 S or less. As described above, one of the roles as a gasket is to prevent the combustion gas from leaking from the combustion chamber to the outside. Furthermore, the gasket used together with the pressure sensor as described above needs to be able to accurately transmit the load change due to the fluctuation of the combustion pressure to the pressure sensor. In such a role, if the gasket has a rough surface, the air tightness is reduced, that is, the pressure inside the combustion chamber is lost, and the change in the load to the pressure sensor is not transmitted linearly, resulting in poor sensor output accuracy. End up. Therefore, the surface roughness of the gasket constituting the present invention is set to 3.2 S or less.

  The gasket preferably has a Vickers hardness of Hv 60 or more and 90 or less. In order to effectively obtain the effect of the gasket, it is desirable to use a smooth gasket surface, that is, a material having a low surface roughness. One aid for realizing a gasket having such a smooth surface is to have a Vickers hardness of Hv 60 or more and 90 or less. If Hv90 is exceeded, when the spark plug is attached to the engine with the specified torque, the gasket cannot be sufficiently deformed with respect to the load applied to itself, and contact with the flange of the spark plug or the engine head There is a possibility that the airtightness may be reduced due to a decrease in adhesion on the surface. On the other hand, in the case of Hv60, although it can be used as the sensor output, a decrease in the output value is confirmed. Therefore, if it is less than Hv60, there may be a problem in the detection accuracy of the sensor, which is not preferable. In addition, in the case of Hv70, since the drop which generate | occur | produced in the case of Hv60 was not able to be confirmed, it is more desirable to set it as Hv70 or more and 90 or less.

  By the way, a conventional copper-based alloy, for example, a gasket made of brass, has poor creep resistance, and creep deformation occurs due to heating / cooling associated with engine driving / resting, and a shaft for fixing the spark plug to the engine. The force is reduced, and screw loosening occurs due to vibration of the engine itself during use. Also, for example, a gasket made of phosphor bronze is superior to the above-mentioned brass in its initial creep resistance, but the stress relaxation rate decreases to the same level as brass when used repeatedly for a long time. May occur.

  Therefore, the gasket is 0.80 to 1.20 mass% Ni, 0.50 to 1.10 mass% Sn, 0.03 to 0.07 mass% P, 97.63 to 98.67 mass%. It was made of a copper-based alloy as Cu. It is a copper-based alloy, and can have excellent creep resistance characteristics when the Ni content is 0.80 to 1.20 mass%. This can be presumed that the Ni component exists as fine precipitates in the Cu structure and the creep resistance is improved. If it is less than 0.80% by mass, the stress relaxation characteristics are small and creep deformation tends to occur. On the other hand, if it exceeds 1.20% by mass, the precipitates become large, and the performance of Ni will be dark. The stress relaxation characteristics cannot be improved, and the excellent creep resistance characteristics cannot be obtained. Further, by containing Sn as 0.5 to 1.10 mass% and P as 0.03 to 0.07 mass%, it is possible to improve the hardness as an alloy and obtain good ductility. Therefore, it is possible to obtain a gasket that can improve output and improve sealing performance.

  Hereinafter, a spark plug with a combustion pressure detection function according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a half sectional view of a state in which a spark plug with a combustion pressure detecting function is attached to an internal combustion engine. As shown in FIG. 1, the spark plug 100 is provided around the insulator 10 toward the distal end side from an approximately central portion in the longitudinal direction of the insulator 10 and the insulator 10. Holding metal shell 20, center electrode 30 held inside insulator 10, ground electrode 40 joined to metal shell 20, terminal metal fitting 50 provided on the rear end side of insulator 10, gasket 60 and a pressure sensor 70.

  First, the insulator 10 will be described. The insulator 10 has a shaft hole 11 inside along the axis O direction, which is the longitudinal direction, and is formed in a substantially cylindrical shape by firing alumina or the like as is well known. A diamond portion 12 protruding outward in the radial direction is formed at a substantially central portion in the axis O direction, and a rear end body portion 13 is formed at the rear end side of the diamond portion 12. On the other hand, the front end side of the diamond portion 12 is formed with a front end side body portion 14 having a diameter smaller than that of the rear end side body portion 13 and a leg length portion 15 having a taper shape with a smaller diameter and being reduced in diameter toward the front end through the step portion 16. Has been. A corrugation 17 for increasing the creeping distance between the terminal fitting 50 and the metal shell 20 is formed at the rear end portion (upper portion in FIG. 1) of the rear end side body portion 13.

  In the shaft hole 11 of the insulator 10, a stepped portion 17 is formed at the distal end portion of the distal end side body portion 14 and has a surface that engages with the center electrode 30. The center electrode 30 has its rear end protruding in the radial direction so as to engage with the stepped portion 17 and is formed by processing a nickel-based alloy (for example, Inconel 600 or the like: trademark) into a rod shape. A copper-based alloy 31 is inserted in the interior in order to improve heat sinking. A wear resistance improving member 32 (a noble metal such as platinum or iridium and an alloy thereof or a base metal such as a tungsten alloy) is joined to the tip portion to improve wear resistance. On the other hand, the rear end side is electrically connected to the terminal fitting 50 through the glass seal 5 and the resistor 6. A high voltage cable (not shown) is connected to the terminal fitting 50 via a plug cap so that a high voltage is applied.

  As with the center electrode 30, a nickel-based alloy or the like is used for the ground electrode 40 that forms the spark discharge gap G with the center electrode 30. The longitudinal section thereof has a substantially rectangular shape, and the end portion 41 may be provided with a wear resistance improving member 42. On the other hand, the rear end side of itself is joined to the front end surface 21 of the metal shell 20 by, for example, resistance welding.

  The metal shell 20 is made of a substantially cylindrical iron-based material, and holds the insulator 10 on its inner peripheral side on the outer periphery of the insulator 10. Specifically, a step portion 22 is formed on the inner peripheral surface of the metal shell 20, and the step portion 16 of the insulator 10 is brought into contact with the step portion 22. A metal plate packing 7 may be interposed between the step portion 22 and the step portion 16. An inner hole having substantially the same diameter as the outer diameter of the front end side body portion 14 of the insulator 10 continues on the rear end side of the step portion 22. Further, on the rear end side, the inner hole is enlarged to accommodate the diamond portion 12. In order to attach the spark plug 100, a tool engaging portion 23 having a polygonal shape such as a hexagon is formed on the outer peripheral surface of the portion in which the diamond portion 12 is accommodated. On the rear end side of the tool engaging portion 23, a caulking lid 24 in which a part of the metal shell 20 is bent (clamped) radially inward is formed, and the insulator 10 is fixed to the metal shell 20 integrally. When the caulking lid 24 is caulked, talc (talc) 8 and annular packings 9 and 9 can be provided to prevent leakage of combustion gas from the combustion chamber and improve airtightness. A flange portion 25 is formed on the distal end side of the tool engaging portion 23 so as to project radially outward in the entire circumference, and the distal end surface of the flange portion 25 is formed on the outer surface of the internal combustion engine IC as a seating surface 26. Faces facing each other are formed. When attached to the internal combustion engine IC, the gasket 60 and the pressure sensor 70 are inserted into the male screw 28, and are rotated by the tool engaging portion 23, and the male screw 28 is tightened to the female screw provided in the plug hole of the internal combustion engine. As a result, the spark plug 100 is attached.

The gasket 60 used for this attachment is manufactured as follows.
A copper base alloy in which Ni is 1.00% by mass, Sn is 0.90% by mass, P is 0.05% by mass, the inevitable component is included and the balance is Cu, and the thickness is 1.5 mm. Process. Next, punching is performed so as to obtain a gasket outer shape. Thereafter, it is gradually heated to 500 ° C. over 1.5 hours, and the state at 500 ° C. is maintained for 1 hour. And a gasket is completed by annealing to room temperature (annealing process). In addition, you may perform suitably the grinding | polishing and the grinding process for adjusting the shape of a gasket.

  The pressure sensor 70 has the following general configuration. The case member 71 is a member made of stainless steel (for example, SUS304) that forms an annular bottom portion that can accommodate the annular piezoelectric element 72 therein. On one end surface side (the upper surface side in FIG. 2) of the piezoelectric element 72, an electrode plate 73 for extracting a combustion pressure signal, and an insulation made of alumina or the like for preventing a short circuit between the electrode plate 73 and the case member 71 are provided. A plate 74 is disposed, and the insulating plate 74 contacts the inner surface of the case member 71. On the other hand, a stainless steel annular pedestal 75 is disposed on the other end surface side (lower surface side in FIG. 2), the annular pedestal 75 and the case member 71 are in contact with each other, and the piezoelectric element 72 is sandwiched between the case members 71. The inner peripheral surface of the case member 71 is covered with a rubber insulating tube 76 in order to prevent contact with the electrode plate 73 and a short circuit.

  The pressure sensor 70 is attached in a state in which a preload is applied in the axial direction from the outside of the case member 71. When the preload is changed, a charge is generated on the surface (upper surface and lower surface) of the piezoelectric element 72, and the electrode The sensor output is taken out by the plate 73 and the output lead wire 76 connected to the electrode plate 73. Since the annular pedestal 75 and the case member 71 are made of a conductive material, they can have a common potential with the engine head. Accordingly, an output lead wire is not particularly required on the lower surface side of the piezoelectric element 72, but it goes without saying that the output may be taken out separately by the output lead wire.

The gasket constructed as described above has a Young's modulus of 130 kN / mm ² . For this reason, the spring constant of the gasket is large, and the lift amount (displacement amount) of the spark plug that varies depending on the combustion pressure can be transmitted to the pressure sensor with high sensitivity, and excellent sensor output characteristics can be obtained.

The gasket has a 0.2% proof stress of 172 N / mm ² . That is, since it has a 0.2% proof stress of 250 N / mm ² or less, the true contact area becomes relatively large, and the performance can be maintained over a long period of time as a gasket.

  Hereinafter, a test for confirming the effect of the gasket of the present invention was conducted. Table 1 shows the gaskets of the present invention as examples and the gaskets used for comparison as comparative examples. In Examples and Comparative Examples 1 and 2 shown in Table 1, the material alloy is rolled into a plate shape and punched and annealed as in the present invention. For further comparison, in Comparative Examples 3 and 4, the following test was also performed on a gasket having an S-shaped cross section used for a normal spark plug, and in Comparative Example 3, a pressure sensor serving as a combustion pressure detection function was installed. The same test is also conducted for a spark plug (M14) that is not provided. The nominal diameter of the male thread of the spark plug used in the following evaluation test was M12. The completed gasket has a thickness of 1.5 mm, an inner diameter of φ12 mm, and an outer diameter of φ16.7 mm.

(Sensor output evaluation test)
With respect to the sensor output evaluation test, the test was performed in the measurement system 300 shown in FIG. The air chamber 310 includes an electromagnetic valve AIN that connects a high-pressure air generator (not shown), an electromagnetic valve AOUT that connects the air chamber 310 and the atmosphere, a test measurement port 311, and a reference measurement port 312. The electromagnetic valve AIN and the electromagnetic valve AOUT are air valves that are opened and closed by known electromagnetic solenoids. The solenoid valve AIN and the solenoid valve AOUT are configured such that when no voltage is applied, the valve is closed and air is shut off, and when the voltage is applied, the valve is opened and vented.

  An aluminum bush 313 having a nominal diameter M12 inserted therein is attached to the test measurement port 311 of the air chamber 310. The connection between the air chamber 310 and the aluminum bush 313 is connected in an airtight state at the contact portion between them, and only the threaded hole formed through the communication communicates the inside and outside of the air chamber 310. A spark plug 100 is attached to the aluminum bush 313. When mounting, the gasket 60 is disposed in contact with the seat surface 26 of the flange 25 on the rear end side of the male screw 28 of the spark plug 100, and the pressure sensor 70 is mounted on the rear end surface of the aluminum bush 313 and the seat of the flange 25. A preload is applied in such a way that it is sandwiched between the surface 26 via a gasket 60. Regarding the attachment of the spark plug 100, the tightening torque is 17.5 N · m.

  The output lead 76 of the pressure sensor 70 is input to the charge amplifier 330 (KISTLER 5011), and the output is input to the oscilloscope 350. A reference pressure sensor 320 (KISTLER 6052A) is attached to the reference measurement port 312 of the air chamber 310, and its output is input to the charge amplifier 340 (KISTLER 5011). Connected to input.

  When performing the measurement, the electromagnetic valve AIN is opened with the electromagnetic valve AOUT closed, and air is applied at 2 MPa for 0.3 seconds. After the air is applied, the electromagnetic valve AIN is closed and the electromagnetic valve AOUT is opened to return the pressure in the air chamber 310 to atmospheric pressure. This series of operations is performed within one second, and the outputs from the charge amplifiers 330 and 340 are measured by the oscilloscope 350 continuously for several seconds. The value when the output by this measurement is stabilized is taken as the measured value.

  The correlation between the output of the pressure sensor 70 and the output of the reference pressure sensor 320 is obtained from the measured value, and the decrease in the output of the pressure sensor 70 when the output of the reference pressure sensor 320 is 100% is calculated as the output distortion rate. As shown in FIG.

(Seal evaluation test)
On the other hand, an evaluation test was performed with a measurement system 400 shown in FIG. Since the measurement system 400 has the same configuration as that of the measurement system 300 of the sensor output characteristic evaluation test, the same parts are denoted by the same reference numerals and description thereof is omitted.

  The air chamber 310 includes a solenoid valve AIN and a test measurement port 311. The aluminum bush 313 is fixed to the test measurement port 311 similarly to the sensor output test, and the spark plug 100 is attached to the aluminum bush 313 via the gasket 60 and the pressure sensor 70. The leakage air measurement case 410 surrounds and is fixed to the spark plug 100 and the aluminum bush 313. The measurement case 410 is filled with a liquid (for example, ethanol), the level (water level) fluctuates due to leaked air, and the amount of leaked air can be measured. For this reason, the leaked air measurement case 410 has a scale on its side surface like a graduated cylinder. In addition, the leakage air measurement case 410 may be provided with an electromagnetic valve EIO so that liquid and air filling the inside can be arbitrarily taken in and out.

  As described above, since the sealing performance depends on the real contact area of the gasket as shown in Equation 2, the true contact area is calculated from the load applied to the gasket. The load applied to the gasket can be measured using a load washer (KISTLER 9135AA, not shown) separately from the measurement system 400. FIG. 6 is a graph in which the true contact area is calculated from the measured load and the 0.2% proof stress inherent to the gasket shown in Table 1, and this is the horizontal axis and the amount of air leakage is the vertical axis.

  In FIG. 6 showing the results of the sealing property evaluation test, the measurement is performed before and after the heating vibration test, assuming before and after the actual vehicle travel. In the heating vibration test, a spark plug attached to an aluminum bush was placed in a thermostatic bath, the temperature was raised from 50 ° C. to 200 ° C. over 1.5 hours, held at 200 ° C. for 1 hour, and then over 1.5 hours. Return to 50 ° C. This temperature cycle is defined as 1 cycle, and 8 cycles are performed. The first four cycles are vibrated at an acceleration of 294 m / s (30 G) and 50 to 500 Hz in the axial direction of the spark plug in the thermostat, and the latter four cycles have the vibration direction perpendicular to the axis under the same conditions. The initial axial force indicates the axial force applied to the gasket when the spark plug is attached with a specified torque.

According to the above test results, it can be confirmed that when the spring constant is small, output distortion occurs and the output loss of the pressure sensor 70 increases. According to this evaluation test, the embodiment of the present invention has a large spring constant, that is, a large Young's modulus, so that even if the lift amount of the spark plug is small, the pressure sensor is not absorbed by the gasket. It can be seen that it is possible to transmit stress to. In addition, since the Young's modulus is not too large and the 0.2% proof stress is 250 N / mm ² or less, the examples of the sealability evaluation test have a small amount of air leakage and the airtightness as a gasket. It can be confirmed that it is excellent.

  Furthermore, the performance of the spark plug with a combustion pressure detection function brought about by the surface roughness of the gasket and the Vickers hardness was verified.

(Surface roughness Ry)
A plurality of gaskets of the material configuration (Cu-1Ni-0.9Sn-0.05P) used in the above examples are prepared, and polishing and grinding are performed at different times, and the surface roughness Ry is measured. As a result, gaskets having surface roughness Ry shown in Table 2 of 0.5S, 1.6S, 3.0S, 3, 2S, and 10S were obtained. A spark plug with a combustion pressure detection function is constructed using gaskets having different surface roughness Ry, and the measurement system of the above sealing property evaluation test is used. The effect of the surface roughness Ry on the airtightness was confirmed. Note that the surface roughness Ry is measured with respect to the portions indicated by arrows d1, d2, and d3 in FIG. 7 in the direction of the arrow by using the slitus of the surface roughness meter, and the surface roughness Ry is obtained from the average. Moreover, the gasket used for the Example in the above-mentioned sensor output evaluation test and the sealing property evaluation test has a surface roughness Ry of 3.0S.

  As a result, the air leakage amount is 0 to 0.1 ml / min. For those having a surface roughness Ry of 0.5S, 1.6S, 3.0S, 3, 2S. It was a good order (indicated as “OK”). On the other hand, when the surface roughness Ry is 10S, 50 to 100 ml / min. Therefore, in this comparison, it is relatively inferior and determined as “NG”. From these tests and results, it was confirmed that the smaller the surface roughness Ry, the better the airtightness, but excessively smoothing the surface leads to an increase in man-hours and costs. If the value is about 3.2S, it is judged that the performance is sufficiently exhibited as a gasket.

  Next, the effect of the Vickers hardness of the gasket on the output and airtightness was confirmed. The test product similarly formed the gasket made from Cu-1Ni-0.9Sn-0.05P. In addition, a plurality of gaskets are created so that the Vickers hardness is variously changed by variously changing the annealing conditions when forming. As a result, gaskets having Vickers hardness Hv shown in Table 3 of 60, 70, 85, 90, and 110 were obtained. Spark plugs with combustion pressure detection function are configured using gaskets with different Vickers hardnesses, sensor output using the same measurement system as in the sensor output test, and measurement system in the sealability evaluation test. In the same manner as described above, the influence on the airtightness assuming the initial wearing situation was confirmed. The hardness of the created gasket is 3 for each of the two exposed cross sections (see FIG. 8B) by exposing the AA cross section passing through the center point of the gasket as shown in FIG. Each point (P) is measured with a Vickers hardness tester, and the hardness is obtained from the average. The sensor output test, the sealing property evaluation test, and the test for verifying the influence of the surface roughness Ry on the airtightness are all those having a Vickers hardness of Hv85.

  As a result, when the output value in the sensor output test described above, that is, when the Vickers hardness Hv is 85, is 100%, the output of the Vickers hardness Hv of 70, 90, 110 is almost the same (100%). It was confirmed that the output with Vickers hardness Hv of 60 was slightly reduced (91%). As for the amount of air leakage, those with Vickers hardness Hv of 60, 70, 85, 90 are all 0 to 0.1 ml / min. The order was good, and “OK” was determined. On the other hand, the one having a Vickers hardness Hv of 110 is 30 ml / min. Therefore, in this comparison, it was relatively inferior and determined as “NG”. From this result, it was confirmed that any Vickers hardness Hv of 60 or more has no problem as a sensor output. However, when the Vickers hardness Hv is 60, a slight decrease in output is recognized, so it can be said that the Vickers hardness Hv is preferably 70 or more. On the other hand, regarding the airtightness, when the Vickers hardness Hv is 110, the amount of air leakage is larger than the others, so it can be said that the Vickers hardness Hv is desirably 90 or less.

    As described above, various evaluations were performed using the present invention as examples. At this time, the gasket is attached in contact with the seating surface 26 of the flange 25 of the metal shell 20, but the gasket and the pressure sensor 70 may be replaced and mounted without being limited to this form. That is, there is no problem even if the pressure sensor 70 is sandwiched between the gasket and the seating surface.

1 is a half sectional view showing an entire spark plug with a combustion pressure detecting function provided with a gasket of the present invention and how it is attached to an internal combustion engine. It is an enlarged view around a pressure sensor and a gasket. It is a figure which shows the measurement system of a sensor output evaluation test. It is a graph which shows the relationship between the spring constant and the output distortion rate of a pressure sensor obtained using the measurement system of FIG. It is a figure which shows the measuring system of a sealing performance evaluation test. It is a figure which shows the relationship between a true contact area and the amount of air leaks obtained using the measurement system of FIG. It is a top view for demonstrating the measurement location of the surface roughness Ry of a gasket. It is (a) top view for demonstrating the measurement location of the Vickers hardness of a gasket, (b) It is AA sectional drawing.

Explanation of symbols

60 Gasket 70 Pressure sensor 100 Spark plug

Claims (4)

A spark plug that performs spark discharge at the front end side in the axial direction and has a metal shell provided with a flange projecting in a direction perpendicular to the axial line at the rear end side of the male screw;
An annular flat gasket disposed on the distal end side of the flange,
An annular pressure sensor comprising a pressure sensitive element;
A spark plug with a combustion pressure detection function, comprising:
The gasket is made of 0.80 to 1.20 mass% Ni, 0.50 to 1.10 mass% Sn, 0.03 to 0.07 mass% P, 97.63 to 98.67 mass%. It consists of a copper-based alloy as Cu,
When the Young's modulus of the gasket is E (kN / mm2),
100 ≦ E ≦ 170
A spark plug with a combustion pressure detection function characterized by satisfying   The spark plug with a combustion pressure detecting function according to claim 1, wherein the gasket has a 0.2% proof stress of 250 (N / mm2) or less.   The spark plug according to claim 1, wherein the gasket has a surface roughness Ry of 3.2 S or less.   4. The spark plug according to claim 1, wherein the gasket has a Vickers hardness of Hv 60 or more and 90 or less.

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