JP2010049856A - Spark plug with thermal sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug with a thermal sensor capable of more precisely carrying out temperature measurement, through restraint of spark exhaustion at the tip part of a center electrode. <P>SOLUTION: The center electrode 20 has a contact point 71 of a thermocouple 70 formed inside a tip part 22. At the tip part, a ring-shaped electrode member 80 made of a precious metal alloy is fitted in such a form as to surround an outer periphery of the tip part 22 in a peripheral direction including an outer periphery edge 23 of a tip face 21 of a base material of the center electrode 20. An outer periphery edge 83 of a tip face 81 of the electrode member 80 forms an angle part at the tip part 22 of the center electrode 20. Spark discharge against a grounding electrode takes place with the angle part as a starting point, so that exhaustion of the center electrode 20 itself is restrained. Therefore, a state of thermal draw around the contact point 71 is hard to vary, so that a temperature indicating value measured by the thermocouple 70 is hard to vary even during a long period of use of the temperature-measuring plug. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spark plug with a temperature sensor that can accommodate a temperature sensor in a tip portion of a center electrode and can measure the temperature of the center electrode.

In recent years, the internal combustion engine has been reduced in size and performance, and the temperature in the combustion chamber tends to rise. Spark plugs are used for ignition of internal combustion engines, but in developing such spark plugs, it is necessary to consider the influence of the thermal load received from the internal combustion engine. Therefore, a spark plug with a temperature sensor (a temperature measurement plug for an internal combustion engine) in which a temperature sensor is accommodated in the center electrode has been developed so that the thermal load received by the spark plug can be confirmed (see, for example, Patent Document 1). .) In the spark plug with a temperature sensor described in Patent Document 1, a thermocouple is inserted into a center electrode provided with an insertion hole extending in the axial direction, and the tip of the center electrode is melted together with the thermocouple to form a thermocouple contact. By doing so, it functions as a temperature sensor and both are fixed.
JP 9-35849 A

  However, the spark plug with a temperature sensor of Patent Document 1 has a temperature sensor (thermocouple) disposed in the tip when the tip of the center electrode is consumed due to spark discharge between the ground electrode and the volume decreases. The degree of heat extraction of the center electrode changes in the vicinity of the contact). For this reason, as the center electrode is consumed, the temperature value measured by the temperature sensor (hereinafter referred to as “temperature indication value”) greatly deviates from the new one (before the center electrode is consumed). There was a problem that. Thus, it is conceivable to suppress wear of the center electrode by bonding a noble metal tip such as Pt to the tip surface of the center electrode. However, since the center electrode is mainly composed mainly of Ni and has a thermal conductivity different from that of Pt, the obtained temperature indication value is different from the temperature indication value obtained by the conventional spark plug with a temperature sensor. There is a problem that it becomes difficult to effectively use past resources (such as temperature measurement data).

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a spark plug with a temperature sensor that can suppress the consumption of sparks at the tip of the center electrode and can perform temperature measurement more accurately. And

  A spark plug with a temperature sensor according to the present invention has an insertion hole formed along an axial direction, and the insertion hole is inserted into the insertion hole, with a center electrode having a bottomed cylinder shape closed at the tip of the insertion hole. A temperature sensor that is fixed in the insertion hole in a state in which the temperature measurement unit is disposed in the tip of the center electrode, and an axial hole that extends in the axial direction. And an insulator that holds the center electrode, a metal shell that surrounds and holds the insulator in a circumferential direction, one end portion is joined to the metal shell, and the other end portion is directed toward the tip of the center electrode. A spark plug with a temperature sensor, wherein the tip of the center electrode includes an outer peripheral edge of a tip surface of the base material of the center electrode. Take the outer circumference of the section in the circumferential direction Wherein the electrodeless member.

  According to the present invention, the electrode member provided at the front end portion of the center electrode includes the outer peripheral edge of the front end surface of the center electrode base material and surrounds the outer periphery of the front end portion of the center electrode base material in the circumferential direction. Since it is provided, the ridge angle portion where the starting point of the spark discharge is easily induced by the concentration of the electric field is constituted by the electrode member. If a spark discharge occurs between the ground electrode and the electrode member due to the concentration of the electric field, the spark discharge is less likely to occur between the ground electrode and the tip of the base electrode base material. It is possible to suppress the consumption of the tip of the center electrode. And, if the consumption of the tip of the center electrode can be suppressed and fluctuations in the volume at the tip can be suppressed, even when the spark plug with temperature sensor is used over a long period of time, the accuracy of the temperature sensor's measured temperature fluctuations can be suppressed sufficiently. Temperature measurement can be performed.

  By the way, the heat conductivity of the electrode member provided at the tip of the center electrode is different from the heat conductivity of the center electrode base material. A difference occurs in the state. Therefore, in the spark plug with a temperature sensor according to the present invention, 1.7 ≦ d ≦ 3.0 [mm] may be satisfied, where d is the outer diameter of the tip of the center electrode. If the outer diameter d of the front end portion of the center electrode is less than 1.7 mm, the proportion of the volume occupied by the electrode member at the front end portion of the center electrode is larger than the base material of the center electrode. Then, the heat extraction performance of the center electrode as a whole changes, and there is a possibility that an error between the temperature value (temperature indication value) of the center electrode measured by the temperature sensor and the actual temperature of the center electrode increases.

  In addition, since the electrode member is provided on the outer periphery of the front end portion of the center electrode base material including the outer peripheral edge of the front end surface of the center electrode base material, an edge portion that is likely to start a spark discharge due to electric field concentration is determined by the electrode member. Composed. When the outer diameter d of the tip of the center electrode is larger than 3.0 mm, the center of the tip surface of the center electrode moves away from the ridge angle portion, so that the induction of the starting point of the spark discharge due to the concentration of the electric field at the ridge angle portion is the center. It becomes difficult to reach the tip surface of the electrode. Then, a spark discharge occurs between the ground electrode and the tip surface of the center electrode, the center electrode is consumed, and there is a possibility that the temperature indication value indicated by the temperature sensor is shifted.

  Further, in the spark plug with a temperature sensor according to the present invention, a bottom wall portion formed at the tip portion of the center electrode and closing the insertion hole so that the center electrode has a bottomed cylindrical shape is formed on the center electrode. When the thickness in the axial direction is h, 0.5 ≦ h ≦ 1.5 [mm] may be satisfied. When the thickness h of the bottom wall portion of the center electrode is smaller than 0.5 mm, the center electrode cannot have a sufficient volume in the bottom wall portion, and the ratio of the volume occupied by the electrode member at the tip portion of the center electrode is It becomes large with respect to the base material of the center electrode. Then, the heat extraction performance of the center electrode as a whole changes, and there is a possibility that an error between the temperature value (temperature indication value) of the center electrode measured by the temperature sensor and the actual temperature of the center electrode increases.

  On the other hand, when the thickness h of the bottom wall portion of the center electrode is larger than 1.5 mm, the center electrode originally has a sufficient volume at the tip portion, so even if the center electrode is consumed by spark discharge, the heat extraction performance at the tip portion The influence on the temperature indication value indicated by the temperature sensor is also small. For this reason, a spark plug with a temperature sensor having a center electrode having a bottom wall thickness h greater than 1.5 mm is not covered by the present invention.

  Moreover, in the spark plug with a temperature sensor according to the present invention, when t is a radial thickness of the electrode member on the tip surface of the center electrode, 0.2 ≦ t ≦ 0.5 [mm] is satisfied. Also good. If the thickness t in the radial direction of the electrode member is smaller than 0.2 mm, the electrode member itself is consumed by spark discharge, and there is a possibility that a sufficient effect for suppressing consumption of the center electrode cannot be obtained. In general, it is known that a base electrode base material using an alloy such as Ni is more likely to cause discharge (emit electrons) than other metals. For this reason, when the thickness t in the radial direction of the electrode member is reduced and the outer peripheral edge of the front end surface of the base electrode of the center electrode approaches the ridge angle portion as the entire center electrode including the electrode member, electric field concentration at the ridge angle portion The starting point of the induced spark discharge is shifted to the center electrode base material side where discharge is more likely to occur, leading to the consumption of the center electrode, and there is a possibility that the temperature indication value indicated by the temperature sensor is shifted.

  On the other hand, when the thickness t in the radial direction of the electrode member is larger than 0.5 mm, the proportion of the volume occupied by the electrode member at the tip end portion of the center electrode is larger than that of the center electrode. Then, the heat extraction performance of the center electrode as a whole changes, and there is a possibility that an error between the temperature value (temperature indication value) of the center electrode measured by the temperature sensor and the actual temperature of the center electrode becomes large.

  In the spark plug with a temperature sensor according to the present invention, when the length of the electrode member extending from the front end surface toward the rear end side in the axial direction of the center electrode is w, 0.6 ≦ w ≦ It may satisfy 1.4 [mm]. When the length w of the electrode member in the axial direction is less than 0.6 mm, the outer peripheral surface of the base material of the center electrode approaches the ridge angle portion of the entire center electrode including the electrode member, and is induced by electric field concentration at the ridge angle portion. Further, the starting point of the spark discharge moves to the base material side of the center electrode that is more likely to be discharged, leading to the consumption of the center electrode, which may cause a deviation in the temperature indication value indicated by the temperature sensor.

  On the other hand, if the length w in the axial direction of the electrode member is larger than 1.4 mm, the proportion of the volume occupied by the electrode member at the tip of the center electrode is larger than that of the center electrode. Then, the heat extraction performance of the center electrode as a whole changes, and there is a possibility that an error between the temperature value (temperature indication value) of the center electrode measured by the temperature sensor and the actual temperature of the center electrode becomes large.

  In the spark plug with a temperature sensor according to the present invention, the electrode member may be made of a noble metal or an alloy containing a noble metal as a main component, and may contain at least one of Pt, Ir, and Rh as the noble metal. Use of a noble metal or an alloy containing a noble metal as a main component as the material of the electrode member is desirable because it has high spark wear resistance. And as a noble metal, Pt, Ir, Rh, etc. can be utilized, and it is preferable to contain at least 1 or more types among them.

  In the spark plug with a temperature sensor according to the present invention, the electrode member may contain a precious metal of 65 wt% or more and 100 wt% or less. When Pt or an alloy made of Pt is used as the material of the electrode member, if the Pt content is 65% by weight to 100% by weight, the electrode member itself can be prevented from being consumed by spark discharge, and the center electrode is consumed. Can be suppressed, which is desirable. When an alloy having a Pt content of less than 65% by weight is used as a material for the electrode member, the electrode member is consumed by spark discharge, and there is a possibility that a sufficient effect for suppressing the consumption of the center electrode cannot be obtained.

  Hereinafter, an embodiment of a spark plug with a temperature sensor embodying the present invention will be described with reference to the drawings. First, with reference to FIGS. 1 and 2, a structure of a temperature measuring plug 100 in which a thermocouple 70 as an example of a temperature sensor is accommodated in the center electrode 20 as an example of a spark plug with a temperature sensor will be described. FIG. 1 is a partial cross-sectional view of the temperature measuring plug 100. FIG. 2 is a perspective view showing a cross section near the tip 22 of the center electrode 20. In FIG. 1, the axis O direction of the temperature measurement plug 100 will be described as the vertical direction in the drawing, the lower side will be described as the front end side of the temperature measurement plug 100, and the upper side will be described as the rear end side. In FIG. 2, the upper side of the drawing is the tip side of the temperature measuring plug 100.

  A thermometer plug 100 shown in FIG. 1 has a configuration substantially the same as that of a general spark plug in appearance, and generally includes an insulator 10 that holds a center electrode 20 in its own shaft hole 12, and a metal shell 50. It has the structure hold | maintained in the cylindrical hole 55 of this. The center electrode 20 forms a spark discharge gap GAP with the ground electrode 30 joined to the metal shell 50, and a thermocouple 70 is accommodated in the center electrode 20. The thermometer plug 100 enables the heat received by the center electrode 20 from the combustion chamber to be measured by the thermocouple 70.

  Next, the center electrode 20 will be described. The center electrode 20 uses a rod-shaped electrode formed of a Ni alloy as a base material. The center electrode 20 is held on the distal end side in the shaft hole 12 of the insulator 10, and the distal end portion 22 protrudes from the distal end of the insulator 10. Further, as shown in FIG. 2, an insertion hole 25 is formed in the center electrode 20 along the direction of the axis O, and the insertion hole 25 is closed by the bottom wall portion 24 at the distal end portion 22. That is, the center electrode 20 has a bottomed cylindrical shape, and a thermocouple 70 described later is accommodated therein.

  Further, the distal end portion 22 of the center electrode 20 is slightly reduced in diameter in order to provide a gap for self-cleaning during smoldering with the inner peripheral surface of the shaft hole 12 at the distal end of the insulator 10. The tip portion 22 is provided with a ring-shaped electrode member 80 made of a Pt alloy. In addition, as a material of this electrode member 80, it is preferable to use the alloy which has at least 1 or more types of noble metal of Pt, Ir, and Rh as a main component, and a noble metal content is 65 to 100 weight%. The electrode member 80 includes an outer peripheral edge 23 of the tip surface 21 of the base material of the center electrode 20, is provided in a form surrounding the outer periphery of the base material in the tip portion 22 in the circumferential direction, and is integrated with the base material of the center electrode 20. ing. More specifically, the outer periphery of a portion of the distal end portion 22 of the center electrode 20 from the distal end surface 21 of the base material to the length in the direction of the axis O of the electrode member 80 (length w in the direction of the axis O described later) is The diameter of the electrode member 80 is further reduced by the thickness (diameter thickness t described later), and the electrode member 80 is fitted to the reduced diameter portion and integrated with the base material of the center electrode 20. The outer peripheral surface 86 of the electrode member 80 provided in this way is continuous with the outer peripheral surface 26 of the base material at the front end portion 22 of the center electrode 20, and the front end surface 81 of the electrode member 80 is also the base material of the central electrode 20. It has a form that is continuous with the tip surface 21. That is, the outer peripheral edge 83 of the distal end surface 81 of the electrode member 80 forms a ridge angle portion at the distal end portion 22 of the center electrode 20.

  Next, as shown in FIG. 1, the center electrode 20 is electrically connected to the terminal fitting 40 on the rear side (upper side in FIG. 1) via the seal body 4 and the ceramic resistor 3 provided in the shaft hole 12. It is connected to the. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown) so that a high voltage for spark discharge is applied.

  Next, the thermocouple 70 will be described. In the present embodiment, as an example of the temperature sensor, a thermocouple 70 shown in FIG. 2 is accommodated in the insertion hole 25 of the center electrode 20. The thermocouple 70 is formed by inserting different types of metal wires (for example, chromel-alumel wires) 72 and 73 into a sheath tube 75 made of a heat-resistant alloy and fixing them with insulating powder such as magnesia. An end portion is joined to the bottom wall portion 24 that closes the insertion hole 25 of the center electrode 20, and a contact 71 for measuring temperature is formed. The thermocouple 70 extends in the shaft hole 12 of the insulator 10 along the axis O to the rear end side, penetrates the seal body 4, the ceramic resistor 3, and the terminal fitting 40 from the rear end of the temperature measuring plug 100. Exposed to the outside.

  Next, the ground electrode 30 will be described. The ground electrode 30 shown in FIG. 1 is formed in a rod shape from a metal having high corrosion resistance. As an example, a nickel alloy such as Inconel (trade name) 600 or 601 is used. The ground electrode 30 has a substantially rectangular cross section in the longitudinal direction, and the base 32 is joined to the distal end surface 57 of the metal shell 50 by welding. The tip 31 of the ground electrode 30 is bent toward the tip 22 of the center electrode 20, and a spark discharge gap GAP is formed therebetween.

  Next, the metal shell 50 will be described. The metal shell 50 is a cylindrical metal fitting for fixing the temperature measuring plug 100 to the engine head (not shown) of the internal combustion engine. The metal shell 50 extends from a part of the rear end side body portion 18 of the insulator 10 to the leg length portion 13. The insulator 10 is held in the cylindrical hole 55 so as to surround the part. The metal shell 50 is made of a low carbon steel material, and a tool engaging portion 51 to which a spark plug wrench (not shown) is fitted and a mounting portion 52 in which a screw thread to be screwed into a screw hole (not shown) of the engine head is formed. And have. Further, a hook-shaped seal portion 54 is formed between the tool engaging portion 51 and the attachment portion 52 of the metal shell 50. A gasket 5 is formed between the mounting portion 52 and the seal portion 54 by bending the plate body into an annular shape to prevent airtight leakage when the temperature measuring plug 100 is mounted in a mounting hole (not shown) of the engine head. Is inserted.

  A holding portion 56 that protrudes inward is provided at the position of the attachment portion 52 in the cylindrical hole 55 of the metal shell 50, and the step portion 15 of the insulator 10 is held via the annular plate packing 8. Further, a thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51. And between the inner periphery of the cylindrical hole 55 of the metal shell 50 from the tool engaging portion 51 to the caulking portion 53 and the outer periphery of the rear end side body portion 18 of the insulator 10, the annular ring members 6, 7 Is interposed between the ring members 6 and 7 and talc (talc) 9 powder is filled. By the caulking of the caulking portion 53, the insulator 10 pressed toward the front end side in the cylindrical hole 55 is supported between the caulking portion 53 and the holding portion 56, and the center electrode 20 and the like are accommodated in the shaft hole 12. And the metal shell 50 are integrated.

  Thus, by providing the ring-shaped electrode member 80 that circumferentially surrounds the outer periphery of the distal end portion 22 including the outer peripheral edge 23 of the distal end surface 21 of the base material of the center electrode 20, the contact with the ground electrode 30 due to electric field concentration is provided. The ridge angle portion that easily induces the starting point of the spark discharge between them is constituted by the electrode member 80, and the consumption of the center electrode 20 is suppressed. When the center electrode is consumed, the heat value in the vicinity of the thermocouple contact changes, and the measured temperature value (temperature indication value) may be different from the value before consumption. With the measurement plug 100, the influence on the temperature indication value can be effectively reduced even when the temperature measurement plug 100 is used for a long time. However, the temperature measuring plug 100 is a plug used for a test in the design of a spark plug or an automobile, and the electrode member is not provided on the center electrode of the spark plug to be tested. In the present embodiment, an electrode member 80 using a noble metal such as Pt having a different thermal conductivity from the central electrode 20 made of an Ni alloy is provided at the tip 22 to reach the temperature indication value of the thermocouple 70. In order to reduce the influence, the sizes of the electrode member 80 and the center electrode 20 are defined as follows.

  As shown in FIG. 2, when the outer diameter at the distal end portion 22 of the center electrode 20 is d, in the present embodiment, the size of the outer diameter d is defined as φ1.7 to φ3.0 [mm]. . An electrode member 80 is provided at the distal end portion 22 of the center electrode 20. However, it is necessary to ensure a certain size in order to suppress wear caused by the spark discharge of the electrode member 80 itself, and the outer diameter d of the distal end portion 22 is small. If the diameter is smaller than 1.7 mm, the ratio of the volume occupied by the electrode member 80 to the volume occupied by the base material of the center electrode 20 at the tip 22 becomes large. Due to the difference in thermal conductivity between the base material of the center electrode 20 and the electrode member 80, when the volume ratio occupied by the electrode member 80 increases, the heat extraction performance of the center electrode 20 as a whole changes and is measured by the thermocouple 70. There is a possibility that an error between the temperature indication value of the center electrode 20 and the actual temperature of the center electrode 20 becomes large.

  In addition, since the electrode member 80 is provided on the outer periphery of the distal end portion 22 including the outer peripheral edge 23 of the distal end surface 21 of the base material of the center electrode 20, the distal end surface of the outer peripheral edge 83 of the distal end surface 81 of the electrode member 80 is A ridge angle formed by 81 and the outer peripheral surface 86 is formed. Since the base material of the center electrode 20 is made of an Ni alloy and emits electrons more easily than the electrode member 80 made of a Pt alloy, discharge is likely to occur at a lower voltage. However, electric field concentration is likely to occur at the ridge angle portion, and the ridge angle portion surrounds the distal end surface 21 of the base material of the center electrode 20. Therefore, even if the electrode member 80 constitutes the ridge angle portion, the starting point (generation position) of the spark discharge is induced at the ridge angle portion, and a spark is generated between the ground electrode 30 and the outer peripheral edge 83 of the electrode member 80. Since discharge tends to occur, the consumption of the center electrode 20 can be suppressed.

  Here, when the outer diameter d of the distal end portion 22 of the center electrode 20 is increased, the center of the distal end surface 21 of the base material is moved away from the outer peripheral edge 83 of the distal end surface 81 of the electrode member 80, and a spark due to electric field concentration at the ridge angle portion. The induction of the discharge starting point is difficult to reach the front end surface 21 of the base material of the center electrode 20. Specifically, when the outer diameter d is larger than φ3.0 mm, a spark discharge occurs between the ground electrode 30 and the tip end surface 21 of the base electrode 20, and the center electrode 20 is consumed, and the thermocouple 70 There is a possibility that a deviation occurs in the indicated temperature value.

  Next, regarding the bottom wall portion 24 of the center electrode 20, when the thickness in the direction of the axis O is h, in the present embodiment, the thickness h is regulated to 0.5 mm to 1.5 mm. When the thickness h of the bottom wall portion 24 of the center electrode 20 is larger than 1.5 mm, the center electrode 20 originally has a sufficient volume at the tip portion 22, so even if the center electrode 20 is consumed by spark discharge, the tip portion 22. The influence on the heat-drawing performance of the thermocouple 70 is small, and the influence on the temperature indication value indicated by the thermocouple 70 is also small. For this reason, a thermometer plug having a center electrode having a thickness h of the bottom wall portion larger than 1.5 mm is excluded from the scope of the present invention.

  When the thickness h of the bottom wall portion 24 of the center electrode 20 is smaller than 0.5 mm, the center electrode 20 cannot have a sufficient volume in the bottom wall portion 24. Then, as described above, the ratio of the volume occupied by the electrode member 80 to the volume occupied by the center electrode 20 at the tip end portion 22 increases, and the heat extraction performance of the center electrode 20 as a whole changes, and the temperature indicated by the thermocouple 70. There is a possibility that an error between the indicated value and the actual temperature of the center electrode 20 becomes large.

  Next, on the tip surface 21 side of the base material of the center electrode 20, when the radial thickness of the electrode member 80 is t, the size of the thickness t is regulated to 0.2 mm to 0.5 mm. If the thickness t of the electrode member 80 is smaller than 0.2 mm, the electrode member 80 itself is consumed by spark discharge, and there is a possibility that a sufficient effect for suppressing the consumption of the center electrode 20 cannot be obtained. In addition, as described above, the center electrode 20 made of Ni alloy is more likely to cause discharge than the electrode member 80 made of Pt alloy (emission of electrons is easier). For this reason, when the thickness t of the electrode member 80 is reduced and the outer peripheral edge 23 of the front end surface 21 of the base material of the center electrode 20 approaches the ridge angle portion (the outer peripheral edge 83 of the electrode member 80), induction is caused by electric field concentration at the ridge angle portion. The starting point of the spark discharge thus made moves to the base material side of the center electrode 20 which is more likely to be discharged, leading to the consumption of the center electrode 20, and the temperature indication value indicated by the thermocouple 70 may be shifted.

  On the other hand, if the thickness t of the electrode member 80 is greater than 0.5 mm, the ratio of the volume occupied by the electrode member 80 to the volume occupied by the center electrode 20 at the tip portion 22 increases, and as in the above, the heat of the entire center electrode 20 is increased. The pulling performance changes, and there is a possibility that an error between the temperature indication value of the center electrode 20 measured by the thermocouple 70 and the actual temperature of the center electrode 20 becomes large.

  Next, when the length in which the electrode member 80 extends in the direction of the axis O is w, the size of the length w is defined as 0.6 mm to 1.4 mm. If the length w of the electrode member 80 is greater than 1.4 mm, the ratio of the volume occupied by the electrode member 80 to the volume occupied by the center electrode 20 at the tip portion 22 increases, and as in the above, the heat extraction of the center electrode 20 as a whole. The performance changes, and there is a possibility that an error between the temperature indication value of the center electrode 20 measured by the thermocouple 70 and the actual temperature of the center electrode 20 becomes large.

  On the other hand, when the length w of the electrode member 80 is smaller than 0.6 mm, the distance between the tip end surface 81 of the electrode member 80 and the outer peripheral surface 26 of the base material of the center electrode 20 becomes close. As described above, the center electrode 20 made of Ni alloy is more likely to cause discharge (electrons are more likely to be emitted) than the electrode member 80 made of Pt alloy. For this reason, when the length w of the electrode member 80 decreases and the outer peripheral surface 26 of the base material of the center electrode 20 approaches the ridge angle portion (the outer peripheral edge 83 of the electrode member 80), a spark induced by electric field concentration at the ridge angle portion. There is a possibility that the starting point of the discharge moves to the base material side of the center electrode 20 which is more likely to be discharged, and the center electrode 20 is consumed.

  Moreover, about the material of the electrode member 80, in this Embodiment, it contains at least 1 or more types of Pt, Ir, and Rh as a noble metal, and the content of the noble metal is 65 to 100 weight%. It prescribes. If the content of the noble metal in the electrode member 80 is small, the spark wear resistance of the electrode member 80 is reduced and the electrode member 80 itself is consumed by spark discharge, so that a sufficient effect for suppressing the consumption of the center electrode 20 is obtained. There is a risk of being lost. According to Example 5 to be described later, if the electrode member 80 is formed of a noble metal or an alloy having a noble metal content of 65 wt% or more, the wear of the electrode member 80 itself due to spark discharge can be suppressed, and the wear of the center electrode 20 can be suppressed. It was confirmed that it can be suppressed.

  Needless to say, the present invention can be modified in various ways. For example, as shown in FIG. 3, the tip surface 181 of the electrode member 180 is provided closer to the tip than the tip surface 21 of the base material of the center electrode 20 at the tip 22 of the center electrode 20 similar to the present embodiment. The outer peripheral edge 183 of the electrode member 180 may extend inward in the radial direction and cover the outer peripheral edge 23 of the base material of the center electrode 20. In addition, the electrode member 80 is provided in the circumferential direction so as to surround the outer periphery of the base material in the circumferential direction at the distal end portion 22 of the center electrode 20.

  Moreover, although the thermocouple 70 was mentioned as an example of a temperature sensor, the size conditions which can measure the temperature of the center electrode 20 which becomes high temperature 1000 degreeC or more at the time of engine operation, and can be accommodated in the inside of the center electrode 20 are set. Any temperature sensor that satisfies this requirement can be used.

[Example 1]
Next, an evaluation test was performed in order to confirm the effects of providing the various regulations described above. First, an evaluation test was performed in order to confirm the effect of defining the thickness t in the radial direction of the electrode member 80 provided at the distal end portion 22 of the center electrode 20 to 0.2 mm to 0.5 mm.

  In this evaluation test, a plurality of center electrodes having an outer diameter d of φ1.7 mm and a bottom wall thickness h of 0.5 mm were prepared. Also, using Pt (100% by weight), the outer diameter is 1.7 mm, the length w in the direction of the axis O is 1.0 mm, and the thickness t in the radial direction is 0.1 mm to 0.7 mm every 0.1 mm. Seven types of ring-shaped electrode members prepared by differentiating the above were prepared. And after processing the front-end | tip part of a center electrode according to each electrode member, while joining both, the thermocouple was integrated in the center electrode and the sample of the thermometer plug was produced. Further, for comparison, a reference sample of a thermometer plug in which no electrode member was provided on the center electrode (that is, the radial thickness t of the electrode member was set to 0 mm) was prepared.

  First, a reference sample for comparison was assembled into an in-line 6-cylinder DOHC direct injection engine having a displacement of 2000 cc. Then, the engine was started, the accelerator was at full throttle (6000 rpm), the temperature of the reference sample was measured when the rotational speed was stabilized, and the measurement result was recorded as the reference temperature. Next, each sample was similarly assembled to the above-mentioned engine, the accelerator was set to full throttle (6000 rpm), the temperature was measured when the rotational speed was stabilized, and each sample was recorded as the first measured temperature. Then, the difference between the first measured temperature and the reference temperature is obtained for each sample as a temperature deviation Δθ1, and is graphed in FIG. 4 so that the relationship with the thickness t can be understood.

  Furthermore, the driving of the engine was continued for 100 hours, and the temperature of each sample after 100 hours of use was measured and recorded as the second measured temperature for each sample. After the test, the difference between the first measurement temperature and the second measurement temperature was determined for each sample as a temperature deviation Δθ2, and as shown above, the relationship between the first measurement temperature and the second measurement temperature was plotted in FIG.

  As shown in FIG. 4, it can be seen that the temperature deviation Δθ1 increases as the radial thickness t of the electrode member increases. In other words, as the proportion of the volume occupied by the electrode member having a lower thermal conductivity than the center electrode itself at the tip of the center electrode increases, the heat extraction performance at the tip changes, and the center electrode measured by the thermocouple It can be confirmed that the error between the temperature (first measured temperature) and the actual center electrode temperature (reference temperature), that is, the temperature deviation Δθ1 increases. When the allowable value of the temperature deviation Δθ1 is set to 5 ° C. (the temperature deviation measured at the center electrode of the spark plug, which becomes a high temperature of 1000 ° C. or higher when the engine is running, is set with an error within 0.5% as a target. In the case), it was found from the graph of FIG. 4 that the thickness t in the radial direction of the electrode member should be 0.5 mm or less in order to satisfy the allowable value.

  Further, as shown in FIG. 5, it can be seen that the temperature deviation Δθ2 increases as the thickness t of the electrode member decreases. As the thickness t of the electrode member decreases and the outer peripheral edge of the front end surface of the base material of the center electrode approaches the outer peripheral edge of the electrode member (that is, the ridge angle portion where spark discharge is likely to occur with the ground electrode), Spark discharge is likely to occur between the electrode base material and the center electrode is consumed, resulting in a temperature rise, temperature fluctuations before and after use for 100 hours (difference between the first measurement temperature and the second measurement temperature), That is, it can be confirmed that the temperature deviation Δθ2 increases. Similarly to the above, in order to satisfy the allowable value (within 5 ° C.) of the temperature deviation Δθ2 set to make the temperature measurement error within 0.5%, the radial thickness t of the electrode member is set to 0 from the graph of FIG. It was found that it should be 2 mm or more.

[Example 2]
Next, an evaluation test was performed in order to confirm the effect of defining the length w in the axis O direction of the electrode member 80 provided at the distal end portion 22 of the center electrode 20 to 0.6 mm to 1.4 mm. In this evaluation test, a plurality of center electrodes having an outer diameter d of φ1.7 mm and a bottom wall thickness h of 0.5 mm were prepared. Also, using Pt (100% by weight), the outer diameter is 1.7 mm, the radial thickness t is 0.5 mm, and the length w in the direction of the axis O is 0.2 mm to 2.0 mm every 0.2 mm. Ten kinds of ring-shaped electrode members prepared by differentiating the above were prepared. And after processing the front-end | tip part of a center electrode according to each electrode member, while joining both, the thermocouple was integrated in the center electrode and the sample of the thermometer plug was produced. Further, for comparison, a reference sample of a temperature measurement plug was prepared in which no electrode member was provided on the center electrode (that is, the length w of the electrode member in the direction of the axis O was 0 mm). Each sample was subjected to the same evaluation test as in Example 1 (under the same engine conditions) to obtain a temperature deviation Δθ1. FIG. 6 is a graph showing the relationship between the length w of the electrode member in the direction of the axis O and the temperature deviation Δθ1.

  Further, using Pt (100% by weight), the outer diameter is φ1.7 mm, the radial thickness t is 0.2 mm, and the length w in the axis O direction is 0.2 mm to 2.0 mm every 0.2 mm. Ten kinds of ring-shaped electrode members prepared by differentiating the above were prepared. And after processing the front-end | tip part of the center electrode produced similarly to the above according to each electrode member, while joining both, the thermocouple was integrated in the center electrode, and the sample of the thermometer plug was produced. Each sample was then subjected to a 100-hour endurance test similar to Example 1, and the temperature of each sample after 100 hours of use was measured to determine the temperature deviation Δθ2. FIG. 7 is a graph showing the relationship between the length w of the electrode member in the direction of the axis O and the temperature deviation Δθ2.

  As shown in FIG. 6, it can be seen that the temperature deviation Δθ1 increases as the length w of the electrode member increases. This is because, as the proportion of the volume occupied by the electrode member having a lower thermal conductivity than the center electrode itself at the tip of the center electrode increases, the heat-drawing performance at the tip changes. Similarly to the above, in order to satisfy the allowable value (within 5 ° C.) of the temperature deviation Δθ1 set to make the temperature measurement error within 0.5%, the length w of the electrode member in the direction of the axis O from the graph of FIG. Was found to be 1.4 mm or less.

  Further, as shown in FIG. 7, it can be seen that the temperature deviation Δθ2 increases as the length w of the electrode member decreases. As the length w of the electrode member decreases and the outer peripheral surface of the base material of the center electrode approaches the outer periphery of the electrode member (that is, the ridge portion where spark discharge is likely to occur with the ground electrode), This is because a spark discharge is generated between the outer peripheral surface of the base material of the center electrode by jumping over the ridge angle portion, and the center electrode is consumed. In order to satisfy the allowable value (within 5 ° C.) of the temperature deviation Δθ2 set so that the temperature measurement error is within 0.5% as described above, the length of the electrode member in the direction of the axis O from the graph of FIG. It was found that w should be 0.6 mm or more.

[Example 3]
Next, an evaluation test was performed in order to confirm the effect of defining the outer diameter d of the front end portion 22 of the center electrode 20 to φ1.7 to φ3.0 [mm]. In this evaluation test, four types of center electrodes having an outer diameter d of φ1.6, φ1.7, φ3.0, φ3.1 [mm] and a bottom wall thickness h of 0.5 mm were prepared. Also, Pt (100% by weight) is used, the outer diameter is φ1.6, φ1.7, φ3.0, φ3.1 [mm], the radial thickness t is 0.5 mm, and the length w in the axis O direction is w. Four types of ring-shaped electrode members having a thickness of 1.4 mm were prepared. And after processing the front-end | tip part of a center electrode according to each electrode member, while joining both, the thermocouple was integrated in the center electrode and the sample of the thermometer plug was produced. In addition, a reference sample in which no electrode member was joined was prepared as a reference for obtaining the temperature deviation Δθ1. Each sample was subjected to the same evaluation test as in Example 1 (under the same engine conditions) to obtain temperature deviations Δθ1 and Δθ2. The results of this evaluation test are shown in Table 1.

  As shown in Table 1, it can be seen that the temperature deviation Δθ1 increases as the outer diameter d of the tip of the center electrode decreases. This is because, as the proportion of the volume occupied by the electrode member having a lower thermal conductivity than the center electrode itself at the tip of the center electrode increases, the heat-drawing performance at the tip changes. Similarly to the above, in order to satisfy the allowable value (within 5 ° C.) of the temperature deviation Δθ1 set to make the temperature measurement error within 0.5%, from Table 1, the outer diameter d of the tip of the center electrode is φ1. It was found that it should be 7 mm or more. In addition, in the sample having an outer diameter d of φ3.1 mm at the tip of the center electrode, the center of the tip of the center electrode base material is separated from the outer rim, and the influence of electric field concentration due to the ridge angle portion forming the outer rim becomes less likely. Since a spark discharge occurred between the ground electrode and the front end surface of the base electrode base metal, it was invalidated.

  Then, when the temperature deviation Δθ2 was obtained for two samples in which the temperature deviation Δθ1 satisfied an allowable value and the outer diameter d of the tip of the center electrode was φ1.7, φ3.0 [mm], as shown in Table 1. And 1.6 and 1.2 [° C.], respectively. Both satisfy the allowable value (within 5 ° C.) of the temperature deviation Δθ2 set to make the temperature measurement error within 0.5% as described above, and from this, the outer diameter d of the tip of the center electrode is It has been found that φ1.7 to φ3.0 [mm] is sufficient. In Table 1, it can be seen that the greater the outer diameter d of the tip of the center electrode, the greater the proportion of the volume of the center electrode at the tip, and the less the amount of wear due to spark discharge with respect to the volume.

[Example 4]
Next, an evaluation test was performed in order to confirm the effect of defining the thickness h of the bottom wall portion 24 of the center electrode 20 to 0.5 mm to 1.5 mm. In this evaluation test, three types of center electrodes with an outer diameter d of φ1.7 mm and a bottom wall thickness h of 0.4, 0.5, and 1.5 [mm] were prepared. In addition, a ring-shaped electrode member using Pt (100 wt%), having an outer diameter of φ1.7 mm, a radial thickness t of 0.5 mm, and a length w in the axis O direction of 1.4 mm was prepared. . And after processing the front-end | tip part of each center electrode according to each electrode member, while joining both, the thermocouple was integrated in the center electrode, and the sample of the thermometer plug was produced. In addition, a reference sample in which no electrode member was joined was prepared as a reference for obtaining the temperature deviation Δθ1. Each sample was subjected to the same evaluation test as in Example 1 (under the same engine conditions) to obtain temperature deviations Δθ1 and Δθ2. The results of this evaluation test are shown in Table 2.

  As shown in Table 2, it can be seen that the temperature deviation Δθ1 increases as the thickness h of the bottom wall portion of the center electrode decreases. This is because, as the proportion of the volume occupied by the electrode member having a lower thermal conductivity than the center electrode itself at the tip of the center electrode increases, the heat-drawing performance at the tip changes. Similarly to the above, in order to satisfy the allowable value (within 5 ° C.) of the temperature deviation Δθ1 set to make the temperature measurement error within 0.5%, from Table 2, the thickness h of the bottom wall portion of the center electrode is set to 0. It was found that it should be 5 mm or more.

  And when temperature deviation (DELTA) (theta) 1 satisfy | filled tolerance and the thickness h of the bottom wall part of a center electrode calculated | required temperature deviation (DELTA) (theta) 2 about 0.5 mm and 1.5 mm, as shown in Table 2, respectively, 1.6, 1.3 [° C.]. All satisfy the allowable value (within 5 ° C.) of the temperature deviation Δθ 2 set to make the temperature measurement error within 0.5% as described above, and from this, the thickness h of the bottom wall portion of the center electrode Was found to be 0.5 mm or more.

  Note that the greater the thickness h of the bottom wall portion of the center electrode, the greater the proportion of the volume of the center electrode in the tip portion, and therefore the degree of consumption due to spark discharge with respect to the volume becomes smaller. Although not shown in Table 2, if the thickness h of the bottom wall is greater than 1.5 mm, the center electrode originally has a sufficient volume at the tip, so even if the electrode is consumed by spark discharge, The effect on pulling performance is small. For this reason, it has been confirmed that even with the center electrode in which no electrode member is provided at the tip, there is almost no temperature deviation Δθ2 before and after the evaluation test in which the engine is driven for 100 hours. In order to achieve the effects of the present invention, it is desirable that the thickness h of the bottom wall portion of the center electrode is 1.5 mm or less (that is, 0.5 mm to 1.5 mm).

[Example 5]
Next, an evaluation test was performed in order to confirm the effect of using a noble metal as the material of the electrode member 80 and setting its content to 65 wt% to 100 wt%. In this evaluation test, a center electrode having an outer diameter d of φ1.7 mm and a bottom wall thickness h of 0.5 mm was prepared. In addition, as an electrode member material, an alloy of Pt and a center electrode material (Ni), and six kinds of materials (however, the Pt content is varied by 10 wt% between 50 wt% and 100 wt% (however, , Pt content of 100% by weight does not contain Ni). From each material, ring-shaped electrode members each having an outer diameter of φ1.7 mm, a radial thickness t of 0.5 mm, and a length w in the axis O direction of 1.4 mm were prepared. And after processing the front-end | tip part of a center electrode according to an electrode member, while joining both, the thermocouple was integrated in the center electrode and the sample of the thermometer plug was produced. In addition, a reference sample in which no electrode member was joined was prepared as a reference for obtaining the temperature deviation Δθ1.

  Each sample was subjected to the same evaluation test as in Example 1 (under the same engine conditions) to obtain temperature deviations Δθ1 and Δθ2. FIG. 8 is a graph showing the relationship between the Pt content of the electrode member and the temperature deviation Δθ1, and FIG. 9 is a graph showing the relationship between the Pt content and the temperature deviation Δθ2.

  As shown in FIG. 8, it can be seen that the temperature deviation Δθ1 increases as the Pt content of the electrode member increases. This is because, as the proportion of the volume occupied by the electrode member having a lower thermal conductivity than the center electrode itself at the tip of the center electrode increases, the heat-drawing performance at the tip changes. However, since the electrode member satisfies the provisions of Examples 1 to 4, even if the electrode member is formed from Pt (Pt content: 100% by weight), the temperature measurement error is within 0.5%. Therefore, the allowable value (within 5 ° C.) of the set temperature deviation Δθ1 is satisfied.

  Next, as shown in FIG. 9, it can be seen that the temperature shift Δθ2 increases as the Pt content of the electrode member decreases. This is because as the content of the noble metal in the electrode member decreases, the electrode member itself is more easily consumed by spark discharge, and a sufficient effect for suppressing the consumption of the center electrode cannot be obtained. In order to satisfy the allowable value (within 5 ° C.) of the temperature deviation Δθ2 set so that the temperature measurement error is within 0.5% as described above, the Pt content of the electrode member is set to 65 wt. It was found that it should be more than%. More specifically, when the Pt content is 60% by weight, the temperature shift Δθ2 is 5.3 ° C., and when the Pt content is 70% by weight, the temperature shift Δθ2 is 4.4 ° C. It is desirable if the Pt content is 63.4% by weight or more.

2 is a partial cross-sectional view of a temperature measurement plug 100. FIG. 3 is a perspective view showing a cross section near the tip 22 of the center electrode 20. FIG. It is a perspective view which shows the cross section of the front-end | tip part 22 vicinity of the center electrode 20 for demonstrating the electrode member 180 as a modification. It is a graph which shows the relationship between the thickness t of the radial direction of an electrode member, and temperature deviation (DELTA) (theta) 1. It is a graph which shows the relationship between the thickness t of the radial direction of an electrode member, and temperature shift (DELTA) (theta) 2. It is a graph which shows the relationship between the length w of the axial direction of an electrode member, and temperature deviation (DELTA) (theta) 1. It is a graph which shows the relationship between the length w of the axial direction of an electrode member, and temperature deviation (DELTA) (theta) 2. It is a graph which shows the relationship between Pt content of an electrode member, and temperature deviation (DELTA) (theta) 1. It is a graph which shows the relationship between Pt content of an electrode member, and temperature deviation (DELTA) (theta) 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Insulator 12 Shaft hole 20 Center electrode 21 Tip surface 22 Tip part 23 Outer peripheral edge 24 Bottom wall part 25 Insertion hole 30 Ground electrode 31 Tip part 32 Base part 50 Main metal fitting 70 Thermocouple 71 Contact 80 Electrode member 100 Thermometer plug

Claims (7)

A center electrode having a bottomed cylindrical shape in which an insertion hole is formed along the axial direction, and the insertion hole is closed at the tip of itself,
A temperature sensor that is inserted into the insertion hole and is fixed in the insertion hole in a state in which a measurement unit that measures temperature is disposed in the tip of the center electrode;
An insulator having an axial hole extending along the axial direction and holding the central electrode in the axial hole;
A metal shell that surrounds and holds the insulator in the circumferential direction;
A ground electrode having one end joined to the metal shell and the other end bent toward the tip of the center electrode;
In a spark plug with a temperature sensor equipped with
The front end portion of the center electrode is provided with an electrode member that circumferentially surrounds the outer periphery of the front end portion of the base material of the center electrode including the outer peripheral edge of the front end surface of the base material of the center electrode. Features a spark plug with temperature sensor.   2. The spark plug with a temperature sensor according to claim 1, wherein when the outer diameter of the tip of the center electrode is d, 1.7 ≦ d ≦ 3.0 [mm] is satisfied.   A bottom wall portion that is formed at the tip of the center electrode and closes the insertion hole so that the center electrode has a bottomed cylindrical shape is 0 when the thickness in the axial direction of the center electrode is h. The spark plug with a temperature sensor according to claim 1, wherein: 5 ≦ h ≦ 1.5 [mm] is satisfied.   4. The structure according to claim 1, wherein the thickness of the electrode member on the tip surface of the center electrode in the radial direction satisfies t ≦ 0.2 ≦ t ≦ 0.5 [mm]. Spark plug with temperature sensor as described.   In the axial direction of the central electrode, when the length of the electrode member extending from the front end surface toward the rear end side is w, 0.6 ≦ w ≦ 1.4 [mm] is satisfied. The spark plug with a temperature sensor according to any one of claims 1 to 4.   The said electrode member consists of an alloy which has a noble metal or a noble metal as a main component, and contains at least 1 or more types among Pt, Ir, and Rh as a noble metal. Spark plug with temperature sensor.   The spark plug with a temperature sensor according to claim 6, wherein the electrode member contains 65 wt% or more and 100 wt% or less of a noble metal.

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